Sanibel report formulation of a comprehensive plan based on natural systems

[From the U.S. Government Printing Office, www.gpo.gov]

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Formulation of a Comprehensive Plan Based on Natural Systems
by John Clark

I~~~~~h Coneraion'

Foundtion

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Board of Trustees

Ernest Brooks, Jr., Chairman
William H. Whyte, Jr., Vice-Chairman
John A. Bross
Louise B, Cullman
Dorothy H. Donovan
Maitland Edey
Charles H.W. Foster
David M. Gates
Charles Grace
D. Robert Graham
Nixon Griffis
Philip G. Hammer
Walter E. Hoadley
William T. Lake
Richard D. Lamm
Lord Llewelyn-Davies
Cruz Matos
David Hunter McAlpin
Tom McCall
The Conservation Foundation is a non-profit
Richard B. Ogilvie
William M. Roth : 0research and communication organization
James W. Rouse dedicated to encouraging human conduct to
sustain and enrich life on earth. Since its
William D. Ruckelshaus
Anne P. Sidamon-Eristoff founding in 1948, it has attempted to provide
James Hopkins Smith : intellectual leadership in the cause of wise
Barbara Ward (Lady Jackson) management of the earth's resources. It
Pete Wilson is now focusing increasing attention on
one of the critical issues of the day-how
George M. Woodwell
to use wisely that most basic resource, the
William K. Reilly, President land itself.

U. S. DEPARTMENT OF COMMERCE NOAA
COASTAL SERVICES CENTER
2234 SOUTH HOBSON AVENUE The
CHARLESTON, SC 29405-2413
Sanibel

Report
Formulation of a Comprehensive Plan Based on Natural Systems

by John Clark

Property of CSC Library

,~J~ig, p, 0 0The Conservation Foundation
Washington, D.C.
rCk ::
rx C ::;

The Sanibel Report
Photographs are by John Clark and Robb Turner
Library of Congress Catalog Card Number: 76-56987
ISBN Number: 0-89164-040-1
Design: Carl L. Nelson Associates, Inc.
Copyright � 1976 by The Conservation Foundation
All rights reserved
Printed in the United States of America

The Conservation Foundation
1717 Massachusetts Avenue, N.W.
Washington, D.C. 20036

INTRODUCTION

On November 5, 1974, the citizens of Sanibel Island, conversion of wetlands into golf estates, the county zoning -
Florida, took their destiny into their ownhands. More than of Sahibel would have allowed a population of more than
a thousand of them went to the polls; a sizable major- 90,000 (currently, the peak season population is about
ity-64 percent-voted to incorporate the island as a city, 12,000). Not only was nature's zoning violated by such
empowered to cope firmly with the pressures of develop- inappropriate uses, but life and property were endangered
ment. A building boom, spurred by the construction in by the obvious threat of tropical hurricanes.
1963 of a causeway joining Sanibel to the southwestern On December 16, 1974, a-few weeks after the vote for
Florida mainland, had soared nearly out of control, deplet- incorporation, the new Sanibel city government took over.
ing the resources of the 12-mile-long barrier island. It immediately issued a moratorium on new building
Lying broadside to the path of seastorms andyhurri- permits and began to devise a 'trategy for conserving its
canes, Sanibel stands as the major defense against batter- threatened land and water resources, its beaches and
ing storm waves and hurricanes in central Lee County-a mangroves, its drinking water and wildlife-in a word, its
stance that also makes the island beach a treasure trove of remarkable quality of life.
seashells. Each year nearly a million people visit Sanibel to The Sanibel Planning Commission began work on the
collect shells, walk the beach, or enjoy the other natural new comprehensive plan within a few days after the
values of the island. A major site for birding, fishing, and installation of the new city government. To provide
nature study, Sanibel also lures more than 800,000 visitors professional assistance, the city engaged the Philadelphia
annually to its J.N. "Ding" Darling National Wildlife planning firm of Wallace, McHarg, Roberts and Todd, and
Refuge. the Chicago law firm of Ross, Hardies, O'Keefe, Babcock
Until 1974, Sanibel was governed by the Lee County and Parsons. The planning process is described in some
Board of Commissioners. Despite Sanibel's unique charac- detail in Part III of this report.
ter, the board classified the island as though it were any The process reached its culmination on July 19, 1976,
mainland area ripe for intensive development. By permit- when the plan received final approval, ordinances were
ting construction of condominiums on frontal dunes and passed, and the general moratorium on development was

lifted. The Sanibel Plan povides for long-term conserva- results from anibel's location in a storm hazard area; a
tion of natural resources as well as a reasonable amount of severe hurricane could result in catastrophic property
growth. The planning methods adopted: 1) set a future damage and perhaps serious loss of life. The island's highly
limit on population consistent with natural limits, notably permeable soils, unsuitable for septic tanks, also limit the
those -imposed by water resources and by the imperative of type and intensity of development. In addition, much of
evacuation before hurricanes; 2) distribute the permitted Sanibel's surface is occupied by mangroves and interior
number of new structures (about 2,000) over the develop- wetlands, which serve as important habitats for animals
able land in accordance with the carrying capacity of the and vegetation and perform other vital functions as well.
natural systems; 3) establish a strong set of performance Many of these wetlands are included in natural preserves,
standards for all development; 4) develop a scientific plan some governmental and some private, which together
for restoration of past ecologic damage (particularly to the occupy more than 45 percent of the island's surface.
water systems); and 5) provide for the highest level of The Sanibel Report serves several purposes. It formally
continuing public participation. conveys The Conservation. Foundation's conclusions -and
The Conservation Foundation contributed to the plan- recommendations to the Sanibel-Captiva Conservation
fning process, not on behalf of the city government, but at Foundation and to the citizens of Sanibel. It describes the
the invitation of private citizen organizations concerned Sanibel natural systems study in detail. It presents verba-
about natural systems. These organizations, particularly tim those elements of the Sanibel Plan that deal with
the Sanibel-Captiva Conservation Foundation, wanted to major natural systems. In sum, it presents a basic case
assist the planning effort by preparing a detailed natural study of how the carrying capacity of a natural system can
systems analysis as well as recommendations for the be determined and then used in formulating a comprehen-
conservation of natural resources and natural systems. The sive land-use plan. The lessons learned on Sanibel Island,
Conservation Foundation was asked to help, and funds for based on solid, scientific study, apply not to Sanibel alone,
the work were raised by the Sanibel-Captiva Conservation but to countless small communities whose ecology imposes
Foundation from philanthropic organizations. natural limits to growth.
The Conservation Foundation began its study of Sani- The Conservation Foundation extends special thanks to
bel's natural systems in May- 1975, through a team led by our those who made our Sanibel study and this publication
senior ecologist, John Clark. Our work focused particularly possible: the Sanibel-Captiva Conservation Foundation,
on the carrying capacity of the natural systems. After a and particularly Mr. Erard A. Matthiessen; the American
series of meetings to discuss our findings and recommenda- Conservation Association, the Mary Cary Flagler Charita-
tions with members of the Sanibel-Captiva Conservation ble Trust, the Andrew W. Mellon Foundation, the Anne S.
Foundation, I presented them to the City Council on Richardson Fund, and the Taylor Foundation.
September 16, 1975. Many of those recommendations
-though not all of them-were accepted by city officials
and are reflected in the adopted plan.
The Conservation Foundation undertook its Sanibel William K. Reilly
work not only to help the citizens of Sanibel protect their President
natural systems, but also in an effort to improve the The Conservation Foundation
methodology of conservation. Specifically, we hoped to
demonstrate the contribution that a thorough study of November 1976
natural systems can make to the local planning process.
Sanibel is particularly appropriate for such a demonstra-
tion because natural constraints on its development are
unusually strong. The most dramatic of these constraints

Acknowledgments vii
Our research on the natural systems of Sanibel and the help is gratefully acknowledged include: Kelly Brooks
publication of this report were made possible by the efforts (University of Florida), Louis C. Burney and Larry Pearson
of members of the Sanibel-Captiva Conservation Founda- (Coastal Coordinating Council, State of Florida), Nathaniel
tion. They raised the funds for the study and also provided P. Reed, Ken Black, and Rudy Rudolph (U.S. Department
extensive on-site assistance. One member of the founda- of the Interior).
tion, Erard A. Matthiessen, is primarily responsible for the We are most grateful to the following foundations for
genesis of our study. Members who made particularly grants in support of our natural systems study and the
important contributions during the progress of the work publication of this report: the American Conservation
-include: Richard Workman, Executive Director; Dewitt Association, the Mary Cary Flagler Charitable Trust, the
Jones, President; and Charles J. Wilson and Ann Winter- Andrew W. Mellon Foundation, the Anne S. Richardson
botham, past presidents. We are also grateful for the help Fund, and the Taylor Foundation.
of Donald Whitehead and Malcolm Beattie.
The continuing support of Porter Goss, Mayor of San-
ibel, and C. Duane White, Chairman of. the Planning
Commission, helped immeasurably. The following Sani- J.C.
belians participated in our workshops: Griffing Bancroft,
Malcolm Beattie, Edward Konrad, Bill Hammond, Mada
Harrison, Phoebie Haynie, Robert Haynie, Dewitt Jones,
Eddie Levy, Patsy Simmons, Donald Whitehead, Charles
Wilson, and Ann Winterbotham.
Members of The Conservation Foundation staff who
contributed to the study were John S. Banta, J. Clarence
Davies, Robert. Healy, Jack Noble, and Jeffrey A. Zinn.
Claudia Wilson assisted with art and editorial matters.
Laura O'Sullivan handled all administrative details of the
work and produced the manuscript. David Sleeper andJerry
Kline edited the manuscript, and Celine Seymour provided
valuable editorial assistance.
Our team of technical experts deserves the highest praise
for their skill and dedicated efforts. The six basic systems
reports (included in the Appendix) were prepared by
Taylor R. Alexander, Mark Brown, William K. Byle,Jr., Eric
J. Heald, Thomas M. Missimer, John B. Morrill, Stanley R.
Riggs, Martin A. Roessler, Durbin C. Tabb, and Richard
Workman. Other. consultants who contributed to the data
base reports, or assisted in other ways, include: Gary
Beardsley, George R. Campbell, James H. Hartwell, Oliver
H. Hewitt,Jane McCarthy, Peter Rosendahl, Albert R. Veri,
Langdon S. Warner, and G. Kenneth Young.
Exceptionally valuable technical contributions were
made by Maurice W. Provost of the Florida Medical Ento-
mology Laboratory, William Hammond of the Environ-
mental Education Center, and D. H. Boggess of the U.S.
Geological Survey. Other advisors and cooperators whose

TABLE OF CONTENTS

Introduction v (central sewage treatment, package plants,
by William K. Reilly septic tanks, urban runoff, calculation of
Acknowledgments vii carrying capacity threshold). Water
Table of Contents ix Level (stage and flow, salt intrusion).
Water Supply. Recommendations
PART 1. THE SETTING 1 (water quality, discharge of polluted
Chapter 1. History of the Island 3 effluents, storm water runoff, pollution
Early History. Recent History. conveyed through groundwater, salt
Development Problems. The intrusion of ground and surface waters,
Incorporation Campaign. Planning. pest control, relevant state and federal
- requirements, water conservation and
PART 2. THE NATURAL SYSTEMS STUDY 17 water level restoration).
Introduction 18 Chapter 3. Beachfront 45
The Natural Systems Study Process. Identification of Gulf and Bay Beaches.
Data Collection, Analysis and Formulation Condition of the Beachfront. Management
Requirements. The Consensus Method. Recommendations.
Citizen Guidance. Chapter 4. Interior Wetlands 55
Chapter 2. Water 25 Identification of Interior Wetland Basin.
Hydrology (climatic conditions, Condition of the Interior Wetlands.
groundwater system). Water Quality General Wetlands Conservation.

Management Recommendations.
Chapter 5. Mangroves 67
Identification of Mangrove Zone.
Condition of Mangrove Zone.
Management Recommendations.
Chapter 6. Uplands 73
Identification of Uplands. Condition
of Uplands. Management Recommendations.
Chapter 7. Special Zones 79
Identification of Special Zones.

PART 3. THE SANIBEL PLAN 83
Chapter 8. Formulating the Plan 85
Chapter 9. The Plan 97
Table of Contents. Abridgment of
The Sanibel Plan.

APPENDIXES 163
Appendix 1. Hydrology 165
by Thomas M. Missimer
Appendix 2. Vegetation 195
by Durbin C. Tabb, Eric J. Heald,
Gary L. Beardsley, Martin A. Roessler
and Taylor R. Alexander
Appendix 3.; Beach Geology 227
by Stanley R. Riggs
Appendix 4. Wildlife Ecology 257
by John B. Morrill, William K. Byle, Jr.,
and Richard Workman
Appendix 5. Estuarine Ecology 271
by John B. Morrill and William K. Byle, Jr.
Appendix 6. Natural Energy Systems 295
by Mark Brown

Note: A detailed table of contents appears at the beginning
of each Appendix and The Sanibel Plan abridgment. References
for chapters 1 through 8 begin on page 93.

The Setting

0r -O~ : :The

Report

CHAPTER 1

HISTORY OF THE ISLAND

The City of Sanibel occupies an 11,000-acre barrier island extended into the open waterways and were interlaced with
on the gulf coast of Florida, near the mouth of the Caloosa- elaborate systems of channels and basins. The huts often
hatchee River in Lee County. (Figure 1) The island has been were perched on pilings along the sides of these channels.
shaped and formed by the wind and the sea into a corduroy When the channels filled with silt they were allowed to
of sand ridges that provide its structure, elevation, and become gardens or rainwater basins, and other mounds
character. Its geological age is only 5,000 years. were built to provide new channels. The maximum popula-
tion of the island was approximately 200 Calusas living in
35 huts.'
Early History Calusa warriors waged furious battles against Ponce de
Leon, De Soto, Menendez, and other explorers who
In 1513, Juan Ponce de Leon and his fellow Spanish dropped anchor near Sanibel. In 1521, Ponce de Leon died of
explorers "discovered" Sanibel Island while searching for wounds inflicted by the Calusas during his return to Florida
the legendary fountain of youth. They found instead an with colonists to begin settlements. Over the years the
advanced Calusa Indian culture with settlements that ex- Calusa culture slowly disintegrated; following. the passage
tended from Charlotte Harbor on the mainland to points 30 of the Indian Removal Act in 1832, the remaining Calusas
miles south. were confined to reservations.
The Calusas believed themselves to be partof the earth In the mid-16th century, Spanish pirates were headquar-
and lived within the supportive capabilities of their natural tered on Sanibel andher sister island, Captiva. Black Caesar,
environment. Their life-style was simple: shells and other a henchman of Florida's notorious Gasparilla, operated
natural materials were used for construction purposes and from Point Ybel, the present location of the Sanibel light-
weaponry. house.
In low-lying areas, the Calusas elevated their structures After extensive exploration and surveying, Sanibel Is-
with piles of shells for protection against high storm water land was purchased in 1831 by the Florida Peninsular Land
as well as from enemies. (Figure 2) The shell mounds often Company (a group of New York investors) as a settlement

4 The Setting

SARASOTA

SARASOTA GLADES
CUT - COUNTY CU

Sanies1-m RLOTTEleon
EN keOkechobee
PUNTA GORDA S ouh
4~~~~~~~~~~~~~~~~

west Flrd Reina
Plnn CHARLocE T
. .OUNTY , " ' A
Z L% LA BELLE
COUN ~~~~~~~~~CL WISTON

APE FA

or HENDRY
COUNTY
COL IERDISTRICT 9
COL UIER

~ '~~LE Southwest Florida
--/...~~~~~ - COUNITY

~-,-.-- NAPL ES %UT atws ord
Regiona-1 Plann ng
Figure 1.
Council
Sanibel is a 12-mile-long ~ -: -
barrier island off the
southwestern Florida MEKXICO
coast. (Source: South- . "'
west Florida Regional
Planning Council). -

History of the Island 5

site because of its good harbor, climate, and general ameni-
ties. The first settlers, who arrived in 1833, lived temporar-
------ _ ---- -- ily in palmetto-thatched huts with floors of shell and sand.
These early settlers envisioned the island as a paradise for
kb ~ ~ - '1 _. .) l<'> ' recreation and health recuperation.
:2 '- - When the settlers arrived, the shell ridges on the island
were six to eight- feet above bay level and the beach was
'**'**- .- 3 K narrow. The mangrove forest along the western shore
$'1 A--: X R 'e, _ -~-:. - <X4-- in P provided the major source of wood. The interior was a
:~-~v'_.e '~ .....o'- -4 " "-;-" - X;grassy plain, dotted with palmettos, so level that one could
see for miles. There were ducks, turkeys, flamingos, curlews,
and deer in abundance. The fruits and vegetables harvested
by the settlers were of superior quality, and led to expecta-
tions that the island would be a profitable agricultural area.
_ _ _ ' - -- But the settlement did not prosper. Most of the settlers
deserted; many left because of a final series of Indian raids in
1836. In 1850, Fort Casey was'erected on the site of a former
settlement. A hurricane destroyed much of the fort on
i--- '-' f 0 ~ ~ _ 'red '> | 0 ho ;0October 6, 1873.
In 1883, Sanibel Island became a government lighthouse
reservation. On August 20, 1884, the lighthouse was
activated and run by various family lighthouse keepers
until 1949 when the responsibilities were turned over to
the Coast Guard Light Attendant Station.
On July 3, 1888, most of Sanibel, except for land around
$ SANIBELN'- /// : Nthe lighthouse and a small portion of the west'end of the
. ~// - > .... island, was released for homesteading. Resettlement be-
0. A // 10 X gan, and with it came Sanibel's first wave of tourists.
� -t~_...// 'V ' Sanibel and Captiva attracted such prestigious sightseers as
.... Theodore Roosevelt, Edna St. Vincent Millay, and Charles
and Anne Lindbergh. Another famous tourist, Thomas
~-- "0 '~ ~~ -X ;Edison, had once been night watchman for the Interna-
tional Ocean Telegraph Company on Sanibel.
Seashells, sport fishing, and wildlife became Sanibel's
-- i*' . .. * .. principal attractions. The island quickly developed into a
.-- -" ..7.__::: ._-v--:- .......favorite vacation site for wildlife conservationists, natural-
- X~.~~~~~~~~ --' g - V- ~ ists, and birdwatchers. Individuals and: organized groups
visited Sanibel to study the island's bird life and ecology.
Despite a series of severe hurricanes (in 1894, 1910, 1921,
and 1926), Sanibel's tourist economy prospered.

0 : 50 MI

6 The Setting

i ns

Figure 2.
Calusa Indians built shell
m ounds on Sanibel to elevate
-BENZ~ ~~~~~~~~~~ . . . . . -l~~~~ ~ .. . . . .. .V~ ~their huts above storm tides.

Recent History Association. The association began a campaign to protect a
"treasured" island. Jay Norwood ("Ding") Darling, an
Agricultural development on Sanibel started about 1883 ardent and articulate defender of wildlife and the natural
and over the next 40 years encompassed most of the environment, spearheaded the group's activities and acted
island's, arable land. (Figure 4) The major agricultural as spokesman in Washington and Tallahassee.
products were citrus fuits and vegetables such as tomatoes, Little growth occurred between 1927 and 1944 (the
squash, and eggplants. Severe hurricanes, with accompany- year-round population was about 100), except for a gradual
ing flood tides ranging from 9 to 13 feet, effectively ended increase in the number of visitors and development of
farming on Sanibel. The last major storm, in 1926, flooded cottages along the gulf coast.2 In the 1950's, however,
the entire island with salt water. The 1926 hurricane left Sanibel's reputation for shell collecting and abundant
financial ruin in its wake, forcing almost half of the wildlife induced a new surge of tourism and a parallel
island's residents-including most farmers-to leave. The growth in residences and services. The last and most
remainder stayed to serve winter visitors and tourists. ' significant spurt of growth began with completion of the
In 1926, residents organized the Sanibel Community causeway in 1963, and continued until 1974 when the new

History of the Island 7

city government intervened with a general moratorium on
new building permits. (Figure 7 and Table 2)
The J.N. "Ding"u Darling National Wildlife Refuge
(established on October 31, 1945) is closely tied to the
history of the conservation movement on Sanibel Island.
Darling first came to Captiva Island in 1936 while serving
as the head of the U.S. Bureau of Biological Survey (later to
become the Fish and Wildlife Service) under Franklin D.
Roosevelt. He was taken with the natural values of the
islands, and made personal, continued efforts to conserve
Sanibel and Captiva for their unique environments and .
wildlife. Darling became a leader of the Izaak Walton
League, was founder of the National Wildlife Federation,
and served on the :National Audubon Society's board of
directors.
The refuge boundary encompasses approximately 4,700
acres of waterways, mangrove forests, and upland. The
refuge brings a vast number of tourists to-Sanibel. In 1975,
more than 1,000,000 tourists visited the island, more than
800,000 of'whom visited the refuge. The refuge is the home
of more than 267 species of birds, including the great
white heron, mottled duck, roseate spoonbill, white and
wo6d ibis, the mangrove'cuckoo, and the grey kingbird.
Alligators- and otter are year-round residents. The
loggerhead sea turtle visits in late spring and summer to
breed. More than 400 varieties of seashells can be found
on the Sanibel beaches. And snook; redfish, trout, and
tarpon provide excellent sportfishing. Figure 3.
Saltwater fishing is one of the
island's major recreational
activities.
Figure 4.
Are of iS4/1nE /E LAND Today, the population of Sanibel at mid-winter peak
~Areas of.S~anibel Island under AREASs FORMERLYvoEseason is about 12,000. It is overwhelmingly white (about
cultivation before the 1926 0 ve =
hurricane. '-50 blacks live on Sanibel) and predominantly wealthy. The
(Source: Cooley) 1970 census figures show that 45.9 percent of the island
residents had yearly incomes in excess of $15,000.3
The population increase in recent years is due generally
to the influx of retired persons, aged 60 and over. In 1970,
approximately 36 percent of the population was in this
category. The retired population, whether year-round or
part-time, takes an active interest in the island's civic
affairs and provides the driving force for a wide array of
community organizations and programs.

8 The Setting

Figure 5.

In 1944, Sanibel Island was
relatively unchanged from its
original state. (U.S. Depart-
ment of Agriculture airphoto)

History of the Island

Table 1.
1944 1975
Land use in acres, 1944 and
Land use incr3,588 interior 2,393 interior
1975 (U.S. Departmentiof 3,200 mangrove 2,800 mangrove
Agriculture)
6,788 total wetlands 5,193 total wetlands

Figure 6. 10.730 total island 10,730 total islands
-6788 total wetlands -5,193 total wetlands
By 1975, Sanibel had under - __
gone drastic changes -roads,
gone drastic changes - roads, 3,942 total upland 5.537 total upland
homesites, canals, artificial undeveloped and
lakes, and filled wetlands are udeveloped areand
apparent in this aerial photo-
graph. (U.S. Department of
Agriculture airphoto)

10 The Setting

i~~~~~~~~~~~~~~~~~~~~~~~~

Figure 7.

The completion of the cause-
way in 1963 between Sanibel
and the mainland precipitated
a~building boom which led to
ten years of ecological devas-
tation to the island.

:,~': ~,,,~ <, Figure 8.
The J.N. "Ding" Darling Na-
tional Wildlife Refuge attracts
more than 800,000 visitors
every year.

Figure 9,
Overlooks highlight the driving
tour trail in the wildlife refuge.

History of the Island 1

: 795 . :; 0 u 0 f 1974-1975

60: ,x10,000

55 - 1973-197

45 -
: 0 : 0045 V : J;0 ;00 001972' -197
40

35:: ' :: 1971-1972
; 30 0:1970-1971

25
1969-1970
20 1968-1969

Table 2. 15 1965-1966 197:
71966
A seven-fold increase in yearly 19631964 964-1965
traffic over the new causeway I 193
demonstrates the rapid growth
of the Sanibel community.
(The years given cover a 12- 15 '
month period from May to-
April.) (Source: Island Reporter)

12 The Setting

Development Problems

There is little question that the completion of the
causeway in 1963 exacerbated Sanibel's development prob-
lems and led to its incorporation as a city. This highway
connection to the mainland provided easy, direct automo-
bile ac cess to the island and precipitated a boom in
residential development which ferry service could not have
supported. An appeal for contributions to fight the Sanibel
bridge and causeway was made, and letters were sent to
newspapers and to the State Improvement Fund protest-
ing "the giving of 1,026 acres of Bay bottom fishing
grounds to the county commissioners for right-of-way ing waters. The sequence of significant events from 1967 Figure 10.
purposes for the Punta Rassa-Sanibel causeway."4 Other- to enactment of the moratorium on new building permits
objections cited were adverse changes of water flow and on December 16, 1974, is given in I the following chronol- arge water birds such as this
destruction of the scallop bed off Pine Island (both of ogy. egret populate the wildlife re-
which actually occurred after construction). Court actions 1967: Sanibel and Captiva Island citizens ofanibel.
were brought on January 30, 1961, but in July the state's groups successfully opposed a proposal for a large trailer
high court upheld -the bond issue. Construction began in park on Sanibel, claiming adverse impact on wildlife and
January 1962. overcrowded conditions on the island. The Lee County Figure 11.
The three-mile causeway (built by Lee County with a Commission hired consultants to develop a countywide
bond issue of $3.9 million) was officially opened on May comprehensive land-use plan to include Sanibel and Cap- Zoning of the land near the
26, 1963. It laid the foundation for increasing concern by tiva Islands.5 causeway landfall was an
islanders for the future of their environment. Within a few 19:Cty plannigcosltants recomeedSan- important issue in 1969.
months of the opening of the causeway, the right of ibel and Captiva for intensive-use, high-density urban
Sanibel's existing independent zoning authority (created development. Included was-a four-lane expressway which
by act of the Florida Legislature in 1959) was successfully would bisect the wildlife refuge. These recommendations
challenged in court. Islanders were left with no control were successfully opposed by Sanibel-Captiva residents and
over the extensive growth which was to result. In 1967, civic organizations. Nevertheless, the islands were zoned
Sanibel-Captiva islanders began strong efforts to preserve for high-density development and increased business and
and protect the character of the islands and their surround- commercial use. The islanders were able to prevent some

History of the Island 13

unfavorable zoning, however, and began petitioning Lee InJune, the county commissioners established a Sanibel-
County for the passage of a 35-foot height limitation for Captiva Planning Committee to formulate a comprehen-
buildings on Sanibel.6 sive proposal for designation of the islands as areas of
1969: The Sanibel Island Planning Board, an independ- environmental concern with comprehensive zoning and
ent citizen organization, successfully opposed a request to land-use provisions. The cooperative island-county com-
Lee County for industrial zoning on Sanibel Island. Sanibel mittee was composed of two Lee County commissioners,
residents worked out a solution for the rezoning of 90 two members of the Sanibel-Captiva Planning Board, one
acres of land near the causeway entrance. (Figure 11) member from the Sanibel Community Association, one
1970: A temporary (six-month) building height limit of member from the Sanibel-Captiva Chamber of Commerce,
35 feet for Sanibel and Captiva Islands was passed in April and one member from the U.S. Fish and Wildlife Service.8
by the Lee County Commission with-the encouragement of In July, the county adopted an interim density limit of
the Captiva Civic Association, Sanibel Community Associ- 18 apartment units or 22 motel units per acre.
ation, .Sanibel-Captiva Chamber of Commerce, Audubon 1972: Considerable effort was spent during the year on
Society, and Sanibel-Captiva Conservation Foundation, the planning process. In December, a series of public
with 90 percent of the "freeholders" in the islands in favor. hearings on the comprehensive land-use plan was held and
Opposition consisted of the Fort Myers Board of Realtors, the plan was modified by the Sanibel-Captiva Planning
Jamestown-Beachview, Inc., and the Captiva Island Corn- Committee. The plan called for a population ceiling of
pany.7 . about 41,000 persons and provided for no more than
In October, the county extended the 35-foot limit to 14,852 housing units. It recognized the inevitability of
January 15, 1971. The Sanibel-Captiva Planning and substantial growth over present levels. (In March 1975, the
Zoning Board studied all zoning requests for island prop- Sanibel Planning Commission reported there were 4,250
erties and commented on them to the County -Zoning housing units on the island). It was, however, a. far cry
Board and commissioners. from the population densities anticipated by the Lee
1971: The Sanibel-Captiva Planning Board succeeded in County Planning Commission. County zoning ordinances
having a permanent height limitation ordinance passed by then in effect would have permitted housing for a popula-
the county. However, an accompanying ordinance for low- tion of up to 90,000.
density construction and a 100-foot beach setback line was 1973: Construction on Sanibel and Captiva Islands
not approved. increased by 72 percent over 1972. The-intense develop-
ment began to tax public sewerage and water supply
systems. Freshwater rivers were filled in and mangroves
obliterated. Digging for real estate lakes caused intrusion
of salt water into freshwater rivers and -the sewerage
problems were perceived as a threat to the public health of
the islanders.9
Lee County established a county planning commission
in the spring of 1973 and hired a qualified planner and a
staff. The planner was relieved of duties in August and the
delayed Sanibel-Captiva plan was activated in September
-but quickly halted by court action requiring it tobe part of
~~~~~~~~~~~Figure 12. ~~~~~~a county-wide plan.The island's civic groups requested a
In 1973, protection of the in- building moratorium until this plan could be implemented.
terior wetlands and water ba- The- voters rejected Lee County's proposal for sewer
sins was a major goal of Sani- districts on Sanibel-Captiva because it was considered to be
bel citizens. ill-suited for the island's needs.

14 The Setting

The Incorporation Campaign formed to promote passage of the referendum. In addition,
a group called Save our Sanibel (SOS) was formed to
Failing to convince Lee County of the merits of more publicize the struggle for-incorporation nationally.
strictly controlled development, the Sanibel-Captiva Plan- The principal opposition was led by members of the
ning Board next considered home rule. The board con- Chamber of Commerce who formed an Action Committee.
ducted a study of the pros and cons of incorporation and The Chamber of Commerce itself was divided over incor-
the cost of city government. The board also conducted a poration, the most vehement opposition coming from land
straw vote" of island residents which showed that incorpo- developers and builders. Attempts were made to block
ration sentiment was favorable. approval of the new charter in the state legislature and in
A town meeting called by an ad hoc "Commission of the courts, and to dissuade citizens from voting for
Five" was attended by 300 residents who generally sup- incorporation. A new Florida law, the County Powers Act
ported initiating a study of the merits of home rule and (which permitted counties to tax unincorporated areas for
other alternatives for self-government. It was decided not "municipal purposes"), sidetracked the cost-of-
to include Captiva in home-rule attempts because of the government issue which was expected initially to be a
need for county support of beach erosion protection. major factor in the campaign. Under the act, Sanibel would Fgure 13.
A new group called the Sanibel Home Rule Study Group have had its taxes increased by the county to pay for The experience gained in pro-
(a nonprofit corporation) was created in November 1973. municipal services if it had not incorporated tecting Sanibel's beaches, wa-
ters, and living resources read-
By December, the decision to seriously consider incorpora- Sanibel Island represented a rich tax base for Lee ily appliestoother barrier
tion had been made and funds were raised to hire an expert County and served as a symbol of development prosperity. islands.
to explore the island's alternatives. At this point, Lee
County hired a new county planner.
The framework for the new city was designed, a draft ...7
charter prepared, and public meetings held to discuss the '-
implications of this move. In March 1974, residents met at
the Sanibel Community Association to vote on placing an
incorporation referendum on the ballot. By a vote of 436 to
358 the referendum gain ed a place o n the November
ballot.
The proposed new charter called for a five-person city -
council, elected to four-year terms, and for a city manager.
The new city would have zoning power and the authority
to develop and implement a land-use plan that controlled
growth and preserved environmental values. The incorpo-
ration proposal included the right to:
1) create a new zoning ordinance consistent with the
special needs of the' island;
2) develop a master plan guaranteeing orderly growth
and protection of the environment, and
3) set and enforce density ratios, height restrictions on
buildings, and setback lines from the beaches.10
The dominant theme of the incorporation campaign
was the need to secure stronger local control over decisions
concerning land use on the island. The study group
disbanded and a new organization, Sanibel Tomorrow, was

History of the Island 15

Through 1974, Sanibel transactions had been accounting process of selecting a planning consultant.
for 40 percent of the county's condominium sales. The real In April, the City Council selected as planning consul-
estate tax base for Sanibel for 1975 was $104.5 million."ll tants the firm of Wallace, McHarg, Roberts and Todd
During the legislative process for incorporation, the chair- (WMRT). WMRT was asked to design the plan and
man of the Lee County Commission and one commissioner "recommend zoning code and zoning map, building regu-
wrote to Sanibel residents to dissuade them from home rule. lations or codes and subdivisions, and other pertinent land-
The county cooperated with the Sanibel-Captiva Chamber use regulations." The planning consultant also was respon-
of Commerce to work against incorporation. sible for receiving public input through interviews and
On November 5, 1974, 85 percent of the Sanibel voters workshops with "representative groups." In addition,
turned out to register their views on the incorporation WMRT coordinated and received assistance from the
proposal. The vote was 689 to 394 in favor of the community through 10 task force committees, appointed
referendum. A month later, the five-member City Council by the Planning Commission.
was elected by the voters, and Porter Goss was elected Concurrently, citizen organizations searched for an or-
mayor by the council. The councilmen included two ganization that could assist the city by providing a detailed
members of the Chamber of Commerce's Action Commit- description of the natural systems of Sanibel, and by
tee, the chairman of Sanibel Tomorrow, Inc., the former suggesting means for conservation of natural resources and
president of the Sanibel-Captiva Planning Board, Inc., and natural systems. The Conservation Foundation was se-
the president of Caretta Research (a nonprofit group lected, and in March a campaign was initiated by the Sani-
established to foster research on loggerhead turtles, genus bel-Captiva Conservation Foundation to raise funds from
Caretta-). charitable organizations for its work. In May, initial funding
On December 16, 1974, the government of the City of became available and work began. The natural systems
Sanibel officially took office and began the administration study was designed both to provide information useful to'
of the island as an independent municipality. The new the city and to test a planning approach that could be
government immediately passed several resolutions which instructive to Florida. and to the nation regarding local
became effective upon passage. No new building permits implementation of coastal zone management and, in partic-
or zoning changes were to be issued for at least 90 days, or ular, barrier island resources management. The results of -
until a comprehensive land-use plan was adopted. Only the natural systems study are presented in the chapters that
those builders who had received permits before the incor- follow.
poration vote and who had actually broken ground within
60 days thereafter were allowed to continue construction.
A flood of new building permits issued by Lee County in
the interim between the referendum and December 16 (42
in all, totalling $9,618,400 in-construction costs) prevented
the halting of all new development-but the intensive
development problem had been somewhat alleviated.'2

Planning

Because the Sanibel City Council was elected to control
growth on the island through--the development of a
reasonable land-use plan, replanning became a top priority
item for the new government.
Early in 1975, the Sanibel Planning Commission devel-
oped specifications for a new land-use plan and began the

The Natural Systems Study

I ar
o -:: :The
f 0 -- _ _Report 1

18 The Natural Systems Study

Part II of the book presents The Conservation Founda- those we suggested, or that, conversely, the optimum
tion's natural systems study and the major results for each development pattern for the island might require modifi-
of four elements: 1) analysis of the island's ecosystem; 2) cation of certain of the natural systems protection mea-
identification of the principal ecological zones; 3) diagno- sures suggested.
sis of the condition of these zones; and 4) suggestions for Data Collection, Analysis, and Formulation of Require-
management requirements to conserve the island's natural ments: The basic approach to the natural systems study
systems and resources. The chapters in this section are was, first, to formulate a data collection plan from a
organized along those lines-the identification, condition, preliminary survey of Sanibel and from existing knowl-
and management recommendations are given separately edge of the ecosystem and natural resources; and second, to
for each ecological zone. Because subsurface hydrology divide up the necessary work along disciplinary lines
spans all zones on the island and, in fact, determines the (hydrology, botany, wildlife biology, etc.) -for assignment to
characteristics of each zone, it is dealt with separately and survey teams. To assist these teams in coordinating their
presented first.
The Natural Systems Study Process: The Conservation
Foundation engaged a team of experts to assist with its
carrying-capacity assessment and formulation of conserva-
tion requirements. The experts furnished individual re-
ports that were integrated into a program of environmen-
tal management specifications. In addition to a variety of
consulting specialists, The Conservation Foundation team
included staff experts in law, planning, ecology, economics,
and administration.
The Conservation Foundation (CF) began its natural
systems ::study in May 1975.
As the study progressed through the summer, CF made
the data collections draft consultant reports, and prelimi-
nary findings available to the Sanibel-Captiva Conserva-
tion Foundation (SCCF), the citizens of Sanibel, the Plan-
ning Commission, and the planning consultants, Wallace,
McHarg, Roberts and Todd (WMRT). Some results, how-
ever, were available as early as June.
CF's basic task was to develop principles and require-
ments for future development which could prevent dam-
age to the remaining natural systems, and principles and
requirements for restoration of past damage to the natural
systems.
It must be stressed that the management program
resulting from these recommendations was designed to i
attain maximum protection and perpetuation of the natu-
ral systems of the island, particularly through optimization Figure 14.
of the basic water systems that govern their health. CF Preservation of the island's
realized that other planning policies developed by the city / various water systems is es-
could impose constraints on development in addition to sential to maintenance of its
overall ecosystem.

Introduction 19

G;. Kenneth Young; water quality, by Thomas Missimer;
and birds, by Oliver Hewitt.
Both WMRT and CF gave first priority to identifying
and classifying the subsystems of the Sanibel ecosystem.
(Tables 3, 4) These subsystems, termed "ecological zones
in the plan, were described in initial maps of zones prepared'
-by CF in June and July 1975. With modifications and
refinements by WMRT and the Planning Commission
these zones furnished the basis for the permitted uses,
densitdylimits, and performance standards contained in the
Sanibel Plan.
The various water-related aspects of the Sanibel Plan
demonstrate that successful protection of the Sanibel
environmentt depends primarily on proper water manage-
ment (insect control, for example, is included in the plan's
water-related section because water management is the key
to success in combating mosquitoes, the major insect pest
on Sanibel).
Restoring and conserving the island's water system
require actions both by the public and private sectors. On
the public side, substantial capital outlays as well as
moderate operational costs are required for improvements.
Control of private development is also essential, and many
of CF's recommendations were so oriented.
Figure 15. efforts and in clarifying and reevaluating their work plans, The major natural hazard affecting occupation of Sani-
Sections of the road on the The Conservation Foundation organized workshops, held bel is the tropical hurricane. Sanibel shares with all other
mainland end of the Sanibel informal meetings,- circulated relevant progress informa- barrier islands of the Atlantic and Gulf of Mexico extreme
causeway are so low that they
-can flood completelybefore tion, and e ncouraged direct communication between par- vulnerability to hurricanes. Evacuation is the major defense.
hurricane evacuation begins, ticipants. Altogether, 18 technical consultants were in- The rate at which automobile traffic can move over the
thus blocking all escaping volved, along with a panel of special technical advisors, causeway to the mainland limits the speed of evacuation and
traffic. The six principal natural systems reports produced by imposes a limit on population and therefore on residential
the consultant teams are included as an appendix. The density. (Figure 15) Regarding potential threats tolife and
subjects covered are hydrology, vegetation, beach geology, property, wildfires are much less a problem than hurri-
wildlife ecology, estuarine ecology, and the natural energy canes; actually, they may have a strong beneficial effect on
system. the interior wetlands ecological zone.
In addition to these systems reports, a number of data Both permitted uses and residential density limits in the
base reports were produced. The data base reports are not Sanibel Plan are governed by a set of regulations-or
included in this document, but copies are available from performance standards-that control the design and
The Conservation Foundation. They include the following construction of residential development. In their absence,
six subjects: plant survey, by Taylor Alexander; reptiles, density allocations would have to be reduced to provide for
amphibians, and mammals, by George R. Campbell; water the conservation of natural systems and natural resources.
quality and wetlands management and performance data Recognizing that Sanibel is composed of several different
for sewage plants, by Albert L. Veri and Langdon Warner; zones with particular characteristics and varying toleran-
the pollutant-loading capacity of the interior wetlands, by ces, a separate set of standards is applied to each zone.

20 The Natural Systems Study

GULF BEACH GULF INTERIOR WETLAND BASIN
BEACH MID-ISLAND RIDGES
FRONT BEACH BACK BEACH RIDGE UPLAND LOWLAND UPLAND

The Gulf Beach Zone includes the area between the The Gulf Beach Ridge Zone The Interior Wetland Basin Zone is the interior bowl which serves as a fresh water The Mid-Island Ridges Zone comprises the
state setback line and the city boundary 300' offshore. is the major ridge imme- reservoir. It is composed of parallel systems of ridges and swales with corresponding major ridges along the cehtral axis of the
There are two subareas within this zone-the Front diately behind the beach. bands of vegetation. There am two sub-areas within this zone - lowland and upland. Island and includes the highest elevations.
Beach and the Back Beach. The Front Beach extends It is stabilized by dense The lowland area is composed of low ridges and wide swales and experiences extended In most areas this zone divides the Bay-
from the city limit to Mean High Water. Sand in this vegetation. Blind Pass- periods of flooding each year. The upland consists of higher, broader ridges and Mangrove watershed from the Interior
subarea is in constant motion. Sand migrates. between a subarea within this narrower swales. and is characterized by less frequent flooding and more upland Wetlands watershed.
the berm and offshore barsm and is transported by long- zone-is of very recent vegetation types.
shore currents. The Back Beach comprises that area formation and susceptible
between Mean High Water and the the state setback to dramatic change.
line. Sand in this subarea is moved by wind and water
and stabilized by vegetation, forming low dunes.

CLIMATE CLIMATE CLIMATE CLIMATE
Salt Spray Salt Spray

GEOLOGY GEOLOGY GEOLOGY GEOLOGY
Oxidized barrier sands and shells

SUBSURFACE HYOROLOGY SUBSURFACE SUBSURFACE HYDROLOGY SBSRFACE
HYDROLOGY HYDROLOGY

Fresh Water Table Aquifer Fresh Water Table Aquifer
Saline Shallow Aquifer
SURFACE HYDROLOGY SURFACE HYDROLOGY SURFACE HYDROLOGY SURFACE HYDROLOGY
Mean High Water
Seasonal High Water Table at Surface
Seasonally Flooded Seasonally Flooded

10 Year Storm Flooding 10 Year Storm Flooding 10 Year Storm Flooding 10 Year Storm Flooding
25 Year Storm Flooding

SOILS SOILS SOILS SOILS
Oxidized Barrier Sands and Shells Thin Organics Organics over Sand Marl Thin Organics

VEGETATION VEGETATION VEGETATION VEGETATION
Widely scattered herbaceous vegetation and shrubs. Sea grape, yucca. bay cedar, Vegetation varies according to elevation and water levels. West Indian Flora. Cabbage palmetto,
Sea Oats, railroad vine, sea spurges, beach plum, sea saltbush, marsh elder, saw palmetto, seagrape, gumbo limbo,
purslane, bay cedar, yucca, salt bush. invasion of cabbage palmetto, wax Swales: Cordgrass, sawgrass, andropogon, water hyssop. buttonwood, cattails, spat- Jamaica dogwood, Florida privat. wild lime,
Australian ine. myrtle, coconut palm. terdock, hydrilla, chara. duckweed. wigeongrass. strangler fig, wild coffee, myrsine, joewood,
Invasion of Australian Pinn. Low ridges: Marsh elder, leather fern, wax myrtle, cabbage palmetto. wax myrtle, sea oxeye, poison ivy, Virginia
Invasion of Brazilian pepper and Australian Pine. creeper, prickly pear cactus, bowstring
hemp, century plant. Invasion of Australian
Pine, Brazilian pepper, and cajeput.

WILDLIFE WILDLIFE WILDLIFE WILDLIFE
Loggerhead Turtle. Bottle-nosed Dolphin, Otter. Manatee, Box Turtle, Gopher Tor- American Alligator, Box Turtle, Chicken Turtle, Soft Shell Turtle, Green Anole. Gopher Tortoise, Green Anole, Key West
Brown Pelican, Snowy Egret. Red-breasted Merganser, toise, Green Anole, Key Key West Anole, Five-lined Skink., Florida Watersnake. Ribbon Snake, Southern Anole. Five-lined Skink, Six-lined Racerunner,
American Oystercatcher, Semipalmated Plover, Piping West Anole, Five-lined Toad. Green Treefrog, Squirrel Treefrog, Southern Leopard Frog, Pig Frog, Opossum, Black Racer, Indigo Snake, Coral Snake.
Plover, Snowy Plover, Wilson's Plover, Black-bellied Skink. Six-lined Racerunner. Armadillo, Marsh Rabbit. Sanibel Rice Rat, Sanibel Cotton Rat, Raccoon, Otter, Diamondback Rattlesnake. Southern Toad,
Plover. Ruddy Turnstone, Willet, Knot, Least Sandpiper, Mangrove Watersnake. Florida Bobcat. Pied-billed Grebe, Anhinge, Least Bittern. Mottled Duck. Blue-winged Green Treefrog, Squirrel Treefrog,'Opossum,
~~~Table 3,~ ~~Dunlin, Semipalmated Sandpiper, Western Sandpiper, Black Racer, Indigo Snake, Teal, King Rail. Virginia Rail, Sora, Common Gallinule, Killdeer, Spotted Sandpiper, Armadillo, Marsh Rabbit, Sanifel Rice Rat,
~~~~Table 3. ~ Sanderling, Herring Gulf, Ringbilled Gull, Laughing Coral Snake, Southern Common Snipe, Belted Kingfisher. Long-billed Marsh Wren, Swamp Sparrow. - Sanibel Cotton Rat, Florida Panther, Flor-
Gull, Forster's Tern, Least Tern, Royal Tern, Sandwich Toad, Green Treefrog, ida Bobcat, Bobwhite, Smooth-villed Ani,
Tern, Caspian Tern, Black Skimmer. Squirrel Treefrog, Bob- Red-bellied Woodpecker, Great Crested Fly-
Sanibel's major eco- white, Smooth-billed Ani, catcher, Purpie Martin, Fish Crow, Starling,
Red-bellied Woodpecker, White-eyed Vireo, Prairie Warbler, House
logical zones as Great Crested Flycatcher,. Sparrow, Cardinal.
Purple Martin, Fish Crow,
interpreted by Wallace, Starl ing, White-eyed
Starling, White-gyed
~~~~~~~~~~~~~McHarg, Roberts ~~wVire.o, Prairie Warbler,
McHarg, Roberts
House Sparrow, Car-
and Todd. dinal.

Introduction :21

These standards incorporate a number of the requirements
recommended by CF.
Each type of residential development has the potential
for a particular combination of environmental disturban-
:p af~~nf~l~~ litle '50 fY10 ~~~ ~ces. The amount of natural systems damage that may result
from any disturbance depends upon the characteristics and
vulnerabilities of.the specific subsystem involved. Protec-
:MANGROVES - :tion of the: three water-based ecologic subsystems must
:MANGROVES ::-TIDALFLATS MAGBAY BEACH - : also include controls on the fourth subsystem, the uplands,
particularly on land modification activities associated with
The Mangrove Zone includes ali areas of red, black and white mangroves. as well as The Bay Beach Zone extends from site preparation for development. The necessary
the tidal flats and hardwood hammocks within them. Much of this zone, including the city's boundary 300' into the
all areas of red mangrove, is subject to daily tidal flooding. Other areas of the zone are bay to a setback line approximately constraints may have to encourage, and in some cases
subject to extended periods of flooding every year. 100' behind the Mean High Water adjustment of
Line. It isa lower energybeach require, adjustment of traditional Florida standards of
than the Gulf Beach, and include t density, desig, preparation,
areas of marine grasses n the residentialdensi ty, project design, site preparation,drain-
bay bottom, It includes both
sand beach and mud beach. age, and other performance factors.
The development requirements recommended by CF
CLIMATE CLIMATE
can be administered conveniently through the city's site
GEOLOGY GEOLOGY plan reviewprocess. Well-conceived st andards can imple
Oxidized Barrier Sands and Shells Muds, Organic Materials, Sandsstandards im.e
and Shells ment the specific environmental objectives set out in
I_ .SUBSURFACE HYDROLOGY : .. :� ; . ; : SUQBSURFACE HYDROLOGY :: : :_ :regulations. and also provide equity and predictability for
developers in the approval process.
: : Saline Shallow Aquifer There is a second important requirement for a compre-
SURFACE HYDROLOGY . . SURFACE HYDROLOGY hensive environmental program for Sanibel-restoration,
Mean High Water-
the repair of existing damage to the natural systems. The
major elements of the recommended program are: water
10 Year Storm Flooding level restoration and flood control in the interior wetlands
- V- :25 Year Storm Flooding ;basin; drainage restoration in the mangroves; vegetation
SOILS X SOILS restoration in all four subsystems; and beach profile resto-
Peat Deposits Salt Flats Muds, Organic Materials, Sands
and Shells ration
VEGETATION . VEGETATION The Consensus Method: In conducting the natural
Mostly mangroves with hardwoods at higher elevations. Vegetation responds to ele- Sand beach: Sea oats, railroad ral
vation and tidal patterns. Red mangroves predominate to the mean high tide line. vine, sea spurges, beach plum, systems study our consulting experts not only performed
black mangroves predominate to slightlyhigher elevations above the mean high tide sea purslane, bay cedar, yuccast m sur cn s l ieerton pther
0 ~~~~line. ~~o bush. I nvasion of Australian . ithe surveys and determined the condition of the systems,
Red mangrove, black mangrove, white mangrove, buttonwood. Seagrape, gumbo Pine
limbo, palmetto Mud beach: Red mangroves they also identified management requirements and formu-
: Submerged beach: Marine grasses lated recommendations. In order to reach a consensus on
WILDLIFE 1 : WILDLIFE requirements and recommendations, the following proce-
American Alligator, Green Anole, Mangrove Watersnake, Marsh Rabbit. Otter, Florida Loggerhead Turtle, Bottle-nosed
Panther, Manatree, Bottle-nosed Dolphin, Brown Pelican,.Double-crested Cormorant, Dolphin. Otter. Manatee. Brown dure was devised: 1) Survey team members wereconsulted
Great Blue Heron, Green Heron, Snowy Egret, Louisiana Heron, Little Blue Heron,
Pelican, Snowy Egret, Red-breasted
Blackcrwned Night HeronYellow-crowned Night Heron, White Ibis Roseate Spoo Mrganser America Oyster- by CF staff members during the course of their work; 2)
bill, Lesser Scaup Duck; Red-breasted Merganser, Bald Eagle, Osprey, Clapper Rail.
American Oystercatcher, Piping Plover, Snowy Plover, Wilson's Plover, Blackbellied tcher Sempalmatedthe team by CF;
Plover, Ruddy Turnstone. Eastern Willet, Laughing Gull. Least Tern, Black Skimmer. Piping Plover. Snowy Plover,
Wilso,'s Plover. Black-bellied
Plover. Ruddy Turnstone, Willet, 3) a draft of .conclusions based upon the comments was
Knot, Least Sandpiper. Dunlin,
Semipalmated Sandpiper, Western prepared; 4) a final workshop was held to refine and
Seanipalmated Sandpiper, Western
Sandpiper, Sanderling, Herring consolidate the re rements and ndations; 5) a
Gull, Ringbilled Gull. Laughing
Gull, Forster's Tern. Least Tern. revised draft was sent to the team members; and 6) a
Royal Tern, Sandwich Ter.of recommendations-based
Caspian Tern, Black Skimmer. formal, preliminary set of recommendations-based upon

22 The Natural Systems Study

25 Year Flood Tides / .-,�,- /
10 Year Flood Tides

Salt Water T e

Barrier Sand and S eaI
Clayor rMa;rl Confining Layer,,? lllujllIllIIl[lllillilll I ~IIIII l 1 l iii lilt ill llill l[Illllll~lllllil I II i 1111111111111111111111
Saline ShallowAquifer:

GULF BEACH GULF INTERIOR WETLAND BASIN
BEACH MID-ISLAND RIDGES
FRONT BEACH BACK BEACH RIDGE UPLAND LOWLAND UPLAND
~~~~~~~~~~ULNMI-SADRIDGES
The Gulf Beach Zone includes the area between the state T:he Gulf Beach Ridge Zone The Interior Wetland Basin Zone is the interior bowl which serves as a fresh water reservoir. The Mid-Island Ridges Zone comprises the
setback line and the city boundary 300' offshore. There is the major ridge immedi- It is composed of parallel systems of ridges and swales with corresponding hands of vege- major ridges along the central axis of the
are two subareas within this zone-the Front Beach and ately behind the beach. tation. There are two sub-areas within this zone-lowland and upland. The lowland Island and includes the highest elevations.
the Back Beach. The Front Beach extends from the city It is stabilized by dense uar ea is c omposed of low ridges and wide swales and experiences extended periods of In most areas this zone divides the Bay-
limit to Mean High Water. Sand in this subarea is in con- vegetation. Blind Pass--a flooding each year. The upland consists of higher, broader ridges and narrower swales, Mangrove watershed from the Interior Wet-
stent motion. Sand migrates between the berm and off- subarea within this zone- and is characterized by less frequent flooding and more upland vegetation types, lands watershed.
shore bars and is transported by longshore currents. The is ofvery recent formation
Back Beach comprises that area between Mean High Water and susceptible to dramatic
and the state setback line. Sand in this subarea is moved change.
by wind and water and stabilized by vegetation, forming
low dunes.
FUNCTIONS FUNCTIONS FUNCTIbNS FUNCTIONS
Storm Protection Storm Protection Flood Protection Storm Protection
Shoreline Stabilization Flood Protection Maintenance of Water Quality Flood Protdctio i
Maintenance of Marine Life Shoreline Stablization Maintenance of Fresh Water System Maintenance of WaterQuality
Maintenance of Wildlife Maintenance of Water Maintenance of Island Wildlife Maintenance of Fresh Water System
Quality
The Gulf Beach Zone is the Island's first defense in storm Maintenanceof Fresh Since the elevation of the Interior Wetland Basin is lower than the adjacent zones, it serves The elevation of the Mid-Island Ridges Zone
and flood when the impact of storm waves erodes the sand Water System as a storage area for flood waters until they are absorbed into the aquifer. Water Quality provides flood protection. This zone helps
reservoir in the berm, The low dunes of the Back Beach is protected by the filtering function of soil and vegetation. This zone is crucial to the maintain water quality by the filtering func-
are reservoir of snd which may be eroded after the ar The Gulf Beach Ridge is maintenance of the fresh water lens. It also has the capacity to maintain and improve tinns of soil and vegetation. Much fresh water
arein a reservoirof sandthus protecting pich maybe eroded afterthe berminnd a dike which buffers flood water quality, and provides food, shelter, water, and nesting areas to wildlife, including runoff e nters the ground in the Mid-island
ina seere storm, thus protecting property further inlnd tides and storm winds, pre- the American alligator. Ridges Zone, halting inward intrusion of
on the Beech Ridge. Th. natural profile of the Gulf Beachs t m wi p.
on the Beach Ridge. The natural profile of i the Gulf Besch vents increased flooding salt water from the Bay and thus maintain-
Zone is a wesponse to processes of wind. currents, and waves, in the interior (unless over- ing the fresh water lees.
Undistrubed, it is in a state of balance with natural forces, topped by waves) and con-
thus "stabilizing" the shoreline. The Front Beach supports tibutes to whoreline stc-
- . . . . ~~~~~~tributes to shoreline eta-
the marine life for which Sanibel is famous, and is an im- bilization. Water quality
portant feeding area for island wildlife. The low dunes of is maintined byrthe ail-
the Back Beach are an important nesting area for wildlife, fering function of soil and
the loggerhead turtle being a prime example. vegetation. Much fresh
water runoff enters the
ground in the Gulf Beach
Ridge Zone, halting inward
intrusion of salt water from
the Gulf and thus main-
taining the extent of the
fresh water lens.

ELEMENTS ESSENTIAL TO FUNCTIONS ELEMENTS ESSENTIAL ELEMENTS ESSENTIAL TO FUNCTIONS ELEMENTS ESSENTIAL TO FUNCTIONS
TO FUNCTIONS
Storm Protection and Shoreline Stabilization: Storm Protection and Shore- Flood Protection: Flood Protection:
-Natural profile of beach line Stabilization: -Water storage capacity -Elevation of ridge
-Sand reservoir in berm, bars and dunes -Shoreline stabilization -Free-flowing water circulation
-Gradual and dispersed runoff from land and storm protection Maintenance of Water Quality:
-Loegshore send movement functions ofthe Gulf Maintenance of Water Quality -Gradual and dispersed runoff
-Hardy dune vegetation Beach Zoe -Free-flowing water circulation -Filtration of runoff through vegetation and
-Natural configuration -Gradual and dispersed runoff soil
Maintenance of Marine Life and elevation of ridge -Filtration of runoff through vegetation and soil
-Access to beach -well established hardy -Restriction of industrial and domestic wastes discharged into interior wetland Maintenance of Fresh Water System.
-Good water quality vegetation -Water quality function of Gulf Beach Ridge and Mid-Island Ridges Zones -Recharge of runoff to fresh water lens
-Drainage of runoff to interior wetland
Maintenance of Water Maintenance of Fresh Water System: -Aquiclude between shallow saline aquifer
Maintenance of Island WildlifeQult
-Acc.ees nto bheach Quality -Recharge of runoff to fresh water lens and fresh water lens
-Access to beach -Gradual and dispersed -Sufficient water levels -Elevation of ridges
-Abundant marine life runoff -Aquiclude between shallow saline aquifer and fresh water lens
-Filtration of runoff -Free-flowing water circulation
Table 4. through vegetation and
soil Maintenance of Wildlife:
-Good water quality
Maintenance of Fresh Water -Fresh water system
The functions of Sani- System: -Access towater
bel's major ecological -n,~a$Rechergef rnff to --Nativevegetation of value to wildlife
fresh water lens
zones as interpreted -Drainage of runoff to
interior wetland
by Wallace, McHarg, -Aquiclude between shal-
~~~~~~~~~~~~~~~~~~~~~Roberts and _T~low saline aquifer and
Roberts and Todd. fresh water laos.

Introduction 23

-.- _" - comments on the revised workshop draft-was prepared
_ ____ _ 25_Year Flood Tides for presentation to the City Council on Septembef 16,
1975. The final recommendations included minor revi-
sions in response to additional data or analysis provided by
iii>_~ iii<~ =11111~ i0~~ Dlii 111 r i IIthe consultants after September 16.
Sat Water ' ' . ' Peat Deposit- � .' . : .' '. i
.. - Muds, Organic Materials. Sands and Shell ' The consensus method is an efficient and economic way
-' � lll.'lllll � l'-'.�'- . l. '%Clay or Marl Confining< Iayer. ; to get a wide spectrum of technical talent to reach recom-
MANGROVES mendations useful to management. Its success is condi-
:ANGROVI : :: :I - BAY BEACH : - tioned upon these four requirements: 1):The technical
MANGROVES E I TIDAL FLATS V"MANGROVES : : : , : experts must already -have experience in their fields of
The Mangrove Zone includes all areas of red, black and white mangroves, as well as the The Bay Beach Zone extends expertise; 2) they must be encouraged to review past
tidal flats and hardwood hammocks within them. Much of this zone, including all areas from the city's boundary 300' they be eview
of red mangrove, is subject to daily tidal flooding. Other areas of the zone are subject into the bay to a setback line literature on the area to spend time in the field, and to
to extended periods of flooding every year. approximately t100' behind the field, to
Mean High Water Line. It is collect such new. data as. are needed to confirm their
lower energy beach than theto
G gulf Beach. and includesareas general understanding of they must each be
of marine grasses on the bay understanding m,
bottom. It includes both sand
beach and mude beach.sand required to report in writing on their investigations and
findings, and 4) they -must be well prepared for decision
FUNCTIONS FUNCTIONS
Storm Protection Storm Protection sessions by receiving, in advance, progress reports of col-
Flood Protection Shoreline Stabilization in
MaShoreine Sabilization Maintenance of Marine Life leagues' work, preliminary findings, and so forth.
Maitenance of Water Quality Mainteannce of Wildlife
Maintenance of Marine Life
Maintenance of Wildlife The Bay Beach Zone buffers the
impact of stormr wenns. The Citizen Guidance:, An essential element of the study
The dense canopy and roots of the mangroves buffer storm winds and tidal surges. The natural form of the Bay Beach
arching prop-oots of the red mangrove and the roots of the black mangrove trap sediments is a response o natural processesfrequent consultation with a panel of
and stabilize and extend the shoreline. Mangroves preserve water quality by filtering suspended of wind, currents, and waves.
material and assimilating dissolved nutrients. Mangroves maintain the highly productive marine Undisturbed, it is in a state of Sanibel citizens selected by the project sponsor to ensure
ecosystem and provide food, shelter, and nesting areas for wildlife. balance with natural forces,
thus "stabilizing" the shore.
line. The Bay Beach is a feed- that the environmental specifications would be most useful
ing area for island wildlife.
Beds of marine g.rassesin sub- to the community. The aim here was to enrich the process
aerged portions of the beacn by providing opportunities for early interchange between
are important d y andg a n be
feeding areas for marine life. the natural systems analysts and citizens of the island. This
approach provided the opportunity to adjust the program
while work was in progress.
The Conservation Foundation team worked closely with
its sponsor, the Sanibel-Captiva Conservation Founda7-
ELEMENTS ESSENTIAL TO FUNCTIONS ELEMENTS ESSENTIALTO tion, in structuring the consultations as a series of work-
St-Horm Protection Shoreline Stabi on and Land Biding Storm Protection and Shoreline shops with the citizen panel. The 13 cooperating pan-
Stabilization:
Maintenance of Water Quality: S-Natural prfile of beach elists were a diverse group of SCCF members. They
-Healthy mangroves -Gradual and dispersed runoff included a local banker, two land developers, a memb
-Restriction of domestic and industrial wastes discharged into Mangrove Zone from land included a local banker, two land developers, a member of
-Water circulation -Longshore sand movement
--Hardy beachvegetation the planning commission, an editor of the local news-
Maintenance of Marine Life:
-Healthy mangroves Maintenance of Marine Life: paper, and several other citizens.
-Good water quality -Mangroves
-Marine grass beds The workshop series was divided into two sections. The
Maintenance of Island Wildlife: -Access to beach
-Healthy mangroves -Good water quality. first five sessions focused on providing panelists with the
-Abundant marine life
Maintenance of Wildlifeah technical information required to make intelligent assess-
-Good water quality
--Abundant marine life ments concerning the environmental needs of the island.
The remaining four sessions were devoted to discussions
of policy options and the development of environmental
criteria with which to evaluate the emerging land-use plan.
The five technical workshops were held in conjunction

24 The Natural Systems Study

with the scientists' work on the island. The scientists
presented background information at the workshops and
discussed with panelists the scientific principles and tech-
nical considerations pertinent to the formation of an
environmentally sound land-use plan. Each meeting was
devoted to a specific environmentaLdiscipline: vegetation,
birds, hydrology, insect control, and beach erosion.
Following the workshops, three sessions were held to
discuss the specific options implicit in the presentations by
the scientists. At a fourth and final meeting, CF's initial
recommendations were incorporated into a preliminary
presentation to the Planning Commission. This presenta-
tion was made to the commission at a public meeting in
August 1975.
From the beginning it was recognized that a high level
of understanding would be required for the-panelists to
grasp the complex interrelationships among mechanisms
which govern natural systems, because this understanding
must be achieved if citizens are to make perceptive
judgments on issues of environmental importance. There-
fore, the panelists were educated in basic natural systems
knowledge before their opinions on recommendations
were requested. The results indicated that citizens can be
aroused to participate and learn natural science fundamen-
tals if they believe their contribution can affect the result.

CHAPTER 2

WATER

1i~~~. Hy~~~~drol~on the dry season (November through May).,5 Because of the
1. Hydrology
localized nature of thunderstorms, the distribution of
Water is the major factor in all the ecological zones on rainfall varies considerably across the island, but averages
Sanibel Island. It sets the conditions that distinguish the about 42 inches per year.6
zones, and it affects the soils, vegetation, and wildlife in Hurricanes and other tropical storms sometimes affect
each. At the same time, it ties the various zones together Sanibel's hydrologic system. In the past, intense rainfall
through complex changes in flow and water quality. during hurricanes and tropical storms has caused extensive
(Figure 16) flooding, and complete tidal overtopping of the island
occurred during several severe hurricanes.
Between 1830 and 1968, 23 hurricanes and 23 tropical
Climatic Conditions storms or depressions passed within 50 miles of Lee
County.'7 According to Jordan, the probability of a tropical
Sanibel Island has a subtropic climate with an estimated storm or hurricane passing through the Gulf of Mexico is
average temperature of 740F. An average temperature of 50 percent for a given season.'8
830 occurs during August, and an average of 640 during
January.'3 A killing frost takes place every few years.14
An easterly wind blows across Sanibel most of the year Groundwater System
except during the 15assing of winter frontal systems and
tropical storms. There are at least two deep artesian aquifers underlying
About 70 percent of the rainfall on Sanibel Island occurs Sanibel Island that yield significant quantities of water: the
during sporadic thunderstorms throughout the wet season Lower Hawthorn aquifer and the Suwannee aquifer.
(une through October). The remaining 30 percent falls in Neither aquifer is- directly recharged on the island. The

26 The Natural Systems Study

INTERIOR-WETLANDS MID-
NHi'+ BvEPAACio- /' TrSPIP,,RATioDFJ L ISLAND PINE ISLAND
GULF OF BEACH = NIWTUAL WJAT-R LOSS RIDGE SOUND
MEXICO RIDGE LOWvW WATER-
VtSrATiVE ImVAsIo/4
ERo5oi = LO ss WETLAID sirEs WASHO4F
o0 OEACA ANb, DRAINED J

:SA~. \JAYE& I:NTPO E #O
vatC4- c -aTAL LAKES ' ' ' -' ' i'
A146 CANLs5 TREATIENT PLA GROUND WATER
/ 5/) WAT'~~' :~GROUND WATER / /
/ 0 t N T R \ J~tz ' . R R ~ziP _ . ~ "..'.-, i' . * ,0 ,.. � . ' .'.,AQUIFER'*

/////>ttY$.Ai0j [::tt~~.~. g S / /- Figure 16.

iSAT WATER XNyTRUl~g e CcEASSS The ecology of the entire
\ wITH PWpXcED FE-SH+WATER HEAP island depends on the healthy
DEEP WELL -M :RVPOUS,BUT _UcTunATS Wti ' WAT. TAL-E functioning of the interior
E~ASEAE iR1swiopl LEAY, c LAY LAYER LEVEL. SHALLOW ARTESIAN AQUIFER wetlands.

Lower Hawthorn aquifer is positioned near the contact Suwannee aquifer are nearly 1,000 mg/l at the top of the
between the Hawthorn Formation and the underlying aquifer, and increase progressively with depth. Extreme
Tampa Limestone, while the Suwannee aquifer lies near variations of water quality in each aquifer occur from well
the contact between the Tampa Limestone and the under- to well on the island. The freshwater zone occurs at
-lying Suwannee Limestone. (Table 5) different depth- intervals in nearly every well, and some-
Artesian head pressure within these lower aquifers times does not occur at all.
ranges from 16 to 32 feet above mean sea level on the Little is known about other characteristics of these
island. The highest head occurs on the eastern part of the aquifers, such as transmissivity, storage coefficient, sus-
island and decreases to the west. Daily fluctuations of 1 to tained yield, draw-down, or permanence of quality. Some
2 feet occur due to tidal and atmospheric pressure varia- artesian wells on Sanibel leak, discharging poor quality
tions.19 water into fresher zones.
The Lower Hawthorn and Suwannee aquifers generally The top of the shallow artesian aquifer occurs between
contain saline water-or water that has at least 1,000 25 and 30 feet below mean sea level in the Pleistocene
milligrams per liter (mg/1) of dissolved solids.20 Vertical Limestone. It is normally separated from the overlying
change in water quality within the saline-water aquifers is water-table aquifer by a heterogeneous mud stratum, and
shown in Table 5. The water in the upper part of the Lower separated from the lower artesian aquifers by carbonate
Hawthorn aquifer is highly saline. A relatively thin zone of clay beds in the Tamiami Formation. There are some areas
fresh water, containing 600 mg/l to 1,000 mg/l of dis- where the upper confining bed is extremely thin, or does
solved chloride, occurs near the base of the lower Haw- not exist. Leakage between the shallow artesian and the
thorn aquifer. Dissolved chloride concentrations in the water-table aquifers is possible in these areas.

Water *27

Water levels in the shallow artesian aquifer fluctuate deposited, or through downward leakage and selective
daily with the tides. The range of these fluctuations is a osmotic differentiation. The lower chloride concentrations
function of the distance to the nearest tidal water body, and may be the result of partial flushing during deposition, or
the permeability of the aquifer. Water levels in the shallow recent flushing.
artesian aquifer are .not greatly responsive to seasonal There is no known recharge to the shallow artesian
water level variations in the overlying water-table aquifer. aquifer other than possible downward leakage, which
Water quality varies considerably in the shallow arte- occurs only under special conditions. Leakage of water
Sian aquifer, but the entire aquifer is saline. Chloride values between the shallow artesian aquifer and the water-table
often exceed concentrations in seawater, usually about aquifer is strictly a function of head differential and
19,000 mg/l in the vicinity of Sanibel. These high chloride vertical permeability. During high tide periods, the water
waters may have formed when the strata were originally level in the shallow artesian aquifer usually stands above
the water table, and potential leakage is upward. During
the low part of the tidal cycle, the water level in the
FORMATION LITHOLOGY QUIFER CHORDECOTEN shallow artesian aquifer usually drops below the water
iii g0R0 24 6 012
do' - 0N-SHELL il ; -' LjA'R-TORLE � 2 : D 8 i table, and possible leakage is downward. When the water
U d GRAI CLA AND SAN D FE -:
l ,,,. C/LIMESTONE . : . ...E. table is high for an extended period, such as after heavy
t9 AN 0 0 HALLOW; ;: rainfall, the water table may remain above the artesian
0O- M EE. CLAT RAND ... G
ASuaaR O=DjP f _water level through numerous tidal cycles. To some degree,
XSAY,GNEEN,AND WHITE CLA IALNE leakage between the two aquifers occurs continuously. The
0 .N-WITE.SA..D LIMESTONE vertical permeability of the mud stratum is the primary
TAWAMI AI GRLAYEY, OA/RPATIC SAND r- control of the quantity leaked.
�OR"T'�N " The uppermost 20 to 25 feet of sediment on Sanibel
Island is unconfined, consisting of quartz sand, shell, and
GRAYCLAYERPOOR-YATIC SAN ~ some minor percentages of carbonate mud in the lower
beds. The saturated part of this layer is termed the water-
zU~~.. ............ .. ,-,,,,,osII Ltable aquifer.
W R.ITE PNOSPATIC LIMESTONE = Climatic factors primarily control water table fluctua-
i ,TM IMESTONE -MRL LOWEN N : tions on Sanibel, with secondary effects caused by man's
TAR LI...MES . :ONE--
GRAY AND GREEN MARL --==== ADUWITFEOPAXR activities. The water table rises in response to recharge,
FORATION WHITE ARL.
FORMATION GRAY MANTY LIMESTONEAL 8} and declines when water is discharged from the aquifer.
_-:------_:__ 1 The only natural source of freshwater recharge on the
GRAY-WRITE PHOSPHATIC MARL Z--NE---N
MOSRAY-WNITEPvdSPHATICARL --WNF island is rainfall. In the absence of freshwater recharge,
RA,."LIMESTONE., :...:Csaline water may recharge the aquifer laterally from the
LIMESTON E TN SLIGHL .HPATIC sea, through the surface water system, or from the underly-
L IME STONE
TOO- L - . 1 D ing shallow artesian aquifer. Natural discharge from the
- TANLIYMETONE,5OME PL ,.I SUON.EE aquifer includes evaporation, evapotranspiration, ground-
,j- . AQPU'FE"R \ water discharge to the sea, and discharge to streams or
Ed_ t N .ONNEE lakes. Some recharge to the aquifer results from man's
Table 5. I LIMEYTONE TAN LIESTORE SALIN
Tale5 4� ~dMWE4STONE TAH Ll ,,, , \ 5WATEN activities, such as inflow from deep artesian wells, inflow
Sanibel Inssof treated sewage effluent, and septic tank discharges.
Sanibel Island's subsurface
geologic formations, including 500- Discharge from the aquifer also has been altered by man.
chloride concentrations in EXPLANATION An enhanced surface drainage system now discharges
groundwater (from test hole D:E .. some water to the sea (Figure 17), and a minor amount of
L-193). (Source: D. Boggess) RANG ::ECLARMARL LIwater is pumped for irrigation.

28 The Natural Systems Study

When the water table is high on Sanibel, a much greater tanks flows through the soil to pollute ground and surface
quantity of fresh water is stored, and the wetland areas are waters. Fertilizers, pesticides, and other pollutants further
filled with surface water. When the water table is low, the degrade the water. The water-table aquifer is polluted with
quantity of water in storage decreases and wetland areas salt water.
tend to dry. A heavy influx of nutrient-laden wastewater into the
The fresh water stored in the water-table aquifer:has a eastern segment of the Sanibel River has caused blooms of
great natural variation in quality. Even small perturbations undesirable vegetation that have depleted dissolved oxy-
can result in upward pluming or other saline intrusions, gen. General. stagnation and the -deposition of organic
and tidal overtopping sometimes occurs. Without an detritus :have caused low values of dissolved oxygen to
adequate quantity of fresh water stored within the water- occur throughout much of the interior drainage system.
tableaquifer, the present flora and fauna on Sanibel Island Pathogens can exist in untreated or partially treated
could not exist. F 0 : :sewage. Diseases can also originate from protozoan orga-
nisms living in sewage. Entero viruses present still
2. Water Qualit: another health hazard. Although their presence in sewage
does not guarantee an epidemic; they do present a constant
The quality of Sanibel's surface water is substandard. threat of infection. The hepatitis virus, for example', which
Sewage from 20 package plants and more than 2,000 septic can 'exist in shellfish living in polluted water, can infect
- f S ; R f 73 , R \ 0 - =

Figurer 17.

Solid fill, which replaced the
wooden bridges on Sanibel
during the 1960's, has choked
water flows and cut off many
segments of the wetlands. The
small culverts shown here do
not provide adequate
circulation.

Water 29

of effluent. In the off-season (summer months), treatment
drops to about 0.225 MGD. The designed capacity of this
plant is 1.2 MGD, with a total of 975 connections either
existing or currently being installed. Secondary treatment
is provided by two large aeration tanks in combination
with two retention lagoons for bacterial breakdown of
pollutants. (Figure 18) Effluent can apparently be disposed
of on an adjacent, ifabandoned" golf course (at Beachview
Country Club Estates,, which is currently undeveloped)
using spray irrigation but it appears that most of it enters
the groundwater directly. In the summer months, effluent
amounts to 500,000-600,000 gallons a day. The possible
presence of pathogenic organisms prevents spraying this
effluent on lawns or the golf course of developed adjacent
residential areas. However, effluent that is appropriately
treated could bera valuable asset in view of the need for
surface water replenishment in the fresh water manage-
ment area.
The Jamestown Beachview plant is adjacent to the
Sanibel River. Effluents from two retention lagoons enter
-directly into the groundwater and move quickly into the
river, causing severe water quality problems. (Figure 19)
The plant pumps up to 0.5 MGD into the lagoons and the
water level has reached as high as 2-4 feet above that of the
Figure 18. humans who drink the water or eat the shellfish.2e river. This hydrostatic head of water enhances the flow of
Sanibel's soils, as identified by the U.S. Soil Conserva- pollutants into the river. Recent dissolved-oxygen data and
Highconcentrations of nutrient tion Service, are Canaveral' and Basinger types-marine
in the sewage. plant's treatment unpublished tests by the Florida Department of Pollution
lagoon -- indicated by the thick deposits of, sand and shell. These soils are characterized by Control indicate that the section of the Sanibel River
layer of algae at the surface - rapid permeability (greater than 20 inches per hour) and a adjacent to the plant may persistently violate both federal
leads to pollution of adjacent water table generally at-depths of 10 to.40 inches below the and state water-quality standards.23 Dissolved-oxygen ev-
waters by infilttion. surface for 2 to 6 months.22 els regularly fall below the 4 ppm (parts per million)
These soil conditions impose moderate to severe limita: standard. The owners of the plant have been directed by
tions on many types of land uses, including the excavation the Florida Department of Pollution Control to seal the
of ponds, and the building of foundations and roadbeds. bottom of the two lagoons to prevent migration of
Also, Canaveral soil is not considered suitable for septic pollutants through the groundwater and surface-water
tank drainfields and sewage treatment lagoons because of systems. (Figure 20)
its rapid permeability.
Package Plants
Central Sewage Treatment
At present, the 20 package plants on Sanibel service
The Jamestown Beachview Wastewater Treatment approximately 300 dwelling units (principally hotels,
Plant, serving the eastern end of the island, is the largest motels,'and condomimiums along Gulf Drive), and should,
treatment facility on :Sanibel. During the winter, or"peak" if properly operated, provide a higher level of treatment
season, this plant treats 0.5 MGD (million gallons per day) than septic tanks.24 Several of them, however, cause or

30 The Natural Systems Study

I 1 I I I I
I : I I : SEWAGE

V-- ' r~~~~~s - -~~~~~ RIVER

AQUIFER Where pollutants from sewage
lagoons have entered surface
~~~~~~LEAKAGE TO:~ ~and groundwaters on Sanibel,
GROUND1_~~~~ ~ WTR.serious water quality problems

contribute to problems involving excessive nutrients in the cause suitable physical conditions for minimal septic tank
receiving waters5 There has never been a coordinated efficiency (particularly soil absorption) simply do not exist
plan for wastewater treatment on the island. Many plants on Sanibel. Effluent that reaches the water-table aquifer,
are hapazardly designed, improperly located, and poorly carrying bacteria and nutrients, saturates the soil and
operated. State regulations on treatment plant function are pollutes the groundwater. Soils on Sanibel are of such high
not sufficient to prevent serious degradation of Sanibel's transmissibility that the polluted groundwater can move
water-table aquifer-quite simply, they are not designed rapidly through the soil and into surface water.
for the difficult soil and water combination found on the . It is impossible to estimate how much of Sanibel's water
island. (There is no law in the State of Florida setting pollution problems may result from septic tanks. Scientific
minimum setback lines for package plants.) Worse still, research in coastal areas has shown that severe eutrophica-
several sewage plants are currently reported to be in tion of coastal waters-with resulting fish kills, noxious
violation of even the minimal state regulations. There is odors, and public health dangers-can result from septic
little water-quality data for the groundwater surrounding tanks too close to surface waters.
these plants-all of them, however, are located near small In septic tank operation, wastewater from a home flows
lakes, the Sanibel River, or mangroves and interior wet- into a concrete tank where the solids settle to the bottom
lands. Several plants have persistent breakdown and main- to be decomposed by bacteria into organic matter. Nutri-
tenance problems. ents released during this process flow into drainage areas
through subsurface tiles. Further percolation through the
Septic Tanks ground completes the treatment process. The nutrients
often are taken up by trees and Shrubs, or absorbed into soil
Approximately two-thirds of the households on Sanibel particles. If the distance between a septic system and water
use septic tanks. Excess phosphate and nitrogen (which is is insufficient, the liquid waste leaching through the soil is
particularly mobile in groundwater-) is the probable cause inadequately treated and can pollute the water with a variety
of most over-fertilization and excess algal growth in of substances. The most troublesome pollutants are nut-
Sanibel waters. As population density increases, far more rients, particularly nitrogen compounds. Nitrate (NO3),
serious groundwater pollution may become evident, be- which is particularly mobile in groundwater, is the probable

Water 31

bacteria-and there is growing doubt about this-they do
not remove -certain dissolved pollutants, particularly ni-
trates. Also, recent research indicates that viruses can
travel long distances through groundwater-which further
complicates the septic tank problem.
L. B. Leopold, a U.S. Geological Survey hydrology
expert, has reached the following conclusions: 1)) . . for
soil cleansing to be effective, contaminated water must
move through unsaturated soil at least 100 feet," and 2)..
no source of pollution such as seepage field [should be]
closer than 300 feet to channel or watercourse."2 Leopold
added that even this setback does not prevent dissolved
materials such as nitrates from enriching the water, thus
potentially creating a biotic imbalance through eutrophica-
tion.
In a coastal area, a setback of 300 feet would be a safe
starting point, unless local soil and groundwater conditions
are particularly unsuited for nitrate removal-in whlich
case an even greater distance should be considered. (Table
6) Setback standards that provide for nitrate removal are
particular!y important for Sanibel because nitrogen is the
controlling nutrient for algal-growth in the island's inte-
rior wetlands and mangrove areas.
Urban Runoff

Every acre of land on Sanibel is washed with 1.5 million
gallons of rainfall each year. Pollutants washed from paved
surfaces, roof tops, and fertilized lawn areas enter the soil
and eventually can affect the water system.
Under natural conditions, rainfall drains through vege-
.tation as overland flow or through the soils via groundwa-
ters-thereby receiving'highly effective purification and
treatment. (Figure 21) In an urban area, the typical storm
cause of most estuarine eutrophication. drainage system is designed to short circuit the natural
State regulations typically require absorption fields of system, and remove rainwaters as rapidly as possible.
Figure 20. septic tanks to be set back a minimum distance from the Runoff from an urban area frequently has characteristics
edge of any stream, lake, open ditch, or other body of water similartoraw sewage. Contaminated runoff can be caused
Effluents from the sewage into which unfiltered effluent could escape. The purpose of by yard refuse, septic tanks, garbage dumps, stagnant
plant leak directly into the the setback is to allow for removal of pollutants-particu- water, car washing, vehicle drippings, construction and
Sanibel River, polluting its larly coliform bacteria and other water-borne pathogenic maintenance operations, insect spraying (mosquito con-
waters and covering them
with a thick algae layer organisms-from wastewater through soil purification trol), and fertilizers?27
similar to the one covering before it reaches the adjacent body of water. Although The extent to which urban runoff contributes to Sani-
the sewage lagoon. these setbacks may be sufficient for removal of pathogenic - bel's water quality problem is not known-but is believed to

32 The Natural Systems Study

be substantial. The problem will, of course, increase as
Figure 21.
population increases.
Calculation of Carrying Capacity Threshold Most of the rainwater that
falls on this porous road
will enter the soil and be
Consultant G. Kenneth Young performed an analysis of cleansed; blacktop roads
the relation of population and residential density to the _ shunt the water directly
natural assimilative, capacity of the interior wetlands of :: Ed -_ to drains without purification.
Sanibel.28 The purpose was to determine whether the - -:
wetlands had a pollution-loading threshold that if passed
would seriously threaten any of the wetland's three major
functions: 1) ability to assimilate wastes; 2) use as a
wildlife habitat; and 3) potential as a secondary water
supply.
The results of the holding capacity analysis are shown
in Table 7. The curve represents the calculated holding
capacity of the wetlands based upon a threshold of 4.0 ppm
of oxygen; that is, to avoid violation of the federal
minimum allowable oxygen standard of 4.0 ppm, it is
necessary to remain below the curve. The curve suggests
that there is a limit to waste loadings, that per-capita
loadings increase at a rate even greater than population o
increase (because of increased non-point loading from
increased land surface in use), and that the capacity of the
wetland may have been exceeded already (as shown, in
fact, by the degraded water quality of the Sanibel wet-
lands).

3. Water Level
0
Over the past 20 years, the natural drainage system of
Sanibel Island has been channelized and expanded for a
number of reasons. The former "course" of the Sanibel Table 6.
River was modified-deepened and widened. A network of SITE-DEPENDANT
canals and ditches was connected to it. An eastern subbasin RISK Generalized representation of
was terminated by a series of deep tidal canals at Beach o pollution risk from nutrients
and pathogens as related to
Road, where a structure to control water level was built. A septic tank setback distance.
western subbasin was extensively ditched, and the flow
direction was reversed-discharge now occurs at Tarpon
Bay through a control structure. (Figure 22) During high
water conditions, water still may escape at the western 0 50 100 150 260 250 300 350
part of the island. Roads cross the channel at several Distance From Source toSurface Water

Water 33

locations, with small culverts running beneath them. The
culverts do not provide adequate connections, and during
high water conditions interior flooding sometimes occurs.

Stage and Flow

Rainwater rarely discharges. through the surface-water
system of Sanibel Island. Sufficient rainfall must accumu-
late to raise the stage more than 2.5 feet above mean sea
level before sustained discharge can occur at the control
structures. According to U.S. Geological Survey stage data,
this stage has been attained only twice since November
1970.29 Minor discharges have occurred many times during
the wet season because of leakage at both control struc-
tures, and because of tampering with the Beach Road
control. (Figure 23)
Sanibel's present drainage system has had a pronounced
effect on the water-table aquifer. Since the canals and
ditches are dug through very permeable sand and shell,

Figure 22.

Existing water control struc-............ .......-................ .... : . ..........
ture at Tarpon Bay will have ...... .. ........._ . soo+36 ........... ....................................
to be improved to protect 34 -..N.::....i .....:i. i.........:...j:-........: ........ ANYPINT BELOW
.................. BOVE .....................--:----:-:--CURVE Is

3 2- ::::: ...................INCEA
....i:..:.. I.....E.L.. ' . .v ......::::...:..::::i..:::...:.::...........................:

(for.-..::..:. ......................... p :..

Table. so iiiiiiiiiiiiiiiiiioiiiiiiiii b p IoSIN PEOPLEAK
2a .ld cap y . Id e i.
tants) shown by population :DENSIT12,000 PEOPLE

Maximum loading capacity

34: The Natural Systems Study

saline water into the interior surface and groundwater Figure 23.
systems through uncontrolled or poorly controlled canals
that are connected to tidal water bodies;- 3) massive This water control system at
intrusion of highly saline water during tidal overtopping Beach Road was vandalized
caused by intense storms; 4) upward leakage from the so often it finally had to be
underlying shallow artesian aquifer; 5) discharge of highly plugged with concrete in 1975.
saline water at the surface through improperly con-
structed, damaged, or uncontrolled artesian wells; and 6)
pumping and dispersing highly saline water into the
interior parts of the system?3
Saline intrusion has important ramifications for the
island's ecosystems. Vegetation not adapted to salt water is
destroyed by increases in salinity; Farming on Sanibel, for
example, was ended by hurricane tides that covered the
island in 1910, 1921, and 1926.31 Many freshwater wildlife
species cannot tolerate higher salinities. Finally, saline
intrusion into the water-table aquifer causes problems for
many residents who use this water for household needs.

4. Water Supply

In a barrier island environment such as Sanibel, suffi-
cient supply of fresh water is a major problem. Under
normal conditions, a shallow, unconfined aquifer, which
contains fresh water, exists just below the land surface.
Under conditions of limited urban settlement, when the
water in the water-table aquifer flows rapidly out of the demand for water is minimal, this source of fresh water
aquifer and into the adjacent canal where there is a could supply most of the demand, and can be replenished
positive gradient. This discharge from the groundwater by natural rainfall. Excessive withdrawals from this fresh-
system has increased the rate of recession during the dry water reservoir upset the hydrological balance of the
season, and has caused temporary depletion of storage in groundwater system. This system is extremely vulnerable
the aquifer. to dramatic change primarily from three causes:-saltwater
intrusion (from flooding or groundwater), pollution from
Salt Intrusion surface runoff, and effluent percolation.
Prior to 1973, Sanibel purchased water from the Pine
Salt intrusion into Sanibel's ground and surface waters Island Water Association, which tapped the comparatively
is a major problem-and it has worsened as development shallow freshwater Upper Hawthorn aquifer. Escalated
has increased. The problem is caused principally by lower- growth on Sanibel in the early 1970's caused increased
ing the water level in the interior basin. With the head demand and led to problems of water supply. Since the
pressure thus reduced, salt water can intrude into the freshwater aquifer supplying Pine Island from the main-
freshwater areas in six basic ways: 1) intrusion of water land was also limited, supply problems for Sanibel soon
directly from the sea into the water-table aquifer (Ghyben- became apparent. The critical balance between -water
Herzenberg intrusion); 2) leakage or intrusion of highly entering the ground and withdrawals from shallow wells

Water 35

was upset. When Sanibel installed its own water supply 5. R ecommendations
system (the Island Water Association [IWA]), the only
water available to IWA of a treatable quality was found at
depths between 500-600 feet.
Water Quality
In November 1973, IWA put its first brackish water
treatment plant into service on Sanibel, utilizing the elec- There 'are four principal threats to water quality on
trodialysis demineralizing or desalination process. The Sanibel: 1) discharge of polluted effluents; 2) storm water
plant draws brackish water from wells 500-600 feet deep runoff; 3) pollutants conveyed through groundwater; and
which tap the Lower Hawthorn aquifer. The:- Lower 4) salt intrusion of ground and surface waters.-
Hawthorn aquifer is a water resource which is recharged The Conservation Foundation recognized the urgent
from a vast region, located many miles from Sanibel. As need for a central sewage system, but was concerned that
opposed to the shallow water-table aquifer on the island, the island might not be -able to- assimilate the effluent
no detailed study has yet' determined the Hawthorn discharge into the ground. Certainly the area of the
aquifer's supply capacity with respect to regional water interior wetlands and river adjacent to the present disposal
demands. The USGS office in Fort Myers, with support site for the Beachview plant is grossly polluted. Higher
from the city and IWA, is conducting a study of the Lower levels of treatment may help, and better receiving areas
Hawthorn: aquifer in order to determine Sanibel's needs may be found. Nevertheless, the ocean disposal option
versus; regional supply and demand. should not be dismissed at this time. Federal requirements
Construction of the existing system began in late 1972 appear to permit ocean disposal of secondary effluent
and went into service in November 1973 (with the first of under certain conditions.
four phases of the treatment plant in service, it produced The combined effects on Sanibel's surface waters of
1,200,000 gallons per day). This plant, which has since runoff pollution and leaching of sewage have -been esti-
been expanded to a capacity of 1,300,000 gallons, is mated by G. K. Young. Young has calculated that, with the
currently the primary source of water for both Sanibel and best expected levels of treatment of sewage effluent, the
Captiva. The fixed interconnection between the two origi- combined effect would overwhelm the assimilative capac-
nal systems (from Pine Island) is still in place and ready ity of the wetlands-leading to unacceptable water quality
for service. On an emergency basis, water can be transmit- when the total island population approached 20,00033 Thus,
ted from Pine Island to Sanibel, and from Sanibel to Pine there is a definite water quality limit to the occupancy of
Island. Suitable metering devices are becoming available. Sanibel.
The water plant on Sanibel draws brackish water from Discharge of Polluted Effluents (point-source)
deep wells located near the plant site. The water is treated
by aeration and filtration, and then chlorinated for distri- Direct discharge of wastes as concentrated point-sources
bution in a reservoir on the site. All of the required is not now a major problem on Sanibel and should not
mechanical, chemical, and distribution equipment is in become so in the future. It appears that neither sewage
operation.32 effluent nor industrial wastes are discharged directly into
The IWA distributes the treated water from its main Sanibel waters at the present. Since water quality on
plant near Rabbit Road to two remote pumping sta- Sanibel is so easily degraded, however, the city should take
tions-the Sanibel Booster Station (near the intersection of precautions to ensure against any such discharge in the
Periwinkle Way and Dixie Beach Boulevard) and the future.
Captiva Substation (located approximately one mile from
the south end of Captiva Island on State Road 867). These
two pumping facilities distribute water to the east end of Contaminants that are washed off land surfaces into
Sanibel and to the north end of Captiva, respectively. surface waters by rainstorms (diffuse sources, or non-

36 The Natural Systems Study

point pollution) are now responsible for some water the shallow groundwater and into the open surface waters.
quality degradation and are likely to become a severe The sources are septic tanks, package plants, and the
problem in Sanibel's future unless a definite control Jamestown-Beachview treatment plant.: The Conservation
program is initiated. The Conservation Foundation made Foundation recommended the following:
the following recommendations to the Planning Commis- 1) The appropriate long-term solution is replacement
sion and WMRT: of all existing facilities (septic tanks, package plants, etc.)
1) On-site retention of storm water should:be standard with a modern island-wide secondary sewage treatment
practice for all residential and commercial developments, system with off-island disposal of effluent, or an advanced
thus eliminating any diversion of storm waters to the system with the effluent used to recharge the groundwater.
interior and wetlands water system, or to the gulf or the 2) Short-term solutions would involve upgrading the
bay. This can be accomplished by installing detention operation of the Jamestown-Beachview sewer plant and all
ponds and infiltration enhancement devices such as deficient package plants, and applying strict standards to
"French drains." Rainfall should be retained on the island location of leaching fields for any new septic tanks or
to the maximum extent possible because it is Sanibel's only package plants. Leaching fields should be set back a
natural source of fresh water. s ufficient distance so that contaminants do not reach
2)f Impervious surfacing should be kept to a minimum, surface waters. This may require a setback of several
and unsurfaced roads should be used to the maximum hundred feet from the edge of adjacent surface waters for
extent possible. Special standards are required for Sanibel package plants.
because of the high pollution vulnerability of its waters. Individual septic tanks set back less than 150 feet
For example, blacktop parking lots and hard-surfaced invariably contaminate surface waters with excess nutri-
roads and driveways should be discouraged. Sand and shell ents. ~anibel, because of saturated, highly permeable soils
roads and driveways should be encouraged, along with a with low organic content, obviously must have ,higher
wide variety; of permeable surfaces available for parking standards than other coastal areas. Therefore, a setback
lots or patios. - greater than 150 feet is needed. The following specific
3) To provide:sufficient filtration and purification of suggestions for septic tanks were offered:
runoff water from developed parts of the island it is 2.1) In most cases, a 300-foot maximum setback should
necessary to require a buffer strip of natural soil and provide for removal of excess nutrients before entering
vegetation around all open water areas. This will permit surface waters.
infiltration and vegetative scrubbing (removal of contami- 2.2) A lesser setback in the range of-200-250 feet might
nants) of runoff before it reaches open water areas. The permit the minimal required removal of nutrients and
buffer is particularly important where there are definite pathogens under certain situations; research specific to
sources of pollution, such as lawns or golf courses, that each site will be needed to confirm this recommenda-
would be heavily fertilized or treated with pesticides. A tion.
setback of 150 feet would be effective and should provide 2.3) Immediate research should be conducted in the
sufficient filtration potential where chemical applications 200-250 foot range to establish island-wide standards
are moderately heavy. The buffer might be required for present use; it will be necessary to retain the
routinely but its width decided on a case-by-case basis, with minimal 200-foot setback.
project sponsors required to show that a lesser distance 2.4) Later, a detailed research program to explore the
would meet the water quality standards. 250-300 foot and 150-200 foot ranges could be mounted
with a view to developing multiple standards that are
Pollution Conveyed through Groundwater sensitive to the hydrologic differences between ridges,
interior wetlands, and shore sites.
The most threatening water pollution problem of 2.5) In addition to setback requirements, it is recom-
Sanibel may be the leaching of sewage pollution through mended that the drainage pipes of the absorption field

Water 37

be placed at least four feet above the highest expected zation or eutrophication of the water, which 'leads to algae
annual groundwater level. On Sanibel, where the blooms-and oxygen reduction : 0
groundwater beneath the septic tank- absorption field
can rise to the level of the discharge pipes, the saturated Salt I-lntrusion of Ground and'Surface Waters
soils cannot absorb the effluent. In the worst situations,
the unpurified effluent may even rise- to the surface Indirect pollution of the surface waters and water-table
where ,it will drain directly into an adjacent body of aquifer of Sanibel by saline ocean water is a serious
water. problem. Because of salt intrusion the water is rendered
- 3) All sewage-treatment ponds should be sealed to unfit even for watering-lawns in many parts of the island
prevent sewage infiltration-of the water-table: aquifer and over many months of the year. Salt water enters surface
pollution of surface waters. : and groundwaters in four ways: 1) by infiltration through
4) The goal is that water leaching through the ground both gulf and bay sand-shell ridges that enclose the
shall not degrade surface waters; specifically, it should not interior wetlands basin; 2) by passing through and around
contain higher concentrations of contaminants at its point the control structures at Tarpon Bay and Beach Road;, 3) by
of entry than the maximum -permitted for surface water storm surge inundation of the island during heavy storms
(by water quality standards). A principal difficulty, and one and hurricanes;; and 4) by upward leakage of saline water
that requires the broad:: setback, is the control of nitrogen. through the clay seal that underlies the shallow surface
Unlike phosphorous, nitrogen is quite mobile- in ground- - aquifer. Once in the island water system, the salt tends to
water. Nitrogen control is necessary to prevent overfertili- sink and remain (salt water being heavier than fresh); salt

Figure 24.
One of the first dune replant-
ings since plan adoption; the
beach grass should prosper
and in time develop a natural
beach ridge (low dune). '

38 The Natural Systems Study

:becomes more concentrated in surface water bodies because
'of evaporation.
Eachcause of salt intrusion has a different remedy. The
Conservation Foundation recommended the following:,
1) Infiltration through the gulf and bay ridges can best
be remedied by maintaining a positive head of water in the
interior basin. That is, the' city should make the strongest
possible efforts to maintain the level of water in the basin
above the high tide' level of 'the surrounding sea for as
much. of the year as possible. The water management level:
restoration program outlined on page 39 would provide
this remedy.
2) Passage of salt water around and through the control
structures can be remedied by improvement of the control .-
structures through state-of-the-art engineering.
3) Storm surge damage can be remedied or mitigated
by restoring and protecting the beachfront and lidgeline
(Figure 24); prohibiting the digging of man-made lakes for
borrow-pits and refilling-as many existing lakes as possi-
ble; preventing construction of. any waterways directly
connecting the island to marine waters; and refilling as
many existing canals as possible. (Figure 25)
4) Upward leakage of saline water through the clay seal --
can be remedied-by keeping a positive head in the interior
basin and by preventing any puncturing of the seal by use of short-lived, benign chemicals. (Figure 26)gure 25.
excavation, structural penetration, or drilling of wells. 2) -The city should incorporate into its water manage-
Existing open test well holes should be plugged. These ment program an element for maintaining the best possi- An example of the type of
remedies are discussed further in the chapter on uplands. ble level of mosquito control through an effective water canal that depletes ground-
water and allows saltwater
management program. penetration.
Pest Control
Relevant State and Federal Requirements
The major pest of Sanibel is the salt marsh mosquito,
although there are some problems -with biting flies. Sanibel's water quality protection efforts should supple-
Ecologically damaging pesticides may reach Sanibel's sur- ment the programs of federal and state agencies. The
face water systems by runoff, groundwater flow, or direct extensive water quality program, under the Federal Water
aerial application to the water surface. In an ecosystem Pollution Control Act of 1972, P.L. 92-500, is operated in
such as Sanibel's, great care must be taken to avoid Florida through the state's Department of Environmental
chemical pollution. The Conservation Foundation recom- Regulation (DER). Among its various elements, this pro-
mended the following: * gram requires the elimination of polluted-discharges, the
1) While the authority for pest control operations maintenance of high standardsof water quality, and control
clearly lies with the Lee County Mosquito Control District, of polluted storm runoff water.
the city should discourage the Lee County Mosquito The Federal Water Act requires that all discharges of
Control Commission from the use of chemicals for control- pollutants to water be eliminated, and establishes a sched-
ling mosquitoes on the island, except for the emergency ule for cleanup to be accomplished by 1983. Accordingly, all

Water _39

.i-- .: such discharges to the water of Sanibel Island should be tions. For example, the present minimum requirements
terminated. This includes -all point-source discharges to for septic tanks set by the state (a setback of 50 feet from
surface waters of the island,-including the Sanibel River open water, 75 feet from wells, and 36 inches above
(and its tributaries), ponds, man-made lakes, and all wet- seasonal high-water level) are totally inadequate for Sani-
lands. Point-source pollution.includes all polluted effluents bel.
'collected and conveyed by' pipes, channels, ditches, or
conduits -of any kind.- (Each such point-source .requires -a .Water Conservation and Water Level Restoration
* permit from the DER certifying that the discharge creates
no significant pollution problem.)- -. - The development of Sanibel has significantly lowered
� Sanibel cannot,- however, simply rely on federal and water levels throughout the island. Restoration of natural
state gqvernments to protect and-restore its waterquality. levels (or as near to those levels as can be achieved) is
There are now widespread violations of federal and. state . essential to push back and displace the invasion of salt
pollution regulations on' Sanibel, notably- in. instances water, to provide improved water quality, to conserve
where. sewage has leached through groundwater and. into fresh water, to perpetuate wetlands, to control mosquitoes,
: ' :' open surface waters. ;- and to benefit vegetation and wildlife.
In addition, the natural. systems of Sanibel require The-water-table aquifer of the interior basin serves-as a
* special protection that is not provided by present regula- major potential secondary water supply for home use. This
basin should be treated as a reservoir and protected as
such. Soil and vegetative elements should be preserved,
water quality should be protected, and storage capacity and
replenishment should be maximized. If its condition is
maintained, it can supply- utility water for the home and
yard from widely spaced individual wells.
Studies confirm that the major values of the interior
basin are enhanced by the highest possible water levels.
Accordingly, a policy of water-level restoration was recom-
mended to the city. (Table 8)
In this connection, it is important to note that improv-
ing the flood conveyance capability of the Sanibel River
and other parts of the system will cause the average water-.
table level to decrease. As it now stands, with a fixed
height of 2.5 feet at the Tarpon Bay control structure, the
water several miles away along the river may stand at 3 or
4 feet. If the channelways are cleared, the water level will
drop at these more distant points and the total Storage
capacity of the basin will be reduced. Therefore, the
Figure 26. Tarpon Bay control structure must be elevated above 2.5
feet if the channelways are cleared in order to maintain the
Little is known of the true present storage capacity of the system.
~~~~~~~ecologic effects of the new ~Although restoration would benefit all parts of the
generation of chemical poi-
sons such as fenthion used island, it would particularly benefit the interior wetland
on Sanibel to control insects, PT CI B -r basin. Water there should be elevated to the highest
but EPA research in 1976 practicable level in the rainy season. It should then be--
has led to increased concern. maintained at the highest practicable level through the dry

40 The Natural Systems Study

PINE ISLAND SOUND

GULF OF MEXICO

season. This requirement was identified independently by .. .. ...........'""" .......
most of The Conservation Foundation's consultants, and in
separate, earlier studies by Johnson Engineering, Inc.,34 ..........
Provost,35 and Boggess.36 Different water management :
tactics may be required for each of the four major segments:.:
of the interior wetlands basin. (Figure 27)
The Conservation Foundation recommended the fol-
lowing:
1)- The water level should be about four feet above
mean sea level at :seasonal maximum in each segment.
Such a; level may be difficult to achieve, however, because
of natural soil porosity in most of the segments, and other
factors such as leaks in the natural sealing layers of clay. It LEGEND
appears advisable to install a fixed sill up to 3 feet above
mean sea level with options to 3.5 feet and 4 feet. Sills &- WATER CONTROL
should be designed to permit drainage of the system for ! STRUCTURE EXISTING
occasional remedial flushing, as recommended in the . ., FRESH WATER MANAGEMENT
Johnson Engineering study.37 AREABOUNDARY

Water 41

SAN CARLO BAY

TARPON BAY Figure 28.
Water levels in Sanibel's
2~~~U~~~ cz~~~~~~~~~~interior are recorded to de-
0 WILDLIE ' R E c+,: FUGE ' 0 : V: St: t termine ecological relation-
ships involving water level.

TARPON BAY (+ .5') e ' (2.5'
. . . .: - . . .: .

: ....... . .. Sanibel's interior wetlands

and regulator controlled by
_ :.' � . ....i 0 f i:

structure at Tarpon Bay and

�HH7~~~~~~~~~~ / - o I / /tal control is recommended
for future management.
N 0 .... 3000 6000.. ACRES (Source: Johnson Engineer
........... -- . ..:.:.:-:-:':.:.:.:.. m .:.:. :.: - - � Figure 27. :

'.ES-::: : !:iiiiiiiiR MiiAiiiiii ni ...... : - : Sanibel'sinterior wetlan, Sanibel
:FRESH WATER MANA1G-EMENT :Island Fresh Water Manage-
ment Area).

42 The Natural Systems Study

2) The city should attempt to plug any major leaks that
permit the loss of fresh water from the interior basin. The
Tarpon Bay and Beach Road outlets should be improved to LEVEL
prevent the bypass of water around them and leakage of
water through them. Other significant water outflows +6
around the rim of the basin should also be identified and
remedied. Excavations or structural penetrations of the
clay layer separating the water-table aquifer and shallow
artesian aquifer should be prohibited.
3) --Water-level restoration may cause excess water to +5
accumulate at the eastern and western ends of the interior
wetlands system. If a practicable means can be found,
excess water in the western part of the wetlands might be
discharged to the J. N. "Ding" Darling Refuge. Excess
water from the east end of the wetlands basin might be +4
discharged into the artificial saltwater canals for the
purpose of flushing them and improving their water
quality.
4) Restoration of natural levels in the interior basin
will increase reliance on the Sanibel River and tributary
drainages to remove storm waters rapidly and thereby +3
avoid flooding; some channel improvements should be
undertaken for this purpose.
5) Outside the interior basin, the city should also try to
restore natural water levels. This restoration would require
that drainage be prohibited and that existing adverse +2
drainage conduits be filled up or otherwise blocked.

KEY
Present Water Level +1
Fluctuations \

Probable Historic :
V:- _- -Water Level
Fluctuations
MSL
Theoretical Water
Level Fluctuations
With Control
Structures Set At
3 Feet Above MSL -1
JAN ; FEB: MAR APR

Water 43

RAINY SEASON

/ x,

/ X

PROBABLE HISTORIC
AVERAGE WATER LEVEL

: / : : X PRESENT AVERAGE
WATER LEVEL

N%~~~~~~~~~~~~~~~~~~ ~~~~~~Table 8.
Water control structures,
/ 0channelization, and other
-~ _... -_ < :modifications to the water
systems alter groundwater
levels and runoff rates.
Water systems can be restored,
I_ I .1however, with appropriate
engineering. (Drawing pre-
MAYL JUN JUL AUG SEP OCT NOV DEC pared by Langdon Warner).

CHAPTER 3

BEACHFRONT

Identification of Gulf and Bay Beaches Soils: Because of extremely mobile conditions of the
sediments, the beaches have not developed soil strata. The
The Gulf Beach Zone includes the area between the ocean beaches consist of oxidized barrier sands and shells.
state setback line, approximately 150 feet inland from The bay beaches are made up of mud, organic materials,
mean high water, and the city boundary 300 feet offshore. sands, and shells.
There are two subareas within this zone: the Front Beach Sanibel's gulf (oceanside) beaches are backed by a
and the Back Beach. The Front Beach extends from the city temporary berm at the high tide mark and a relatively
boundary to mean high water mark. Sandin this subarea is permanent line of dunes. Mild summer waves add sand to
in constant motion, migrating between the-berm and the berm, and prevailing onshore winds move sand from
offshore bars, transported by longshore currents. The Back the berm to the dunes. During .heavy storms and hurri-
Beach comprises the area between mean high water and canes, the berm may be completely reclaimed by the ocean,
the state setback line. Sand in this subarea is moved by at which time the dunes must erode to replenish the lost
wind and water, and stabilized by vegetation. sand. The berm moderates these changes by providing a
The Bay Beach Zone extends from the city's boundary reservoir of sand available to either dunes or beach as
300 feet into the bay to a setback line of about 50 to 100 needed.
feet behind the mean high water mark. It is a lower-energy A sandy beach exists on the bay shore near the eastern
beach than the Gulf Beach, and includes areas of marine end only. The rest of the bay is mud and silt.
grasses on the bay-bottom. Vegetation of the Beachfront: Sanibel's beaches support
Surface Hydrology: The seawater in the beach zone the beach plum-railroad vine-sea oats association.
rapidly percolates through the sand and shells into the Grasses, herbs, and shrubs on the beach are often
water-table aquifer and into the shallow artesian aquifer. A inconspicuous and widely scattered. They have extensive
10-year storm flood inundates the entire beach and all root systems and offer limited shade to insects, crabs, and
other zones of the island except the Gulf and Mid-island small reptiles. They usually produce an abundance of seeds
Ridges. A 25-year flood inundates the entire island. which serve as food for many wildlife species. Some

46 The Natural Systems Study

Figure 29.
The Australian pine has invaded
much of Sanibel, including
the beachfront.

velop fruits which. are eaten by birds, mammals, and and woody plants such as necklace pod, Spanish dagger,
humans. All of these plants are salt:tolerant, and their- and sea- grape.38 In.many places along the back beach,
extensive root systems .stabilize dunes. They are an inte- Australian pine, an introduced species, has displaced the
gral part of the island's- buffer system against storm waves. native vegetation. (Figure 29) '
and high tides. -.' Marine grasses cover much of the bay beach just
The beach plum-railroad vine-sea oats association of seaward of the intertidal zone, providing food and habitat
species has been especially successful at adaptnig to beach for many marine species.
conditions. They include low-growing perennials such as ' Wildlife of the Beachfront: Birds of the sand beaches
seaside primrose, railroad vine, sea ragweed, sea; oats, include: brobwn pelican. (Figure 30), snowy egret, red-
beach madder, and sea purslane. They also include the breasted merganser, American oyster catcher,* semipal-
semishrubs beach plum and bay cedar. Farther back from mated plover, piping plover, snowy plover,* Wilson's:
the water, where low dunes occur, are lantanas, crotons, plover,* blackbellied plover, ruddy turnstone, willet, knot,

Beachfront 47

than other reptiles on the beaches of Sanibel, but m y
other reptiles *and amphibians are found on the sand
beaches, including: alligator, ornate diamondback terrapin,
gopher tortoise, southeast five-lined skink, six-lined race-
.runner, eastern glass lizard, Florida water snake, southern
Figure30.leastsandpiperdunlnsemipalmateder, eas tern
black racer, eastern coachwhip, indigo snake, eastern
diamondback rattlesnake, southern' toad, Cuban tree frog,
and several species of marine turtles39-
Offshore Marine Ecosystem:: The offshore marine eco-
system includes 70 species of fish and approximately 400
species of mollusks. They inhabit arange of :areas includ-
ing non-vegetated waters, sea grasslands; algae mats,
mangrove roots, rock pilings, oyster bars, and sea walls.
The fish and mollusks provide a complex and rich food
supply for manatee, dolphin, otter, fish, birds-d mand.4m0
The tremendous molluscan population can be attributed
Figure 30. least sandpiper, dunlin semipalmated sandpiper, western to the mosaic pattern of the bottom environment, current
sandpiper, sanderling, herring gull, ring-billed gull, laugh- patterns, and variations in salinity.41
The brown pelican is one of g gull,* Forster ls tern least tern,* royal tern, sandwich
Sanibel's many endangered
specie's mnof birds a e tern, Caspian tern, and black skimmer.* * Nesting on ornear Sanibel Island
The loggerhead sea turtle has received more publicity

Figure 31.

Bulkheads like the one shown
here cause deflection of sand
away from the beach and give
a false illusion of security to
these condominiums located
near the ocean's edge.

48 The Natural Systems Study

Condition of Beachfront itself. It results from the greatly increased number of
shellers, which causes more competition for the better
Sanibel's front beach is in good condition. Except for shells. The number of shellers visiting the Sanibel beach
Point Ybel and the Blind Pass area, it is in virtual increased from about 50,000 in 1960, to 250,000 in 1975.
equilibrium, neither receding nor advancing. This is likely (Figure 3) It is possible, however, that the declining
a temporary state, and therefore it should not be inferred abundancef certain prize shells has occurredbecause of
that the beach has permanently survived the effects of natural or man-induced environmental changes.
recent oceanfront development. 'The placement of bulk- The bay beach:(on San Carlos Bay from Point Ybel to
heads, condominiums, and commercial structures has :Woodrings Point) has been receding since the causeway
created a precarious situation along a considerable portion
of the beach. (Figure 31) Serious damage to the beach will
occur during hurricanes or heavy winter storms. Wave
-energy reflected from the bulkheads and buildings will . .
scour a great amount of sand from the upper beach and i . . .
wash it away. If the waves are sufficiently severe, they may . ' . . .: '. . .
undermine and damage beachfront buildings and bulk- .. ' .. ' '.:' . ":
heads. (Figure 32) There has not been a severe hurricane
at Sanibel since the causeway opened andthe development:
boom began.
The natural restorative powers of the beach have been
jeopardized by alteration of the back beach. Development
along the beachfront has centered on the frontal ridge
(dune) system, the same sand-storage area that naturally ..
stabilizes the beach. The ridges have been flattened for . . . . . ....
landscape and building purposes. In other areas, the . . ' � . .' .
stabilizing vegetation has been destroyed by foot and
vehicle traffic. With the dunes removed, there is no sand to
replace beachfront supplies that have been washed away.
Also, the houses, hotels, and condominiums are exposed to
damage by storm waves.
The populations of wildlife species that depend upon '
the beach environment have declined, some seriously.
Many of the former bird nesting areas in the dunes and the
back beach have been destroyed. Also, the number of ' .'.': . ' . ' :
loggerhead sea turtles nesting on Sanibel beaches has
declined drastically. Invading Australian pines now consti-
tute a major portion of back-beach vegetation, having
displaced plants such as the sea grape and necklace pod.
Because of shallow rooting, Australian pines are especially Figure 32.
prone to windthrow. The fallen trees and exposed root B hea s a ender i
Bulkheads may be undermined
systems interfere with the movement of turtles to and
~~~~~~~~~from the:~' nesting sites' useless; natural means for shore
.Shell collecting along the Sanibel beach has declined, but protection are much more
the decline cannot be attributed to changes in the beach effective.

Beachfront 49.

Figure 33.
Hundreds of thousands of per-
sons collect shells on Sanibel
beaches.

was built, possibly due to high.er water velocity and greater based on the recognition that the beach is an all-important
littoral scouring. Like the gulf beach, it has been altered by buffer area between land and sea-and that alterations of
bulkheads and buildings. Piers and canals have had addi- its natural condition are likely to reduce its ability to
tional- effects. Point Ybel itself appears to be eroding. function as a buffer. It should be the city's public policy to
Management will definitely be required. . manage the island's whole beachfront as a unit, so as to
The Blind Pass area at the western end of Sanibel is an restore its natural condition and protect it against further
entirely different case. (Figure 34) The beach and inlet damage. The main thrust of the protection program
dynamics cause the beach to change form constantly. Long should be to maintain the beach profile, including preven-
bars and peninsulas are formed, then closed, creating tion of sand removal or any other alteration of any part of
temporarily land-locked lagoons, or bayous. The inlet itself the beachfront. (Figure 35)
alternately opens and closes. Noticeable changes can occur The ocean beach is Sanibel's principal attraction for
in only a few years. (-See Chapter 7 on Special Zones for a visitors and residents alike. While shell abundance and
further discussion of the Blind Pass area.) diversity have been seriously lowered, the beach itself
remains relatively intact. Sanibel's beach has not been
Management Recommendations for Beachfront subjected to a major hurricane since 1960. Because of
Zone extensive beachfront development, the beach is far less
able to withstand a hurricane than it was 16 years ago.
The beachfront policy of the City of Sanibel should be Thus, in addition to inflicting massive damage to struc-

The Natural Systems Study

Figure 34.

The westernmost portion of
Sanibel is Blind Pass, an area
of shifting sandsand unstable
shorelands.

Figure 35.

Groins and other structures
designed to retain sand on
beaches have a disappointing
history of failure; management
techniques that respect the
Powers of nature are more
effective.

Beachfront 51

tures, the next major hurricane may well cause '.extensive
.-* ~ ~ ~ ~ ~ ~ ~~- :and permanent damage to the beach itself. (Figure 36)
The dune ridges are held in place by sea oats, railroad
vine, and other dune and beach plants. The fragile network
of vegetation growing on shifting dunes is adapted to
withstand the rigors of wind, Ssand and salt-but not
human feet or beach buggies and other vehicles. When the
mantle of vegetation is broken, the dune movement is
accelerated to a. point where plant growth cannot keep
pace with the shifting sand. -
The Conservation Foundation made the following rec-
ommendations for protection of the front beach (water's
edge to vegetation line) and the back beach (vegetation
line inland t3othe setback line):
1) The city should adhere strictly to the state's ocean
setback line of approximately 150 feet inland from the
*vegetation line of the beach (this is considerably inland of
the mean high water line). There should be no bulkheads
or major structures of any kind in this buffer area except
for boardwalks or other access ways to the beach.: o
2) A setback line should be defined by the city for the
bay beach (from Lighthouse Point to Woodrings Point),
using criteria compatible with those applied by the state

Figure 36.

Building on the beach is'excep-
tionally foolhardy because the
structures eventually can de-
stroy the beach.

Figure 37.
A setback of 50 to 100 feet is
recommended for the San Car-
los Bay shore from Point Ybel
to Woodrings Point.

52 -The Natural Systems Study

Figure 38.

This shore home is built back
from the beach, thus preserving
the native vegetation and the
geologic structure of the
beachfront.
for the oceanfront setback. The criteria would dictate -a
setback of less width (50-100 feet) than the ocean standard
since the bayside beaches have lower energy regimes than
the oceanfront beaches.
3) Integrity of the beach should be maintained along
the whole beachfront. Wherever sand dunes and ridges
have been leveled or lowered, they should be restored to
their original condition and revegetated.jThere should be
no further grading, excavating, or other alteration of the i
frontal ridge line.
4) Sand should not be removed from any part of the
beach (from the inner edge of the setback line out to the
300 feet jurisdictional boundary of the city), since sand
removed for any purpose subtracts from the beach-sand
budget and upsets the profile.
5) There should be no removal of native vegetation
within the setback area. Sea oats and other natural vegeta-
tion are needed to bind and hold the back beach together.
(Figure 38) Exotics such as Australian Pine should be
removed andreplaced with native vegetation to the extent
practicable.
6) Any traffic on the frontal sand dune ridge should be
discouraged (access to the beach should be by boardwalks
over the sand). (Figure 39) Keeping the ridgeline at its
highest elevation is essential to eliminate saltwater inun- Figure 39.
dation of the wetland areas during large storms, and to Elevated boardwalks are reco
provide the fullest sand storage potential for the beach mended for crossing beach
profile. ridges (sand dunes).

Beachfront '53

7) There, should be no: traffic (foot or vehicular)
through any part of the setback buffer area in which terns,
plovers, skimmers, and turtles breed during the period
May through August. This may require preventing tres-
pass into, many private property areas. Owners and their
guests should cross the area on a single path or otherwise
avoid disturbing nesting activities.
8) _Means should be taken to ensure that other govern-
mental jurisdictions (such as Lee County or Captiva Island)
should not block littoral transport to Sanibel with groins
or other structures, nor cut off sand, supply to the coast
from inland via rivers. Also, the replenishment of beaches
on the updrift side should be encouraged to protect Captiva
from erosion. (Figures 40, 41)
State and federal regulations can lend important sup-
* port to Sanibel's beach protectionefforts. The state ocean-
front setback line has been noted. Federal regulations
under the Flood Disaster Protection Act may strongly
influence beachfront development.
Figure 40.

Captiva Island to the north of
Sanibel has lost much of its
seafront to erosion; the loss
of this valuable buffer zone
increases the likelihood of
damage from tropical storms.

Figure 41.

With the beach on Captiva
Island virtually gone, riprap
structures must be used to
support the road.

CHAPTER

INTERIOR WETLANDS

Identification of the Interior Wetland Basin were formed by segments of the slough Thewestern
segment was separated by low beach ridges south of
The Interior Wetland Basin Zone is the interior bowl Tarpon Bay from the eastern segment. The system was
which serves as a freshwater reservoir. It is composed of unified only during the high water stages.
parallel systems of ridges and swales with corresponding The drainage characteristics of the eastern subbasin
bands of vegetation. There are two subareas within this differed considerably from the western subbasin.43 In the
zone-lowland and upland. The lowland area is composed east, the "course" of the Sanibel River was straighter,
of low ridges and wide swales, andit experiences extended although it transected most of the low ridges at oblique
periods of flooding each year. The upland consists of angles. The only "tributaries" to the slough in the east were
higher, broader ridges and narrower swales, and is charac- the natural swales transected by the slough. During low
terized by less frequent flooding and more upland vegeta- flow conditions, water in the eastern basin moved to the
tion types. east, and during high water conditions it broke through the
Surface Hydrology: Because of-the nearly instantaneous Gulf Beach Ridge and discharged into the Gulf of Mexico
infiltration of rainwater, few barrier islands develop a just west of Point Ybel. In the west, the slough meandered
natural type of channelized interior drainage system. considerably because of the low relief, of the ridges. (Figure
Sanibel Island is different in that a partially channelized 43) There were several "branches" to the slough. During
interior drainage system, the Sanibel River (more accu- low flow conditions, water flowed to the west; and during
rately a slough), developed rather late in its geologic high water, it broke through the Gulf Beach Ridge and
history. (Figure 42) Beach ridge geometry, variable per- discharged into the gulf at a point about 2.5 miles east of the
meability, and vegetation patterns all- contributed to the Blind Pass Bridge. Two other systems drained through
formation of the Sanibel River at some time during the mangroves to Pine Island Sound to the north, and through a
last 1,000 to 1,500 years of the island's 5,000-year history.42 series of interconnected ponds to tidewater to the west.
Before human alteration, the slough meandered over an The Sanibel River was only a drainage way and never a
irregular course nearly eight miles long. Two subbasins true stream. Flow occurred only during times when the

56 The Natural Systems Study

Figure 42.

The Sanibel River is central
to the island's ecosystem and
this water system makes
Sanibel unique among gulf
coast barrier islands.

water table was high and infiltration of precipitation was This freshwater drainage and storage system spawned,
inhibited. Under original conditions, the storage: curve the development of many wetland communities which
probably would have risen very slowly during May, June, depend on the seasonal changes and freshwater recharge
and July because of spotty, generally light rains.44 In to hold back the intruding saline waters.
August through October, the generally heavier rains fell on Soils: Soils of the Canaveral series have developed in the
a reservoir whose storage capacity was reduced substan- interior basin. They consist primarily of organic deposits
tially by fall high tides. If rains were sufficient, as they over sands: Tabb found surface deposits of calcium carbo-
probably were nearly every year, washout occurred. If less nate soils (called marl) to be an important constituent in
substantial, the rise in interior storage would terminate in swale-bottom soils. These soils are %formed in shallow
mid-to-late October and then decline through seepage and water under conditions of intense sunlight, high tempera-
evapotranspiration until the next rainy season. Tabb ture, and rapidly fluctuating dissolved oxygen and pH.46
estimates that in the eastern system 14.4 inches of rain Tabb also found a well-developed lens of limy material.
could have raised the water table to four or five feet above This may be hardpan, derived from precipitation of
mean sea level before washout.45 organic material and minerals in solution at the contact

Interior Wetlands 57

between the water table and overlying oxygenated sands. thus impounding surface waters and retaining moisture.
Tabb wrote: "If this is true hardpan, then it may represent Such marls probably were important in maintaining the
the long-term position of the water table during the dry hydroperiod, providing shallow but intermittent ponding;
season of pre-drainage times and thus an interesting and maintaining soil saturation between shores. This has
reference point for discussion of future water management important ramifications for the floral and faunal commun-
because it would suggest that the water table seldom fell ities inhabiting the zone.
out of direct contact with the marl of the swales."47 Vegetation of the Interior Wetlands: Twenty years ago,
Several properties of the marl-rich soils are important. the low interior wetlands were open, grassy, and essen-
Periodic saltwater-saturation of these soils raises the pH to tially treeless. Vegetation patterns -were controlled by
a level where normal'nitrification halts at the nitrite stage. natural factors including wind, water-table level, salinity,
Toxic amounts of nitrite may accumulate with application - and elevation of the land. Because Sanibel -has a periodi-
of ammonium fertilizers or sewage effluents. cally brackish water-table aquifer, almost all 'plant'species
Marl also has the ability to seal otherwise porous soil, are at least partially salt tolerant. Spartina bakerii, the
principal-interior wetlands plant, requires seasonal flood-
ing with fresh to brackish water. This ability to prosper
under a varying salinity regime permitted the cordgrass
Spartina to become the dominant plant community on
much of the wetlands. In association with the cordgrass
were sawgrass, bead grass, water-hyssop, and sea purslane.

Figure43. NATURAL DRAINE ISLAND

SAN CARLOS

Figure 43. --- NATURAL DRAINAGE PATHS[TABB, 1975'
Historic drainage patterns in 4 HISTORIC OVERFLOW(TABB, 1975)1 2
the Sanibel interior wetlands;
during flood periods water A
broke through the two main
ridges in the four locations NORTH
shown.

58 The Natural Systems Study

On the almost imperceptible elevations were salt bush and
a number of grasses and perennials, and cabbage palms SAI/BEL ISLAND
were evident on the highest ridges.48 ,JPtr HASIrATS
Today, along the Sanibel River and in low swales, the
buttonwood-wax myrtle-sea oxeye association is very
evident. Also appearing in the swales are cordgrass,.
sawgrass, andropogon, water-hyssop, cattails, spatterdock, T.
hydrilla, chara, duckweed, and wigeongrass. Cordgrass is : X Figure 44.
still common, though covering a much smaller area than it F i 'ge 4.
once did. (Figure 45) * * The original main ecological
WV_ --T areas of Sanibel (Source:
A number of these species: have high food value for Cooleya
ducks and birds. Wigeongrass, a submerged aquatic found Cooley
in both the river and ditches, is a major source of food' for

Figure 45.

Lack of proper water.manage-
ment has permitted various
shrubs to infiltrate the open
cordgrass meadows and endan-
ger the entire interior wetlands
subecosystem.

Interior Wetlands 59

waterfowl. Cordgrass provides edible roots and seeds for high peak flows and allowing more freshwater recharge.
rails, songbirds and ducks and, to a lesser extent, sandpip- The microflora also greatly aid in maintaining and im-
ers. Purslanes disseminate an enormous number of seeds proving water quality in the wetlands.
which are eaten by songbirds and rodents. Cabbage palm Wildlife of the Interior Wetlands: Ten species of aquatic
provides fall fruit for robins, warblers, woodpeckers, fish birds nest in the interior wetlands, and six more are known
crows, and raccoons. to frequent them. The area also serves as an alternate
Many of these plants also provide refuge in the form of refuge for a number of species which normally reside in or
an almost impenetrable barrier to human and animal visit the saline mangrove areas. Aquatic birds of predomi-
hunters. Sawgrass, with its sharp-edged leaves, provides a nantly freshwater habitat include: pied-billed 'grebe,*
sanctuary for ducks, as well as supplying a limited amount anhinga,* least bittern,* American bittern, mottled duck,*
of food. Cattails serve as roosts and nesting areas for birds blue-winged teal,* king rail,* Virginia rail, sora,:common
and fish.49 gallinule,* killdeer,* spotted sandpiper,* common snipe,
Native vegetation of the low ridges includes marsh belted kingfisher, long-billed marsh wren,* and swamp
elder, cordgrass, leather fern, wax myrtle, and cabbage sparrow.50
palmetto. The Brazilian pepper, a noxious weed, is rapidly Although alligators are Sanibel's most spectacular aqua-
dominating many areas in the interior basin. : tic animal, there are many other important reptiles and
Figure 46. In addition to the previously mentioned food and amphibians of the interior wetlands. Aquatic reptiles and
habitat: functions that .the interior wetland vegetation -amphibians include: alligator, snapping turtle; striped mud
The few dozen alligators left provides for wildlife, it serves important hydrologic func- turtle, Florida mud turtle, Florida box turtle, red-bellied
on Sanibel are one of the is- tions. The grasses and low shrubs slow runoff, preventing terrapin, yellow-bellied terrapin, peninsular cooter, Florida
land's major tourist attractions. chicken turtle, Florida soft-shelled turtle, common iguana,
green anole, southeast five-lined skink, Florida water
, 0 snake, Florida brown snake, southern ribbon Snake, south-
ern ringneck snake, southern black racer, eastern coach-
whip snake, indigo snake, yellow rat snake, eastern dia-
-, - ~:~ mondback rattlesnake, southern toad, green tree frog,
-/~ - -, 0 g msquirrel tree frog, Cuban tree frog, southern leopard frog,
pig frog, and eastern narrow-mouth toad.&51Mammals of
the interior wetlands are listed on page 74 .
Small, freshwater animals are abundant here, and
provide food for many creatures. Insects also are abundant,
as are crayfish and mussels in varying quantities. Mullet,
tarpon, Gambasia, bream, bass, and garfish live in the river
and provide a bountiful feast for anhingas, crows, ibises,
herons, egrets, gallinule and stilts.52

Condition of the Interior Wetlands

Aerial photographs of Sanibel in 1944 show the interior
-~,~~~~~~~~~~~ ~wetlands as broad grassy. meadows, with shrubs and trees
found only along the two major ridges. Since the 1940's,

Nesting on Sanibel Island

60 The Natural Systems Study

man has altered the physical character and vegetative
patterns of the wetlands in three-major ways: 1) physical
alterations, such as clearing, filling, lake excavation, and
flattening dunes; 2) alterations of the hydraulic system,
including drainage, channelization, and impervious pav-
ing; and 3) introduction of exotic plant species which, due
to their hardiness, have crowded out the native vegetation.
Each alteration has interfered with the ecological integ-
rity of the wetlands, and of the island ecosystem. By
modifying the native plant, animal and ater systems, the
historic habitat diversity has been reduce The vegetation
of the Sanibel wetlands is continuing to undergo rapid
change. Major losses have occurred to cordgrass and
sawgrass. Together these two species provided both food
and refuge for ducks, song birds, and mammals.53
The most important alteration of the interior wetland
system has been the lowering of the water table. Before the
dredging of the Sanibel River and the installation of the
water-control structures, the wate r level fluctuated from
slightly below mean sea level (MSL) to five feet above
MSL during floods. Water levels changed with every
rainfall, often raising the water table two to three inches
for each inch of rainfall.54 The two control structures at
Tarpon Bay and Beach Pond have reduced fluctuations in
water level by setting the maximum water level in the
interior at heights varying from 2 to 3 feet above MSL-
water control structures are now set at 2.5 feet above
mean low water.
Construction of canals and drainage ditches has had a
pronounced effect upon the water table over large areas of
the island. The deep tidal canals at the eastern end of the
island have permanently lowered the water table. Canals
have been spaced so closely on some parts of the island
that the water table probably does not range much above
sea level.55
Road building and mosquito ditching have altered
drainage pathways considerably, replacing a system of
gradual runoff by one given to greater extremes of flood-
ing and drought. (Figure 48) This system-though less
efficient than a purely natural system-does allow down- Figure 47.
ward percolation of fresh water for storage, and it acts as a
sponge for increased water levels during the wet summer Sanibel's water birds are de-
season. Historically, when flooding occurred its duration pendent upon the values of
the mangrove subecosystem.

Interior Wetlands 61
supply. This freshwater replenishment cycle competes
with salt water, which quickly replaces depleted fresh
water. The constant push and shove between fresh and salt
water makes preservation of thef reshwater replenishment
cycle a major consideration in any future development of
the 'island. A reduction of fresh water in the s ystem will
result in greater quantities of salt water--a phenomenon
detrifmental to water qual ity.:
The plan 'for lcontrolling mosquitoes on sanibe, as
initially conceived, was ingenious-but it was never suc-
cessfully implemented, and problems have persisted. Low-
ered water levels in the interior wetlands' favor mos-
quit -breeding. The control system, .whicht has r had little
maintenance since the early 1960's, was never completed
as designed, and has been disrupted by roadway blockages.
Lack of enthusiasm for water management and biological
control of mosquitoes, and emphasis on toxic chemical
control by the county, have contributed to the deterioration
Figure 48. of Sanibel's control system. The insecticides in use on
Sanibel appear to behighly toxic and therefore potentially
In wetlands areas, roads and damaging towildlife. For example, recent unpublished tests
db~~~~~~~~~~itches with inadequate pro-appear to show the principal insecticide;, fenthion, to be
visions for water flow cause
visions for water flow cause toi t aquatic species in concentrations. of fractions iof
serious loss of wildlife habitat .
and can harm other ecological .parts per billion. What m ay have saved'Sanibel's wildlife
:values as well. from greater past. damage is that fenthion seems to evapo-
rate when it is heated by the aircraft's exhaust system (along
with diesel oil, the application medium). Thus, the fenthion
may evaporate while the oil falls and itself becomes the
was brief--excess water passed easily over beach ridges to effective anti-mosquito toxin.
the gulf.56 Water quality in the Sanibel River and other parts of
The altered. interior drainage system has caused a rapid the rinterior, drainage system varies considerably. The
recession of water levels during the dry season. The salinity of the water in any particular segment' of the
control structures at Tarpon Bay.and Beach Road are not system is controlled by climatic factors, proximity to a
adequate, leaking water both :in and- out. Evaporation source .of saline-water leakage, :the quality of water in
losses also have been increased because of the additional adjacent parts of the water-table aquifer, and the character-
amount of exposed surface water. In short, water-control. istics of the drainage way. Heavy nutrient influx, stagna-
devices which were built to control water level are allow- tion, and deposition, of organic detritus all degrade the
ing too much water to leave the wetlands. As a result, the general quality of the water.58
water table has been lowered, damaging nativevegeta- Salinity, varies seasonally with recharge and discharge.
tion.57 In most parts of the surface-water system, chlorides
The high permeability of Sanibel's soils results in direct decrease during the wet season as a result of flushing and
contact between rainfall and the water-table aquifer. Many dilution by rainfall. In some parts of the Sanibel River,
factors control the natural water. system, such as the high-chloride water at the bottom is trapped because of
duration of rainfall that replenishes the groundwater bottom irregularities.59 The trapped water decreases in

62 The Natural Systems Study

areas, and is a useful indicator for delineating the two
zones. The original patterns, however, have been seriously
altered. Because of a lowered watertable, Spartina areas
are easily invaded by upland woody plants and exotics such
as Brazilian pepper. These quickly reproduce and replace
large areas of native vegetation.60
The Brazilian pepper became popular as a landscape
shrub in Florida in the mid-1950's. Today, it is out of
control in many areas. On Sanibel it has produced a closed
canopy over much of the abandoned farmland on the
eastern part of the island. It has become dominant in the
interior wetlands where it outcompetes Spartina for sun-
light. The Brazilian pepper can also cause itching, rashes,
sneezing, and severe sinus congestion. The appropriate
nonchemical control is cutting and removal--new sprouts
in a Spartina marsh renovated in this manner could be
controlled by burning.61
The wildlife-carrying capacity of the island's interior
wetlands has dropped considerably. For example, increas-
ing salinity, excavation, and perhaps pesticides appear to
be lowering the populations of birds, reptiles, and amphi-
bians. Raising the water table and increasing the storage
capacity of the water-table aquifer will lower the salinity
intrusion, and might boost wildlife populations.62
General Wetlands Conservation

The Conservation Foundation recommended the fol- Figure 49.
lowing general conservation practices:
1) As a general rule, there should be no excavation in oman pat hei
the dominant plant of the in-
wetlands for the following reasons: Vegetation would be terior wetlands, occurs in large
obliterated; water flow disrupted; soil layers destroyed; -clumps when there is suffi-
pollutable catchments formed; and drainage and drying out cient water at its roots.
of wetlands facilitated. Accordingly, excavation should take
chlorides only by dilution, which occurs during periods of place only when required for essential public purposes
high water. Chlorides increase during the dry season (mosquito control or wildlife enhancement, for example)
because evaporation and evapotranspiration losses cause and should be limited in extent (not more than 10 percent
concentration of dissolved solids. of the area).
The vegetative zonation of the interior wetland is 2) Generally, there should be no filling of wetlands.
determined by a combination of water level and salt The soil cover would physically obliterate the wetlands and
tolerance. Spartina bakerii, the naturally dominant wetland disrupt their function as completely as excavating them
plant, prospers with alternative flooding of fresh and would.
brackish water. (Figure 49) The saw palmetto is often 3) Generally, there should be no land clearing, grading,
found in the transition zone between upland and wetlanid or removal of natural vegetation, since vegetation is an

Interior Wetlands 63

important element of wetlands function. An exception swale) can -proceed without degrading the interridge
should be made, however, to permit control and removal wetlands swales, although care will be needed to assure
of noxious exotic plants (such as the Brazilian pepper) and that the swales are preserved.
other undesirable invader species (shrubby plants) in the To protect the swales, as well as to maintain water
interior wetlands. These should be removed mechanically quality and satisfy other environmental requirements,
or by controlled burning. residential development of high ridges will undoubtedly
4) Discharge or release of pollutants into the wetlands have to take a new form.-Along the narrower ridges,
should be prevented. There may, however, be some capac- houses should be laid out in narrow rows. Access roads
ity for the wetlands to absorb certain storm-runoff pollu- should be bridged over the interridge swales.
tants and thereby function as a "land treatment" system. Hurricane protection requirements will also affect
Any such pollutants should not exceed the calculated housing style. Most of the high ridges will be covered by 5
receiving capacity of the system and should not degrade to 7 feet of water when Sanibel is inundated by the
surface water or groundwater below allowable standards. predicted 10- or 12-foot surge of water from an intense
5) There should be no solid-fill roads or similar struc- hurricane. Therefore, all houses on the ridges will probably
tures in wetlands because they obstruct water flow. Also, have to be elevated on stilts five to'-seven feet above
fill for any. such structures must normally come from natural ridge elevation to meet federal flood insurance
excavation, which is in itself damaging. If some roadways requirements. (Figures 50, 51).
do become necessary, they should be elevated on pilings Acceptable Uses: As the above constraints suggest, the
rather than placed on fill. natural characteristics of wetlands are such that the preser-
vation of their functional integrity precludes virtually any
Management Recommendations for Interior development within the cordgrass portions. Roads
Wetlands through wetlands are not adequately controlled by regula-
tions. A great deal of ecological damage has already been
It should be the public policy of the City of Sanibel to caused by public and private roads that cut through such
ensure that wetlands remain functionally intact. Whatever areas on .the island. Specific requirements should be given
their use, they should not be altered in-ways that would to prevent water blockage and other disturbances from
degrade their natural function. roads. Minimum elevations should be established to facili-
Lower, or low-ridge-and-swale, wetlands are found tate evacuation.
principally in the interior basin. They occupy roughly 60 Recreational use of Wetlands would be enhanced by the
percent of that basin. Some low-ridge-and-swale areas installation of light-duty, elevated (pile-supported) struc-
have been considerably altered, but a restoration program tures such as blinds, catwalks, piers, and similar open
should return them to good health. structures. (Figure 52) If properly controlled, these should
High-ridge-and-swale sections of the interior wetlands not have a major detrimental effect on water systems and
basin are characterized by cabbage plum hammocks. The. estuarine resources. Nevertheless, even these should be
principal plant indicator of the swales is Spartina, but' designed and built to cause minimum impact by shading,
other marsh plants may also identify the swales as signifi- water-flow interruption, and site disruption. They should
cant wetland plant communities. A number of the ridges be elevated above the 10-year flood-return height and
appear to be wide enough and sufficiently elevated above should have very low ground coverage (no more than
seasonal high water levels to be developed for housing. about 0.5 percent surface alteration). Any area disrupted
However, the interridge wetland swales in the high-ridge- when installing these facilities should be fully restored to
and-swale areas should be protected following the same its natural condition.
general standards given previously for low-ridge-and- Restoration of Wetlands: Protection of wetlands,
swale wetlands. though essential to prevent future disruption, is insuffi-
Residential development of the ridges (high-ridge-and- cient to undo damage already done. For that, a restoration

64 :The Natural Systems Study

has invaded the wetlands.
Relevant Federal and State Regulations and Policies: Figure 50.
Interior wetlands are protected by a number of federal and Two types of elevated homes
state laws, regulations, and policies. Most critical, perhaps, under construction: platform-
elevated type (above); piling
are the federal. regulations adopted July 25, 1975, under hung type (below).
Section 404 of the 1972 Federal Water Pollution Control
Act. These regulations require a permit from the Army
Corps of Engineers for any excavation .or filling of desig-
nated wetlands. Although. permits :must satisfy many

erable need for restoration of Sanibel's interior wetlands.
A restoration Program for interior wetlan thds dcouaeld
provide additional benefits of water supply water quality,
mosquito control, fire protection, and wildlife-habitat. The s
Conservation Foundation made the following recommen-C
datlkns: regulations demonstrates: "As environmentally vital areas, Figure 51.
1) Return the water systems (that is, water levels, [wetlands] constitute a productive and valuable public
flows, etc.) to as near their original state as possible, and resource, the unnecessary alteration or destruction of A completed example of a
remove all significant existing obstacles to the passage of which should be discouraged as contrary to the public platform-elevated home.
water in interior wetlands. interest." Federal regulations may mean a virtual end to
2) Take allpractical measures to prevent saltwater residential development of wetlands.
intrusion of interior wetlands. On October 3, 1975, the Army Corps of Engineers
3) Remove all exotic and adverse local vegetation that advised the city that it intended to exercise regulatory

Interior Wetlands 65

Figure 52.
Properly designed elevated
ramps, walkways, and piers
enable people to use wetlands
without harming therm; the
walkway and pier shown per-
mit owner to cross between
house and boat.

jurisdi ction over th e Sanibel wetlands under Phase I of that the first floors f all new residences be built above the
Sectio n 404 of the 1972 F e deral Water Act. This means that 100-year flood level, and that fill may ot be used to
every project proposed for the interior wetlands must have elevate houses in coastal "high hazard" areas.
a permit from the Corps, and w ill be reviewed by the US. Federal an d state action s, th ough strongly supportive of
Fish and Wildlife Service, the National Marine Fisheries local protection efforts in Sanibel, fall short of providing
Service, the Environimental Protection Agency, and other all needed'protection. The city needs to provide protection
federal offices. Also, the pro visions of the National Envi- of water supply, water quality, and wildlife habitat.
ronmental Policy Act will be invoked. All this machinery is There are virtually no relevant federal or state regula-
aimed at eliminating the alteration or degradation of tions to assist in restoration efforts, although the county
wetlands. mosquito control program does involve water manage-
As already noted, the development of Sanibel's high ment action on the island.
ridges will also be affected by federal regulations intended
to reduce the disastrous consequences of hurricane flood-
ing. These regulations, adopted by the Department of
Housing and Urban Development pursuant to the Flood
Disaster Protection Act of 1972, press localities to require

CHAPTER 5

MANGROVE S

Identification of Mangrove Zone - ; mangrove commonly grows at the l owe st elevations where
its prop roots experience daily flushing and brackish water.
The Mangrove Zone includes all areas of red, black, and Just inland of this, a mix of understory reds and larger
white mangroves, as well as the tidal flats and hardwood black mangroves proliferates. Subject to frequent flushing,
hammocks within them. Much of this zone, including all these are particularly affected by storm tides. High black
areas of red mangrove, is subject to daily tidal flooding. mangroves are flooded during seasonal rains and tides.
Other areas of the -zone are subject to extended periods of Here a shrub layer develops, populated by saltwort and
flooding every year. glasswort. At the. highest elevation along the estuary,
Surface Hydrology and Soils: The lower Mangrove Zone where water is confined by natural features, a mixture of
(red mangroves) is inundated daily by high tides; most of black, red and sometimes white occurs. These trees seem to
the upper zone (black mangroves) is flooded on spring thrive in standing water and are adversely affected during
tides; and the entire zone is seasonally or annually flooded. periods of drought. Buttonwood also occurs on the higher
Even the slightest amount of storm flooding will totally elevations. Because of the nature of the substrate and due
inundate this zone. to very low light conditions, only special plants can coexist
Peat deposits and salt flats are building up because of here. Algae, fungi, some halophytic shrubs, and many
trapping of sediments by the vegetation and a rising sea epiphytes thrive.
level. Mangroves form dense, almost impenetrable thickets
Vegetation in the Mangrove Zone: Mangrovesgrow on which buffer the physical forces of storms. They clean
the bayside of Sanibel Island and in the bayous at the west water by trapping silt, nutrients; and toxic substances, and
end of the island. They are usually found wherever the they prevent land erosion. More importantly, they play a
shore is tidally influenced and protected from ocean waves. leading role in providing wildlife habitat (Figure 53), and
Dominant species include the.red, black, and white man- in the general ecological productivity of the island. The
grove, and the buttonwood. mangrove system is the critical feeding and breeding area
Although a mixture can be found in each area, the red for many shore birds, reptiles, and amphibians, and certain

68% The Natural Systems Study

breasted merganser, bald eagle,* osprey,* clapper rail,*
American oyster catcher,* piping plover, snowy plover,*.
Wilson's plover,* black-bellied plover, ruddy turnstone,
eastern willet,* laughing gull,* least tern,* and black
skimmer.*
iNesting on or near-Sanibel Island

Figure 53.- (far left)
Mangrove forests should be
protected because they pro-
vide a multitude of natural
values, including habitat for
,water birds such as the egret
hiding in this photo.

mammals. All the mangrove species contribute to the food
chain, although their contribution is not always imme-
diately available. For example, black mangrove-generated
nutrient is flushed into the estuary during late summer and
fall, and becomes part of the mosquito-fish-bird cycle.
Heald and Tabb describe the flow of energy provided by
mangrove detritus at the basic level: first traveling
through bacteria and fungi, then through approximately
12 species of crustaceans, and finally to a number of
important sport and commercial species of fish which act
as top carnivores.63
The mangrove intertidal zone, with its nearby shallow
estuary, is a prime nursery and feeding ground for marine
species such as shrimp, mullet, snapper, red drum, and
blue crab. It is also an excellent fishing area. Tarpon and
snook, both dependent on mangrove systems, are the most
renowned fish in the area. Mangrove snapper, redfish, and
spotted sea trout are also sportfishing favorites.
Wildlife in the Mangrove Zone: The mangrove forest
and bays serve as one of the richest bird habitats on the
island. Twenty-one nesting species, as well as six migrants,
have been listed by Hewitt. Aquatic birds of predominantly
saltwater habitat include: brown pelican,* double-crested
cormorant,* great blue heron,* great egret,* green heron,* Figure 54. (near left)
snowy egret,* Louisiana heron,* black-crowned night Mangrove creeks are important
heron,* little blue heron,* yellow-crowned night heron,* feeding areas for egrets and
white ibis,* roseate spoonbill, lesser scaup duck, red- other water birds.

Mangroves 69

Several reptiles and amphibians are part of the man- brackish habitat effectively isolated from the rest of the
grove food web. Tidal wetland reptiles and amphibians estuary.
include: alligator, crocodile, ornate diamondback terrapin, Organic production in parts of the impoundment ap-
green anole, mangrove water snake,'yellow rat snake, and pears too high for the natural removal processes -(mixing
eastern diamondback rattlesnake.64 and- flushing). For this reason, heavy organic buildup-
Most of the mammals of Sanibel can be found in the occurs, restlting in high BOD levels, methane production,
mangrove zone at tires (see page 74). and a dominance of blue-green algae. The :construction of
the scenic roadway across these already poorly flushed.
Condition of the Mangrove Zone systems aggravated the :problems. In fact, consultants have
Figure 55. (below) observed: severe hypersalinity (salinity in excess of 50
The combination dike-and- Conservation Foundation consultants estimated that percent) in early June. Mangroves within'the confines �of
road at the wildlife refuge 2,800 acres of mangroves exis t today, the major portion of' the road: system appear to be stressed.65 (igure 56)
(white strip in photo) has which (2,300 acres) is-located in the J N. "Ding D arling
cut off water circulation n
and thus reduced certain National Wildlife Refuge.
habitat values.

Figure 56. (far right)
Vegetation on the mainland The Wildlife Refuge: The dike at the wildl.de refuge
fringe (left) is more vigorous prevents effective tidal penetration into mangrove
than vegetation on the man- swamps and shallow bayous. (Figure 55) Seasonal rains are
grove islands immersed in
the impounded water of the insufficient to maintain an alternative freshwater habitat,
wildlife refuge (right). so the area seems to exist as a highly unstable,- somewhat

70 The Natural Systems Study

Figure 57.
Seventy acres of thriving man-
groves were killed (gray area,
upper right) after they were
isolated from the estuary by
a road and flooded when the
adjacent excavation was
dewatered (left).

As -a result of low oxygen, variable salinity, and a tion of the mangrove communities within the artificial
stressed flora, the fauna also suffers. Only a few species of impoundment since they are evidently reacting adversely
fishes and invertebrates can withstand low oxygen condi- to an effect induced by the impoundment levees.
tions. Therefore, species diversity is low, but the few The Dixie Beach Boulevard Area: A tract of about 70
successful species can exist in large numbers. acres of tidal mangroves east of Dixie Beach Boulevard was
In certain areas, the soil salinities have become suffi- recently killed when an adjacent area was dredged and
ciently high to cause the formation of salterns or "salinas" filled.66 (Figure 57) Excessive flooding with fresh water
consisting of open sand areas with 'sparse, stunted black :during construction caused heavy mortality of trees within
and white mangroves. the tract; the culvert beneath Dixie Beach Road was
Infared and aerial photographs, indicate that red and inadequate to release the increased water. Although larger
black mangroves have suffered stress reactions. Conserva- culverts were installed early in 1974,: and 40 acres re-
tion Foundation consultants recommend careful examina- planted with mangrove seeds, most of the tract still is

Mangroves 71

deprived of adequate tidal circulation. Its chances for Captiva Road. The inland end of each ditch was largely
recovery are unknown. stagnant at the time of the field survey. These stretches
To the west of the boulevard, the mangrove community probably are not effective in controlling mosquitoes-cy-
ranges from a tidal red- mangrove at the bay edge to prinid (mosquito predators) populations were very low in
supratidal, high elevation, mixed mangrove community comparison to those existing in the more seaward portions
(black, red, and white mangroves). Mosquito ditches of the ditches.
penetrate this community- from the bay_ to the Sanibel-
Management Recommendations for Mangroves

The protection of mangrove forests should be an
essential part of Sanibel's environmental program. As in
the case of the interior wetlands, the protection of the
functional integrity of mangrove wetlands precludes virtu-
ally any alteration. The same protection is therefore
needed against excavation, filling, grading, draining, vege-
tation clearing, release of pollutants, solid roadways, and
other blockages. It is particularly important that mangrove
areas not be drained; by canals or otherwise.
The only appropriate structures in mangroves are the
pile-supported recreational ones--suggested for low-ridge-
and-swale interior wetlands. (Figure 58)
Restoration of mangrove systems is required in several
damaged areas. The large tract of damaged mangroves
along Dixie Beach Road should be restored to full func-
tioning condition by providing adequate water flow be-
neath the boulevard and such other actions as are required:
Also, any other areas that have been damaged by impound-
ment, drainage, or other actions should be restored by the
most expeditious means possible.

Figure 58.
Elevated catwalks such as this
in the wildlife refuge are pre-
ferred because they do not
block water flows.

CHAPTER 6

UPLANDS

Identification of Uplands northwest Cape Sable appears today (an extensive grami-
noid cover with lines of cabbage palm on the slight
The Gulf Beach Ridge Zone is the major ridge imme- ridges).67
diately behind the beach. It is stabilized by dense vegeta- The ragweed-castor bean association is a group of
tion. herbaceous annuals which readily invades newly cleared
The Mid-island Ridges Zone comprises the major areas. Alexander describes 18 "recovery" plants associated
ridges along the central axis of the island, and includes the with this group.68
highest elevations. In most areas, this zone divides the Cabbage palm is the most ubiquitous plant on the
bay-mangrove watershed from the interior wetlands island. It appears as stands-lines of trees along ridges
watershed. -and is especially common in transition areas between
Surface -Hydrology and Soils: The upland areas are the upland ridges and the interior wetlands.
inundated only during major hurricanes, and are the driest The West Indian tropical hardwood flora-which prob-
part of the island. There is no naturally existing surface ably is scarce historically-occurs only on Wulfert Point
water here. All rain immediately percolates into the and the narrow upland ridges.
ground because of the high'soil permeability and relatively The Australian pine-cajeput-Brazilian pepper category
high elevation. represents the introduced species of the island. They rarely
Soils of the uplands are immature, thin organics of the occur together; each tends to form pure stands and
Canaveral series. In some places they have high salinity eventually outcompetes native species.
because of salt spray and hurricane overtopping. The island's slash pine probably represents a relic
Uplands Vegetation: Sanibel's uplands vegetation is community. Its natural habitat is shared with the saw
largely secondary-or seriously impacted by exotic plants. palmetto.
In places. it is desertlike in appearance because of its More information on current vegetation of the island is
adaptations to drought. About 1900, the island vegetation presented in the section of this chapter dealing with the
probably resembled an extensive prairie, much like condition of the uplands.

74 The Natural Systems Study

Wildlife of the Uplands: Although the uplands cannot plant on the island-and it continued to be so two decades
compete with other habitats on Sanibel for size and variety later.
of birds, 11 species do nest there, including: pileated Farming practices in the past eliminated much of the
woodpecker, smooth-billed ani, red-bellied woodpecker, native vegetation, leaving the uplands vulnerable to altera-
great crested flycatcher, purple martin, fish crow, starling, tion by an invasion of exotics. A new dominance of
white-eyed vireo, prairie warbler, house. sparrow, and Australian pine and Brazilian pepper has changed historic
cardinal.69 wildlife patterns and lowered the productivity of the soils.
Upland reptiles and amphibians include: Florida box Unaltered upland habitat is now in short supply.
turtle, gopher tortoise, common iguana, green anole, Key Exotic Plant Invasions: Australian pine and Brazilian
West anole, southeast five-lined skink, ground skink, six- pepper represent the worst of the island's vegetation
lined racerunner, eastern glass lizard, Florida brown snake, problems. Each almost always becomes the dominant plant
southern ribbon snake, southern ringneck snake, southern after it occupies, an -area. Alexander says the two plants
black racer, eastern coachwhip snake, indigo snake, yellow "have proved to be disastrous to the natural ecosystem."72
rat snake, coral snake, eastern diamondback rattlesnake, The Conservation Foundation's consultants believe that
greenhouse frog, southern road, green tree frog, squirrel these species should be removed where they occur, and
tree frog, and Cuban tree frog.70 should not be planted in the future. Australian pine can be
The mammals of Sanibel's uplands often appear in controlled by fire and poison. Stump sprouting is common,
other ecological zones as well. Three rare or endangered so cutting in itself is not a permanent control. Two species Figure 59.
mammal species are found on the island: the Florida should be considered for replacement: slash pine and
bobcat, the cotton rat, and the Florida panther. Both the southern red cedar. excavation:of artificial
lakes on Sanibel has caused
bobcat- and the panther are secretive and seen infrequently. The cajeput (or punk tree) is another exotic capable of many ecological problems,
The raccoon, marsh rabbit, feral domestic dog, roof rat, dominating a natural habitat. Seed supply is always availa- including loss of wildlife
and house mouse are common. One gray squirrel, a few ble on the trees. Should an area be disturbed and seeds and degraded water quality.
gray foxes, mink, andround tail muskrats have also been
sighted on the island. The mammals found on Sanibel
include: opossum, armadillo, marsh rabbit, house mouse,
roof rat, Sanibel rice-rat, cotton rat, raccoon, otter, Florida
panther, Florida bobcat, feral domestic cat, and domestic
dog.71

Condition of Uplands

The major ecological alterations to Sanibel's uplands
areas appear to have been caused by farming, invasions of
exotic plants, and excavation of artificial lakes and water-
ways.
Farming: Farming has caused widespread changes in
basic vegetation patterns. For example, a cabbage palm
proliferation followed the abandonment of farming. Ap-
parently, this had been a common species on the island but
it did not spread until the late 1920's when it exploited the
land lying fallow after the 1926 hurricane. In 1955,
according to Cooley, cabbage palm was the most common

Uplands 75

STRAIGHT SIDES AND POLLUTION LOADING FROM
DEPTH RESULT IN NO RIM -- URBAN WASHOFF AND
OR BOTTOM VEGETATION WASTEWATER SEEPAGE

:
DEAD AND DYING PLANTS AND
SEDIMENTATION FALL TO BOTTOM

LIMIT OF LIGHT PENETRAT!ON
GROUND ~_...~,~ FOR PHOTOSYNTHESIS -+
WATE R DELETED OXYGEN IN VIOLATION
:EXCH ANC2E. . 0' OF FEDERAL STANDARDS.

Figure 60. i ; ACCUMULATE D BUILDUP OF
Improperly designed man- . .
made lakes can become .PENETRATION OF CLAY LAYER
grossly polluted in only RESULTS IN SALT WATER INTO
afew years 0. .. GROUND WATER AQUIFER'P

released at a time of favorable soil -moisture, a- closed these lakes typically have no provision for drainage, the
community of cajeput would develop. Cajeput is salt salt water will remain for long periods. (Figure 60)
tolerant and can invade mangrove communities on the The excavations have had pronounced effects on the
brackish water margins. Furthermore, it is not controllable water-table aquifer both in the construction phase and
by fire. after completion. Several of the lakes and canals were dug
Artificial Lakes. Many artificial lakes, ponds, and other too deeply, removing all or part of the confining clay and
gbodies of water have been excavated on Sanibel Island marl stratum. This permits upward leakage of high chlo-
during the last 10years. These excavations,knownas "real ride water from the shallow artesian aquifer into the
uestate lakes," were dug mostly to obtain fill material for water-table aquifer. During excavation of several ponds, a
surrounding land in order to meet housing regulations and dewatering process was used, which caused wide disper-
obtain septic tank permits. These have caused a number of sion of high chloride water from the lower part of the
ecological problems. (Figure 59) water-table aquifer. The pumping also could have caused
The lakes have exacerbated the salt-intrusion problem. upward leakage of saline water from the shallow artesian
In the island's undeveloped state, most of the salt water aquifer.
thrown up by storms would run off in a short time. But a In addition to aggravating the salt problem, the man-
hurricane surge will fill the man-made lakes, and salt water made lakes cause another serious form of delayed pollu-
will intrude deeply into the groundwater system. Because tion. Loading of the lakes in the interior wetlands with

76 The Natural Systems Study

sewage wastes, fertilizer-pesticide runoff, and sediments
will lead to gross pollution in the future. Lake pollution is a
delayed reaction-its true dimensions do not appear for
several years. At present, the majority of- lakes on the
island have not yet become rancid, but some are polluted
and others will become so in the future.
All the lakes now provide a free water surface which
facilitates evaporation and causes the water table in
adjacent areas to recede at more rapid rates than in the
past. All waterways on Sanibel
In summary, the lakes now act as accumulation basins should be protected.

Figure 62.
Internal canals connected to
the sea can damage the island
ecosystem by draining the
land and causing intrusion
of salt water.

Uplands 77

for highly saline water, septic waste, and organic detritus. and cause salt water to leak upward.
Depressed oxygen conditions prevail in many of the :4) Disturbance of natural vegetation should be limited
excavations and lakes.73 . to the minimum necessary for each building site and for
basic landscaping. -
Management Recommendations for Uplands 5) .No canals should be constructed which connect to
salt waters. (Figure 62)
While the focus of attention should be directed toward Artificial Lakes: To maintain ecologic balance in real
the conservation of the areas of high ecological sensitivity estate lakes, great care must be taken both in excavation
previously discussed, habitation of the ridges and other and in filling..Water quality degradation in these man-
upland areas of Sanibel must also be closely controlled. The made lakes. increases over time,. often accelerating as
principal need is to ensure that development of uplands is projects are -built. The lakes gradually accumulate pollu-
compatible with water quality and water-level protection.- tants and sediments and can become grossly polluted if not
:Site Preparation: To protect water quality and water properly designed and maintained. The Conservation
resources, development sites' should be. prepared with Foundation recommended the following measures:
special care. The following measures were recommended 1) Lakes should be deep enough to provide at least four
by The Conservation Foundation: feet of water at the lowest water stage to ensure that
1) No alteration of existing natural waterways or rooted aquatics such as cattails do not take over. (Figure
tributaries should be permitted; water should not be 63) -...
pumped for dewatering of excavations or related purposes. 2); Lakes should be shallow: enough to permit the
(Figure 61) maintenance' of acceptable water quality through wind
2) Artificial drainage ways should be confined within turnover-generally no deeper than seven or eight feet
the boundaries of each separate project area and should not below seasonal high water (at greater depths, wind turn-
drain into wetlands or surface waters. over is unlikely to prevent an accumulation of polluting
3) There should be no excavation or underground substances in the deeper water at the:bottom).
installations which penetrate the clay seal (or aquaclude) 3) Lakes should also be wide enough to ensure mainte-

, NATIVE MEAN LOW WATER
VEGETATION
+ 1-2 FT
AVERAGE
a- WATER LEVEL

MIN -2

Figure 63. DISTANCE AND SLOPE -2"E
DEPENDS ON SURFACE 5
Recommended design features AREA OF POND (AVG = 5 TO 8)
for artificial lakes.

78 The Natural Systems Study

nance of water quality through wind turnover (a seven-
foot-deep lake should have dimensions of more than 500
feet to provide for turnover).
4) The edge configuration of lakes should provide for
acceptable wildlife habitat without an overgrowth of
cattails. Also, a naturally vegetated and undeveloped wide
buffer should be provided around the lakes of a width
sufficient to control runoff pollution and provide wildlife
habitat.
5) Provision should be made for routine weed control
and maintenance dredging to remove accumulated sedi-
ments and pollutants from all real estate lakes.

CHAPTER7

SPECIAL ZONES

Identification of Special Zones
except for a narrow channel near the shore of Sanibel. The
Four special ecological subsystems were identified for sand bar at the inlet indicates that the magnitude of tidal
city management purposes: flushing is not great. Wind-induced flushing is reduced by
1) Blind Pass area (geologically unstable ridges at west the sinuous nature of the bayous and blockage of wind by
end of island, interspersed with lagoons with high suscep- Australian pines and mangroves. Density differences
tibility to pollution); caused by evaporation and rainfall produce some flushing,
2) Filled land (areas where ecology has been adversely but the sand bar hinders this.
altered by artificial fill); If, as suspected, flushing is minimal, then pollutants
3) Preservation spot zones (confined areas that serve from adjacent human activities should be prevented from
unique and valuable ecological purposes); and entering the system. Consideration should also be given to
4) �Refuge areas. Although the wildlife refuge is not increasing flushing. The inlet could be dredged to improve
under city jurisdiction, it was believed desirable for pur- circulation, and the old cut to the east could be reopened to
poses of coordination with the city to classify the refuge by improve flushing. These "improvements" would be made
the following subsystems: impounded mangrove; main in opposition to natural trends and would require mainte-
mangrove forest; Tarpon Bay; Ladyfinger Lake; interior *nance dredging.
wetlands (including Bailey Tract); and Lighthouse Point. The Conservation Foundation made the following re-
Blind Pass Area: At the western end of Sanibel is the commendations regarding the Blind Pass area:
ecologically distinct Blind Pass area. Most of this land has 1) Human occupancy of the area should be severely
been created in the past 200 years, and it has undergone limited.
many changes. (Figures 64, 65, 66) Several brackish, 2) No runoff from any adjacent urban development
fingerlike bayous extend through this area. projects should be discharged into the heads of Dinken
The waters of this area-Clam Bayou, Old Blind Pass, Bayou or Old Blind Pass.
and Blind Pass-exchange with waters from the Gulf of 3) No sewage or septic tank effluents should be dis-
Mexico through an inlet at the southwestern corner of charged or allowed to leach through the groundwater and
Sanibel Island. The shallow inlet is guarded by a sand bar, reach the lagoons.

80 :The Natural Systems Study

Figure 64.

The highly productive and geo-
f4.~~~~~ 2 g g g 0 ~~~~~~~~~~~~logically active Blind Pass area

problems.

- Figure 65.

Blind Passare now closed off
p-- 83~i~s~sr~i~j~ from tidal circulation and
flushing; effective pollutant
removaland dilution have
therefore been stopped.

nrm,- -----------
0~~~~~~~~~~~~~~~~~~~~~~~ ~ '; - i *-a -oi.i 4I

Special Zones 81

1859 ~~~~~1883 1928 19 1948

1958 1~~~~~960
Figure,66.

Recent ecologic history of
Blind Pass area, 1859-1961..
(Source: Duane Hall and
Assoc., 1975.)

The Sanibel Plan

r'
The
: : : : :: : .
anibel
t: -_- : arort
,. V .,~ e

84 The Sanibel Plan

Part III describes the planning process and the Sanibel
Plan, and also how the natural systems study by The
Conservation Foundation was useful to the planners.
The Planning Commission began work on the compre-
hensive plan for Sanibel shortly after the new city govern-
ment took office in December 1974. By March 1975, the
commission had prepared specifications for the planning
study and in May the data gathering began. Preliminary
reports by Wallace, McHarg, Roberts and Todd (WMRT)
and The Conservation Foundation (CF) were delivered in
July, August, and September. In December, the first draft
of the Sanibel Plan was available for public review. During
the next seven months, the plan and the regulations were
modified according to public reviews. InJuly 1976, the plan
received final approval, and the moratorium on new
building permits ended.
Part III consists of two chapters: the first reports on the
planning process; the second presents an abridged version
of the final- plan. Chapter 8, "Formulating the Plan," was
prepared jointly by CF and WMRT-William H. Roberts,
partner of WMRT -in charge of their studies, is the
principal author. The chapter focuses generally on interac-
tions of those involved in the planning process and
specifically on the roles of WMRT, as planning consul-
tants to the city, and CF, as ecological analysts sponsored
by-the Sanibel-Captiva Conservation Foundation (SCCF).
Chapter 9, "The Plan," is a photo-reproduced abridg-
ment of the official Sanibel Plan (the formal title is
"Comprehensive Land Use Plan, City of Sanibel, Lee
County, Florida"). The plan's table -of contents is also
included and indicates the full scope of the plan. The
material in Chapter 9 is reproduced directly from the plan
and is intended to emphasize natural systems, the subject
of this report.
A limited number of copies of the complete plan are
available from the Planning Commission, City of Sanibel,
Florida 33957, for $15.00 each.

CHAPTER 8

The Sanibel Plan resulted froma total community effort In June 1975, WMRT began developing base maps and
which involved extensive interactions among citizens, socioeconomic data pertaining to historic and projected
government officials, and consultants. The role of the urbanization of the island, and at about the same time the
Sanibel Planning Commission was to gather and analyze CF team of 16 scientists began field studies. It was agreed
data, to determine community needs, and finally to present that WMRT would assist and supplement CF's work by
a comprehensive plan to the mayor and City Council for giving spatial definition to various conditions found in the
adoption. Plan formulation was a dynamic process wherein field studies; for example, as the CF team developed
the public, their representatives, and the consultants working papers WMRT began interpreting aerial photo-
measured impacts, considered alternatives, and refined the graphs to show distribution of plant types, and produced a
plan to its final form. (Tables 9, 10) vegetation map of the entire island. The best topographic
The principal consultant to the city was the planning information available was from a USGS survey that
firm of Wallace, McHarg, Roberts, and Todd. WMRT indicated contours at five-foot intervals. WMRT repro-
engaged Fred Bosselman of Ross, Hardies, O'Keefe, Bab- duced this at the same scale (1:1000) as the vegetation map
cock, and Parsons, as legal consultant; Johnson Engineers, and examined the correlation between vegetation and
for utilities; and J.H.K. Co. for traffic studies. The Conser- topography. Similar maps and testing procedures included
vation Foundation in cooperation with the Sanibel-Captiva surface waters, groundwaters, and historic geology. In each
Conservation Foundation privately conducted a thorough case the planners and their natural scientists asked the CF
ecologic study of the island This was a unique and team to verify information based on their field work so
fortunate situation because in most cases the planning that the base data remained consistent.
consultant must undertake such environmental studies WMRT proposed that the island be described .according
entirely within his own contract. The CF study provided to ecological zones. These zones were identified by CF as
WMRT with more complete documentation of the island distinct regions of the island having particular ecological
environments than would usually be available in planning conditions and functioning systems.
programs of this type. CF scientists first suggested distinct habitats be deli-

86 The Sanibel Plan

neated, but this was considered too specifically related to
wildlife. The CF team evaluated WMRT maps and zone
descriptions to ensure that the data had been interpreted
correctly, and recommended minor modifications.
Progress reports, working papers, and maps showing
the results were presented at public meetings of the
Sanibel Planning Commission and made available for
public inspection. The next step was to determine the
relevance of this data in preparing a comprehensive plan
for Sanibel's future. Descriptive data on roads, utilities,
land uses, population, and other socioeconomic conditions,
along with environmental factors, were discussed by the
commission, members of special task forces, and residents S.W. Regional Planning -
and property owners. Council
When the island's present conditions and capacities Lee County
'were determined, it was possible to make projections of
urbanization trends and evaluate the city's capacity to
accommodate and service further growth. The planners on the Plan
projected alternative dimensions of future urban growth
on the island and measured the commensurate demand for
land and public services. Previous zoning for Sanibel by
Lee County would have allowed up to a total of 30,000
dwelling units on Sanibel. It was clear to everyone that this
level of development not only would totally obliterate the
natural environment but also could not be serviced by safe
streets, adequate water, or sewage disposal facilities. Also,
Sanibel's economic base as a resort offering unspoiled
beaches, a wildlife refuge, and the quiet ambience of a
small village would be lost. Furthermore, the health, Citizen Task Forces
safety, and welfare of the residents would be serious Appointment byPlanning Commission
for data collection, survey needs and
jeopardy. The planners discovered critical benchmarks of ifor datacollection survey needs and :
urbanization and population growth that might be accom- desires, review and assist consultant
modated-but if these levels. were surpassed, economic tasks.
sacrifices and other compromises would be necessary. One Environment
such constraint involved the limits of available technology Commercial and economic factors
and land area for disposal of treated effluent. Another was Residential and subdivisions
the capacity of the causeway to accommodate evacuation of Water
residents to the mainland in the event of a hurricane. Also,
the quantity and quality of potable water from the Lower Parks and Recreation
Hawthorn aquifer was uncertain, and the capacity of the Legal
island road system for substantially greater traffic volumes Civic and Social
was limited. Real Estate and Development Interests
WMRT presented options to the Planning Commission
that allowed the city to consider alternative levels of

Formulating The Plan 87

THE STRUCTURE FOR PLANNING STUDIES BY OTHER GROUPS

State of Florida Sanibel Captiva Conservation Foundation
Local Government Comprehensive Planning and The Conservation Foundation
Act. 1975-CH 75:257 "Natural Systems of Sanibel"
Director of Studies: J. Clark
Local liaison in Sanibel: R. Workman

Sanibel City Council
Mayor, Porter J. Goss
Zelda P. Butler, Vernon G. MacKenzie, Natural Science Consultants
Charles R. LeBuff, Jr., Francis P. Bailey, Jr. M. Brown-Energetics.
Responsible for adoption of a Comprehensive G. Campbell-Reptiles and Amphibians
Plan as a City Ordinance T. Missimer, J. Hartwell, P. Rosendahi-
Hydrology
O. Hewitt-Avian Life
-J. Morrill, W. Byle, Jr. -Marine Ecosystems
S. Riggs-Geology/Beach System
Sanibel Planning Commission D. Tabb,WM. Roessler, G. Beardsley, E. Heald-
Chairman, C. Duane White Wetlands and Mangrove Communities
Ann Winterbotham,Anina Hills, Lee Roy Friday, T. Alexander-Vegetation
Don Marshall, Joseph R. McMurty, George Tenney, A. Veri, L. Warner-Water Quality
Emily Underhill; Planning Director: Sam Shannon
Responsible for preparation of Comprehensive Plan
for consideration by City Council

Other Input
Island Water Association
Chamber-of Commerce
Civic Groups
Planning Consultant: WMRT
Planning: Wallace, McHarg, Roberts and Todd
Partner-in-Charge: William H. Roberts
Jonathan Sutton, Anne W. Spirn
Legal: Ross Hardies O'Keefe Babcock and Parsons Table 9.
Fred P. Bosselman, Charles L. Siemon Comprehensive planning
Economics: Dr. J.C. Nicholas integrated diverse and
Engineering: Johnson Engineering extensivegroups
Traffic: J.H.K.

88 The Sanibel Plan

commitment of public funds to provide for alternative
levels of future population. Options of 6,000, 8,000,16,000, Instruct consultants Analysis of Review of Consideration
and 24000 dellin unit wereteste. On he bais ofInstruct consultants Anal ysis of Review of Consideration
and 24,000 dwelling units were tested. On the basis of and assist in assem- projections options and selection
adassist-in assem- projections options and selection
projected impacts, the Planning Commission recom- " ,f
.o bling-and review of and for of options for
mended that a plan be developed based on 6,000 dwel- b and revi o
C" 'A maps and reports. problems future growth and
lings-2,000 more than the 4,000 units existing in 1975. .E ' ,
E " ~Set general objec- planning protection.
Once a tentative hypothesis had been developed regard- tives. 6,000 dwelling
Cc 0 tives. 6,000 dwelli
ing a total number of dwelling units to be accommodated option chosen.
9 ~~~~~~~~~~~~~~~~~~~~~~~~option chosen.
during the period of the plan (Florida law requires revision
every five years), the next task was to allocate those units
among the various ecological zones. It was necessary to
determine the tolerance of island environments to pro-
jected growth so that residents could appreciate the Data Interpretation Development Options for
preciate t h e D a ta pretation ~DeveloPment Options for
dimensions of prospective environmental impact before it gathering of data and of options health,
gatheringof data and of options L~health,
occurred. To do this, WMRT planners and CF natural & docu- projections. for future safety and
scientists first described the intrinsic function of each . mentation - Define plan- planning welfare
o mentation Dfine ,panne planning � welfare
ecological zone in maintaining the natural systems within . of existing ning problems. protection
the respective zone, and then described the interrelated 0 E conditions, basis f
systems between zones. The WMRT chart of ecological 0 o socio- Plan.
functions is a major product of this task. (See page 22.) economic
WMRT then p6sed these questions to the natural and envi-
scientists: What are the relative' orders of importance of ronmental
these environments given that some future growth on the
island is desirable and inevitable? How much tolerance to Description and deline- Environmental inventory,
change is there in each zone and what impact will it have? ation of ecological zones; functions, and guidelines
What guidelines are necessary to protect and rehabilitate review of C.F. Studies for management
Sanibel environments?
The planners developed a complex formula to distribute
equitably the 2,000 additional units (Tables 11, 12). This
formula took into account the relative suitability of each
ecological zone to accommodate dwellings, and the prox- Field studies by Description of Recommendation for
imity to human support systems such as existing sewer and natural scientists habitats and function- enviro nmental manage-
water lines, fire stations, and egress routes in the event of *ing environments ment and regulations
evacuation. Also, the level of private investment in terms
of development improvements was considered, as was the
level of "build out" in established subdivisions where
homes already had been built. The final product of this
formula allocated densities to all land on Sanibel varying
from one dwelling for each 33 acres to five dwellings per -
acre. Lower densities were allocated to environmentally Island Water Association; Chamber of Commerce, Various Civic Groups
fragile or hazardous lands and higher densities to areas r A
where the environment could tolerate change and where
support systems were available.
Having established the broad parameters of the plan,

Formulating. The Plan 89

Review preliminary Review of Review and Review and City Council
plan; test feasibility Plan elements adopt Plan comment adopts Plan
and impact of and public for submis- State of Florida by City
plan elements. input. sion to City County of Lee - Ordinance
Council S.W. Florida
R.P.C.

Permitted land Develop plan elements: Develop
uses and develop- safety, human support Regulations
ment intensity systems, protection of and
allocation environment, inter- - Administrative
government coordination, Procedures.
land use, economics.

Environmental protection
performance standards;
review of C.F. Studies

Review and comment
on draft Plan

Table 10.

As this chart indicates, com-
prehensive planning was a
complex process.

THE PLANNING PROCESS - approximately one year duration

90 The Sanibel Plan

West East TOTAL GROWTH SECTOR
West Central Central East ALLOCATION ALLOCATION

1. Accessibility to Causeway 1 2 3 4
2. Distance from Existing Commercial 2 1 4 3
and Institutional Facilities 1 3 4 2
3. Availability of Fire Protection 1 3 4 2
4. Availability of Police Protection 1 3 4 2
5. Proximity to Water Service 1 3 4 2
6, Proximity to Sewer Service 1 2 4 3
7. Relative Amount of Developable Land 3 2 4 1 West 280
14%
Totals 11 19 31 13
Sector Index 14 23 32 24 West Central 460.
8. Dwelling Units r 280 460 780 480 23%
2000
Residential
Units
East Central 780 F
Table 11.

Planning sectors ranked by East 48
availability or proximity of
services. (Source: Sanibel
Plan).

the Planning Commission then held ptiblic hearings that
specifically addressed problems of density. Individual lots,
established subdivisions, partially completed condominium
projects, and open parcels of land were reviewed to
determine the feasibility of recommended densities and to
make adjustments that seemed fair. This process, which
took four months of arduous labor, including hundreds of
hours of public hearings, eventually added 1,800 units to
the plan's 6,000-unit ceiling. Few compromises to the
intent of the plan were, made but major accomplishments
were achieved in terms of public support for a plan that
would greatly reduce the pace of urbanization.
While this was occurring, Fred Bosselman and Charles
Siemon of Ross, Hardies, O'Keefe, Babcock and Parsons
drafted a set of comprehensive performance standards for
the environmental protection of each ecological zone,

Formulating The Plan 91

HAZARDOUS/PRIME ENVIRONMENTAL VESTED RIGHTS DWELLING UNIT
LAND ALLOCATION ZONE ADJUSTMENT ADJUSTMENT ALLOCATION

Beach & L| Unimproved 10
Beach Setback 7I Land
,+ .

-- Mangrove I 1 |. Improved with 1.2
Roads

-_ Hazardous Areas Interior Wetland W | m Improved with 9 6
16.7% (1) Lowland Water/Electricity
339 D.U. 10
. Interior Wetland Improvedwith .6
Upland Sewer.

VBIsand� Pass 4 __ 50% Units Built

Unimproved i.

0 0 4 Interior 1I0 Improved with 1.2
Interior - 0- - Water/Electricity
Areas 11
1 Beach '10 Improved with .61
1,661 1 0 .Ridge Footings Constructed |

Improved with .6
. Sewers

Improved with 6
50% Units Built

+ratio of d.u. allocation by zone/area

dwelling units added per applicable improvement Table 12.

Steps in the residential unit
alloc ation process d eveloped
for land-use management on
RESIDENTIAL UNIT ALLOCATION PROCESS foSand Iselanagmnto
Sanibel Island.

92 The Sanibel Plan

based on the recommendations of the Planning Commis- Only a few months after the adoption of the Sanibel Plan
sion and consultants, and incorporating many of the the citizens of Sanibel had an opportunity to express their
suggestions offered by CF in its interim report. These views at the polls. The terms of Mayor Porter Goss and
guidelines included setbacks from the beach and from Councilnien Charles LeBuff and Francis Bailey-all strong
water bodies, restrictions on clearance of vegetation and supporters of the plan-expired in November 1976. Coun-
topographic disturbance for home building, and limits on cilman Vernon McKenzie, whose expertise as a former top
the size of areas covered by impervious materials (in order official of the U.S. Public Health Service had been invalua-
to. ensure groundwater recharge). Also, certain plants were ble in the planning process, chose to resign for reasons of
termed undesirable and recommendations for their remo- health. Thus four of the five council seats were up for
val were made. Strict controls for on-site sewage disposal election, with only Vice Mayor Zelda Butler (also a key plan
were proposed as supplementary to state and-local health proponent) guaranteed another two years in office.
requirements. For the three incumbents the verdict came early: No one
Environmental factors influenced several elements of challenged them. But for the vacancy caused by McKenzie's
the plan but were focused primarily in the section called resignation, a contest was joined. Duane White, chairman
"Protection of Natural, Environmental, Economic, and of the Planning Commission, filed for the seat, as did
Scenic Resources." Environmental factors also played a Carol Quillinan, a. representative of the Concerned Prop-
large part in the plan's development regulations, which erty Owners' Association, who had been highly critical of
included a description of permitted uses in each ecological the plan. The public viewed the contest as, in effect, a
zone and environmental performance standards-for new referendum on-the new plan.
construction in any zone. On November 2, 1976, the-voters gave Duane White
The Planning-Commission and' its consultants went more than 70 percent of the vote. The citizens who had
through a laborious process in considering ways to protect worked hard on the planning process considered it a clear
the environment while also accommodating the problems vote of confidence a mandate for planning.
of property owners and builders. The commission held At Lee County elections on the same day, some of the
months of public meetings to hear the pros and cons of strongest opponents of planning on the Lee County Com-
alternative means to achieve environmental conservation mission were replaced by the voters. Moreover, the voters
without unnecessary hardship. The social cost of depriving of Lee County supported, by more than 60 percent, an
landowners of their expectation to build according to initiative petition, placed on the ballot through the efforts
previous zoning was considered very seriously by the of a group of high school students, supporting a .5 mill tax
Planning Commission and consultants. levy to finance the purchase of Six-Mile Swamp, one of the
The final step in the planning process was to make the major freshwater wetlands remaining in the county.
plan internally consistent so that all future land uses and
improvements to human support systems were planned
and' could be financed. Administrative regulations were
written to provide orderly consideration and issuance if
permits, and to hear amendments to the plan. After
considering five drafts for a comprehensive plan, the City
Council obtained reviews by state, regional, and county
governments. The council then held its own public hear-
ings on the entire plan before adopting the final version in
July 1976.

* * .* * =

References 93

14. Maurice W. Provost. 1953. "The Water Table on Sanibel."
Bureau of Sanitary Engineering, Florida State Board
of Health. (Mimeo) (Hereafter cited as "Water Table
(For Chapters 1 through 8) on

1. Elinor:M. Dormer. 1975. The Sea Shell Islands, A History 15. Thomas M. Missimer and Durward H. Boggess. 1974. "Fluc-
of Sanibel and Captiva. Vantage Press, New York. tuations of the Water-Table in Lee County, Florida,
1969-73." U.S. Geological Survey, Open File Report
2. SanibeliPlanning Commission. Comprehensive Land Use No. 74019.
Plan, City of Sanibel, Lee County, Florida. 'Adopted:
July 19, 1976,,City of::Sanibel Ordinance: No. 76-21. 16. The Conservation Foundation. "Sanibel Natural Systems
(Hereafter cited as Comprehensive Land Use Plan.) Study. Preliminary Summary of Findings and Recom-
mendations." Presented to the Mayor and Council
3.: Jane-McCarthy. 1975. Sanibel Island: A'Cultural, Political, of the City of Sanibel on September 16, 1975. (Un-
and Social Profile. Data Base Report Series, The Con- published)
servation Foundation.
17. U.S. Army,-Corps of Engineers. 1969. "Beach Erosion Con-
4. / The Island Reporter.; Various issues from March 1975 trol study on Lee County, Florida." Corps of Engin-
through July 1976. eers, Jacksonville District, Jacksonville, Florida.

5. Aileen Lotz. "An Island Acts to Save Itself: The Sanibel 18. C.L. Jordan. 1973. "The Physical Environment: Climate."
Story." Florida Environmental and Urban Issues. lInA Summary of Knowledge of the Eastern Gulf of
April 1975, Volume 11, No. 4. FAU-FIU Joint Center, Mexico. The State University System of Florida, In-
Florida Atlantic University, Boca Raton, Florida. stitute of Oceanography, St. Petersburg, Florida.
(Hereafter cited as The Sanibel Story.)
19. Boggess. "Fresh-Water System of Sanibel."
:6. Ray Kennedy. "Eden Fights Back." Sports Illustrated. Feb-
ruary 3, 1975. 20. R.A. Krieger, J.L. Hatchett and J.L. Poole. 1957. "Prelimi-
nary Survey of the Saline-Water Resources of the Uni-
7. GThe Island Reporter. ted States." U.S. Geological Survey, Water Survey,
Water Supply Paper 1968.
8. Aileen Lotz. "The Sanibel Story."
21. Dormer. The Sea Shell Islands.
9. Ibid.

10. Ibid.
22. U.S. Department of Agriculture. 1971. "Guide for Interpre-
ll~ ~ ~~~~~~~. . .ting Engineering Uses of-Soils." U.S. Government
11. Sanibel Planning Commission. Comprehensive Land Use
Printing Office; Washington, D.C.
Plan.

12. Aileen Lotz. "The Sanibel Story." : :: 23. Thomas M. Missimer. "Water Quality Survey." Sanibel Data
Base Report Series, The Conservation Foundation.
13. Durward H.Boggess. 1974a. "The Shallow Fresh-water Sys- (Hereafter cited as "Water Quality.")
tem of Sanibel Island, Lee County, Florida, with Em-
phasis on the Sourcesland Effects of Saline Waters." i 24. Albert R. Veri and Langdon Warner. "Water Quality and
Florida Department of Natural Resources, Bureau of Wetlands Management and Performance Data for
Geology, Report of Investigation. No. 69. (Hereafter vation Foundation. (Hereafter cited as "Water Quali-
cited as "Fresh-Water System of Sanibel.") ty and Wetlands Management.")

94 References

25. Dormer. The Sea Shell Islands. 40. Sanibel Planning Commission. Comprehensive Land Use
Plan.
26. Luna F. Leopold. 1968. Hydrology for Urban Land Plan-
ning -- A Guidebook on the Hydrologic Effects of Ur- 41. John B. Morrill and William K. Byle, Jr. "Estuarine Ecology."
ban Land Use. Geologic Survey Circular 554. U.S. Sanibel Natural Systems-Reports. See Appendix.
Geologic Survey, Washington, D.C.
42. Thomas Missimer. "Hydrology."
27. R. Burke, II. 1971. "A Survey of Available Information
Describing Expected Constituents in Urban Surface 43. Ibid.
Runoff, with Special Emphasis on Gainesville, Flori-
da.'" 44. Morrill and Byle. "Estuarine Ecology."

28. G. Kenneth Young. "The Pollutant Loading Capacity of 45. Durbin C. Tabb, Eric J. Heald, Martin A. Roessler, "Vegeta-
the Interior Wetlands." Sanibel Data Base Report Ser- tion." Sanibel Natural Systems Reports.- See Appen-
ies, The Conservation Foundation. (Hereafter cited dix.
as "Pollutant Loading Capacity of Wetlands.")
46. Ibid.
29. Thomas M. Missimer. "Hydrology." Sanibel Natural Systems
Reports. See Appendix. 47. Ibid.

30. Ibid. 48. George R. Cooley. 1955. "The Vegetation of Sanibel, Lee
County, Florida." Rhodora, Journal of the New Eng-
31. Veri and Warner. "Water Quality and Wetlands Manage- land Botanical Club, Vol. 57.
ment."
49. Tabb, Heald, Roessler, et al. "Vegetation."
32. Sanibel Planning Commission. Comprehensive Land Use
Plan. 50. Oliver H. Hewitt. "Birds." Sanibel Data Base Report Series,
The Conservation Foundation.
33. G. Kenneth Young. "Pollutant Loading Capacity of Wet-
lands." 51. Cooley. "Vegetation of Sanibel."

34. Johnson Engineering. 1975. "Preliminary Plan, Sanibel Is- 52. Tabb, Heald, Roessler, et al. "Vegetation."
land Fresh Water Management Area." Prepared for
the Sanibel-Captiva Conservation Foundation, Inc. 53. Sanibel Planning Commission. Comprehensive Land Use
(Hereafter cited as "Fresh Water Management.") Plan.

35. Provost. "Water Table on Sanibel." 54. Provost. "Water Table on Sanibel."

36. Boggess. "Fresh-Water System on Sanibel." 55. Missimer. "Hydrology."

37. Johnson Engineering. "Fresh Water Management," 56. Sanibel Planning Commission. Comprehensive Land Use
Plan.
38. Sanibel Planning Commission. Comprehensive Land Use
Plan. 57. Ibid.

39. George R. Campbell. "Reptiles, Amphibians, and Mam- 58. Missimer. "Hydrology."
mals." Sanibel Data Base Report Series, The Conser-
vation Foundation. 59. Johnson Engineering. "Fresh Water Management."

References 95

60. Tabb, Heald, Roessler, et al. "Vegetation."

61. Ibid.

62. Campbell. "Reptiles, Mammals and Amphibians."

63. Tabb, Heald, Roessler, et al. "Vegetation."

64. Campbell, "Reptiles, Mammals and Amphibians."

65. Tabb, Heald, Roessler, et al. "Vegetation."

66. Ibid.

67. Tabb, Heald, Roessler, et al. "Vegetation."

68. Taylor Alexander. "Survey of Sanibel Vegetation." Sanibel
Data Base Report Series, The Conservation Founda-
tion;

69. Hewitt. "Birds."

70. Campbell. "Reptiles, Mammals and Amphibians."

71. Ibid.

72. Tabb, Heald, Roessler, et al. "Vegetation."

73. Missimer. "Water Quality."

CHAPTER 9

THE SANIBEL PLAN

ACKNOWLEDGMENTS t Section 2.2.2: Circulation 1I11
Section 2.2.3: Sewage Treatment 114
PROLOGUE 101 Section 2.2.4: Solid Waste t
Section 2.2.5: Power t
ARTICLE 1 - PREAMBLE t Section 2.2.6: Storm Drainage 117
Section 2.2.7: Fire t
Section 1.1: Purpose and Objectives t Section 2.2.8: Police t
Section 1.2: Consistency and Feasibility Section 2.2.9: Medical Facilities
of Plan t & Public Health t
Section 1.3: Economic Assumptions of Plan t Section 2.2.10: Education t
t Section 1.4: Coordination of Plan with Section 2.2.11: Insect Control 120
This symbol identifies Plans of Surrounding Areas ?
deleted sections of The Section 1.5: Implementation of Plan t Part 2.3 - Protection of Natural,
Sanibel Plan. Environmental, Economic and Scenic
ARTICLE 2 - ELEMENTS OF THE PLAN Resources
Many of the figures
mentioned in the text Part 2.1 - Safety Section 2.3.1: Preservation of Ecological
do not appear in this Functions Relating to Health
abridgment. Section 2.1.1: Hurricanes 102 Safety and Welfare 123
Section 2.1.2: Fire Safety 108 Section 2.3.2: Coastal Zone Protection t
~~~~~~Footnotes appear ~below ~Section 2.3.3: Wetland Protection 136
th e column of type in Part 2.2 - Human Support Systems Section 2.3.4: Wildlife Preservation 137
which the colectn ofcWle in
which the reference is Section 2.3.5: Vegetation Preservation 140
contained. Section 2.2.1: Water Supply 109 Section 2.3.6: Historic Preservation t

98 The Sanibel Plan

Section 2.3.7: Scenic Preservation 141 Section 3.1.18: Open Body of Water t
Section 3.1.19: Parcel of Land t
Part 2.4- Intergovernmental Coordination Section 3.1.20: Person t
Section 3.1.21: Plan t
Section 2.4.1: Intergovernmental Coordination t Section 3.1.22: Recreation Vehicle t
Section 2.4.2: Effect of Plan on Adjacent Section 3.1.23: Resort Housing t
Areas t Section 3.1.24: Restaurant t
Section 3.1.25: Secondary Treatment t
Part 2.5 - Land Use Section 3.1.26: Site Alteration t-
Section 3.1.27: Street Classification t
Section 2.5.1: Permitted Uses 142 Section 3.1.29: Subdivision t
Section 2.5.2: Residential Development In-
tensity 145 Part 3.2 - Maps
Section 2.5.3: Housing t
Section 2.5.4: Commercial Development 146 Section 3.2.1: Map Status t
Section 2.5.5:- Institutions t Section 3.2.2: Development Intensity Map t
Section 2.5.6: Recreation and Open Space 150 Section 3.2.3: Permitted Uses Map t
Section 2.5.7: Conservation t Section 3.2.4: Ecological Zones Map t
Section 2.5.8: Community Design t
Part 3.3 - General Requirements
ARTICLE 3 - DEVELOPMENT REGULATIONS
Section 3.3.1: Residential Densities t
Part 3.1 - Definitions Section 3.3.2: Residential Yard Requirements t
Section 3.3.3: Clustering t
Section 3.1.1: Amusement, Entertain- Section 3.3.4: Commercial Uses t
ment or Commercial Recrea- Section 3.3.5: Commercial Yard Requirements t
tion Establishment t Section 3.3.6: Screening and Location of
Section 3.1.2: Automobile Service Station t Commercial Uses on Land
Section 3.1.3: Coastal Construction Set- Adjoining Residential Uses t
back Line t Section 3.3.7: Home Occupations t
Section 3.1.4:- Developer t Section 3.3.8: Height Restriction t
Section 3.1.5: Development t I Section 3.3.9: Accessory Uses t
Section 3.1.6: Drive-In t Section 3.3.10: Off-Street Parking i
Section 3.1.7: Dwelling Unit t Section 3.3.11: Lawfully Existing Uses t
Section 3.1.8: Duplex - t Section 3.3.12: Partially Developed Land t
Section 3.1.9: Exotic Species of Plant t
Section 3.1.10: Land t Part 3.4.- Permitted Uses
Section 3.1.11: Lawfully Existing Use i
Section 3.1.12: Lot t Section 3.4.1: Permitted Uses t
Section 3.1.13: Mobile Home t Section 3.4.2: Gulf Beach t
Section 3.1.14: -Mobile Home Park t Section 3.4.3: Gulf Beach Ridge t
Section 3.1.15: Multifamily Dwelling t Section 3.4.4: Special Blind Pass Area t
Section 3.1.16: Native Plants t Section 3.4.5: Interior Wetland - Uplands t
Section 3.1.17: Non-competing Species of Plant t Section 3.4.6: Interior Wetland - Lowlands t

The Plan 99

Section 3.4.7: Mid-Island Ridge t Section 3.9.4: Development in the Mangrove
Section 3.4.8: Mangrove Forest t Forest Zone 157
Section 3.4.9: Bay Beach t Section 3.9.5: Development in or affecting
Section 3.2.10: Filled Land t the Bay Beach Zone 158
Section 3.9.6: Development in the Filled
Part 3.5 - Subdivisions Land Zone - 159
Section 3.9.7: Coverage and Clearance in
Section 3.5.1: Plat Required t Commercial Districts 160
Section 3.5.2: Design Standards . t
Part 3.10 - Paved Surface Construction Standards
Part 3.6- Mobile Homes and Recreation
Vehicles Section 3.10.1: Paving Materials 160

Section 3.6.1: Use of a Mobile Home ARTICLE 4 - ADMINISTRATIVE REGULATIONS
in Development t
Section 3.6.2: Mobile Home-Construction Part 4.1 - Introduction
Standardst v
Section 3.6.3: Existing Mobile Homes Part 4.2- Authorityand Purpose
Section 3.6.4: Recreation Vehicles t
Section 3.6.5: Temporary Construction Section 4.2.1: Legal Authority : t
Off ices t Section 4.2.2: Designation of Local Planning
Section 3.6.6: Other Regulations t Agency
Section 4.2.3: Relation to Comprehensive
Part 3.7 - Flood and Storm Proofing Plan t
Part 4.3- Definitions
Section 3.7.1: Flood Proofing 153
Section 3.7.2: Certification of Flood Proofing t Section 4.3.1: Statutory Definitions
Section 4.3.1: Statutory Definitions t
Section 3.7.3: Emergency Shelter Space t
Section 4.3.2: Other Definitions t
Section 3.7.4: Emergency Water t
Section 3.7.5: Non-residential Structures t Part 4.4 - Standards

Part 3.8 - Site Preparation Section 4.4.1: Permit Required t
Section 4.4.2: Basis for Issuance of Permit t
Section 3.8.1: Site Preparation 153 Section 4.4.3: Permits Required for Govern-
mental Development t
Part 3.9 - Environmental Performance Standards Section 4.4.4: Compliance with Other Laws t

Section 3.9.1: Development in the Gulf Part 4.5 - Short Form Permits
Beach, Gulf Beach Ridge and
Special Blind Pass Zones 154 Section 4.5.1: Development for which
Section 3.9.2: Development in the Interior Applicable t
Wetland Zone 155 Section 4.5.2: Procedure for Issuance
Section 3.9.3: Development in the Mid- of Development Permit-
Island Ridge Zone 156 Short Form t

100 The Sanibel Plan

Section 4.5.3: Commencement and Completion t
Section 4.5.4: Development Permit-Short
Form Permit Conditions t

Part 4.6 - Development Permits

Section 4.6.1: Application Requirements t
Section 4.6.2: Prehearing Public Meeting t
Section 4.6.3: Technical Assistance t
Section 4.6.4: Hearing Before Planning
Commission t
Section 4.6.5: Order Approving or Denying

Section 4.6.5: Order Approving or Denying
Development Permit t
Section 4.6.6: Commencement and Completion t
Section 4.6.7: Subdivision Plats t

Part 4.7 - Completion Permits

Section 4.7.1: When Required t
Section 4.7.2: Standards for Issuance t

Part 4.8 - Amendments to Plan

Section 4.8.1: Persons Entitled to Propose t
Amendments
Section 4.8.2: Application Procedure t
Section 4.8.3: Specific Amendments t
Section 4.8.4: General Amendments t

Part 4.9 - Notice, Hearing and Decision on
Amendments

Section 4.9.1: Public Meeting t
Section 4.9.2: Technical Assistance t
Section 4.9.3: Hearing Before Planning
Commission t
Section 4.9.4: Recommended Decision t
Section 4.9.5: Council Action t

The Plan 101

How wonderful are Islands! Islands in space,
likethis one I have come to,
ringed by miles of water....
An island from the world and the world's life.

Anne Morrow Lindbergh, Gift From the Sea

"WHEREAS, RESIDENTS OF SANIBEL ISLAND IN LEE COUNTY, FLORIDA, DESIRING TO HAVE THE
RIGHTS OF SELF-DETERMINATION, TO THE FULLEST EXTENT ALLOWED BY LAW, IN THE PLANNING
FOR THE ORDERLY FUTURE DEVELOPMENT OF AN ISLAND COMMUNITY KNOWN FAR AND WIDE-
FOR ITS UNIQUE ATMOSPHERE AND UNUSUAL NATURAL ENVIRONMENT, AND TO INSURE COM-
PLIANCE WITH SUCH PLANNING SO THAT THESE UNIQUE AND NATURAL CHARACTERISTICS OF THE
ISLAND SHALL BE PRESERVED, DO SEEK THE BENEFITS CONFERRED ON MUNICIPAL CORPORATIONS
BY THE CONSTITUTION AND LAWS OF THE STATE OF FLORIDA."

-from an Act relating to Lee County, establishing and organizing a municipality to be known and designated as the City of Sanibel and enacted by theV
Legislature of the State of Florida.

102 The Sanibel Plan

direction of their approach. (See Figure 1.)
The winds in a hurricane circulate counter-
ARTICLE 1: PREAMBLE t clockwise around a center or eye. The most
intense winds are those in the quadrant to A diagram outlining
the front right of the direction to which the "State of Florida Re-
BlARTICLE 2: ELEMENTS OF Astorm is heading. The storm tide is the gional Planning Coun-
result of the continuous winds piling up cils," which originally
0 : X : :0TH X - *E PL AN I Ad water in front of the wind and the height appeared in Article 1
depends upon the velocity of the wind and the of the Sanibel Plan,
Part 2 1 : Safety : distance that the wind is- blowing over water. appears as Fig. 1 in
Part2.1: Safey Chapter1.
Each of these three types of storm has differ-
ent ramifications in regard to warning time,
evacuation procedure and potential damage.
Section 2.1.1: Hurricanes
1. Storm from the West. (Figure 1, Storm No. 1)
A. BACKGROUND DISCUSSION A storm from the West is likely to be preceded
by a flood tide. The timing and size of the
Threat tide will depend on the exact location of the
The Island of Sanibel is subject to the periodic storm and the phase of the tides. If the storm
passage of hurricanes. A hurricane is a tropical approaches from the west and makes landfall just
north of Sanibel so that Sanibel is in the dan-
cyclone with sustained winds of 74 mph or greater gerous quadrant, the winds of the hurricane will
that is typically accompanied by heavy rain and gerbusuadrantane
thunderstorm activity. Hurricalines have struck , build up water from over the entire distance of
the continental United States with winds as high the storm s circumference and will produce ex-
as 250 mph. Hurricanes represent a wide variety tremely high tides. Depending on the severity of
of threats to various parts of the United States. the storm's intensity, its size and speed of
In the interior reaches heavy rains- and wind ; forward motion, flooding of parts of the evacua-
often produce floods and destructive tornadoes. tion route could occur up to 10 hours in advance
of a westerly approaching storm.
Near the coast high winds propel loose objects
through windows, doors and even walls, and lift
off roofs. At the coast, the impact of hurricane
winds and low barometric pressure on adjacent 2.- Storm from the East. (Figure 1, Storm No. 2)
water bodies have reached nearly 25 feet and The second general direction of approach is from
have inundated vast portions of low-lying coastal across the mainland of Florida, the exiting
land. These flood waters may spread inland at storm. Historically a good number of storms
30 mph and some locations may be inundated have made landfall between Miami and West
for 10 or more hours depending upon the speed of Palm Beach and have exited north of Sanibel.
advance of the storm and the topography. With such a storm evacuation of the island
involves movement toward the storm, which
For Sanibel the storm tide represents a poten- would create severe traffic complications.
tially devastating and dangerous event. The Once the storm passes out into open water
storm tide level predicted for Sanibel during extreme tides may result. In one such storm
the 100 year storm is 13.5 feet, a level that Punta Rassa recorded flood tides of greater
would inundate the entire island, and would be than 14 feet.
surmounted by large scouring and battering waves.
The erosive power and battering impact of such a 3. Storm from the South. (Figure 1, Storm No.3)
waterflow would seriously threaten the integrity The third general storm type is the southerly
of most structures on Sanibel and the life of approaching storm. Donna in 1960 followed
any person stranded on the island. Of course, les- such an approach during its passage through
ser storms can and will produce storm tides capable the Fort Myers area. Because the storm winds
of flooding the entire island. The 1926 hurricane will initially come from across the mainland,
did just that, and forever changed the charac- no substantial tide will be built up before
ter of Sanibel's use by wiping out the Island's the storm's arrival. If the westerly portion
farming economy. of the storm remains over water, however, a
flood tide will succeed the eye. If the
For planning purposes it is useful to con- southerly approaching storm eye passes at or
sider the hurricane threat in terms of three to the West of Sanibel, flood tides may pre-
general types of storm according to the cede the storm depending upon the distance

The Plan 103

to the West the eye passes. In fact a one route for evacuation from Sanibel --
passing storm 100 or more miles to sea might well across the Causeway, Punta Rassa, and State
flood the entire Island. In recent years Road 867.
two storms passing within 300 miles have
produced flood tides which have almost In many places the evacuation route is a
broken over the Gulf Beach Ridge. narrow two-lane road with little or no
shoulders with elevations as low as 4.0 feet
The actual direction of approach of a storm msl. This evacuation corridor is poorly
may be southeast, southwest or some other suited for the vital task of evacuating the
variable and as a result the actual storm Sanibel populace. Even if the evacuation
-effects on Sanibel for any particular storm route proper were upgraded, feeder road
will be-widely variable. Nevertheless, it flooding on Sanibel, tree and utility pole
is possible to identify a range of impacts falls, discontinuous road design and storm
that can be expected. The passage of a conditions on the Island will inevitably
hurricane within 50 or so miles of the Island diminish the load capacity of the evacuation
would probably produce storm tides of 5-13+ route. In addition, portions of the same
feet msl with 5+ foot waves on top and sus- route will be used by as many as 102,000
ta'ined winds of 75-150 mph. mainland evacuees who live in other low
lying coastal parts severely limiting the
Refuge capacity of the route that will be available
for Sanibel evacuees. If the mainland evac-
Since Sanibel's ground elevation averages uees begin to clog the evacuation route, or
approximately 5 feet or less the Island is if the route is blocked by a fallen tree or
extremely vulnerable to flood tides of greater a camper blown over by the wind, the route
than 5 feet. It is therefore necessary that will quickly back up leaving those still on
each person on the Island when a hurricane the road at the mercy of incoming storm
warning is received have an opportunity to tides. If the route were blocked in Fort
reach safe refuge prior to the arrival of the Myers so that the first evacuating car from
effects of a hurricane. Sanibel was halted, the line of traffic
would back all the way up to Sanibel and
Off-Island Refuge some persons would be unable to reach the
Causeway. Although two lanes are theoreti-
The National Hurricane Center advises that at least to
evacuation from low lying coastal areas is section, it woul d be unwise to use both
necessary in order to protect human life from highway lanes for evacuationbecause emer-
hurricane floods and.winds. According to the gency and control vehicles would not have
gency and control vehicles would not have
National Hurricane Center, evacuation into access to the evacuation route in order to
elevated buildings located in a low lying monitor and control the evacuation and keep
coastal area with the physical and develop- the route clear. The initiation of wrong-way
mental characteristics of Sanibel, is not a flow would be difficult and time consuming,
satisfactory substitute for evacuation away and could well upset an otherwise controll-
from flood areas. Elevated refuges are not a able evacuation.
substitute for evacuation from the Island,
because the refuges would be isolated during
and after the storm by high water, downed On-Island Refuge
trees and hazardous conditions. The unavail-
ability of medical services, delay in the There is currently very little on-Island
restoration of essential services, outbreak hurricane refuge -- elevated to 13.5 feet msl
of disease, and inadequacy of food and water on piling foundations, with pilings, walls
supplies that could result from that isolation and roofs capable of withstanding the 100 year
could subject refugees to an additional and storm and located away from the coastal high
unnecessary threat to their health and safety. hazard area on Sanibel. Even though on-Island
refuge is not a substitute for evacuation off
the Island, such refuge must be available as
In recognition of the hurricane hazard on an emergency measure for individuals trapped
Sanibel and the inherent deficiencies of on- on the Island, especially in the event of a
Island refuge, the City of Sanibel must plan closing of the evacuation route by tree fall
for the evacuation off the Island of all of or other event. Additional on-Island refuge
the persons who will be on the Island when a must be developed as a part of any future
hurricane warning is issued. There is only growth on the Island.

104 The Sanibel Plan

Warnings and Evacuation Time anticipated that a maximum of 10 1/2 - 11 1/2
hours will be available for evacuation prior
The National Hurricane Center expects to be to the arrival of storm conditions. This
able to predict the arrival of a hurricane period is comparable to the time frame which
within 100 miles of Sanibel on the -basis of the National Hurricane Center recommends for
information available 24 hours in advance of planning purposes for South Florida coastal
arrival of the eye of the storm. However, locations. THE VARIABLES THAT ARE INVOLVED
because it takes approximately 6 hours to IN A HURRICANE AND ITS EFFECT ON LAND COULD
code, process, and analyze the data and trans- RESULT IN AS LITTLE AS SIX HOURS FOR EVACUATION.
mit the warning, ordinarily Sanibel can ex-
pect to receive a warning 12-18 hours in
advance of arrival of the eye of the storm. Evacuation Capacity
The number of persons that can be safely
Nevertheless the entire warning period is not evacuated from Sanibel therefore depends
available for evacuation because there will be
upon the amount of time available for evacu-
a cut-off time prior to the actual arrival of ation, multiplied by the evacuation rate per
the storm. That cut-off time will occur be- hour. This figure compared to the popula-
hour. This figure compared to the popula-
cause adequate time is no longer available for tion on the Island when a hurricane warning
an evacuee to complete the evacuation trip to
high ground before the effects of the storm sponse rate, indicates watt percentage of
strike the evacuation route. This may be be-
persons who want to evacuate can be success-
cause of preceding flood tides or because the fully evacuated. It is incumbent upon the
evacuation routes are clogged with mainland the percentage is as
City to ensure that the percentage is as
evacuees.
Data gathered during hurricane approaches in, near 100% as is possible.
the Gulf of Mexico indicates that storm con-
ditions of high winds and tides sufficient'to The many variables involved in a hurricane
flood the Causeway,depending on the direction approach make it very difficult toestimate
of approach of the storm and the storm's inten- the number of persons that can be success-
sity,could reach the Island and the evacuation fully evacuated from Sanibel in the face of
routebetween 4 to 6 hours or more before actual an approaching hurricane. These variables
arrival of the hurricane eye, In addition, include population, warning time, response
heavy rains may precede the eye of the storm time, rod capacity, mode of evacuation,
by' 6-12 hours and -could flood parts of the storm intensity and speed, direction of
evacuation route on the Island and on the main- approach, recent hurricane history and time
land. High winds may also arrive 6 or more of year among others.
hours in advance of the eye of the storm felling Evacuation Population
trees and blocking the route. The ubiquitous
Australian pine which lines the roads of Sanibel The number of persons to be evacuated is not
is particularly vulnerable to windthrow. The easy to calculate. Sanibel is a seasonal
evacuation of the Island must be terminated far resort with fluctuating populations. During
enough in advance of flood tides, the clogging the months of September and October the
of the route with mainland evacuees, and heavy Sanibel population is at an off-season low
winds and rains, to ensure that the last according to water, sewer and traffic data.
evacuee has more than adequate opportunity to Even within that period the population varies
reach safe refuge prior to the arrival of storm especially near Labor Day when population
conditions. Since it is estimated that a mini- spurts upward to perhaps 85% of peak, a week-
mum of one hour will be required for an evacuee end that has been subjected to extreme hurri-
to reach the relatively high ground portion of canes several times since 1935. Nevertheless,
the evacuation route, the evacuation should be dangerous hurricanes have appeared as early
terminated at least one and one half hours as June 9 and as late as December 2 within
before the predicted flooding of any portion the last 50 years. Audrey (June 27, 1957),
of the evacuation route would make the route Alma (June 9, 1966) and Agnes (June 19, 1972)
impassable for any of the reasons described are a few of the hurricanes that have made
above. The life of an evacuee trapped on the landfall early in the "hurricane season."
Causeway, Punta Rassa or other low lying part Audrey killed 600 persons and did $200,000,000
of the evacuation route during a hurricane worth of damage.
would be in serious jeopardy.
In addition experience in developing resort
Based on all available information, it can be communities in Florida indicates that season-

The- Plan 105

al fluctuations in population become less With the exception of a small portion of U.S. 41,
acute with the passage of time. The peak the evacuation routes both on the Island and on
population which is on the Island during the mainland are all two-lane urban arterials
major summer holidays now, is increasingly or rural highways. "The capacity and service
likely to be on Island year-round. volumes of two-lane highways are expressed in
total vehicles per hour, regardless of the
Evacuation Population distribution of traffic by direction."l The
ideal uninterrupted flow capacities of a two-
Due to the inability to forecast with pre- lane highway of good geometric design is 2000
cision the numbers of persons likely to be vehicles per hour. This assumes 12 foot lanes,
on the Island in the event of a hurricane, a lateral clearance of at least 6 feet from
it is only prudent to plan to evacuate the pavement edge to side obstruction, unrestricted
peak or holding capacity of the Island. This sight distances of 1500 feet, level vertical
can be determined-based upon the number of alignment, -and no trucks or large vehicles in
housing units, apartments, and resort accom- the traffic flow.
modations existing on the Island.
While numerous isolated examples exist of
Warning Time measured peak hour volumes of 2000 to 2200
The National Hurricane Center indicates that a vehicles per hour, it must be recognizedthat
these volumes are basically unstable and cannot
hurricane warning upon which an evacuation usually be sustained for an extended period of
order could be predicated will be issued be- usually be sustained for an extended period of
tween 12 and 18 hours before arrival of the time. Under such unstable low, critical den-
toen Ho r footides, high winds sities will be incurred which will cause stop-
storm center. However, flood tides, high winds
and-go conditions. Under stop-and-go condi-
and heavy rains may arrive between 4 and 12
and neavy rains may arrive between 4 and 12 tions the maximum rate at which cars can move
hours prior to actual arrival of the eye of tions the maximum rate at which cars can move
the storm, away from a stopped condition is 1500 passenger
cars per lane per hour. Actual capacity will
be less than this depending upon the amount of
Response Time time the vehicles are stopped and the incidence
The amount of time necessary to warn and impel of slower accelerating vehicles.
evacuees depends on a host of factors including
recent storm history, prior personal experience, The conditions existing on many of the evacua-
community planning and understanding of the tion routes are substantially below typical
magnitude of the threat. The National Hurri- design standards. For example, Periwinkle Way,
cane Center estimates that 80% of the persons the major arterial on the Island and primary
in hurricane hazardous areas in South Florida evacuation route, has a pavement width of 18
have never experienced a hurricane. When Donna feet or 9 feet per lane with lateral clearances
passed through Fort Myers in 1960 there were of 4 feet. Assuming that 5% of the traffic will
only 300 persons living on Sanibel. Neverthe- betrucks, these substandard factors will reduce
less, given the magnitude of the hurricane the vehicle capacity of the arterial by 30%.
threat on the Island,; the City must undertake Therefore, for uninterrupted flow conditions,
planning and educational programs to ensure an the maximum capacity ofthe arterial would be
efficient and timely response to-an evacuation 1400 vehicles per hour.
order.
Another factor which must be considered is the
effect of inclement weather on traffic flow. An
Road Capacity and Mode of Evacuation evacuation being conducted during the time
period of 6 to 18 hours before arrival of the
The primary mode of transportation during evac- full force of the hurricane may experience heavy
rains and high winds. While extensive data on
availability, suitability, and carrying capac- the effect of these road conditions or road
ities of other modes such as boats, trucks, capacity is lacking, numerous observations indi-
and buses and experience of other jurisdic- cate that vehicle speed and density can be
tions during hurricane evacuations suggest severely restricted. A 40% reduction in capacity
that only minimal numbers of persons will use is suggested as reasonable under severe weather
these alternative modes. Consideration should
conditions.
be given however, to the use of school buses
normally located on the Island to evacuate
those persons without access to private auto- IThe Highway Capacity Manual, 1965 Edition HRB,
mobiles. Special Report, #87, Page 299.

106 The Sanibel Plan

The above traffic engineering factors suggest 12-8 Weather begins to seriously deteriorate,
that a reasonable and prudent evacuation route more persons decide to evacuate and the
capacity during hurricane conditions (6-18 hours system begins to slow down from ex-
prior to landfall or proximity of the hurricane cessive loading.
center,is approximately 700 to 800 vehicles per
hour. Where evacuation route is subject to 12-6 Weather continues to intensify; evacua-
other specific hazards such as local flooding, tion efficiency reduced by tree falls
road debris, or fallen trees such as is the and adverse driving conditions. Storm
case in Sanibel, the actual volume of vehicles tides which will flood portions of the
moving out of the danger area could be consider- evacuation route are forecast for 8-5
ably less;. Unfortunately, there are no analyti- hours prior to eye arrival. (Depending
cal techniques to estimate the reduced flow from upon direction of approach ) Evacua-
these potential environmental interruptions. tion across the Causeway is terminated
at 6% hours.
Again, judgment and prudence suggests that a
factor of 10% to 20% reduction in capacity would 8-5 Storm tide floods low points on evacua-
not be unreasonable to account for these interrup- tion route -- route impassable.
tions.
4 Persons remaining on Island begin to
move to on-Island refuge. Roadways
Based on the above discussion, the City can with low elevation are flooding and
reasonably expect to evacuate between 560 and tree falls continue as the weather con-
800 cars per hour. tinues to intensify.

The following is an example of the sequence of 5-3 Storm tides begin to flood the Island;
events -preceding a hurricane strike: roads below five feet become impassable
because flooding inhibits clearing of
HURRICANE APPROACH X if - fallen trees. Power is knocked out by
winds and falling trees.
HOURS BEFORE
ARRIVAL OF EYE 2 Weather continues to intensify. Wind
blown debris becomes dangerous; on-
48-36 National Hurricane Center (NHC) Island refuge is accessible by foot
issues hurricane watch for area in- only Glass windows not covered would
celuding Sanibel. be broken by debris driven by high winds.
Flood tides continue to rise.
47-25 Hurricane is monitored and predic-
tions of movement are updated at 6 X1 Storm tide inundated; waves pass over
hour intervals. (2-3 hours if at major portion of the Island, winds con-
all possible). D tinue to intensify. Persons who have
not yet reached safe refuge are trapped
24 Data on hurricane collected by NHC in non-elevated structures.
for predicted landfall.
;18-12 Hurricanewarningised for areaThe island is inundated; waves pass over
18-12 Hurricane warning is issued for area
major portion of the Island. W-inds of
150 miles: either side of the pre- 75-120 mph strike the Island. The most
dicted landfall. Warninc received by
intense portion of the hurricane in the
Sanibel police chief. Decision is
made to evacuate. Evacuation order
is issued and emergency plan is insti-
tuted. Evacuation

18-11 Hurricane warning and evacuation Analysis of the evacuation capacity of the Island
orders are delivered to each person during the approach of a hurricane reveals that
on the Island by emergency teams. the City can anticipate that between 4,900 and
Evacuation begins as a small trickle 6,250 cars can be evacuated depending upon the
of cars which steadily builds. severity of the storm if there are no major
calamities which disrupt the evacuation route
15-12 Evacuation reaches its peak. for more than one hour of the evacuation period.

The Plan 107

B. THE PLAN FOR HURRICANE SAFETY Population

In response to this hurricane threat the City of 1) The City should limit and manage growth so
Sanibel shall undertake to implement the follow- that the population on the Island when a
ing plans and policies including evacuation, hurricane warning is issued will not be
population limitation, on-Island refuge, build- substantially in excess of the evacuation
ing codes and capital improvements: and on-Island refuge capacity of the Island.
Overloading the emergency system will reduce
Evacuation efficiency and deprive residents and visit-
ors of a reasonable opportunity to reach
1) The City shall provide each person on the safe refuge.
Island when a hurricane warning is issued
the opportunity to evacuate from the Island 2) Future growth should be accompanied by and
-and to encourage persons to evacuate in a coordinated with,to the maximum extent
timely fashion. practicable, improvements in the Island-
evacuation system and increases in the
The City should continue to develop and amount of on-Island refuge. It is only in
improve the preliminary evacuation plan anticination of such improvements that the
that was adopted on July 2, 1975. present population should be allowed to
expand, because the evacuation capacity is
2) The City should maintain a 24-hour communi- already taxed during certain times of the
cations link with emergency weather informa- hurricane season.
tion sources.

3) The City should coordinate with Lee County
and the City of Fort Myers in the develop- On-island Refuge
ment of an off-Island emergency plan for
evacuation which will control traffic on It is the policy of the City to develop and
State Road S867 and identify emergency improve off-Island evacuation as the principal
shelters. refuge for its population. On-Island refuge
is not a substitute for evacuation and is nec-
4) The City should upgrade the Island circula- essary only for those who are unable to leave
tion system for improved traffic flow the Island.
efficiency and roadways elevated above
early storm flood levels and improve storm 1) The City should make arrangements with the
drainage. owners of all buildings on the Island which
could serve as on-Island refuge, for the
5) Incoming traffic should be controlled at use of hallways and other common areas of
the Causeway toll booth as soon as a hurri- buildings as emergency shelters. Such
cane warning is issued which includes areas should be stocked with emergency
Sanibel. food, water and medical supplies. Such
structures should be constructed on pilings,
6) The City should make provision for the elevated above 13.5 feet msl, have wind
rental or, if necessary, the purchase of resistant walls and roofs, be located back
three tow trucks for use in assisting dis- from the coastal high hazard area.
abled vehicles during an evacuation.
2) All future buildings that are of a type
7) The City should develop an equipped emer- which have common spaces, should be de-
gency fallen tree and pole removing team veloped in a manner amenable to use as an
for clearing fallen trees from the evacua- emergency shelter. Use of such areas should
tion feeder routes. be agreed upon during the approval of such
development.
8) The City should maximize warning capabil-
ity including Island-wide sirens. 3) The City should develop a City Hall or other
municipal structure designed to serve as
9) The City/should develop a procedure by emergency on-Island refuge for the maximum
which the cut-off time for evacuation can number of persons commensurate with the
be identified and enforced during the other anticipated uses of such municipal
evacuation. structures.

108 The Sanibel Plan

Building Codes consequences of that threat and appro-
The Sanibel Building Code should-be amended to priate responses for Sanibel given its
provide that: particularly vulnerable situation.

1) All development on Sanibel shall be designed
to withstand the wind and water pressures ection 2.1.2: FireSafety
associated with a 100 year storm.

2) All development in the Gulf Beach and Gulf A. BACKGROUND DISCUSSION
Ridge shall be carried out on piling found-
ations capable of withstanding wind and\water Currently, fire-fighting equipment is located
forces associated with a 100 year storm. at the ain station atPalmRidge Road and an
at the main station at Palm Ridge Road and an
3) Emergency potable water capacity shall be unmanned substationlat Rabbit and Sanibel-
included in all structures containing more Captiva Roads. The fire-fighting staff in-
than 4 residential units, commercial struc- cludes two (four imminently) paid personnel
tures of greater than 3,000 square feet of (administrative assistant and equipment cap-
floor area, and hotels and motels. X tain) and fifteen volunteers (one of whom is
Capital Improvements the Fire Chief).
1) The City should upgrade the Island circula-
tion system to provide efficient access to The service area includes the entire Sanibel
the evacuation route unimpeded by flooding Fire Control District, the boundaries of
from the interior wetlands.
which coincide with the City of Sanibel.
2) The City should construct a multipurpose Future planning of fire protection services
- municipal building which can be used for is currently tied closely to the Island Water
emergency refuge. Association Distribution System. Until re-
3) Additional emergency vehicles should be cently, only one fire hydrant existed on:
provided for use during a hurricane, as Sanibel, the remainder of the Island being
well as tree and utility pole removal serviced by seven fill pipes which require a
equipment. pumper back-up to provide adequate nozzle
pressure. The Water Association anticipates
4) The City should develop and support an
efficient and effectivewarning system. the installation of hydrants throughout the
Island to conform to requirements of FLre
5) The City should provide maximum feasible Insurance Underwriters. This is discussed in
elevated refuge during the development of further detail in Section- 2.2.7, Fire. The
any other municipal structure. existing equipment, which is also described
in Section 2.2.7, provides pumper capabilities
and reserve tank equipment sufficient to serve
Education and Study
areas not served by hydrants or fill pipes, or
1) The City should conduct an extensive too far from bodies of water which may be tapped
educational program to maximize citizen
understanding of the threat of hurricane
and the appropriate responses thereto.

2) The City should encourage persons to Future demands of the Fire Department will be
respond to early warnings and hurricane most critical within the interior portions of
watch in order to lessen the evacuation the Island that are not in close proximity to a
burden after a hurricane warning is body of water or fill pipes. Some areas fall
issued. beyond the recommended response distance of
three miles. At the east end of the Island,
3) The City should contact the National
Weather Service and anyt other agency of approximately 500 dwelling units and 13 commer-
government with expertise in the field cial establishments lie beyond this 3 mile
of hurricanes and floods, and attempt to radius. Plans and recommendations to improve
develop future studies and programs on fire service are discussed in Section 2.2.7 of
the extent of the threat to Sanibel, the this report.

The Plan 109

B. WILD FIRES fire fighting equipment should be provided and
adequate standards such as road widths should
Certain areas of Sanibel are particularly f : be observed. The City should consult with the
prone to large recurring fires. These fires Florida Forest Service to establish a fire
are a natural occurrence in low-lying areas of management program and to determine adequate
the interior during periods of drought and are : safety standards.
an important factor in the ecology of the in-
terior wet-land. Low-lying areas within the in-
terior wetland are dependent on fire to burn C. OTHER FIRES
off accumulated dead plants, to release nutri- Accidental fire in buildings is potentially-a
\ ents to the soil, and -to ukill- invading woody 30major problem with respect to protection of
shrubs and trees. Fire stimulates healthy residents and property because of inadequate
facilities and fire-fighting personnel. The
vegetative regrowth, thereby maintaining the
flood storage capacity .of the wetland and.: major shortcomings today are the absence of
benefitting wildlife.; 0 0 adequate water pressure and hydrants in close
proximity to the densely developed sections of
When man chooses to live in this environment, the Island. In particular, multi-story buil-
fire becomes a potential hazard rather than a dings pose a special problem in that several
resource and man's activities even increase dwellings are not accessible to fire-fighting
the chances of fire. -r rescue equipment. Problems of access are
further complicated because several buildings
It is paradoxical that man both inhibits fire . do not have sufficient areas of stable paved
and increases the intensity and frequency of , areas that can support heavy fire-fighting
fire. When fires are inhibited by man, dense, equipment.
highly flammable debris accumulates on the
ground. This extensive "build-up" of fuel D. PLAN FOR FIRE SAFETY
rarely occurs in nature where periodic fires The City should coordinate its activities with
burn off accumulated debris. In addition, the Fire District to assure that adequate fire
man is a primary cause of fire. Thus the protection and safety are afforded the citif-
presence of human habitation in certain areas zens of Sanibel.
of Sanibel has increased both the likelihood
of intense, destructive fires and the hazard
to human life and property. Two large, in- Part Human Support
tense fires in the interior wetlands occurred
during the past five years. Both fires
swept over extensive areas of the interior
and burned out of control for hours before Section 2.2.1: Water Supply
they were brought under control. Fortunately
these fires were controlled before they reached
areas of dense residential development. Fur- A. BACKGROUND DISCUSSION
ther development of this fire hazard area must Adequate supply of fresh water is a major con-
be limited and restricted. Measures must be straint upon future growth and development in
Fig. 1,"Geological taken both in existing developments and in the City of Sanibel. The hydrologic element
Sections," referred planning new residential developments to re- of the Island is basically composed of surface
to in the text onthis duce hazard to life and property. New devel- water bodies, a water table aquifer, a shallow
page, appears as Fig. artesian aquifer, the Lower Hawthorn Aquifer
8 in the Hydrology opment should be confined to the edges of the and the Suwannee Aquifer. (See figure 1
Appendix. interior wetland basins in the upland area.. which is a log of the geologic formations and
Hazard should be reduced by a management pro- aquifers underlying Sanibel.) The Suwannee
gram of controlled burning and maintenance of and shallow artesian aquifers and the upper'
high water levels. Buffer zones should be part of the Lower Hawthorn Aquifer contain
maintained around areas of residential or saline water with more dissolved solids than
commercial developmentand water pressure it is considered economically acceptable to
should be maintained at sufficient levels for treat. The surface water bodies and the
efficient fire fighting. Proper access for water table aquifer contain substantial quan-

110 The Sanibel Plan

tities of both saline and relatively non-saline B. FUTURE SUPPLY FACTORS
water, however the use of these bodies as a To date, the analysis of future water supply
potable water source is extremely limited be- by the Island Water Association has dealt
cause of their importance to the continued with the following factors:
viability of vegetation and wildlife on the
Island, the control of mosquitoes, and the 1. the cost of pumping and treatment, Fig 2 "Geological
bodies' geologic and hydrologic character (See e ref
figure 2). The Lower Hawthorn Aquifer is the 2. the cost of storage and distribution, and Sections," referred
current source of the domestic water supply to in the text on this
for Island residents. The Island Water Associa- 3. the cost of securing well sites, drilling page appears as Fig.
tion owns and operates the public water system of wells, and piping cost to transport intheHydrology
on Sanibel. := 7 ; water to the treatment plants. Appendix.

In the case of Sanibel the costs for well drill-
Prior to 1973, the I.W.A. purchased water from ing and water transportare relatively easier
the Pine Island Water Association which tapped a to predict and plan for than are other costs.
shallow fresh water aquifer on the mainland. How- Cost figures relating to quality of water sources
ever, escalated growth on Sanibel in the early and the amount of treatment necessary to produce
1970's increased demand, and supply problems de- potable water are considerably more uncertain.
veloped, largely associated with decreased yield Quality and quantity of water are major concerns,
and increasing salinity of the mainland well water. including:
In November of 1973, the Island Water Association
put a brackish water treatment plant into serviceer o.
on Sanibel, utilizing an electrodialysis demineral-- from the lower level of the Lower Hawthorn
ization or desalination process to treat water Aquifer eSee figure i)at a depthof 500-
from wells 500-600 plus feet in the Lower Hawthorn 650 feet. This is a slightlyrsaline aquifer
Aquifer. The Lower Hawthorn is a part of the
Floridan Aquifer,; a state and regional water re- ppm. The water body is approximately 200
ppm. The water body is approximately 200
Floridan Aquifer, a state and regional water re- feet thick and salinity generally increases
source which is recharged in the center of the with depthk The Lower Hawthorn Aquifer is
State. The Island Water Association plant has a artesian with a pressure of approximately
capacity of 2.1 million gallons and serves Captiva 30 feet above mean sea level. Increasing
as well as Sanibel. The fixed connection withdrawals from the aquifer generally result
between the Pine Island Water Association and the
Island Water Association is in place and maintained in the inflow of more saline water.
by both associations for emergency use. A 2 million
2. Future growth in Lee County, especially in the
gallon treated water storage reservoir is located- western portion of the county will involve
at the I.W.A. plant and a second 2 million gallon increased extraction of water from the Lower
reservoir is located east of Dixie Beach Blvd. The Hawthorn Aquifer which may have a substantial
I.W.A. is currently undertaking an expansion program; effect on the quality of the water in the
of treatment plant and distribution systems intended Lower Hawthorn under Sanibel.
to increase system capacity to approximately 7000
connections (adequate to serve about 6000 dwelling 3. As salinity increases the extent of treatment
units on Sanibel with the remaining connections required increases, with marked increase in
used for commercial uses or for connections on cost and decrease in plant capacity.
Captiva).
Unfortunately the extent, quality, and hydrologic
character of the Lower Hawthorn is not known. The
The Island Water Association distributes the treated City is cooperating with the U.S.G.S. and the Island
water from its treatment facilities directly Water Association to study the hydrology of the
to some areas of the Island and two remote Lower Hawthorn in order to increase the understanding
pumping stations - the Sanibel Booster Station about the aquifer and its properties. The data that
near the intersection of Periwinkle Way and do exist suggest that the amount of water that will
Dixie Beach Boulevard, and the Captiva Sub- be available for Sanibel that can be treated with
station located approximately one mile from the the existing equipment may be limited, and that
south end of Captiva Island on State Road 867. amount may be reduced as a result of water extractions
These two remote pumping facilities distribute on the Island and inland. Cape Coral, the Estuaries
water to the east end of Sanibel and to the and other proposed developments are anticipated to
north end of Captiva respectively. draw upon the Lower Hawthorn for water and this

The Plan 111

increased use may adversely affect the quality of plan including an educational program
water in the aquifer beneath Sanibel. designed to encourage sound water conserva-
tion practice.;
Wells on the Island into the Lower Hawthorn indicate
a high degree of variation in water quality from 5. The City should develop a program which
well to well, and the "fresh" water zone occurs would lead to the plugging of all existing
at different depths in nearly every well. This unused wells which are drawing water from
introduces further uncertainties in attempting the Lower Hawthorn Aquifer.
to develop additional water supply, particularly
in the absence of adequate knowledge of aquifer 6. The City should continue to monitor and
properties. With highly saline water above,-- investigate the general hydrology of the
below and on several sides of the production Island.
zone, problems of saline water migration must
be anticipated. Because of the prospective limita- 7. The City should assist in the implementa-
tions on adequate future water supply several tion of the improvements necessary to up-
alternatives for supply and conservation were grade the Fire Protection system of the
considered. These included desalination of sea Island.
water and such conservation measures as dual
plumbing systems involving "gray water systems"
for toilets and irrigation. At this time these Sectio n 2.2.2: Circulation
are either economically unacceptable, hazardous Section 2.C.: Circulation
to public health, or inapplicable or impractical
on Sanibel and are therefore not now acceptable
as policy for future planning. The water supply A. BACKGROUND DISCUSSION t
situation on Sanibel undoubtedly requires effect-
ive measures to be taken to minimize water use
B. PLAN FOR CIRCULATION
and conserve the supply. One important conserva-
tion element needing urgent attention is the The plan recommended for traffic circulation is one
plugging of existing unused wells tapping the that improves existing facilities up to a moderate
Lower Hawthorn formation. These wells are contri- Level of Service. Major improvements are proposed
buting to the salinity of the City's water supply in terms of a new bypass road to take some of the
resource which, along with other factors, might traffic off Periwinkle Way,and continuation of Gulf
ultimately render it useless.
Drive which serves the same purpose. As the improve-
No expansion of supply capacity should be con-- ments are implemented, operational characteristics can
sidered until additional data on water quality be further modified by speed limits, signaling, parking
and quantity in the Lower Hawthorn is available. restrictions, turning movement restrictions and,.at
special situations, even one-way traffic flow and
other measures necessitated by circulation problems._
C. WATER SUPPLY AND'FIRE PROTECTION t

Specific elements of the Plan for circulation are
D. THE PLAN FOR WATER SUPPLY as follows:
1. The City shall investigate the hydrology
of the Lower Hawthorn Aquifer as soon as
is reasonably possible. 1. All future circulation improvements shall be
evaluated to assure that the objectives set
2. No expansion of water treatment facilities
or increased withdrawals of water from the
Lower Hawthorn further than those described maintained.
in this section should be considered until
the study of the hydrology of the Lower 2. The City should initiate a program which would
Hawthorn is made. provide for the undertaking of the roadway
improvements identified previously in this
3. The City should investigate the feasibility section as first priority - short term improve-
of acquiring the Island Water Association
ments. The program should be structured to
for operautility. as a municipality ownedpublicinclude planning and engineering studies,
design standards, development plans and
4. The City should develop a water conservation funding alternatives.

112 The Sanibel Plan

& � ~~~~PINE ISLAND SOUND

JN 'DINGOAR ING
WILDLIFE REF E

LEGEND

*@ BYPASS

GULF DRIVE CONNECTION

ROAD IMPROVEMENTS

The Plan 113

SAN CARLOS BAY

: : :

TARPON BAY

N 0 1000 3000 6000

CIRCULATION PLAN

114 The Sanibel Plan

3. The City should, upon completion of the exist attributable at least in part to the sewage
improvements identified as first Priority, effluent discharge.
initiate studies to determine the appropriate-
ness of undertaking the improvements previously The rest of the Island relies on septic tanks for
identified as second priority. waste treatment. These septic tanks contribute to
water pollution and pose potential health problems.
4. The City-should investigate the feasibility of Sewage may not be adequately treated because of
alternate means of transit on the Island; in low-lying ground, high water table and soils that are
particular, bus service. Off-Island funding unsuitable for septic tanks and drainage fields.
-� for such a project should be explored and a Surface and ground water quality on Sanibel has
demonstration project should be included to been documented in Conservation Foundation studies3
test public response to such a service. as generally poor, impaired by salt water intrusion
and excessive nutrient loads. A majority of the
5. The use of bicycles should be encouraged by Island's 4000 residential units are on septic tanks,
the City as an alternative form of transporta- many of which may afford inadequate treatment in
tion. This program: should include the de- very permeable soils or high water table. The USGS
-rates the Canaveral soil, which is most prevalent
velopment of an extensive biking system through- on Sanibel, as being severely restrictive for septic
out the Island. tank use.

Section 22.3: Sewage Treatment Untreated or inadequately treated sewage effluent
Section 2;-2-3: SewagisTreatme~nt 0can cause serious health problems. Certain species
of bacteria, protozoa and viruses in sewage can
cause severe diseases in man. Enteric bacteria
A. BACKGROUND DISCUSSION may include serious pathogens which could possibly
exist in untreated or only partially-treated
sewage. These include the salmonella bacteria,
Treatment and recharge of waste water is extremely which can live in moist soils for as long ascteria,
important to the water cycle of Sanibel. Along w a
70 days, and the organisms which cause bacillary
with recharge and runoff, it is an important source dysentery, typhoidandparatyphoid Also disease
of water return to the ground and surface water
systems, which is then utilized by man, plants, as a result of rcontamination by sewage. In addi-
and animals. It is critical to the health and tion to these threats to a community, entero
safety of residents that sewage effluent be
treated to a high level and returned to the ground presenrd A
in a condition which does not risk polluting though their presence insewae onstant uarantee
an epidemic, they do present a constant threat
surface or ground water resources. of infection. Of significance here, for example,
Presently, there is one major treatment plant is hepatitis virus, which can exist in sewage
on Sanibel, Jamestown Beachview, with over 975 polluted water, in shellfish living within that
hookups* and a planned system design for 3500
hookups*. The peak capacity is 1.2 million
gallons per day. In addition to the Jamestown- * Hookups - connections
Beachview plant, which serves parts of the major
area of existing development on the east end of ** Biochemical Oxygen Demand
the Island, there are 20 package treatment plants.
These primarily serve large subdivisions, condominiums, *** Suspended Solids
and commercial uses. Table "a" of the Phase I
Report lists these plants, their service area, 1Florida Air and Water Pollution Control Act, Florida
their capacity, type of discharge, number of Statutes 403.061 et seq.
connections, and current operating data in terms
of BOD and SS. Several of the plants are operating 2"Interior Wetlands Water Quality Management" Albert
within State standardsl and Federal standards Veri Associates, Aug. 31, 1975, p.7
under the Federal Water Pollution Control Amend-
ments of 1972 of 90%/90% for BOD**/SS***(Suspended 3"Sanibel Natural Systems Study, Preliminary Summary
solids). Water quality tests2 adjacent to some of Findings and Recommendations", The Conservation
of them suggest that very high nutrient levels Foundation, September 16, 1975, pp. 2-17.

The Plan 115

environment and eventually infect susceptible Several alternatives for effluent disposal should
humans who drink the water or eat the shellfish.1 be studied further including "sheet application;"
In summary,there is evidence that in built up areas "ridge and furrow," "ponding with percolation" and
there- is need for more effective treatment and "spray irrigation following ground application."
disposal of sewage than by septic tanks. It may be necessary to have advanced treatment
of the effluent prior to disposal, and detailed studies
must show that soil conditions and hydrologic
B. SUMMARY OF EXISTING CONDITIONS conditions will permit safe disposal in all seasons.

The problems of disposal of sewage effluent pose
At present the 20 package plants on Sanibel service severe constraints on future development on
approximately 300 dwelling units and should if Sanibel given that public health and environmen-
properly operated provide a higher level of treat- tal protection are primary goals ofthe City.
ment than septic tanks in terms of BOD and suspen- On-site disposal with septic tanks is appropriate
ded solids. Several of them nevertheless cause only in limited areas of the Island and must
or contribute to a problem in terms of excessive fully conform with the standards of the State of
nutrients in the receiving waters. The Jamestown- Florida, Chapter 10D-6. Disposal of treated
Beachview plant which serves 975 connections in the effluent in San Carlos Bay or the Gulf of
East and East Central Sector of the Island has an Mexico are environmentally and economically
expansion potential to 3500 connections. prohibitive as also is deep well injection of
treated effluent to lower aquifers. The City
must control future growth in line with the capa-
city of the disposal system along with strictly
The effluent from this plant conforms to State enforced controls for septic tanks and undertak
enforced controls for septic tanks and undertake
standards in terms-of BOD and SS. However, under- detailed studies that include specific proposals
ground flow from its inadequate treatment lagoons for improving the quality of effluent from all
to the adjacent Sanibel River has caused the Florida package plants and provide suitable techniques
Department of Environment Regulation to direct
Jamestown-Beachview to seal the bottom of its lagoons.
Dissolved nutrients, principally nitrogen and
Dissolved nutrients, principally nitrogen iand The degree of waste water treatment before dis-
phosphorus, found in high concentration in the
effluent from this secondary sewage treatment plant posal i ntimately assoiated with health and
c apae hygiene in the community. Also the effect of
are capable of stimulating algal blooms. Such
algal blooms may produce a variety of undesirable chemical characteristics of the waste water
effects, including depressing dissolved oxygen dictates to a large degree the appropriate
levels below Federal water quality standards.
Jamestown-Beachview has plans to include the package waste water.1
plants along Gulf Drive within its service area to the
system.
Exploration of means to integrate the planning and
At present, Jamestown-Beachview disposes of its management of the fresh water system would help
effluent on the 18-hole golf course at achieve maximum conservation of water. Such a managed
Beachview Country Club Estates which is currently system would be enhanced by the infiltration of
undeveloped. In the summer months this amounts to treated effluent to the surface aquifer.
500,000-600,000 gallons a day. The probable pres-
ence of pathogenic organisms prevents spraying of For very low density residential development which
this effluent on lawns or the golf course of an meets the performance standards, septic tanks could
adjacent residential development -- "The DuneS." remove pathogenic organisms satisfactorily if suitably
However, appropriately treated effluent could be located where soils and water table may be suitable.
a valuable asset in view of the need for surface For most development, however, only off-site treat-
water replenishment in the fresh water management ment will be satisfactory. One method for providing
area. such treatment would be for the City to acquire

l"Health and Hygiene Aspects of Spray Irrigation"
1 Health Hazards of the Human Environment, WHO 1972, by Charles A. Sorber and Kurt J. Guter. American
rev. 1973, Chapter, "Soil and Land", p. 94. Journal of Public Health, January, 1975.

116 The Sanibel Plan

Jamestown-Beachview plant from Jamestown-Beachview , B. Update the Jamestown-Beachview Facilities to
upgrade the lagoon and tie in all uses in the City's Serve Existing Capacity:
East Sector and East Central Sector. Other methods
are being examined by City consulting engineers and 1. Inspect, inventory and repair
by an EPA grant-supported project. Only by such existing equipment and lines: 125,000
studies can a rational decision on these matters be
made. 2. Landscape site line, ponds,
etc.: 100,000
Preliminary estimates of costs for two options of
providing extended and improved collection and 3. Personnel and equipment: 50,000
sewage treatment for existing and future connections:
(is as follows ) 4. Contingencies: 125,000

Option 1, Acquire Jamestown Beachview System with Subtotal $400,000
Minor Improvements
Total for Option 1: $1,922,000
$1,900,000 -- if treatment plant is held at existing
-capacity of 1,200,000 mgd capacity C. Collection System East of
Tarpon Bay Road: 3,368,000

Option 2, Acquisition and Major Improvement to D. Expansion of the Jamestown- -
Collection fand Treatment Beachview Facility to 1,625,000 gallons
per day, installation of equipment
$6,528,000 -- if treatment plant is increased to obtain advanced treatment
to 1,625,000 mgd capacity and higher level of (Tertiary)*and installation of
treatment is achieved and expansion of collec- master pumping facilities to the
tion system.. golf course 575,000

Johnson Engineering prepared the cost estimates E. Collection along Gulf- Drive from
for these options as follows: Tarpon Bay to Rabbit Road 663,000

Total for Option 2 $6,528,000

A. Acquisition of the Jamestown-Beachview
Facilities: It is, of course, feasible that improvements to the
collection and treatment systems could be financed
1. Replacement cost of plant $484,000 and implemented without acquisition of Jamestown-
and equipment: Beachview by the City of Sanibel. In that case, the
cost to Jamestown-Beachview will be approximately
Replacement cost of real $400,000 for improvements in Plan A and $6,528,000
estate and improvements: 100,000 for Plan B improvements.

Replacement cost of lift
stations: 525,000
C. THEPLAN FOR SEWAGE TREATMENT
Replacement of sewer lines: 804,000 1. Provide an adequate waste water treat-
ment system for each and every residential
Replacement cost of force and commercial unit within the City.
mains: 216,000
2. Immediately investigate the desirability
Replacement cost of profess- of public acquisition of the Jamestown-
ional services: 213,000 Beachview sewage collection and treatment
system. The Jamestown-Beachview facility
Subtotal Replacement is located in the center of an extensive
Cost: $2,342,000 collection system and is located close
to two possible effluent disposal areas.
Acquisition price at Although the plant appears well constructed
approximately 65% and in good condition a thorough appraisal
of replacement cost: 1,522,000 is necessary.

The Plan 117

3. Develop and implement a program to provide Secti 2.r Solid VVaste -
increased waste water treatment capacity 2.2 S o
for the growth and development permitted
under the Plan. In so doing, maintain
close liaison with Federally sponsored.
studies for this region, in order to insure Section 2.2.5: Po er t
that the regional plan is acceptable to the
City and that the City maintains its
eligibility for Federal grant assistance. �Section 2.2.6: Storm Drainage

4. Undertake detailed technical studies to A. BACKGROUNDDISCUSSION
determine acceptable systems and locations
for disposal of treated effluent.
Storm water runoff characteristics are a direct
function of the amount of precipitation, con-
5. Connect all existing package plants to dition and density of vegetation or other ground
the central system as soon as is practic-- cover, the structure and texture of the soil or
ally possible. other surface material and its saturation level.
Topography also affects storm water flow, per-
colation, and overflow rates. Water infiltrates
6. Require that all package plants be improved each soil type at a specific rate, characteris-
so that effluent meets Federal and State tically rapid at first, then levelling off
standards and wherever necessary shall until it is no longer absorbed. If precipitation
exceed those standards to avoid negative continues, depressions fill, water accumulates,
environmental impacts. and overland flow occurs.
Runoff is increased by urban development when
7. Prohibit the use of septic tanks in all areas there is a high coverage of impermeable surfaces
where sewers are available and in any event such as roads, patios, roofs, parking lots and
only where physical conditions of soils and other hard areas. This causes rapid overland
hydrology permit such disposal according to flow, and erosion of soils. Water can be an
State of Florida Department of Pollution extremely powerful and destructive force on the
Control, Chapter 1OD-6 standards for individ- landscape. Although surges of water from high
ual sewage: disposal facilities and environ- frequency storms are not immediately devastating
mental performance standards described in on the landscape, they do have long-term, nega-
Article 3 of the Plan. tive effects such as the removal of the surface
soil layer, loss of soil nutrients and ultimately
8. Implement a monitoring procedure to ensure loss of vegetation. This process often causes
that all sewage treatment facilities are irretrievable damage to the land surface, as
constructed and managed in conformance with well as degrading water quality with increased
State and local standards. sedimentation and pollution. Such conditions
may require reclamation, particularly when ero-
sion is so severe that it removes the lower soil
D. CONCLUSION horizons, which are more vulnerable to water
The plan recommendations are closely related to the transport. In addition to these impacts, over-
overall objectives of a Comprehensive Land Use Plan land flow also deprives the water table of re-
for Sanibel. The capacity of the sewage collection plenishment, which would otherwise penetrate the
and treatment and effluent disposal systems is surface.
closely related -to projected planned growth.
Future growth will depend upon several unknown Fortunately, the infiltration rate on Sanibel's
factors to provide adequate and safe effluent shell and sand substrate is exceedingly high,
disposal. To bring present conditions of sewage and as a result, overland flow is- almost negli-
treatment up to the standards required to maintain gible. Under natural conditions, rainwater
and improve environmental quality will incur costs quickly replenishes the ground water table and
not yet fully determined but expected by the City's overland flow of water from one area to another
planning consultants to be of the order of magni- would be virtually negligible. This condition,
tude indicated by Sewage Treatment Option 2. however, is not maintained in urban development

118 The Sanibel Plan

areas unless storm water is managed by having Large open areas of highly permeable soils must
adequate areas of permeable soil and vegetation. be set aside as detention areas, catchment areas;
vegetated swales and filter beds should be used
Damage resulting from increased impermeable sur- to ameliorate the force of excess runoff and
faces and improper drainage solutions have al- recharge it. Vegetated swales which follow
ready' been recorded on Sanibel primarily along the natural contour are effective and economical
the Gulf Beach. The majority of condominium means of directing water flow.
developments along the Gulf Beach directs storm
drainage from their roofs and parking lots The Natural Storm Drainage System can achieve
through channels and pipes on to the beach. This the following:
practice has three very harmful impacts. First, -
the fresh water is not being recharged to the 1. Maximize recharge
ground water in the Gulf Ridge Zone where it 2. Minimize runoff
interfaces with the salt water system and dimin- 3. Minimize erosion and siltation
ishes the threat of further salt water intrusion / 4. Minimize vegetation removal
from the Gulf. (See functional diagrams of sub- 5. Minimize maintenance and drainage system
surface water flow in discussion of Ecological costs
Zones, Section 2.3.1.) Secondly, the peak dis- 6. Improve water quality
charges from these storm drainage systems are 7. Enhance flow in Sanibel River
greater than those generated from overland flowe
under natural conditions. Therefore, harmful An invaluable resource to the Island-wide natural
erosion of the beach and beach vegetation is drainage system is the interior wetland. This
caused. Thirdly, the pollutants and debris from 3588 acre depression in the central area of Island
parking lots are deposited on the beach, thus roughly bordered by Periwinkle Way, Sanibel and
degrading one of the Island's most valuable Captiva Road on the north and Gulf Drive on the
resources. south provides an important role in terms of storm
water storage, during both high frequency as well
The environmental damage caused by such made- as more intense storms. The main drainage way of
The environmental damage caused by such inade- the interior wetland is the Sanibel River.
quate storm damage systems on Sanibel represents a
real threat to several valuable ecological func- Historically, the Sanibel River was a semi-contin-
tions on Sanibel, such as maintenance and re- uous slough system that originated in the vicinity
charge of the fresh water lens, maintenance of of the present Tradewinds Subdivision and during
water quality, and maintenance of natural vegeta- high water conditions emptied into the Gulf of
tion and wildlife habitats. Mexico near the present "Colony" motel and apart-
ments. In 1960 the River was channelized for mos-
The method of dealing with storm water drainage quito control purposes. -The primary objective was
so as to minimize harmful impact of urbanization to concentrate the surface water in one channel and
on the environment is to preserve and utilize to maintain as constant a water level as possible.
the inherent capabilities of the site to absorb Water level control structures were installed at
water effectively with minor modifications to Tarpon Bay and at Beach Road, and are the only
land configuration. By careful site planning - river outlets to salt water under normal conditions.
and maximizing the areas of site that retain and
and maximizing the areas of site that retain and County roads through the interior wetlands crossed
absorb storm water, costly piping, channels and
culverts can be reduced. A "Natural Drainage, the river over bridges early in the Island's de-
velopment. However, these bridges were eventually
System" that is sympathetic to natural processes velopmentd However thes fi Inmany cases the
replaced by culverts and fill. In many cases the
causes the least environmental disruption, and
can be less costly to build and maintain. Most inverts of the culverts were placed at elevations
important, the problems and solutions are local- higher than the normal level of the water in the
ized to the project site and not imposed on ad- river. These changes in invert elevations have
jacent land. caused unanticipated problems in the interior
drainage system. The water level control structures
In order to retain Sanibel's native vegetation existing today permit the intrusion of salt water
and wildlife habitats, the existing ground water which degrades water quality.
system must not be disrupted. It is therefore
a policy of the City in this Comprehensive Plan that More importantly in terms of storm drainage and
the storm water produced by five-year storm conditions the health, safety and welfare of the Island's
will be collected and retained and recharged on the residents, constrictions in the interior drainage
site of any urbanization. system cause flooding. During periods of heavy

The Plan 119

rainfall in the rainy season, moderate to severe The condition of the interior wetlands storm
flooding occurs in some areas. At times substan- drainage system can be improved and numerous
tial portions of major highways are covered (see other benefits gained by the City if the
map'of existing highway conditions, Section 2.2.2) following proposals are carried out:
often to a depth of six to eight inches. This
is partly due to incorrectly sized and im- 1. Culverts under the following roads
properly placed culverts. The combination of should be replaced with culverts or
improving intra-basin flow in the interior wet- culvert pipes to permit flow at: all
lands as well as raising the roads (see Section levels of the River:
2.2.2) will give greater flood protection to
emergency evacuation routes in the event of a .Beach Road
hurricane. Constricting culverts reduce the .Sanibel-Captiva Road
anibeCTarpon Bay Road
velocity of the flow in the river, and effec- Tapn Bay Road
tively prevent adequate flushing of salt water Casa Ybel Road
from the interior of the Island because of the
density- relationship between fresh and salt 2. Rebuild the water control structuresat
water. Typically this results in the discharge Tarpon Bay and at Beach Road so as to pre-
from the Island of the overlying fresh water vent salt water intrusion.
Land the retainage of the lower strata of salt
water, thus greatly reducing water quality in The preliminary cost estimates related to this
the interior wetlands. Plan for storm water drainage and flood control
in the interior wetlands are as follows:
In their 1975 study dealing with ways in which
to rejuvenate drainage in the interior wetlands, 1. Water Control and Drainage Structures:
Johnson Engineering pursued the following ob-
j ectives:l ' 5- .Tarpon Bay Weir Structure $100,000
.Beac;h Road Weir Structure 60,000
Primary: .Beach Road Box Culvert 67,000
.Sanibel-Captiva Road Box Culvert 112,000
Preserve the Sanibel River as a natural, .Tarpon Bay Road CulvettPipe 12,000
free-flowing fresh water system. -Casa Ybel Road Culvert Pipe 10,000
Supporting: 0 0 0 0 0 .Rabbit Road Culvert Pipe 10,0,00

1. Remove bottlenecks in the existing channcl 2. Miscellaneous Structures
to improve the flood control system . t Pipes
.Culvert Pipes 3 0 ,30,000
2. Improve the existing riverine system to
provide for a continuous free-flowing 3. Channel Improvements
stream.
.Removal of major blockages
3. Reverse the existing trend toward salt only 20,000
water intrusion. Return the River to a
fresh water environment, ultimately pur- TOTAL COST: $421,0001
ging all salt water from the lystem.

4. Establish a plan for the protection and It is presumed that this special drainage and
management of the Sanibel River to insure flood control project will qualify for grants
the preservation of this natural resource in aid from off-Island resources. The Federal
for the enjoyment of future generations.2 government's Department of Housing and Urban
Development, the State of Florida Department
of Natural Resources and Lee County Mosquito
Control District are all potential sources of
l"Preliminary Plan, Sanibel Island Fresh Water
Management Area" for the Sanibel-Captiva Con-
servation Foundation, Inc., Johnson Engineering,
Inc., 1975.
2bid. 1Johnson Engineering, op.cit.

120 The Sanibel Plan

funding. Even if these off-Island sources are e
not forthcoming, the project could be funded Section 2.2.1 i: Insect Cntrol
locally with a debt service of approximately
.15 mills.
A. BACKGROUND DISCUSSION
B. Plan For Storm Drainage
1. Mosquitoes
1. The drainage improvements described Florida legislation establishes procedures for mos-
in the Preliminary Plan for- the; quito and other arthropod control.1 Chapter 388
Sanibel Island Fresh Water Manage- allows creation of districts for the purpose of
ment. Area should be implemented. raising money through taxation. These districts
can adhere to city, town or county boundaries or
2. To complement the drainage im- any portions thereof. A district must submit
provements, the: following policies its control plan to the Division of Health, which
should be observed: then must be approved before operations begin.
The Board of Commissioners of such a district
a) The Storm Drainage System will may condemn land needed, within the district. A
provide for the gradual and special Act, Chapter, 67-1630, creates the Lee
dispersed drainage of excess County Mosquito Control District. Ultimate
surface runoff such that run- ag : responsibility for suppressing mosquitoes is in
off from within the boundaries, the hands of the Board of Commissioners of the
of the proposed development will Lee County Mosquito Control District.r District
approximate natural rates, volumes, activities are coordinated with the requirements
Eand direction of flow from that of the County Health Department.
parcel.
The following text provided by Lee County Mos-
b) The Storm Drainage System will quito Control District describes the problems
not result in any surface run- - and opportunities for mosquito control on Sanibel:
Off across or onto the-beach.
"The tropical climate that is the essence of the
c); The Storm Drainage System will island's appeal also results in a lesser known
not reduce the volume or increase distinction. Sanibel is'the largest producer of
the rate of water flow from any salt marsh mosquitoes in the world. Although more
parcel draining to the interior than twenty different species of mosquitoes are
wetland or Fresh Water Management collected during a normal year, Aedes taenior-
Area. hynchus is the principal problem. This mosquito
and the island itself, has been the object of
3. A City appointed committee should partici- extensive study by highly qualified scientists
pate and advise in the consideration of for many years.
fresh water management programs.
"During the years 1948-52 the Florida State Board
of Health carried out a major mosquito research
Sectirona 2.2.7^ Fire : F . : project on Sanibel, and in 1953, Dr. Maurice
Section 2.2.: Fire t Provost, Director of the Florida Medical Entomol-
ogy Laboratory, published a report of this
Se C tio n; 2.2.8:: Po |i ce:t work entitled "The Water Table on Sanibel Island."
That comprehensive study, and the report by
Dr. Provost, detailed the basis for control of
Section 2.2.9: Medical Facilities and Aedes taeniorhynchus on the island.
Gil Id f Public Health' V : "AIn 1958, the Lee County Mosquito Control District
was created to provide control of mosquitoes in
almost all of Lee County, including Sanibel.
$Secti�on 2.2.10: 0.Education't :This special district is governed by a Board
-cOn0 Ecti, of six commissioners, who are elected on a non-
partisan basis for four year terms. Chapter 67-
1630, Laws of Florida, provides that one member
of the Board must be a resident of either
Sanibel or Captiva Island. One of the first
actions of the Board of Commissioners was to
'In accordance with State Law 67-1629

The Plan 121

implement Dr. Provost's basic plan for Sanibel; "Since extensive mosquito breeding areas will con-
and for the past eighteen years a significant tinue to exist, an organized control program is
portion of the District's effort, far in excess necessary. The Lee County Mosquito Control District
of the island's financial contribution to the uses helicopters to determine the extent of mosquito
program, has been expended on Sanibel. breeding on over seventy-five thousand acres of Lee
County coastal marshes. When mosquito larvae are
"The salt marsh mosquito problem is two-fold. present in great numbers, it is necessary to larvi-
The interior fresh water swales originally were cide - i.e. to apply a material to the water to kill
the most prolific producers of mosquitoes, with the immature mosquitoes before they emerge as adults
the semi-tidal mangrove areas on the bay side of The comprehensive program of salt marsh inspections,
the island constituting, in comparison, somewhat and subsequent larviciding when necessary is pres-
less a problem.- Dr. Provost's plan for the ently the most efficient and effective work carried
interior swales was simple, and rather easy to out by the District. However, even with extensive
accomplish. Taeniorhynchus is a flood water larvidicing, many adult mosquitoes emerge to plague
mosquito - i.e.,the female deposists eggs on the residents of the island. When this happens,
damp soil rather than in water. These eggs can the District carries out a limited program for
lay dormant for long periods, and hatch only when chemical control of adult mosquitoes.; There are a
they are flooded - normally by; rainwater or in number of disadvantages to this type of work.
the mangrove areas by high tides. Thus, control Frequently, results are unpredictable and erratic.
of this mosquito in the interior of the island Applications of chemicals often must be repeated as
is primarily a matter of maintaining a high reinfestation of populated areas occurs from migrat-
water table. Dr. Provost recommended thirty ing flights of mosquitoes, and resistance to certain
inches above the mean low water, or about two insecticides is a very real problem. These factors,
feet above sea level, as a minumum. The District together with the extremely high cost involved,
has attempted to maintain this level over the combine to keep chemical control of adult mosquitoes
years, and has encountered three problems. to a minimum which will provide acceptable control.
First, evaporation and transpiration on the is- It is the policy of the Board to restrict this work
land are tremendous. Dr. Provost estimated that to the areas and times of greatest need.
this water loss can exceed one inch a day. Sec-
ond, the island is porous, and the water literally
leaks out. Third, residential and other building
in low areas has resulted in strong resistance "To assure that adulticiding is carried out to the
by some property owners to a high water table. best advantage, truck traps are used to sample
In spite of these problems, the water management adult mosquito populations seven nights each week
program carried out by the District has accom- during the summer months. Mosquitoes collected are
plished the purpose intended, and extensive transferred to the District's laboratory, where
salt marsh mosquito breeding in the interior they are identified as to species and sex. This
wetlands is a thing of the past. Several information is used as a yardstick to determine
groups on the island are now pushing for a where adult control work should take place and
constant water table higher than that realized when. Male flood water mosquitoes emerge about
up to now. If this can be accomplished; the one to two days sooner than the females do. There-
interior wetlands will be relatively unimportant fore, if a trap collection contains a significant
as a producer of Aedes taeniorhynchus in the future. number of male mosquitoes, it is too soon to
adulticide, because it is certain that many female
"The semi-tidal mangrove areas are an entirely mosquitoes are still in the larval stages, and a
different problem. A portion of this area was premature application of insecticide would be a
eliminated when the Lee County Mosquito Control . waste of the taxpayers' money. In addition, the
District constructed what is now a five mile wild- staff carries out several tests each year to detect
life drive through the Ding Darling Refuge. In possible resistance to insecticides. Live adult
addition, a system of ditches in the major breed- mosquitoes are collected and transferred to an
ing areas has been accomplished over a period insectary, located in the laboratory. Here they
of years. These ditches serve as permanent reser- are given a blood meal, to assure that a large
voirs where fish may live when the main body of quantity of eggs will be laid by the female
the marsh is dry. Not only does this provide mosquitoes. These eggs will be hatched, and the
minnow access to mosquito larvae, these ditches larvae treated with various concentrations of
have enlarged and enhanced the marshes as nursery insecticide. This determines the susceptibility
or spawning areas for many species of fish, shrimp, of Sanibel mosquitoes to each insecticide that
and crab. Unfortunately, permit requirements enact- the District uses. In this way, the minimum
ed to control rampant development in coastal areas dosage necessary for adequate control is determined.
have effectively stopped mosquito control work of These tests also reveal when resistance to particular
this type. material is developing. If this occurs, use of

122 The Sanibel Plan

that insecticide would be terminated. C. THE PLAN FOR MOSQUITO CONTROL ON SANIBEL

"To keep abreast of the latest developments in mos- A totally ecological approach requires strict
quito control work, the District frequently cooper- adherence to the following:
ates with established research agencies. Presently,
this work is being expanded to evaluate the poten- 1. A consistent high water table in the interior
tial of biotic agents such as pathogens, parasites wetlands should be maintained - (in general
and predators, as well as genetic manipulation of the higher the better, consistent with other
mosquitoes. All of these biological controls, have land uses). This will virtually eliminate
undergone thorough study by research groups. Many salt marsh mosquifo breeding in these areas.
show excellent potential in the laboratory, and are
ready for testing under actual field conditions. 2. Drainage patterns should be kept as natural
The District has entered into an agreement with the as possible. The proposed improvements to
the drainage system should be carried out
USDA, Gulf Coast Mosquito Research Laboratory, (see Section 2-206 on Storm Drainage) in
Lake Charles, Louisiana, for field research on order to increase intra-basin flow. The
Reesimermis nielseni, a mermithi nematode, and drainage improvements will enable retention
with the World Health Organization Collaborating of a more consistent water level in the
Center for Biological Control on Bacillus Interior Wetlands, thus exposing less area
sphaericus. In the past, research ofthis type to the successful hatching of mosquito larvae.
has been restricted to controls of human diseases,
This new program will consider the potential for 3. A population of larvivorous fish should be
reducing overall pest mosquito populations as maintained wherever possible on the Island.
well, and will be the first large scale attempt
to use biological controls in an organized 4. Mosquitoes should be controlled in the larval
mosquito abatement program. Cooperative work stages whenever possible, generally keeping the
of this type assures the residents that the Island free of biting adults. Larvicides should
program carried out by the Lee County Mosquito be chosen on the basis of safety both to humans
Control District is constantly updated, and that and wildlife and applied in a lawful manner.
the benefits of new research are incorporated
here, even as they- a-re being developed." 5. Chemical control of adults should be kept to a
minimum, consistent with acceptable control
and lawful application.
2. Sandflies
6. Research should be encouraged which should lead
to alternate methods of control, thereby avoiding
Mosquitoes are not the only pests on Sanibel. dependence on a chemically oriented mosquito
Sandflies are becoming an increasingly serious control program.
problem "for which there is rarely any easy,
cheap or fully effective remedy. lb The use of 7. City Manager should be directed to obtain the
personal insect repellants, treated screens and best Federal and State and Local advice concerning
air conditioning has had good results in main- mosquito control on Sanibel.
taining a comfortable balance with these
insects.

18Lee County Mosquito Control District - March 1976.

lbJohn R. Linley and John B. Davies, Sandflies and
Tourism in Florida and the Bahamas and Caribbean
Area.

The Plan 123

activities. Six ecological zones have been
Part 2 3: Protection of N ,aturDa- ,+,, orl identified on Sanibel, three of which are fur-
8=rt'2�3: CX8otection Lf 6t ra BAA 8VLiJ IV 8 |ther divided into sub-areas -- Gulf Beach, Gulf
\Enviro i men a =Beach Ridge, Interior Wetland Basin, Mid-Island
Environmental! Ridges, Mangroves and Bay Beach. The Gulf
-Economic a d Beach Zone is subdivided into Gulf Front Beach
Economic a nd and Gulf Back Beach and the Interior Wetland
Basin is composed of Upland and Lowland sub-areas.
Scenic Resources A Special Blind Pass Zone is designated in the
Blind Pass area.

The following is a brief description of each
ecological zone,
Section 2.3.1: Preservation of :
Gulf Beach Zone.
Ecological Functions
The Gulf Beach Zone includes all land seaward of
Relating to Health, the Coastal Construction Setback Line. There are
two sub-areas within-this zone:
Safety and Welfare.
'fSafety andWelfareGulf Front Beach: This is the most active
beach zone and includes the area between mean
A. BACKGROUND DISCUSSION high water and the City's boundary 300 feet
offshore. Sand in this zone is in constant
Sanibel's natural environment performs many in- motion. Sand migrates between the berm and
valuable functions for man at no cost; it buf- offshore bars and is transported up and down
fers storm winds and flood tides, stabilizes the coast by longshore currents. Examination
the shoreline, purifies water, and maintains a of historical surveys and aerial photographs
fresh water system which supports a rich wild- over the past thirty years shows that erosion,
life and lush vegetation. These functions sup- and accretion of sand along the beaches are
port the health, safety and welfare of every cyclical in many areas with a 20 or 40 year
Sanibel resident and must be preserved, period before the process is changed. This
zone maintains several functions critical to
Different parts of the Island contribute in public health, safety and welfare. It is the
varying degrees to each particular function. Island's first defense in storm and flood
For planning purposes the Island has therefore when the impact of waves erodes the sand res-
been divided into ecological zones, each with ervoir in the berm. The natural form of the
particular-characteristics, specific contribu- Gulf Beach Zone is a response to natural pro-
tions to health, safety and welfare functions, cesses of wind, currents and waves. Undisturb-
and varying tolerance to the range of man's ed, it is in a state of balance with natural

WEST EAST
WEST CENTRAL CENTRAL EAST
ECOLOGICAL ZONE SECTOR SECTOR SECTOR SECTOR TOTALS
A GULF BEACH 45 117 55 42 259
B BAY BEACH - - 40 18 58
C MANGROVE 416 - 339 13 768
D1 INT. WETLAND: LOWLAND 59 504 364 - 927
D2 INT. WETLAND: UPLAND 82 410 438 930
E1 SPECIAL BLIND PASS AREA 303 - - - 303
E2 GULF BEACH RIDGE 53 200 160 67 480
F MID ISLAND RIDGE 383 - 340 75 798
G FILLED LAND 142 446 878 383 1849
TOTAL 1483 1677 2614 598 6372

Note: Acreage approximate. Source: WMRT

124 The Sanibel Plan

forces, thus "maintaining" the shoreline.
This area also supports the marine life
for which Sanibel is famous, and is an im-
portant feeding area for Island wildlife.
Gulf Back Beach: This zone, though less
dynamic than the front beach, also absorbs
considerable impact from storm generated
wind and waves. It is a reservoir of
sand which may be eroded after the berm in
a severe storm, thus protecting property
further inland on the Beach Ridge. The
dunes are an important nesting area for
wildlife, the loggerhead turtle being a
prime example. The vegetation of the Back
Beach is particularly important, as it
stabilizes and holds the sand.

Both parts of the Gulf Beach Zone have a very
low tolerance to man's activities. -Removal of
sand, disposal of storm water runoff, excessive
foot traffic or any vehicular traffic can quick-
ly induce major erosion and other impacts on the
0beach. Strict regulations are therefore requir-
ed to maintain this zone. Removal of sediments
from the beach and construction of any sort
which would change the configuration of the
beach or inhibit sand movement should be prohib-
ited. Wildlife access to the beach should be
maintained and public access to the beach should
be confined to elevated walkways. Because of
their shallow root system, Australian pines are
not a suitable plant in this zone and should be
selectively thinned and removed from the beach
zone so that hardy native dune vegetation can
be introduced and managed.

Bay Beach Zone
The Bay Beach Zone extends along the Island's bay LEGEND
Tshoreline and is also an "active beach" zone. Al-
though the Bay Beach is a lower energy beach than ACRES DEVELOPED
the Gulf Beach, it nevertheless serves the same IN SUBDIVIDED LAND
valuable storm and flood protection, shoreline sta- ACRES REMAINING
bilization, marine life and wildlife habitat and IN SUBDIVIDED LANDING
feeding functions. The natural processes are sim-
ilar and so, too, are the constraints to develop- ACRES DEVELOPED
ment. Regulations, the same as those outlined for ELSEWHERE
the Gulf Beach Zone in the performance standards,
are required to maintain the functions of this zone. U ELSEWHERE

A GULF BEACH
Mangrove Zone B BAYBEACH
The Mangrove Zone includes as well as black and reds C MANGROVE
all buttonwood and white mangrove areas, and the D1 INTERIOR WETLAND BASIN: LOWLAND
tidal flats within and around them. This zone in- D2 INTERIOR WETLAND BASIN: UPLAND ECOLOGICAL
cludes most of the bay portions of Sanibel. In El GULF BEACH RIDGE: BLIND PASS AREA ZONES
ecological and energy terms, it is difficult to con- E2 GULF BEACH RIDGE
ceive of a more valuable and efficient zone. The F MID-ISLAND RIDGE
number of jobs done for man at no cost (save the G FILLED LAND
price of preserving mangroves) is not exceeded by G' FILLEDLAND NEAR CAUSEWAY

-The Plan 125

10,781 TOTAL ACRES

PROTECTED LAND REMAINING LAND- :
4,409 ACRES 6,372 ACRES
West West EEas t WEas t West East East
Central Central Central Central
200 Acres 3878.66Acres 30513 Acres 25 Acres 1483 Acres 1677Acres 2614 Acres 598 Acres
in .3200Ac.Ding"Darl. incl300Ac. DngDarl.

"DING" DARLING
WILDLIFE REFUGE ,
..I- , :f� .... ....

5:: :: :::: :

I f , . . . .

....0 . . . -* -.| Source: WMRT

ACRES DEVELOPED BY SECTOR and ECOLOGICAL ZONE

126 The Sanibel Plan

any other zone. Mangroves protect public health, Excavation of the aquiclude1, filling, the im-
safety and welfare by buffering storm winds and flood pediment or impoundment of natural water flow,
tides from the bay, by stabilizing and extending the the disruption or alteration of natural drainage
shoreline, by maintaining and improving water quality, channels, and the use of septic tanks is greatly
by maintaining the highly productive marine ecosystem, restricted. Impervious paving and the clearance
and providing food, shelter and nesting areas for of native vegetation is controlled. Storm run-
wildlife. A more complete description of the differ- off from paved or developed areas is to be re-
ent types of mangroves is included in Coastal Zone, tarded and dispersed slowly to the natural hy-
Section 2.3.2 of the Plan. This zone also has a low drologic system. Programs of fire management
tolerance for alteration by man. Its existence is -and water level control should be instituted.
dependent on the regulation of activities in adjacent Wildlife corridors should be established con-
areas. Clearing of mangroves and excavation or fill- necting nature preserves to the Sanibel River,
ing in mangove areas are governed by the performance and providing for wildlife movement along the
standards in Article 3 of the-Plan. River.
I~nterior Wetland Basin iZone : j : 0 -Upland Interior Wetland: The upland area is
The Interior Wetland Basin Zone is the interi- characterized by less frequent flooding than the
or storm water drainage bowl of the Island lowland area and more upland vegetation types.
which has formed as a fresh water reservoir. It is more tolerant to human activities and
It is composed of parallel systems of ridges therefore is easier for development to meet the
and swales with corresponding bands of vegeta- same performance standards as those for the low-
tion that either tolerate the persistent wet- land. Filling, excavation of the aquiclude and
ness of the swales or fluctuating conditions of the use of septic tanks are strictly restricted.
the ridges. There are two sub-areas within The impoundment of natural water flow or dis-
this zone -- lowland wetlands and upland wet- ruption of natural drainage channels is also
lands. The lowland area is composed of low controlled. Wildlife corridors should be estab-
ridges and wide swales; the upland consists of lished connecting nature preserves to the Sani-
higher, broader ridges and narrower swales. bel River.
The entire zone is the major recharge area for
the fresh water aquifer. The City should conduct a study to determine the opti-
mum water level elevation in the Interior Wetlands
Lowland Interior- Wetland: The lowland Zone. The demands of the fresh water system, mosquito
area typically experiences extended peri- control, fire control, and flooding should all be
ods of flooding each year. Since it is considered in determining this elevation. De-
lower than the surrounding area it serves tailed engineering studies are necessary to
as a storage area for flood waters until determine the best condition to achieve balance
they are absorbed into the aquifer. So between the major objectives. The City should
long as the elevations in the lowlands establish a board to oversee the preparation of
are not substantially increased by filling, a study for the Fresh Water Management areas as
this area will protect the ridge areas well as recommend a policy and control budget
from flooding and maintain recharge to the required for the implementation of a management
fresh water lens. This zone has a -"fire program.
ecology." Periodic fires burn off accumu-
lated dead plants, release nutrients to
the soil and kill invading woody shrubs Gulf Beach Ridge Zone
and trees. These large, recurring fires
are t hazard to human settlement in this The Gulf Beach Ridge Zone is the major ridge
are a hazard to human settlement in this
area but are essential to the maintenance dividing the Gulf and the Interior Wetland
Basin. It extends to the western end of the
of this zone. This area also has the
capacity to maintain and improve water Island and includes upland areas of Blind Pass
quality, and provides food, shelter, water Keys. The Blind Pass area is included in this
and nesting areas to many of Sanibel's zone because of its very recent formation.
most renowned wildlife, including the Amer- Thirty years ago Silver Key was in the Gulf
ican alligator. Beach Zone and as this area is highly unstable
and susceptible to dramatic change, it may be
beach again in the future. The Gulf Beach Ridge
Zone serves many valuable functions in the main-
1The aquiclude is the clay layer which separates tenance of the health, safety and welfare of
the shallow saline aquifer and the water table Sanibel residents. The ridge buffers flood tides
aquifer. and storm winds and prevents increased flooding

The Plan 127

in the interior (unless overtopped by waves) and deposited in the offshore ebb delta. The
contributes to shoreline stabilization. Main- shape of the ebb delta and the sediment
tenance of elevation and vegetation are the keys movement within the delta is then strongly
to the protection of these valuable functions. controlled by the interaction of the ebb
Vegetation stabilizes the ridge and prevents and flood currents with the offshore wave
erosion of the soil. Much fresh water runoff- system and the longshore currents. The
enters the ground in the Beach Ridge Zone, halt- sand stored in the ebb delta is now avail-
ing inward intrusion of salt water from the Gulf able for littoral transport onto the down-
and thus maintaining the extent of the fresh drift beach system. Also, high energy
water lens. Soil and vegetation in the ridge storms and floods flush out the inlet and
filter runoff and protect water quality. move the sand laterally to be used to ab-
sorb the storm energy in the adjacent fore-
Although this zone is crucial to health, safety and beach areas. Thus an inlet system plays an
welfare, it is more tolerant to residential develop- important role in sediment storage for use
ment than other more sensitive zones on the Island. as an energy sponge during storms and has
The one area of exception is the Blind Pass area, built-in sediment bypass mechanisms. Con-
which is extremely intolerant to alteration and haz- sequently, inlet systems represent an in-
ardous to human settlement and is discussed separate- tegral part of the overall sediment budget
ly later. Excavation which results in lowering the of the coastal system and contribute to the
elevation of the ridge or in penetration of the aqui- overall natural ability of the system to
clude is prohibited. Disruption or alteration of roll with the energy punches with minimal
natural drainage channels and the use of septic tanks adverse effects. Modification and/or sta-
is severely restricted. Storm runoff from paved or bilization of- an inlet will limit or elim-
developed areas is to be retarded and dispersed slow- inate this ability, increasing the poten-
ly to the natural hydrologic system. Storm runoff tial for accelerated shoreline erosion re-
from paved or developed areas to the beach is strict- suiting from major storms."'
ly controlled. Impervious paving and clearance of
native vegetation is restricted and native beach ridge All standards for the Gulf Beach Ridge Zone should
vegetation should be planted in areas which are not be applied here with several further restrictions on
well vegetated. changing or developing this area. Permanent human
settlement in this high hazard area should be re-
Special Blind Pass Zone: The Blind Pass area is stricted -to very low density or prohibited if possi-
the youngest and the least stable part of the ble. Any activity which would result in the altera-
Island. It is an inlet system very susceptible tion of or interference with inlet dynamics and
to dramatic change both in a storm and over time. Island building functions in this area should be
This has been borne out by Stanley Riggs1 in a prohibited. The precise boundaries of this area
study cited in Morrill and Byle2 and through should be determined by a detailed geological survey.
aerial photographs of the area over the past
thirty years. One hundred years ago most of the Mid-Island Ridges Zone
existing Blind Pass Area was non-existent. Over
the past century this area has been constantly This zone comprises the major ridges along the central
changing; the shoreline has shifted, accreting axis of the Island and includes the highest topo-
then eroding. "The 'loss' of sand into inlets is graphic elevations. In most areas this zone divides
at most a temporary thing, and even then the Bay-Mangrove watershed from the Interior Wetlands
only where there are 'new' inlets, which do watershed. Like the Gulf Beach Ridge, this zone is
not yet -have tidal deltas, does this become also important in providing storm and flood protec-
a major process. Any sediment that is trap- tion, in recharging the fresh water,aquifer, and in
ped in the inlet itself is ultimately moved preventing degradation of water quality. This zone
either in or out into the tidal delta stor- is the most tolerant for urban development with the
age bins. Since the ebb currents are gen- application of regulations set forth in Article 3 of
erally the dominant inlet force, most sand the Plan to protect crucial health, safety and wel-
moving into an inlet will ultimately be fare functions. Excavation which results in lowering
the elevation of the ridge or in penetration of the
aquiclude is prohibited. Storm runoff from paved or
iStanley R. Riggs, Geology of the Natural developed areas is to be retarded and dispersed slowly
Beach Systemn SanibelIsland Florida 1975. to the natural hydrologic system. Natural drainage
channels are not to be disrupted or altered. The use
2Duane Hall and Associates, 1975, cited in J.B. Mor-
rill and W.K. Byle, Jr., "Preliminary Survey of the
Marine Ecosystem Surrounding Sanibel Island," 1975. 1Stanley Riggs, op. cit.

128 The Sanibel Plan

A -~

GULF BEACH GULF INTERIOR WETLAND BASIN
I ~~BEACH
BEACH MID ISLAND RIDGES
FRONT BEACH BACK BEAC H RIDGE UPLAND LOWLAND UPLAND
FRONTBEACH I BACK BEACH IG
The Gulf Beach Zone includes the area between the The Gulf Beach Ridge Zone The Interior Wetland Basin Zone is the interior bowl which serves as a fresh water The Mid-Island Ridges Zone comprises the
state setback line and the city boundary 300' offshore. is the major ridge imme- reservoir. it is composed of parallel systems of ridges and swales with corresponding major ridges along the central axis of the
There are two subareas within this zone-the Front diately behind the beach :bands of vegetation. There are two sub-areas within this zone - lowland and upland. Island and includes the highest elevations.
Beach and the Back Beach. The Front Beach extends It is stabilized by dense The lowland area is composed of low ridges and wide swales and experiences extended In most areas this zone divides the Bay-
from the city limit to Mean High Water. Sand in this vegetation. Blind Pass- periods of flooding each year. The upland consists of higher, broader ridges and Mangrove watershed from the Interior
subarea is in constant motion. Sand migrates between a subarea within this narrower swales. and is characterized by less frequent flooding and more upland Wetlands watershed.
the berm and offshore bars and is transported by long- zone-is of very recent vegetation types.
shore currents. The Back Beach comprises that area formation and susceptible
between Mean High Water and the the state setback to dramatic change.
line. Sand in this subarea is moved by wind and water
and stabilized by vegetation, forming low dunes.

CLIMATE CLIMATE CLIMATE CLIMATE
Salt Spray Salt Spray

GEOLOGY GEOLOGY GEOLOGY GEOLOGY
Oxidized barrier sands and shells

SUBSURFACE HYDROLOGY SUBSURFACE SUBSURFACE HYDROLOGY SUBSURFACE
HYDROLOGY HYDROLOGY

Fresh Water Table/Aquifer Fresh Water Table Aquifer
Saline Shallow Aquifer

SURFACE HYDROLOGY SURFACE HYDROLOGY SURFACEHYDROLOGY SURFACEHYDROLOGY
Mean High Water
Seasonal High Water Table at Surface
Saoe Seasonally Flooded

10 Year Storm Flooding 10 Year Storm Flooding 10 Year Storm Floodi ng 10 Year Storm Flooding

25 Year Storm Flooding

SOILS SOILS SOILS SOILS
sells :sol~~~~~~~~~~~~s ~~I sl SOILS
Oxidized Barrier Sands and Shells Thin Organics Organics over Sand Marl Thin Organics

VEGETATION VEGETATION VEGETATION VEGETATION
Widely scattered herbaceous vegetation and shrubs. . Sea grape, yucca, bay cedar, Vegetation varies according to elevation and water levels. West Indian Flora, Cabbage palmetto,
Sea Oats, railroad vine, sea spurges, beach plum, sea saltbush, marsh elder, saw palmetto, seagrape, gumbo limbo,
purslane, bay cedar, yucca, salt bush. Invasion of cabbage palmetto, wax Swales: Cordgrass, sawgrass, andropogon, water hyssop, buttonwood, cattails, spat- Jamaica dogwood. Florida privat, wild lime,
Australian Pine. myrtle, coconut palm. terdock, hydrilla, chara, duckweed, wigeongrass. strangler fig, wild coffee, myrsine, joewood,
Invasion of Australian Pine. Low ridges: Marsh elder, leather fern, wax myrtle, cabbage palmetto. wax myrtle, sea oxeye, poison ivy, Virginia
Invasion of Brazilian pepper and Australian Pine. creeper, prickly pear cactus, bowstring
hemp, century plant. Invasion of Australian
Pine, Brazilian pepper, and cajeput.

WILDLIFE WILDLIFE WILDLIFE WILDLIFE
Loggerhead Turtle, Bottle-nosed dolphin, Otter, Manatee, Box Turtle, Gopher Tor- American Alligator, Box Turtle, Chicken Turtle, Soft Shell Turtle, Green Anole, Gopher Tortoise Green Ane ey West
Brown Pelican, Snowy Egret, Red-breasted Merganser, toise, Green Anole, Key Key West Anole, Five-lined Skink, Florida Watersnake, Ribbon Snake,:Southern IAnole, Five-lined Skink, Six-lined Racerunner,
American Oystercatcher, Semipalmated Plover, Piping West Anole, Five-lined Toad, Green Treefrog, Squirrel Treefrog, Southern Leopard Frog, Pig Frog, Opossum, EBlack Racer, Indigo Snake, Coral Snake,
Plover, Snowy Plover, Wilson's Plover, Black-bellied Skink, Six-lined Racerunner. Armadillo, Marsh Rabbit, Sanibel Rice Rat, Sanibel Cotton Rat, Raccoon, Otter, Diamondback Rattlesnake, Southern Toad,
Plover, Ruddy Turnstone, Willet,. Knot, Least Sandpiper, Mangrove Watersnake, Florida Bobcat, Pied-billed Grebe, Anhinga, Least Bittern, Mottled Duck, Blue-winged Green Troefrog, Squirrel Treefng, Opossum,
Dunlin, SemipalmaTed Sandpiper, Western Sandpiper, Black Racer, Indigo Snake, Teal, King Rail, Virginia Rail, Sera, Common Gallinule, Killdeer, Spotted Sandpiper, Armadillo, Marsh Rabbit, Sanibel Rice Rat,
Sanderling, Herring Gulf, Ringbilled Gull, Laughing Coral Snake, Southern Common Snipe, Belted Kingfisher. Long-billed Marsh Wren, Swamp Sparrow. Sanibal Cotton Rat, Florida Panther, Fier-
Gull, Forster's Tern, Least Tern, Royal Tern, Sandwich Toad, Green Treefrog, ida Bobcat, Bobwhite, Smooth-villed Ani,
Tern, Caspian Tern, Black Skimmer. Squirrel Treefrog, Bob- Red-bellied Woodpecker. Great Crested Fly-
white, Smooth-billed Ani, catcher, Purple Martin, Fish Crow, Starling,
Red-bellied Woodpecker, White-eyed Vireo, Prairie Warbler, House
Great Crested Flycatcher, Sparrow, Cardinal.
Purple Martin, Fish Crow,
Starling. White-eyed
Vireo, Prairie Warbler.
House Sparrow, Car-
dinal.

The Plan 129

' - - , .

MANGROVES

MANGROVES TIDAL FLATS MANGROES BAY BEACH

The Mangrove Zone includes all areas of red, black and white mangroves, as well as The Bay Beach Zone extends from
the tidal flats and hardwood hammocks within them. Much of this zone, including the city's boundary 300' into the
all areas of red mangrove, is subject to daily tidal flooding. Other areas of the zone ane -: bay to a setback line approximately
subject to extended periods of flooding every year. 100' behind the Mean High Water
Line. It is a lower energy beach
than the Gulf Beach, and includes
areas of marine grasses on the
bay bottom. It includes both
sand beach and mud beach.

CLIMATE CLIMATE

-GEOLOGY GEOLOGY
Oxidized Barrier Sands and Shells Muds, Organic Materials, Sands
and Shells
SUBSURFACE HYDROLOGY SUBSURFACE HYDROLOGY

Saline Shallow Aquifer

SURFACE HYDROLOGY - SURFACE HYDROLOGY
Mean High Water

10 Year Storm Flooding
25 Year Storm Flooding

SOILS SOILS
Peat Deposits Salt Flats Muds, Organic Materials, Sands
and Shells

VEGETATION : VEGETATION
Mostly mangroves with hardwoods at higher elevations. Vegetation responds to ele- Sand beach: Sea oats, railroad
vation and tidal patterns. Red mangroves predominate to the mean high tide line, vine, sea spurges, beach plum,
black mangroves predominate to slightly higher elevations above the mean high tide sea purlane, bay cedar, yucca,
salt bush. Invasion of Australian
Red mangrove, black mangrove, white mangrove, buttonwood. Seagrape, gumbo Pine
limbo, palmetto Mud beach: Red mangroves
Submerged beach: Marine grasses

WILDLIFE WILDLIFE
American Alligator, Green Anole, Mangrove Watersnake, Marsh Rabbit, Otter, Florida Loggerhead Turtle, Bottle-nosed
Panther, Manatree, Bottle-nosed Dolphin, Brown Pelican, Double-crested Cormorant, Dolphin, Otter, Manatee Brown
Great Blue Heron, Green Heron, Snowy Egret, Louisiana Heron, Little Blue Heron, Pelican, Snowy Egret, Red-breated
Pelican, Snowy Egret, Red-breasted
Black-crowned Night Heron, Yellow-crowned Night Heron, White Ibis, Roseate Spoon- Meranser, American Oyster-
bill, Lesser Scaup Duck, Red-breasted Merganser, Bald Eagle, Osprey, Clapper Rail,
American Oystercatcher, Piping Plover, Snowy Plover, Wilson's Plover, Blackbellied catcer Seipmated Plover
Plover, Ruddy Turnstone, Eastern Willet, Laughing Gull, Least Tern, Black Skimmer. Piping Plover, Snowy Plover,
Wilson's Plover, Black-bellied
Plover, Ruddy Turnstone, Willet,
Knot, Least Sandpiper, Dunlin,
Semipalmated Sandpiper, Western
Sandpiper, Sanderling, Herring
Gull, Ringbilled Gull, Laughing
Gull, Forster's Tern, Least Tern, RY
Royal Tem, Sandwich Tern,
Caspian Tern, Black Skimmer.

130 The Sanibel Plan

25 Year Flood Tides
10 Year Flood Tides

'und Storage i
Se~~~~~~~~~;

-~ :*. r~- Salt Water shmater
.-. Fresh Water Table Aqaifer
Barrier Sand and Shell - .
Clay orMar l Confining Layer ' lliil l Illlllllll llllll 11 11 1 1 JIIH I I I IIIIII 1111 I lIIIIIII 11 I I11 11 I 11 tllllllll llIIIillll11 [~ H l~H11ii1t~ 1~ Iti 1it 1t~H1i
�r~ ~~ '~-":":'"i~'-Saline Shallow Aquifer:

GULF BEACH GULF INTERIOR WETLAND BASIN
BEACH MID-ISLAND RIDGES
FRONT BEACH I BACK BEACH RIDGE UPLAND LOWLAND UPLAND
RIDGE
The Gulf Beach Zone includes the area between the state - The Gulf Beach Ridge Zone The Interior Wetland Basin Zone is the interior bowl which serves as a fresh water reservoir. The Mid-island Ridges Zone comprises the
setback line and the city boundary 300' offshore. There is the major ridge immedi- It is composed of parallel systems of ridges and swales with corresponding bands of vege- major ridges along the central axis of the
are two subareas within this zone-the Front Beach and ately behind the beach. tation. There are two sub-areas within this zone-lowland and upland. The lowland Island and includes the highest elevations.
the Back Beach. The Front Beach extends from the city It is stabilized by dense area is composed of low ridges and wide swales and experiences extended periods of In most areas this zone divides the Bay-
limit to Mean High Water. Sand in this subarea is in con- vegetation. Blind Pass-a flooding each year. The upland consists of higher, broader ridges and narrower swales. Mangrove watershed from the Interior Wet-
stunt motion. Sand migrates between the berm and off- subarea within this zone- and is characterized by less frequent flooding and more upland vegetation types. lands watershed.
shore bars and is transported by longshore currents. The is of very recent formation
Back Beach comprises that area between Mean High Water and susceptible to dramatic
and the state setback line. Sand in this subarea is moved change.
by wind and water and stabilized by vegetation, forming
low dunes.
FUNCTIONS FUNCTIONS FUNCTIONS FUNCTIONS
Storm Protection Storm Protection Flood Protection Storm Protection
Shoreline Stabilization Flood Protection Maintenance of Water Quality Flood Protection
Maintenance of Marine Life Shoreline Stabliization Maintenance of Fresh Water System Maintenance of Water Quality
Maintenance of Wildlife Maintenance of Water Maintenance of Island Wildlife Maintenance of Fresh Water System
Quality
The Gulf Beach Zone is the Island's first defense in storm Maintenanceof Fresh Since the elevation of the interior Wetland Basin is lower than the adjacent zones, it serves The elvio of the Mid-Island Ridgs Zone
and flood when the impact of storm waves erodes the sand Water System as a storage area for flood waters until they are absorbed into the aquifer. Water Quality provides flood protection. This zone helps
reservoir in the berm. The low dunes of the Back Beach is protected by the filtering function of soil and vegetation. This zone is crucial to the maintain water quality by the filtering func-
are a reservoir of sand which may be eroded after the berm Th e Gulf Beach Ridge is maintenance of the fresh w a ter lens. It also has the capacity to maintain and improve tions of soil and vegetation. Much fresh water
i n a severe stor m, thus protecting property further inland a dike which buffers flood water quality, and provides food, shelter, water, and nesting areas to wildlife, including runoff enters the ground in the Mid-Island
n ac Ridge. sT h nthusra profie of ther Gulfach tides and storm winds, pre- the American alligator. Ridges Zone, halting inward intrusion of
on the Beach Ridge. The natural profile of the Gulf Beach vents increased flooding salt water from the Bay and thus maintain-
Zone is a response to processes of wind, currents, and wanes' in she interior lunless over- ing the fresh mater lens.
Undistrubed, it is in a state of balance with natural forces, topped by waves) and con-
thus "stabilizing" the shoreline. The Front Beach supports tributes to shoreline sta-
the marine life for which Sanibel is famous, and is an i- bilization. Water quality
portant feeding area for island wildlife. The low dunes of is maintained by the fil-
the Back Beach are an important nesting area for wildlife, tering function of soil and
terng function of soil and
the loggerhead turtle being a prime example. vegetation. Much fresh
water runoff enters the
ground in the Gulf Beach
Ridge Zone, halting inward
intrusion of salt water from
the Gulf and thus main-
taining the extent of the
fresh water lens.

ELEMENTS ESSENTIAL TO FUNCTIONS ELEMENTS ESSENTIAL ELEMENTS ESSENTIAL TO FUNCTIONS ELEMENTS ESSENTIAL TO FUNCTIONS
~~~~~~~~~~~~~~~~~~~~~TFNTOSELEMENTS ESSENTIAL TO FUNCTIONS T UCIN
TO FUNCTIONS
Storm Protection and Shoreline Stabilization: Storm Protection and Shore- Flood Protection: Flod Protection:
-Natural profile of beach line Stabilization: -Water storage capacity -Elevation of ridge
-Sand reservoir in berm, bars and dunes -Shoreline stabilization -Free-flowing water circulation
-Gradual and dispersed runoff from land M and torm protctio Maintenance of Water Quality:
-Longshore sand movement functions of the Gulf Maintenance of Water Quality -Gradual and dispersed runoff
-Hardy dune vegetation Beach Zone -Free-flowing water circulation -Filtration of runoff through vegetation and
-Natural configuration -Gradual and dispersed runoff soil
Maintenance of Marine Life and elevation of ridge -Filtration ofrunoff through vegetation and soil
-Access to beach -well established hardy -Restriction of industrial and domestic wastes discharged into interior wetland Maintenance of Fresh Water Systems
-Good water quality vegetation -Water quality function of Gulf Beach Ridge and Mid-Island Ridges Zones -Recharge of runoff to fresh water lens
-Drainage of runoff to interior wetland
Maintenance of Water Maintenance of Fresh Water System: -Aquiclude between shallow saline aquifer
Maintenance of Island Wildlife Quaintenneoy
-Acntenances s to bea h ldl -Quality -Recharge of runoff to fresh water lens and fresh water lens
-Access to beach -Gradual and dispersed -Sufficient water levels -Elevation of ridges
ru~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Eeain offrde
-Good water quality runoff -Aquiclude between shallow saline aquifer and fresh water lens
~-Abue~doet marine ~life ~--Filtration of runoff -Free-flowing water circulation
through vegetation and
soil Maintenance of Wildlife:
-Good water quality
Maintenance of Fresh Water -Fresh water system
System: ~~~~~-Fresh water system
System: -Access to water
-Recharge of runoff to - . st ae
-Recharge of runoff to -Native vegetation of value to wildlife
fresh water lens
-Drainage of runoff to
interior wetland
-Aquiclude between shal-
low saline aquifer and
fresh water lens.

The Plan 131

~--" ; : 25 Year Flood Tides
10 Year Flood Tides

'i,*. - . . .: > Muds Organic Materials Sandsand Shell:

:,: a~ .. : ,' . .. ,: '' . .'Cay or llarl Confining Layer

MANGROVES

MANGROVES J TIDAL FLATS MANGROVES BAY BEACHV

The Mangrove Zone includes all areas of red, black and white mangroves, as well as the The Bay Beach Zone extends
tidal flats and hardwood hammocks within them. Much of this zone, including all areas from the city's boundary 300'
of red mangrove, is subject to daily tidal flooding. Other areas of the zone are subject into the bay to a setback ine
to extended periods of flooding every year.: approximately 100' behind the
Mean High Water Line. It is a
lower energy beach than the
Gulf Beach, and inclades areas
of marine grasses on the bay
bottom. It includes both sand
beach and mud beach.

FUNCTIONS FUNCTIONS
Storm Protection Storm Protection
Flood Protection - Shoreline Stabilization
Shoreline Stabilization Mainten.ance of Marine Life
Maintenance of Water Quality Mainteannce of Wildlife
Maintenance of Marine Life
Maintenance of Wildlife The Say BeachZonebuffersthe
TheBAY Bec Zone baters the
The dense canopy and roots of the mangroves buffer storm winds and tidal surges. The actural form of the Bay Beach
arching prop-aoots of the red mangrove and the roots of the black mangrove trap sediments eatras f orm of the Bay Beach
and stabilize and extend the shoreline. Mangrbves preserve water quality by filtering suspended of ind, currents, and waes.
material and assimilating dissolved nutrients. Mangroves maintain the highly productive marine Undisturbed, it is in a state of
ecosystem and provide food, shelter, and esting areas for wildlife, balance with natural forces,
thus "stabilizing" the shore-
line. The Bay Beach is a feed-
ing area for island wildlife.
Beds of marine grasses in sub-
merged portions of the beach
are important nursery and
feeding areas for marine life.

ELEMENTS ESSENTIAL TO FUNCTIONS ELEMENTS ESSENTIAL TO
FUNCTIONS
Storm Protection, Shoreline Stabilization and Land Building:
-Healthy mangroves Storm Protection and Shoreline
Stabilization:
Maintenance of Water Quality: -Natural profile of beach
-Healthy mangroves -Gradual and dispersed runoff
-Restriction of domestic and industrial wastes discharged into Mangrove Zone from land
-Water circulation -Longshore sand movement
-Hardy beach vegetation
Maintenance of Marine Life:
-Healthy mangroves Maintenance of Marine Life:
-Good water quality -Mangroves
-Marine grass beds
Maintenance of Island Wildlife: -Access to beach
-Healthy mangroves -Good water quality
-Abundant marine life
Maintenance of Wildlife:
-Access to beach
-Good water quality
-Abundant marine life

ECOLOGICAL ZONES: FUNCTIONS

132 The Sanibel Plan

--45 dH~~~~~~~~~~brrr~~~~~~~yyrr~~~~~~~l\\hti~~~~~~~~lllllelll� ~ ~ ~ ~ ~ ~ ~ ~~~l

GULF BEACH IGULF INTERIOR WETLAND BASIN

FRONT BEACH BACK BEACH BEACH UPLAND ILOWLAND UPLAND
RIDGEI

Management Guidelines Mangement Guidelines Management Guidelines

Storm Protection and Shoreline Stabilization Storm and Flood Protection Flood Protection
eo~~~~~~~ntopt ~ ~ ~ ~ ~ ~ ~ ~ 1 -ttuet tsbobtn dducadShrline Stabilization ot'ttteseoeseieftenyodstndo
Id.-netjentuteeett eoeseteted be-hcess -?uhbtdslennthehitud. betttntddeet-tntttutdtsotetltes.1-
-n-- .en, 1 ul ..eohntsneleosdtktot sete oudot.Itos- tdelsyjn.-tnpestebcieW-esyes-e-e'iefneeteuu

d-- -im --i- ~~~~~~~~~~Maintenance of Water Quality
R- 6 -ettt nnff ften d paee d -ndeetpdsns et btnh - &tslihttotus~ttei b- deudlnsbs
dAettel ensIbtesod LI'tnn -tatnnoee tetsee.- Mointinnotuna pa.eIn etou ,ad di-p-odten
-i- .tbLnestutee -tidenon eteetnttssiliinhibttet resent i-stit tnte ieehed -, gea dana es nunet 1-tt p-sdo ddntepd snes
Osnt-n hotut d-u-tss -otstcen. ed It-eettttniedondh-til i.ns ,- . -.nniee otendie-atueusu-lss

.ppite AstsIe i~ts en- Sen .. eash teth handy nose dun osetnu. slpd -.,o I-un dtt-, edit Maintenance of Fresh Water System
Maintenance of Marine Lifa and Wildlife th Cult R.sc Zen. -ettentsh-tedfetdfte sesbtoteten
ni t -tensotdbohttnteoen Maintenance of Water Quality dsneotsdot,,od nytieusunf-ne
d -nt d geed...tatn -oetttesultdptet ff -R~ Ie-dtnffesnnpetu-set.

Maintenance of Fresh Maintenance of Island Wildlife
Water System W dintsin setd stat, dot
daittoin dtinadetintnnentsd. d - &deeWdtidninesde
- nstimtiesinesiiss Wdi-tin f-ehseatetsyotnt
.n n tee 1 te-n I , --beesuinildeidesabee
besidntdssiee efn- ud bet-e Canttni diifeo-it-tsstteetotsn Sl i,
udtneouttstddtnahteattdnd- P-eideueitdtistentdtssnte sntpe senotnn-esdttdtstiu
-~ni -e h- etaate eth setIuds. - 4 Pneutd ne eeiietldsotd let sidttSt
nointobnnethatseet~~~~~ ~~~~ Inset, 6stsde uetstoMseoebntouteddbeo:
-Ltsededonededdtnnpsntdeuseteoe. 0 -Setitteaadalsseesesdsbee diiie tm- i

The Plan 13

MANGROVES
MID-ISLAND RIDGES ~~~~~~~~~~ ~~~MANGROVES TIDAL FLATS MANGROVESBABEC

Manragement Guidelines Management Guidelines Management Guidelines
FodProtection Storm Protection Shereline Stabilization, Land Building Storm Protection and Shoreline
o-n fi-nodil Stobilizntion

MainteariaceLof Water Oelt t QualityooIihoofhooIVeO rf.
Mo,,,to,,o~~~o~~oofo,,d o~~ooo,,od~~~oooff Maintain Waer'alt O,s,lu,oin p,..VI ooow-ooi

oodooI, O,,o~~~~~~~~~~~~~~~~~~~~Ift, qolo odo"-Iof nd ind-soia~ose dioag'i-tfodooo e -.o f Iff -o'f
-.u 1.idfofoo;o~'s,O io,,Oo-. _Aflof ffo0hodoo o'o
Maintenance of Fresh Water System i-ba,,ooa of
naof --ho of --offoof,,V,oa-eff,,nl:-- - nofof',00 off, offfVoorofoff,oifo. -.1 1-fl Iho-d
e~~~~~~~~~~~~~~~~~~f~~~~~~~~odoof oooieoooo,.- rofel.o eoIo, fo 0,01-blo 6o oo
OoYffifldfaioni, of ru.fo offfinf'0l. fIlod, oii:Ioo' fofo oOofff
.- x .1,ooiffeaio of -oioofoo-1oo~ooo Maintenance of Marine Life and Wildlife-OrfoAslioPooohOooif
- to, go~~~~~~dol~~o,, obo,,. ~~~~~Maintenence of Marine Life and
- POfibif oo~~~ooofooo of ffoof,,,ofoao. nI~~~~~ofo'ooafo, floe,,0, ~~Wildlife

M'o-ilfo Aorodioo gof bol-'ii,
- nooo, -od,liofof10to fof

- l'0ofboi,ofoM,gf, ofoj-fxifi'oooo-fo
d- li l 000,uo~ooff.fl,oOooodofod

W- Oifj -w0 to.Iifooo, of aid I
Iwlood --O,doo,d Zoioodt.-

ECOLOGICAL ZONES. MANAG-NEMENT GUIDELINES

134 The Sanibel Plan

of septic tanks, impervious paving, and the clearance Gulf Beach
of native vegetation is severely restricted. - The delineation of the Gulf Beach Zone is based upon
setback recommendations by the State of Florida De-
Filled Land partment of Natural Resources presented to the City
during 1975. The setback line was determined on the
This is a man-made zone, created artificially by dis- of beach profilesand shoreline dynamics and is
turbing the natural topography and vegetation of an intended to protect the beach zones from environmen-
area for real estate development purposes. In most tal degradation and construction. The Gulf Beach
cases the area delineated on the maps of Ecological Zone is characterized by widely spaced non-woody
Zones has been elevated to approximately five feet plants and semishrubs. Sea spurge, sea purslane and
above mean sea level either by importing fill
sundrops are common perennials. Railroad vine occurs
or by excavation within the site area. The Pur- quite frequentlyr along-with sea oats and-grass
pquite frequently, along with sea oats and grass.
p ose of such mod ificationsg lando that isoftenwet Beach plum, bay cedar, yucca and salt bush are shrub
been to transform low lying land that is often wet
beean ~Sitbl frdeelpmntito hgand semishrubs plants found along the beach stand.
and unsuitable for development into high dry land Australanpines have beennaturalized and spread
Australian pines have been naturalized and spread
associated in some cases with lakes, lagoons and along the upper portions of the beach.
canals formed by dredging below the water table.
Bay Beach
For planning purposes, only the larger areas of
filled lands were mapped, thereby excluding The delineation of the Bay Beach Zone is based on
spoil areas from mosquito ditches and canals that a 50 foot setback from the Mean High Water Line along
did not cover extensive areas. Some of the areas the Bay Shore. Detailed examination of beach pro-
have been filled for twenty years or more, so files and shoreline dynamics similar to that conduc-
that grasses and woody plant materials have ted by the State along the Gulf Beach was not under-
established. Other areas that are more recently taken. However, since the Bay Beach is less dynamic
filled are bare but for the invasion of scatter- than the Gulf Beach, which averages a 200 foot set-
ed weeds. back, a smaller setback was chosen. It is recommend-
ed that in the future the City of Sanibel conduct a
survey using similar criteria to those employed by
Permitted land uses and development intensity for the State. Typical vegetation on the Bay Beach
such development are described in 2.5.1 and 2.5.2 from Lighthouse Point to Woodring Point is the
and regulated by Article 3 of the Comprehensive sameas that foundon the Gulf Beach. These in-
Plan. D:;0 off : t 0 t; : go 7 clude sea spurges, sea purslane, sundrops, rail-
road vine, yucca, salt bush and Australian pine.

DELINEATION OF ECOLOGICAL ZONES Gulf Beach Ridge
In order to map the ecological zones, the plan- The delineation of the Gulf'Beach Ridge Zone is
ners depended heavily upon published sources based upon studies by the Conservation Founda-
available during the summer of 1975 and field tion -- "Environmental Habitats" map ("Beach
studies. These included U.S.G.S. topographic Ridge") -- and on U.S.G.S. topographic survey
mapping with five foot contour interval, aerial which was used to delineate areas at or above
photographs, recommended coastal construction five feet elevation. Some of the species char-
setback by the Department of Natural Resources, I acteristic of the beach stand are also character-
State of Florida, and studies by natural scien- istic of the ridge. These include: yucca, bay
tists for Sanibel-Captiva Conservation Founda- cedar, salt bush and a few of the herbaceous
tion. The boundaries of the zones are shown on perennials. Also cabbage palm, sea grape, wax
the Ecological Zones, Existing map. The City myrtle and the ubiquitous Australian pine can be
is undertaking a program to provide a one-foot found here.
topographic survey of the entire City and, upon
its completion, will review and revise as
Special Blind Pass
appropriate all of the boundaries on a City-wide
basis. Until that can be accomplished no evidence The delineation of the Special Blind Pass Zone
regarding potential shifting of zone boundaries is based on a study of shoreline changes in the
should be accepted to avoid prejudicing rights of Blind Pass area over the past 100 years (Duane
neighbors. Applications for permits received prior Hall Associates, 1975). The Blind Pass area is
to the revision of the boundary lines but not decided adjacent to the Blind Pass Inlet most of which
prior to such revision, will be decided on the basis has been deposited or subject to major changes
of the revised boundary lines. over the past 100 years.

The Plan 135

The vegetation of this area is very much the Mangroves
same as that of the Gulf Beach Ridqe, although
there is much more Australian pine and only a - the deli neation ofgrove areasZone is based on
the map of mangrove areas provided by Conserva-
small area- of cabbage palm, sea grape, wax tion Foundation consultants. This map was re-
myrtle and marsh elder.
fined by reference to a 1" = 800' aerial photo-
graph flown in the summer of 1975. This zone
Mid-Island Ridge a
includes all areas of buttonwood, red, black and
white mangroves. A few woody and non-woody
The delineation of the Mid-Island Ridge Zone is species occur in conjunction with red, black and
based on the Conservation Foundation's "Environ- - white mangroves. Air plants and orchids grow
mental Habitats" map and on the U.S.G.S. topograph- epiphytically while sea oxeye is common and wax
ic survey to delineate areas at or above five feet myrtle and bay cedar occur sporadically in the
elevation. understory.

Species of the West Indian flora and several intro- It is apparent from the preceding descriptions
duced trees are characteristic of this area. In- of ecological zones that some zones are more
cluded in the desirable woody native category are tolerant of development than others. The charts
cabbage palm, saw palmetto, gumbo limbo, sea grape, describing Ecological Zones (2.3.1-3(a) (b) (c)
Jamaica dogwood, Florida privet, wild lime, stran- summarize the conditions; hazards; guidelines
gler fig, wild coffee, myrsine, joewood, wax myrtle, for environmental management in all zones. It is
bow string, hemp, century plants and air plants. clear that extensive areas of Sanibel are not
Vines such as virginia creeper and poison ivy are suitable for urban development and that in most
common while several perennials can be found as well. cases health, safety and welfare and environ-
Brazilian pepper, Australian-pine and cajeput have mental, protection will only be achieved by strict
invaded the ridge, frequently displacing the West adherence to the performance standards described
Indian vegetation. in Article 3 of the Plan.

Filled Land
Interior Wetland: Lowland
The delineation of the Lowland Interior Wetland Zone The delineation of Filled Land Zone is based upon
is based primarily on that area of the interior aerial photographs; maps of Historical Ecological
identified as "wetland" by the 1975 Johnson Engin- Zones by Conservation Foundation Studies1, and field
eering study of the Sanibel Island Fresh Water Man- inspection by the planning consultants. Determina-
agement area for the Sanibel-Captiva Conservation tion of these areas was on the basis of land that
Foundation. This "wetland" area experiences a sea- had apparently been disturbed by topographic change
sonal high water table at the ground surface or and clearing of vegetation for real estate develop-
higher.. Additional areas of lowland interior wetland ment purposes. Only those areas where such activi-
were identified by natural scientists in their 1975 ties were apparent over a large area and achieved an
studies for the Conservation Foundation and identi- elevation of approximately five feet above mean sea
fied in their "Environmental Habitats" map. The low level were included. Several categories of filled
swales in the wetlands are vegetated with cordgrass, land exist within these areas including some which
saw grass, sea purslane and buttonwood frequently have variations in topography, vegetation, and water
invaded by Brazilian pepper. bodies.

Interior Wetland: Upland B. PLAN FOR THE PRESERVATION OF ECOLOGICAL FUNCTIONS
RELATING TO HEALTH, SAFETY AND WELFARE
The delineation of the Upland Interior Wetland Zone
is based on the Conservation Foundation's The plan for the preservation of the ecological
"Environmental Habitats" map and is subject to functions of the Island of Sanibel is provided for
occasional high water table and flooding and is through the adoption of the development regulations
generally less than five feet elevation. On and performance standards set forth in Article 3 of
slightly higher and drier ground, salt bush, the Plan. A map identifying the various ecological
marsh elder, leather fern, wax myrtle and cabbage zones is officially adopted along with specific
palm grow. Chara spp, Hydrilla spp, duckweed and standards for development, based on the ability of
wigeon grass are aquatic plants associated with each ecological zone to tolerate such future devel-
inland pools and canals. Brazilian pepper has opment.
successfully invaded both the lowland and upland
while Australian pine is confined to the slightly 1"Sanibel National Systems Study" by John Clark,
higher shell ridges. Project Director, The Conservation Foundation.

136 The Sanibel Plan

Section 2itting seepage of salt water into the ground
Section 2.3.2: Co astal Zone water system. The salt intrusions can, if per-
:Protection t mitted to continue, cause a marked change in
the ecosystem of the Island.

Section 2.3.3: Wetland Protection An appropriate balance must be achieved between
the management requirements of the interior
A. BACKGROUND DISCUSSION t wetlands and the safety of the Island residents.
B. THE HYDROLOGY t It is possible that a water level of about 3.0
C. VEGETATION :t :; 0 : : : 0 0 f 0 0 feet could possibly be maintained if more con-
trol structures and outflow barriers were in-
D. WILDLIFE t ; :: : : : stalled. Missimerlsuggests that setting the:
E. WATER LEVEL. water stage at 3.0 feet at the existing control
structure would not be adequate to achieve the-
The wetlands serve as an integral part of 3.0 feet level throughout the wetland and that
this Island's natural system, without which the water level would have to be controlled in
its whole ecology would suffer. The key to steps.
their health rests in establishing an appro-
priate water level and protecting water Therefore once the water table is initially
quality. A water level (equal to the level, adjusted to 2.5 feet above msl, some of the
of the :"hard pan" under buttonwood ridges as major problems now evident in Sanibel will be
suggested by Tabb and Roessler) would allow automatically ameliorated. It is likely, how-
year-round populations of insects to thrive ever, that specific action will have to be
while permitting native marsh vegetation to taken to eradicate as completely as possible
prosper. the Brazilian pepper. Most other introduced
plants may disappear with a change in water
Water quality will be improved by the controls) level.
and improved flow in the Sanibel River will
prevent most of the present salt water intru- It is likely that more detailed technical
sion and allow flushing of that which may study for water management will find that the
accumulate. The prevention of salt water pol- most practical solution is a system that has
lution of the interior will enhance wildlife fixed structures at different elevations.
habitats and-increase the utility of the fresh Under natural conditions the elevation of
water Xlens. : ;i; ; 0 standing water varies greatly: however, in the
absence of good topographic surveys, these re-
The reduction of salt water contamination in commendations cannot be specific regarding
the river will sustain fresh water vegetation elevations.
and associated animal species, which include
the anhinga, bitterns, rails, many more bird
species, the river otter, bass, bluegill and F. PLAN FOR WETLAND PROTECTION
others too numerous to list. All these would
In order to establish the most suitable water
be eliminated if the fresh water system were to
level, more detailed topographic and engineering
be lost to a salt water system.
studies must be done. Fixing the now movable
However, high elevations for control structures control structures at Tarpon Bay and Beach Road
at their existing elevation of 2.5' will only
should be investigated since, at abnormally high
tides and low interior water levels, the salt partially achieve the desired result. However,
water overtops the structures. Intruding salt 0 fixing these structures at a higher elevation
water flows inland as a density current, and without further study would threaten existing
spreads throughout the existing stream channel, roads and buildings with flooding on the Island
in some cases entering ponds or other water
bodies. Under drought conditions, fresh water 1Missimer, 'Sanibel Island: Hydrology",1975,
level sometimes drops below mean sea level, per- Prepared for the Conservation Foundation,Inc.

The Plan 137

during higher intensity storms. Until the plan pollute the waters, and can directly harm
for storm drainage in the interior wetland is some species and disrupt the marine environ-
implemented (see Section 2.2.6) this drainage ment in general. Larger mammals co-exist
will also have several important benefits in poorly with humans because they need-sizeable
terms of wetland management. undisturbed areas in which to roam, where
hiding places are abundant and where smaller
It is also imperative that the River, the ditches, prey exist. If these requirements are met,
the ponds, and lakes be freed from any sewage the thrill of seeing a bobcat or panther in
pollution. These water bodies are now largely , the wild could remain a possibility on
eutrophic showing low levels of oxygen at depth Sanibel.
and wide fluctuations at the surface. The
cause (and remedy) for this is not immediately
apparent. Obviously it is due to the organic
Birds co-exist well-with man as long as their
materials reaching the water (whether from
food source is plentiful and uncontaminated,
pollution, natural plant decay, fertilizers or
and they have private areas for nesting and
other). In any event, this should be studied and
raising their~young. Unfortunately, this has
appropriate remedial action taken (such as dred- not been the case with reptiles and amphi-
ging out deposits, etc.) The filling-in with bians which have been deliberately sought
undesirable vegetation is an inescapable out- and exterminated. Snakes are sensitive to
come of high-nutrient levels; this is now human intrusion, many being very secretive
evident in scattered places along the River and less adaptable to environmental modi-
where algae bloom can be seen. Not only is fications than warm-blooded creatures. Next
this unsightly vegetation,: but it has to deliberate killing of these creatures,
negligible value for wildlife. habitat destruction has been a major cause
of their decline. Most lizards, snakes,
turtles and crocodilians have very specific
Section 2.3.4: Wildlife Preservation water demands though somewhat less specific
$action2.3.4: Wildlife Preservation
food requirements.

A. BACKGROUND DISCUSSION t
B. BIRDS t
C. REPTILES AND AMPHIBIANS t Regulations which would set the tone of a
D. MAMMALS t sanctuary island can be legislated. Lowered
E. MARINE LIFE t speed limits, speed bumps and speed rumbles,
F. CONCLUSION would decrease the chance of roadkills;
Unfortunately the fauna of a small land area areas cordoned off would allow for non-
almost- always suffer as human population in- interrupted nesting; maintenance of every
creases. It- is an objective of the Plan to in- historical habitat would allow for all spe-
dicate a way to lessen this negative stress. cies to have a place to live; improvement
Basically an attitude of benign co-existence with of habitat through encouragement of native
wild creatures must be wholeheartedly accepted by vegetation would give desirable species the
the public. Attitudes are unlegislatable but, best chance while rigorous monitoring should
with positive education such as that undertaken inhibit pollution of its air and waters.
by Sanibel-Captiva Conservation Foundation,
great strides can be made..
Each wildlife group has its own requirements
and tolerances. Marine biota is sensitive G. THE PLAN FOR WILDLIFE PRESERVATION
to excessive sedimentation, toxicity and
nutrient pollution and changes in configu- The City should give further consideration
ration and vegetation in their nesting and to enacting regulations which would encourage
sanctuary areas.. Over-harvesting of .fish the preservation of the Island's natural
and live shells is, of course, a quick way wildlife and would set the tone of a sanc-
to extermination. High speed power boats tuary island.

138 The Sanibel Plan

Swamps - Wetlands

Buttonwood - Conocarpus erecta
Red mangrove - Rhizophora mangle
Black mangrove - Avicenni nitida
White mangrove - Laguncularia racemosa
Endangered O
% PINE ISLAND
Muhly grass - Muhlenbergia capillaris
Varnish leaf - Dodonaea viscosa SOUND
Christmas berry - Lycium caroliranum
Molina - Maytenus phyllanthoides

Stands

Slash pine - Pinus elliottii
Live oak - Quercus virginiana

Exotics Which Should Be Discouraged on
Sanibel

Australian pine - Casuarina equisetifolia :: : : :;
Casuarina cunninghamiaria
Brazilian pepper.- Schinus terebinthifolius
Cajeput - Melaleuca qulnquenervia
+Guava - Psidium quajava
+Bowstring hemp - Sansevieria thvrsiflora :
+Life Plant - Brvophvllum pinnatum &
related species GULF OF MEXICO
Vitex trifolia
Wedelia trilobata

As an additional measure for achieving maximum LEGEND
ecological preservation of vegetative values,
the City should develop a program for re- JAMAICA DOGWOOD
(Piscidia piVipula)
placing with more beneficial vegetation all Pscidia piscipula
undesirable species of plant, including BUTTERFLY ORCHID
Australian pines, the Brazilian pepper and (Epidendrum tempense)
the melaleuca tree from City-owned land, and GUTTA PERCHA MAYTEN (Maytenus phyllanthoides)
encourage other levels of government with land JAMAICA CAPER (Capparis cynophallophora)
ownership and private individuals on Sanibel
to do the same. : ^PERSIMMON (Diospyros virginana moiseri)
t EVERGLADES COCOA (Chrysobalanus icaco pellocarpus)

WHISK FERN
(Psilotum nudum)

O DWA RF CENTURY PLANTS
(Agave spp.)

m SLASH PINE
(Pinus elliottii)

+ Do not present a problem if controlled. (uercus virgmana)

The Plan 139

SAN CARLOS/"BAY

~~ Y~~ K\ ~TARPON BAY
Y -~~ '~-~~ S ~ -

'~--N INGDA~UN ILDLIFE REFUGE

N0 1000 3000 6000

Source: Harvey Roberts and Richard Workman, 1975 EXCEPTIONAL VEGETATION

140 The Sanibel Plan

include but not be limited to the identi-
~Section 2.35 Vegetation fication of plant individuals that should
p~reservation ~~be preserved, arrangements for the trans-
; 0 X0Preservation 0 ma planting of appropriate individuals to
other parcels on the Island, and the lo-
A. BACKGROUND DISCUSSION t cation of appropriate native species of
B. THE PLAN FOR VEGETATION PRESERVATION: plant for landscaping. Among the species
In order to protect the vegetation values of plant which the committee may encourage
the preservation of are:
identified in this section, it is necessary
that the City of Sanibel:

1) Prohibit the introduction of exotic
species of plant which tend to out- PLANTS WHICH SHOULD BE PROTECTED:
compete or otherwise displace native Beaches
species of plant;
Sea oats - Uniola daniculara
2) Encourage the removal of undesirable Railroad vine - Ipomoea pes-caprae
exotics currently existent on the Sea purslane - Sesuvium portulacastrum
Island; Bay cedar - Suriana maritima
Beach madder - Ernodea littoralis
3) Limit clearing of native vegetation; Beach plum - Scaevola plumieri

4) Protect valuable native species-of Dunes
plant from destruction; and
Joe-wood - Jacquinia kevensis
Sea grape - Coccolobis uvifera
5) Encourage the use of native species of Necklace pod - Sophora tomentosa
plant in the landscaping of future de-
velopments. Ridge
To achieve those ends, performance standards
are set out in Article 3 of this Plan which Red stopper - Euqenia axillaris
set forth certain restrictions -on the de- White stopper - E. rhombea
velopment of land in regard to exotic and Coco -plum - Chrvsobalanus icaco pellocarpus
native species of plant. However, the stan- Jamaica caper - Capparis cvnophallophora
dard and criteria for development activity Coral bean - Erythrina
are not sufficient to achieve Island-wide Strangler fig - Ficus aurea
protection of vegetation values. Therefore, Gumbo limbo - Bursera simarouba
the vegetation committee, as created by City Snowberry - Chiococca alba
Ordinance, should be responsible for en- Mastic - Mastichodendron foetidissum
couraging sound ecological management of Catclaw - Pithecellobium kevense
vegetative resources in those portions of Jamaica dogwood - Piscidia piscipula
the City for which future development is White indigo berry - Randia aculeata
not proposed. That Committee should be an Joe-wood - Jacquinia Kevensis
advisory body responsible for collection, Saw Palmetto - Serenoa repens
analysis, and dissemination of information Butterfly orchids - Epidendrum tampense
on basic ecological principles as they re- Tillandsia spp. except Spanish Moss
late to Island vegetation. The Committee Whisk fern - Psilotum nudum
should, in addition, make available to the
best of its ability expert assistance for Interior Wetlands
any person on the Island who desires help
with the clearing or landscaping for a Cordgrass - Spartina bakerii
development activity. Such assistance may Sawgrass - Cladium jamaicense

The. Plan. 141

conservation of the coastal environment.
Section 2.3.o: Historic Preservation Scenic preservation of the J. N. "'Ding" Dar-
ling Wildlife Refuge is within the aegis of
Section 2.3.7: Scenic Preservation the U. S. Federal Government. To date this
has been accomplished with no negative impact
on the Island. It is most important that the
A. BACKGROUND DISCUSSION Sanibel-Captiva Conservation Foundation ex-,_
ercise maximum control of scenic resources in
Sanibel Island is renowned for the natural its several land holdings in mangrove and wet-
beauty of its gulf beaches and subtropical land areas so that these are enjoyed in their
landscape. These are important economic natural state by visitors.
as well as aesthetic resources for-both :
residents and visitors. Sanibel's repu- The other major vantage for the Island's
tation as a unique retreat of unspoiled scenic resources is that of the major road-
beauty continues to attract more residents ways which give access to- all envirohments
hand tourists annually. The parts of the and land uses. These roads generally follow
Island experienced by most visitors and the Island's two natural ridges and are con-
residents are most subject to degradation nected by several roads which cross the in-
and therefore require some measureof pro- - terior. Periwinkle Way, Gulf Drive, and the
tection and regulation. These are the . Sanibel-Captiva Road, are the City's main
beaches and the wildlife refuge, and the collector streets and commercial arteries
major roadways that provide access to with fairly high traffic volumes.
them.
Most Island businesses are located along
The beaches in the East and East Centrala Periwinkle Way and many of the Island's
Sectors of the Island are to some degree; tourist accommodations are on Gulf Drive.
impacted by large condominiums which are . Land along the Sanibel-Captiva Road is rela-
constructed close to the beach with no tively undeveloped except for the Blind Pass
visual screen. As a result, these are no commercial area and scattered residential
longer the "unspoiled" beaches which have subdivisions. The variety of visual ex-
long attracted visitors to Sanibel. How- perience along these roads today is due to
ever, at the western end of the Island and the alteration of man-made environment and
in some areas of single family homes on the the natural landscape.- This pattern of
eastern end, single family houses are set- intermittent commercial development separated
back sufficiently from the beach and sur- by stretches of dense trees and shrubs close
rounded by dense vegetation so that they do to the road gives a casual atmosphere to even
not impair the scenic values of the beach. the busiest roads.
In this way the "natural" character of the
shoreline is preserved for all to enjoy, - In order to preserve the casual scenic
resident and visitor alike.' quality, future commercial uses should be
concentrated in pockets along the road,
A beach setback and buffer of dense vege- separated by recreational and residential
tation should be employed in any new de- uses in much the same manner as they are today.
velopment near the beach whatever the Existing trees or plants in the road right-of-
density or land use. In addition to the way should not be removed except where they
scenic impact, storm protection is enhanced are a traffic or storm hazard, are a nuisance,
by such a strategy. It also benefits or where necessitated by street improvements.
marine and wildlife that use the beach for If removal of trees becomes necessary, provi-
nesting and feeding. Restriction of buil- sion should be made for replacement with
ding heights to 45 feet above mean sea approved plant species. Vegetation buffers
level is also important with respect to should be established to preserve scenic
scenic preservation of the beach zones as quality even as further development or road
are several other regulations proposed for improvements occur. :Such buffers can also ac-

142 The Sanibel Plan

commodate bicycle and pedestrian paths. In com- include space for ornamental planting,
mercial areas, curb cuts should be kept to a bicycle and pedestrian circulation.
minimum and shell should be used in parking lots
instead of impervious paving such as asphalt. 4. Concentrate future commercial uses on
These standards will contribute to the preserva- Periwinkle Way and Sanibel-Captiva Road
tion of the "casual" retreat atmosphere and serve in pockets, rather than spreading them
safety and storm drainage purposes simultaneously out in a continuous strip.
Signs for commercial establishments should be 5. Encourage the use of shell surfacing for
clearly- legible, and integrated with the vegeta- : parking areas to maintain a casual re-
tion buffer. Neon and flashing signs should be treat atmosphere.
prohibited in all areas.
6. Integrate signs with the roadway buffers.
Three major cross-Island routes, Casa Ybel Road,
Tarpon Bay Road and Rabbit Road, provide a 7. Prohibit neon signs and flashing signs.
totally different experience of the Island's
various natural landscapes. These roads cross
through the heavily treed upland interior wet-
lands to the grassy lowland interior wetland and Part 2.4: Intergovernmental
the Sanibel Slough, to-the Gulf Beach Ridge and _
Gulf Drive. Vegetation buffers should be estab-o dination
lished, and residential uses should be concen- C
trated in upland areas where houses can be
screened by trees.
Part-2,5: Land Use
These standards for maintaining scenic quality
are consistent with other objectives of the
Comprehensive Land Use Plan, and are in many Section 2.5.1: Permitted Uses
cases, also recommended for other reasons
such as storm protection, traffic safety,
and water quality maintenance. The adoption A. BACKGROUND DISCUSSION
of specific standards for regulation of sce- The use of land and buildings in the City of
nic preservation will allow Sanibel to accom- Sanibel should be determined by the capacity
modate more urban growth while preserving the of natural and man-made environments to ac-
beauty of its natural areas and roadways. commodate such uses without hazard to health,
safety and welfare of the citizens and
visitors to the City. The determination of
B. THE PLAN FOR SCENIC PRESERVATION permitted uses also should take into account
The follow are the gene Iral policies for t .existing patterns of development and the need
to maintain compatibility with existing uses
scenic preservation and are implemented in as far as possible.
Article 3 of the Plan:
Historically the Island has developed as a
1. Vegetated buffers should be established
1~. �~v~egetated buffers .~ bresidential community catering to a fairly
where feasible along the Gulf and Bay
where feasible along the ulf and Bay wide income range with diverse dwelling types
Beaches up to a setback line. and small commercial and service establish-
ments that serve both the resident and tourist
2. Encourage dense vegetation within the population and also provide employment. In
beach buffer to screen development be- recent years there has been a significant in-
hind the setback line. Use hardy na- crease in the proportion and number of condo-
minium apartments, most of which are rented
tive plant species such as seagrape for a portion of the year as a conse-
which can withstand storm winds. gquence of rapid growth since 1970, new
commercial establishments have developed giving
3. Establish vegetated buffer strips on rise to shopping centers and "strip commercial"
major roadways. These buffers should development. These land use trends have

The Plan 143

generally utilized land more intensively than addition to recreation and conservation land
in the past and as a consequence greatly modi- uses, low intensity residential uses are
fied the natural environment. Traffic conges- permitted, and commercial use is permitted
tion, increased storm water runoff,'beach at one designated area near the Blind Pass
erosion air and water pollution and other Bridge.
negative impacts have resulted from such inten-
sive land uses and the visual character of the The Interior Wetlands include two ecological
Island has changed dramatically. zones. The uplands are the elevated ridges
of the wetlands that are generally not wet
The Comprehensive Plan provides that the type but are subject to occasional high water table
and intensity of future land uses permitted and flooding. The lowlands are subject to
shall be determined by the capacity of the seasonal high water table and generally wet,
Island to accommodate further development in an having plant materials and wildlife associated
orderly manner with minimum negative impact. with wetland ecology. In the Wetland Uplands,
In addition to these overall considerations, recreation, conservation, horticulture, agri-
environmental factors intrinsic to each ecolog- culture and low intensity residential uses
ical zone, compatibility with existing land uses, are permitted. Also commercial uses in desig-
availability of adequate human support systems nated areas, education facilities and public
'and compatibility with all elements of the Plan ' facilities. In the Wetland Lowlands recrea-
influenced the choice of permitted uses and tion, conservation, horticulture, and low
development intensity. Regulations pertaining intensity residential uses are permitted.
to permitted uses are described in 3.2.1 thru 8.
development intensity is described in 2.5.2. The Mid-Island Ridge Ecological Zone comprises
the major ridge along the center of the Island
The general principles on which the use regula- and includes the highest elevations. This
tions are based are as follows. In the Gulf factor plus its distance from both the Gulf
Beach Ecological Zone, permitted uses should be and the Bay, make it a relatively protected
restricted to recreation and conservation uses location for development; also the natural
that will not cause degradation of the natural environment is the least fragile and dynamic
environment, because this zone is a fragile and of any on the Island. Roads and other human
dynamic system providing;protection from storms, support systems are either in existence or
habitat for wildlife and recreational amenity planned for the Mid-Island Ridge, and the
for people. In the Gulf Beach Ridge, recreation historic pattern of development is that of
and conservation uses are encouraged, and-single mixed land uses at moderate and low densi-
family detached, attached, and multifamily resi- ties. Low intensity residential uses are
dential and resort housing and accessory uses permitted. Also commercial, restricted
are permitted. This zone is landward of the commercial, public facilities including
beach environment by virtue of a setback and is government offices, schools -and utilities
generally on land having an elevation of at least along with recreation and conservation are
five feet above mean sea level. It can accommo- permitted.
date various -land uses provided that they are in
moderate or low intensity and that standards for The Mangrove Forest Ecological Zone comprises
site modification and building construction are all areas having substantial growth of button-
designed to protect the natural environment and wood, red, black and white mangroves. Such
all property. It is the policy of the Plan not areas are generally low lying and wet, and
to permit further intensive urban development provide rich habitat for wildlife performing
in this ecological zone and that open space diverse and important ecological functions.
should be preserved to maximum degree feas- Land use permitted in the Mangrove Forest
ible. For these reasons on the Gulf Beach Zone are low intensity residential, recreation
Ridge moderate residential densities are - and conservation.
permitted along with accessory uses, selected
on the basis of compatibility with existing The Bay Beach Ecological Zone is also an
land uses and current or prospective avail- active beach zone, extending along the Island's
ability of human support systems such as Bay Shore line and delineated by a 50 foot set-
utilities and traffic access. back from the mean high water line at the
shore. Permitted uses are restricted to boat
The Special Blind Pass area is not currently docks, marinas, recreation, and conservation.
developed as intensively as the eastern
sections of the Island, nor does it have the The Filled Land Ecological Zone has been
same level of human support systems. In created artificially by disturbing natural

144 The Sanibel Plan

topography and vegetation for real estate Wetland Uplands
development. The areas delineated on the map .Recreation & Conservation
of Ecological Zones0 include the major area on .Public Facilities
the Island where such disturbance has taken .Educational Facilities
place, are generally at five feet elevation, .Commercial*
and have had the majority of natural vegetation .Restricted Commercial*
removed. Permitted uses in the Filled Land .Residential
Ecological Zone are moderate and low inten- .Single Family Detached
sity residential; Commercial and'Restricted .Duplex
Commercial in designated areas; public facil-
ities including government offices, schools, Special Blind Pass
utility and recreation facilities. - .Recreation & Conservation
.Public Facilities (beach oriented)
.Commercial*
The Comprehensive Plan provides for thercial
.Residential
above permitteduses to be developed in the .Single-Famil Detached
respective ecological zones subject to
development intensities specified in 2.5.2 .Duplex
and the provisions of,Article 3.

Gulf Beach Ridge
.Recreation & Conservation
B. THE PLAN FOR PERMITTED USES
.Public Facilities (beach oriented)
.Commercial**
.Residential
This section of the Plan discusses the .Single Family Detached
general principles from which futureper- .Duplex
mitted uses are derived, and it is the in- .Multi-family
tent of the Plan to permit the continuation .Resort Housing (in areas having a 3.0 or greater
of all existing uses. The regulations con- Development Intensity)
trolling permitted uses are set forth in
Article 3 of the Plan. Mid Island Ridge
.Recreation & Conservation
.Agriculture
.Public Facilities
.Commercial*
.Restricted Commercial*
PERMITTED USE- .Residential
- by ECOLOGICAL ZONE - .Single Family Detached
.Duplex
Multi-family
Gulf Beach
.Recreation & Conservation Filled Land
.Elevated Walkways
.Recreation & Conservation
Bay Beach .Agriculture
.Recreation & Conservation .Public Facilities
.Boat Docks & Marinas .Commercial*
.Restricted Commercial*
Mangroves .Residential
.Recreation & Conservation .Single Family Detached
.Residential .Duplex
.Single Family Detached .Multi Family
.Resort Housing (in areas having a 5.0 Development
Wetland Lowlands Intensity)
.Recreation & Conservation
.Public Facilities
.Agriculture
.Residential * in areas designated on the Permitted Uses map
.Single Family Detached ** as an accessory use to the Resort Housing

The Plan 145

valuable or hazardous areas should have pro-
Section 2.5.2: Residential:: X portionally less growth. The formula also
t eook into account capital investments al-
:D : f :leavelopment mnte nity ready made to prepare land for development and
the degree to which a project or subdivision
was improved and built out. Theresult of
this process allocated 2000 dwellings across
A. BACKGROUND DISCUSSION the Island in densities ranging from one
dwelling per thirty-three acres to three
dwellings per one acre depending upon the
location, ecological zone and the extent of
The constraints imposed by hurricane safety, improvement to the land. Once the units were
water supply and sewage disposal demonstrate allocated under the formula the Planning
general principles clearly that unlimited X Commission made adjustments taking into account
consideration of existing development patterns
to health, safety and welfare of the public. and the extent to which existing subdivisions
To minimize these hazards it is essential to and projects are consistentwith the-goals,
limit the total number of dwelling units - objectives, and policies of the Comprehensive
(including hotel andmotel units, trailer Plan. In some cases adjustments were made to
spaces, condominiums, duplexes and single ensure that the density allocation would not
family homes) to between six and seven \ permit higher densities than would be con-
thousand. This will represent a growth of sistent with the character of existing resi-
over 50% from the'4000 units established to dential areas.
exist in 1975.

No development is permitted in the beach set-
raeIf the dwelling contsumption andt sewage g back zones but these areas were allocated a
range the water consumption and sewage gener- residential density, all of which must be built
ation can probably be handled in a manner
consistent with the public health, safety and landward of the setback line.
welfare, based on present knowledge. Further
data could, of course, indicate a need to
reduce or increase these limits. Moreover,
by keeping the number of persons using the All of the adjustments had the aggregate effect
Island to these levels, it should be possible that allocated densities ranged from one
with careful planning to safeguard the lives dwelling per thirty three acres to five per
of the people on Sanibel and Captiva in case acre and possibility for 3,580 additional
of all but the most extreme hurricanes. dwellings under 100% build out conditions. A
more realistic projection is that approximately
two-thirds of this number will in fact be
built during the effective period of the Plan.
On this. basis the Comprehensive Plan is based
To allocate roughly 2000 new units throughout upon 6000-6500 total dwelling units in the
the City, the factors which determine the - -
appropriateness of various residential inten-
sities were analyzed including municipal
economy, physical land capability, and service
capability. Using an allocation formula (des-
sribed in the Appendix to the March 1976 B. PLAN FOR RESIDENTIAL DEVELOPMENTINTENSITY
draft of the CLUP) tentative density allocation
was prepared.
The distribution of residential development
intensity shall be in accordance with the
The formula took into account the relative density allocation on the Development Inten-
proximity of all areas to existing human sity Map at City Hall (the Development
support systems and to the ecological zones. Intensity Map in this section is a repre-
Policies were developed that future growth sentation of the official Development Intensity
should be directed to areas where services Map and is provided in this Plan for informa-
are available and that environmentally tional purposes only.

146 The Sanibel Plan

Section 2.5.3: Housing -

Section 2.5.4: Commercial
Development o
:D XvepmnPINE ISLAND SOUND
A. BACKGROUND DISCUSSION
In the course of evaluating the desirability of
various types of commercial development for the o
City of Sanibel studies were undertaken of the
commercial land use patterns of other cities of
a size similar to Sanibel, but it became appar-
ent that the existing experience of other com-
munities was not a logical pattern on which to
base the plan for Sanibel for a number of
reasons:

1. Unlike most communities Sanibel is located
at the end of a long, dead-end road and
therefore attracts almost no casual travel- o
lers passing through on their way elsewhere.
Thus Sanibel needs fewer of the typical
roadside type of commercial use than most
communities its size.

2. Sanibel attracts a unique blend of tourists \\\ :
with special interests (e.g. shell collectors,
fishermen, tennis players, etc.). Because
no other community attracts a similar mix of GULF CO
tourists, no other community provides a
pattern on which commercial land uses can be
based.

3. Residential accommodations for tourists
(which have often been included in the
category of commercial land uses) are under-
going a rapid metamorphosis. The distinc-
tion between temporary accommodations for
tourists and permanent residential accommo-
dations is becoming blurred as condominiums
offer short-term rentals and time sharing
plans while traditional resorts add larger
dwelling units and condominiums. Thus the LEGEND
past experience of any community may not be
a useful guide to its future.
EXISTING MOBILE HOME PARK

Given these unique circumstances of Sanibel RESIDENTIAL
and the rapid changes taking place in the (at densities permitted by Density Allocation Plan)
tourism industry, it is difficult to make
definitive, long-term projections about the RC COMMERCIAL
need for various types of commercial uses in Sc(uses as permitted by Commercial Zoning map)
Sanibel. Therefore the City should proceed n RECREATION: GOLF COURSE
cautiously, allocating enough land to permit
a limited number of additional commercial
uses, but not overzoning large areas for CONSERVATION
commercial purposes.

The Plan 147

SAN CARLOS BAY

TARPN BAY

.7DIN~~UNWILDLIFE REFUGE

PERMITTED USES

148 The Sanibel Plan

4. ~~~~~PINE ISLAND SOUND

1.0

GULF OF MAEXICO

REFUGE.I

LEG END

o NO DEVELOPMENT
.03 1 D.U. per 33.34 Acres .
.05 20.0
.1 I 10.0
.2 5.0
.3 3.34
.5 2.0
.7 1.43
1.0 1.0
1.5 0.67
2.0 0.5
2.2 0.45
2.9 0.35
3.0 0.34
4.4 0.23
6.0 0.17 Source: WMRT

The Plan 149

Because of Sanibel's isolation and small
size there is clearly .no need for such
C < - C commercial uses as warehousing, wholesaling
or other uses serving.a large region. As a
result the plan for commercial land uses is
restricted to retail/service uses and resort
housing.
Retail and Service Uses
The majority of retail and service uses
should be urged to concentrate in the
Commercial districts shown on the Permitted
Uses Map. Four such districts have been
mapped around existing commercial clusters
along Periwinkle Way running from Bailey
Road to the center of the Island, and each
contains substantial land available for
SAN CARLOS BAY additional commercial construction. One
small commercial district has been placed
at the west end of the Island to serve the
shopping needs of the people of Captiva and
, he isolated residences in the western sector
of the City.
4.4
To provide additional areas to meet the con-
venience shopping needs of Island residents,
several zones for restricted commercial uses
have been identified in areas that are access-
.OS605 .5*<\X , ible to residents, and small scale retail and
service uses not located in shopping centers
0 would be consistent with the ambience of the
area. One such Restricted Commercial (RC)
district has been mapped on the heavily
developed eastern end'of the Island. A
4.4 / second Restricted Commercial use is located
/ : 2.0; I 1 .2 i _ :j at the eastern boundary of the mid-island
Commercial area, in order to provide for a
transitional area leading in to the major mid-
.2.0 n . . . ' sR3 , island commercial area. Another small Pe-
stricted Commercial district has been so
located to serve the needs of residents in
the west central sector.

Restricted commercial districts permit most
ordinary retail and office uses but impose a
maximum floor area limitation of 1500 square
feet for most sturctures. There is no such
size limitation in the commercial district.

1.5 All of these districts in the aggregate provide
sufficient land for the retail and service needs
of the City for the near future.

Because of the unique nature of the City it is
difficult to estimate such needs far in ad-
vance. If the failure rate of retail and
service establishments increases it may be
N 0 100 3000 6000 ACRES necessary to reduce the commercially zoned
area. On the other hand, if a demand for more

such uses is apparent then additional land
could be added to thecommercial districts.

150 The Sanibel Plan

Resort Housing Many other areas in this state willingly pro-
vide for and eagerly solicit the trade of such
Another type of income-producing use in the visitors. But Sanibel offers unique charms,
City of Sanibel is resort housing. Prior to for which some people will pay a premium while
the construction of the Causeway such housing they exist--but if they are destroyed by over-
took the form of small fishing camps and use, the City will have little to offer.
beach resorts. The construction of the
Causeway brought more and bigger beach resorts. For this reason resort housing has been
identified primarily in the Gulf Beach
The late sixties saw a statewide boom in the Ridge areas and given a density of no
construction of condominiums extending into less than 3.0 per acre which may be calcu-
the early 1970's.Lee County permitted the con- lated to include land in the setback zone.
struction of numerous condominium complexes, These are the areas where such densities
some of which were constructed at locations can most easily be accommodated consistent
dangerously close to the water and built at with the overall land use Plan.
densities that detracted from the character
of the Island as a desirable living environ- iMany of the finer beach resorts in Florida
ment. and throughout the world have been developed
at low densities of five or six units per
By 1975 it was clear that a massive overbuild- acre. Such densities permit the provision
ing of condominiums had taken place throughout of amenities and services that will attract
the State. Despite special tax incentives more selective tourists willing to pay a
some 70,000 condominium units remained unsold. premium for Sanibel's special character.
A number of sizeable projects on Sanibel be- -'-
came insolvent and virtually unoccupied, I 0 Because of the changing nature of the tourism
creating-problems of policer and firen prcotecd - industry it is not easy to make distinctions
creatingproetionm and tax delinquency. ad fe between various types of resort housing at
the present time. However, to encourage the
Meanwhile, other condominium projects were construction of facilities having a unified
moving more and more into the resort hotel ownership and operation, only such facili-
business with widely advertised short term ties are to be permitted to operate restaur-
rentals. ants and shops as an accessory use. Access
to such accessory uses must be provided from
These dramatic and rapid changes in the nature within the resort complex ratherthan from
of the tourism business on Sanibel have had the street or public way.
numerous adverse impacts on the environment.
The entire character of the community as a low- B. PLAN FOR COMMERCIAL DEVELOPMENT
density settlement compatible with the natural
environment has been threatened. The unique Commercial Development should occur in the
environmental character of the island, which areas delineated on the Permitted Use Map
has provided the primary attraction for both and will be regulated by the requirements
tourists and permanent residents, is now in set forth in Article 3.
danger.
Nor is the option of converting the Island Secion 2.5: I stitution t
to an urbanized, high-density recreational 5 ec on tutions'
community along the lines of Miami Beach
worthy of serious consideration. The Island's Section 2.5.6: Recreation an
isolation would make it a highly uneconomic Section2 ,. e
competitor with heavily urbanized resort areas Open Sace
even on the unlikely assumption that the resi-
dents of the City someday choose that goal. A. BACKGROUND DISCUSSION

Clearly, then, the protection of the char- Federal, county, municipal, and private recrea-
acter and long range base of the tourism tion facilities and open space exist on Sanibel.
industry demands a significant reduction in The Federally owned and administered areas --
the density of resort housing accommodations. J.N. "Ding" Darling Wildlife Refuge, Lighthouse
The City has no desire to cater to tourists Point, the Bailey Tract, and the Perry Tract --
who,prefer to vacation in a high-density attract thousands of visitors from all over the
urbanized type of environment. country. Other areas in public ownership include

The Plan 11

Turner Beach and several picnic areas and beach all major streets and in the right-of-way within
access points, as well as the elementary school vegetation buffers.
which has a baseball diamond, basketball courts,
and a playground. Two private golf courses Considerable interest has been expressed in a
are planned and there are several private tennis center for youth and in public recreation facili-
courts and limited marina facilities open to ties for active sports such as baseball and foot-
the public for a fee. The Sanibel-Captiva ball. These facilities should be centrally lo-
Conservation Foundation owns extensive land cated. Recreation facilities should be associ-
in the interior wetland and maintains nature ated either with an existing center such as the
trails in one area. . Community Building or the school, or with a new
youth center. The Mid-Island Ridge Zone along
For a City its size, Sanibel appears to have an Periwinkle Way is particularly well suited to
abundance of certain types of recreation facili- intensive recreation uses. Although several
ties and open space. However, many of these. options exist for public acquisition and improve-
facilities are also used by the thousands of ment of land for active recreation, the Plan
tourists who come to Sanibel each year and by recommends a site in the middle of the Island
day visitors who come primarily to the beach as the preferred location.
or to the J.N. "Ding" Darling Wildlife Refuge.
Thus, despite miles of wide, white sandy beach
and 3500 acres in the "Ding" Darling Refuge, The Youth Center is needed to cater to young
Sanibel residents experience overcrowding of people for organized groups such as scouts
some recreation facilities during the peak E and other youth groups and for informal gather-
tourist season. Degradation of the dunes and ings of individuals. This should be located
beach ridge and inadequate parking at beach,. where active fun and noise would not be dis-
access points, hazardous bicycle routes and tracting to the pleasure of others -- near
insufficient facilities for youth are major Tarpon Bay at the west end. It could alterna-
problems of recreational deficiency on the Island tively be related to the Community Center where
today.: - the advantages of multipurpose indoor and out-
door space would allow such varied activities
The major shortage of suitable facilities area as dancing, arts-and crafts, continuing educa-
tion and informal relaxation. This is an ur-
is at the beach. Parking is inadequate and the tion and informanl relaxation. This is ammunity thatur-
dunes are eroded by constant foot traffic at the gent ne
more heavily used access points. Parking for caters to its young people.
cars and bicycles, restrooms, bathhouses, and
elevated walkway access to the beach should be
provided at the major access points. The dunes
and beach ridge and the dune and beach ridge Sanibel now has two marina facilities sufficient
vegetation should be restored. In order to limit to dock approximately 52 boats. Boating is par-
the number of visitors to the beach areas so ticularly popular in Florida and Sanibel offers
that overcrowding and degradation are minimized, uniquely fine recreational boating both in the
adequate beach access is provided in several Gulf and Bay. Fishing is exceptionally ood
areas of the Island so as to disperse the beach and there is ample variety of choice for the
usage over a wider area and reduce the over- pleasure boater who wishes the tranquility and
usaro wding of specific locations. solitude of being out on the water. In order
crowding of specific locations. to meet continued demand for boating facilities
for the next increment of population growth on
famous beaches and otherfresources. This is a Sanibel, it is proposed that permits be granted
famous beaches and other resources. This is a
for 50% additional boat slips and support facili-
major impact on the Island and must be planned ties.
for so that the social and environmental values
are protected and so that the commerce generated
by such visits can be a benefit to the City and
its residents.
In the recreation plan, priority should be given
Bicycle paths have been marked along selected to solving the problems of beach access and
Sanibel roads. These are presently very hazard- parking and to bicycle paths, since both these
ous because there is insufficient space for have important public safety elements. Secondly,
bicycles on many roads which are presently planning for a youth center and public recreation
carrying very high volumes of automobile traffic. facilities should be initiated and acquisition of
Bicycle paths should be outside the pavement of land for these facilities considered.

152- The Sanibel Plan

Cost estimates for the Recreation Element are 5. Restore dunes and beach ridges and dune and beach
summarized as follows: ridge vegetation in areas of erosion near the
beach access points.
1. Parking provision for 1000 cars:
6. Explore further the needs and funding
i - 10 lots approximately 1 acre each, requirements for a youth center on Sanibel.
land at $15,000/ac $150,000 Implement a planning program to provide this
facility within five years.-
ii - grading and surfacing with
shells, markers, etc. at $.50 7. Provide centrally located additional public
per foot, 10 lots @ $20,000 recreation facilities for active sports.
each - 200,000 X This item to be given first priority.
Subtotal i: $350,000
8. Grant permits for 50% additional boat
2. Shelters, restrooms and changing slips and support facilities provided
rooms: that no additional inlets be cut from the
Gulf or Bay.
i - 5 structures @ $20,000 each 100,000
ii - 5 access boardwalks to 9. Investigate alternative sites for providing marina
beach 25,000 facilities on Sanibel.
Subtotal ii $125,000
3. Active recreation park: Section 57: on er ati
Section2.5.7: Conservation
i- - 4 tennis courts @ $8,0000 $32,000
2 hard court areas 16,000
other play areas and equip-on 2.5.8: Community Designt
ment 22,000
ii - play fields, grading and
equipment 50,000
iii - land cost 80,000

Subtotal iii:P $200,000 ARTICLE 3: DEVELOPMENT
TOTAL: $675,000 X REGULATIONS
Costs for the Youth Center are not included in
this estimate because of inadequate information
regarding sites and program. Part 3.1: Definitionst

B. PLAN FOR RECREATION AND OPEN SPACE Part 3.2:t M p t
Part 3.: Maps'
1. Maintain existing recreation facilities.
2. Maintain and identify all existing beach Part .: General
access easements and restrict public
access across private property except
where such easements exist.
3. Provide parking at selected beach access
points, also restrooms, bathhouses, Part 3.4: Permitted Usest
bicycle parking, and an elevated walkway

access to the beach.: :: Part 3.5: Subdivisionst
4. Provide bicycle paths throughout the
Island outside the pavement of major and
streets and in the right-of-way within Part : Mobile nomes
the vegetation buffers. (see Section
2.2.2) Recreation Vehiclest

The Plan -153

;art 37f:-Flobd tod to be elevated to 13.5 feet mean sea level,
Part 3.7: Flood and Storm : : - all utility service systems shall be flood
proofed to at least the first habitable
Proofing floor;
5) provides that all utility facilities be
flood proofed to at least 13.5 mean sea
Section 3.7.1: Flood Proofing level.

A deve opment permit ha d emonstrated that the Section 3.7.2: Certification of Flood-
proposed development: Proofingt
1) provides for the elevation of the
lowest floor to be used for habitation
or commercial purposes of all new con- Section 3.7.3: Emergency Shelter
struction or substantial improvements Spacet
of existing buildings:
a) to or above 13.5 feet mean sea
level in all areas within five Section 3.7.4: Emergency Water
hundred (500) feet of San Carlos
ay, Pind Ithsland ulfof Mexico.nd Section 3.7.5: Non-resident Structurest

b) in all other areas of the Island
to or'above 7;5 feet mean sea
level until the Administrator of Part 3.8:- Site Preparation
the National Flood Insurance
program has provided surface ele-
vations for the 100- year flood Site
then to or above the elevation Section 3.8.1: Site Preparation
specified as the level of the
100 year flood
In addition to all other standards of the Comprehen-
2) provides that any portion of any new sive Plan any development which is carried out within
construction or substantially improved the'City of Sanibel shall be subject to the following
building required to be elevated to or standards during development:
above 13.5 feet mean sea level that
portion of the structure which is below 1) During development and construction, ade-
13.5 feet mean sea level will only be quate protective measures shall be provided
used for parking, storage, utility rooms, to minimize damage from surface water to
workshops and other uses normally asso- the cut face of excavations or the sloping
ciated with accessory buildings, surfaces of fills.
3) provides that any portion of any new con-
struction or substantially improved building 2) Erosion and sediment control measures.
required to be elevated to or above 13.5 shall be coordinated with the sequence
feet mean sea level which is below 13.5 of grading, development, and construc-
feet mean sea level with the exception of tion operations. Control measures such
support pilings shall be constructed of as hydrxoseeding, berms, interceptor dit-
"breakaway" or other material which will ches, terraces, and sediment traps, shall
allow storm-driven wind and water to pass be put into effect prior to the commence-
through the lower portions of such buildings ment of each increment of the development/
without threatening the integrity of the construction process.
slevated portions of the building;
3) Sediment basins (debris basins, desilting
4) provides that in any new construction or basins, or silt traps) shall be installed
substantially improved building required in conjunction with the initial grading

154 The Sanibel Plan

operations and maintained through the
development process to remove sediment Part 3E9: Environmental
from runoff waters draining from land
undergoing development.

4) Soil and other materials shall not
be temporarily nor permanently stored
in locations which would result in Section 3.9.1: Development in the
the unnecessary destruction of vege-
tation. Gulf BeachGulf Beach

5) The permanent vegetation shall be Ridge and Special Blind
installed on the construction site as Pass Zones
soon as utilities are in place and
final grades are completed.
A development permit shall be granted for develop-
6) Final grading and removal of vegetation ment or site alteration only if the applicant can
shall not occur more than 30 days demonstrate that the proposed development or site
prior to scheduled finishing. alteration:

7) All on-site facilities shall be properly
maintained by the owner so that they
do not become nuisances. Nuisance 1) will not result in diminution in the amount
conditions shall include but not be of sand, silt, shell, sediment, or other
limited to: improper storage re- geologic component which make up the beach,
sulting in uncontrolled runoff and or interfere with natural patterns of wind
overflow; stagnant water with concomitant and water movement of sand, silt, shell, sedi-
algae growth, insect breeding and odors; ment or other geologic components of the beach;
discarded debris; unnecessary noise; and
safety hazards created by the facility's 2) will not result in the removal of sand, silt,
operations. shell, sediment or other geological component
of the Gulf Beach Ridge, reduce the elevation
8) Construction waste materials or construction of any portion of the ridge, or otherwise alter
by-products shall be controlled on site to the natural configuration of the ridge in a man-
prevent nuisance and shall be disposed of ner that diminishes the effectiveness of the
in the same manner as other solid waste. ridge as a protective barrier against storm
surge;

Hydrology
3) provides for the gradual and dispersed
drainage of surface runoff such that
runoff within the boundaries of the
parcel proposed for development will
approximate natural rates, volumes and
direction of flow; included shall be
a requirement for containment on site
of the runoff from a 5 year storm (un-
less otherwise provided in common with
other site); and further, coverage with
impermeable surfaces shall be no greater
than 20% of the gross area of the parcel
proposed for development;

4) will not disturb, break or penetrate the
aquiclude or clay layer at the bottom
of the freshwater lens, permit salt-
water intrusion or otherwise endanger
the integrity of the freshwater lens.
If in order to comply with the flood

The Plan 155

proofing regulations of this Plan it 10) provides that all landscaping will only
is necessary toqdrive pilings below involve the use of native- species of
the level of the aquiclude, such plants or exotic species which do not
penetration shall be sealed according outcompete or otherwise displace na-
to the best technology available to tive species of plant,
avoid saltwater intrusion;
Wildlife
5) will not involve the use of a septic
tank unless the design and location 11) will minimize any necessary inter-
of the proposed disposal system is in ference with the natural use of the
strict compliance with Section 10D-6 beach for feeding, foraging, resting,
of the State Sanitary Code, as inter- nesting and breeding by indigenous and
preted by the City Manager; further, migratory birds, shellfish, marine fishes,
any existing or proposed residential sea turtles and other wildlife. Such
or other use which generates sewage or interference shall include the destruc-
other waste water shall be connected tion or diminution of organisms or
to a sewer whenever such service be- material upon which wildlife feed.
comes available as determined by the City;

6) will not result in the discharge of treated or Miscellaneous
untreated sewage or other human waste from 12) will not interfere with the customary
a boat into the waters of the City of Sanibel. rights of the public to access to and
use of the active beach.
Vegetation

7) will not result, in areas seaward of the
Coastal Construction Setback Line, in the Section 3.9.2: Development in the
direct or indirect removal, destruction, InteriorWetIand Zone
depletion or digging out of vegetation
which contributes to beach stability, in-
cluding but not limited to Sea Oats, Uniola
paniculata; Fingergrass, Chloris glauca: A development permit shall be granted for
Railroad vine, Ipomea pescaprae; Sea purs- development or site alteration in the Interior
lane, Sesuvium portulacastrum; and Seagrape, Wetland Zone only if the applicant has demon-
Coccoloba uvi feraj; strated tha-t the proposed development or site
alteration:
8) will not involve, in areas landward of the
Coastal Construction Setback Line, the un- l
n ecessary removal of native vegetation which 1) provides that all construction, excavation
necessary removal of native vegetation which
or improvement of any natural or artificial
stabilizes soils, serves as a buffer to body of water will re sult in:
storm surge, and provides wildlife habitats- body of water will result in:
as identified in 3.1.9 (11k in no case shall
a) a depth of greater than 4 feet during
greater than 30% of the gross area of any the lowest water stage of the year in
parcel proposed for development be cleared order to restrict the growth of roote d
unless the additional area is covered with order to restrict the growth of rooted
the Australian pine, Casuarina; the-Brazilian aquatics such as cattails;
pepper, Schinus terebinthifolius; or Melaleuca,llll
Melaleuca quinquenervia. Any portion of the
parcel in excess of 30% which is so cleared produce maximumwater movement by pre-
shall be revegetated with native or non- vailing winds;
competing exotic species of plant which stabil-
2) provides for the gradual and dispersed
ize soil and serve as a storm buffer; drainage of surface runoff such that run-
9) provides for the removal of exotic species off within the boundaries of the parcel
of plant which outcompete or otherwise displace natural rates development will approximate
native species including the Brazilian pepperal rates, volumes and diretion of
or Florida holly, Schinus terebinth-
or Florida holly, Schinus terebinth- flow; included shall be a requirement for
ifolius; the Cajeput or Punk tree, containment on site of the runoff from a
Melaleuca quinquenervia, within the 5 year storm (unless otherwise provided
boundaries of the parcel proposed for in common with other site); and further,
development or site alteration; coverage with impermeable surfaces shall

156 The Sanibel Plan

be no-greater than 10% of the gross area 8) provides for the removal of exotic species
of the parcel proposed for development of plants which outcompete or otherwise dis-
in the Wetland Lowlands and 20% of the place native species including the Brazilian
gross area of the parcel proposed for pepper or Florida holly, Schinus terebinthi-
development in the Wetland Uplands; folius; and the Cajeput or Punk tree, Mela-
leuca quinquenervia, within the boundaries
3) will not impede, impound or otherwise of the parcel proposed for development or
interfere with the natural flow of water site alteration.
in the Sanibel River or Slough;
9) provides that all landscaping will only
4) will not disturb, break or penetrate the involve the use of native species of plant
aquiclude or clay layer at the bottom of or non-competing species of plant ;
the freshwater lens, permit saltwater in-
trusion or otherwise endanger the inte- Wildlife
grity of the freshwater lens. If in order
to comply with the flood proofing regula- 10) will minimize any necessary interference
tions of this Plan it is necessary to drive with the natural use of the interior wetlands
pilings below the level of the aquiclude, for feeding, foraging, resting, nesting and
such penetration shall be sealed according breeding by indigenous and migratory birds,
to the best technology available to avoid shellfish, fishes and other wildlife. Such
saltwater intrusion; interference shall include the destruction
or diminution of organisms or material upon
5) will not involve the use of a septic tank which wildlife feed;
unless the design and location of the
proposed disposal system is in strict com-
pliance with Section 10D-6 of the State Wildfire
Sanitary Code, as interpreted by the
City Manager; further, any existing 11) includes safeguards against wildfire, and
or proposed residential or other use if possible is designed in a manner to
which generates sewage or other waste permit use of controlled fire in- the interior
water shall be connected to a sewer
whenever such service becomes availableing nd
as determined by the City' Evegetation and of destroying accumulated
as determined byQ the Citynatural debris which represents a wildfire
6) will not result in the discharge of hazard.
treated or untreated sewage or other
human waste from a boat into the waters
of theC"ity of Sanibel.:: �- X 7 Section 3.9.3: Development in the
Vegetation Mid-Island Ridge Zone
7) will not involve the unnecessary re-
moval of native vegetation which sta- A development permit shall be granted for
bilizes soils, increases recharge and development permit s hall be granted for
bilizes soils, increases recharge and
provides wildlife habitats; in no case development or site alteration in the Mid-
shall igreater than 20% in Wetland Low- Island Ridge Zone only if the applicant has
shall greater tn 20%in Wetland Lo- demonstrated that the proposed development
lands and 30% in the Wetland Uplands or site alteration:
of the gross area of any parcel pro-
posed for development be cleared unless
the additional area is covered with the
Australian pine, Casuarina; the Brazilian
pepper, Schinus terebinthifolius; and the Geology
Melaleuca, Melaleuca quinquenervia. Any 1) will not result in the permanent unnecessary
portion of the parcel in excess of 20% in lowering of the natural elevation of any
the Wetland Lowlands and 30% in Wetland portion of the parcel proposed for develop-
Uplands which is so cleared shall be re- ment by excavation, digging, grading, or A
vegetated with native non-competing exotic other removal of sand, silt, shell, or
species of plant which stabilize soil, in- soil, except for the installation of
crease recharge and provide wildlife habitats; swimming pools.
x ,~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Plan 157

Hydrology native or non-competing species of::plant;
2) provides for the gradual and dispersed 7) provides for the removal of exotic species of
drainage of surface runoff such that plant which outcompete or otherwise displace
runoff within the boundaries of the par- native species including the Brazilian pepper,
cel proposed for development will approx- or Florida holly, Schinus terebinthifolius,
imate natural rates, volumes and direction the Cajeput or Punk tree, Melaleuca cuinque-
of flow; included shall be a requirement nervia within the boundaries of parcel pro-
for containment on site of the runoff
from a 5 year storm (unless otherwise posed for development or site alteration.
provided in common with other'site); and
further, coverage with impermeable surfaces
shall be no greater than 30% of the gross Section 3.9.4: Development in the
area of the parcel proposed for develop-
ment; Mangrove Forest Zone

3) will not disturb, break or penetrate the
aquiclude or clay layer at the bottom of A development permit shall be granted for
the freshwater lens, permit saltwater intrusion development or site alteration in the Mangrove
or otherwise endanger the integrity of the Forest Zone only if the applicant has demon-
freshwater lens. If in order to comply with strated that the proposed development or site
the floodproofing regulations of this Plan it
is necessary to drive pilings below the level
of the aquiclude, such penetration shall be Geology
sealed according to the best technology
1) will not result in the permanent lowering
available to avoid saltwater intrusion;
of the natural elevation of any portion of
the parcel proposed for development by ex-
4) will not involve the use of a septic tank
cavation, ditching, dredging, digging, filling
unless the design and location of the proposed
or other disturbance of sand, silt, soil,
disposal system is in strict compliance with sediment, accumulated detritus, or other
Section O10D-6 of the State Sanitary Code, as
geologic or biologic component of the mangrove
interpreted by the City Manager; further any
existing or proposed residential or other use
which generates sewage or other waste water
a) maintain freshwater levels in the interior
shall be connected to a sewer whenever such wetland;
service becomes available as determined by
b) protect the health, safety and welfare of
the City; the City from disease-carrying insects;

5) will not result in the discharge of treated . c) manage the mangrove forest as a viable
or untreated sewage or other human waste natural community.
from a boat into the waters of the City of
Sanibel.
Hydrology

Vegetation .:: : : 2) will not restrict, impede, impound or other-
wise interfere with the tidal flow or in-
6) will not involve the unnecessary removal of fluence in the mangrove forest, or similarly
native vegetation which stabilizes soil and interfere with drainage in the mangrove
provides wildlife habitats; in no case shall forest;
greater than 30% of the gross area of any
parcel proposed for development be cleared 3) provides for the gradual and dispersed
unless the additional area is drainage of surface runoff such that runoff
covered with the Australian pine, Casuarina; from within the boundaries of the parcel pro-
the Brazilian pepper, Schinus terebinthifolius; posed for development will approximate
and the Melaleuca, melaleuca quinquenervia. natural rates, volumes and direction of flow;
Any portion of the parcel in excess of 30% included shall be a requirement for containment
which is so cleared shall be revegetated with on site of the runoff from a 5 year intensity

158 The Sanibel Plan

storm and further, coverage with impermeable breeding by indigenous and.migratory
surfaces shall be minimized and in any event birds, shellfish, fish and other indigen-
shall not exceed 1% of the gross area of the ous wildlife. Such interference shall
include the destruction or diminution of
parcel proposed development organisms or material upon which wildlife feed.

4) will not disturb, break or penetrate the
aquiclude or clay layer at the bottom of the
freshwater lens, :permit saltwater intrusion Section 3.9 eelpment
or otherwise endanger the integrity of the Affecting theRBay
freshwater lens. If in order to comply with Beach Zone
the floodproofing regulations of this Plan Beach Zone
it is necessary to drive pilings below the
level of the aquiclude, such penetration
A development permit shall be granted for de-
shall be sealed according to the best tech- velopment or site alteration in the Bay Beach
nology available to avoid saltwater intru- Zone only if the applicant has demonstrated that
sion; the proposed development or site alteration:
5) will not involve the use of a septic
tank or other mechanisms or devices Geology
that could result in the discharge of
sewage or other waste within the 1) will not result in the diminution in the
Mangrove Forest; amount of sand, silt, shell, sediment or
06) will not result in tthe discharge oft 0 0 0 0 0 other geologic component which make up the
6) will not result in the discharge of
treated or untreated sewage orother beach, or interfere with natural patterns of
treated or untreated sewage:or other
nhuman waste from a boat into the waterswind and water movement of sand, silt, shell,
human waste from a boat into the waters
sediment or other geologic component of the
of the City of Sanibel.beach.

Vegetation Hydrology

7) twill fnot0 involve the unnecessary rev- : 00 0 2) provides for the gradual and dispersed drain-
moval of any native vegetation which age of surface runoff such that runoff within
s;gexists as a natural buffeor prto storm f : the boundaries of the parcel proposed for de-
surge, stabilizes soils or provides
gwildlife habietats, sinoludinsr but not velopment will approximate natural rates,
volumes and direction of flow; included shall
limilted tot Red mangrove,: iRhizophora be a requirement for containment on site of
mangle; Black: mangrove,: Avicenniau the runoff from a 5 year storm, (unless other-
lgermlnns; and White mangrove, Laquncu- wise provided in common with other site); and
laria racemosa further, coverage with impermeable surfaces
shall be no greater than 10% of the gross area
8) provides for the removal of exotic of the parcel proposed for development;
species of plant which outcompete or
otherwise displace nat'ive.species includ- 3) will not involve the use of a septic tank or
ing the Brazilian pepper or Florida other mechanisms or devices that could result
holly, Schinus terebinthifolius; the in the discharge of sewage or other waste
Cajeput or Punk:tree, Melaleuca quinque- within the Bay Beach;
nervia within the boundaries of the parcel
proposed for development or site altera- 4) will not result in the discharge of treated or
tion, untreated sewage or other human waste from
a boat into the waters of the City of
9) provides that all landscaping will onlyboa t i nto the waters of the City ofbe
involve the use of native species of
plant or non-competing species of plant.
Vegetation
Wildlife
5) will not result in the direct or indirect
10) will minimize any interference with the removal, destruction, depletion, or
use of the mangrove forest for feeding, digging out of natural vegetation which
foraging, resting, nesting, shelter and contributes to beach stability, including

The Plan 159

but not limited to Sea oats, Uniola aquatics such as cattails;
paniculata; Fingergrass, Chloris qlauca;
Railroad vine, Ipomea pescaprae; Sea b) a bottom slope and alignment that will
purslane, Sesuvium portulacastrum; Red man- produce maximum water circulation.by
grove, Rhizophora mangle; Black mangrove, prevailing winds;
Avicennia germinans; White mangrove,
Languncularia racemosa; and Seagrape, 2) provides for the gradual and dispersed drain-
Coccoloba uvifera; : age of surface runoff such that runoff from
within the boundaries of the proposed devel-
6): provides: for the removal of exotic species opment will approximate natural rates, volumes
of plant which outcompete or otherwise and direction of flow; included shall be a
displace native species including the requirement for containment on site of the
Brazilian pepper or Florida holly, Schinus runoff from a 5 year storm. (unless otherwise.
terebinthifolius; the Cajeput or Punk Tree, provided in common. with other site); and
Melaleuca quinquenervia within the boundar- further, coverage with impermeable surfaces
ies of parcel proposed for development or shall be no greater than 30% of the gross
site alteration; area of the parcel proposed for development;

7) provides that all landscaping will only 3) will not disturb, break or penetrate the
involve the use of native species of plant aquiclude or clay layer at the bottom of
or non-competing species of plant. the freshwater lens, permit saltwater intru-
sion or otherwise endanger the integrity
of the freshwater lens. If in order to comply
with the floodproofing regulations of this
8) will minimize any necessary interference Plan it is necessary to drive pilings below
with the use of the beach for feeding, the level of the aquiclude, such penetration
foraging, resting, nesting: and breeding by shall be sealed according to the best technol-
indigenous and migratory birds, sea turtle, ogy available to avoid saltwater intrusion;
shellfish, marine fishes and other wildlife.
Such interference shall include the destruction 4) will not involve the use of a septic tank
or diminution of organisms or material upon unless the design and location of the proposed
which wildlife feed, disposal system is in strict compliance with
Section 1OD-6 of the State Sanitary Code;
Miscellaneous as interpreted by the City Manager; further
any existing or proposed residential or other
9): will not interfere with the customary rights use which generates sewage or other waste
of the public to access to and use of the water shall be connected to a sewer when-
beach. ever such service-becomes available as
determined by the City;

5) will not result in the discharge of treated
Section 3.9.6: Development in the or untreated sewage or other human waste
from a boat into the waters of the City of
Filled Land Zone Sanibel.

Vegetation
A development :permit shall be granted for de-
velopment or site alteration in the Filled Land 6) will not involve the unnecessary removal
Zone only if the applicant has demonstrated that of native vegetation which stabilizes soils,
the proposed development or site alteration: : increases recharge and provides wildlife
habitats; in no case shall greater than 30%
Geology-Hydrology of the gross area of any parcel proposed for
development be cleared unless the additional
1) provides that all construction, excavation area is covered with the Australian pine,
or improvement of any naturaor r artificial Casuarina; the Brazilian pepper, Schinus
body of water will result in: terebinthifolius; and the Melaleuca, Melaleuca
quinquenervia. Any portion of this parcel
a) a depth of greater than 4 feet during in excess of 30% which has been cleared shall
the lowest water stage of the year in be revegetated with native or non-competing
order to restrict the growth of rooted exotic species of plant which stabilize soil,

160 The Sanibel Plan

increase recharge and provide wildlife habitats; Part 3.10: Paved Surface

7) provides for the removal of exotic species o -
of plant which outcompete or otherwise Construction Standards
displace native species including the
Brazilian pepper or Florida holly, Schinus
terebinthifolius; the Cajeput or Punk tree,
Melaleuca quinquenervia within the boundaries Section 3.10.1: Paving Materials
of the parcel proposed for development or -
site alteration;
In order to reduce surface runoff, attendant
8) provides that all landscaping will only- erosion and degradation of water quality, all
involve the use of native species of plants paved surfaces shall be constructed of permeable
or exotic species which do not out-compete nor material as is best practicable taking into
otherwise displace native species of plant account the intensity of use anticipated and
best engineering and construction practices.
When paved surfaces are required they shall
Section 3.9.7: Coverage and Clearance be constructed of asphalt, or other material
of equal durability, and shall be constructed
in* Commercial Districts in accordance with City standards.

In those areas designated as Commercial C on the
permitted uses map:
1) Notwithstanding the provisions of any other
section of this part, a developer of a
commercial use in an area designated as
Commercial District C on the Commercial ARTICLE 4: ADMINISTRATIVE
Districts Map may: REGULATIOS t

a) cover up to 50% of the gross area of
the parcel proposed for development
with impermeable surfaces; and

b) clear vegetation from up to 50% of
the gross area of the parcel proposed
for development.

2) Any developer of a commercial use desiring
to clear in excess of that permitted or
required in the ecological zone in which
the proposed development is located as
provided by this section shall prepare a
site plan indicating the vegetation to be
removed. Any rare vegetation or other
particularly valuable stands or examples
of vegetation shall be preserved in the
50% of the parcel that is not cleared.

The Plan 161

WA ~~ECOLOGICAL
0~~~c
'ZONES: HISTORIC
GULF BEArCH FRONT BEACH
PINE ISLAND SOUND~~~~~~~~~~~~~~~~~~~~~~~~~[ GULF BEAH; BACK BEACH
[BYBEACH
MANGROVES
SAN CARLOS ~~~~~~~INTERIOR WETLAND BASHIN LOWLAND
SAN CARLOS/BAY H~~~ INTERIOR WETLAND BASIN, UPLAND
aw~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GULF BEACH RIDGE
[] GULF BEACH RIDGE; BLIND PASS AREA
MID-ISLAND RIDGE$

CITY

SANIBEL
GULF OF MEXICO ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~LEE COUNYLORIDA
PREPARED BY.
WMRT - WALLACE, M-.HARG. ROBERTS -TOD
PLANNSERS PH-LADELPHI-A PA

163

A pThe

:SiL~e

165

APPENDIX1

HYDROLOGY 167
Area Description 167 Intrusion Through Canals 183
Climatic Conditions 168 Tidal Overtopping 1 84
Rainfall 168 Upward Leakage from the Shallow
Hurricanes and Tropical Storms 169 Artesian Aquifer 184
Geologic Setting 169 Intrusion from Deep Artesian Aquifers 184
Deep Geology 169 Intrusion Related to Pumping and
Shallow Geology 170 Other Construction Procedure 185
Ground-water System 171 The Hydrologic Cycle i 85
Deep Artesian Aquifers 172 Water Budget of the Interior Wetlands 186
Shallow Artesian Aquifer 174 Inflow Factors 187
Water-Table Aquifer 175 Outflow Factors 188
-Surface Water System 177 Mass Balance of the Annual Water Budget 190
Present Interior Drainage System 178 Annual Water Storage in the Interior Wetlands 190
Stage and Flow 179 Conclusions 191
Water Quality 179 Recommendations 191
Ponds, Real Estate Lakes,.Excavations 181 Summary 192
Saline Water intrusion 182 Acknowledgments 192
Density or Ghyben-Herzberg Intrusion 183 Literature Cited 192

167

APPENDIX 1

HYDROLOGY

by Thomas M. Missimer

For many years, Sanibel- Island, numerous detrimental effects on the to the north. The island has a curved
Florida, has been an attraction to natural environment. If the unique shoreline with the convex portion fac-
both tourists and shell collectors natural environment on the island is ing south and generally has an east-
alike. In the past decade tourism to be preserved for the enjoyment of west axis. It comprises a land area
and urban development have rapidly the present and future generations, of 10,730 acres (Veri and Warner, 1975)
grown on the island (WRT, 1975). proposedmodifications to the hydro- or about 18 square miles (Missimer
During this time periodthe nat- logic system must be carefully eval- 1973a).
ural hydrologic system on the island uated before being permitted.
has been modified so as to provide a The island consists dominantly of
more comfortable environment for The acceleration of urban develop- numerous sets of individual beach ridges
residents and visitors. These modi- ment in the 1970's has necessitated with intermediate swales as described
fications include: the excavation the need for detailed information with by Missimer (1973a; 1973b). Land sur-
of drainage ditches for mosquito reqard to the natural and man-altered face on most of Sanibel lies three to
control purposes, the excavation of hydrologic system on Sanibel Island. five feet above mean sea level with
canals to provide boat access to It is the purpose of this report to the highest point being nearly 11
tidal water bodies, the excavation provide a concise summary and interpre- feet above mean sea level near
of real, estate lakes to provide tation of the available hydrologic data Wulfert (Figure 2). High beach
fill material to raise the land from Sanibel Island with emphasis on ridges at Wulfert and others ex-
surface altitude, the construction criteria for proper management of the tending along the Sanibel-Captiva
of paved roadwaysfor transportation, water resources. A detailed scientific Road to the east form a topographic
the construction of shallow wells for analysis of all data is beyond the high, which is a surface water
irrigation, the construction of deep scope of this report. drainage divide. A similar set of
artesian wells to provide water for high beach ridges causes a drainage
municipal supply, and implacement of divide to occur in the south running
septic tanks. AREA DESCRIPTION parallel to Gulf Drive on the west
of Tarpon Bay Road and nearly
Most of the modifications to the Sanibel is a barrier island located parallel to the shoreline on the
hydrologic system on Sanibel Island along the southwest Florida coast (Fig- east side. The area between these
have been effective in their purposes, ure 1). It is the southernmost island surface water divides consists of
but these modifications have also had in a chain that extends about 50 miles low-lying beach ridges and swales

168 Appendixes

82ls5' 8200' 8e45g
1I I 82012' 30" 10 7'30 5 2'30" 800
1 ~ -:: $ ClA*R"LOTTE e2630' I I

26o4,' -- RtarE M)R80 9

~~~~~~L E

:o3 :730" - EXPLANATION
APPROXIMATE BIUNDARY

ThelCity on SanibeL has IS untr

; E The City of Sanibel has a subtropi- standard 8-inch type, but Station 2
cal climate with an estimated average is also equipped with an automatic
(trom perature 1974� g

Fig.Lush vegetation covSanibelsland Fig 2- Map showing theroad network interior drainage system, perainfall gauge locations andgeneral geographic
the natural parts of Sanibel. Man- 4a). occurs averatghe temmperhature of about accurate of the two.lslando
and isa s dthe "inaterior gwet-h 83F ours over the month of August andlocatedear

ands." The Snbel Slow-lying nor thern shore, in the anuary. In Lee County, about 70 percent
vicinity of Blind Pass, and in iso- A"killing" frost occurs once every few of the total annual rainfall occurs
lated parts of the interior wet- years a sub(Propvo stadard 8nh type , June through.
The higher beach ridge areasc cA prevailing mild easterly wind the annual total occurs during the
Ltai various shrubs, trees,and blows across Sanibel most of the yeare
grove swamp is dominantsalong the 83,F occurs over the month of August and

grasses while the wetland areas except during the passing of winter (Missimer and Boggess, 1974). This
contain marsh species (See Alexander, frontal systems and tropical storms. same rainfall occurs on
(1975). A more complete discussion of climate Sanibel Island as is shown in Table 1,
totals are shown for Stations 1 and 2
on Sanibel and for Page Field near
In the natural state, the only Fort Myers.
non-tidal surface water bodies on RAINFALL
Sanibel were some isolated raponds Daily rainfallis monitored by Most of the rainfall on Sanibel
located in mthedeeper swales and the the U.S. Geological Survey at two Island, like the mainland, occurs
Sanibel Slough. Today the island locations on Sanibel Island. Station 1 during sporadic thunderstorms, which
contains-numerous man-made lakes, ponds, is located at the home of Mr. Robert occur randomly throughout the wet
canals and ditches. England on the eastern part of the season. During the early part of

Hydrology 169

last documented storm which completely
flooded the island with seawater
1971 1972 1973 1974 1975 - occurred in 1926 and was responsible
,S#l S#2 P.F. S#1 S#2 P.F. S#l S#2 P.F. S#1 S#2 P.F. S#l S#2 P.F. for the failure of agriculture on the
Jan. 2.45 - 0.85 1.32 1.19 0.77 3.60 3.16 3.14 0.03 0.08 0.36 07 .3 0.26 island (Warner, 1975)
Other intense hurricanes which
Feb. 1.90 - 1.55 2.07 1.77 2.14 2.37 1.19 2.23 0.51 0.42 0.81 0.62 0.38 0.27 caused significant tidal flooding
occurred in 1921, 1910, 1894 and
Mar. 0.14 - 0.55 5.35 4.75 4.72 4.02 3.12 3.89 0.00 0.00 0.03 0.90 0.67 1.47 1873.
Apr. 0.90 - 0.70 0.00 0.00 0.27 1.43 1.57 1.71 0.56 0.27 0.11 1.25 0.97 0.80
During the time period 1830
May 1.33 - 3.97 0.52 0.57 5.20 2.15 0.23 0.78( 3.44 1.95 2.40 3.97 2.79 2.78 to 1968, 23 hurricanes and 23
tropical storms or depressions
Jun. 2.67 - 6.18 7.82 7.34 7.86 6.13 5.39 3.99 18.94 16.26 20.10 2.11 2.29 12.35 passed within 50 miles of Lee
Jul. 3.59 - 9.50 3.84 3.57 9.72 5.87 7.52 9.57 7.73 9.68 14.47 - - 10.00 neers, 1969). Army Cordi ng to Jordan
neers, 1969). According to Jordan
Aug. 9.50 6.36 8.06 8.49 3.57 16.22 7.68 6.23 8.66 7.05 5.32 7.70 -(1973), the probability ofa trop-
ical storm or hurricane passing
Sept. 15.25 17.88 9.21 4.17 3.61 2.33 9.47 8.94 8.38 4.95 3.16 4.31 - through the Gulf of Mexico is 50
percent for a given season. A
Oct. 5.16 5.40 6.49 1.03 0.94 2.20 0.86 0.36 0.16 0.65 0.19 0.19 - - more complete discussion of hurri-
Nov. 0.33 0.42 0.16 5.41 5.26 3.85 0.66 0.62 O.lo 0.72 1.36 1.46 cane frequency in relation to
Sanibel Island is given by Riggs
Dec. 1.14 1.06 0.30 1.32 1.30 1.43 1.95 1.73 1.72 1.67 0.68 0.89 (1976).

Tot. 44.36 - 47.32 42.34 37,75 56.71 46.19 40.06 44.33 46.15 39.37 52.83
Geologic Setting
S#1 is Station 1 on Sanibel Island
S#2 is Station 2 on Sanibel Island
P.F. is Page Field, near Fort Myers
DEEP GEOLOGY
Table 1 - Monthly and Annual Rainfall atSanibel Stations 1 and 2 and at Page Field (in inches) Sanibel Island is a thin veneer
of quartz sand and shell lying on
the wet season, most of these storms culations used later in this report, top of a thick accumulation of lime-
form to the southeast and move to the an average value of 42.00 inches is stone, sandy carbonate muds, dolo-
west and northwest. Often the storms used for the entire island (average mites, and quartz sands.. The entire
do not reach Sanibel during this time of Stations 1 and -2). sequence is more than 15,000 feet
period. This rainfall pattern is thick. Only the upper 1,000 feet of
responsible for larger annual totals these sediments are of any great
occurring on the east coast of Florida HURRICANES AND TROPICAL STORMS significance in the understanding of
and progressively lower annual totals the island's hydrology and, thus,
occurring to the west (Benson and Hurricanes and less intense these are the only strata discussed
Gardner, 1974). During the later part tropical storms are significant herein (Figure 3).
of the wet season, thunderstorms form climatic factors which sometimes
at any place or any time and a more affect the hydrologic system of The deepest geologic unit pene-
random distribution occurs. Sanibel Island. In the past, in- trated on the island is the Suwannee
tense rainfall during hurricanes and Limestone of Oligocene age. This
The Sanibel Island rainfall data tropical storms has caused extensive unit is encountered at depths vary-
fits the regional pattern. For ex- flooding, and-complete tidal over- ing between 650 and 750 feet below
ample, during the three-year period topping of the island has occurred land surface. It consists mostly of
from 1972 through 1974, the Page during several severe hurricanes, limestone with some interbedded quartz
Field Station averaged 51.29 sand and carbonate mud.
inches while Stations 1 and 2 on Many intense hurricanes have
Sanibel averaged 44.89 and 39.06 passed over or near Sanibel Island. The lower Miocene Tampa Limestone
inches, respectively. The distribu- Historically, Hurricane Donna in 1960 lies unconformably above the Suwannee
tion of rainfall varies considerably and the "Labor Day" Hurricane in 1935 Limestone. This formation is poorly
from point to point on the island caused extensive flooding,but com- defined and quite impossible to dis-
over any given year. Hence, for cal- plete overtopping did not occur. The tinguish from the overlying unit. It

170 Append ixes

SECTION BENEATH SANIBEL ISLAND
DEPTH (FEET)
PLEISTOCENE '_ ..':-BARRIER ISLAND SANDS AND SHELL DEPTH (FEET)
RECENT - ' MARINE. MUD, SAND, AND SHELL
EROSION SURFACE +20
PLEISTOCENE--
PESOE'RECENT - SANDY LIMESTONE
100 - CARBONATES - UNCOMFORMITY
a- PHOSPLIMTESCTOHNEELL S 0 [GULF OF MEXICO PINE ISLAND SOUND
TAMIAMI _ X _ GREEN PHOSPHATIC SANDY MARL .....
FORMATION .
200- � SANDY PHOSPHATIC ZONE
- ' UNCOMFORMITY

300- _ li

PHOSPHATIC LIMESTONE
3- 0 - . . - .....

-_- - CLAYEY MARL
700- - RECENT SHALLOW MARINE CLAY, SLT, AND SAND40

SUWANNEE
SHAWTHORN 0 1 2 3 :4 W5EPLE MILES

400-
: - ::FORMATION

500- OXIDIZED BARRIER SAND AND SHELL
El UNOXIDZED BARRIER ISLAND SAND

SnibeLIMESTONE IslaRECENT PEAT DEPOSITS

to late Miocene iSOUNDage D. Peck, DEPOSITSt.ORGANIC MATTER ISAND MUD ANDSHELL
CLAYEY MARL

tion lies conformably n MEStop of the pigersonal ized glcommunication) of Sanibel Island consistsperpendicular the island axis. (from Missimer (1973a) and

carbonate mudand gray-green carbonate countered at depths varying between SHALLOW GEOLOGY A
900-

Fig. 3 - Generalized geology of the deep formations underlying
S anibel Island. (from Missimer 1973was)

consists primarily of phosphatic sandy The Tamiami Formation overlies There is a distinct lack of de-
limeston e with be ds of marly limestone the Hawthorn Formatio n unconformably. tailed information on the deep
a nd carbonate mud. This unit ranges from middle Pliocene geologic formations underlying Sani-
to late Miocene in age (D. Peck, Dept. bel Island. All of the availabl e
The middle Miocene Hawthorn Forma- data used in this discussion were
depth variation to the top of each of aloosaatcee Marl-Fort Tompson are represented in the shallow se-
Tampa Limestcone.This forma t i o of -hpersonal communication) and consists taken from Missimer: (1973a) and
the above discampaussed formations. This ormation sequence o fgreen the mainland. Bogguence (1974a).
seismic reflection dtata (issimclays, which consists of gray carbonate mud and
l ightgray phosphatic li me s tone, sandyvities clay mixed with variable amounts of
carbonate mud and gray-green carbonate countered at depths varying between SHALLOW GEOLOGY
clay. The top of the unit occurs at 50 and 80 feet below land surfaces.
depths ranging from about 160 feet to The Sanibel Island sequence was
about 250 feet below land surface. A Plio-Pleistocene age limestone deposited on top of the previously
Folding in the subsurface has been unit lies above the Tamiami. This described Pleistocene limestone unit.
suggested as the cause for extreme unit probably correlates to the Three distinct stratigraphic units
depth variation to the top of each of Caloosahatchee Marl-Fort Thompson are represented in the shallow se-
the above discussed formations. This Formation sequence on the mainland. quence (Figure 4). The lowermost,
hypothesis was made on the basis of The dominant lithology of this unit lying immediately above the limestone,
seismic reflection data (Missimer, is light gray, hard limestone, which consists of gray carbonate mud and
1974; Missimer and Gardner, 1975). contains numerous solution cavities. clay mixed with variable amounts of

Hydrology 171

quartz sand, shell, and limestone
fragments. This unit is generally
fragments. Thisunit is generally -MEAN GRAIN DIAMETER ( UNITS) vs. DEPTH (FEET)
fine-grained material and usually con-
fines the underlying limestone, but
localities do exist where this unit L-1452 L-1454
consists dominantly of sand and
shell. A fine to very fine gray sand -10 0o 1% 20 30 40 5s -1 0% 10 20. 3% 4% 50
overlies the mud stratum. This sand 0 0 I
is nearly homogeneous and generally I J
contains about one to three percent , lo
carbonate mud. The uppermost unit
consists of beach ridge sand and
shell. These strata are hetero- 20 . 20
geneous with the shell lenses and
sand beds, oriented generally paral- -
lel to the direction of associated 30 30.
beach ridges (See below).

A number of minor sediment de- 40 40
posits occur on or around the island.
Some fine-grained organic muds occur L-1456 L-1458
in areas bordering Pine Island Sound.
Several feet of peat have been de- -10 0% 1$ 2% 3% 40 5% -1% o0 10 20 30 40 50
posited adjacent or beneath the older 0 0
mangrove forests. Minor soil de-
velopment has occurred on the island 0lo
where fine material has filled some
of the low-lying swales between beach
ridges. Some "freshwater" organic marls 20 . 20
have been reported to be forming in parts
of the interior wetlands area (Tabb et
al, 1976). 30 30

It is important to note the coarsest
deposits in the island sequence occur 40 40
near the surface and the mean grain dia-
meter of the sediments decreases with
depth (Figure-5). Hence, permeability
of the sediment decreases with depth. Fig. 5 - Diagram showing variation in mean grain diameter of the sediment with depth. (from Missimer, 1973a).

The sand and shell portions of the is-
land consist of between seven and twelve
unique sets of beach ridges with each set surface water drainage to a certain de- of water.. These zones are termed
containing a different number of individual gree. These concepts will be discussed the lower Hawthorn aquifer and
ridges (Missimer, 1973b). Figure 6 shows in more detail later in the report. the Suwannee aquifer (Sproul and
the location of all defined beach ridge others, 1972). Both aquifers are
sets with the truncation lines being the A more rigorous and complete discus- artesian or confined from the over-
outer boundaries. The individual beach sion of the geology, age, and origin of lying shallow ground-water a'nd
ridges within each set are subparallel, Sanibel Island is given in Missimer surface-water systems. Hence,
but ridge orientation between sets is (1973a) and Riggs (1976). neither aquifer is directly re-
different (See Figure 7). There are sys- charged on the island.
tematic variations in relative altitude
of individual ridges within each set and Ground-water System The only information presently
there are relative differences between available on the geology of the
sets. The above-mentioned concepts are lower artesian aquifer system comes
very important because: (1) the primary DEEP ARTESIAN AQUIFERS . from a test hole made by the Island
sediment fabric is parallel to the beach Water Association (L-1533) and
ridges in each set and permeability is There are at least two deep various logs made by the U.S. Geo-
related to sediment fabric; (2) varia- aquifers underlying Sanibel Island logical Survey of existing wells.
tions in land surface altitude control that yield significant quantities The lower Hawthorn aquifer is

172 Appendixes

Water Quality.'- The lower Hawthorn
and Suwannee aquifers generally
contain saline water or water that
by definition has at least 1,000
\ t : BEACH RIDGE SET LOCATIONS 0 milligrams per liter (mg/l) of
BEACH RIDGE SET LOCATIONS dissolved solids (Krieger and others,
It < X 1957). Vertical change in water
quality within the saline water aq-
uifers in test well L-1533 is shown
in Figure 8. Dissolved chloride
concentration is used for compari-
son instead of dissolved solids.
The relationship between these para-
a _t:O4\\\\>st cuA~z::y7- P Sty X a-_ meters is given in Figure 10. It
should be noted that the water in
the upper part of the lower Haw-
thorn aquifer is highly saline or
contains dissolved solids in excess
19N of 10,000 mg/l. A relatively thin
zone of "fresh" water, containing
600 mg/l to 1000 mg/l of dissolved
chloride, occurs near the base of
%'~~ ' - i0 g s__~ the lower Hawthorn aquifer. Dis-
: ~L ; m< 5 - Auk; - no' / solved chloride concentrations in
the Suwannee aquifer are nearly
1000 mg/l at the top of the aquifer
- TRUNCATION LINES: : . o � ; and increase progressively with
RADIOCARBON DATE LOCATIONS
0O 2 MILES Extreme variation of water qual-
ity in each aquifer occurs from well
to well on the island. The "fresh"
water zone occurs at different
depth intervals in nearly every well
and sometimes does not occur at all.

Fig. 6- Map showing beach ridge set locations on Sanibel Island.(from Missimer, 1973a). General Discussion. Little is known
about the characteristics of each aq-_
uifer, such as transmissivity and
positioned near the contact between The head pressures measured on Sani- storage coefficient. No standard
the Hawthorn Formation and the bel generally fit the pattern establish- multi-well pump test has been made to
underlying Tampa Limestone, while ed by Boggess (1974b) for Lee County. give the necessary information on sus-
the Suwannee aquifer lies near the Local deviations from the regional pat- taned yield, drawdown, and permanence
contact between the Tampa Limestone tern as seen on the island are the prob- of quality.
and the underlying Suwannee Limestone able result of leakage of water out of
(Figure 8). It is not known whether corroded or damaged well casing into At least 40 deep artesian wells exist
these zones are hydraulically con- overlying aquifers, pumpage, or discharge on Sanibel Island. Many of these wells
nected because of the lack of detaileof f wild" flowing wells. The county-wide are not properly constructed and are prob-
geologic data (See previous section). potentiometric surface for the lower Haw- ably leaking poor quality water into
thorn and Suwannee aquifers shows a de- fresher zones as described in other areas
Water Levels. Artesian head pressure cline in artesian pressure has occurred of Lee County by Sproul and others (1972).
within the lower aquifers ranges from over large areas during the past 20 years Some deep artesian wells are discharging
16 to 32 feet above mean sea level on and recharge to the system comes from water wildly at land surface and in some
the island. The highest head occurs outside Lee County (See Figure 9). Since cases contaminating the water table
on the eastern part of the island and water flows perpendicular to the potentio- aquifer.
decreases to the west. It is not known metric contours, it is suggested that the
what season ranges in head occur on the recharge area for the system lies some- The City of Sanibel takes its munici-
island, but daily fluctuations of one where to the northeast, possibly in High- pal water supply from the "fresh" water
to two feet occur due to tidal and at- lands County or further north, but the zone in the lower Hawthorn aquifer. Even
mospheric variations (Boggess, 1974a). exact area is not known. though the city uses an electrodialysis

Hydrology 173

Fig. 7 - Aerial photo of Sanibel Island showing individual beach ridges as visible in 1944.

174 Appendixes

pened at McGregor Isles or other areas Water Quality. Water quality varies con-
REPORT OF INVESTIGATION NO. 69 of Lee County (Sproul and others, 1972). siderably in the shallow artesian aq-
1E 5 RoI CRHLORIDE CONTE NT uifer. Dissolved chloride concentrations
Em SEE FORMANLgTOLY AQUIFER I SIOX) Most of the information contained in range from 2,250 mg/1 to 30,900 mg/l with
%� '~ O ..A-l.Tl......D .E XI ~: this discussion comes from Boggess (1974a) numerous intermediate values (Figure 14).
AYO . '... and Boggess (1974b). The high chloride values exceed concentra-
-3 ~iHYRO ..... I ORYCOYEW 0 I Xtions in seawater which usually run about
7--0_-_ '~ -19E ,eSHALLOWARTESAN AQUIFER 19,000 mg/l in the vicinity of Sanibel.
SHALLOW A RTESIAN AQUIFER D
S........ : -~ S.. These high chloride waters may have formed
:XSAKYLEOR Numerous observation wells have when the strata were originally deposited
EOAATSOOYA A,=TEYrSOPOYRr SANDS goW-. _ ' been driven into the upper part of or concentration may have occurred through
,=.,~~~~~r~~~ ....r~:~ ~~~~~~downward leakage and selective osmotic dif-
the Pleistocene limestone (See page ferentiation. The lower chloride concen-
176), which forms the shallow ar- trations may be the result of partial
tesian aquifer beneath the island.
-00 : - tesian aquifer beneath the island. 0 flushing during deposition or modern flush-
The top of this aquifer occurs be-
i- - ....- ..................-: tween 25 to 30 feet below mean sea 1ng.
Zc- a 0 SOYAO.I5AS SO ? Vlevel (Figure 11). Locations of the
borings from which the stratigraphic
'"0 . ...... =~--- ,sn T ) and hydrologic data in-Figure 11 were General Discussion. There is no known
,~aYADCR*--R WF.. . . . . derived are given in Figure 12. recharge to the shallow artesian aquifer
D . R..TOYAIO.Y O"OY POYSKSOTYEIARZS.S.. AOiA AD other than possible downward leakage,
................... - I F-RSO The shallow artesian aquifer is which occurs only under special condi-
- '"I+"FTIC"" - O-::LIA-SYA fnormally confined from the overlying tions. Leakage of water between the
water-table aquifer by a previously shallow artesian aquifer and the water-
-.% ...... . R : ;-- ---- A.;.described heterogeneous mud stratum table aquifer is strictly a function
4 \and is confined from the lower of head differential and vertical per-
artesian aquifers by carbonate clay meability. During high tide periods
� . RNIYM5WN.,::yU*E beds in the Tamiami Formation. the water level in the shallow artesian
There are some areas where the upper aquifer usually stands above the water
S. A YOAX I confining bed is extremely thin, table and potential leakage is upward.
� :o: WE:: 0,...........: sandy, or nonexistent. Interaquifer During the low part of the tidal cycle,
leakage between the shallow artesian the water level in the shallow artesian
-I. - and the water-table aquifers is aquifer usually drops below the water
possible in these areas. table and potential leakage is downward
EXPLANATION (See Figure 15). When the water table
..... SOAR 2CLoA~OS . ...O.. .. I ....... D Water Levels.- Water levels in the is high for an extended period, such as
shallow artesian aquifer fluctuate after heavy rainfall, the water table
with the tides on a daily basis. The may remain above the artesian water
- Log showing te Dgeologic formations, lithology, aquifers, range of tidal water level fluctua- level through numerous tidal cycles.
~~~~~Fig.ht~~ Lsmttions in the aquifer is a function of
and chloride concentrations in water from test hole L-1533. distance to the nearest tidal water
(from-Boggess, 1974a). body and the permeability of the aq-
uifer. Hence, the lowest tidal ef- Leakage between the two shallow aq-
ficiencies usually occur near the uifers is dynamic -- it is continuously
middle of the island and the highest occurring to some degree. However, only
desalination system for water processing, adjacent to the shorelines. Also, the the net quantity of water leaked up or
it is extremely hazardous to design a well greater the distance from the tidal down has any significance. Since verti-
field without adequate knowledge of the water body, then the greater is the cal permeabilityalso controls the quan-
aquifer properties. It is not known wheth- time lag between a given tidal change tity of water leaked, along with head
er a sustained yield of adequate quality and the corresponding water level differential, it is important that the
water can be maintained over a long time change in the aquifer. Figure 13 mud stratum be preserved so as not to
period so as to keep the system functional. shows water level fluctuations in well enhance vertical water movement that
The problem is probably not one involving L-1408 as compared to tidal fluctua- would degrade water quality in the water-
quantity of water, but one involving qual- tions recorded at Point Ybel. Note table aquifer.
ity of water. With highly. saline water the similarities and the slight time
above, below, and on several sides of the lag. Water levels in the shallow ar-
production zones, the system can expect tesian aquifer are not greatly re- The information contained in this
future problems. It is possible that a sponsive to seasonal water level varia- portion of the report comes from Boggess
decline in head could initiate migration tions in the overlying water-table (1974a) and analysis of data recently
of highly saline water like what has hap- aquifer. collected by the U.S. Geological Survey.

Hydrology 175

22p, 10 : : 05 602-6 0 55 SO 05 tO* St2 E beds (See page 170). The saturated part
.1210 I *000 ftE Id RlE I R5 2060 R I A
of this sequence is termed the water-table
- CHARLOTTE COUNTY aquifer (Figure 7).
-- tg t t A- ;1 Water Levels. Water table fluctuations
2- |\ i jon Sanibel Island are controlled primar-
ily by climatic factors with secondary
'AF L\ H effects caused by man's activities. The
water table rises in response to recharge
and declines when water is discharged
0 lure :O\' .st .% '000 [~_ t| 0 ;/ 0 from the aquifer . The only natural source
40- hb~~~~ ~~ 2., b* of freshwater recharge on the island is
: .~ '~ l < OX -\ > ]^ < DU - - > \9 E / @ c, By rainfall. Figure 17 shows the relation-
~4? 0 : X ab' I>n�g i, HER~h~hA~r~ship between monthly rainfall and posi-
tion of the water table in well L-1403.
� L'niU Sr IAC" In the absence of freshwater recharge,
a6c'~~~~~~~~~ \ <s\ saline water may recharge the aquifer lat-
st _ 1~~\ O\x~ ) C~or ~ foO\ J | _erally from the sea, through the surface
VCpeCool U water system, or from the underlying shal-
i low artesian aquifer (See page 180). Na-
. T WA 0 Z\ < 0 x Em \ *\ X | 'tural discharge from the aquifer includes
evaporation, evapotranspiration, ground-
0 O\ oe -\ �8' water discharge to the sea, and discharge
-% to streams or lakes. Some recharge to
.,0- %% \ 5 0 : 0Cthe aquifer is the result of man's activ-
,n C, - - \ j: ities, such as inflow from deep artesian
~ \A \ 0o '9 wells, inflow of treated sewage effluent,
and septic tank discharges into the aq-
,3+3 0 } by. - ^S : >o %a uifer. Discharge from the aquifer has
1 � ' 0 :S r --- - 0 also been altered by man in that the en-
EXPLA-ATON- ',, r -t )X1LEEhanced surface drainage system now dis-
EXPLPIANATION LEE charges some water to the sea and a
COUNTY
CONTROL POINT 4e FLORIDA minor amount of water is pumped for ir-
(1966-73 DATAI C rigation. The range in water table posi-
CONTROL OINT A, ; -, t '"'d tion varies from year to year based on
0 1944-50 DATA) I POTEIOMETRI cONTO variations in recharge and discharge.
+:30�----- (1944-50) 0
*2-' =-POTENTIOMETRIC CONTOUR
(1966-731 CONTOUR INTERVAL IO FEET (3METRES) The position of the water table rep-
DASHED WHERE INFERREO DATUM IS MEAN SEA LEVEL
resents the quantity of water in storage
aI II I [ I i X I I I! I I| in the ground. When the water table is
high in Sanibel, a.much greater quantity
Fig. 9 - Potentiometric surface of the lower Hawthorn and Suwannee aquifers in Lee County 1966-73 and 1944-50. of freas are fi is stored dand the wetland
(from Boggess, 1974b) areas are filled with surface water.
When the water table is low, the quan-
tity of water in storage is decreased
and wetland areas tend to dry. The
highest and lowest recorded positions
WATER-TABLE AQUIFER termediate soil water, and capillary fringe of the water table are shown in Figure
water subzones all have important roles in 18 and a theoretical cross-section of
controlling both entry and exit of water the island showing the high and low
Unconfined water at shallow depths from the aquifer at land surface. The upper positions of the water table is shown
beneath land surface is divided into two surface of the saturated zone, thewater in Figure 19. Note that the water table
zones: the unsaturated zone in which air table, is defined as "that surface in an un- in the interior part of the island often
and water exist in variable proportions, confined water body at which pressure is at- drops below mean sea level during the
and the saturated zone in which water fills mospheric" (Lohman and others, 1972). dry season.
all of the pore space. When water enters
the ground-water system at land surface, On Sanibel Island the uppermost 20 to Altered Discharge. Construction of
it passes through several subzones in the 25 feet of sediment is unconfined and con- canals and drainage ditches has had
unsaturated zone before reaching the satur- sists of quartz sand, shell and some minor a pronounced effect upon the position
ated zone (Figure 16).- The soil water, in- percentages of carbonate mud in the lower of the water table over large areas of

176 Append ixes

A A

~.~ . :- :
a -.
8sadand and shell Wate,-T_ al;
Water-Table

Aquifer
__-"' Pe se

2000 O 1fine ....
Ld DIMileVERTICAL EXAGGERATION X 290 ; S 0

------ ------ ___'- ___
Iuwanneeaquifers. (from .oIggess 7 4)= Water-Table Aquifer
Finesgrain snd

3 1000- Fine to ery fine grain. ,,a"eysand

c3 : �Clay or marl, shells in lower part, sandy in -ls layer
D - : : ; o : : ---'fShLimestone h
Artesian
the -- LO lCATION OF SECAL Al F ErTIONS Cavity Aquifer
Sand
a: I II
0 1000 2000 3000 4000 5000 .6000

DISSOLVED-SOLIDS CONCENTRATION,MILLIGRAMS PER LITRE

Fig. 10 - Relation between dissolved chloride and dissolved solids in water from the lower Hawthorn and Fig. 11 - Diagram showing the position of the shallow artesian aquifer and the position and
Suwannee aquifers. (from Boggess, 1974b). thickness of the water-table aquifer. (from Boggess, 1974a).

the island. The deep tidal canals at water levels during the dry season aquifer is related to proximity to tidal
the eastern end of the island have per- than previously existed (compari- seawater and net vertical leakage. High
manently lowered the water table. An son of Provost data and Boggess chloride waters tend to occur in the
example of the effects of a drainage data). The control structures at low-lying areas and lower chloride waters
canal on the water table, located in Tarpon Bay and at Beach Road are in the upland areas.
another part of Lee County, is given in not adequate and leak water both in
Figure 20. A drainage canal was con- and out. Evaporation losses have Chloride concentrations in the
structed during 1971 about one mile also been increased by the addi- water-tabIe aquifer generally increase
from the observation well. As can be tional amount of atmospherically with depth throughout the island (Fig-
seen, the water table has been perma- exposed surface water. All of the ure 21). The chloride concentration
nently lowered several feet and storage recharge and discharge factors varies with time because of variations
has been depleted (See:Missimer and will be discussed in more detail on in harge and discae fro t
Boggess, 1974). The deep tidal canals page 185. in reharg e and discharge from the aq"
have been spaced so closely on some parts uifer. A relatively small quantity
of the island that the water table prob- of potable water exists in the aquifer
ably does not range much above sea level. on an annual basis. In reality, only
Water Quality. Quality of water varies tains any significant quantity of water con-
considerably in the water-table aquifer. tains . any significant q .o ler
The altered interior drainage Dissolved chloride concentrations range with less than 1,000 mg/l of dissolved
system--the Sanibel River and con- from mg/l in well L-1401 to 23,200 mg/l solids.
nected ditches and canals--has in well L-1516 (Boggess, 1974a). The
caused a more rapid recession of areal distribution of chloride in the High chloride water exists in parts

Hydrology 177

of the aquifer. This water contains ness, approximately 15 feet, by the Surface Vater System
chloride concentrations in excess of permeability, 900 gallons/day/foot. em
19,000 mg/1, which is the approximate The calculation yields a value of 13,500
seawater concentration in the vicinity. gallons/day/foot. This value is only
Boggess (1974a) has suggested that the an estimate of the average for the en- Few barrier islands in the world
high chloride waters indicated the pre- tire aquifer. It probably varies more have developed any natural type of
sence of evaporite beds. It is the than 100 percent from area to area. channelized or partially channelized
opinion of the author that the high interior drainage system. The reason
chloride water is the result of a com- . that a surface drainage system does not
bination of the following factors: usually develop on most barrier islands
tidal overtopping, selective uptake General Discussion. It has recently been
oftwater by plants ion exclusion),ve upt and suggested that some municipal use be made iS that the sediment, generally sand or
cofnwatera by plants (ion exlusion), and of the "fresh" water in storage in the gravel, allows nearly instantaneous in-
concentration by evaporation of water in aquifer. This practice would be an ex- filtration of precipitation because of
the sands, such as described by Hellwig aquifer. This practice would be an ex-
(1974). The relative high density of tremely unwise procedure because of the high rates of vertical permeability.
natural variation in water quality. Even
the water and the low flow gradend ts a relatively small amount of pumping of
keep the water in place and tend to "fresh" water from the upper part of the that a partially channelized interior
cause continued concentration.ve- drainage system, the Sanibel Slough,'
ment (pluming effect) of the saline water developed rather late-in its geologic
Precise properties of the water-table that exists at the base of the aquifer. history. Beach ridge geometry, vari-
aquifer have not been measured on Sanibel Tidal overtopping could cause such a sys- able permeability, and vegetation pat-
Island. However, using the grain size fail and the impact of such a sys- terns all contributed to the formation
data given by Missimer (1973a), values of tem could further alter the hydrologic of the Sanibel Slough at some time
storage coefficient and permeability can system. during the last 1000 to 1500 years of
be estimated. Because the mean grain the island's 5000-year history. The
diameter (Figure 7) and the degree of slough meandered almost exclusively
sorting' decreases with: depth (Missimer through beach ridge sets 5 and 6
(1973a), the storage coefficient also
(1973a), the storage coefficient also 0 In summary, without an adequate (Figure 6) over an irregular course
decreases with depth. A storage co- quantity of water in storage within the nearly 8 miles long. Two "mini-basins"
efficient of about 0.3 is estimated water-table aquifer, the present flora were formed by segments of the slough
for the upper sands and shell and a and fauna on Sanibel Island could not with the western segment in beach ridge
storage coefficient of about 0.15 is exist. set 5 being separated by some low beach
estimated for the lower sands. An
average of 0.23 is estimated for the
entire aquifer thickness on Sanibel.
The coefficient of permeability also 8'12'30 2'30 8200
decreases with decreasing mean grain 26,30
diameter. Using the method of Fair
and Hatch (1933), a gross estimate of t
the coefficient of permeability is
calculated at 900 gallons/day/foot. r-IB
Some special observations about per- 0Sso ,
meability should be noted: perme- SANCARLOS SAY
ability estimates of the upper sedi- - 5 i <
ments in the aquifer vary between 800
and 2,000 gallons/day/foot with values ,' 3O
parallel to the sediment fabric prob- EXPLANA7TON
ably much greater than perpendicular ELL LOR TRTs HOLE .
to it (See page 170); permeability es- L-14
timates in the lower part of the aq- ROFL WATER TLE O WN OL-NFIG . 0
uifer range from 90 to 500 gallons/ ',0
day/foot; horizontal permeability is V - L
probably much greater than vertical 9
permeability because of vertical vari- 26025'
ation in grain size, composition dif-
ferences, and sediment fabric.

Transmissivity is estimated by
mul T ransmissivity is estimated by thick- Fig. 12- Map showing the location of wells, observation wells, and test borings on Sanibl Island. (from Boggess, 1974a).
multiplying the average aquifer thick-

178 Appendixes

ridges south of Tarpon Bay from the slough meandered considerably because remained in groundwater storage in sets
eastern segment lying in ridge set 6. of the low relief of the ridges in set 5. 5 and 6. The low-lying part of these
The system was only unified during high There were several "branches" to the beach ridge sets was, and still is, the
water stages. slough. During flow conditions, water interior wetlands.
flowed to the west and during high wa-
The drainage characteristics of ter, it broke through ridge set 8 and
the eastern "mini-basin" differed con- discharged into the Gulf at a point PRESENT INTERIOR DRAINAGE SYSTEM
siderably from the western "mini-basin." about 2.5 miles east of the Blind Pass
In the east, the "course" of the Sanibel Bridge. In the past 20 years, the natural
Slough was- straighter, although it drainage system of Sanibel Island has
transected most of the low ridges in the The Sanibel Slough was only a been channelized and expanded for a num-
set at oblique angles (Figure 7). The drainage-way and never a true stream. ber of reasons. The former "course" of,
only "tributaries" to the slough in the Flow only occurred during times when the Sanibel Slough was modified, deepened,
east were the natural swales transected the water table was high and infiltra- and widened. A network of canals and
by the slough. Durinq flow conditions. tion of precipitation was inhibited. ditches was connected to it. The
water in the eastern "basin" moved to The "break-out" phenomena of drainage eastern "mini-basin" was terminated by
the east and during high water condi- into the Gulf was a rare event and was a series of deep tidal canals at Beach
tions it broke through ridge set 7 and not as catastrophic as implied by Road, where a water level control
discharged into the Gulf of Mexico just Provost (1953). During times of normal structure was constructed. The
west of Point Ybel. In the west, the or moderately low water condition, water western "mini-basin" was extensively

70~~~~~.5 -LL L-E 308
I W1LL L-lNOB 268201230 0 : 10I 7'30" 5 230' :8200'

2.0 , , | , l| I FI

3' '~O4, . SAN CARLOS BAY

I ' I I' ' I1EL

- \ U l UO - U
NUMBER IS CHLORIDE

APPARENT BOUNDARY WHERE
L-1408,~~ August~~ 4i\~ 9,I~ 1971.n~ (fOID CONCENTRATIONS Ol
TIi E L OR EXCEED SEA WATER. M I4LE
S I\III\III~CLORIDE

IIIIUIII 11111 i- i PFig. 14 - Map showing chloride concentrations in water from the top of the shallow artesian aquifer on
A I / L \ \ .Sanibel Island.

VI '

-I5 AXUGaO

Fig. 13 - Diagram showing records from the tide gauge at Point Ibel and well
L-1408, August 4s9, 1971. (from Boggess,1974a).

Hydrology 179

ditched and the flow direction was surface-water system should be maintained
reversed so that discharge occurs at at the highest possible level. Also,
Tarpon Bay through a control structure. in order to maintain the surface-water W LL L-1408
During high water conditions, water stage during the dry season, the total 2. A:
still will "break-out" at the western surface area of canals and ditches should\ /\ /
part of the island (See page 177). be minimized so as to prevent excess
Roads cross the channel at several lo- evaporation losses. l
cations. Because the small culverts
that run beneath the roads do not The present controlled water stage
provide adequate connections, the of 2.5 feet at each control structure is 45
system is now segmented., During high the highest practical level at those re- ell L-141S
water conditions, interior flooding spective localities. If a higher stage
sometimes occurs because of the under- were maintained, extensive flooding
sized culverts. "of low lying upstream areas would
occur. In parts of-the interior ToE Ar wINT YBEL
wetlands area, as defined by Johnson izo
STAGE AND FLOW, Engineering (1975), a water level of
about 3.0 feet could possibly be A , A
maintained if more control struc-
Water rarely discharges through tures and outflow barriers were in- \TO lA0 I I A I
the surface-water system of Sanibel stalled. Such a project would re-
Island. Sufficient rainfall must quire a large scale investigation of 05
accumulate so as to raise the stage water impoundment techniques applic- I
above 2.5 feet above mean sea level able to Sanibel Island. It isthe
before discharge can occur at the opinion of the author that even if
control structures. According to the surface-water stage were main- -05
U.S. Geological Survey stage data col- tained at 3.0 feet during the wet
lected upstream of the Beach Road con- season, the recession of the water
trol structure, a sustained 2.5-foot table would still reach low levels U V U U
stage was only attained twice, Sep- similar to present, but the added G -' 5 G 6 U 7 U 9
tember-October, 1971 and June-July.,l974, storage would slow the rate of re-
since November, 1970 (Figure 22). Dur- cession. Hence, the hydroperiod Fig. 15-Diagram showing record from well L-1408 in the shallow
ing the two discharge periods, signifi- would be extended with enhanced en- artesian aquifer with superimposed record from well L-1415 in
cant quantities of water flowed through vironmental conditions for the flora the water-table aquifer.
the control structures. Boggess (1974) and fauna. The extended hydroperiod
estimated that during the storm of Sep- would probably increase the biomass
tember, 1971, about 500 million gallons of the vegetation. Dissolved chloride concentration
of water flowed into Tarpon Bay and varies seasonally with recharge and dis-
about 100 million gallons discharged at charge. In most parts of the surface-
Beach Road. Some minor discharge has water system, chlorides decrease during
occurred numerous times during the wet the wet season as a result of flushing
season because of leakage at both control and dilution by rainfall. In some parts
structures and because of tampering at of the Sanibel River high chloride
the Beach Road control. water at the channel bottom is trapped
Water quality in the Sanibel because of bottom irregularities (See
The present drainage system of Sani- River and other parts of the in- Johnson Engineering, 1975). The trapped
bel Island has had a pronounced effect terior drainage system varies con- water decreases in chlorides only by di-
on the water-table aquifer (See page 175). siderably. The salinity of the lution, but the dense water mass only
Since the canals and ditches are dug water in any particular segment of flushes during high water periods. Chlo-
through very permeable sand and shell, the system is controlled by climatic rides increase during the dry season be-
water in the water-table aquifer flows factors, proximity to a source of cause evaporation and evapotranspiration
trapidly out of the aquifer and into the saline water leakage, the natural losses tend to cause concentration of
adjacent canal when there is a positive quality of water in adjacent parts dissolved solids.
gradient. This discharge out of the of the water-table aquifer, and the
ground-water system has increased the channel characteristics of the drainage- The greatest source of saline water
rate of recession during the dry season way. Heavy nutrient influx, stagnation, entering the Sanibel River is seawater
and has caused temporary depletion of and deposition of organic detritus all that leaks into the system at the two con-
storage in the aquifer (shortened the degrade the general quality of the water trol structures. Whenever the tide rises
hydroperiod). Hence, the stage of the (Missimer, 1975). above 2.5 feet mean sea level, seawater

180 Append ixes

enters the system directly. During the
dry season as the freshwater head in the :A~r4tC.2:4l cIt244 %.iiirT~$~
interior declines, leakage occurs through .~_ .,.-..--.~~------~---.
the structures alTh 4most continuously. Th iI 24t-T. I
leakage phenomena is illustrated in Fig- .-i*-'--'- FI
ures 23 and 24, in which the seasonal 1----~---~t i---
fluctuations in chloride concentration are _____ l ~ ~ ~ *I
shown at the top and bottom of sites lo- -t ~ ~ . >
cated upstream of the Beach Road and U 3 .......
Tarpon Bay controls, respectively. Note =4 __
tehigh bottom chlorides. After U. 4jz1
the denser seawater leaks through in t-'---- - --
the- structures, it migrates a con- ___ IB ~ --~--- ___-
siderable distance upstream as a 03. :-- .. E-
density current. As the surface- . ........
water head declines, the high Z _____ _____F-_. -._
chloride water migrates further IP -1 i~- t

/LAND SURFACE >____ -l----
oJ A . . . -- ... L

UBROOTZONE c o 5- 1,
0 ~~~~~~~~~~I- 1- t-1 W H
N W ~ ~ TVir\VZ
0 ~~~~ t~~~~ ~~~-v X~~7_ - v r4.

INTERMEDIATE SOIL MOISTURE: i jt I+
7t-~~~I

CAPILLARY FRINGE: WATER U.1; . i- ---

--WATER TA9LE w- ~ j -L- -i

ul ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ s

a~~~~~ ~~~~ ~ ~~ ~ c FT Jt -.1 ' -t_ I

u~~~~~~~~~a~~~ - b-'-
Fi. 6 Dara hoig iison f usufcewte.(Fom11. 91 97I Z 17
Missier an Bogess, 974)
Fig.17 Hyrogaph f wll -143 ad mothl ranfal a staion2 o SaibelIslndFebuar 197-Deembr, 974

Hydrology 181

upstream. Under certain conditions, should be removed from the bottom of level of the surrounding land surface
such as during high winds, the the drainageways and the new system for the purpose of meeting housing
-density stratification can-be be designed so as to allow oxidation of regulations and to obtain septic tank
disturbed and mixing occurs, which any deposited organic materials. permits.
leaves the entire water column Treated sewerage effluent should not
salty (See Boggess, 1974a). be permitted to enter the system. A These excavations have had pro-
study should be made of impoundments nounced effects upon the water-table
Where deep artesian wells of water in the interior wetlands. aquifer both in the construction
discharge saline water into the phase and after completion. Several
interior drainage system, dis- of the lakes and canals were dug-too
solved chlorides increase signifi- deep and part or all of the confin-
cantly. For example, Boggess POing mud stratum was removed, hence,
(1974a) showed that continuous permitting upward leakage of high
discharge of water, containing chloride water from the shallow ar-
a chloride concentration of 5,850 Many ponds, lakes, and canals tesian aquifer into the water-table
mg/l from well L-1472, raised the have been excavated on Sanibel Is- aquifer. During excavation of sev-
dissolved chloride concentration land during the past 10 years. These eral ponds, a dewatering process was
in the Sanibel River in October, excavations were dug mostly to obtain used (pumping) which caused wide dis-
1971. The well was capped in fill material in order to raise the persion of high chloride water pumped
late October, 1971 and the effects
dissipated by the end of November,
1971.

Heavy influx of nutrient-
laden wastewater into the eastern
segment of the Sanibel River has
caused blooms of-undesirable vege-
tation and has helped deplete dis-
solved oxygen (Missimer, 1975).
General stagnation of the water and
the deposition of organic detritus
has caused low values of dissolved
oxygen to occur throughout much of
the interior drainage system.

During hurrican conditions, : �
when tidal overtopping occurs, the -..\
seawater which enters the interior
drainage system could take years to
flus because of poor channel con-
nections. Most of this dense water ar
accumulates at the base of the
water-table aquifer. -as

The present state of the Sanibel
River should be modified in order to
improve environmental quality. If the
interior salinity were to rise above
ten parts per thousand for extended
time periods, extensive vegetation -.8E
changes could result (Tabb and Manning, .':
1961). To improve the system, the LOW IN FEET, REFERRED
bottom irregularities should be elimi- HIGH TO MEAN SEA LEVEL
nated in the main channels of the
Sanibel River and bottom gradients
should be established. The culverts
at road crossings should be improved. Fig. 18- Highest and lowest positions of the water table on Sanibel Island.
The control structures at the ends of
the system should be properly recon-
structed. Accumulated organic detritus

182 Appendixes

from the lower part of the water-table bel are given in Boggess (1974a) and water directly from the sea into
aquifer. The pumping stress could Missimer (1975). the water-table aquifer (Ghyben-
also have caused upward leakage of Herzberg intrusion), 2) leakage
saline water from the shallow artesian In summary, the concept of the; or intrusion of highly saline wa-
aquifer. All of the lakes now provide real estate lake on Sanibel can work ter into the interior surface-and
a free water surface which facili- if proper water quality criteria are ground-water systems through un-
tates evaporation of water and causes used in rtheir design. The lakes can controlled or poorly controlled
the water table in adjacent areas to be larger, shallower, and oriented canals that are connected to tidal
recede at more rapid rates than in in consideration of wind stress to en- water bodies, 3) :::massive intrusion
the past. The finished lakes now act hance oxygenation of the water.- of highly saline water of all or
as accumulation basins for highly parts of the island during tidal
saline water., septic waste, and organ- overtopping caused by intense
ic: detritus:. Depressed oxygen con- Saline vater Intrusion storms, 4) upward leakage from
ditions prevail in many of the excava- the underlying shallow artesian
tions and lakes (Missimer, 1975). aquifer, 5) discharge of highly
Since Sanibel is an island, it is saline water at the surface through
Lakes and excavations of any type surrounded by seawater on all sides. improperly constructed, damaged,
should be6limited in depth so as to := Highly saline water directly underlies or uncontrolled deep artesian wells,
prevent saline water leakage from be- ... i- theisland in the shallow artesian aq- and 6) pumping and dispersing of
low and to allow sufficient concentra- Uiferand in several deeper artesian aq- highly saline water into interior
tions of dissolved ::oxygen in the water uifers. Henc:eII,'-the "fresh" water part parts of the system.
column to prevent accumulation of or- of the water-table aquifer is deli-
ganics 1at the bottom (enough to oxi- cately- -positioned and is in constant
;dize the organics). Perhaps a reason- danger of, being intruded by highly
able depth limitation would be five saline water. There are basica-lly DENSITY OR GHYBEN-HERZBERG INTRUSION
feet below mean sea :level for any exca- six ways in which highly saline-
vation on the island. More data on water can intrude the "fresh" water
lakes, ponds, and excavations on Sani- areas: 1) density intrusion f t Along:the shoreline of Sanibelm,;
f0 9 0 the water-table aquifer comes in di-
rect contact with seawater. Since
seawater is denser than freshwater,
. Highest:Water Table Position it tends to sink to the base of the
iLowest Water Table Position water-table aquifer and forms a
/: : Land Surface : : : wedge (See Badon Ghyben, 1888-89;
Herzberg, 1901; Todd, 1953).

INTERIOR WETLANDS PINE ISLAND The position and geometry of the
GULF OF MEXICO P I: -.SOUND saltwater wedge along the coast of /
Sanibel is controlled by the water dens-
ity contrast, permeability of the water-
- - - - - - - -e --l-: -table aquifer, and the level. or head of
: f \ : : : / � : ::: fresh water in the aquifer. Since the
\ / / water-table aquifer is underlain by
Aquifer ~'/ less permeable muds, the intrusion of
: :>\ ~ :: Water-Table Aquifer / seawater is mostly horizontal. Because
0High Water / High Water water levels in the water-table aquifer
Salt Wedge Position \ / / - Salt Wedge Position fluctuate with seasonal variations in
Low Water Salt Wedge Position / : recharge and discharge, the position
\Low :a e /SW / of the waltwater wedge also fluctuates.
: : .:~/ / \/ When interior water levels are high,
.. - / // - -- 'the seawater is forced outward and when
water levels are low, the wedge moves
toward the interior of the island.
Mud Stratum
Seawater does not usually intrude
more than about 500 feet inland from
the Gulf under natural conditions even
during very dry periods when the water
Fig. 19 - Diagram showing the theoretical position of the water table across Sanibel Island during high and low water table positions. table is low (only available data comes

Hydrology 183

from the western Gulf Drive area). The
reasons that the intrusion is not very
great a-re ':- the aquifer is only about
O- 0 -
fifteen to twenty feet thick, the
intruding :seawater must pass across
the alignment of the sediment fabric, 2
and the base of the waterr-table aquifer
already contains saline water, which 4 4 -
causes a minimal density contrast.
There are few available data on this
sh~ : : : : 6-
type of intrusion on Sanibel. Verti- WELLS L-3 AND 504 ARE
cally, nothing is known about the WELL I-FOOT APART AND SCREENED
ranges and effects of lateral sea- 8 AT DIFFERENT DEPTHS.
water migration along thenorthern WELL ,L-503 WELLS L-1496AND 1497 SIMILARLY
LOCATED AND SCREENED.
shore of the island. 0 I0 I LE L
WELL
WELL L-1530 LL
32-1~ ~12

%~~~~~~~~~~~~~~~
.B 16 - 16 WELL L-L504
. W~ 16- 16 WELL L-1497

20 20
\J \\j b::-~~~~~~ I I I 20I I

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Ir
o 0 2000 4000 6000 0ooo o 2000 4000 6000 6000 10,000

Fig. 20 - Hydrograph of well L-730, 1969-73. (from Missimer LL
and Boggess, 1974). 4 S I 7 I
1~~~~~~~~~ 2o-8oo~,o

U-
w
6-
INTRUSION THROUGH CANALS 3 WEL L.i559
1969 0 ~~~~~~~~~~~~~~0 --
I-

F 8-

Saline water intrusion is fa-
cilitated by the construction of
uncontrolled tidal canals (Figure 25).L15
On the eastern part of Sanibel, sev- 12--
eral large canals were cut well below
mean sea level almost entirely across 14 -
the island. The water-table aquifer
in the vicinity of this area prob-
ably no longer contains any fresh-
water. Once the highly saline water
enters the water-table aquifer, it It-
is extremely difficult to flush it
outbecauseof thelo water table 20 a q
gradient. 0 2000 4000 6000 8000 10,000 12,000 4,000 16P00 18,000 20,000 2p00 24,000
CHLORIDE CONCENTRATATION,MILLIGRAMS PER LITER
The two control structures at
the ends of the Sanibel River also
allow intrusion of highly saline wa-
ter into the interior (See page 178). Fig. 21 - Graphs showing increase in chloride content of water with depth in the water-table aquifer.

184 Appendixes

The structures are frequently over- up or down depending upon the rel- INTRUSION FROM DEEP ARTESIAN AQUIFERS
topped during high tides, and leakage ative position of the tide at any
occurs through them during most of given time in relation to the posi-
the dry season. tion of the water table at the cor- Some of the deep artesian aq-
responding time (Figure 15). Hence, uifers underlying Sanibel contain
only the net amount of leakage over large quantities of highly saline
a sustained time period is signifi- water (See page 172). Numerous
TIDAL OVERTOPPING: cant. deep wells tap these aquifers.
Many of these wells contain iron
Under natural conditions the casing, which tends to corrode and
All or part of the island is amount of upward leakage is mini- rupture after an extended time
periodically flooded by seawater mal, but when the vertical con- period. Corrosion holes in the
during severe storms. Some of the nection between the two aquifers casing permit deep artesian wa-
intruded seawater is flushed out is improved; large quantities of ter to leak into any of the over-
during the storm, but large volumes saline water can leak upward. Sev- lying aquifers including the water-
enter the surface-and ground-water eral excavations on the island were table aquifer from the well bore
systems on the island. Since the dug into or below the mud stratum (Figure 26).
highly saline water is denser than and upward leakage did occur. The
fresh water, it tends to sink to highly saline water-that results
the lowest points in either system. from leakage often enters adjacent
Much of the dense water is trapped parts of both the ground-and sur-
in bottom lows in the Sanibel face-water systems.
River channels, lake bottoms, and
at the base of the water-table W D
aquifer. It generally remains in >
place and is slowly diluted. No ., W
data has been collected immediately : - .
after a major tidal flood on
Sanibel. Xc 3 1.: .....3 ..
co: a ' ~ ~ ~-'- . Z

Ci\:~~~~... --- ......... .
UPWARD LEAKAGE FROM THE , a............
SHALLOW ARTESIAN AQUIFER 0 a
: -i U - : l - - / i: i ' - i-

shallow artesian aquifer can leak L -:--: 1: LL
upward into the water-table aquifer U.
under certain conditions. Leakage I 1 \ cc
is controlled by vertical perme- . -
ability and the head differential -----Y -u
between the water table and the r- + j 'L 1 - W
potentiometric surface of the ... 4- 1
_ z
shallow artesian aquifer, which -
fluctuates with the tides (See U --:- :-
Figure 26). In most parts of the _- - . +_
island, the upward leakage is :
minimal because of the presence ..
of the mud stratum that causes : c
low vertical permeability values. - -- - - i
Also, since the head differential i - ii' .. :: :-
is dependent on tidal fluctuations ; i � 1 e i i <3 1 i ..i
in the shallow artesian aquifer, 197 i 19 9l- 1973 19 71L
it is not usually more than a few
feet. Potential leakage is either Fig. 2 - Surface water stage upstream of the Beach Road control structure, January 1971 to September 1974.

Hydrology 185

Highly saline water from the
deep artesian wells commonly enters
both the surface- and shallow ground- 0
water systems of Sanibel because of I0 I
uncontrolled discharge of water outi - - - . ..
of the well at land surface. The .; - ........ ......
deep wildly flowing wells tend to::::.:. . -::-. ::-:: :-::
cause widespread contamination of
freshwater areas, particularly dur- : .. -- - - .
ing the dry season. Uncontrolled --}, - -
discharge of water from these deep : : :::: .::...-: ; :
wells also tends to lower the head LU
pressure in the aquifer being tapped L
for the island'ls municipal supply. 8

INTRUSION RELATED TO PUMPING: :.:. :::.:: :-:-: :::: :
AND OTHER CONSTRUCTION PROCEDURE a: - A ' 7

__ - I ........... . ....., ................
During the excavation of lakes, 1-
ponds, and canals and during constru:c-
tion of-buildings, certain practices -------
were used that tended to cause in- . S
trusion of highly saline water into X . -..: 5
freshwater areas. Several shallow CO---- .... ..... .....
wells were often installed and- pumped -
rigorously to dewater the upper part 0 - +
of the water-table aquifer in order I - - : i '-''' -
to facilitate excavation. The heavy < - -- -4 . :- it :
pumping in the relatively small areas 3 1- -
tended to draw saline water from the -4
base of the water-table aquifer and Z l- L - - -
to create-a stress which caused up- - .
ward leakage from the shallow arte- z : : : -
sian aquifer. The pumped water,i '::.Nu -.--.: :0- - ' ' _:_:e_.: . ' '--i -' .
often highly saline, was some- t : - .
times discharged into freshwater : -- ...
areas. 4

The implacement of cement -
'i O
pilings was sometimes-accomplished 0 * e
by jetting them into position with I 971 7a 73 7 19 75
forcefully pumped water. Often, 0
the water used in the process was
drawn directly from the Gulf of Fig. 23 - Surface and bottom chloride concentrations in the Sanibel "River" upstream of the Beach Road control structure, January,
Mexico to the construction site, 1971 to July, 1975.
which was usually located in a
freshwater area. These practices
are no longer permitted on Sanibel.

earth's surface under variable precipitation, infiltration, and
natural conditions. Water is con- other recharge and discharge
The Hydrologic Cycle tinuously being recycled from the factors, is termed the hydrologic
liquid and solid state at and under cycle.
the earth's surface,-back to the
Water is, perhaps, the most gaseos state in the atmosphere
unique fluid on earth. It occurs and vice versa. The cyclic process,
in all three forms -- gas, liquid, which includes evaporation, evapo-
and solid -- on or near the -transpiration, condensation,

186 Appendixes

On Sanibel Island the quan- Water leaves the system in gaseous Water Budget
tity of water entering and leaving form through evaporation and evapo- of
the surface- and ground-water sys- transpiration and in liquid form by of the Interior Wetands
tems is controlled to the greatest surface water runoff and ground wa-
degree by the atmospheric processes ter discharge. A number of other
involved in the hydrologic cycle factors related to man's activities A water budget is a quantitative
(Figure 27). The only source of also affect the changing volumes of expression of the amounts of water
fresh water is from rainfall. All water. The hydrologic cycle is treat- entering and leaving any given area
other water entering the system is ed quantitatively in the water bud- through processes involved in the
saline to some degree or wastewater. get analysis. hydrologic cycle. The budget is cal-
culated by carefully considering each
of the inflow and outflow processes
and evaluating their quantitative -
A - significance.
O
O An annual water budget is herein
calculated for the interior wetlands
x __ _-_ _--.- ---_= .;- - ._ area of Sanibel Island. Inflow
.. '' 1 1. 7 -'- - _- 9 7t�i*-tt t -1 factors considered in the cal-
LU ao . -. - y-.-W-i----- -.-------..S.,- ..- .. . culations are: precipitation,
W..- : -' l_ .:. .2_:c-._Jl!�.' -t t' surface water inflow, ground-
-+---- - water inflow, upward leakage, arte-
-, ----- -- : ....
; 18 i . Y 5 7e_. + ; g A; Tbo - i -- Is sian well discharge, and waste-
UU6- -: _ /- : -t- water inflow. Outflow factors con-
QW : -1i -- = 4 t 7-7-- t - sidered in the calculations are:
- 'n ;:' -: :- -:--:-"'.: -:-: '-: :-: AI T, :^L: T,:i ': : I : ' - : evaporation, evapotranspiration,
pumpage, surface water outflow,
.._~0 -': ' ' : -~'0~:0 ' _'- r. '4 i 0 ' ; . .groundwater outflow, and in un-
: : :'. :';:: ::.: ": ;- z � .-::n-..._ - :--. _.:.= .-= _z::_*.: ;- ' : :':: :1 - balanced systems, changes in
--: - j,'.= T-i"-_ i .......................- .- - � � groundwater storage, and changes
_________ I10~~~~ _ in surface water storage.
............;. .... -__ . -. ..._....... . . . .. . . .

....__ -.R_ _: ____i :: _ The interior wetlands area
can be considered a small basin.

Z' ---10 j - -1_1~ .. f_ 1-i-i -: /7. ji- -l/ ;1k: total area (Johnson Engineering,
Z h-: . 1975). Of the total area, about
0 8:: :: : : :: : : 1 : ::'1 ::1 t-!' i-:Q"A: : :': : -'. -- 8 100 acres consist of open
di :; -i\ d-I:: ; J : :: :.|.11:..|!Iii surface water..such as canals and
II I --- 5 -;;\ - --t i- 4-1- -i- + t_ I : - -- s ~- !'lakes. The wetlands area receives
~ C :- : - -- :: : : -.A bout 42 inches of rainfall per
[-- -Ii \ 0 . -- : :~7: ': ' __ ' - / year.
o -- /. ,' t i -: The water budget for the wet-
,Z 5: i s -A 0 I I . I.\A,&_ : = : )l , :. . 4 lands area is calculated only for
0O 1-: :- -:::- the surface water system and the
3=.':-- 0A' ' ' ' i - i ji water-table aquifer. Only fac-
I : ; : tors affecting these systems are
013:::> i;i I! L__ ' 1:- - . 1 ::i:c : i i . evaluated. All volumes are cal-
_91 -- .:-.-:--.- - .--- . - ; t --.- - : .... :- :-:-'-i-.- " -, culated in acre-feet of water.
O . o . - . , .: : :: : : . - One acre foot of water is equal
t J i -~~~i o ~~~~to thevolume needed to flood one
-z acre of land surface to a depth
19 71 19 7a 19 73 19 71- 19 75 of one foot, assuming a uniform
flat surface.

Calculations of the water bud-
Fig. 24 - Surface and bottom chloride concentrations in the Sanibel "River" upstream of the Tarpon Bay control structure, April, 1971 get are made only for an average
to July, 1975. annual period. There is not enough

Hydrology 187

the wetlands and tidal water bodies. areas, other than the sea. Since
Inflow into the system comes prin- the wetlands area is not directly
cipally from rainfall, but the other bounded by the sea and lies sever-
less important factors have some ef- al hundred feet inland on all sides,
fect. subsurface lateral migration of sea-
A. J ~ v E . : water does not directly affect it
Precipitation. Rainfall data has been (See page 183).
collected by the U.S. Geological Sur-
vey at two gauge sites on the island There is an inward flow gradient
since 1971. The three full years of in the water-table aquifer only during
record indicated that rainfall aver- a short period of the year. Consider-
ages about 42 inches per year on the ing the magnitude of the inward
island (See page )gradient (less than 0.5-foot per mile),
the time duration, and the transmis-
The quantity of inflow caused by sivity of the aquifer, groundwater
precipitation or rainfall is calculated inflow is near zero.
by multiplying the basin size in acres
times the average amount of rainfall
(equation 1). Upward Leakage of Groundwater. Water
levels in the shallow artesian
P = AB � RA (1) aquifer, which underlies the water-
table aquifer, fluctuate with the
P = precipitation tides. There is usually an upward
gradient during the high part of
AB = area of basin the tidal cycle and a downward gra-
dient during the low part. However,
RA = average annual rainfall during most of the year, the posi-
tion of the water table is lower
P = (42 in/12 in/ft) (3617 acres) than the potentiometric surface of
the shallow artesian aquifer during
P = 12660 acre-feet/year (la) the major part of each tidal cycle.
The result is that a net amount of
Hence, the average amount of upward leakage of water occurs. The
inflow due to rainfall on the wet-
lands is 12,600 acre-feet for an
average year.
Fig. 25 - Diagram showing seawater intrusion caused by construc-
tion of an uncontrolled canal vs. a controlled canal. (from Surface Water Inflow. The only
Sherwood and Grantham, 1966). sources of surface water inflow
into the interior wetlands are
data control to give meaningful anal- leakage of water through the con- UNCONFINED Fresh
data control to give meaningful anal- AQUIFER Water
ysis to any specific year. Shorter trol structures at Beach Road and
time period calculations, such as Tarpon Bay Road and tidal over-
months or weeks, are meaningless be- topping during severe storms. Since SECONDARY Fresh
cause of natural climatic variation tidal overtopping does not occur ARTESIANAQUIFER
and lack of control. The purpose of frequently, it is not considered 'd
the calculations made in this report a significant factor. The leak-
is to illustrate the present mass age at the control structures is
balance of the system estimated to be near one acre-
foot per year. This is only a
rough estimate since there is no
INFLOW FACTORS 0 practical means of measuring it.
Groundwater Inflow (lateral). This
The interior wetlands area of recharge factor involved only the
Sanibel Island is located more or less lateral migration of seawater into Fig. 26 - Diagram showing inter-aquifer leakage through well
in the central part of the island with the system because no adjacent bores. (from Boggess, 1968).
at least one beach ridge set acting parts of the water-table aquifer
as a "buffer" on all sides between are connected to other recharge

188 Appendixes

DA = 730 acre-feet per year (3a)

Wastewater Inflow. Many homes and
businesses on Sanibel Island dispose
of wastewater through septic tanks.
Those units not utilizing septic
tanks dispose of liquid waste through
package or larger scale treatment
Condensation 1 1 111 I Precipitation facilities. A rough estimate of the
4,'""iD\ 4,44,-1 1 zdaily influx of treated and untreated
wastewater which enters the interior
wetlands area is about 1 million
gallons per day. The- annual volume
Evapotranspiration Evapotranspiration of wastewater entering the system is
vra at S given in equations 4 and 4a.
Evaporation Surface-water (4)
Evaporation - XInfiltratin, Discharge Evaporation w x 365 days/year
1 n 1 t '3.26 x 105 gallons/acre-foot

:. = Outflow :Outflow / B WI = (1.0 x 106 gallons/day) (365
Water-table Aquifer -/ Seawater -- days/yr)
Seawater Intrusion IUpward Lkage / Intrusion 3.26 x 10' gallons/acre-foot

..........- - l - - - - _ _WI = 1,120 acre-feet/year (4a)

Confining Mud
..- ........ --ll=Confining MOUTFLOW FACTORS

-// / / 7/ In the absence of detailed data,
Shallow Artesian Aquifer it is most difficult to accurately
quantify the outflow part of the hydro-
/,/ / / / / / / a/ /7/! / / / J / / / 7 / /logic cycle. Losses occurring due to
evaporation and the evapotranspiration
are the most difficult to calculate.
Figure 27. Diagram showing the hydrologic cycle on Sanibel Island The evapotranspiration will be calcul-
ated and backchecked using better known
parameters.
annual rate of upward leakage is wells contribute a significant
estimated to be near 0.01 feet/year. quantity of water to the water-
table aquifer. It is estimated Evaporation. Evaporation is the
The total inflow contributed that at least six deep wells are conversion of water from liquid
to the interior wetlands by upward discharging water into the wet- into gaseous form. A significant
leakage is given in equations 2 lands area. They are each prob- quantity of water is lost from
and 2a. ably flowing at an average vol- the hydrologic system of Sanibel
ume of about 75 gallons per minute. through evaporation. There are
UL = AB . CL (2) Equations 3 and 3a give the con- three types of evaporation losses
tribution of artesian wells to the on the island. Water evaporates
UL = total annual upward leakage system. from free water surfaces, from
vegetated water surfaces, and from
AB = basin area DA = NA . Fr (3) soil at differing rates.

CL = coefficient of leakage DA = total annual inflow from Many factors control the
_ deep artesian wells evaporation loss rate from a free
UL = (3617 acres) (0.01 ft) water surface, such as tempera-
NA = number of wells ture, wind intensity and direc-
UL= 362 acre-feet/year (2a) tion, solar radiation flux,
relative humidity, heat diffusion
Artesian Well Discharge. Wildly rates, water turbidity, vapor
flowing and leaking deep artesian DA = (6) (121.67 acre-feet per year) pressure, and many others (Penman,

Hydrology 189

1948; Monteith, 1965; Wartena, Bv = vegetated water surface efficient of 0.7 for the entire basin
1974; Brutsaert, 1975). Since it area in question. The method is considered
is not possible to mathematically to yield a high error percentage. The
consider all of the atmospheric Cp = pan coefficient for excess calculation for ET is given in equa-
factors, the evaporation loss rate sfae tins 6 and 6a.
is estimated according to pan
evaporation loss rates (Kohler, BL = basin area (water surface ET = BL CET . Ep (6)
1954; Brutsaert and Yeh, 1970). area excluded)
The estimated annual loss rate ET = annual evapotranspiration losses
for a free water surface on Sani- Ce = pan coefficient for-soil
be, based on pan evapo ration, is evaporation BL = basin area (surface water
bel, based on pan evaporation, isexcluded)
53 inches per year (Geraghty and E = (100 acres) 53 in/yr)
others, 1973). 12 in/ft
(15ot(0he4rs0) (5193) 12 in/t CET= pan coefficient of evapo-
(15 acres) (0.40) (53in/yr) + transpiration
Evaporation losses are sig- 12 in/ft
nificantly increased when aquatic ( 53 n/yr) annual pan evaporation
plants cover the free water sur- (3517 acres)(0nnual p an evaporate
face. The increased loss is in
some part due to transpiration = 3594 acre-feet/yr (5a) s)(0.7)(53 in/yr)
losses. Regardless of which factor 12 in/ft
is dominant, the additional water Evapotranspiration. Transpiration ET = 10,873 acre-feet/year (6a)
loss is estimated to be at least is the process of water expulsion
forty percent above the free water from plants into the atmosphere. Pumpage. There are several small
surface loss rate (See Weert, 1974). Some water lost by plants is actually diameter domestic wells that tap the
Of the free water surface area in evaporated from the surface area of water-table aquifer in or near the
the interior wetlands, about 15 per- leaves and other parts of individual wetlands area. However, the esti-
cent of it is affected by aquatic plants. Hence, the total process of mated volume pumped from these wells
plant losses. water loss caused by plants is is so small as tohave no significant
termed evapotranspiration. effect on the water budget. The
Recent experimental work in volume pumped is only a fraction
evaporation losses from sands indi- In the natural system, plants of an acre-foot of water, which is
cates that these losses are a small act much like pumps. Water enters generally used for irrigation.
percentage of the losses occurring the plants through the roots and Surface Water Outflow. Surface water
at a free water surface (Hellwig, Surface Water Outflow. Surface water
at a free water surface (Hellwig, exits through the stem and leaves.
1973a; 1973b; 1973c). By using the discharge is not a common occurrence
All the climatic and environmental on Sanibel Island. Discharge occurs
grain size data of Missimer (1973a), factors that affect rates oftevapor- on Sanibel Island. Discharge occurs
factors that affect rates of evapor- naturally only during high water
the water level data of the U.S. Geo- ation also affect evapotranspira- conditions (See page 177). Leak-
logical Survey, and the experimental tion (ET). Since each different age out of the system is common at
data of Hellwig (1973c), the evapora- plant species has its own unique the control structures. Also, some
tion losses from the soil is estimated physiological characteristics, all th e control structures. Also, someah
to be 20 percent of the pan evapora- physlologlcadicfhfarreant ET Ioss rates water is discharged through the Beach
to be 20 percent of the pan evapora- plants have different ET loss rates. Road structure when it is opened by
tion rate for the area of the interior The size and density (biomass) of structurewhen it is opened by
wetlands. The greatest losses occur structure n
wetlands. Thegreatest losses occur plants both necessitate natural areal individual persons. It is esti-
during infiltration and when the variations in water loss rates from mated that discharge occurs for
water table is near land surface. plants. about 10 days at a rate ours for
When the water table recedes to a
position lower than three feet below Little is known about the ET cubic feet per second in an aver-
land surface, the evaporation loss characteristics of the individual age year. The volume also includes
is nearly zero (See Hellwig, 1973c). plant species that populate Sanibel leakage. The total volume is given
Island. However, some qualitative in equations 7 and 7a.
The calculated evaporation loss assertions concerning relative water
for the wetlands area is given in losses by certain plant communities So = D - t (7)
equations 5 and 5a. are implied. Relatively high ET So = annual surface water discharge
E = (Bw.Ep)+(Bv..Ep)+(BL-Ce-Ep) (5) losseants occur infloating aquatic D = average rate of discharge
s c htotal annual evaporation losses s .hp c nt = time duration of discharge
E = total annual evaporation losses species. The marsh plant community
B water surface area also tends to show greater ET losses So = (10 ft3/sec)(60 sec/min)
Bw = water surface area than the upland plant community. (60 min/hr)(24hrs/day)(10 days)
Ep = estimated annual pan One standard approach to calcula- 43,560 ft3/acre-ft
evaporation rate tion of ET losses is to use a pan co- So = 20 acre-feet/yr. (7a)

190 Appendixes

Groundwater Outflow. An outward gra- In an unbalanced system, where
dient toward major tidal water bodies a progressive decline in water levels
in the water table aquifer only oc- is observed through several years, a Table 2. Mass balance of the
curs during the wet season (Gulf of correction must be added to the equa- hydrologic budget for the
Mexico and Pine Island Sound). The tion in order to achieve mass bal- interior wetlands of Sanibel
wet season gradient is usually less ance. The correction factor is the Island.
than two feet per mile and, hence, change in storage. 1
little ground water is discharged Inflow Factors Outflow Factors
into the Gulf and Pine Island Sound. In the wetlands of Sanibel, the
system generally shows no change in P 12,660 S = 0
Where the water-table aquifer storage from year to year. Hence,
borders tidal canals, a significant no storage factor is needed to bal- SI 1 E = 3,594
quantity of water is lost from the sys- ance the budget equation. Within
tem. A rather large amount of water a given year, the volume of water GI 0 ET = 10,873
leaks from the ground water system at in storage varies considerably. The
and around the Beach Road control water budget or mass balance equa- UL = 362 Pu = 0
structure. The total quantity of wa-n tion is given in equation 8. The
ter leaked to tidal canals is esti- volumetric analysis of the mass ba- DA = 730 So = 20
mated to be about 100 acre-feet/year. lance is given in Table 2.
WI = 1,120 Go= 100
A large quantity of ground-
water flows laterally into the P+ SI + GI + UL:+ DA + WI (8) 14,873 ITOTAL 14,587
surface water system of the in-
terior wetlands where much of the = A S + ET + Pu + So+ Go 1
water is lost to evaporation. All values are in acre-feet/yr.
Hence, this water loss has al- P = average annual precipitation
ready been calculated.
Si= annual surface water inflow

MASS BALANCE OF THE ANNUAL WATER BUDGET G= annual groundwater inflow ANNUAL WATER STORAGE IN THE INTERIOR WETLANDS

UL= annual upward leakage During the year a certain
amount of, water is held in tempor-
ing and leaving the hydrologic DA= annual artesian well discharge ary storage in both the water-table
system of Sanibel varies from A
system of Sanibel varies from: Xoi aquifer and the surface water sys-
yeartion ofth e posWI = annual waste water inflow tem on the island. The maximum
tionnof wthe water inflow
tiur ofac he water stabe both theah I 0 Xquantity of water in storage during
surface water stage both reach the wet season is much greater than
similar highsAand lows from year A = change in total storage the wet season istymuch greater than
the minimum quantity in storage
to year. There are no progres- The net
sive water level trends occur- E annual evaporation during the dry season
~~~~~~ring in the shallow groundwater ~charge in storage from the maximum
ring in the shallow groundwater
system of Sanibel at present. ET = annual evapotranspiration part of the water lost from the sys-
tem through E, ET, and other factors.
Since this analysis deals Pu = annual pumpage Herein, the storage loss of the sur-
,with an average year in a: sys- \ : R : - face water system and water-table aq-
tem where similar quantities of so = annual surface water outflow uifer is treated as a whole. Equa-
water are held in storage from tions 9 and 9a give the total maximum
year to year, inflow into the Go = annual groundwater outflow quantity of water in storage in the
system must be equal to outflow wetlands area, while equations 10
and 10a give the minimum quantity.
from the system in an average Note that the inflow total does Equations 11 and la yield the total
year. This concept of account- not equal the outflow total in Ta- annual charge in storage.
ing for all volumes of water ble 2. This is caused by errors
entering and leaving the system in the process of evaluating each Sm = (BL AT Cs ) + (B W
is termed mass balance. It factor involved. The entire anal- max L
is analogous to conservation of ysis is rather subjective and should + (B. (AT WT) Cs) (9)
mass and energy in physics. Wa- be considered semi-quantitative.
ter is neither created nor de- More data and a refined mathematical Sx = maximum quantity of water
stroyed in the hydrologic system, treatment would be needed to improve in storage (both surface-
but it only changes form. the analysis. and groundwater systems)

Hydrology 191

gBLB = basin area excluding surface dry season minimum there is probably grading the control structures at
water area little or no freshwater by definition Beach Road and Tarpon Bay. New
(water having less than 1000 mg/l dis- structures of the "flapper-type"
AT = maximum saturated thickness solved solids).. Also, the 4-foot range set to maintain a minimum surface
of the water-table aquifer in water-table fluctuation is a minimum water stage of 2.5 feet at the
value, which makes the 3,458 acre-feet outflow points would appear advis-
Cs = storage coefficient of the the greater annual change in storage. able. It is clear that the chan-
water-table aquifer nels should be cleared of organic
detritus and the new channel de-
Bw = area of surface water signed to allow maximum oxygenation
-w t, areabf surface ctr C onclusionS of the water. A new channel with
WT = average maximum thickness established uniform gradient and of
of surface water depth enough to discourage growth of
ax = (3517 acres) (17 ft) -ithThe following conclusions are made cattails is needed. Large box cul-
Smax = (3517 acres) (i7 ft) with regard to maintaining the beneficial verts are needed at points where roads
natural qualities of the hydrologic sys- cross the channel. The designing of
(0.23) + (100 acres) tem on Sanibel Island or improving it. the system should incorporate the po-
'5 ft' + 'inn 8 0 acrtential for maintaining the water
(5 ft) + (100 acres) (1) The channelized surface wa- levels at 3.0 to 3.5 feet or higher in
ter system of Sanibel Island is in poor the interior wetlands if this should
(17 ft - 5 ft)(0.23) environmental condition. Highly saline prove feasible (See Recommendation
= 14,527 acre-feet (9a) water enters the system through leaky No. 5).
control structures at Beach Road and
Tarpon Bay. Dissolved oxygen is low and (6) A permitting system should
Smin = (BL ' Al s Cs) + highly saline water is trapped in bottom be developed regulating all newly pro-
depressions. posed deep artesian wells and permis-
(B~w-: 5 )o '+ w *- sible water use criteria should be
0 (A5 - Ws) * Cs) (10) (2) It appears necessary to pro- developed. All "wildly flowing" wells
(1)s hibit excavation-construction of tidal or any deep artesian wells that are
:; S. . = minimum quantity of wa- canals. 2 ~ damaged or improperly constructed
mn ter in storage (both (3) Any interi should be plugged completely as soon
ter in storage (both (3) Any interior excavations as possible.
surface- and ground- to be dug on Sanibel, such as chan-
water systems) nels, canals and real estate lakes,.
As = minimum saturated thick- should be discouraged and designed
ness of the water-table according to exacting standards Recommendations
aquifer which will guarantee maintenance
Ws = minimum thickness of of acceptable water quality. The
surface water depth of such excavations should in The following recommendations are
Smin = (3517 acres) (13 ft) (0.23) no case be greater than5 feet be- aimed at specific additional actions
low mean sea level. The banks should needed to insure the soundest program
+ (100 acres)(3 ft) + be gently sloped. The excavations of natural resource management.
should be sloped and oriented to al-
(100 acres) (13 ft - 3 ft) low maximum oxygenation by prevailing (1) Cooperative programs between
1,6acefewinds. It is also suggested that the U.S. Geological Survey and the
(0.23) = 11,069 acre-feet to restore past damage dissolved City of Sanibel should be maintained
(10a) oxygen enhancement and/or artificial and strengthened in order to continue
circulation devices be installed in the collection of relevant hydrologic
AS = Smax - Smin (11) existing degraded water bodies such data.
as wind-driven air pumps or wind-
AS = (14,527 acre ft) - 11,069 driven paddle wheels. (2) A detailed investigation
of the deep artesian aquifers under-
acre ft) = 3,458 acre feet (4) Liquid waste should not lying the island should be made. It
(lla) be permitted to enter the surface should include test holes, a multi-
water system. It is clear from the well pump test to determine aquifer
The volume of water calculated as evidence that the use of septic properties, detailed water quality
the total AS is considered by the author tanks on Sanibel be discontinued. analyses, and the establishment of
as a close approximation of the maximum several deep observation wells.
volume of real freshwater in the sys- (5) The Sanibel "River", sys- The pump test should be made as
tem. It should be noted that-at the tem could be greatly improved by up- soon as possible.

192 Append ixes

(3) All deep artesian wells reflect changes in storage within the
should be located and investigated. aquifer. Climatic factors and the Literature Cite
activities of man control water level
(4) A feasibility study changes within the aquifer. Alexander, T. 1975. Report on the
should be made of disposal of liquid Plants of annibel: The Conserva-
waste by deep-well injection or by Fresh water occupies the upper tion Foundation, Washington, D.C.
land-spreading in uninhabited areas. part of the water-table aquifer. The
position of the fresh water in the Badon, Ghyben, W. 1888-89. Notae in
hyd system is precarious.verband met de voorgenomen putboring
poundment should be made to find The freshwate r zone can easily nabij Amsterdam: Tijdschrift van
out the feasibility of maintaining The freshwater zone can easily
be intruded by saline water in het Koninklijk Instituut van
at 3.0 or 3.5-foot water stage innumber of natural ways and can Ingenieurs. The Hague, 21 p.
the interior wetlands. This study aue b ns acit
should include the making of a one- Benson, M.A., and Gardner, R.A. 1974.
foot interval contour map of the The channelized surface The 1971 drought in South Florida
island to aid in drainage analysis. water system of Sanibel Island is and its effect on the hydrologic
water systemnof Sanibel Island is
in poor environmental condition. system, U.S. Geological Water Res.
Highly saline water enters the Invest. 12-74, 46 p.
_U~maa~ -ures at Beach Road and Tarpon Bay~system through leaky control struc-
Summrary :Xtures at Beach Road and Tarpon Bay. Boggess, D.H. 1968. Water-supply
Dissolved oxygen is low and highly problems in southwest Florida: U.S.
saline water is trapped in bottom Geol. Sur. Open-File Rept.
~~~~~depressions. ~No. 68003, 27 p.
Sanibel Island is underlain
by at least three major aquifers: Boggess, D.H. 1974a. The shallow
the unconfined, water-table aquifer, fresh-water system of Sanibel
the shallow artesian aquifer, and A Island, Lee County, Florida, with
the lower Hawthorn-Suwannee Aquifer. Ak-9mtemphasis on the sources and effects
All of the aquifers are separated of saline waters: Fla. Dept. of
by confining clays or muds which Nat. Res., Bur. of Geol. Rept. of
tend to inhibit natural vertical The author sincerely thanks Invest. No. 69, 52 p.
water movement. the residents and friends of Sani-
bel Island for providing various Boggess, D.H. 1974b. -Saline ground-
Municipal water supply for the types of information. Without the water resources of Lee County,
City of Sanibel is taken from wells interest and aid of these people, Florida: U.S. Geological Survey
tapping the lower Hawthorn aquifer. this report would never have been Open-File Rept. No. 74-247, 62 p.
There is considerable variation in written.
water quality within this aquifer and Brutsaert, W. 1975. A theory for
its capacity to yield sustained quan- Special thanks is extended local evaporation (or heat
tities of adequate quality water is to Mr. Durward Boggess and his transfer) from rough and smooth
unknown. staff of the U.S. Geological Survey surfaces at ground level: Water
in Fort Myers. �Mr. Boggess' re- Resources Res., v. ll, p. 543-550.
The shallow artesian aquifer search on Sanibel Island has pro-
underlies the island at depths rang- vided nearly all available hydro- Brutsaert, W., and Yeh, G.T. 1970.
ing from 20 to 30 feet below mean sea logic and geologic data collected Implications of a type of em-
level. Water levels in the aquifer to this time. His understanding pirical evaporation formula for
fluctuate with the tides. This aq- of the hydrologic system and in- lakes and pans: Water Resources
uifer generally contains highly sa- sight has provided a strong data Res., v. 6, p. 1202-1208.
line water. Because of the tidal s h
linewater. Because of the tidal base for the establishment of valid
fluctuation, the poor quality water Fair, G.M., and Hatch, L.P. 1933.
in the shallow artesian aquifer can criteria governing proper manage- Fundamental factors governing the
leak upward into the water-table aq- ment of the water resources of the streamline flow of water through
uifer and cause degradation of water island. sand: Jour. Amer. Water Works
quality. In the natural system, the Assoc., v. 25, p. 1551-1565.
quantity of leakage is relatively Mr. Richard Workman of the Sani-
small, but man's activities, such as bel-Captiva Conservation Foundation Geraghty, J., Miller, D.M., Van der
excavation of deep lakes and canals, is greatly acknowledged for his effort Leeden, F., and Troise, F.F. 1973.
can cause greater leakage rates. in collecting hydrologic data and his Water atlas of the United States,
leadership in developing water re- Water Information Center, Port
Fluctuations of the water table source management programs. Washington, N.Y.

Hydrology 193

Heald, E.J., and Tabb, D.C. 1976. Lohman, S.W., and others. 1972. Riggs, S.R. 1975. Geology of the
Vegetation. The Conservation Definitions of selected ground- natural beach system, Sanibel
Foundation, Washington, D.C. water terms - revisions and con- Florida: The Conservation
ceptual refinements: U.S. Geol. Foundation , Washington, D.C.
Hellwig, D.H.R. 1973a. Evaporation Survey Water, Supply Paper 1968,
of water from sand, 1: Experi- 21 p.
mental set-up and climatic in- 0 0 Sherwood, C.B. and Grantham, R.G.
fluences: J. Hydrol., v. 18, Missimer, T.M. 1973a. The deposi- 1966. Water control vs. sea wa-
p. 93-108. tional history of Sanibel Island, terintrusion, Broward County,
Florida: M.S. Thesis, Florida Florida: Fla. Geol. Sur., Leaflet
Hellwig, D.H.R. 1973b. Evaporation State University, Tallahassee, No. 5.
of water from sand, 2: Diurnal Florida, 121 p.
variations: J.:Hydrol., v. 18, Sproul, C.R., Boggess, D.H., and
variations: J. Hydrol., v. 18,
p. 190-118. Missimer, T.M. 1973b. Growth rates Woodard, H.J. 1972. Saline-water
of beach ridges on Sanibel Island, intrusion from deep artesian
Florida: Trans. Gulf Coast Assoc. sources in the McGregor Isles area
Hellwig, D.H.R. 1973c. Evaporation F l orida:- Tras., Gulf Coast ASSC. 3of Lee County, Florida: Fla. Bur.
of water from sand, 4: the in- Geol. Inf. Circ. No. 75, 30 p.
fluence of the depth of the wa-
0 ter-table and the particle size ; Missimer, T.M. 1974. Structural con-
distributibn of the sand: riltrol of late Tertiary sedimentation Tabb, D.C. and Manning R.B. 1961.
Jour. Hydrol., v. 18, p. 317-327. in southwest Florida: p Geol. Soc. A checklist of the flora and
Am. Abstracts with Programs, v. 6, fauna of northern Florida Bay and
Hellwg, DH.R. 4 Epor n padjacent brackish waters of the
Hellwig, D.H.R. 1974. Evaporation p. 872. Florida mainland collected during
of water from sand, 5: the Missimer, T.M. and Boggess, D.H. the period of July, 1955 through
effect of evaporation on the 1974. Fluctuations of the September, 1960: Bull. Mar. Sci.
concentration of salts dissolved water-table in Lee County, Gulf and Carib., v. 11, p. 552-649.
in water stored in sand: Jour. Florida, 1969-73, U.S. Geol.
Hydrol., v. 21, p.. 101-110. Sur. Open File Rept. No. 74019:, Tabb, D.C., Roessler, M.A. and
41 p. Beardsley, G.L.- 1975. Interior
Herzberg, B. 1901. Die Wasserver- wetlands, from the biological
sorgung einiger Nordseebader, Missimer, T.M. and Gardner, R.A. perspective, Sanibel, Florida,
Jour. Gasbeleuchtung and Wasser- 1975. High-resolution seismic The Conservation Foundation,
versorgung, v. 44, Munich. reflection profiling, a useful Washington, D.C.
tool in mapping shallow aquifers
Johnson Engineering Inc. 1975. Pre- underlying part of Lee County, Todd, D.K. 1953. Sea-water intru-
liminary plan, Sanibel Island Florida: U.S. Geol. Sur. Open sion in coastal aquifers: Trans.
fresh water management area, for File Rept. (in review). Am. Geophys. Union, v. 34, p. 749-
the Sanibel-Captiva Conservation
Foundation, Inc., 50 p. Missimer, T.M. 1976. Hydrology.
The Conservation Foundation,
Jordan, C.L. 1973. The physical en- Washington, D.C. U.S. Army, Corps of Engineers. 1969.
vironment: Climate: in A sum- Beach erosion control studyon
mary of knowledge of the Eastern Monteith, J.L. 1965, Evaporation Lee County, Florida: Dept. of
Gulf of Mexico, The State Uni- and environment: Symp. Soc. the Army, Jacksonville District,
versity System of Florida In- Empir. Biol., v. 19, p. 205-234. Corps of Engineers, Jacksonville,
stitute of Oceanography, St. Florida.
Petersburg, Florida, p,. II All-- Morrill, J.B. and Byle, W.K., Jr.
II A/22. The Conservation Foundationlogy, Veri, A.R., and Warner, L. 1975.
Interior wetlands water quality
Kohler, M.A. 1954. Lake and pan Washington, D.C. management, The Conservation
evaporation: U.S. Geol. Survey Penman, H.L. 1948. Natural evapor- Foundation, Inc., Washington,
Profess. Paper 269, p. 127-148. ation from open water, bare soil D.C. (in press).
and grass: Proc. R. Soc. Lond.,
Krieger, R.A., Hatchett, J.L. and Ser. A, v. 193, p. 120-146. Wartena, L. 1974. Basic difficul-
Poole, J.L. 1957. Preliminary ties in predicting evaporation:
survey of the saline-water re- Provost, M.W. 1953. The water Jour. Hydrol., v. 23, p. 159-177.
sources of the United States: table on Sanibel Island: Bureau
U.S. Geol. Survey Water, Supply of Sanitary Engineering Florida Weert R. van der and Kamerling, G.E.
Paper 1374, 172 p. State Board of Health (mimeo). 1974. Evapotranspiration of wa-

194 Append ixes

ter hyacinth (Eichlornia crassi-
pies): Jour. Hydrol., v. 22,
p. 201-212.

WMRT. 1975. A summary of Phase I
planning studies toward a com-
prehensive land use plan. City
of Sanibel, Florida. Wallace,
McHarg, Roberts and Todd, Phila-
delphia, Pa.

195

APPENDIX 2

VEGETATION 197
Mangrove Communities 198
-The Ecological Role of Mangroves 198
The Sanibel Survey 200
Community Descriptions 201
Summary and Conclusions 206
Interior Wetlands 206
Pre-Developing Conditions 207
Interior Lowlands Soils 211
The Leaky Saucer Theory 212
Interior Wetlands As Habitat 213
Lowland Aquatic Fauna 215
Conclusions 219
Upland Communities and Vegetation Management 220
Existing Conditions 221
Exotic Plants 221
Fire 222
Soil Salinity 222
Endangered Communities 222
Beach 223
Storms 223
Plant Pests 223
Pineland 223
Endangered Species 223
Useful Native Species for Landscaping 223
Wetland Species 223
References 224
Recommendations 225

197

APPENDIX 2

VEGETATION

by Durbin C. Tabb, Eric J. Heald, Gary L. Beardsley, Martin A. Roessler, and Taylor R. Alexander

Tropical BioIndustries Develop- increasingly well-documented under The information and recommenda-
ment Company was commissioned by The careful investigation. Their more tions presented in this report are
Conservation Foundation to conduct a important roles include production a distillation of the collective ex-
reconnaissance survey of the upland of materials basic to many natural perience of its authors in South
vegetative communities, the interior food chains, specialized habitats Florida environments, including
wetland complex, and the mangrove for aquatic species of economic im- Sanibel Island, and of field observa-
communities of Sanibel Island. In portance, buffer zones for flood pro- tions made on site in June 1975. Two
this, the professional staff of tection, freshwater recharge, and field trips, each of 3 days duration,
Tropical BioIndustries constituted filtering and cleansing of water were made by a 4-man team from Tropical
part of a larger task force assembled emanating from adjacent upland areas. BioIndustries and by Dr. Taylor
by The Conservation Foundation to It should be noted, however, that the Alexander, Botany Department, Uni-
produce baseline documentation of the above roles are not common to all wet- versity of Miami.
natural resources 6f the island. The land systems and are not performed
completed document, describing the with equal efficiency; hence, general- The program consisted of as-
vegetative system, also includes izations can be misleading. sembling available literature con-
information of geology, hydrology, cerning Sanibel, followed by field
marine environments, mammals, birds, The existence and efficient verification to produce a base vege-
and reptiles, and is offered as an functioning of most wetland systems tation map and community descrip-
information source around which a results from the subtle interplay of tions. Recommendations offered for
realistic land-use plan- for Sanibel natural parameters; for instance, wa- consideration in this report were
can be formulated. The task force ter flow patterns, duration of inun- developed as a result of discussion
placed primary emphasis on wetland dation, dissolved nutrient levels, among ourselves and with John Clark,
systems since these are often soil type, and depth. Most of these Conservation Foundation, following
severely threatened and easily dis- parameters can be easily disrupted analysis of the field observations,
rupted natural communities. or altered by ill-planned human
activities, causing significant, fre- We are indebted to Mr. Richard
The roles of wetlands, both quently deleterious, and often irre- Workman of the Sanibel-Captiva Con-
freshwater and saline, are varied, versible changes in the total role servation Foundation for his invalu-
and their significance is becoming or "value" of the wetland community. able assistance during field trips

198 Appendixes

and for local knowledge freely im- red mangroves frequently create roots of reds and pneumatophores of
parted for our benefit. John Clark, islets which gradually grow in size blacks, as well as the often densely
as coordinator of the task force, by a process of accretion of silts situated trunks, form an effective im-
is to be complimented on a clear around the numerous prop-roots. pediment to the forward progression of
delineation of the objectives of the Similarly, in quiet backwater areas, wind-driven tidal surges.2
study. The authors donated the time the prop-roots of red mangroves and
required for report writing, map the pneumatophores of black mangroves Food Chain Support: The most sig-
production and interim conferences trap sediments and gradually elevate nificant biological roles played by
following the systems survey, since or extend land surfaces. The pro- mangrove communities, in our opinion,
the production of this resource cess is well documented.i12 In the are those as wildlife habitats and as
evaluation for use in land planning 40 or 50 years since photography was contributors to estuarine food chains.
is believed to be clearly in the first available, several instances It is primarily these factors which
public interest. of the closure, partial filling, or have led to -increased investigation
subdivision of bay systems by man- and public demands for adequate pro-
groves has been recorded.' tection of mangrove systems.

The ability of reds and blacks The undoubted importance of the
RJI MangProve ~n~81:Communities t to trap debris has led to specula- mangrove-dominated estuaries of South
tion on their importance as physi- Florida has often been emphasized.
cal filters; removing suspended Several commercially valuable marine
materials from the water column. species, such -as pink shrimp, mullet,
Increased attention and scien- This they undoubtedly do, but the gray snapper, red drum and blue crab,
tific investigation over the past 10 biological significance of such re- which use the estuaries as a nursery
to 15 years has produced adequate moval is obscure. South Florida bay and feeding ground, has been listed.4
documentation of the importance of systems vary seasonally and from It has been shown that at least one
specific community associations in the year to year between extreme clarity species of economic and reational
maintenance of highly productive estu- and extreme turbidity. No correla- value, the spotted seatrout, appears
arine ecosystems. These high levels tion between either condition and to be dependent on the estuary during
of productivity are manifested in overall productivity or changes in the greater part of its life cycle.5
obviously tangible values such as com- community structure and water clarity A measure of the potential of such
mercial and sports fisheries, as well has.yet been demonstrated. nursery areas is the volume of the
as in abundant bird populations. It commercial shrimp catch from the Dry
has also become apparent that all man- It has been postulated that man- Tortugas grounds, which in 1973 ex-
grove communities do not perform grove communities remove dissolved ceeded 16 million pounds, with
identical roles or contribute in sim- primary nutrients (principally in- revenue of over $14 million paid to
ilar fashion to estuarine food chains. organic ions) from waters flowing fishermen.
Consequently, it seemed desirable, in through them from upland sources. In-
preparing assessments of the resource dications are that coastal mangrove Red Mangroves: Tidal and river-
base of Sanibel Island, to classify communities are dependent to some ine red mangrove forests in South
and assess as fully as possible the extent on nutrients emanating from up- Florida produce annually over eight
role and importance of the island's land areas.3 On the other hand, the metric tons dry weight per hectare of
mangrove communities, rather than State's best developed mangrove forests leaf and twig debris, the maiority
merely describing their geographic lie at the seaward end of the vast saw- of this being leaf material.6 In
o tidal andriverine situations most
location. grass regions of Everglades National tidal and riverine situations most
THE ECOLOGICACL RO~LE OF MANGROVES ; Park, where dissolved nutrients are leaf breakdown occurs under submerged
in extremely low concentrations after r at least dampcoditions. In
Among the roles attributed to man- the fresh water has passed slowly these situations fallen red mangrove
grove communities by various workers through the sawgrass. It has also been leaves are quickly subjected to the
are: land building and stabilization, suggested that certain mangrove com- grazing or browsing activities of
filtering of suspended material, as- munities (particularly black man- several species of invertebrates.
similation of dissolved nutrients, groves) contribute to estuarine pro-
storm wave attenuation, aquatic and ductivity by providing a source of The most important means of energy
terrestrial wildlife habitat, and dissolved primary nutrients in organic transfer (i.e., utilization of plant
contribution to estuarine food chains. form.3 Thus, the picture is unclear, material by animals) in a detrital sys-
The latter three roles are probably and the processes involved are not well tem depends upon the ability of bacteria
of much greater overall significance understood. and fungi to break down and assimilate
than the former three. resistant plant substances such as cellu-
The importance of mangroves as loses and lignins. Soon after a red
General Function: As primary buffers against hurricane-generated mangrove leaf falls from the tree its
colonizers of emergent oyster bars, storm waves is indisputable. The prop- tissues are invaded by several species

Vegetation 199

of fungi and bacteria. The complex se- Black Mangroves and Mixed communities, thus, are flooded only
quence of microbial succession has been Species Forests: Black mangrove- by seasonal rains and extreme sea-
detailed by Fell and Master.7 dominated plant communities form in sonal tides. Consequently, the
many areas a continuum of tree cover forest floor is irregularly submerged
The net result of this microbial stretching from-the approximate mean and emergent, but is rarely complete-
invasion is a relative increase in high tide line, or somewhat below it, ly dry. Black mangroves are over-
the potential food value (as measured to higher areas affected only by whelmingly dominant, although white
by protein content) of any specific R storm tides. The ecological roles of mangroves can be locally very common.
particle of disintegrating leaf. When these communities are obviously varied Salt-tolerant plants such as glass-
such a particle, relatively rich in and different parts of the forest wort and saltwort often form a sparse
protein of microbial origin, is in- almost certainly contribute to estu- to dense ground cover. Most of the
gested by a detritus feeder the only arine food chains in different ways. leaf litter produced by these forests
components of the particle which are - There are three major types of com- probably decays in situ, since flush-
in an easily digestible form are the munities as described below. ing by rainwater runoff or seasonal
bacteria and fungi, along with nema- ' tides is infrequent and weak. Much
todes and protozoa which may be feeding 1..- "Tidal' black mangrove commun- - of the breakdown product is thus re-
upon them. i ities. These are forests in which the cycled within the community, or forms:
visual dominant is the black mangrove, peat. An unknown proportion is
In South Florida this important . . but in which considerable numbers of transported out of the high black
trophic level of detritus feeders reds may exist, often as an understory forest by tides and runoff.
(primary consumers) appears to include to the larger blacks. In places the
roughly 12 species of crustaceans (4 understory reds may account for- almost ' An important biological function
amphipods, -4 mysids, 2 carideans, 1 40 percent of individuals, and perhaps of the high black mangrove systems is
penaeid.and a xanthid crab), 6 fishes, 25 percent of the total above-ground their apparent role in the mosquito
2 polychaetes, several copepod and tree biomass. linked food chain.' The wet-dry
isopod species, and larval chironomids. fluctuations experienced by the higher
'These forests are found under portions of the black mangrove forest
:Although many individual food several situations. Commonly, they are a prerequisiteyfor the successful
chains are involved, the principal flow occupy a slightly elevated natural propagation of salt marsh mosquitoes.9-.
of energy follows the pathway: man- levee behind the shoreline red mangrove These breed in enormous numbers when
grove debris-and detritus - bacteria - 'stands of large islands and along many shallow flooding occurs over eggs de-
and fungi- _primary consumers (de- water courses They also frequently posited earlier on exposed ground.
tritus consumers) _- secondary con- form the center portions of small is- The resultant aquatic larvae, which
sumers (lower, middle, and top lands. Extensive tracts also occur in feed on particulate organic detritus,
carnivores). ' ' " areas where the shoreline levee-is provide seasonally abundant food
- absent or indiscernible. In these source for a select group of fishes,
The secondary consumers, which situations major portions of the forest notably Gambusia affinis and Fundulus
include virtually all the important are more distant from open tidewater or confluentus, which are adapted to ex-
sport fish and most commercially im- creeks and the proportion of red man- ploit the shallow and ephemeral wa-
portant species, are basically car- groves, though still significant, is ters of the high black mangrove zone
nivorous, and depend, directly or somewhat reduced. and adjacent grass marshes.
indirectly, on the omnivorous or
herbivorous primary consumers and The tidal black mangrove commun- As these waters gradually dry up,
converters we have just discussed. ities are, for the most part, in fre- the fish populations, having meanwhile
Details of the food habits of most Squent contact with tidal waters. In produced several broods of young, move
of the organisms involved are given many places they may be close to the back into more permanent waters in the
by Odum and Heald.8 level of mean high tide and are "tidal" black mangrove and red man-
strongly flushed by the higher tides grove zones, or become concentrated in
We have referred to primary of the year which transport from the disappearing upland fresh and brackish
consumers such as small fish and forest a considerable percentage of ponds. Wading birds congregate at the
crustaceans as removers and export- the accumulated debris and detrital receding ponds and exploit the con-
ers of detritus from red mangrove products. These "tidal" communities, centrations of easily available prey.
systems. This cycle can only oper- particularly in their seaward por- An indication of the magnitude of this
ate efficiently if the consumers tions, probably perform roles similar food source 1 provided by Kahl's
have ready access to the detritus to those of tidal red mangroves. estimates '�that a breeding colony
source. -A system of narrow creeks of wood stork (Mycteria americana) con-
and shallow ponds, coupled with 2. "High" black mangroves. sisting of 6,000 pairs and their young
strong tidal action, is necessary for These "non-tidal" systems range from require 1.2 million kilograms (2-1/2
effective penetration of the marsh clearly supratidal to spring tide million pounds) of small fishes during
by these organisms. elevations. The majority of these a 60-65 day nesting period.

200 Appendixes

By such pathways, the high man- gations was the 1974 series of black The Setting: It has been esti-
grove communities apparently contribute and white verticals produced by Lee matedl� that 5,120 acres of mangroves
to the support of adjacent estuarine County at a scale of 1"=300' for tax formerly existed on Sanibel. We esti-
waters, provided that their function purposes. Additional black and white mate that 2,800 acres exist today and
is not impeded by larvicide spraying, photography at scales of 1"=1000' and we believe that the earlier figure of
ditching or impounding. 1"=2000' (U.S. Dept. of Agriculture, 5,120 acres to have been in error.
Soil and Conservation Service, 1944 The major portion of these (2300 acres)
3. "Impounded" forests. These and 1970 series) was also used for are included in the J.N. "Ding" Darling
forests are characteristically oc- reference purposes. Photo-interpreta- Wildlife Refuge. Additional mangroves
cupied by a mixed black and red man- tion was also greatly aided by a series exist north of Wulfert Road, near
grove community, although in some of oblique, false-color, infra-red Wulfert Pass on Runyon Key, Albright
places white mangroves predominate, aerial photographs taken by Mr. W. Byle Island, Silver Key, fringing Dinken
and in others an almost monospecific of Environmental Services Unlimited Bayou, Clam Bayou, Old Blind Pass, and
stand of blacks occurs.; These for- and provided by The Conservation Blind Pass. Of these, the mangrove
ests are found in situations where Foundation. and beach ridge community on Bowman's
natural levees, perhaps old beach Beach is protected as a park or wild-
ridges or storm drift lines, are life refuge.
sufficiently complete to cause im- Field observations providing
poundment of spring tide waters and ground truth" for the apparent regis- Two ancient beach ridges are ap-
local rainfall for considerable periaphy, were per- parent in the mangrove forest associa-
ods of the year. During drought tion (Figure 1). Running roughly east-
and by numerous spot checks of photo-
periods evaporation from such im- and by numerous spotchecks of photo- to-west they divide the system into an
poundments leads to hypersaline con- graphic features. In the course of outer, middle, and inner system with
ditions and can cfield obervations we determined, as , tidal effect and amplitude diminishing
death of trees. fully as possible, species dominance, in a landward direction. Tidal flush-
vegetative form, geographic extent ing is strongest in the outer system,
Breakdown of forest litter oc- of specific associations, and tidal practically non-existent in the west-
curs largely within the impounded relationships. The overall classi- ern pockets of B and C, and moderate
area, producing copious deposits of fication or characterization of to strong only in the vicinity of
flocculent organic particles so specific communities was determined scour channels of the eastern halves
richly colonized with sulfur bacte- by combinations of features which we of B and C.
ria that they often assume a purple and other workers have found to be
cast. Fresh water or tidal flow is reasonably reliable indicators in The excursion distance of a parti-
evidently inadequate to transport other areas of South Florida. Among cle will be long in sector A but ex-
this floc or "liver mud" from the these are species mix, salinity, tremely short in C. In fact, organic
system during "average" years, with amount and character of leaf litter, production in the western ends of B
the result that the floc layer at- pneumatophore height, periphyton and C appears greater than the abil-
tains depths in excess of two feet communities, substrate characteris- ity of mixing and flushing to assimi-
in places. Such organic masses, if tics, and the presence or absence of late by oxidation, or remove the ma-
disturbed or flushed from the im- certain fish and invertebrates. terial to the adjacent bay. For this
poundments by hurricanes, may cause reason, heavy organic buildup occurs
massive oxygen depletions in ad- in those shallows with a resultant
jacent estuarine waters .12 With thetime and resources high BOD, methane production, and a
available it was possible only to
Liver mud was found up to 5 inches in classify the majdominance of blue-green algae in the
thickness within the natural impound- ties and to assess their respective system. The construction of the
ment on Sanibel Island. We suspect roles and importance in the light scenic roadway across these already
that drying of the impoundment during of previous experience of similar poorly flushed systems can only
the winter allows oxidation of the community "types" in other South aggrevate the problems and, in fact,
floc, and hence prevents buildup to Florida locations: we observed severe hypersalinity
greater depths. (i.e., salinity in excess of 50/,oo)
in early June, and mangroves within
THE SANIBEL SURVEY We also attempted a preliminary the confines of this system of roads
determination of possible interrela- appear to be stressed.
tionships between the coastal man-
Delineation and evaluation of grove communities and freshwater As a result of low oxygen, vari-
mangrove communities was accomplished runoff from adjacent uplands, since, able salinity, and a stressed flora,
by extensive ground observation in in the event of a close relationship, the fauna is also stressed. Only a
conjunction with aerial photography future human activities in upland few species of fish and invertebrates,
at a variety of scales. The base areas could affect the functioning which are euryhaline and adapted mor-
photography used during field investi- of mangrove communities. phologically or physiologically to

Vegetation 201

withstand low oxygen conditions, can 30 feet in height; 40 percent blacks deeply penetrating tidal channels and
occur in areas B and C. Thus, species to 40 feet and occasional white man- swales meandering around the fringes
diversity is low, but the few success- groves up to 40 feet. Size range of of discreet blocks of forest, many of
ful species bcan exist in large num- trees is relatively narrow, the canopy which are, in effect, shallow basins
bers. is virtually closed at 25 feet, very with slightly raised rims.
little discrete clumping of species
is evident, and tidal influence is The low-lying channels with wide
COMMUNITY DESCRIPTIONS moderate to strong. We observed no tidal swales are mostly colonized by
well-defined tidal swales or creeks; red mangroves, some of which are 50
For convenience of description tidal inundation appears to be in the feet high. The canopy is dense and is
we have recognized six categories of form of a uniform sheet flow. virtually closed at 25 feet. Black
mangrove communities. They are prin- mangroves tend to occur in patches,
cipally, though not exclusively, geo- South of this community, where where they may constitute up to 30
graphical in character. They are as the shoreline curves eastward away percent of the individual total. These
follows: - from Wulfert Rad, a much more varied areas, and the shallow basins which
set of communities occurs as far they drain, are frequently inundated
(1) communities east of Wulfert south as Holloway Bayou. A typical and are well flushed by normal tides.
Road, between Wulfert Channel in the "composite" transect from the abrupt The basins are characterized by a mix-
north and Kesson Bayou in the south; edge of the upland "escarpment" to ture of red and white mangroves to
Pine Island Sound would be as follows. 50 feet in height, forming a relative-
(2) forests within the Refuge ly open canopy beneath which Batis
stretching from Kesson Bayou east to The most landward community con- occurs in sparse clumps.
the western shore-of Tarpon Bay that sists of a narrow band of red man-
lie external to the "Darling Memorial groves 25 to 30 feet high located in a Just north of Holloway Bayou a
Drive" levee; shallow swale which is virtually con- tongue of high land projects south-
tinuous from north to south along the east toward Kesson Bayou and the
(3) areas contained within the edge of the upland. Standing water, mangrove communities to the south,
confines of the "Darling Memorial from higher than average tides and east and west, on both sides of the
Drive" levee, 7 from local rainfall, is a frequent bayous, again become more uniform.
feature. Tidal flushing, however, is They are strongly influenced by tidal
(4) eastern shores of Tarpon Bay weak and a considerable leaf litter - action, except in the extreme east
to Dixie Beach Boulevard; layer is accumulating. close to the upland, and consist of
9. o :a mix of red and black mangroves to
(5) communities east of Dixie Seaward of this line lies a 30' in height. Reds tend to predom-
Beach Boulevard; slightly wider band dominated by an inate increasingly as one approaches
open forest of 25' black mangroves the open bayous, but blacks are still
(6) miscellaneous islands and with a sparse understory of reds. frequently encountered.
pockets on the southern aspects of the This zone is somewhat more strongly
island. influenced by tides, although a litter -(2) Kesson Bayou to Tarpon Bay:
buildup is evident. Such buildup is This tract contains the major portion
Within each of these geographic areas, relatively uncommon in tidal forests of the most ecologically significant man-
one to several biologically distinct strongly dominated by black mangroves groves on the island. As can be seen
communities exists. The approximate because gastropods, such as Melampus from the vegetation map, the dominant-
bounds of these are indicated on the coffues, usually consume fallen leaf communities are tidal red or mixed red
vegetation map (See Figure 1) at a material sufficiently rapidly to pre- and black mangroves. The overwhelming
scale of 1"=1000'. vent accumulation. feature is the complex system of red
mangrove islets and interconnecting
(1) East of Wulfert Road: From The weak to moderate tidal nature bays from Hardworking Bayou to Tarpon
the shore of Wulfert Channel-Blind of the above communities is explained Bay.
Pass, for a distance of approximately by a slightly elevated berm which lies
one-third mile south, the mangrove forest seaward. This is characterized by a Very little time was spent in
is remarkably uniform in character. It dense forest of somewhat spindly reds examining these island systems since
commences seaward of an abrupt and well- to 20 feet in height, with a few scat- they appeared to be very similar in
defined scarp at the margin of high tered blacks of similar height. The nature-to the familiar islands of
elevation lands on which sea grape, saw latter are probably much older than the Whitewater Bay and Florida Bay,--and
palmetto, cabbage palm, yucca, wax former. to the systems-in Fahkahatchee Bay
myrtle, and saltbush are dominants. studied by Carter et al.14 Their
Between this point and the open important role as exporters of de-
The mangrove forest is composed shoreline of Pine Island Sound, the trital material, and as shallow water
of approximately 60 percent reds to forest becomes variously dissected by and edge habitats, is well documented.

202 Append ixes

65
62
62 c~

62# 02 ~~~~~ ~~~~~~626 6
65

62~~~~~~~~~~~~~~~~6 4 2

622 626

SANIBEI.-MANCROVE COMMUNITIES ~2

LEEN -white mangrove dominant sorne hulottwoeod, tow red: non-tidal

60 - Strnogly tidal rod Or Mixod mangrove 06 62a a6
65 - Predominantily block mangrove, moderately tidal 6 .< . �I
64 - Weakly tidal red of mixed mangrove >6
65 - Moderately tidal MIXed M30grOVo a t00 2000 3000 6
06 - Naturallt impounded mangroneo (mostly blacks) anod salterns
67 - Scruh red and white mangrove, SCALE tIN FEET
68 - Mangroves damaged in 1973
6 2 ato 672 - Same as above but located within the
artificial impoundment formed by the 10'Dn
Darling Momorial Drive

---Ridge axis
A - outer
8- Middle Sub- system
C - Inrer

Vegetation 203

A~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

6l VS2 686

w ~~~~~~~~~~FIGURE 1: SANIBEL - MANGROVE COMMUNITIES

204 Append ixes

Toward the seaward reaches of Seaward of the impoundment edge, a ditches would produce little ecol-
this ridge-swale complex the swales mixed species tidal community occupies ogical benefit since the fill would
are characterized by black and white a narrow band along the shore of the undoubtedly become colonized by
mangroves ("high" mangrove communi- bay system. Florida holly and Australian pine.
ties), in addition to a few surviving These would compete successfully with
buttonwoods. In certain areas the At the eastern extremes of this any mangroves which were planted or
soil salinities have become suffi- unit the pattern changes, the natural which germinated naturally. Consider-
ciently high to cause the formation impoundment expires and the mangrove ation should be given to the construc-
of salterns or "salinas" consisting community ranges from a tidal red man- tion of a series of shallow, roughly
of open sand areas with sparse grove at the bay edge to supratidal, circular, lakes incorporating the
stunted black and white mangroves. high elevation, mixed small red, black heads of all the ditches. The lakes
The next ridge seaward of this zone and whites within a distance of 400- would be approximately 3.5 feet MLW
of incipient salterns is variously 500 feet. Numerous mosquito ditches maximum depth, with a mean depth
occupied by red mangroves, gumbo penetrate this community from the bay between 2.5 and 3.0 MLW. In addition
limbo and remnant cabbage palms. to the Sanibel-Captiva Road. The upper to providing a marked improvement in
The mangroves tend to occupy the (inland) 300-350 feet ends of each ditch water quality, they could become a
lower slopes of the ridge and are were largely stagnant at the time of useful recreational boating and fish-
building up a deep, dry litter layer. the field survey. ing facility.

It is unlikely that any practi- The southern (or southeastern) (3) Communities within the con-
cal corrective action, such as portions of this tract, between the fines of the "Darlinq Memorial Drive":
pumping water from areas south of the entrance to the refuge and the outlet Three "sub-units" can be easily dis-
Sanibel-Captiva Road, can be under- of the Sanibel River along a mosquito- cussed within the artificial impound-
taken. In any case, it is entirely control ditch into Tarpon Bay contain ment (culverts beneath the "Drive"
possible that the defoliation of Xsignificant acreages of mangroves and connecting the impounded area with
buttonwoods and the formation of associated vegetation which are only the open estuary do not materially
salterns results from the current weakly influenced by tidal action. modify the impounded nature of this
"drought cycle" which southwest They are, for all practical purposes, area because they permit so little
Florida appears to have been experi- non-tidal. A relatively high ground tidal exchange). The sub-units are:
- encing for the past 6 or 7 years, elevation and a natural berm to sea- (a) Large tracts of mangroves in
rather than from any artifical low- ward combine to restrict tidal in- the swale-ridge system lying north of
ering of the Sanibel surface and fluence. the Sanibel-Captiva Road, particularly,
ground waters. in the western portions of the impound-
North from Sanibel-Captiva Road ment.
Seaward of this final ridge lies the land falls gradually for approxi- Except in exceptionally low spots
a community of partially impounded mately one-fourth mile in a series of where ponds occur, the mangrove com-
black mangrove forest between 500 and parallel ridges and swales. The ridges munities ofthe swales are a mixture
1000 feet in width. The trees are are colonized by wax myrtle, Brazilian of reds, blacks-and whites, with reds
densely situated and of a relatively pepper, sea grape, and occasional cab- predominating. Tree heights exceed 30
uniform height at 10-12 feet. Water bage palms and gumbo limbos. Leather feet in places, but the average canopy
depth at the time of the survey (late fern forms the dominant ground cover. level is between 14 and 20 feet. Deep
May) was 2-3 inches, but observation Buttonwoods occupy the low swales litter layers are present in most
of pneumatophore height indicates a with a ground cover of dense Borrichia places. Standing water which occurs
places. Standing water which occurs
maximum seasonal standing water level in places and equally dense Batis in in a few ditches and ponds is an un-
of approximately 4 inches. A buildup others. The buttonwoods exhibit ob- common feature. Salinities in late
of flocculent material to 4 or 5 inches vious defoliation as a result of ex- May ranged from 8-12 ppt.
in places suggests that the impounding cessive soil salinities to dryness.
effect is strong although drying in The absence of Spartina spp. is perhaps The alternating ridges are oc-
winter may allow oxidation and thus a result of predominantly dry soil con- cupied by cabbage palm, papaya, button-
limit the depth of deposition. Salini- ditions. Batis, Borrichia and Acro- wood, gumbo limbo, and invading Brazil-
ties undoubtedly rise in excess of 70 stichum are all capable of surviving ian pepper. The latter is also en-
ppt during the dry season, although in soils of low moisture content. croaching on the higher elevation "dry"
recent rains had moderated this to mixed red and black mangrove communi-
41 ppt in late May.; Black mangroves These 350 foot stretches are prob- ties. These mangrove communities
are overwhelmingly dominant, compris- ably a minimal effectiveness in con- appear to have become established in
ing over 95 percent of all individuals. trolling mosquitoes. Cyprinid popu- earlier times when either fresh water
The northwestern reaches of the natural lations were very low in comparison levels were higher than at present or
impoundment formerly stretched west to those existing in the more sea- prior to the reduction in tidal pene-
into the section now artificially im- ward portions of the ditches. Fill- tration resulting from-construction of
pounded by the "Memorial Drive" levee. ing of the upper reaches of the the "Memorial Drive."

Vegetation 205

(b) Communities fringing open strongly tidal. A mixed community, (6) Miscellaneous Island and
waterbodies. These were formerly fully dominated in most areas by red man- Peninsular Communities: This cate-
tidal fringing mangroves with reds groves to 25 feet, is characteristic. gory has been retained to describe
dominating. They are now only weakly Tidal penetration, by way of several the small units of mangroves, mostly
affected by tides and show signs of wide, ill-defined swales, forms an of recent origin, which occur in the
stress, perhaps in response to rela- effective mechanical export mechanism northwestern sector of the Island
tively rapid large scale changes in to Tarpon- Bay and Pine Island Sound for between-Dinken Bayou and the Gulf of
standing water level. This is par- detritus produced within the mangrove Mexico.
ticularly evident on the landward communities. The exceptions are a few
sides of the open water areas where small areas where black mangroves in- The shorelines of Clam Bayou,
unusual prop-root branching at a uni- crease in dominance close to the up- Blind Pass, Old Blind Pass, and the-
form elevation is very evident. land tracts north of Periwinkle Way. small associated island are occupied
Here the parallel ridge system dampens by tidal red mangrove communities up to
These mangrove communities, as or blocks tidal effect and the estab- 100 feet in width. They are vigorously
detritus producers and wildlife hab- lished mangrove communities are prob- flushed by tidal action near the mouths
itat, no doubt still contribute sig- ably not effective contributors to of the bayous and less so toward the
nificantly to the resource-base of Tarpon Bay. inner reaches, although daily tidal
the impoundment, although their for- inundation and export of detritus is
mer significance to Pine Island Sound North and west of Lady -Finger Lake sill evident. Few white or black man-
is reduced by virtue of their im- lie the remnants of an old mangrove groves were observed-within these
poundment. Since they are apparently forest in which large specimens of all communities.
under stress they probably produce three species are found. In the vicin-
lesser amounts of detrital material ity of Woodring Point very little of Landward of the t idal fringg red
than formerly. the forest area is'strongly tidal; a mangroves a buttnwood-black mangrove-
shoreline sandbarhas formed and pre white mangrove complex is encountered
shoreline sandbar has formed and pre- in a few locations. These communities
(c) Mangroves -previously vents direct tidal access on all but are inundated only by high spring ties
included in a natural impoundment. spring tides. Further south the- ef- and are no
These occupy the-southeastern portion fect of tides is more strongly evi- detritus to adjacent bayous.
of the "impoundment," seaward of a dent as tide-waters penetrate the
large mosquito ditch and levee. The forest from Lady Finger Lake and
natural black mangrove impoundment adjacent coves with low shorelines. Clam Bayou, Old Blind Pass, and
described earlier extended westward Blind Pass exchange with the Gulf of
for about one half-three fourths mile (5) East of Dixie Beach Mexico waters through an inlet at the
into the present artificial impound- Boulevard: The only extensive and southwest corner of Sanibel Island.
ment. White mangroves are now more significant mangrovestand in -this The inlet is generally shallow and
numerous in this portion than in its area is a 70-80-acre tract of strong- guarded by a sandbar except for a narrow
more natural analog to the east. The ly tidal mangroves. Excessive flood- channel near the shore of Sanibel. The
increased occurrence of-whites may be ing and fresh water during construc- sandbar at the inlet indicates the
a reflection of their apparently tion of an adjacent development re- magnitude of tidal flushing is probably
greater tolerance of hypersaline con- sulted in heavy,mortality of trees not great. The sinuous nature of the
ditions. Color differences in the within the tract, the culvert beneath bayous and blocking of wind by Austra-
May, 1974 infrared photography and Dixie Beach Road being inadequate to lian pines and mangroves reduces wind-
shading discrepancies in 1970 series release the increased input of water, induced flushing. Density differences
vertical aerials indicate a stress caused by evaporation and rainfall
reaction among reds and blacks, will produce some flushing, but the
perhaps in response to hypersaline The tract was formerly a fully sandbar again will hinder this.
conditions or to excessively rapid tidal community, dominated by red
changes in water level. We recom- mangrove, although the construction If, as we suspect, flushing is
mend careful examination of this of Dixie Beach Boulevard resulted minimal, pollutants from adjacent
and other mangrove communities within in a significant diminution of human activities should be prevented
the artificial impoundment since they tidal influence. A few surviving from entering the system and con-
are evidently reacting adversely to an white mangroves are recovering and sideration should be given to modi-
effect induced by the impoundment introduced red mangrove seedlings fications to increase flushing. If
levees. - are becoming established. The tract desired, the inlet could be dredged
might benefit from the installation to improve circulation and the old
(4) Tarpon Bay to Dixie Beach of one or two additional culverts cut to the east could be reopened to
Boulevard: Mangrove communities in along Dixie Beach Boulevard, but a improve flushing. These "improve-
the rough triangle between Lady Finger realistic assessment of this must ments" would be made in opposition
Lake, Dixie Beach Boulevard, and Peri- await the re-establishment of a more to natural trends and would require
winkle Way are for the most part mature forest. maintenance dredging.

206 Appendixes

Summar and Conclusions nmunities. If this is so, the instal- solved nutrients from adjacent develop-
Suyand Conclusions lati on of additional culverts beneath ments are prevented from entering this
the "Memorial-Drive" to increase the tract. High nutrient levels could pro-
1. The tidal mangroves (62 and tidal component is a feasible remedy. mote an undesirable growth of green
65 of.Figure 1) are productive and We would guess that four additional and blue-green algal mats on the forest
contribute significant quantities of culverts, positioned where tidal floor before a shade canopy can become
detritus to the Gulf and to Pine flows are strong to the outside of re-established.
Island Sound. This material is im- the "Drive," would provide a strong
portant to the detritus food chain.15 tidal component to the bay system, 7. The mangrove communities to
thus moderating the dry season sa- the north of Sanibel-Captiva Road are
Since these mangroves are asso- linities. unlikely to be greatly influenced by
ciated with high productivity which human activities in upland areas. The
is assimilated via a detritus food web If the stress is a response to road forms an effective barrier to any
to produce sport and commercial fishes rapidly rising impounded water levels northward overland flow, which would,
and shellfishes, and since mangroves in the rainy season, the additional in any event, be minimal because of the
occur in soils which are comprised of culverts would also serve to minimize porous soils of the island ridges.
organic peat materials which, when this. Urban development of upland tracts
dredged, contribute ammonia, carbon east of Wulfert Road or north of
and high BOD, it is concluded that the . We do not believe that the di- Periwinkle Way could conceivably
remaining tidal mangroves be considered version of more fresh water from up- produce runoff waters of interior
remaining tidal mangroves be considered
for preservation. land into the impoundment is a prac- quality, but this eventuality can
tical or desirable method of moder- be forestalled by reasonable plan-
2. The: mangrove communities in ating salinity. There will probably ning practices, such as maximiza-
the complex tract east of Wulfert Road be little or no available fresh water tion of green space, stringent
are by far the most ecologically sig- to be diverted at the height-of the limiting of impermeable surfaces, and
nificant of any which remain outside dry season when it is needed. Fur- detention of initial runoff from
the National Wildlife Refuge. In many thermore, the mangroves within the impermeable surfaces and lawns.
respects they are superior to the com- artificial impoundment have not
munities in thelsodutheastern-portion i historically been highly dependent 8. The mangrove communities of
of the: refuge. They are , for the most upon large volumes of fresh water; Sanibel Island have apparently evolved
part, effectively tidal, and must be they were formerly a predominantly independently of the interior and
consideredas usefulontributors to tidal community. upland fresh water system. They do
considered as useful contributors to
the resource base of Pine Island Sound, not appear to be dependent upon, nor
an important sports and commercial 5. Mangroves fringing Tarpon are they unduly influenced by, surface
ffishery area. Bay show no signs of adverse reaction hydrological events in the interior
to human activities (drainage and of the island.
3. Probably the most "valuable" urbanization of adjacent uplands).
mangrove system of the island is the They are subjected to strong tidal
inlet and bay complex within the refuge, action which tends to ameliorate any
external to the "Darling-Memorial adverse water conditions emanating
Drive." . from mosquito-control ditches and urban
development in the Sanibel River sys-
4. Mangroves within the confines tem.
of the "Memorial Drive" are under stress
of undetermined origin. Nevertheless, 6. The tract of mangroves re- The interior "wetlands" of
they and their associated bays apparent- cently killed by excessive flooding Sanibel Island covered approximately
ly serve as an attractive seasonal bird (impounding) is slowly regenerating. 3,200 acres (1944, aerial photos), of
feeding habitat. They probably no Although the mortality was in excess which 1,100 acres are presently
longer contribute significantly to ad- of 90 percent, the survivors are now impacted by roads, canals, and real
jacent bay systems. -This may be con- securely recovered. Red mangrove estate development (1974, tax maps).
sidered a trade-off, whereby a diminu- seedlings re-introduced by Mr. William These wetlands are delineated by a
tion of the support role of mangroves Byle are becoming established and series of old beach ridges which
to adjacent bays is mitigated by an in- should continue to flourish if adequate appear to limit lateral surface flow
creased feeding habitat for bird life-9 tidal ingress and egress are maintained. rather completely. The wetlands
An assessment of the advantages which themselves contain a complex series of
Within the "Memorial Drive" the may be gained by the installation of low relief (barely discernible from
inner bays become hypersaline during the additional culverts cannot be attempted the ground) parallel ridges and inter-
dry season and this condition may be until the forest reaches a more mature vening swales. All these topographic
responsible for the observed stressed stage. Precautions should be taken to features are expressions of deposi-
condition of specific mangrove com- ensure that runoff waters high in dis- tion and erosion by ocean currents

Vegetation 207

as described by Missimer,16 Shepard areas which are subjected to perma- flowing west into a series of inter-
and Wanlessl7and El-Ashry.18 nent flooding or prolonged periods connected ponds which formed the
of soil saturation sufficient to per- exit to tidewater for this system.
The relationship between under- mit development of "indicator" plant Because there was no barrier "across
lying seawater and the fresh water and animal associations. Thus, to the grain" near tidewater, this sys-
lens on the island has been discussed qualify as wetlands, Sanibel Island : tem probably drained earlier than
from the hydrologic and engineering interior lowlands should have, as any of the others and, conversely,
point of view by Boggess19 and plant dominants, at least some of the became hypersaline sooner than the
Provost20, while the very complex plant species found to be character- others during the drought. This
matter of long-term fluctuations in istics of South Florida coastal wet- pattern remains unchanged to the
sea level have been discussed by lands generally. Concurrently, it present and should have the fewest
Bruun2lwith respect to erosion of would be expected that at least some freshwater indicators present as a
shoreline and Provost22 with respect aquatic vertebrates and invertebrates result.
to coastal development. would also occur-there. The word
used by biologists to define the Subsystem 2 appears to have
Water quality determinations periods of flooding or soil satura- headedin the region just west of
were made at various locations on the tion is "hydroperiod" and, for South the present Rabbit Road and the main
island by Boggess19 and Schreiner.23. Florida generally this may persist Gulf beach ridge and extended west
for the duration of the rainy season to its outlet through the beach
All these accounts give an im- in- areas having little or no water- ridge at Point A in Figure 2. Since
pression that water levels in the shed runoff, to periods of 10-12 its outlet crossed an active beach,
interior were subject to wide fluctu- months in the southern Everglades it probably was virtually a self-
ations over short, as well as long, -where the watershed is very large. sealing system as interior head pres-
time periods and that these fluctua- sure declined with draw-down.
tions were related tc (1) rainfall On Sanibel Island, where rain-
periodicity and amount, (2) occur- fall amounts seem to differ substan- Subsystem 3 appears to have
rence of over-drainage when storage tially from comparable areas of the originated near the main east-west
was lost due to natural break-out of mainland25 , we might expect the ridge (route of the Sanibel-Captiva
the impounded waters, and (3) cyclic hydroperiod to differ in duration Road) about 1.5 miles south of Tarpon
changes in sea level. from nearby mainland areas. Bay in a z-shaped lake system and ex-
tended west and then north, to empty
Narrative accounts24,25 of the into the mangrove marsh via an old
physical appearance of the interior outlet through the ridge about 1.5
of the island during earliest settle- miles west of the present junction
ment all describe broad, open vistasCNDTION of Rabbit and Sanibel-Captiva Roads
of "grassland" broken at intervals by c (point B). There is a hint, on the
clusters and rows of cabbage palms. 1944 aerial photography, that there
Viewing the island now, it is evident mwas a high-water connection or inter-
Not much is known about the
that there has been a significant no cmingling of impounded waters of sys-
change in vegetation which is dis- drainage charactems 2 and 3 before drainage. This
cussed at length below. A widely lowlands of Sanibel Island now genm- and the following system are prob-
held assumption is that alteration erally known as the interior wet- ably the oldest water storage areas
lands.
of surface water storage accompanying from a geologicallstandpoint.
mosquito control26 has been respon- Although the interior lowlands Subsystem 4, by far thelargest
sible for the changes. We believe Subsystem 4, by far the largest
that fires, farming, and more recent of the systems, originated behind
invasion by exotics have contributed as a single management unit for pur- the Gulf beach about 1 mile west of
poses of mosquito control and flood
invgreatly to this chang e poses of mosquito control and all theseood the present-day Tarpon Bay Road and
factors are part of a complex serites control generally, we believe there extended eastward in virtually a
is evidence (1944 aerial photos) that
of environmental impacts on the nat- straight line to the extreme east end
ural system. Each event,.in effect, there once were at least four sepaf c of the present-day Gulf Drive where
set the "machinery of change" in rate collector or/ basin systems it cut an outlet through the beach'
(Fingue 2), each'of which had its Own
motion and these changes agure 2), each i(point C). As with Subsystem 2, this
intermittent interior stream and out-
in progress. would have been a self-closing sys-
let to tidewater, prior to modifica-
tem; its outlet would have filled with
In reviewing the probable past drifting sand by littoral drift, thus
history of the interior lowlands, Subsystem 1 was confined on the reducing the chance for additional
it should be made clear what is meant east, north, and south by old sand loss of fresh water until such time as
by us when we mention wetlands. Wet- ridges, but no such ridge blockea heavy rains once again filled the
lands of Sanibel Island are those accumulating rainwater there from basin forcing another break-out.

208 Append ixes

\ " 117

SANINEL-WETLAND BASIN SYSTEM

Ridge axis
Natural drainago path
H?'f' Hi 0h - weato0r co0n ne0ctIoI0n
Appnoximrate beach margin 0 IDSS 2000 3000
Boundriy betweoen b each and intact or
D Traina~~~~a cyctoen ~~SCALE IN FEET -

Vegetation 209

~SANIBEL ISLAND/

FIGURE 2: SANIBEL -WETLAND BASIN SYSTEM

210 Appendixes

The quantity of storage in the In addition, the present water this estimate. Something closer to
interior, required to breach the Gulf management system is designed to pre- the actual rise may be estimated by
beach ridge, is of considerable in- vent accumulation of water sufficient examining the implications of an
terest to us. In that context, Provost to break out over the beach while pre- observation during July (John Clark,
is quoted as follows: venting the over-drainage that such personal communication) that a 2-inch
"blow-outs" entailed. The effect on rain resulted in a 10-inch depth of
When summer rains raised the interior water storage hydrograph or impoundment in swales. Since this
basin water high enough, the storage curve has been to truncate rain must have been very nearly the
beach at the mouth of Sanibel the highs and lows in water level first of the rainy season, and coming
Slough, east of what is now while preventing intermittent, early as it did "on the heels" of an ex-
Periwinkle Way, would be rainy season ponding which leads to ceptionally dry period, we believe it
breached and a small Mississippi optimal mosquito-breeding conditions. is likely that most of the rain which
River would flow into the Furthermore, the presence of at least fell on the dry sandy ridges quickly
Gulf of Mexico. In 1949 some fresh-to-brackish water in the ran off to the adjacent swales. Al-
we calculated this water channels within the system during though, admittedly, a simplification,
loss at 2000 acre-feet, or drought water provides refuge for re- the ratio of rain to impoundment depth
700,000,000 gallons. With sidual populations of mosquito-eating of 2 to 10 inches (i.e., 1:5) strongly
all this head of water gone, fishes. suggests that there are five times as
the surf would rebuild the much ridge surface as swale area in
beach, so that by the next During pre-drainage times the Subsystem 4. Going further, if we
June the dry basin, virtually storage curve would probably have risen assume that the ridges are 12 inches
devoid of minnows, renewed very slowly during May, June, and July higher on the average than the swale
its storage of rainwater because of spotty, generally light bottoms, we arrive at 1,408 acres of
while hatching billions of rains.19 In August, September and ridge at about +3 feet relative to
mosquito eggs into larvae October the generally heavier rains MSL, and 352 acres of swale, whose
with hardly a threat from -fall on a reservoir whose storage bottom elevation was about 2.0 feet
their greatest potential capacity has been r duced substantially relative to MSL. In a basin of this
enemies.20 by fall high tides. If rains were configuration whose bottom elevation
of sufficient magnitude, which we be- according to Provost varied between
It interests us that Provost does lieve they were nearly every year, .10 and 18 inches relative to Mean Low
not mention that abnormally heavy there was wash-out. If less sub- Water, or about 2 to 3 feet relative
rains caused this wash-out. It gives stantial, the rise in interior stor- to Mean Sea Level, we have calculated
a clue, in the absence of measured age would terminate in mid-to-late that the runoff from a 2.4-inch rain
rainfall amounts, that such wash-outs October and then decline through over the entire 1,760 acres would pro-
were not uncommon prior to drainage. seepage and evapotranspiration-losses duce 350 acre-feet, or enough to fill
We have more to say about this below. until the next rainy season. The the swales level with the tops of
actual mechanics of this annual pat- their adjacent ridges. Beyond that,
In addition to the four systems tern are discussed elsewhere in it would take 12 inches of rainfall,
described above, there are a number these reports. assuming no losses, to raise the level
of smaller rainwater catchment areas of Subsystem 4 to full pool at eleva-
between "younger" ridges behind the Proceeding on the assumption tion +4 feet MSL. According to these
present Gulf beach. One of these that there actually were four major very simplistic calculations, we pro-
lies just behind the beach in the catchment systems on the island pose that the pre-drainage Subsystem 4
vicinity of the dead end on Gulf prior to development, and using Sub- would hold up to 14.4 inches of rain
Drive and has its outlet(s) in what system 4 as an example, we have before blow-out.
is now called the Perry Tract. arrived at a rough indication of
impoundment depth and storage pos- Examination of the U.S.G.S. "topo"
According to our best estimates, sible before breaking through the sheets show several places along the
prior to development, Subsystem 2 beach. To do this we use the ratio beach ridge which are lower than 5
contained 588 acres of low ridge and between 2,000 acre-feet of discharge feet. Almost all these areas are
swale catchment and storage area. described by Provost20 and our esti- present or former locations of fresh-
Subsystem 3 contained 1,240 acres and mate of 1,760 surface acres in pre- water wash-outs. The Perry Tract has
Subsystem 4 contained about 1,760 development Subsystem 4. If the two drains, the westernmost probably
acres. These have been physically re- system were a shallow tray with per- the oldest, which are presently
duced in size to 425 acres, 941 acres, fectly flat bottom, we might assume blocked by a fully developed beach
and 1,027 acres, respectively, by de- that the 2,000 acre-feet of dis- formation.
velopment and Subsystems 2, 3 and 4 charge would have raised interior
have been made one by dredging of the storage about 1.1 feet. In fact, Today, Subsystems 2, 3, and 4
Sanibel River channel and numerous the ridge and swale topography of have been made into one collector-
tributary.ditches. the interior lowlands complicates drainage-mosquito control system by

Vegetation 211

excavation of the Sanibel River parently discontinuous, occurring erable importance to anyone consider-
canal and a series of tributary under the sandy "buttonwood" ridge, ing disposal of nitrogen-enriched
ditches which divert most of the sur- but is absent from under the ad- effluent on Sanibel Island, where the
plus fresh water to Tarpon Bay. jacent marl-bottomed swales. If marls probably are also of freshwater
this is true hardpan, then it may origin, but which are subjected to
In order to understand the exist- represent the long-term position periodic salt intrusion.
ing drainage system and its ecologi- of the water table during the dry
cal implications, we turn to Boggess.19 season of pre-drainage times and The pH of the sodium saturated
Among the many aspects of island thus an interesting reference point soil was sufficiently high that
hydrology described was an estimate for discussion of future water man- normal nitrification following
(p. 27) of 600 million gallons of agement because it would suggest that application of ammonium sulfate
discharge through Tarpon Bay and the water table seldom fell out of equal to a band rate of 100
Beach Road outlets (500 million and direct contact with the marl of the pounds of N per acre was halted
100 million gallons, respectively) swales. at the nitrate stage, with net
following heavy rains, averaging _ accumulations up to 192 ppm of
about 24.5 inches at two gauge sta- The presence of marls deserves nitrate nitrogen but negligible
tions (8 inches in August and 16.5 considerable attention. Apparently nitrates."
inches in September, 1971). This most of the marl soils of South On p. 21 they state the problem more
provides some estimate of rainfall Florida, including surface marls succinctly as follows:
required to produce the 1949 wash- of Sanibel, are of bio-chemical ori-
out20 of 700 million gallons. gin and are formed through calcium The potential for accumulation
carbonate precipitation by a com- of toxic amounts- of nitrite
plex, shallow-water microflora following salt inundation and
INTERIOR LOWLAND SOILS dominated by blue-green algae. Such leaching is obvious, with urea
soils are formed in shallow water being the least desirable N
The accounts by Missimerl6 and under conditions of intense sunlight, source to be used when such a
Boggess19 of surface and sub-surface high temperature, and rapidly (i.e., potential exists.
soils and rock formations on Sanibel daily) fluctuating dissolved oxygen
form an excellent basis for the gen- and pH. Such conditions would have The toxicity mentioned is assumed
eral consideration of water supply, prevailed in open savannahs domin- to apply to agricultural crops; that
hydrology and engineering, but omitted, - ated by Spartina bakeri. Marl is the milieu in which Volk and Orth
except in passing, reference to sur- formation does not take place in work. But their comments may be equal-
face deposits of calcium carbonate deeper, shaded water. The blue-green ly important for future wetland vegeta-
soils of biological origin called marl. marl producers are replaced by green tion on Sanibel, should these areas be
We. found marl to be an important con- algae in shaded locations such as used for reclamation of sewage effluent.
stituent of swale-bottom soils-and of those now developing under the tree From this, we would urge extreme caution
widespread occurrence in Subsystems canopy invading the Sanibel swales. in using the marl-rich areas of the in-
3 and 4. While they are, quantita- terior lowlands for sewage disposal so
tively, not particularly impressive, The fundamental process of marl long as salt intrusion is a potential
we believe they have extraordinary formation has been described recently problem.
ecological significance. by Gleason and Spackman28 who also
quote pertinent literature. Over Finally, Harper 33 indicates that
In examining canal bank exposures large areas of South Florida marl Spartina bakeri, one of the wetland
for marl deposits we also found one deposits of both fresh water and indicators formerly dominant on these
well-developed lens of semi-consoli- brackish water origin are widespread, lands, is associated with "calcareous
dated limey material which greatly as indicated for Dade County.29 The soils" which we interpret as marl or
resembles the hardpan found in acid importance of these to agriculture and mixtures of marl and sand.
sand country of the adjacent main- to natural plant distribution can be
land. Until we can prove otherwise, grasped by reading Department of Agri- In the absence of time to map the
this may prove to be an example of culture soil surveys30 and Craighead.31 aerial extent of these marls we were
"beach rock" mentioned by Missimer, Such soils are very complex from forced to make -a few assumptions. One
but we believe it to be true hardpan drainage, salt relationship, and nutri- of these was that marl formation is a
derived from precipitation of organic ent balance standpoints, and one of slow process and that marls would be
material and "migrating" minerals in the few papers discussing chemical best developed in the geologically
solution at the contact between the and physical management of marl soils older parts of the island. That would
water table and overlying oxygenated is provided by Volk and Orth.32 be systems 3 and 4 of the interior. A
sands. The "type" exposure is lo- Their comment (Abstract, p. 1) re- second assumption was, following the
cated at the junction of Island Road garding behavior of nitrogen in fresh- prior reasoning, that marls would be-
and Tarpon Bay Canal on the west bank water "Perrine marl" which has been come progressively less important in
of that canal. The exposure is ap- saturated by salt water is of consid- the more recent swales of system 2 and

212 Appendixes

in swales near the beach ridge. Our out much of systems 3 and 4, calls to greater than loss of water to the at-
travels on the island appear to sub- mind a leaky pan or saucer resting on mosphere. With that, ground water is
stantiate this pattern with marl being a sand bed having greater or lesser recharged abruptly and becomes one
visually absent from the beach ridge water-holding capacity. Although with the swales. From then until the
depressions. greatly over-simplified, that is, end of the rainy season the "leaks"
generally ignoring the hydrology of in the "saucer" are closed, not to be
The point of such emphasis on soils under varying rainfall condi- opened until the following winter.
marl, alone or mixed with sand, lies tions, the theory goes as follows.
in its ability to seal otherwise porous
soil, thus impounding surface waters The interior basins are basically Two factors probably have major
and, once wet, to retain moisture. porous sand with water table at a mini- influence on what happens to this
-xperience with marl as a sealan wasmum level in spring. On top of this filled system. Under pre-drainage
gained during construction of shrimp "dry" sand are water-retaining marly conditions there may have been a
culture ponds on an elevated, crushed
culture ponds on an elevated, crushed areas in a ratio of approximately 5 rather rapid adjustment in island
rock base at Florida Power and Light acres of exposed sand to 1 acre of marl. groundwater downward sometime in late
Company's Turkey Point electrical gen-
Company's Turkey Point electrical gen- During spring drought the water table is October and November, for it is known
erating plant site in Dade County. We at a distance below the surface so that that the South Florida high-water
learned that a four-inch thick layer
of marnled theffectively a sflrdcthck layer - the tops of the sand ridges are dry and, levels of September and October fall
of marl effectively sealed such sub- for a time, water repellent. Later they off rather rapidly as the prevailing
stratum against leaks in ponds having absorb much water . southeasterly winds of summer are
average depths of three feet and maxi-
rmumage depths of rsix e feet. and max- replaced by powerful northeasterlies
Add early rainy season showers at a of October and, in rapid succession,
XThere are many swales in' the Sanibel weekly or greater intervals and observe by northwesterlies (i.e. polar fronts)
interior that have marl or sandy marl that there is immediate impoundment in of November and December. Such wind
deposits of equal or greater thickness : the marl-bottomed swales. Continue ob- shifts tend to push the summer's
and we ohave seen these areas covered serving and one sees loss of impoundment accumulation of fresh water from
immediately after early rainy season depth; some water being lost to evapora- South Florida coastal marshes which is
shower s. It is our y view that such marls tion and plant transpiration while some replaced rapidly by high salinity water
were extremely important in maintaining seeps into the adjacent ridge and downward of adjacent Gulf. On Sanibel, where there
the hydroperiod and providing shallow toward the water table. If the rains are is no large tributary watershed contri-
but intermittent ponding prior toalbeing of minor character this lateral and down- buting runoff-to the island interior, we
but ditchermittent p ondaing prior to beward seepage has only a minor effect on would expect a rather rapid reduction in
ditched, as well as maintaining soil
saturation between showers. ground water level. If subsequent rains ground water level then as a result of
saturatione btweglschwated insucthe p ositsare delayed, as is commonly the case on tide height reduction and wind-sweeping
swales. Thus any ditchbing l which t Sanibel, the marl saucer drains, but being losses of surface water. This might
tended to crosssuch swales Thus any ditching which andmarl, the soils stay-moist and wetland shorten the winter interval when the marl
draw off the temporary ponding of plants begin their annual growth period. swale impoundment and ground water were
contiguous. If no beach wash-out occurred
May, June, and July would tend to In due course a second and third rain in the hypothetical year this water level
reduce the aquatic-character of the
falls. If of minor character and widely adjustment should not result in immediate
swales, if not the soil moisture.
swales, if not the soil moisture. separated in time the above process is drought, just a "slump" from +4 to +3 foot
In thte lattercontext, nsuch marils repeated with little increase in ground of storage.
saturated, by capillr noit necessarily water level below but with repeated inun-
underlying ground water -is in; close dation and drying of the swales. During Under present drainage conditions,
contact. This would tend to soften pre-drainage times each inundation of the the lower-than-natural level of drainage
the impact of drainage through ditch- swales would permit invasion of brood control structures would have been
ing on plants requiring higher de- stock of fishes and other aquatic draining offf "surplus" waters from the
grees of psoil moisture, but the organisms as well as hatches of insects beginning of the time that storage levels
tendency then would be away from having aquatic larvae. overtopped those controls. This could,
true wetland to a: marginal upland . :when coupled with the falling tides and
water budget favored by plants not Finally, at some time each year, pushing winds of October and November
geared to standing in water (es gt perhaps in late August, tide levels cause an abrupt end ot the hydroperiod
geared to standinazilian peppwater (e.versus Spartna). around and under the island begin to or at least reduce the contact between
rise. This causes a rise in the ground the swale waters and ground water.
water and automatic loss of potential This, in turn, would quickly permit
storage capacity in the sand bed under evapotranspiration to remove remaining
THE LEAKY SAUCER THEORY the saucer. At the same time rains in- surface waters.
crease in frequency so that the swales
The presence of marl in swales remain flooded and seepage downward With the system intact, the wetland
alternating with sandy ridges through- from the ridges and impoundments is character of the interior, including

Vegetation 213

shallow surface flooding of the swales As it happens, areas where inter- The above discussion points out
probably lasted from June through Decem- mittent ponding and drying are the rule the difficulty revolving around
ber. With drainage, these conditions are also prime producers of marsh mosqui- management of marshes where the same
probably prevail only in smaller, toes and a few species of specialized factors which tend to favor small,
unditched areas. marsh fishes, such as Gambusia affinis, desirable fishes and'many showy birds
Fundulus confluentus, Poecilia latipinna also guarantees maximum production
and Cyprinodon variegatus. Not incident- of mosquitoes and a few other obnoxious
INTERIOR WETLANDS AS HABITAT ally, these fishes are major forage insects having aquatic larvae. It is
species for highly prized wading birds a dilemma that requires very careful
such as white ibis and most of the herons consideration.- It may be the most
and, when driven to adjacent bays by critical decision to be considered.
Judging by word-of-mouth reports receding water levels of fall and winter,
there were no extensive areas of per- of numerous sport fish including tarpon, If the future planning of Sanibel
manent fresh-water habitat on Sanibel snook, ladyfish, snappers and crevalle Island involves raising the water table,
Island prior to settlement. A few jack. It is probably safe to assume there will be a reinstatement, at least
natural ponds can be seen scattered that abundance of such small fish is in such managed areas, of the conditions
about the island in 1944 aerial photo- directly proportional to the acreage of which fostered larger -aquatic insect
graphy, but we believe the recent flooded shallow marsh available to them, populations and greater number of oppor-
profusion of lakes, borrow pits, and it is the presence, beginning early tunistic killifishes, all of which
ditches, and drainage channels in the in the rainy season, of extensive marsh thrive on alternating flooding and
wetlands has greatly increased lake ponding which permits maximum numbers of drying of the marsh.
habitat. In addition, while the 1944 these fishes to be produced. It is also
photography clearly shows a permanent important in an ecological sense if not The value of edge vegetation in
channel where the Sanibel River now strictly in-a biological sense to consi- wetland pond situations is usually very
exists, even this has been increased der these small fishes as "annuals." high. On Sanibel natural ponds are
by dredging. Under such conditions generally surrounded by Spartina bakeri,
we would expect an increase in fresh- buttonwoods, leatherferns, occasional
water aquatic plants and animals as an empirical nature, which indic a number of other
very high winter mortality and red mangroves, and a number of other
well as a significant increase in vgrasses, shrubs, and vines. In addi-
permanent water edge which has direct resultant small brook stock to begin tion, cattails, Thypha sp. are rela-
bearing on wildlife use of the area. each new spring crop even though they tively common and stonewort, Chara
have a life expectancy potential of hornemannii, occurs in greater or lesser
On the basis of the-above gen-or more years. abundance wherever water is clear.
eralizations, and in light of our Widgeon grass, Ruppia maritima, is also
experience in similar areas (e. g., widespread in coastal brackish marshes,
Cape Sable marshes) in South Florida Fishes would probably have been as well as in the Sanibel River and
which have not been extensively the same species as are presently older development waterbodies less than
altered by man, we have concluded found on the island, but freshwater three feet deep at low water stage.
that the aquatic fauna of predevel- centrarchids (i.e. sunfishes) such Ruppia is of special interest because
opment Sanibel Island interior as largemouth bass, Micropterus sal- of its wide tolerance to high turbidity
wetlands had an overwhelming pre- moides; bluegill, Lepomis macro- levels, as well as to salt. Duckweed,
ponderance of species capable chirus; spotted sunfish, or shell- Lemna sp., has been observed at numer-
of withstanding alternating wet-dry cracker, Lepomis punctatus and redear ous locations in the river, as well as
conditions and considerable sunfish, Lepomis microlophus, would in ponds which are over-enriched.
tolerance to low oxygen and salt, have been far fewer in number while
the latter important if winter mosquitofish, Gambusia affinis;
drying drove these animals to the marsh killifish, Fundulus conflu- While Lemma is valuable as
adjacent bays. We expect that the entus; sheepshead minnow, Cypri- food for waterfowl, its presence
insect fauna then, as now, was domi- nodon variegatus and rainwater killi- generally indicates poor mixing
nated by saltmarsh mosquitoes. Aedes fish, Lucania parva would also have and high nitrogen inputs. Chara
sollicitans and A. taneorynchus. There flourished in greater numbers. Other is used as food by waterfowl and
probably were larger numbers of biting Fundulus species would also have been offers habitat for fish-food or-
flies, family Tabanidae, then than at common, passing seasonally from bay ganisms, but because it grows so
present. Drainage has reduced the habi- to interior waters, as were the rapidly may produce anaerobic
tat of all these. The dragonfly popu- sailfin mollies, Poecilia Latipinna. black muds resulting from decay
lation probably was large but restricted Spotted gar, Lepisosteus platyrhincus, of shaded-out lower stem masses.
to fewer species such as Libellula aur- and least killifish, Heterandria for- It is an indicator of hard water
ipennis, and Cannacria gravida, which mosa, which are found on the island where calcium is abundant. Al-
easily tolerate salinity of 15 to 20 ppt now in small numbers, probably were though Chara is best developed
as larvae. never abundant. in shallow, clear water, it can

214 Append ixes

grow profusely in clear 20 foot- drier sections of the interior wetlands. Tendipes; several damselfly species
deep lakes. Ruppia maritima seeds The latter are especially abundant in and seven species of dragonflies
and foliage are heavily utilized the overgrown farm lands of Sanibel and of which Libellula auripennis was
by waterfowl and may be the single form one of the major items of food for dominant. The larval stage of the
most important aquatic bird food red-shouldered hawks, Buteo lineatus, latter has been found by us to thrive
plant of coastal South Florida. ' which nest in tall Australian pines in mangrove marshes where salinity
Ruppia is common in brackish bays, .(personal observation). Wetlands are averaged 18 ppt and where the nymphs
saline marshes and freshwater important habitat for other food were exposed to the air by falling
areas up to 8 or 9 feet in depth. animals of the same hawk, which tides of winter. At those times the
S f -7-En Rconsumes: leoparad: frogs, Rana f nymphs cling to the concave under
Shore and ditch; bank vegetation s pipiens sphenocephala; ngrove leaves,
includes wax myrtle, Myrica ceri- frogs, Pyla sp. and small snakes apparently;surviving quite well for
fera, which has some value for wild- and lizards. days at a -time in a saturated atmos-
: life being used extensively by red- phere made possible by capillary move-
winged blackbirds for nest sites. Animals of the interior wet- ment of sub-surface water through the
Where buttonbush, Cephalanthus lands are mostly planktonc, nek-; peat soil. All the dragonflies seen
occidentalis, occurs it is used as tonic, or associated with emergent-,'' ;by us are common in calcium-rich
food by mallard and other ducks as plan. ptant te Periphyton andaufwuchs waters of coastal South Florida,
well as providing excellent roost- communities).-The general paucity - returning to the sea to spawn. Large
ing cover. Primrose willow, Lud- of benthicorganismsint Sanibel numbers of adult blue crabs are strand-
wigia-Peruviana, which has seeds River probably ieflects accumu- ed by receeding surface waters of the
used by waterfowl and willow, Salix lation of organic sediments with southern Everglades area whenever
caroliniana, offer cover and nesting low bottom dissolvedy oxygen levels there is a drought. They simply can-
areas. Gallinules feed extensively: and high levels of hydrogen sulphide. not move overland to open water once
on willow flowers (T. Alexander, Considering the poorly flushed cha- their "home" ponds go dry. This seems
personal communication)t. racter of this waterway we would most likely to happen in Spartina
expect such conditions to arise bakeri and Distichlis spicata grass
The exotic plants, castor bean, naturally. The leaf fall from marshes which are typically cov-
Ricinus communis; Brazilian pepper, marginal vegetation is very heavy ered with shallow strand and pothole
Schinus terebinthifolius, and Aus- and acts as "green manure." When ponds only a few inches deep just
tralian pine now occur frequently large quantities of sewage effluent I as are found on Sanibel.
along canals and the River. Burk- are added to such a system in the
halter et al. indicated no wild- absence of some-mixing force one Among the chordates we observed
life value for them, but it is now should not be surprised over total raccoon, Procyon lotor, in fresh
known that raccoons, opossums, and deoxygenation. The problem is com- water areas, but they and their
wintering robins, Turdus migratorius, plicated by the virtual sheltering signs seemed more common in the
consume vast quantities of- the Bra- from wind with which to circulate marginal wetlands and mangroves.
zilian pepper berries in season. the deep water. This is aggra- Green tree frogs seemed most abun-
Anhingas nest in waterside Austrailian vated by steep banks, narrow width dant in cattails while leopard frogs,
pines and many water birds use them of the cRana pipiens, were observed whelmin vemany
al che::�.canal pi andse overwhelming vege-my
for roosting and feeding perches. tation. The later also screens wet areas, particularly in Bacopa
Doves, both ground dove, Columbigal- the sun's rays preventing light growing in damp soil of the deeper
lina passerina, and mourning dove, penetration in an already dark swales.
Zenaidura macroura, feed on the fine, water. There are some other waters,
winged seeds of Australian pine, as notably in mosquito ditches, which The occurrence of bluegill,
do migrating American goldfinches, are virtually in the same condition. shellcracker and largemouth bass
Spinus tristis. They are usually less of an environ- nests in the canal along the southern
\ f; > mental hazard because they are 0 side of the Bailey Tract and at a
Herbs, vines, ferns, and various few locations in the western reach
flushed, at least pernodically by
gr asses are everywhere abundant in tides or upland runoff. They are of the Sanibel River indicates that
the swales of the interior wetlands usually shallower-than the river these areas have good freshwater
combining to form cover so dense thate control stru conditions throughout the dry season
sand they lack the control struc-
shy or secretive animals are difficult and pollution effects have not yet
tures which so greatly aggravate the
to see. The salt ponds of the island situation in the rivers moved "upstream" from the developed
may be surrounded by salt grass, Dis- areas.
tichlis spicata. Where it occurs one
may reasonably expect to find the cut Common aquatic insects in the The fauna of the interior fresh-
tunnels of rice rats, Oryzomys palus- interior included water beetles, waters is relatively poor compared
tris, which may share space with the Haliplus; backswimmers, Plea sp.; to the mainland and this reflects the
cotton rat, Sigmodon hispidus, in the water scorpions, Ranatra sp.; midges, insular position of Sanibel Island,

Vegetation 215

,plus a somewhat transitory nature of deep in scrub mangrove areas, often form piles of helpless individuals on
the freshwater system. Few primary have deposits of brown to purple window ledges and porch floors.
freshwater fishes (only the centra- ."liver" muds up to five inches thick
chids and gar.) exist, and the centra- which are prodigious producers ofi We believe they have great signi-
chids may have been brought to the hydrogen sulphide. Seasonal flood- ficance as food for numerous birds and
island by anglers. As one would ing to depths of 2 to 10 inches is animals, although this has not been
expect, the tolerant-euryhaline common in the higher elevations. documented in Florida. Adults and eggs
species are dominant, comple- If such flooding is in open, sunny are collected in great numbers and used
mented by normally marine species locations where Batis grows there will as food by man and birds in Egypt and
which can invade freshwaters rich be no liver mud because of dry-season Mexico. They have been imported into
in dissolved solids. oxidation of accumulated organics. England for use as food. They have also
been utilized as food for young
The area west of Tahiti Drive Only a small number of species of game birds in wildlife management
is generally more saline and the fishes and invertebrates occur regularly programs. Water boatmen seem to
flora and fauna reflect this salin- in these shallow, changeable habitats, be the brackish-water counterpart
ity increase. Mangroves become dom- but they often occur in very large num- of salt-marsh mosquitoes found
inant shoreline plants along interior bets. The small sheepshead minnow, slightly higher up on the marsh
shorelines and estuarine invertebrates Cyprinodon variegatus, is the dominant gradient in even more transient
and fishes become more numerous. The fish in such areas. It can tolerate aquatic habitat. We have not seen
inch-long caridean shrimp, Palaemon- salinity ranging between 0 and 140 them occurring in large numbers
etes pugio and P. intermedius, occupy ppt.35 It over-winters in the "floc" with mosquito larvae.
algae an-d-Ruppi maritima beds in ponds within the black mangrove-button-
this area. wood zone of the high tidal-marsh.
Males in iridescent nuptial blues and LOWLAND AQUATIC FAUNA
Prior to drainage, seepage of orange may be found in such ponds begin-
fresh water from the interior pro- ning in December; breeding continues At the time of our visits to
bably prolonged the fresh-to-brackish into May or June. *The young are quick Sanibel Island the interior aqua-
character of marginal wetlands and to colonize newly flooded areas, par- tic milieu was restricted entirely
permitted growth there, on ridges, ticularly in the Batis and Salicornia to borrow pits, development lakes,
of such nominal freshwater plants as zone and ranges from there onto the mosquito or drainage ditches , and
cabbage palms, leatherferns, etc. algal mat of the salterns or salinas the "Sanibel River" system. Within
With drainage this freshening tenden- during the rainy season. Its "pre- the tract bounded on the east by
cy would have been reduced so that ferred" upper salinity range appears Beach Road, on the north by the
halophytes would spread further inland to be about 60 ppt. Sanibel-Captiva Road (S.R. 867),
and, in extreme drought, soil salt on the west by Rabbit Road and on
would have become severe enough to The dominant insect of the chemi- the south by the Gulf Beach Ridge,
kill plants and create plant-free cally changeable, seasonally flooded salinities ranged between 0 and 4
salterns. Our recent observations, marginal wetlands is the water boat- ppt (seawater = ca 35 ppt) which
made during drought conditions, showed man, Corixa sp. of the family Corixi- is well within the upper, limit of
many signs of plant stress in the mar- dae. It is a true bug of the order -10 ppt tolerated by many fresh-
ginal wetlands and the soil chloride Hemiptera, but unlike most such bugs water organisms of South Florida
determinations of Alexander illustrate it has no pronounced, external pierc-
the severity of effect of this salting ing mouthparts and is not predacious. Water east of the Sanibel
on vegetation. These insects are ooze feeders sub- Causeway-Beach Road dividing line
sisting on algae, protozoans, and was uniformly saline to the water
The vegetation of the marginal detritus gathered by the first pair of control at Beach Road where salini-
wetlands described below is dominated legs modified for scraping. It does ty of 31 ppt was measured. Salinity
by salt-tolerant species while the have hidden small piercing mouthparts of 4 ppt west of the control struc-
fauna there is limited in species rich- called stylets with which it sucks ture indicates the effective clo-
ness and consists of insects and B juice from algal filaments. Being sure of the Sanibel River at this
fishes which are noted for tolerance air breathers, they make constant trips point by the closed structure. A
to environmental extremes. Blue- to the water surface to capture a bubble slight leaking through the struc-
green algae dominate in the shallow, of air which envelops them and imparts ture attested to'a modest head of
seasonally flooded to wet soils of the an overall silvery sheen to their bodies water within the river.
marginal wetlands. These algae form as they quickly return to the bottom.
mats 1 to 2 centimeters thick, especial- They winter as adults, laying their Higher salinities were encount-
ly over the saline sands in bright, top-shaped eggs on plant debris. Adults ered around- the periphery (Figure 3)
sunny situations. Anaerobit condi- take wing and fly to new areas at the of the above described interior sec-
tions commonly exist under such mats. beginning of the rainy season. At such tor as in ponds near the Perry Tract,
Shallow permanent ponds, up to 2 feet times they are attracted to lights and in ponds within the Dunes develop-

216 Append ixes 6

0_11~~~~~~~~~~~~~~~~~~~~~~~~~~

5613

'((1K~~~1

SANIBEL-SALINITY i

LEGEND

0 - 5 6 Salinity parts per thousand, June 3- 4

- Sal. opt., May 28- 29 200 30
Road
Streams and canals SCALE IN FEET

Vegetation 217

I'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -

I~~~~~~~~~~~~~~~~~~~~~~~T a.'

I I a3

14 ~~~~~~~~~~~~~~FIGURE 3: SANIBEL-SALINITY

218 Append ixes

ment tract, in the ditch along Tar- outlined and discussed at length.26 In that location there are ponds
pon Bay Road between the bay and the which must be very similar,
Post Office and moving flood tide Our main attention was direct- though much smaller, to the
water in the Tarpon Bay Canal to with- ed, therefore, to the ridge and swales of pre-development Sanibel.
in feet of the second set of culverts swale topography of the interior Those ponds have an average maxi-
near Island Road. There- was some lowlands and what the conditions mum depth of about 24 inches
evidence, discussed in the section must have been which formed them. during the peak rainy season
on upland vegetation, that salt intru- Once again, the marl of Sanibel months of August and September.
sion was widespread around the same becomes important as we read comments - They dry during severe drought
perimeter with effects being most ments such as the following from but their bottom muds, which
noticeable between SR-867 and the p. 146: are composed of marl over quartz
edge of the mangrove forest. Tidal sand, seem never to dry out. The
effect on lake levels was noted in ". . . The periphtyon (marl- dominant large plant is Spartina
the development borrow pit parallel- producing algal community) bakeri which,-under those condi-
ing Gulf Beach Drive. probably functions as a sig- tions, forms spectacular free-
T b nificant primary producer and standing tussocks in the seasonally
This brings us to the probable an integral part of the food flooded centers of the ponds anda
past as well as present condition chain . . Periphyton in dense wall of plants at the pond
of aquatic resources, and the water other areas has been found edges. When the ponds dry, the wet
itself, of the interior lowlands. We to be a food source for may- marl bottom sediments are quickly
have only a few studies to guide us to flies, caddisflies, stone- carpeted by B acopa monnieri and
past conditions on this subject, and flies, snails, scuds, zoo- a small needlerush Eleocharis sp.
only one by Schreiner23 which has plankton, and fish."
attempted to treat the subject of water During the early rainy season
quality from the habitat suitability Continuing to p. 150 we read: months while water levels are still low
viewpoint. and fluctuating, such ponds are "alive"
"Calcareous periphyton develops with mosquito larvae, water boatman
He describes the essential water on plants growing in. a variable and, along their sandy margins, fly
quality and biotic condition of the depth of water though generally (Tabanidae) larvae. According to per-
Sanibel River and his comments the best development of the sonal observation by Fort Myers Beach
(pp. 7-8) regarding the low bot- algae in the upper two feet of mosquito control staff, the mosquito
tom oxygen content, virtual ab- the water column." larvae form dense aggregations in these
sence of benthic organisms other clear waters which can be seen
than the larvae of Chironomid On the same page Gleason and Spackman28 from a low-flying helicopter.
midges, and high levels of hydro- comment on optimal conditions for the There are practically no fish
gen sulfide were supported by marl-forming periphyton community. predators in such ponds until
our own much more superficial later in the summer when water
examination. It cannot be doubt- "In general the periphyton levels have risen high enough to
ed that the present channel is prefers well-lighted open- form shallow, overland connection
acting as a sump for the accu- spaced communities of barely between these temporary ponds and
mulation of organic material of emergent or submerged plants." permanent water where residual
natural and man-made origin. populations of mosquito-eating
His description of the presence Pondering all the clues available, fish have survived the winter
of coliforms and high nutrient including the presumed character of dry-down.
levels added to the conditions pre-development vegetation and rather Ditching has been used to
of oxygen, benthos, etc., sug- limited thickness of marl when allow ingress of such fish to the
gests that the channel of the compared with mainland locations insect food can result in equally
river is in an advanced state we have come to two possibilities imagined, free access by fishes
of overenrichment and is a poor- as to the pre-drainage character to such enormous reservoirs of
to-bad habitat for aquatic organ- of island lowlands: (1) the hydro- insect food can result in equally
isms.- The problem may be further period was too short (e.g. August- large populations of young fishes
complicated by salt intrusion in December) in most years to permit by late summer. The difficult
the manner discussed in the sec- optimum periphyton-marl develop- part of such management is to
tion on marl soils as well as ment, or (2) that the hydroperiod prevent over-drainage, for with
hastening a changeover in the was longer and flooding deep over-drainage goes much of the
river from a green algal community enough to inhibit maximum develop- natural food production potential
to a blue-green system which is ment. We are inclined to the of such marshes and a food-chain
notoriously effective under anae- latter view because of observa- reaction which culminates in reduc-
robic polluted conditions. Other tions made on a large, undrained tion in food supplies for some
problems with the river have been island south of Naples, Florida. piscivorous birds.

Vegetation 219

From these observations, we Water quality in the swales would contributing to it as recharge
would surmise that the swales in have been very high, particularly area.
systems 2, 3, and 4 of the Sanibel in the more temporary early-
lowlands were, with minor differ- season ponds. Dissolved oxygen (2) In order to keep this
ences due to depth potential, would have decreased in the deeper wetland area in a natural state,
virtually identical to the above- water during late summer due to and to maintain the cbrdgrass habitat,
mentioned ponds. If this is true, the decomposition of vegetation it will be necessary to manage water
the interior of Sanibel was almost but probably was not limiting supplies much more effectively than
certainly a wetland whose swales (i.e. below 2 ppm) for benthic has been previously the case. It
contained active marl-forming organisms. appears to us that in order to manage
periphyton during the months of water, retention of rainfall (the
May, June, and July. By August, Nitrogen and phosphorus only natural source of freshwater on
waters would have risen to depths would probably have been vir- the island) is absolutely essential.
of perhaps two feet at which time tually undetectable in water. To accomplish this, effective water-
Spartina bakerii would be virtually level control structures will be
the only emergent plant visible in Inasmuch as wash-outs of the needed at Beach Road and also at
the swales and around their margins. beach, with resultant overdrainage Sanibel-Captiva Road at the Tarpon
Such ponds capture and hold 0 of the system occurred, there would Bay structure, and at any other point
have been massive drying and oxi- where the Sanibel River may be con-
water with the first rains, the depth dation of organic edin
~~~~~~increase be' g~relate dation of organic sediments. Salt nected to saltwater. Other water-
and frequency of such rains. On they intrusion probably occurred at management structures would also be
basis of limited observations. On we such times, at least in the sea- desirable at points along the system.
baestimate that thed oserv ponds have water ward ends of the drained systems. All these should be carefully managed
This would have tended to inhibit and diligently maintained by a respon-
dep ths of a foot or less during May, growth of salt-intolerant woody sible city agency having police powers
June andJuly and the water is very
clear. Bacopa and needlerush can he plant species and gave rise to necessary to prosecute violation of
clear. Bacopa and needlerush can be
clearly seen flourishing on the bottom a community of facultative halo- the function of the system once
during that early rainy season ponding. phytes. installed, in order to prevent the
duringbthat early raingy thse eason pounding. ; * - vandalism and sabotage of control
It is probably during these early structures that has occurred in the
rainy season months, while water levels Inasmuch as the above recon-- past.
are low and variable, and water struction is true, we see a general
extremely clear, that marl formation shortening of the aquatic phase of (3) Elevation of the hardpan
takes place. With the onset of heavy the hydroperiod, fewer aquatic insects, may provide insight into the mini-
rains in August the ponds rise to the including mosquitoes, diminished fish mum desired level of the normal dry
maximum and their waters darken with population with little change in species season water table. Elevation of
tannins from adjacent uplands. The composition, and a tendency toward water in the river has little eco-
lower light levels, thus available overenrichment of permanent water on logical significance but maintaining
to the-benthic periphyton community the island, and growing dominance of dry-season levels-at or about the
as a result of increased depth and upland plants over original wetland hardpan level would ensure contact
turbidity, tend to favor non-marl- vegetation. Farming, fires, drainage, between marl bottoms of swales
forming filamentous green algae species. and pollution have all interacted in and the water table. This, in
Examination of the fine structure of various ways to create the present day turn, would ensure prolongation
the marl might confirm this reconstruc- interior wetland. - of the hydroperiod.
tion of events.
(4) As discussed elsewhere
At slightly higher eleva- rs I a sOs in this report, (Taylor Alexander,
tions leatherfern would have CFonclusiO Section 3) many areas show salt and/
probably dominated just as they or drought effect which only a higher
do now, but there would have (1) From the above descrip- water table would remedy. Mainte-
been no exotic plants and cab- tion it appears to us that the nance of higher water levels to pre-
bage palms and large buttonwoods area south of the Sanibel-Captiva vent this stress may require diking
would have dominated the higher Road between Beach Boulevard and and ditching to protect existing
ridges. Tahiti Road and north of the beach development from seasonal flooding.
ridge, can be considered as essen-
There would-have been large tially and originally a freshwater (5) We have concluded that re-
populations of killifish but habitat, although it has brackish construction of part of the system
very few sunfishes due to a gen- water characteristics because of would, if possible at all, bring with
eral absence of deep, permanent saltwater intrusion. Gulf Drive it larger mosquito populations which
fresh-water bodies now provided may be considered as the southern would be indicative of a "working"
by lakes, borrow pits and canals. extent of land in wetland or system but which probably would not

220 Append ixes

be tolerable to the island residents and allowed the fishes to move over- (19) If only one or two of the
any visitors unless great care is land. three major storage systems experi-
taken in the engineering and manage- enced wash-out at any particular
ment program. (11) The d6minantaquatic organ- time the storage in the others
isms were those adapted to extremes would have acted as a buffer against
(6) Since the several areas of light, temperature, salt, and bio- overdrainage. Combining these sys-
which now receive sewage effluent chemical change, Thus aquatic insects, tems and preventing maximum storage
have eutrophis algal blooms or near aquatic larvae of other insects, such reduced this buffering potential.
bloom conditions, it appears impera- as mosquitoes, killifish, and a few
tive to ensure that non-point sources, tolerant freshwater species, such as (20) The development of the
as well as point sources, of nutrients the spotted gar. island has resulted in lower high-
be lessened and controlled so as to water-stages and, ideally, prevented
be of the highest possible quality. (12) Drainage has been fairly overdrainage through wash-outs.
To this end retention ponds, sand effective in reducing the swale
filters with dry wells and swale areas as intermittent ponds but has (21) The marl soil found in
should be encouraged wherever possi- probably resulted in smaller popu- swales which permits early rainy
ble. Management should plan future lations of insect-eating fishes as season ponding leading to a wet-
development so as to integrate these well as reducing mosquito populations. land hydroperiod for plants can be
devices into a system which would rendered ineffective by canals cut
keep enriched water in and on the across the swales and thus lead to
high ground aslong as possible. (13) Pre-drainagewater qua- invasion by upland plants which are
high ground as long as porssible. lity was probably high with nutrients ccessful than the native
Septic tanks are completely inappro- more successful than the native
priate for management of sewage in 00 virtually undetectable in water. species.
such a system subject to long-term
high water table conditions. (14) ccasional ver-drainage
of the systems by wash-outs of the
(7) In pre-development times beach ridge probably permitted
there were probably four major rapid oxidation of accumulated Upland Cormu nities
natural wetland water "catchment" organics which, in turn, reduced
systems on Sanibel, each with its the oxygen demand during succeeding Vegetation Management
own intermittent outlet to tide- impoundment.
water. Within each of these sys-
tems, which were separated by more- (15) Creation of deep canals
or-less effective major sand has permitted accumulation of anae-
ridges at elevations of five or more robic sediments from natural as well The upland and wetland vege-
feet above Mean High Water,there as man-made sources with resultant tation of Sanibel is largely
were many low ridges separated reduction of populations of desira- secondary or highly disturbed with
from one another by shallow swales.; ble fishes and invertebrates. the exception of the mangrove com-
There appear to be about five times munity (Section 1). The ecosystem
as many acres of these low ridges (16) Freshwater fishes, such is seriously impacted by exotic
as of swale surface area. as sunfish and bass, are now found plants throughout, with the except-
only in newer ponds or in stretches ion of the tidewater mangroves.
(8) Marl is a constituent of of the Sanibel River farthest from The island vegetation at the turn
swale bottoms in many areas and is development because of pollution. of the century was probably that of
believed to have considerable impor- (17) The Tarpon Canal is an extensive prairie, very much like
tance as a "sand sealer" which per- that of northwest Cape Sable today.
mits rapid, shallow flooding of a discharging arge quantities of Here one sees an extensive graminoid
temporary nature during the first fresh water eintoa system which had cover with lines of cabbage palm on
three months of the rainy season. the slight ridges_. Cabbage palms
ment. This water and resultant
were probably the dominant non-
scouring capability might be put
(9) Marl-forming periphyton graminoid on all the ridges except
to use flushing east-end develop-
is productive during those months of mento use flushing east-end develop- the beach on Sanibel.
shallow and fluctuating depths in the
swales. (18) The interior of the island After abandonment of farming,
once had a significantly greater the first species to invade were
(10) Those same months were the freshwater-storage capacity than the same pioneers one sees today
insect-dominated months; reduction now but was subject to loss of that in newly disturbed sites. Wax
of their numbers by predators began water by beach wash-outs. The fre- myrtle, saltbush, and Iva, all now
naturally in August as water levels quency of these wash-outs is not dying out under the canopy of taller=
rose to cover the intervening ridges known. species, were common invaders. Cab-

Vegetation 221

bage palms also underwent a popula- is considered to have been acceler- and need control now and several
tion explosion. The great change ated by drainage and the control of others that could easily become
came with the population explosion wildfire in recent decades. His critical.
of the two common exotics, Aus- comments on "disburbed areas" have
tralian pine and Brazilian pepper. not proved valid in all locations. Casuarina equisetifolia, Aus-
Brazilian pepper is the pressing This is due to the unexpected in- tralian pine, introduced asastreet
problem in the interior lands. vasion of many farmed areas by tree about 1920, has now become the
Success over the native vegetation Brazilian pepper-and the subse- canopy dominant over much of the
is definitely related to increased quent domination of the native island and is capable of encroach-
activity by man, including fires -- flora so as to completely modify ment on every plant community. It
wildfire at first to open the canopy the order of normal secondary has colonized disturbed areas and
for invasion, and fire suppression succession for the region. the beach. Since much of the island
later that allowed the invaders to
has been stressed or disturbed, the
survive until large enough to be Under the community identi- potential of spread into the remain-
fire-resistant. fied as "the mixed subtropical ing "natural habitats" is immediate.
In terms of impacted land and forest climax," Lemon suggests sites Wildfire, hurricanes, and man's
vegetation, the farmed land repre- with "dominants to be Sabal palmetto, activities can oDen the way for
sents the area where development Quercus virginiana, and perhaps immediate invasion. This species is
would cause the least additional Pinus elliottii var. densa." And an abundant seeder and wind-distributed
impadt on the remnant of the ori- then states "There is a good deal of seeds are always available. It is
ginal ecosystem. To return to and concrete evidence of this type of salt resistant and can survive in all
maintain original habitat locally community on Sanibel Island." but the most saline habitats. There
will require considerable effort and Cooley13 lists P. elliottii as are probably two other species of
continuing management. In fact, infrequent in his mixed woods habitat. Casuarina on the island. One produces
Xthe Sanibel Island people know The writer also found saw palmetto, seed and the other spreads by root-
today is what it has always been Serenoa repens, and other pine land sprouting. The latter is a slower but
in the eyes of many; and it may dominants at site 35, as well as extremely potent invader for this
only be practical to try to restore similar locations. Also in the cur- reason. Most native plants tend to
limited parts of the ecosystem to rent field work P. elliottii was die out when shaded by Australian
the pre-development state. If this found at two sites: 4 (near Dunlop pines and cannot reproduce where a
decision is made, these areas should Road) and 30. The above evidence, thick carpet of "needles" accumulates.
be selected with great care. coupled with Roman's 1774 report (in
- Cooley13) of a-grove of pine trees, It is recognized that this tree
The following discussion repre- strongly supports the concept of the is the shade tree for residents and
sents ideas and recommendations previous existence of pine land on does supply habitat for some animals.
that are considered to be important the higher elevations. The possi- However, it should be studied with the
to the future ecological situation bility and desirability of reestab- idea of its restriction to certain
and habitat management on Sanibel. lishment of pine land will be areas and its removal from "wild areas."
discussed later. It can be controlled by fire and poison.
Stump sprouting is common, so cutting
EXISTING CONDITIONS in itself is not a permanent control.
EXOTIC PLANTS It is suggested that two species be
Lemon36 discusses principal considered for replacement of Casuarina
terrestrial communities. His treat- This designation refers to species canopy. These are the native pine
ment of plant communities is also that have been introduced and are (Pinus elliottii, slash pine) and the
still essentially valid. However, therefore not a part of the native native southern red cedar (Juniperus
the community designated "grassland flora. In some cases they have become silicicola). As stated earlier, the
and savannah communities" has so common they are listed in floras slash pine already grows on the island.
parently undergone great changes as "naturalized." In sub-tropical The cedar, common on islands a short
in the last 20 years. It has been Florida there are several species that distance to the north, has been
shrub-invaded and some has been have proved to be disastrous to the observed by the writer to start from
lost to development. The only natural ecosystem. On the premise seed naturally under an Austra-pine
remnants found can no longer be that diversity in habitat and species canopy. This is an exception to the
identified as he described the com- is necessary for stability and to sup- statement made about the inability of
munity. Also his "spartina marsh ply niches for a varied fauna, some native species to become established
community" is so heavily shrub-in- exotic plants are a detriment. These under the thick duff. It is felt that
vaded by Brazilian pepper, wax myr- are the ones that tend to form pure using the two natives as a long-
tle, and saltbush that it no longer stands and eventually out-compete term replacement of Australian pine
looks as he described it, except for native species. There are two of is reasonable. (See additional
very localized areas. This change these on Sanibel that are critical comment below under "storms.")

222 Append ixes

Schinus terebinthifolius, Other exotic species found
Brazilian pepper, was a desirable and considered as possible future TABLE OF SOIL SALINITY
landscape shrub in the mid-1950's problem plants are:
and was not recorded in either the Conductivity in millimhos/cm/251C
Cooleyl3 nor Lemon36 reports, but Psidium guajava - guava
was discussed with concern by Sansevieria thyrsiflora - bow- Site 50 1.0 - old citrus,
Provost27 in 1968. Today it is string hemp unstressed buttonwoods
found in every community, and has Bryophyllum pinnatum - life Wulfert button-2.8 - drought stressed
produced a closed canopy over much plant woods buttonwoods
of the abandoned farmland in the Vitex trifolia Bailey tower 4.3 - marl slough,
eastern part, and has become estab- Wedelia trilobata (site 60) stressed plants
lished and locally dominant in -the Site 49 7.0 - stressed button-
interior wetlands where it is shading woods
out Spartina. Ordinary flooding does FIRE Marsh, south 25-.0'- killed camphor
not kill established plants. There of river, mid- weed
is no known control for old estab- Use of fire to maintain the island
lished plants except removal. Spartina marsh should be considered.
Successful removal by blade, without Presently, this marsh is being invaded Crop plant* response related to
elimination of all native species, by several shrubs as stated earlier. conductivity
was observed in the 80 acres cleared Dead and dying culms are common under
in 1974 by the Island Beach Club. the woody plant margins. The Spartina 0-2 Salinity effects mostly
If a Spartina marsh were renovated and associated graminoids would bene - negligible
in this manner, sprouting and seed- fit from a properkly managed7 burn. It 2-4 Yields of very sensitive
ling Brazilian peppers could possi- is most likely that the original crops may be restricted
bly be controlled by prescribed extent of Spartina in the internal 4-8 Yields of many crops re-
burning. In any event, this plant marsh was related to the wildfires stricted
can follow the same disturbances known to have swept the island during 8-16 Only tolerant crops yield
that Australian pine does and pro- the farming period. If a pineland satisfactorily
duce large seed crops every year. area is established, it too will need 16 Only a few very tolerant
These are mostly bird-distributed. prescribed burning to properly main- crops yield satisfac-
Its total removal is recommended. tain it as a community type. torily

Melaleuca quinquenervia (caje-
put or punk tree) is a third exotic SOIL SALINITY *Tolerances for native species under
capable of dominating a natural consideration on Sanibel are not accurate-
habitat in the same manner as the A few conductivity measurements iy known. However, stress will occur in
previous species. Isolated seed- were made to determine the reason for lowest soils- during droughts. Higher soil,
bearing trees were noted in several certain stress symptoms seen on some given a good water supply, should support
locations. Seed supply is always plants. Most all the samples taken in most plants except where sapray is a
available on the trees and it is low areas showed soil salt content too factor.
estimated about 17,000,000 seeds are high (above 4 millimhos) to allow crop
present on an average-sized tree. farming today. Several of the samples
It needs a wet situation for estab- were taken where old crop rows were
lishment. Should an area be dis- still visible. It is felt that the
turbed and seeds released at a time brackish soil situation has become cri-
bably never extensive in recent
of favorable soil moisture, a closed tical for some of the native species. times and have been encroached by
community of cajeput would develop. This stress is aggravated by drought, introduced and exotic shrubs as
Seed-bearing speciments of this drainage, and the recent rise in well as used for development. They
species were noted in several sites. sea level. (See Table of Soil Salinity.) are mostly associated with the
Cajeput is salt tolerant and can south side of the Island and appear
invade mangrove communities on the to be characterized today by the
brackish water margins just as Bra- ENDANGERED COMMUNITIES occurrence of Dodonea viscosa
zilian pepper does. Furthermore, (varnish lead) in the grassland
it is not controllable by fire. The communities that appear on the highest locations and by
These trees should be removed and critical in terms of survival at Muhlenbergia cappillaris (muhly
probably some control should be this point in time are those desig- grass) on lower locations. These
established over their use as land- nated by Cooleyl0 and Lemon36 as are good rabbit, gopher turtle,
scape trees. grassland types. These were pro- and certain bird habitats. Here

Vegetation 223

_again the exclusion of fire has that Fort Myers has a ban on 1. Maytenus phyllanthoides -
probably been a factor in the planting these as street trees. molina. Small shrub,: salt resis-
dominant species shift. This ban was a result of storm-, tant, will grow in mangrove fringes,
related tree damage. This is red fruit.
Spartina marshes are being further argument for the control
invaded by saltbush, Brazilian of exotic species. .2. Dalbergia ecastophyllum-
pepper, leather fern, and climb- legume vine. Excellent to bind
ing hempweed. The extent of in- PLANT PESTS beach sand, large woody rambling vine,
vasion varies with location. In salt resistant.
every case, as soon as shading Toxicodendron radicans
occurs, Spartina will die out. (poison ivy) has long been recog- 3. Jacquinia keyensis - joewood.
nized as a problem on the Island. Excellent small dense foliaged tree,
It is present in all habitats salt resistantt
except the tide-water mangroves.
This plant should be controlled 4. Chrysobalanus icaco - coco-
C 0 0 Much of the beach (not all - in all areas where the public use plum. Good hedge plant, responds well
was visited) appears to lack a is high. to pruning, not salt resistant.
good cover of native beach and
dune species. Australian pine is PINELAND 5. Spartina bakerii - cordgrass.
frequently tee dominant. In any - ; e Pi- Interesting when isolated as a large
event, a beach well protected by As mentioned earlier, Pinus clump. Good color variation. Fresh
a cover of native species is the elliottii (slash pine) is present and brackish areas.;
best protection against storm on the island and probably repre-
erosion.: Sea oats should be m sents a relic community. It is: 6. Piscidia piscipula - fish
planted extensively. Considera- suggested that this tree be intro- poison tree. Does well in island
tion should be given for planting duced to those locations where saw habitats, leafless in winter.
Ambrosia hispida, coastal ragweed, palmetto occurs in the understory.
landward of the sea oat zone. It On naturally high land it will also 7. Mastichodendron foetidis-
is a common native on many of the be useful as a yard tree. This simum - mastic. Good-sized tree,
coastal islands of the west coast plant requires special handling and good fruit for birds.
and is an excellent sand binder. the State Foresters should be in-
Excessive tracking was observed in volved for plant source and timing. 8. Ipomoea pes-caprae - rail-
several sites. This kills vegeta- Once a few trees are established, road vine. Good beach binder and
tion and invites erosion. natural seeding should occur. ground cover in area subjected to
salt spray.
ENDANGERED SPECIES
STORMS :: : :: 9. Caesalpinia crista - gray
After carefully studying our nicker bean. Thorny vine, ornamental
The Australian pine and the 61 sites throughout the island, it and useful to produce barriers, e.g.
cajeput represent a severe second- was felt that endangered species beach approaches.
ary storm hazard. Not only do is not presently a significant
toppled trees block roads and issue. However, note should be 10. Pinus elliottii - slash pine.
damage buildings, they also create made of the previous comments on Good evergreen tree, storm resistant,
a peculiar condition in the "wild endangered communities. good bird food.
lands., First there is the accu-
mulation of fallen timber that USEFUL NATIVE SPECIES FOR LANDSCAPING WETLAND SPECIES
tends to be caught shy of the
ground where it does not rot Several species seen during The following list comprises the
readily. Of greater ecological the field work can be useful as wetland plant indicators common-to
concern is the pock-marked effect landscape plants. A number of Sanibel Island. Group I are considered
it produces on the surface. This these, such as seagrape and cab- as freshwater indicators, but they may
unevenness is not natural and bage palm, are recognized and are be found in brackish water areas.
does affect the distribution of in the trade. It is suggested Group II are indicators of wet areas
recovery vegetation. The Aus- that the following be considered but are transitional with upland com-
tralian pine forest across the (there are others,�such as the munities. They often form the upper
street from the Conservation several species of Cacti) and possi- boundary between true wetlands and
Office is a good example of this bly an island nursery be established upland areas. Group III are indicators
problem. It should also be noted for a supply. of marine and estuarine wetlands.

224 Append ixes

Group 1: 3. Lugo, A., Sell and S. Snedaker. 12. Tabb, D. C. and A. C. Jones. 1962.
1973. Mangrove ecosystem Effect of hurricane Donna on the
Spartina bakerii, cordgrass analysis. p. El-E60 In The aquatic fauna of North Florida Bay.
role of mangrove ecosystems in Trans. Amer. Fish. Soc. 91(4): 3
Cladium jamaicense, sawgrass the maintenance of environmental 375-378.
quality and a high productivity
Typha spp., cattail of desirable fisheries. Center 13. Cooley, George R. 1955. The vege-
for Aquatic Sciences, Univ. of tation of Sanibel Island, Lee
Bacopa monnieri, water hyssup Florida, Gainesville, Rept. to County, Florida. Rhodora 57: 268-
the Bur. Sport Fish. & Wildl. 289.
Pluchea purpurascens, camphor
weed 4. Idyll, C. P., D. C. Tabb and 14. Carter, M. R., L. A. Burns, T. R.
B. J. Yokel. 1968. The value Cavinder, K. R. Dugger, P. L. Fore,
Sesuvium maritima, sea purslane of estuaries to shrimp. Proc. D. B. Hicks, H. L. Revells and
Marsh and Estuary Management T. W. Schmidt. 1973. Ecosystems
Salix caroliniana, willow (only Symp., La. St. Univ., July 1967: analysis of the Big Cypress Swamp
fresh water) 83-90. and Estuaries. S. Fla. Ecol. Stud.,
U. S. Env. Prot. Agency, Atlanta, Ga.
Group II: 5. Tabb, D. C. 1966. The estuary
as a habitat for spotted sea- 15. Heald, E. J., W. E. Odum and D. C.
Conocarpus erectus, buttonwood trout (Cynoscion nebulosus). Tabb. 1974. Mangroves in the
Spec. Publ. Am. Fish.. Soc. 3: estuarine food chain. pp. 182-189
Borrichia frutescens, sea oxeye 59-67. In Gleason, P. U. (ed.), Environ-
ments of South Florida: Present
Acrostichum danaeaefolium, leather 6. Heald, E. J. 1971. The produc- and Past. Mem. Miami Geol. Soc.
fern tion of organic detritus in a 2: 452 pp.
South Florida estuary. Univ.
yIva imbricata, marsh elder Miami, Sea Grant Tech. Bull. 16. Missimer, T. M. 1973. Growth rates
6. 110 p. of beach ridges on Sanibel Island
Group III: Florida. Trans. Gulf Assoc. Geol.
7. Fell, J. W. and I. M. Master. Soc. 23: 383-393.
Rhizophora mangle, red mangrove 1973. Fungi associated with the
degradation of mangrove (Rhizo- Wanless. 1971. Sanibe
Wanless. 1971. Sanibel
Avicennia germinans, black man- hora mangle L.) leaves in
grove South Florida. p. 455-465 In Island to Charlotte Har-
L. H.- Stevenson and R. R. Colwell bor, West Florida. pp. 170-
Laguncularia racemosa, white (eds.), Estuarine Microbial Eco- 175 n Changing Coast-
lines. McGraw-Hill Book
mangrove logy. Belle W. Baruch Coastalrk, N. Y.
Research Institute, University 579 pp.
Salicornia virginica, glasswort of S. Carolina Press.
8. Odum, W. E. and E. J. Heald. 1972. 18. El-Ashry, M. T. 1966. Photo-
Batis maritima, saltwort Trophic analyses of an estuarine interpretation of shoreline
mangrove community. Bull. Mar. S changes in selected areas
Distichilis spicata, saltgrass Sci. 22 (3): 671-738. along the Atlantic and Gulf
Coasts of the United States.
9. Provost, M. W. 1969. Ecological Univ. of Illinois PhD. Thesis,
control of salt marsh mosquitoes Univ. of Illinois7387
References m : : with side benefits to birds. Proc.
Tall Timbers Conf. on Ecological 19. Boggess, D. H. 1974. The shallow
Animal Control. Feb. 27-28, 1969. fresh-water system of Sanibel
1. Davis, J. H., Jr. 1940. The Island, Lee County, Florida,
ecology and geologic role of 10. Kahl, M. P., Jr. 1962. Bioener- with emphasis on the sources
mangroves in Florida. Pap. getics of growth in nesting wood and effects of saline water.
Tortugas Lab. 32: 307-412. storks. Condor 64: 169-183. Fla. Dept. Nat. Res. Report of
Invest. #69: 1-52.
2. Craighead, F. C., Sr. 1954. 11. Kahl, M. P., Jr. 1964. Food eco-
Land, mangroves, and hurri- logy of the wood stork (Mycteria 20. Provost, Maurice W. 1969. Man,
canes. Fairchild Tropical americana) in Florida. Ecol. Mon. mosquitoes and birds. Florida
Gardens, Bull. 19 (4): 5-32. 34: 97-117. Naturalist, April: 63-67.

Vegetation 225

21. Bruun, Per. 1969. Sea-level rise No. 4. U. S. Dept. of Agric. in so. It will probably be practical
as a cause of shore erosion. J. cooperation with Univ. of Fla. to try to restore only limited parts
of the Waterways & Harbors Divi- Agric. Exp. Station. Text and Maps. of the system to the pre-development
sion, Am. Soc. of Civil Eng. state. Such areas should be selected
31. Craighead, F. C., Sr. 1971. The with great care.
22. Provost, M. W. 1973. Mean high Trees of South Florida. Vol. 1.
water mark and use of tidelands The Natural Environments and Their 2. All remaining tidal mangrove
in Florida. Fla. Sci. 36 (1): Succession. Univ. of Miami Press, communities should be preserved.
50-66. Coral Gables, Fla. 212 pp.
3. The mangrove communities to
23. Schreiner, S.--P. 1974. A water 32. Volk, G. M. and P. G. Orth. 1966. the east of Wulfert Road are effective
quality analysis of the Sanibel Effects of sodium chloride on contributors to the resource base of
River system. Windham College, physical and chemical character- Pine Island Sound. Their preservation
Putney, Vt. Mimeo Rep. to Sanibel istics of Perrine marl. Proc. of is strongly recommended.
Captiva Conservation Foundation. Soil and Crop Science Soc. of Fla.
12 pp.. 26: 12-22. 4. The fringes of tidal mangroves,
predominantly red mangroves, bordering
24. Dormer, Elinore M. 1975. The 33. Harper, R. M. 1927.' Natural Dinken Bayou, OldBlind-Pass, and Blind
Sea Shell Islands, A History of resources of southern Florida. Pass should be preserved. The button-
Sanibel and Captiva. Vantage Fla. St. Geol. Surv.-18th Ann. wood-black-white mangrove complex
Press, 1-210 pp. Rept. 206 pp. landward of these may be considered
-~~~~~- ~expendable.
25. Fritz, Florence. 1974. The 34. Burkhalter, A. P., L. M. Curtis,
Unknown Story of Sanibel and R. L. Lazor, M. L. Beach and 5. A planting program should
Captiva. McClain Printing Co. J.- C. Hudson. N.D. Aquatic be initiated to establish a cover of
1-267 pp. weed identification and control sea oats and coastal ragweed on the
manual. Bur. Aquatic Plant beach dunes, which were devoid of good
26. Anonymous. 1975. Proposals for Research and Control. Fla. stabilizing ground cover at most of
improvements in water flow and Dep. Nat. Res. Tallahassee, the sites visited.
salinity control structures in Florida. 100 pp.
the Sanibel River system. Sani- 6. Serious consideration should
bel-Captiva Conservation Founda- 35. Pearse, A. S. and G. Gunter. be given to leveling the bottom of the
tion. 8 pp. 1957. Salinity. In: Treatise Sanibel River and tributaries to eli-
on Marine Ecology -and Paleoe- minate sediment traps and inhibit
27. Provost, M. W. 1968. Sanibel cology. Vol. I. Ecology - development of anaerobic conditions.
Island: Geology, Topography, ( J. W. Hedgpeth, ed.). p. 143.
Vegetation. Hand-out for Flo- 7. If cost and engineering con-
rida Audubon Soc., Fall Conf., 36. Lemon, Paul C. N.D. Ecology of a siderations permit, thought should be
Sanibel.- 10 pp. Fl Shell Island, Sanibel, Lee County, given to setting aside some additional
Florida. State Univ. College for portions of catchment areas 2, 3, and 4
28. Gleason, P. J. and W. Spackman, Teachers (unpublished, no date, for restoration and management at
Jr. 1974 Calcareous peri- but apparently contemporary with higher water levels, and to diverting
phyton and water chemistry in the Cooley paper, ref. no. 13). surplus from these areas east via the
the Everglades. pp. 146-181 In "leveled" river to the outlet at Beach
Gleason, P. U. (ed.), Environments 37. Tabb, D. C. and R. B. Manning, Road where such flow might move canal
of South Florida: Present and 1961.- A checklist of the flora organic sediments seaward. If this is
Past. Mem. Miami Geol. Soc. 2: and fauna of northern Florida a reasonable alternative to Tarpon Bay
452 pp. Bay and adjacent brackish waters discharge then a sand-trap lake should
of the Florida mainland collected be placed at some point upstream of the
29. Jones, L. A. 1948. Soils, geo- during the period July 1957 through Beach Road structure to prevent silta-
logy, and water control in the September 1960. Bull. Mar. Sci. tion of receiving waters at Lingren
Everglades. U. S. Dept. of Agric., Gulf and Carib. 11 (4): 552-649. Road.
Washington, D. C., Soil Conserv.
Serv., Agr. Exper. Station, Bull. 8. Since nutrients were almost
No. 442, 168 pp. Recommendations certainly limited to undetectable
levels in pre-development waters,
30. Soil Conservation Service, U. S. sewage effluent from any source should
Dept. of Agriculture. 1958. Soil 1. The vegetative communities be kept from interior wetland areas.
survey (detailed-reconnaissance), of Sanibel Island have been severely To this end, consideration of an
Dade County, Florida. Series 1947; impacted during the past 70 years or easterly flowing runoff pattern be-

226 Appendixes

comes even more critical and areas
within' the present developmeht zone
more important for land disposal.

9. Wherever canals exist, all
unnatural (i.e. exotic) vegetation
which contributes debris to the water
should be removed, by hand if necessary.
This applies especially to Brazilian
pepper and Australian pines.

10. Control of Casuarina by fire
and poisoning is recommended in "wild
areas." Pinus elliottii and Juniperus
silicicola (southern red cedar) should
be considered for use as replacement
trees. Similarly, Brazilian pepper
and cajeput should be removed from the
island by a continual cutting program.

11. Spartina and associated grami-
noid communities would probably bene-
fit from a program of controlled burning
to remove invading shrubs.

12. Additional culverts should be
installed beneath the "Darling Memorial
Drive" to increase tidal influence with-
in the artificial impoundment. (We do
not recommend the diversion of fresh
water into the impoundment.)

13. Any decision concerning the
installation of further culverts be-
neath Dixie Beach Boulevard should be
delayed until the character of the re-
developing mangrove community to the
east becomes discernible.

14. No runoff from any adjacent
urban development projects should be
directed into the heads of Dinken Bayou
or Old Blind Pass. Tidal flushing is
probably inadequate to prevent accumu-
lation of dissolved nutrients and par-
ticulate organics. The tidal mangrove
fringe is insufficiently large to be
a significant nutrient scrubber.

227

APPENDIX

BEACH GEOLOGY 229
The Sanibel Island Coastal System 230
Barrier Island System 230
Estuarine System 231
Mainland and River System 232
Inlet System 232
Nearshore Shelf System 232
Climatic System 233
Physical Oceanography 235
Geologic Framework of Sanibel 237
Holocene Sea Level Changes 237
Geology of Sanibel Island 238
Geology of the Nearshore Shelf 242
Geologic Processes of the Coastal Zone 244
Beach Dynamics 244
InletDynamics : 246
Coastal Management of Sanibel Island 248
Beach Management 248
Inlet Management 249
Coastal Setback Lines 249
Conclusions 251
Recommendations 252
Literature Cited 253

229

APPENDIX 3

BEACH GEOLOGY

by Stanley R. Riggs

"If man wishes to build his works on which will dictate to a large extent out the twentieth century. This
the fringes of such a battleground the future responses of the coastal attitude evolved with the development
(the coast), he must understand that zone -- man. The construction of of our life-style which includes sec-
the rules of this ancient battle re- extensive walls of condominiums, ond homes and leisure living along
quire the beach, the berm, and the summer homes, resorts, and highways with the development of major indus-
dunes to shift constantly before the along the beach areas produces -tries in tourism, recreation, and
assault of the sea." "permanent" economic barriers within water-based sports. The attitude of
a highly dynamic, changeable natural man combating nature to control all
C.J. Schuberth, 1971 system. Thus, we take a not-so- potentially destructive natural
fragile natural system that gives coastal processes has been at the
with and modifies itself to the ever- center of the .S. Army Corps of
changing energy regimes and processes Engineers' efforts to develop methods
of the coast, and produce a "quasi- and implement coastal protection
permanent" system that is no longer along the shorelines throughout our
The coastal zone is probably the allowed to change. Thus, we create country. The Corps' philosophy is
most dynamic natural system on the a very "fragile" system that is in an dramatically stated in their publi-
surface of the earth. The continu- increasingly more stressed equilibrium cation entitled Land Against the Sea
ously operating processes of the situation. This stressed system will (1964) in which they conclude-te re-.
waves, tides, and currents, along with exist, however, only until it is sub- port with the statement "Our campaign
the all-too-frequent high energy jected to major periods of high against the encroachment of the sea
storms, are continuously affecting energy. At this time major change must be waged with the same care that
and modifying this buffer zone between will occur and the "fragile" system we would take against any other enemy
the ocean and the land. Sanibel, like 'will ultimately be restored to a threatening our boundaries ." (. 43)
any coastal zone, is both a conse- natural equilibrium, but now at man's Largely because of this philosophy,
quence of its geologic past and a pro- expense. we have approached open defiance and
duct of the dynamic geologic processes challenge. This all-pervasive "man
operating daily and continuously. "Protection of our seacoasts" against the sea" philosophy has not
There is now another major variable has been a priority project through- only been totally unsuccessful, but

230 Appendixes

all too often has culminated in in- to insure compliance with such plan- energy regime of the atmosphere pro-
creased adverse coastal responses. ning so that these unique and natural ducing complex wave, current, and;
Schuberth (1971) states that "if man characteristics of the island shall be storm tide systems which are super-
tries to change these-rules (of the preserved." Through home rule, the imposed upon the normal astronomical
natural beach), he can only fail; great majority of citizens decided to tidal system. This system of main-
andiin his failure he may even under- guarantee the preservation of the land, rivers, estuaries, barrier
mine the fragile hold of these out- "natural systems" which are not only islands, inlets, and nearshore shelf,
posts against the powerful sea." Our the basis of.their economy but which along with the respective energy
present attitude towards the use and also make Sanibel Island unique among regimes and thesresulting processes,
"protection" of the coastal area does coastal islands-. The enclosed tech- represent a total coastal unit. This
modify the coastal environment; the nical report on the beach system of unit is an integral system of environ-
form and magnitude of the modifica- Sanibel Island provides a set of ments and processes in which each part
tion varies with the activity and recommendations based upon the speci- interacts with all other parts; a
the environmental sensitivity. These fications as defined by the natural given process in one part of the sys-
modifications stress a delicately system itself. These are the require- tem will produce responses in each
balanced natural system, generally ments that are dictated by the natural other portion of the coastal unit.
disrupting whatever equilibrium does processes and are essential if the All of the adjacent environments and
exist and thus accentuates the prob- coastal system is going to be pre- the basic processes of each portion
lem and compounds the consequences. served in both a healthy and stable of the system must be included in
non-stressed condition and if develop- developing any management or land use
Minimal detailed geological or ment is going to proceed in a fashion plan. Therefore, I will briefly de-
engineering data are available for to guarantee the greatest safety for ; scribe each part of the coastal unit
the Sanibel IslTand ar The rela- l andproperty. in this section and will get into the
tively few studies which have been pertinent geologic processes and re-
done are good, however very limited. . i ' as tal sponses as they relate to Sanibel
Even though I do not necessarily The Sand ioastal Island in the next section.
agree with the conclusions of this
work, my intent is to use the data as system
a basis upon which to question and
challenge the classic approach of re-
solving the conflict of "man against
nature" within t he Sanibel coagatlstal an extensive barrier chain which ex- BARRIER ISLAND SYSTEM
zone.: I :Ibelieve we can nIo longer? tends from Anclote Key south to Cape
Romano along the Gulf of Mexico coast The estuarine system is bounded
afford to atntack nature as a bad guy of western peninsular Florida. In on the Gulf side by five barrier is-
dthati needs tamingo coustrolling, and the specific area of this study, the lands which extend some 30 miles
molding into bur" ideas ofh the s "way Fort Myers area, the barrier chain south from the Charlotte-Lee County
ofit our efforts w ith this classicn encloses a large estuarine body dom- boundary to San Carlos Bay (Figure 1).
of our efforts with this classic
money-driven approach in attempting inated by Charlotte Harbor with The four northern islands are a rel-
to, derive total: economic development numerous smaller sounds and bays atively narrow and short string of
potential out of the coastal-zone. around the perimeter (Figure 1). The islands which trend north-northwest.
The b Iasic environmental losses, as Charlotte Harbor estuarine system is The islands range from about 200 feet
well as the long range economiccosts bounded to the east and north by the up to a little more than a mile in
and losses to man are incredible. We , very low and swampy lowlands of pen- width and from 4 to 7 miles in length.
insular Florida from which it re- Sanibel Island, which forms an arcuate-
tion that nature is process, that it R ceives the fresh water discharge shaped hook across the southern end
is interacting, that it responds to through three major rivers: the of the Charlotte Harbor estuarine sys-
laws, representing values and oppor- Myakka, Peace, and Caloosahatdhee tem. is considerably larger than all
tunities for human use with certain Rivers. The estuarine system is of the other islands. It is about 12
limitations and even prohibitions to bounded on the Gulf of Mexico side by miles long and varies in width from
certain of these...we must realize five barrier islands, which include about 1/2 mile in its narrowest zone
man's design with nature" (McHarg, Sanibel Island. These islands are to almost 2-1/2 miles at its greatest
1969). separated by five passes which connect width. Since Sanibel is arcuate-
the estuarine system with the Gulf of shaped, it actually trends northwest
Sanibel Island became incorpor- Mexico. Seaward of the barrier on its western edge and curves around
to the northeast on the eastern tip.
ated as a city with a preamble that islands is the Gulf of Mexico with a
reads "...an island community known very broad shallow continental shelf. This produces a generally east-west
far and wide for its unique atmosphere The Gulf waters respond quickly to orientation with a south facing Gulf
and unusual natural environment, and the many frequent fluxes in the basic shoreline which is in great contrast

Beach Geology 231

to the east-southeast facing shore-
4'\ ;lines of the other barrier islands..
The major differences in the size and
orientation of Sanibel reflects a con-
siderably different set of geologic
conditions than are operating on the
,>XX; 0 , .....llazsnS other barriers. This will be dis-
cussed in greater detail later in.
the paper.

�o : A ;3t 0 2 2 i >; \ ; L; /I 0aL I: 0 0 t%4 0 0 0 0 ESTUARINE SYSTEM

Sosp oil/ (OWTIHll tem located behind the barrier islands
nels The brackish waterestuarinefr sys-

PrIV iinlts dominated by Charlotte estuarbor, Pine
-ft o0~~~~~ CIAC0~~~~~~~~~ ~ *l;efIsland Sound, and San Carlos Bay witha
Red -� ep 1a multitude of smaller-coastal embay-

-: "'"' -.* * Q N � loments around the perieters (Figure l) s
This estuarine system represents a
compl ex.set of drowned river channels,

Fig. I - Location mapof the past 10o,000 years, i the Holocne

/~e% ~~~~~~~~~~~~~ytransgression. these very shallow
water bodies range ina depthrfrom
.50~~~~~~~~' ~to 20 c feetexcept-in the major. chan-
nels where water depths range from 10
to 50. feet. The tortuously irregular
shorelines consist largelyof inter-s

tB~~~~~~~~~~b~~~~ ~ ..marsh es, and tidal flats. The brack-
of tihe S s ish waters of the estuaries range
from almost fresh well up to the
mouths of the three main rivers to
almost normal marine around the tidal
inlets on the west. The estuarine
Redfish Pass0 circulation is controlled by the tidal

kwater discharge from the rivers The
norm normal volume of the river discharge
_r, exceeds the normal tidal influx pro-
leaducing higher ebb current velocities
than flood current. velocities through
the inlets (Huang and&Goodell, 1967).

There has 'been only very minor,
..... :. ", ..... w~. '.. erosion or deposition within the
'IO rniri::iar~o estuarine system during the past 100
~' years. The deposition has been in
'm river mouths and the: central regions
of the sounds while the erosion has
-"o' S2 :- . occurred within the tidal channels
(Huang and Goodell, 1967) and along
a few of the more open shorelines.
Huang and Goodell describe the sedi-
Fig. 1- Location map of the Sanibel Island coastal system, Florida. ments within the estuarine system as

232 Appendixes

being dominantly fine quartz sands organic composition. Because of the area; thus, these inlets respond pri-
with abundant, but highly variable, very low stream gradients and rela- marily to tidal processes. Redfish
concentrations of carbonate shell tively low discharges under normal Pass has-been open only since 1926.
hash and some silt and clay. The nonflood flow conditions, brackish
sediments generally become finer water occurs well up the mouths of
away from the channels and in land- the rivers due to tidal mixing.
ward directions. The textural dis-
tribution of the sediments generally The fifth inlet, Blind Pass, also
correlates with the water circula- opens into Pine Island Sound and sep-
tion in the estuarinesystem. The arates Capiva Island tothe north
errs(land derived)sThe surface sediments on the landptiva Island to the north
terrigenous (land derived) sedimentsotte Harbor from Sanibel-to the southeast. Ithis
are inherited: primarily from the area surrounding the Charlotte Harbor
erosion ofadjacent parentrocks estuarine system are primarily Pleis- essentially afrom the direct influnce ofit is
whereas the bioclastic material is tocene sands, shelly sands, and organ- farthest from the direct influence of
a fresh water river discharge and is
largely indigenous. Huang and ic rich sediments. Underlying this consequently the most unstable of the
Goodell believe that the relatively layer of surface sediments throughout five passes. Blind Pass has a drama-
small amount of silt and clay in the area is the Anastasia Formation tic history of migration and closings
the system reflects the lack of a which is dominantly a coquinoid lime- and openings in response to storm
fine-grained parent source. stone with some sand and clay (Puri action. This Pass was closed in 1962
and Vernon, 1964). and re-opened in 1972 in response to
Hurricane Agnes. It has been open
since 1972.

MAINLAND AND RIVER SYSTEM

The mainland area of peninsular L INLET SYSTEM
Florida that bounds the estuarine
NEARSHeRE SHELF SYSTEM
system on the east lies in the geo- Charlotte Harbor is connected
morphic province of the Coastal Low- with the Gulf of Mexico by five inlets
lands (Figure 1). The land is ex- which separate the barrier islands The Florida Platform is an ex-
tremely low in elevation and is very (Figure 1). These inlets might better tremely broad, shallow continental
poorly drained with numerous cypress be thought of as outlets, since their shelf system that extends westward
swamps. The drainage that does exist most essential function and the pro- -approximately 250 km off the coast
flows through three major river sys- cess that generally will control the of peninsular Florida. The outer
tems into the Charlotte Harbor estu- magnitude and stability of the open- edge of this platform is marked by
arine system. The Myakka River, the ings through the barriers is the re- the precipitous Florida Escarpment
smallest of the three rivers, drains moval of the continuous flow of fresh (Figure 2). The nearshore portion
southward from the nearby coastal water drainage being discharged off of the shelf in front of Sanibel
lowlands into the northwest corner the mainland into the estuary. The Island is characterized by two
of Charlotte Harbor. The Peace River, two major inlets, or outlets, which general topographic zones. The
the largest of the three rivers, are fairly stable, appear to carry forebeach, the steepest part of the
drains out of Lake Hancock in the the bulk of the fresh river water and nearshore shelf, extends from the
phosphate district portion of the Polk marine tidal exchange in and out of surf zone down to about the 24-foot
Upland and flows into the northeast Charlotte Harbor. Boca Grande Pass contour on the northwest and to
corner of Charlotte Harbor. The in the north is the primary outlet about the 18-foot contour on the
Caloosahatchee River drains almost due for the fresh water discharge from the southeast end of the Island. This
west from Lake Okeechobee through the Myakka and Peace Rivers, whereas the active high energy zone extends off-
Caloosahatchee Valley and into San very broad San Carlos Bay, on the east shore about one mile. At the base
Carlos Bay in the southern part of the side of Sanibel, is the main outlet of the forebeach, the slope de-
estuarine system. Since all three of for the Caloosahatchee River. The two creases to about 2 to 3 feet per.
these rivers are black water streams intermediate size passes, Captiva and mile and continues seaward as a
that drain the low and swampy coastal Redfish, open into Pine Island Sound relatively flat plain with only
and interior lowlands, the sediment and appear to be only moderately minor topographic features. The
load is extremely low. The sediments stable. These two passes occur op- inner portion of this area is
that are delivered to the estuarine posite the very large Pine Island characterized by a strong north-
system are primarily dissolved ma- which is in the middle of Pine Island west-southeast ridge and swale
terial with only minor suspended sed- Sound. Consequently, there is no topography which has an approxi-
iment, much of which is high in direct major river discharge into this mate relief up to 10 feet.

Beach Geology 233

cell. From October through Feb-
CLIMATIC SYSTEM ruary, a western anticyclonic cell
CLIMATIC SYSTEM separates from the Bermuda high and.
is nearly stationary over the cen- 60-
According to Jordan (1973),, tral Gulf, producing a predominant , a %
the climatic system of the Gulf of air flow from northwest to north over '
Mexico is characterized by a sub- the eastern Gulf. Thus, Jordan con-
tropical high-pressure belt which ex- ludes that in the spring and summer50
tends over or near the Gulf through- the eastern Gulf is influenced pre- .
out the year. From March through dominantly by tropical air masses .I
September, the atmospheric circula- arriving from the south and southeast 40 -. -
tion of the eastern Gulf is charac- and producing a prevailing southern /
terized by a general clockwise air flow. Whereas in the late fall
circulation pattern related to the and winter, the cold air masses from 30 -
areal position on the western por- the continent produce a prevailing
tion of the Bermuda high-pressure northerly air flow which is shown in..

20 -

-- SUMMARY AREA
.......MOBILE
T-----TALLAHASSEE
rTAM PA

J F M A M JJ A S 0 N D J

Fig. 3 - Mean percentage of observations with northerly winds,
i.e., from northwest, north and northeast, for each month of the
) ~ year for the stations indicatbd. (From Jordan, 1973)

\ras9> QCf></X > - X Figure 3. Seasonal wind speeds are
_ -generally highest during winter and
spring and lowest during summer with
the exception of local circulations
associated with thunderstorms (Figures
4 and 5). Thunderstorms are quite
..... ... 2'"~I~I -er tmofhGoMxoFmcpafrequent in the eastern Gulf with
about two-thirds of them occurring from
_61':,~ ~ ~ ~June through September. This reflects
the greater convective activity over the

Hurricanes are a definite part of
/l dthe cl imatic system of the easter n
Gulf. Jordan (1973) states that the
probability of a tropical storm or
hurricane in the eastern Gulf during
____ Iany given year is about 50 percent,
____h,~~~~~ I~~~~~~~whereas the probability of two during
~,~~"- ~any given season is about 15 percent.
~-~..-' ~ The hurricane season starts in June
and extends through November in the
--~ ~~,'A ""southeastern Gulf with very rare
C /~%~Il occurrences in winter and spring.
--~~~ - . ~ Figure 6 shows the hurricane tracks in
the eastern Gulf during the-period
Fig. 2- General bathymetry of the Gulf of Mexico (From Uchupi and Emery, 1968) 1941-1971 while Figure 7 covers the

234 Appendixes

period from 1830-1966 in the Fort
Myers area. Table 1 summarizes some 60 -
of the hurricane frequency data of / - WINDS
Jordan (1973) for the southeast Gulf / STRONG WINDS
area; these storms would directly WEAK WINDSA
influence the Sanibel Island area to t .i. WE_
some extent. The U.S. Army Corps of
Engineers (1969) states that between /
1830 and 1968, 23 hurricanes and 23 /
tropical disturbances have passed /
within a 50-mile radius of Lee County. 40 - /
While there have been 17 hurricanes X
and 14 tropical disturbances between X
1900 and 1968, the latter figures /
represent a relative frequency of one /
major storm every two years. Most of / X
these hurricanes form in other areas
and move into the Sanibel Island area. /
According to Jordan, the hurricanes " A" - _-_.;.X
in the eastern Gulf will generally ;0 _
arrive from the south during June,
whereas the storms in the period from
August to September are more likely
to come closer to land since theyE NE
are more likely to be coming from the E E
southeast. Some hurricanes and E E EE
tropical cyclones do form in the east- N SE SE E E:: NW ESE E NE N E N

0J 0 F M A M J J A S 0 N D J

Fig. 5 - Seasonal distribution of frequency (percent) of strong winds ( > 17 knots) and of weak winds ( < 6 knots) for the summary area.
; 0 0 : N 0 The most frequent direction of the stronger winds is shown for each month at the base of the figure. Multiple directions are shown for
some months. (From Jordan, 1973)

ern Gulf; 14 such storms formed be- The wind systems of the'Gulf
tween 1901 and 1971 (Jordan, 1973). generally respond to the basic seasonal
changes in atmospheric circulation
patterns and to the storm patterns.
* f 40- / Extratropical cyclones or low- Subsequently, the winds and storms af-
pressure centers which form along slow fect the wave, swell, storm tide, and
moving cold fronts are very abundant current systems of the Gulf as well
I MP LE55 - OMILDROATin the eastern Gulf with an average as the volume and rate of fresh water
IO..o EP -_T :TCOMPILE> FO WDEATFUERRUED of 11.1 per year moving inland. The discharge from land. All of these
107O 2O M.P.H. a n T.MPA, FLORIDA. PERIODb
CO O M.. RED uARY , 1930 greatest bulk of these occur in the energy regimes may be affected for
DZO P.U.MIORM0ReE m 1TOAPFRIL2OI 19~3G winter with a decreasing frequency days or weeks at a time. It is during
in the fall, spring and summer. The these abnormal periods of high-energy
extratropical cyclones are most common influx that most of the geologic work
Fig. 4 - Average direction and velocity of winds for one year at in the northeast Gulf where they aver- is done. The coastal system has to
Tampa, Florida. (From U.S. Army Corps of Engineers, 1969) age 9.4 storms per year as compared to be able to respond to these high-energy
the southeastern Gulf where they aver- fluxes in order to maintain an equi-
age 1.7 storms per year (Jordan, 1973). librium system.

Beach Geology 235

Such tides are really wind tides pro- ported in the Sanibel Island and Fort
duced by individual storms and have Myers areas (U.S. Army Corps of
no regularity or predictable height Engineers, 1969). Major storms that
PHYSICAL OCEANOGRAPHY patterns. Storm tides can be ex- approach the Sanibel area from sea-
tremely high, particularly if super- ward are capable of producing
imposed upon normal high astronomical extreme storm tides because of the
Wind conditions in the eastern tides, and can be of any duration. The very broad shallow continental shelf
Gulf suggest that moderate seas exist heightand duration are directly de- area.
throughout the area for most of the pendent upon the magnitude, consis-
year. Table 2 summarizes some of the tency, and duration of the storm
wave data for the eastern Gulf area winds;' this is largely what determines
(Jordan, 1973). According to this the amount of coastal flooding and re-
data the wave directions tend to be suiting damage, as well as the geo-
dominantly from the east and north- logic work done within the coastal Very little detailed work has
east from September through February zone by any given storm. Storm tides been done on the basic current and
and from the east and southeast from up to 12 and 15 feet have been re- circulation patterns of either the
March through August. The waves
from the north and northwest tend to
have greater wave heights than those I .
from other directions, particularly
during the fall and winter, con-\
sequently supplying the heaviest seas
during these seasons. 30�

Swells are also wind-generated
waves but differ from sea waves in
that they have long crests, long
periods, and low steepness, and have
moved out of the influence of the
winds which created them. Table 2
summarizes the swell information
for the eastern Gulf and Figure 8
depicts the swell information
diagramatically for the Gulf off Lee
County between 1932 and 1941.

\-K-K/ 9-47:
The astronomical tides in the
Sanibel area are mixed consisting of
diurnal tides during part of each 9\53
month and semi-diurnal tides during
the remainder of the month. The mean
tidal range varies from 1.1 feet at 8-50
10-s 501
Gasparilla Island to 2.0 feet at
Little Hickory Island while the mean 10-50 8-69 6 -45
diurnal range varies from 1.7 feet 25 I 6-66 0-47
at Gasparilla Island to 2.9 feet at a
Little Hickory Island (U.S. Army Corps 85: 800W
of Engineers, 1969).

Fig. 6 - Hurricane tracts for the eastern Gulf during the period of 1941-1971. Tracks of storms not attaining hurricane intensity have not
been included. Also hurricanes which moved northward over the peninsula of Florida, and which may have influenced the eastern Gulf
Storm tides are not related to to some extent, have been omitted. (From Jordan, 1973)
astronomical tides, but rather occur
in conjunction with any of the major
storm systems previously discussed.

236 Appendixes

.(1926
904
/:*~~~ : .,,,,,~~~SCALE I MILES 1546
: :: : B1~94,9 a 50 t0oo ISO

19,0 \ : . S \ 79

:F _TE DXE. T::_L5 - V_4 4 184

:K / .:1873
Engineers, 1969)

)Ir

L 19r.5 ~ ~ ~ ~ ~ ~ ~ ~ ~F -d-.

JUNE-AUGUST SEPTeMFLP OCTOBER- N OVEMbE

Fig.7 -Paths of tropicalistorms of hurricane intensity that have passed within approximately50-mile to 150-mile radii of Lee Countyfrom 1830 to 1966 inclusive. (From U.S. Army Corps of
Engineers, 1969)

Florida shelf dr of the Sanibel lation within the Tampa-Fort Myers However, to my knowledge, no one has
Island area. The published current area. made detailed, continuous current
patterns (Figure 9) indicate a studies in the nearshore area on a
general northward drift on the shelf Within the zone of the fore- year round or seasonal basis. The
during most of the year (Jones, et beach itself, the longshore currents dominant prevailing wind direction
al., 1973). This northward current are the primary currents; these are during the winter is northeast, which
is produced by eddies in the east- the product of the basic wind would produce a southward longshore
ern shelf area which are driven by patterns and astronomical tides. current and sediment transport. Dur-
the major Loop Current which moves Most of the limited knowledge of the ing the summer, the southwest winds
clockwise through the central Gulf. longshore currents within the Sanibel are dominant producing a northerly
This northward drift inside the 10 area is based upon the indirect drift. However, since the stronger
meter contour in the Tampa-Fort evidence of sediment movement and wind climatic pattern is the winter system,
Myers area has recently been con- patterns. The Corps of Engineers and it is assumed that the net longshore
firmed by drift bottle studies the Coastal and Oceanographic Engi- current system is southerly. This
(Jones, et al., 1973). The latter neering Laboratories have random mea- would be greatly modified by individual
study demonstrated that some other surements of tidal flow in several storms and around inlets where there is
feature, in addition to the wind different inlets made as a result of a complex influence of the tidal cur-
stress, controls the surface circu- their many surveys within the area. rents.

Beach Geology 237

Geologic Framework

of Sanibel
June July j August September j October November to MayI Total

HOLOCENE SEA LEVEL CHANGES
11 4 16: � 21 - 25 7 84
There have been many exhaustive
studies of the Pleistocene sea level
fluctuations; consequently, there is
a pretty good understanding and
agreement of themajornding and level Table I - Hurricane and tropical storm frequency in the southeast Gulf area during the 1901-1971 period. (From Jordan, 1973)
events (Figure 10). The general
character of the most recent
transgression, which began about
17,000 B.P., is depicted in
Figure 11 and shows the results
of numerous studies. The exact Figure 12 shows the recent sea a land area characterized by very low
times and rates of sea level change level rise data of Hicks based on elevations and relief, the rates of
within this most recent Holocene N.O.A.A. tide gauge information at land recession (erosion) or :beach
transgression, which we are still Cedar Key, Florida (Brooks, 1973). zone migration will be very great.
experiencing, is open to consider- This data suggests a four-to-six Several other variables do come into
able academic discussion. However, inch rise in the sea since 1910. play which may either accentuate-or
there is no question about the pre- This is in line with the general 8 eliminate the consequences. of a rising
sent overall trend; this, of course, to 10 inches of sea level rise sea level. These include such -factors
is a most important point with re- during the past 100 years as -de- as the tectonic stability of the area;
spect to the present discussion. veloped by N.O.A.A. for this area "new" sediment supply; orientation
(Brooks, 1973). and geographic location of the spe-
cific coastal system with respect to

The importance of the sea level
information to barrier islands and
SWELL DIAGRAM coastal processes has been dramat- WAVE HEIGHT
IN THE SWELL DIAGRAM THE ically pointed out by many geolog- October - April May - August
LENGTH OF THE BAR DENOTES ists including the work of Riggs and <3 feet 60-65% of observations 80-907 of observations
N THE PERCENTOF THE TIME >5 eet 10-15% of observations 2-6 of berations
THAT SWELLS OF EACH TYPE O Connor (1974), O'Connor and Riggs >12 feet 11 of observations 2-67 of observations
HAVE BEEN MOVING FROM OR
NEAR THEEGIVEN DIRECTION, (1974), Brooks (1973), and Bruun
fI THE FIGURE iN CENTER OF THE (1962) to mention only a few. The WAVE PERIOD
PERCENTAGE OF CALLMS. level of the sea determines the Aaso
| LOW SWELLS (I.CFFT) position of the beach and all associ- >5 seconds 61-747 of observations with the greatest frequency
during the fA h lo t fqy
ll41g _ - M UI EDIUM SWELL5(S6-1ZFEET) ated beach processes with respect to during h e fal
WYlII lII41~rIi n- HIGH W- land. If the level of the sea changes
-- 4i HIGH SWELLS(OVERIZFEET) It9 seconds 5-67 of observations
with respect to the land, the beach
. HIGTHE 5,VELL DIAGRAM APPLIES zone will migrate. Bruun (1962) has .WEL
ONLY TO THEGULF OF MEXICO calculated that on a normal coastline,
rise4~~ ofRTIO~ mayF~ 7S oma7%eo ptember - April May - October
SHOWN IN PREVAILING WINO a sea level rise of one foot may cause <6 feet 72-80tef obser-vati ons 8-93 Oct of obertis
DIAGRAM AT UPPER RTIGHT
a shoreline regression of more than >12 feet 3-6% of observations <2% of observaions
~~ ~b!'~'/ D :one hundred feet. The rate and de-
gree of shoreline response is largely
a function of the rate and magnitude
of sea level change and the geomor- Table 2 - Wave data for the eastern Gulf of Mexico (From Jordan,
phology of the associated land areas. 1973 and based upon the U.S. Naval Oceanographic Atlas, 1973)
Fig. 8 - Swell diagram of portion of Gulf of Mexico off Florida Since, in the Sanibel area, the high-
West Coast. (From U.S. Army Corps of Engineers, 1969) energy coastal system is rising across

238 Append ixes

of the barrier, the modern energy
. regimes operating upon the barrier,
w Ex// y////,/ %/ / / ////@ /// t V M and the modern geologic processes
3W'~/////// I'./// //// f%./4'Wa/// A//f//A I fwhich act in response to the energy
z %////// // v >t regimes. These are the factors that
UpGALE ISN _, /- t must be considered in developing any
- / // - t I management or land use plan for a
ytji l -c 0t gA �barrier island.

-8" - r � , ;

. :- t I : Missimerk (1973) has made an ex-
I: /> 1 : t : 1 / t \ V . :1 YGft///// t 0 tensive study of the stratigraphy and
'J.:: ''t / t : geomorphic features of Sanibel Island,
2fX i 0Xt Itp% ~ :_///////t ~ upon which I have drawn heavily for
:2r ", i .. , ' st p ;w,'4Vk , the data in this section of the paper.
t - s R > V o I f 0 � & f f J- : I i W t - nG-7i-7 '~ : : 0On the basis of 24 drill holes scatter-
:ii 2 : J ...'ILCed across the island, Missimer delin-
t:I :: : 1 _ : ,/ : : eates six basic stratigraphic units
I '4? .I.t�"Afr,'~ : :associated with this system (Figure
24 I : : 13). The basic stratigraphic section
:,, . t for Sanibel Island is reconstructed
'0 0 ftj .F 1 X: L fi on the basis of various published
_ - -- r--- reports and is briefly summarized in
: t I . .. Table 3. The stratigraphic sequence
AMPICON '/ outlined in Table 3 is essentially
P.m 2 % - . :' identical to that developed in(a
I /:'�'4?�43~ very detailed study of the barrier

:Afi:\;:'- _ -~ - 1 sS/�: _ 2__Rocks area by Winston,:Riggs, O'Connor
:: \ tt : i and Brueninger (1968)-. A geologic map
20' ____ -t / _ of the Indian Rocks area and general-
MRUPLized geologic cross-sections through
\ S/I ' l 00;;1 / 70 XX;SAS t st [\SMALL0Nt MBERSEQUA~til~eSPER} 0 the barriers are presented in Figures
// 4 *t 0\ | DAYOPCIIR8RENT / 14 and 15 (Riggs and O'Connor, 1974).

9s' as' ' 8z--- '2 9b' '~ s~ ::e - a,4- e s- ~m 71;o
Missimer's (1973) study of
Sanibel Island included an-extensive
Fig. 9 - Surface currents in the Gulf of Mexico in June. (From Leipper, 1954) analysis of the geomorphic features.
The entirety of the Island consists
of at least 10 and possibly 12 sets
of beach ridges, each set containing
a variable number of individual
the basic climatic energy conditions; GEOLOGY OF SANIBEL ISLAND ridges. Figure 16 shows the orienta-
the shape, slope, and composition of tion of 10 recognizable sets of
the nearshore continental shelf; the ridges numbered from oldest (number 1)
tidal range and nearshore current to youngest (number 10) and demon-
patterns; and the importance of bio- Sanibel Island is part of an strates the varying orientations of
logic agents in the form of both con- extensive barrier island chain which the sets as well as the truncation of
structive and destructive features. extends from Anclote Key south to. Cape older sets by younger sets. The
All of these variables are superim- Romano along the Gulf of Mexico coast oldest obvious beach ridges, Set 1,
posed upon the position of sea level of western peninsular Florida. A are presently occurring below sea
itself to produce the resultant discussion of the origin of these level and in the intertidal zone where
coastal system. Consequently, any barrier islands is largely an academic they are being buried by modern muddy
barrier island system and the associ- exercise and is not crucial to the sands and 2 to 4 feet of peat result-
ated beach system is a complex product problem at hand. Rather, what is ing from deposition within the inter-
of multiple casualty. important is the geologic framework tidal marshes and swamps. Missimer

Beach Geology 239

THOUSANDS OF YEARS AGO
0 5 10 5 20 25 30 35
0

x',, / an!
% ~ ~

~ - ~. '-% - / w~~~~~/ *� Southeastern Caribbean Sea ,
W2" ,, /' " *%w : West Coast Mexico
it
~~~~~~~~~~ fGl \/Paa
*4.L. ra Campeche Bank, Mexico
- 100 - vGuf of Panama
-V)~~~~~ 44 2 East China Sea
- x Australia -o ]
s, shells ,r Southern California
oP~~~~ O~~~~oo'ites *1:~ -;Nigeria
150- coralline algae o , . Argentina
c coral a Bahama Islands
a- West Coast Florida 200 ,00 000 . 2 . 0000 .00
' ~ ' YEAKS GO
....L..J.......L..' , a a a a I , * _.- I * I I i i II t I , it I I 1
Depths and ages of sea-level indicators throughout the world. The solid line is thesea-level curve for the Atlantic continental shelf. Rise in sealevel from 17,000 to 6,000 years ago is the most rapid -
The dotted line is the sea-level curve for the Texas shelfi upsurge yet identified in the geological record. The floods that accom-
panied this 100-meter increase are believed to be the subject of the
deluge legends of ancient peoples. The names on the curve indicate
the locations where the principal oscillations in sea level were discovered.
Thousands of Years Before Present or where their shorelines are most prominent. Sea level has remained
40 35 30 25 20 15 10 5 O relatively constant for the past 6,000 years, and theamplitude of
MSL 0 -0 short-term oscillations is diminishing.
.��".......

:.."
50- -5o
a�~~~~~~~~~~~~~

I00oo- -100

Traz~d-Wiscoin nsgressioi: La t Wisconsin Regression Holocene TransgressionModern -150
-150 M
----' 1 '1 ~...
Late-Quaternary fluctuations of sea level, from compilation of published and unpublished radiocarbon dates and other geologic evidence.
Dotted curve estimated from minimal data. Solid curve shows approximate mean of dates compiled. Dashed curve slightly modified
from Curray (1960. 1961). Probably fluctuations since 5,000 B.P. not shown here.

Fig. 10 - Three published opinions of sea level fluctuations of the past 20,000 to 40,000 years. (Reproduced from Fairbridge, 1960; Milliman and Emery, 1968; and Curray, 1965, respectively)

240 Appendixes

believes that these older beach ridges
were formed when sea level stood 6 to
YEARS BEFORE PRESENT 8 feet below its present level. The
10,000 9000 8000 7000 6000 5000 4000 3000 2000 1000 other old sets of ridges are still
-10 above present sea level, but the
differential relief between the ridges
- Z and swales is being diminished with
0 time due to vegetation growth and
-- the flooding processes during intense
-_5 < ; hurricanes. This slow filling of the
/ W swales with fine-grained sediments
- makes the ridges indistinguishable on
/ --~... W the ground.

;' -;"~ *. ......." Each set of beach ridges may
/ contain upwards to 80 (in Set 5)
individual beach ridges. Missimer
/ _.w~r _ _w_- . 0 U 7 believes that an individual beach
/ /5 g - - � - _5 ridge may be the product of a whole
0 : : / , _.L < * ~ ~././'series of events or storms. Thus,
it appears that each set would re-
f lect a time system which had a
J ' , similar set of conditions. When
- -10 conditions change, a new set of
/ .i.' I/ /
0 ; / /./ g Rr 0 ; : 0 X LTIME . years
- l t zf - / � ./
_: - /- !1 ' / -/ 0 L- -15 !i10 19120 I14o30 !40 41930 14'0 19!0

I. /
7 ,gV; / 0 0 --20 1-
Iii -s

i/ 1/ --25

/:* 1 7. -.-- Bloch (1968) .
.it1 ---L Fujii andFuji(1967) - -30 CER KEYF
!-./' ....---- Scholl and Stuiver (1967) -2
' ! -- Fairbridge (1961)
i : i *-- Milliman and Emery(1968)
_/II i f! l .Curray (1965) 35
/ i / i-- Bloom (in press): S ACO
/ \,- I.. ]. .. Jelgersma (1966, Fig.6, Curve E)
- ~ Coleman and Smith (1964)
L 4: --40

Fig. II - Comparison of a few of the published opinions on sea level fluctuations for the past 10,000 years. (From Curray, 1969) Fig. 12 - Recent changes in sea level as recorded by tidal gauges
in eastern Gulf of Mexico. (Modified from Hicks by Brooks,
1973)

Beach Geology 241

erosional and/or depositional pro-
cesses develop with subsequent
erosion and truncation of the old
set. Another change will bring DEPTII (FEET)
about the deposition of a new set
of ridges with an entirely dif- +0o
ferent orientation. Brooks (1973)
believes that each set of beach
ridges corresponds to definite
climatic events with the periods GUL OF MEXICO PINE ISJLAND SOUND
of erosion and truncation being . ..... .. .
related to warm climatic periods...............

-70. , I; � � � � ' -- -g - --^ - - - - - - - - - - - - -- -- - - -
The present Sanibel Island - - - -
shoreline is one of truncation of
older beach ridge, Sets 5 through 9, -. - l I -' - -,,,;! , :
except along the northwestern portion - ' ' ' ' ', . . .
where set 10 is presently forming (Fi- 4. l-l. , ,,.- � . ...'- I"I ;-.. ,'"''' I';;; II'".I'i ; ; ;;;
gure 16, which appears as Figure 6 in 40o 2 3 5 L
the Hydrology Appendix)., However,
this shoreline of truncation does not
appear to be presently undergoing a
significant amount of shoreline ero-* Modern Estuarine Recent Peat Deposits
sion, nor.has there been any during r Sediments
the past 117 years as indicated by 0 X ' r-~n Recent Estuarine Deposits: Organic Matter,
U.S. Army Corps of Engineers shoreline Sand, Mud, and Shell
studies (Figure 17). This takes on
increased meaning when considered in
light of Missimer's first approxima-
tion that Sanibel has had a prograda- Oxidized Barrier Sand and Shell
tion rate of between 2.5 and 5 feet y Ila
per year throughout its 4,000-to-5,000-
year history and which includes ex- .1 Unoxidized Barrier Island Sand and Shell
tensive periods of erosion. Some
deposition and accretion is presently.
taking place just south of Blind Pass
in ridge Set 10 (Figures 16 and 17).
in ridge Set 10 (FisureS-16 and 17). Muddy Shelly Sand F Relict Estuarine Deposits: Organic Matter,
Missimer believes this set has been Unit J Sand, Mud, and Shell
active for the past 200-years. The
remainder of the Sanibel Island shore-
line seems today to be in a delicate
state of balance whereby neither Pleistocene Limestone f2 Pleistocene Sandy Limestone
erosion nor truncation is presently Unit
taking place. However, neither is
significant deposition nor accretion.
This present delicate balance could
very easily be upset by man's activ-
cities or by some major change within
the natural energy or sediment regime Fig. 13- Idealized section of Sanibel Island perpendicular to the island axis. (Modified from Missimer, 1973)
of this coastal system. There are
too many variables and they are too
complex and poorly known to begin to
predict any natural changes which extent control this variable and . tion of Sanibel Island is not a
might disrupt this delicate balance. possibly keep man's effects to a continuous process with time, but was
However, by knowing something about minimum. A major conclusion from intermittent in nature with periods
the effects of development upon the Missimer's study (1973) that must be of deposition and of intensified
coastal processes, we can to some kept in mind is that "...the deposi- erosion."

242 Appendixes

MODERN a RELICT NEARSHORE a COASTAL GEOLOGY OF THE NEARSHORE SHELF
SEDIMENT MAP- INDIAN ROCKS, FLORIDA f.

:MILES~~~~~ : ------ : r : : - Detailed geologic information
of the nearshore shelf off of
Sanibel Island is extremely limited.
a--n-d- O'CoHONE N However, on the basis of the follow-
_ ing studies and information, a pretty
0J ~ ~ ~ ~ ~ ~ ~ ~ ~~~= good idea of the geology can be de-
13 .veloped:

a. The U.S. Army Corps of
Engineers (1969) drilled 15 shallow
WATER0: ; 0 (15 to 30 feet) holes about 1800
A:' feet offshore of Captiva and Estero
ROCKS 0 NIslands on either side of Sanibel.
Figures 18 and 19 show geologic
FM]:: BARRIER ISLAND SAND T tatgahccross-sections through the holes
: = B > i : MO D ERN **: B'{ARE R ILAS SAND as described by M er (Fig
MODERN 112 BEACH a PASS SAND in the southern Captiva area and in
SEDIMENTS r LAGOONAL MUDDY SAND the northern Estero area respective-
E PELLETAL MUDDY SAND HOLOCENE ly.

F," " OFFSHORE BAR" SAND b. Missimer (1973) worked with
RELICT 24 drill holes on Sanibel Island,
SEDIMENTS LI "LAGOONAL' MUDDY SAND defined the surface stratigraphy of
L SANDY CARBONATE ROCK TERTIARY the Island (Table 3),\and construct-
ed an idealized geologic cross-
section across the island and onto
the nearshore shelf I(Figure 13).

c. I made a detailed study of a
Fig. 14 - Geological map of th e coastal zone, Indian Rocks, Florida. Cross-section locations A-A'and B-B' refer to Figure 15. (From Riggs v ery simil ar co a stal system in the
and O'Conno r, 1974) Indian Rocks area to the north (Riggs
and O'Connor, 1974 and Winston, Riggs
and O'Connor, 1968). This study in-
A NASREaCASA cluded surface mapping and process-
response studies, both utilizing
GEOLOGIC SECTIONS extensive SCUBA diving, and subsurface
INDIAN ROCKS. FLORIDA stratigraphy based upon shallow cor-
~<)p0 ~ ~ ~ ~ 1 C=---- ing. The geologic map is presented
in Figure 14 and several generalized
,0 o I 2 stratigraphic cross-sections are
MILES presented in Figure 15.

The basic stratigraphy of Sanibel,
BBARISLAND SAND as described by Missimer (Figure 13),
8~~~~. IEAHPASS SAND can be roughly correlated with the
- AGOAL MUDDY SAND offshore holes of the Corps of Engi-
.3 PELLETAL MUDDY SAND neers. The section for Sanibel, as
-10 .E "OFFSHORE BAR" SAND defined in Table 3, is almost identi-
20 EE SANDY CARBONATE ROCK (TERTIARY) cal to that which we defined for the
Indian Rocks coastal system (Figures
14 and 15). In the latter area, we
traced the units with drilling from
Fig. 15 - Generalized geologic cross-sections of the coastal zone, Indian Rocks, Florida. The location of the cross-sections is given in Figure the modern estuaries, below the
14. (From Riggs and O'Connor, 1974) barrier, to the nearshore shelf where

Beach Geology 243

each unit was successively exposed
down the forebeach slope. The geo-
logic map of the nearshore (Fuhrege1)- Table 3 - Generalized stratigraphic section of Sanibel Island. See Fig. 13 for the stratigraphic and geographic position
shows the outcrop pattern of each of of each unit within the Sanibel Island system. (Modified from Missimer, 1973; Brooks, 1964; and Huang and Goodell, 1967)
these units and demonstrates the
relationship to the composition of the
exposed surface sediments.

Considering Figures 13, 18 and MODERN ESTUARINE SEDIMENT UNITS
19, the nearshore geology of Sanibel Peat Extensive mangrove swamps and Spartina marshes occur
Island can be'realistically recon- around the estuarine perimeter of Sanibel Island and
structed as follows. The shelly sand produce thin and irregular accumulations of organic
unit (Table 3) extends down the high- plant debris. These deposits are presently being
energy upper forebeach slope to water formed within the intertidal zone and extend down to
depths of 12 to 15 feet which occur about 4 feet below MSL.
between one-fourth and one-half mile
offshore. Below this major slope Muddy Shelly Sand The modern estuarine sediments are primarily fine-
change, the muddy shelly sands are grained quartz sand with variable amounts of silt,
exposed. These fine-grained sediments clay, shell material, and organic matter. These
would extend seaward possibly to the modern sediments are extremely variable in thickness
area of the 24-foot contour, between and depth.
one and two miles offshore. This por-
tion of the seafloor is not affected SHELLY SAND UNIT
by the day-to-day energy levels of the Upper Bed Tan oxidized unit composed of mixed carbonate shell
Gulf. Consequently, these fine-grained i material and fine to medium grained quartz sand. The
Gulf. Consequently, these fine-grained
sediments are exhumed primarily by shell material in this unit ranges from 10% to 90%
biological erosion processes until and averages 50%, and contains abundant Donax variables.
periods of high-energy storms when the This is the surface unit on Sanibel Island and varies
loosened fine-grained sediments are from about 10 to 20 feet in thickness./
eroded by physical processes and inter-
act laterally with the sediments on the Lower Bed Gray nonweathered fine shelly sand. The sand is
forebeach (Riggs and O'Connor, 1974). slightly finer grained and the fine shells are unaltered.
Very little topography generally occurs This unit everywhere underlies the upper shelly sand unit
within this section of the lower fore- and has a maximum thickness of 10 feet.
beach. Seaward of the 24-foot contour
area is a fairly extensive system of MUDDY SHELLY SAND UNIT
northwest-southeast trending ridges with Upper Bed An interbedded sequence of muds and muddy shelly-sands with
up to ten feet of relief, and composed some organic matter. The shells include abundant Cardita
of clean, fine-to-medium-grained shelly floridana and Anomalocardia cuneimeris with some Crassostrea
sands. The ridge and swale structures virginica shells at the base. This unit underlies the
should be extensively explored as a pos- shelly sand unit and varies from 0 to 18 feet in thickness.
sible source of adequate grain size
sediment for beach nourishment projects, Lower Bed A shelly sand bed with some mud which generally occurs on
This basic sequence of sediment patterns top of the limestone. It varies from 2 to 8 feet thick
was generally outl'ined by Gould and: . .where it occurs and contains up to 50% shell material
Stewart (1955) in their broad regional along with abundant limestone rock fragments;
study of sediments of the shelf floor
(Figure 20). In the swales between the PLEISTOCENE LIMESTONE UNIT
ridge structures are extensive outcrops This unit ranges from an indurated and weathered fossili-
of the Pleistocene shell beds and soft ferous, sandy limestone with abundant solution features
fossiliferous limestone (Table 3). The under Sanibel Island to a nonindurated unweathered sandy
extensive exposures that occur in this shell bed on the nearshore shelf. It generally occurs
nearshore area (Brooks, 1975, personal between 20 and 30 feet below MSL.
communication) probably begin to out-
crop in the vicinity of the 30-foot
contour and extend seaward (Figure
21). These rock surfaces provide a
substrate for prolific coral and
sponge growth, along with the abundant

244 Appendixes

associated modern reef fauna and
flora. The organisms associated with
the soft limestone surfaces are ac-. C
tively and rapidly corroding and &
eroding the surfaces producing "new" \
sediment which consists of elastic
terrigenous grains, limestone rock
fragments, fossil shell material,
and modern bioclastic shell material.
This material is then contributed %
to the modern sediment regime during , '*"A
high energy storms. The modern ex-
humation and erosion of the fossil-
iferous Pleistocene limestone and SANIBEL ISLAND
relict estuarine and open bay sedi- .
ments in the nearshore area, as well
as the associated bioherms and reefs V
growing on the offshore rock surfaces, ...:o
are extremely important to Sanibel
Island for two basic reasons:

1. This is the only major source LEGEND
of "new" sediment which is being sup- Scale ....... 1858-1859
plied to the modern barrier island i-oo f0 1939
system. 1967
(AFTER U.S. ARMY CORPS OF ENGINEERS, 1969)
2. This is probably the major
source of much of the modern and
fossil shell material that ends up Fig. 17 - Positions of theshoreline of Sanibel Ilsland in historical times. (From Missimer, 1973)
on the Sanibel Island beaches.

Both of these represent important
natural resources toSanibelma. receded in response to a slowly entire forebeach slope of the near-
rising sea level, the southward- shore shelf and extends i~nland across
The sediment sequences within moving longshore currents deposited the backbeach and above the storm
the Sanibel area suggest that the the sediment as prograding spit-like beach to the dunes. When composed of
barrier formed considerably seaward features. Periodic changes within unconsolidated sand, this broad zone
of its present location on the the sediment and/or energy regimes of is totally flexible and molds itself
Pleistocene limestone surface during the coastal system caused Sanibel to to the energy regime of the ocean
a lower stillstand of the sea. With have a multi-phase depositional his- that is operating upon it at any
the continued rapid rise of the tory with alternating periods of given time; this energy regime is
Holocene sea, the barrier system has deposition and beach ridge accretion both complex and extremely variable.
migrated up and over the open bay and erosion and beach ridge trunca- The beach responds to any energy
and estuarine sediments to near its tion. change to produce a three-dimensional
present position. As sea level rise profile that is in equilibrium with
began to slow down 4,000 to 6,000 Geolosic DProcesses that specific energy regime. Thus,
years ago (Figure 11), Sanibel was s any sand beach has a specific set of
generally in its present location, the- one responses to any set of processes and
butdid not have its present shape. of Coastal on begins to change as soon as a dis-
The history since this time has equilibrium appears. The sand is
been well documented by the detailed shifted back and forth expanding and
beach ridge studies of Missimer contracting the beach zone in direct
(1973). He concludes that the old- response to the disequilibrium
est sediment patterns suggest that established by a change in specific
Sanibel Island was then modified The zone where the ocean comes energy conditions. During high-
into a southeastward prograding and in contact with the land is known as energy periods, which may be a
accretinq spit extending off of the the beach. The beach zone is much single storm or a seasonal pattern,
barriers to the north. As the more than just the area between mean increased wave heights require a
northern Lee County barriers slowly low and high tide; it includes the broad offshore sand apron and off-

Beach Geology 245

shore bar system to break the wave -o
energy prior to reaching the swash -42-
zone. Consequently, great quantities
of sand are pulled off the backbeach
and stored offshore; this produces a ue,,y./ .a
narrow and steep backbeach commonly
called a winter beach. As the energy _
abates, the lower wave heights do not
require the extensive offshore sand
apron and bar system. The sand which
is temporarily stored offshore as an
energy absorber slowly migrates back
up the beach face as one or more
ridge and runnelsstructures, and is
ultimately welded to the backbeach ' A
face. The runnel is rapidly lost, ET
producing a broad shallow beach, - . .___LE - .
commonly called a summer beach. OF

During periods of extremely
high-energy levels on a beach, the -q E
dunes themselves become the storm
berm and washover becomes an active --5
process. The water breaking over
the top of the storm berm carries a
significant amount of sediment over
SaD Oou,.:o ,INt ,BTI-r.u goIINs -
the back side of the storm berm or V I
dune field to produce a br ad struc- 4 I 1 1
tural overwash apron. Overwash is ...1 .: I i-
an important structural part of the l . ......... .
storm beach and, on many barriers, ..... ..
is the basic mechanism for the con- ..t . i....: .i
struction, maintenance, and migra- .
tion of the backside of the island. R' _': -
This overwash process has been r e-- -" i
described in considerable detail by ~ ,,-
Dolan (1972 and 1973), Dolan, et al., .
(1973), and Godfrey and Godfrey
(1973). Overwash is normally asso-
ciated with a migrating or retreat-
ing barrier island in which the _L
sediment supply is not adequate to
maintain a stable shoreline or pro-
duce an accretionary situation. A
W . SCALE INng sea level.:may also scn~e rhA FEET
rapidly rising sea level may also Sand. fine to medium quartz, clean to slightly
silty shelly (SP) or (SP-SM) boo 3o o 6o MO IlO
be the determining factor as to the
e thedetermining factorsh in anys to the Sand fine to medium quartz. slightly silty to
importance of overwash in any given silty shelly (SM)
system. In the case of Sanibel Sit., (ML) shelly contains pockets of clay
Island, there apparently has been in dclayeyfinetomediumquartzsll(SC Number of hammer blows required to advance a solid sample
~~~~~~~~~~~~~~~~~~~~the past an abundant .~ sSand. clayey, fine to medium, quartz. shelly (SC) .spoon (2" (.D. X 2" O.D.) 1 foot using a 300 pound ham-
the past an abundant sediment supply mer falling freely 18 inches. The spoon is 5 feet long and
to go with the slowly rising sea ~--- Usnmeimrdotorddddriven continuously 5 feet where possible.
level. Thus the risland has gem- fLmesftonemedium hard, solutionriddled. ha redpnsltiown rydled,
level. Thus, the island has gen- ~ fossili ferous' nul, Pushed spoon down by hand.
erally grown upward and accreted Limestone, hard, porous, fossiliferous CB-7 Location and designation of core boring
seaward through time. Under these
conditions, overwash as described by * Shell symbol also used in combination with other
the work of Dolan and Godfrey, does M Limestone asfragmentsorthin layers
not play the same role of island
Fig. 18 - Geologic cross-section of the nearshore shelf off of Captiva Island, Florida. (From U.S. Army Corps of Engineers, 1969)

246 Appendixes

-13- Xrl~~jj~v~lii /V19~~T .lmaintenance and migration as it does
43- �0 ~~on some of Sanibe'l's neighboring
~~~ '~~~O~~~o(~ ~barrier islands. Rather, on Sanibel,
the role of overwash is. that of
maintaining a structural berm during
aa 51ANO ~major storms. The consequence is a
EgTLnob IhLAND sediment filling of the swales which
decreases the relief between the
ridges and adds structural support.

Car ,.n~~~~~~~~~~~~~~A beach system is a three dimen-
sional unit. Therefore, beach equil-
ibrium profiles include the areal
shoreline geometry asnwell as the
vertical profiles already discussed.
The shoreline geometry does not have
the same rapid time response that the
-vertical profiles have. Rather,
-~' ---- ;; ; : changes in an areal profile repre-
- AUASSUMED GROULND LINE OETWFEK BORINGS- sent responses to longer term sea-
sonal wind and littoral drift
i ~.................................. patterns, sediment supply or lack
-Ses -'i'iii~iiii~- II 'til4Iiiii~iiiiiiifltIIIiiiiij~jl~ of .and, most important,: to the:
_:~.iiiiiiiiij:- tin' lily i~[ odynamics of associated inlets.
H.~~~~~~~~~~~~~~~~~~~~~iiii:: Z11iii
.... ....::..:::::::::::::::::: ::::::::::::: ..!/....
'o- :::::9m/l:'"'::-~ :::::::: :::::::::::::: I:::: :::::::::::H::::::i-
..... .....iiiiiiiiiiiii iiiiirii' i... Sand beaches are seldom straight
"IllI iiiiii ::::::,n i~iiii~iiis'iiliiiiii~ ........... [iiiiiiiI'fiiiiiiiii jl length varsies d-fr 100. meter:::::s up...
~~~~~~~~~~~~~~~~~~~~....... ~.......... ..... ... ...:::>'::::::: :: :: Eii.~ :::
' ~ iiiiiiiiiii~ii!!ii~ii! .".....~.....:: but consist of sinuous curves and
.....i:::::::::::i :.:-.....i.--~...-.---.~ -..::. i ===================== buul ges called sand waves. The wave
...... ' .-.... ... length varies--from 1:00 meters up to
I : :::::::::::::::::::,:::: :::u:':J:::::::::::;t::::8iiii:
:t:::-::::::::::::::::::::::::::::_ ..........
' i ~~~~~~~~~~....................�......_
........................ . .....-,.........:.--"-......: ::::: ::'" 1,000 meters with amplitudes of 10
o ~-: ::'-::: ::: ::::::::::'":- .................... .Ill
-'O................::::::... ,
.................. that sand waves have a definite
~... ..................... .rhythmic pattern and rate of migra-
......................I. . ........i..iii-ii:a: tion along the shore in response to
E ~5!! !!!!!!!i~::::::::: jiiiiiiii~!iji~!E!~ Tl the littoral drift and storms. The
i! ! ~ !!~:::~ :::::iiiiiiii !!:'
--::::::::::::::::::::::::i::: :: focus of any shoreline erosion is a
.................. n. ::::::::::
::::::::::::::::'... . . . . ;13"::::::::::direct function of the position and
, iiiiiiiiJnn'tiii~~'4~ii~ii~~i: ~phase of the sand wave fields. In
' 1 c1 C1[_ Ca- addition to these intermediate sand
waves, there are larger cuspate
LEGEND structures associated with most' sand
beaches which are usually related to
�i:!5 Sandfinetomediumuarzclean to slightly W5 Limestone medium hard, solution riddled becheswhich are usuallyrelated to
jjsilty shelly(SP) or (SP- M)f fossiliferous inlets and inlet processes.
;t.2 :1T : Sand, fine to medium quartz, slightly siltY to Limestonehard, porous, fossiliferous
silty shelly (SM)
111111W- sil, ~ shelly ~contains pockets of clay 1 Shell symbol also used in combination with
Silt, (ML) shellylootinJ pockets of clay other materials INLET DYNAMICS
Sand, clayey. fine to medium, quartz. shelly (SC) Limestone. as fragments or thin layers

Inlets, or outlets, develop or
Number of hammer blows required to advance a solid sample SCALE IN FEET
spoon (2" I.D. X 2�." O.D.) 1 foot using a 300 pound ham- change in direct response to the basic
mer falling freely 18 inches. The spoon is 5 feet long and
isdriven continuously 5 feet where possible. O aim0 600 jooo gao hydraulic system and storm pressures
PU5#C Pushed spoon down by hand. within the coastal system. They
serve an essential role for four
C6~7 0 Location and designation of core boring sethessetin
sets of hydraulic processes operating
within a coastal zone such as
Sanibel: a) as an outlet for the
Fig. 19 - Geologic cross-section of the nearshore shelf off of Estero Island, Florida. (From U.S. Army Corps of Engineers, 1969) fresh water discharge -off the land,

Beach Geology 247

b) as an outlet for storm tides focus at the inlet. The "loss" of shore ebb delta. The shape of the
developed within-the estuaries, c) sand into inlets is at most a ebb delta and the sediment move-
as a buffer for storm tides gener- temporary thing; and even then only ment within the delta is then strongly
ated on-the ocean side, and d) as- where there are "new" inlets, which controlled by the interaction of the
a- channel for the water exchange in do not yet have tidal deltas, does ebb and flood currents with the off-
response to astronomical tides. The this become a major process. Any shore wave system and the longshore
general inlet response can be sum- sediment that is trapped in the currents. The sand stored in the ebb
marized as follows: inlet itself is ultimately moved delta is now available for littoral
either in or out into the tidal transport onto the downdrift beach
1. Inlets are self adjusting in delta storage bins. Since the ebb system. Also, high-energy storms and
that they open up by flushing or currents are generally the dominant floods flush out the inlet and move the
close down by shoaling (if there is inlet force (Hayes, et al, 1973), sand laterally to be used to absorb
sufficient sediment available) to most sand moving into an inlet will the storm energy in the adjacent fore-
fit the hydraulic pressures at any: ultimately be deposited in the off- beach areas. Thus, an inlet-system
given time.

2. Inlets located near rivers
and carrying a large fresh water s' s'oo' - 4V0' 840, :3'30' 3'00' 830 ' ;i0a'
discharge are generally larger and 2ea'6,. /. at
more stable inlets with respect to 3' :. .
both migration and opening-closing. - "�i;' X 8 'i.:

3. Inlets that are dominantly I t 0\ :.
t-idal tend to be more ephemeral units. i.'\.,. .'..
This-is because a) the lack of a con- 2.............. 2
stant hydraulic pressure as produced ... ,CZCAM 0'
by the river discharge and b) during ,- : r C -
normal conditions tidal fluxing does CC VJC * C .-TAMM BAY
not always supply an adequate C, C
hydraulic pressure to maintain an r C C C E
inlet (particularly if there is an X aC C,
abundant sediment supply) andthe I r
inlet will either migrate/or shoal 3.' SN .:.:.
over. QUARTZ-SHELL SANC
over. (w SOPERCENT QuARTZ) C
50U: PERCENT CCICTZ) C
4. Inlets are natural safety
valves in that during conditions ~ SHELL SAND
of high hydraulic pressure (floods m ALGAL SAND i.: CC CCCCCC....
and/or storm tides) a new inlet 2r - aS
will open where needed to relieve ' .. �
the pressure. When this abnormal F ORAM. SAND SILT
pressure is released, the inlet .-
will close up naturally. Without
this ability, the barrier islands ..
act as dams increasing flood levels
and the resultant damages. 2, BOTTOM CHARACTER \
3' OFF WEST COAST OF s3
5. Inlets will commonly recur FLORIDA
within the same general area as o 10 20 30 40 0 C
needed through geologic time. STIL

Inlets, and their associated CTOaRS N FATHOMS :::::: /
ebb and flood tide deltas or sedi- oo ' : : : : : : : : : i 00'
ment fans, are major sediment 84'3o' W400M s3'30 8300 82,30 8200' alle
storage bins for the coastal system.
These deltas supply the sediment
necessary to maintain an equilib- Fig. 20 - Unconsolidated sediment types on the West Florida Shelf. (From Gould and Stewart, 1955)
rium system among all of the inter-
acting energy regimes which come to

248 Appendixes

plays an important role in sediment
storage for use as an energy sponge
during storms and has built-in sediment
bypass mechanisms. Consequently, inlet
systems represent an integral part of
the overall sediment budget of the
coastal system and contribute to the
overall natural ability of the system
to roll with the energy punches with
minimal adverse effects. Modification
and/or stabilization of an inlet will
limit or eliminate this ability, in-
creasing the potential for accelerated
shoreline erosion resulting from major
storms.

Coastal Management

on Sanibel Island

BEACH MANAGEMENT

Sanibel Island is a product of
and responds to the totality of
geologic processes operating within
the coastal zone. To live and work
within the framework of this deli- BROOKS 1972
cately balanced natural systemi ROCK OUTCROPS AND REEFS
three most important geologic con- !.
cepts must be kept foremost in the LEGEND
minds of all individuals and users.
First, the entire region must be Scattered chart outcrops with sponges,
Oculina, and Sideraster
considered as one interacting sys- Oculina, and Sideraster
ten which includes the adjacent
tem which includes the adjacent ~~~~~~~~~Shall edge reefs, coraline algae and
barrier islands, neighboring inlets, ,j lledeep water coral
the nearshore shelf, and the marshes,
estuaries, and rivers behind the . r Scattered limestone outcrops, coral
Scatchesred iv edstnourosra
barrier. A small change in any part patches and heads
of this overall system could have
considerable effects on some other
portion. Second, the cumulative U
effects of :the:_actions and modifica- er- Pleistocene reefs rejuvenated with
effects of the actions and modifica- hermatypic corals and algae~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~hrmtviccras-ndala
tions by all users and user groups
must be constantly considered. Even
though the actions of one project in
itself may be insignificant with
respect to the overall system, by
the time you accumulate ten or twenty
the time you accumulate ten or twenty Fig. 21 - Rock outcrops and reefs in eastern gulf of Mexico. (From Brooks, 1973)
such projects the results could be
dramatic. Third, the time element
is also critical in that the day-to- other hand, most significant geologic Man's efforts to stabilize, develop,
day processes operate under low en- events, including responses to major and occupy the beach are unfortunately
ergy situations and consequently modifications to the system by man, concentrated in the upper portion of the
require longtime increments for the happen during the infrequent but dra- beach system. This upper backbeach area
results to become apparent. On the matic high-energy storm situations. is an extremely important sediment

Beach Geology 249

response element. It is essential in plex interactions of the entire COASTAL SETBACK LINES
providing stability during periods of coastal system, then we might be
extreme wave energy. The development justified in attempting to modify or In 1971 the Florida State Leg-
and-efforts to stabilize this zone have possibly even control some integral islature enacted a bill that directed
these results: -a) they remove the portion of the system. But at present the Department of Natural Resources
- flexibility required by the natural we are not close to that level of - to develop a "Coastal Construction
system; b) they remove a large portion understanding. This point has been -Setback Line along the Gulf and
Xor make ufnavailable large sand reserves demonstrated time and again as efforts Atlantic shores of the State"
stored in the upper backbeach and the by the Corps of Engineers to modify (Coastal and Oceanographic Engineer-
dunes; and c) they prevent the develop- various inlets have ended in disastrous ing Laboratory, 1975).: As stated in
ment of storm berms and overwash fans results either to the inlet itself or- the legislation, the setback line
necessary to absorb the ocean energy. to the up and down drift sections of shall be determined from a compre-
The inevitable consequences of the con-
The inevitable cationsequences of this z oneis to the coast. For example, our experience hensive engineering study and topo-
tinued modification of thise zone; is to with the attempt to open and control graphic survey and based upon the
thsnarrow and steepen the beach zone, eDrum Inlet, North Carolina, during the following types of data:
thus increasing the energy expenditure past three years has so far failed and
per unit-area of the beach. The results has had dramatic environmental and 1. ground elevations in rela-
.are a predictable increase in rates of economic consequences and it is not tion to historic, storm, and
shoreline erosion and recession during over with yet. hurricane tides,
storms; this erosion is the natural
response of the beach in reestablishing 2. predicted maximum wave uprush,
The complex interdependence of'the
a profile of equilibrium. Sanibel coastal system can be partially 3. beach and offshore ground
demonstrated by Blind Pass. The 43 contours,
percent cross-sectional closure of San
Carlos Bay resulting from the construc- 4. the vegeation line,
tion of the Sanibel Island causeway
added significant back pressure and
stress to the estuarine system. It is
Blind Pass has historically been probable that this has had some long- 6. the dune or bluff line if any
an ephemeral inlet which presently term influence on the reopening of exist, and
has a minor tidal delta associated Blind Pass, as well as increasing inlet
with it. Any ebb tide delta that erosion of the other passes through the 7. existing upland development.
formed beyond the seaward end prior barrier islands. There is little
to 1962, when the pass was open, was question that the causeway has had a The act states that, "upon the
completely lost during the next major direct influence on the hydro- establishment, approval and recorda-
decade when the pass was closed. Blind dynamic system of the estuary, as well tion of such setback line or lines, no
Pass opened in 1972 in response to as the patterns of sediment movement, person, firm,;corporation or govern-
Hurricane Agnes and is now developing and estuarine erosion and deposition. mental agency shall Construct any
a small ebb delta again. The inlet A stressed system will ultimately be structure whatsoever seaward thereof,
only opens and stays open when the brought back into equilibrium when the or make any excavation, or remove any
balance of coastal forces requires it. energy system is adequate to bring about beach material or otherwise alter
When it is no longer required it will the appropriate responses. The arti-ng ground elevations, or drive
close. The forces causing this are ficial-closing of Blind Pass now would any vehicle on, over or across any
not known at present, but some clues probably significantly increase the sand dune, or damage or cause to be
are available. - stress upon the estuarine system damaged such sand dune or the vege-
resulting in ever-increasing erosion tation growing thereon, seaward there-
To interfere with this natural and instability to the other inlets of except as hereinafter provided."
safety valve within a potentially of the system. In fact, any plug-
very high energy Gulf coastal system ging of Blind Pass can only be The Florida Department of Natural
which includes Charlotte Harbor and temporary; the forces of a high- Resources subcontracted the Coastal
associate rivers, barriers, and energy storm on the highly stressed and Oceanographic Engineering Labora-
inlets is not only geologically short- estuarine system would easily blow tory of the University of Florida
sighted, but could increase the po- an artifical plug out of Blind Pass. (COEL, 1975) to make the required
tential danger to life and property. The present pattern of erosion studies and surveys. The criteria
The latter is particularly true criteria
The latter is particularly true if around Blind Pass is temporary until used to develop the setback line for
we can start thinking about the conse- the new inlet system re-equilibrates Lee County can be summarized as fol-
quences two, five or ten years from itself, at which time both sides of lows:
now instead of today. - If we thorough- the inlet will become net deposi-
ly and completely- understood the com- tional systems again. 1. A still water level storm

250 Appendixes

tide of 10.2 feet was used for ing that a) the highest point on (ii) is elevated on adequately an-
computing wave uprush. The 10.2- Sanibel Island is only about 8 feet chored piles or columns to a lowest
foot storm tide level was developed above mean sea level and b) all of floor level or above the 100-year
by COEL through a study of the the figures used in the calculations flood level and securely anchored to
normal yearly high tides and high of the line were very conservative. such piles or columns, and (iii) has
water levels caused by hurricanes Buildings on barrier islands are sub- no basement and has the space below
and expressed as frequency of ject not only to inundation, but aso the lowest floor free of obstructions
occurrence for a certain water to high velocity water flow which can so that the impact of abnormally high
level to be equalled or exceeded. undermine, wash away, or collapse tides or wind driven water is mini-
The 10.2-foot figure was based on the! major structures. The buffer zone mized.,
storm tide level which has a 10 resulting from the setback line does
percent probability of occurrence not eliminate flooding or the The high hazard area is defined
in the next 10 years; however, such resulting property damage. Rather, as that portion of the island which
a storm can happen in any year or it will allow the beach to operate would be flooded with 3 feet or more
on any day of the storm season. normally as well as buffer the water of water moving at a minimum velocity
The National Oceanic and Atmospher- movement so that the damage may be of 3 m.p.h. during the 100-year storm.
ic Administration (NOAA) is cur- somewhat lessened. The calculated 100-year storm level
rently making a storm surge study for Sanibel Island is 10.2 feet above
along the coast of Florida; NOAA's In order for the concept of the mean sea level (COEL, 1975). Most
figure is considerably higher - coastal construction setback line of Sanibel Island would be under 3
(12.2 feet); however, since it is to be most effective, there must feet or more of water during such a
only a preliminary figure it was also be strong controls on the con- storm. However, the zone of high
not used. struction itself. This is now re- water velocities would probably be
quired by the Federal Insurance restricted to the outer perimeter of
2. A wind wave of 6 feet with Administration's regulations for the island, to unvegetated areas, and
a 12-second period was-used as a the National Flood Insurance Pro- to open roads across the island.
typical hurricane-generated wave gram. The requirements for this Consequently, the broader and-more
from which the wave uprush was program are as follows: vegetated the buffer zone, the more
computed for each of the surveyed effective it will be in decreasing
beach profiles. This computation 1. New construction or sub- water velocities. The result, of
yields the information about how stantial improvements of residential course, is a decrease in the loss
far landward the uprush will reach structures within the area of spe- of property and life resulting from
and defines the Velocity Zone: the cial flood hazards are required to any given storm.
zone where considerable structural have the lowest floor (including
damage can be caused'. basement) elevated to or above the The setback line required by
3. Physical and vegetation indi- level of the 100-year flood, the State of Florida is only for the
cators were developed from historical A shorelines that face the open Gulf
erosion data, flooding data, and top- 2. New construction or sub- and Atlantic Ocean. However, hurri-
ographic and hydrographic information stantial improvements of nonresi- canes can have a dramatic impact
gathered from field surveys. These dential structures within the area upon estuarine waters resulting from
indicators were utilized to adjust of special flood hazards are re- the combination of the storm tides
the computed setback line distances. quired to have the lowest floor in the shallow water bodies and fresh
elevated to or above the level of water flooding from discharge off the
The resulting setback figure was the 100-year flood or, together with land. Consequently, the flooding and
calculated for, and measured from, attendant utility and sanitary storm damage can be equally as great
each of the control monuments, which facilities, are required to be flood- along the estuarine shorelines de-
have been surveyed in at approximate- proofed up to the level of the 100-year pending upon the specific storm
ly 1000-foot intervals along the flood. conditions. Therefore, it becomes
Sanibel-Captiva shoreline. The set- 3. Existing uses located on land imperative to establish a setback
back figure for each monument was below the elevation of the -100-year line for the open estuarine shorelines
plotted on a set of aerial plan photo- flood in the coastal high hazard area as well as the Gulf shoreline.
graphs taken in May, 1974, and the shall not be expanded. The buffer zones which result
recommended coastal con~struction
setback line was then drawn between 4. No land below the level of from the establishment of coastal con7
the plotted points. the 100-year flood in a coastal high struction setback lines serve another
hazard area may be developed unless very important function for Sanibel
The recommended setback line the new construction or substantial Island. These areas preserved in
should be considered as the absolute improvement (i) is located landward essentially their natural state are
minimum setback for Sanibel consider- of the reach of the mean high tide, much more available and conducive as

Beach Geology 251

wildlife breeding sites. Such birds continuous state of flux in response development or the implementation of
as least terns, skimmers, and golden to these changes. The barrier,which some coastal erosion measures could
plovers, as well as loggerhead tur- is a product of these various en- have major long-term results with
tles, require extensive backbeach ergy regimes, will respond to dis- respect to the stability of Sanibel
areas for successful nesting. The equilibrium situations and do Island.
vegetated area above the storm beach whatever is necessary to bring the
is essential nesting habitat for ;system back into an equilibrium The technical data and basic
smaller land birds and animals. . state. understanding of the various energy
regimes which dictate the geologic
(6) A barrier island needs processes operating on Sanibel
"elbow room" to respond to these Island, as well as the exact nature
natural processes; significant of the geologic responses within
restrictions, limitations, or this complex coastal system, are
Conbclusions modifications that are put in its very poorly known. -At best, the
way or forced upon it will either system is only known from broad
We can thus come to several a) be eliminated by the periodic regional oceanic and climatic data,
fundamental conclusions about Sanibel high energy regimes operating a review of changes from some old
Island, which is first and foremost a upon the system or b) modify the aerial photos and maps to modern
barrier island with a definite heri- system to the point where the shoreline surveys, and very limited
tage: cumulative responses may bring about on-site station monitoring for
dramatic and undesirable long range tides, currents, waves and sediment
(1) The island itself is an effects including compounding the movement. Therefore, recommenda-
effects including compounding the
integral part of a much larger system original problem.' tions for extensive engineering
of which all parts are intimately projects that involve major eco-
interrelated and interdependent in- These conclusions are founded on basic nomic investments, and more im-
much the same way that the heart is geologic facts and principles. The portantly, involve major structural
to the human body. Any c history of Saibel Island durin thnge modifications of the coastal system
modification of some portion. of the past 5000 years is characterized by should wait until this sketchy data
system will have some effects and re- alternating periods of beach ridge base and understanding is greatly
sponses on most other portions of the development and accretion and periods improved. Past experience drama-
system. of erosion and truncation. From this tically demonstrates that without
we can conclude the following: this approach, whatever equilibrium
(2) The island is a total pro- does exist will be disrupted and
duct of its past geologic history and the problems accentuated, producing
all parts of its present topography, greater adverse consequences in the
soils, water drainage, vegetative (1) Sanibel Island is apparently long term. Thus, in terms of long-
ecotomes, etc., are a total conse- now in a null period, except along the range economics of both the natural
quence of this history. northwestern shore where a period of system and man, it is better to
sediment accretion and beach ridge accept the natural processes as fact
(3) The island is presently a formation has been irregularly taking and as part of a complex set of in-
dynamic geologic unit in which the place for several hundred years. timately interacting variables which- -
geologic processes which produced the we do not fully understand and are
island are still actively operating not capable of controlling. We must
to maintain and/or modify the sys- (2) The process of beach ridge accept the natural processes and be-
tem in response to major changes of accretion occurs during high-energy come more flexible within a totally
the controlling variables. storms and requires a natural equili- flexible natural system. This means
brium profile with an abundant sedi- changing our present conventional
(4) The island, in its natural ment supply. approach to development in which
state, is in equilibrium with the building designs and layout plans are
multitude of energy regimes acting (3) Interferences with either considered universal (e.g., the same
upon the system; and change in the the natural beach profile, such as Holiday Inn that is designed for
energy regime causes- geologic re- the abundant construction which is Orlando would also be put on the
sponses which operate to produce a presently taking place in the upper storm beach of Sanibel Island). This
new equilibrium situation for that beach zones, or a major change in approach is not adequate; the devel-
energy regime. the sediment supply, which could very opment for Sanibel Island must be
well happen as a result of the pro- designed for Sanibel Island itself
(5) Since the complex set of posed erosion-control projects on and be developed around the basic
energy variables are in constant, Captiva Island, could rapidly change processes operating within this
and not always understandable flux, the present system to one of erosion specific dynamic natural coastal sys-
the barrier island also is in a and truncation. Thus, continued beach tem. However, in order to implement

252 Append ixes

this approach, traditional patterns effects upon the natural systems and cerned. If such a setback plan is
of thinking must change. This in- it should be done now before develop- carried -out, it will 1) provide a
cludes conventional attitudes towards ment has progressed any further. natural storm buffer or shock
geologic change such as shoreline absorber which will minimize prop-
fluctuations and inlet migration; (2) Develop a setback plan for erty damage and loss of life
land ownership and ownership rights; construction and which conforms to resulting from major storms, 2)
land-use zoning to include broad the requirements of the Florida allow the beach system to have the
buffer zones, hazard zones, and legislation and should include the necessary "elbow room" to maintain
cluster development; and more strin- following: an equilibrium profile, which in-
gent construction codes along the eludes erosion and accretion, with-
beach zone including building design, (a) The setback lines out economic barriers, and 3)
size, and the type of construction of as recommended by the Coastal and provide a natural area for nesting
homes, motels, condominiums and roads. Oceanographic Engineering Laboratory shore birds, turtles, and other forms
(1975) should be adopted as absolute of wildlife.
"The seam where continent meets ocean minimal construction setbacks for
is a line of constant change, where the Gulf coast. (3) With the establishment of
with every roll of waves, every pulse an adequate setback plan, the natural
of the tides, the past, manifestly (b) Develop a setback line and fluctuating beach processes of
gives way to the future. There is a for construction along the entire- erosion and accretion along the
sense of time and growth and decay, estuarine shoreline of Sanibel. Due Sanibel shoreline should not need
life mingling with death. It is an to the extremely different character correction. Thus, the use of exist-
unsheltered place, without pretense. and variability of the estuarine ing buildings and roads that fall
The hint of forces beyond control, shorelines and the processes operat- within thedbuffer zoneand become
of days before and after the human ing upon them, this will be a diffi- threatened by erosion or act in any
span, spell out a message ultimately cult task and the resulting setback fashion to modify the equilibrium
important, ultimately learned: now lines will be much more variable. profile of the beach, should be
forever, mortality, infinity." . terminated as quickly as possible
(c) All structures sea- so that the shoreline equilibrium
Levenson, 1973 ward of the setback line including can be re-established.
buildings, seawalls, roads,, etc.,
should be identified as non-conform- (4) If shoreline erosion of
ing and scheduled for eventual term- Sanibel Island becomes a dominant
Recommendations: ination. process and extends the beach behind
(d) The beach sand ridge the defined buffer zone such that it
("dune-field") should be re-establish- is determined that erosion control
The following recommendations are ed wherever it has been removed and is necessary, then vertical and
designed to 1) recognize the natural all areas between the setback line lateral equilibrium profiles should
geologic processes that are continu- and the natural vegetation line should be re-established through beach
ously operating along the coastal sys- be revegetated. This vegetative cover nourishment. Fixed structures which
tem of Sanibel Island, 2) establish should be of the native species that distort the natural shoreline pro-
a set of specifications: necessary to have the appropriate salt spray and file or which extend beyond the
a set of specifications necessary to Pp -g r oins,
preserve the coastal system in a other environmental tolerances to natural storm beach (i.e., groins,
healthy, stable, and non-stressed withstand storm effects. jetties, seawalls, and bulkheads)
state, and 3) allow man to develop and s E d
use this unique natural system within - (e) Sanibel Island should
the bounds and limits established by enter the National Flood Insurance (a) Sediment for any
the processes of the system itself; Program and agree to adopt and ' beach nourishment program should not
i.e., in a fashion which will allow strictly enforce floodplain manage- be mined from within the active
the greatest safety for life and ment regulations for all new con- beach system as presently proposed
property. The following considera- struction and substantial improve- for Captiva Island. The active
tions are recommended: ments of structures that fall behind beach extends from the beach ridge
the construction setback line and and storm ridge to the seaward limit
(1) Establish rigid "stress still fall within the coastal high of the lower forebeach (about the 20
limits" to stabilize the dispropor- hazard area as defined by the Federal to 24-foot bathymetric contour) and
tionate growth and development of Insurance Administration. thus excludes the proposed source
Sanibel Island. This should include areas within the ebb tidal deltas
the type, rate and magnitude or (f) The adopted setback and the middle forebeach.
total carrying capacity that the plan should be followed strictly in-
island can handle without major sofar as new construction is con- (b) All sediment used for

Beach Geology 253

beach nourishment should be textur- coastal system and Sanibel will ex-
ally compatible with the existing perience and share the long-term Literature
energy regime and not just filler consequences, whether good or bad,
material. It should have the same of whatever is done on Captiva. This
textural characteristics as the Beconomic barrier" is having a very Brooks, H.K., 1973, The physical
present natural beach sediments; definite long-term adverse impact environment: Geological Oceano-
this also excludes the middle fore- upon the rates of shoreline change graphy: in A summary of know-
beach area as a potential source by modifying the equilibrium profile ledge ofthe Eastern Gulf of
area as is presently proposed for sands and they should not be obtained Mexicos The State University
Captiva:: Island. System of Florida Institute of
from the active forebeach nor.from
the tidal deltas of either Blind or Oceanography, St. Petersburg,
(c) The offshore ridges, Redfish Passes, except for that ob-lorida, p.IIE/ - IE/S.
thatoccur seaward of the 24-foot tained from navigational dredging, Bruun, P.M., 1962, Sea level rise as
bath ric contour, should be as presently proposed. Rather, the a cause of shore erosion. Am.
explored as a potential sourcef of a nourl hi 0
explored as a potential source of nourishment sand should be obtained
texturally compatible beach nourish- offshore beyond the active forebeach 117Soc.130Civil30Eng. Proc., v. 88 p.
mensed.This sediment should117-130.
ment sediment. This sediment should (beyond the 20 to 24-foot bathymetric
also have a high shell content; thus, contour. Captiva Erosion Prevention Commis-
it would also nourish the important of the beach system. The following sion, 1971, Beach erosion control
shell resource ofi the beaches recommendations concern the erosion report and r ecommendaton s for
controls proposals for Captiva Captiva Island, Florida, 24 p.
(5) Blind Pass is a very
dynamic coastal-element which histor-
ically has gone through dramatic - : : Clark, J.,' 1974, Coastal ecosystems:
changes'and will continue to do so. Ecological considerations for

(a) Blind Pass, and the (a) Discourage any modi- The Conservation Foundation,
land immediately adjacent to the Pass fication to Blind Pass including ashion, D.C. 178 p.
closure, relocation, or structural
which is subject to the geologic stabilization, until an extensive 1974, Rookery Bay: Ecological
changes of the pass, should be de- study of both sediment and water constraints on coastal development
clared a natural hazard area in which dynamics of the inlet and asso- (including nine technical reports)
the geologic processes" are allowed to ciated coastal system can delineate The Conservation Foundation,
operate in response to the changing the long-term consequences of such Washington, D.C. 91 p.
energy regimes without any interfer- action. Until then the inlet
ence; that is, within the defined should be allowed to operate nat-
boundaries no further development urally in response to changing Preliminary survey, erosion con-
should be allowed and existing struc- energy regimes. The net sedi- trol program Captiva Erosion
tures that occur within the special ment movement off Captiva
hazard area should be relocated. Island will continue with or with- Prevention District, Lee County,
out the inlet,and the downdrift Florida, 1 - C/9 p.
(b) The permanent access consequences of closure or modi-
road and the bridge between Sanibel fication could be severe to Sanibel Coastal Engineering Laboratory, 1958,
and Captiva Islands should be re- Island. Coastal engineering investigation
located when possible from the active at Captiva Island for County Com-
mouth of Blind Pass to a location (b) Encourage Captiva missioners, Lee County, Florida,
well inside the inlet. This would Island to relocate the shoreroad 22 p., illus..
eliminate a major and vulnerable to the backside of the island along
"economic barrier" which demands pro- with the appropriate connecting Coastal and Oceanographic Engineering
tection and consequently modification bridges. Under present conditions, Laboratory, 1975, Recommended
of Blind Pass and adjacent areas. all efforts to save the road are coastal setback line for Lee
only stalling actions. County, Florida: University of
(6) The people of Sanibel Florida, Gainesville, Florida,
Island should obtain a voice and (c) If beach erosion 42 p.
participation in the decision-making measures continue to be considered
process concerning beach erosion essential, then the use of beach 1974, Coastal engineering study
control for Captiva Island. The nourishment should be encouraged of Captiva Island: Florida Engi-
justification for this is simply that as previously recommended. The neering and Industrial Experiment
Captiva and Sanibel are intimate nourishment sands should be of the Station, University of Florida,
partners of a single interacting same grain size as the natural beach Gainesville, Florida, 131 p.

254 Append ixes

Coastal Plains Center for Marine Dolan, R., Godfrey, P.J., and Odum, cesses in the coastal zone: in
Development Services, 1973, Guide- W.E., 1973, Man's impact on the Coastal Geomorphology, Publ. in
lines for the coastal zone: Barrier Islands of North Carolina: Geomorphology, State University of
Wilmington, North Carolina, Publ. Am. Scientist, v. 61, no. 2, p. New York, Binghamton, New York,
no. 73-5, 16 p. 152-162.- p. 11-42.

1972, Proceedings of seminar on Duane Hall and Associates, 1975, Huang, T.C. and Goodell, H.G., 1967,
planning and engineering in the Captiva Island beach erosion study Sediments of Charlotte Harbor,
coastal zone: Seminar Series no. and plan of improvements Captiva Southwest Florida, Jour. Sed. Pet.,
2, 141 p. Island, Florida: Prepared for v. 37, p. 449-474.
Lee County Board of Commissioners
Coates, D.R., (eds.), 1973, Coastal and Captiva Erosion Prevention Jones, J.I., et al., 1973, The physical
geomorphology: Publ. in Geo- District, Fort Myers, Florida, environment: Physical oceanography
morphology, State University of 1/1 - 6/3. of the Northeast Gulf of Mexico and
New York, Binghamton, New York, Florida Continental Shelf area: in
404 p. 1971, Beach erosion study for A summary of knowledge of the East-
fCurray, J.R., 1969, History of. con- S:Captiva Island, Florida: Fort ern Gulf of Mexico, The State Uni-
ttinental shelves:' *Oin The new : ageMyers, Florida, illus. only. versity System of Florida Institute
of Oceanography, St. Petersburg,
concepts of continent al margin Ducsik, D.W., 1974, Shoreline fot the Florida, p. IIA/1 - IIA/22.
sedimentation, Am. Geological
Institute Short Course Lecture public A handbook of social,
Notes, Philadelphia, Pa., JC/VI/l- economic, and legal considerations McHarg, I.L., 1969, Design with na'
; JC/VI/18 P. regarding public recreational use ture: Doubleday and Company, Inc.,
of the nation's coastal shoreline: Garden City, New York, 197 p.
Dolan, R., 1973, Barrier islands: Massachusetts Institute of Tech-
natural and controlled: in nology Sea Grant Program, The MIT Missimer, T.M., 1973, The depositional
Coastal geomorphology, Publ. in Press, Cambridge, Massachusetts, history of Sanibel Island: M.S.
Geomorphology, State University of 257 p. dissert., Florida State University,
New York, Binghamton, New York, p. FloridaTallahassee, Florida, 121 p.
268-278. 1971, Coastal zone management in
1971 Florida- A status~report to tNorth Carolina Coastal Resources Com-
Florida: A status report to the
___- 1972, Barrier dune system along Governor, the Cabinet and the 1972 mission, 1975, State guidelines
the Outer Banks of North Carolina: Legslature Talahassee, Florida, for local planning in the coastal
-~A'reappraisal.~: Science, v. 176, '11 p., illus. area under the Coastal Area Man-
p. 286-288r.a Xagement Act of 1974, 71 p.
Godfrey, P.J., and Godfrey, M.M.,
1971, Coastal landforms: Cres- 1973, Comparison of ecological O'Connor, M.P., and Riggs, 1974,
centic and rythmic: Geol. Soc. of and geomorphic interactions Mid-Wisconsin to Recent sea level
America Bull., v. 82, p. 177-180, between altered and unaltered fluctuation and time stratigraphy
4 figs. barrier island systems in North of the Northern Outer Banks of
Carolina: in Coastal geomor- North Carolina (abstr.): Geol.
1966, Beach changes on the Outer phology, Publ. in Geomorphology, Soc. America, Abstr. with Prog.,
Banks of North Carolina: Assoc. State University of New York, v. 6, no. 7, p. 894.
American Geog. Annals, v. 56, no. Binghamton, New York, p. 239-258.
4, p. 699-711. Pilkey, O.H., 1973, A shoreline con-
Hayes, M.O., Holmes, L.J., and servationist's guide to Bogue
Dolan, R., and Godfrey, P., 1973, Wilson, S.J., 1974, Importance Banks, North Carolina or a plea
Effects of Hurricane Ginger on the of tidal inlets in erosional and for help: Duke Univ. Marine
Barrier Islands of North Carolina: depositional history of barrier Laboratory, 21 p.
Geol. Soc. of American Bull, v. islands: Geol. Soc. of America,
84, p. 1329-1334, 4 figs. Abstr. with Prog., v. 6, no. 7, 1972, Development of North
p. 785. Carolina's shoreline: Duke Uni-
Dolan, R., and Vincent L., 1972, versity Department of Geology,
Analysis of shoreline changes, Hayes, M.O., Owens, E.H., Hubbard, Durham, North Carolina, 15 p.
Cape Hatteras, North Carolina: D.K., and Abele, R.W., 1973, The
Modern Geology, V. 3, p. 143-149. investigation of form and pro- Puri, H.S., and Vernon, R.O., 1964,

Beach Geology 255

Summary of the geology,of Florida 1969, Beach erosion control
and a guidebook to the classic study on Lee County, Florida:
exposures: Florida Geology-Survey Jacksonville, Florida, Series no.
Special Publ. No. 5, 312 p. 117, S/148-3 p.

Riggs, S.R., and O'Connor, M.P., 1974, U.S. Congress, 1970, Letter from the
Relict sediment deposits in major Secretary of the Army: Lee
transgressive coastal system: County, Florida: 91st Congress,
University of North Carolina Sea 2d Session, House Doc. no.
Grant Pub. UNC SG-74-94, Raleigh, 395/91/2, 74 p.
North Carolina, 37 p.
U.S. Department of the Interior,
State University System of Florida National Park Service, 1974, Cape
Institute of Oceanography, 1974, Hatteras shoreline erosion policy
Proceedings of marine environment- statement: U.S. Government Print-
al implications of offshore ing Office, Washington, D.C.,
drilling in the Eastern Gulf of 150 p.
Mexico, Conference/Workshops, St.
Petersburg, Florida, 455 p. Winston, D., Riggs, S.R., O'Connor,-
M.P., and Breuninger, R.H., 1968,
_ 1973, A summary of knowledge Geologic evaluation of Coastal
of the Eastern Gulf of Mexico, St. Petroleum Company's offshore lease
Petersburg, Florida, 1/1 - VII/ from the Honeymoon Island area
74 p. south to Blind Pass, Pinellas
County, Florida: Part A, Geology,
Stursa, M.L., 1973, Environmental 116 p. and Part B, Utilization of
quality problems: in A summary the sediments and offshore en-
of knowledge of the Eastern Gulf vironments, 74 p.
of Mexico, The State University
System of Florida Institute of
Oceanography, St. Petersburg,
Florida, p. VI/1 - VI/17.

U.S. Army Corps of Engineers, 1971,
National shoreline study: Shore
management guidelines: Center for
the Environment and Man, Inc.,
Hartford, Connecticut, 56 p.
1971, National shoreline study:
Shore protection guidelines: U.S.
Government Printing Office,
Washington, D.C., 59 p.

1970, Shore protection program:
U.S. Government Printing Office,
Washington, D.C., p. 1 - 3.2.

1964, Land against the sea:
U.S. Army Coastal Engineering Re-
search Center, Misc. Paper no.
4-64;43 p.

U.S. Army Corps of Engineers,
Jacksonville District, 1969, Beach
erosion control study on Lee
County, Florida: Jacksonville,
Florida, Series no. 60, 41 p.

257

Subsystems 259
Summary of Information 259
Relations to Man 260
Faunal Inter-relationships 260
The Food Chain 261
The Beach Subsystem 262
Uplands Subsystem 264
Interior Wetlands Subsystem 265
Condition of Wetlands 265
Alligators 266
Vegetation 267
Mangrove Subsystem 267
Birds 268
Literature Cited 269

259

APPENDIX 4

WILDLIFE ECOLOGY

by John B. Morrill, William K. Byle, Jr., and Richard Workman

This report reviews the wildlife of These subsystems, or zones, are The sections that follow discuss
Sanibel including amphibians, reptiles, physiographic provinces based on physical the nature of the system and the sub-
birds and mammals with emphasis on the and vegetative characteristics. In systems, their status as wildlife habi-
characteristics, populations, and inter- reality, many animals move readily from tats, the biology and significance of
actions of species that directly or one zone to another in response to their selected wildlife species, their status
indirectly: biological needs and environmental and requirements. This discussion is
pressures. meant to illustrate situations, problems
and concepts.
1) maintain the integrity of
Sanibel Island's ecological The Gulf Beach Subsystem (about
systems. 650 acres) begins with the Gulf Beach SUMMARY OF INFORMATION
dunes and extends 300 feet offshore
2) provide significant benefits (boundary of city jurisdiction). The species, their abundance, their
to Sanibel's residents and food and habitat preferences and their
guests. seasonality have been reviewed by
The uplands (interior ridges) sub- Hewitt (1975), Campbell (1975), Heald
3) are protected by law or other- system (about 1600 acres) includes and Tabb (1975) and Morrill and Byle
wise given special consider- areas not flooded by seasonally high (1975). Additional inventory data are
ation for their inherent or water levels. recorded by the J.N. "Ding" Darling
acquired status. National Wildlife Refuge and the
Audubon Society's Christmas Bird Counts
The Interior Wetlands Subsystem of Sanibel-Captiva. A general summary
(1857 acres) includes the interior lands of the information resulting from these
SUBSYSTEMS flooded by seasonally high fresh water is given in Table . Food preferences
is given in Table 1. Food preferences
levels. are summarized in Table 2. Species
Our approach to the subject is to that are rare, threatened, endangered,
discuss Sanibel's wildlife separately The Mangrove-Estuarine Subsystem are listed in Table 3; those that re-
for each major ecological subsystem (about 5400 acres) includes tidal swamps, quire special consideration because they
recognized by The Conservation marshes, salt-water tributaries, tidal are restrictea to specific habitats are
Foundation's natural system study team. embayments and peripheral tidal flats. shown in Table 1.

260 Appendixes

RELATIONS TO MAN requirements. However, there is still geological development have resulted
a great need to better understand in a special combination of sub-
Historically, the wildlife of Sanibel's wildlife systems and their systems providing diverse wildlife
Sanibel has been highly valued by both requirements. habitats. Wildlife that come to the
residents and visitors. Following the island find refuge in isolation from
establishment of the J.N. "Ding" An imaginative and creative edu- mainland conditions and may rapidly
Darling refuge on the island, the cational program for the island's expand their populations.
numbers of visitors increased. In 1960, residents, businesses, and visitors
167,500 people visited the island appears to be sorely needed and long Geographically, Sanibel lies
according to the annual narrative re- overdue. While modern landscape near the northern edge of the sub-
ports of the refuge. By 1975 the engineering and land-use programs are tropical land and sea biomes. Con-
estimated total number of visitors to vital for maintaining and conserving sequently, the island and its surround-
the refuge was 829,800 with 160,711 the island's amenities, they may not ing waters exhibit a remarkable
visiting in March alone. suffice without an informed public. diversity of tropical and non-tropical
This might include the establishment plant species (Long, 1973). It is
That shelling and wildlife are the of an active wildlife and natural largely this diversity of natural
island's major attractions are reflect- resources educational program to in- vegetation that makes the island so
ed not only in the refuge visitor clude a visitor orientation center, hospitable to wildlife, especially the
activity reports but also in the space trailside museum, and guided tours. many migratory birds using the Atlantic
and classified ads of the island's two Ideally, an orientation center with Flyway (Hewitt, 1975). Further, warm
newspapers. For instance, in the 15 audiovisual exhibits should be located Gulf waters have virtually eliminated
March 1974 Island Reporter more than at the end of-the causeway on Sanibel. seasonal temperature extremes that
50 percent of the 211 ads were related could limit biological productivity
to the island's natural resources. Of The whole island should be appro- and development. Therefore, both
the space ads 50 percent included motifs priately posted. Major wildlife cross- fauna and flora grow and develop
of wildlife, beaches, fish and shellfish. ings should be indicated with signs throughout the year.
Thus both the tourist and permanent along the roads, particularly Captiva
resident businesses are oriented to a Road, where alligators, river otter, Many of the naturally occurring,
large degree in serving a public that and other wildlife are known to cross native, species of wildlife perform
is attracted to the island for its the roads frequently. Known nesting valuable ecological functions. For
natural amenities. But the natural sites of anhingas, osprey, loggerhead example, alligators make and maintain.
systems have been seriously degraded turtles, burrowing owls, terns, black- shallow open water ponds for their
and the natural resources depleted by skimmers, and other wildlife should be nesting that provides habitat for
unconstrained development. posted with information signs, numerous other organisms. Other more
especially during the breeding season. recent arrivals or introduced animals
A variety of ecological, behavioral, similarly, major nesting and feeding like the armadillo, feral dogs and
and human value parameters (summarized in areas of shore birds should be posted. feral cats may adversely affect the
Table 4) should be kept in mind when plan- balance of native wildlife populations
ning for the conservation of wildlife. The need for a city natural by predation and competition for
"Impact-response" matrices given -in Table resources department should be recog- resources. (In recent historic times
5 reveal how well different species adapt nized--major functions would include bear, deer and quail have become
to man-dominated environments. monitoring, research and management of extinct on the island, the latter
wildlife and their resources. For years probably from predation by feral cats.)
In addition to the physical loss or this role has been admirably filled by
alteration of natural habitats and the the Sanibel-Captiva Conservation The apparent benefits of island
creation of new habitats such as ponds, Foundation, but this group has no formal life are tempered by other geographical
lakes, roadsides, and exotic vegetation, power to regulate or otherwise act in considerations. All of the low-lying
the numbers and diversity of wildlife the public interest. island is exposed to the subtle effects
are being affected by the activities of of the sea as well as the drastic
people seeking to observe wildlife as Faunal Inter-relationships forces of storms. There is a limited,
though they were in a city zoo. This seasonal abundance of fresh water, with
prevailing ignorance of the ecological flooding wetlands, and the more drastic
needs of individual species makes While Sanibel is first and fore- consequences of widespread flooding by
specific plans for conservation difficult most a barrier island, it is part of hurricane-driven salt water.
to formulate. a larger ecological system. Barrier
Obviously, the maintenance of islands offer an environment for wild- Another constraint is the problem
appropriate habitat is the basis for life that differs from the mainland of space itself. Wildlife are limited
healthy wildlife systems. Accordingly, and consequently the species mix and first by the size of the island and
we have indicated a number of valuable abundance pattern is distinctive. second by the amodunt of habitat that
wildlife species and their habitat Sanibel's geographic location and satisfies their individual needs. Con-

Wildlife Ecology 261

Of~ m
sobsysoeo Oiahtitoo S~asoa1 oosoble rceedos socoal
Epecies O ccurrence popul'inO Behavior � plvor
Type of
Food H Status a
B� .- Type of -. O
P. f
Bird 5 c
so a~� - Species
~~1 E7 �j:. 4 i3 ~~~~~~~~~~~~~~~~~~~ " '""':818 x B '~~~~~~~~~~~~~ ~ 0
0 -ic a: as s a
c c
[~~~~.1
Gc~~~~ulfr Beac~h ~PASSERINES -- 20 29 - 2 3
lgerghcad turtle
Rhcc aacc0on0 0 WADERS 1 1 9 8 5 4 1
*hlC. ,x ;::: Amphibians
SHORE 2 1 13 8 15 1 2 3 Littlegrass frog -
...x .xxxDIVERS & DUCKS 4 3 5 6 9 2 1 Florida cricket frog X
cidili . .. l Florida chorus frog x
o-ppXOsmORAPTORS 3 - 1 2 2 2
Rcd-shouldered howk x
Lila~=~ ~ ~ ~~~~~~~~~~d5 ~~~~~~~~~Reptiles
interior metlands TOTAL 7- 25 62 22 32 9 6 5 Gopher tortoise x
D~~L~~~i~eri~~~~~~~cO cciia~~~~igeccctror~ iFlorida brown snake x
Ococh r=oibot o o * x Florida ribbon snake x
Red-winged blackbiod xEastern indigo snake 'x
04-robe, frg c= o o Table 2 - Food of common species of residentor seasonal American alligator x
toL~~~~ceS b~~~ird~~s~ ~birds on Sanibel Island; recorded are the number of species
solicco~~~ o[ " ' which feed significantly on the categories listed. Birds
oo... . Wood stork x
oc... kee. .. X Brown pelican x
roD"~~~~~~CkeL'~~~ ox~~~~~~ a::�~ a~ 0"~ xMagnificent frigate bird x
Sanibel 's subtropical climate is r Southern bald eagle x
ideal for insect reproduction and devel- Osprey x
Table I - Ecological matrix of example wildlife species of four opment; as exemplified by the results American oyster catcher x
major ecological subsystems of Sanibel. of Maurice Provost' s mosquito studies Least tern x
on Sanibel. On the night of September Roseate spoonbill X
15, 1950, Provost captured 365,696 Mangrove cuckoo X
Little blue heron
sequently, the populations of many mosquitoes in a single trap on Sanibel;, Louisianna heron x
species are delicately in balance with measured 45,000 mosquito eggs per square Yellow crowned night
Yellow crowned night-
their limited resources. Destruction foot along the Sanibel Slough the heron x
of these restricted environs can stress following summer and stated that swales Least bittern x
or exterminate populations like the on Sanibel holding half-a-billion eggs White ibis x
gopher tortoise, the burrowing owl to the acre were common (Provost, 1969). Caspian tern x
the mangrove water snake, or the river Black skimmer x
otter. These figures assume staggering Snowy egret x
ecological significance when the variety Great egret x
of herbivorous insects on Sanibel is Burrowing owl x
THE FOOD CHAIN considered along with the number of
Mammals
acres of suitable insect habitat.
Florida panther x
Many species of wildlife are dependent od ane
Round tailed muskrat x
As part of a complex web of life, on mosquitoes and other herbivorous Sanibel Island rice
each species of wildlife represents an insect species. For example, Gambusia rat
energy pathway through the livingworld, and killifish at certain times of the
The animal kingdom must first acquire year feed almost entirely on the
its energy from plants. Herbivorous herbivorous mosquito larvae developing Table 3 - are and endangered Florida wildlife recorded for
Table 3 - Rare and endangered Florida wildlife recorded for
animals perform this first step. On in shallow fresh and brackish waters.. Sanibel Island. (From Florida Environmentally Endangered
Sanibel this task is handled primarily These minnows, in turn, are an LandsPlan).
Lands Plan).
by a wide variety of first order essential food for larger commercial and
consumers: bees, ants, mosquitoes, . game fish, and the many wading birds
flies, grasshoppers, butterflies, cater- for which Sanibel is famous. The adult (pollination of fruit and vegetable
pillars, snails, several birds (e.g., mosquito itself is food for. spiders, crops) and also support insectivorous
ground dove, cardinal and ducks) and toads, nighthawks, and dragonflies. populations of reptiles, amphibians,
several mammals (rats, mice, and the -birds and mammals.
marsh rabbit). Without doubt insects- Still other herbivorous insects,
constitute the major consumer at this such as bees, butterflies, and moths, Further, the herbivorous insects,
trophic level. perform valuable services to man birds and mammals function as "gardeners"

262 Appendixes

___. G_...___hi__ SPECIES The highest trophic level predators,
A. pndig in..s OF a co m
A, Introddig ..... ic, fe~al) WILDLIFE B *~~are the fourth order consumers that may
A. Indironoan WILDLIFE ,
B~. In~tro~d ...vd (tferal) 0S o feed on one or more of the smaller or
C. Potentinl "invdof oce from neighbofimg islnds .an MA N'SssaI0ao
nd i iIACT[It~VITIE ~~r ~ .. .3�5~. ':. ff weaker species. For example, the red-
AND 00 oom 0 5a 0aaro
1ilENVIRONME o5t. gapl. ooennaRZE ( moo. ishouldered hawk will eat herbivores
II. Abonda..nas..M atsma s0 05n .-50 055
A. E--inot MsANa An .00000 .�a0sm= oamouo
A. Endance ti..t ..83- U ~asms~~ffbald~, (rabbit), insectivores (frogs),
B. Officially endangered
C. Offi.i-lly aendangered 1000.00 Of Ccarnivores (snakes), or omnivores (rats
C. Formerly present on island nsvsroason
D. Overabundant, to th nuisance point .ass . .and mice)
Pe0e1ae lon xrxrxxan
III. Presence on Island: Overview or 'Inventory Pen competiton xnx x0x0
A. Full-time (food and nest-site-depoendennt( Otrcdued .n. ..s . .0 ... Lastly, we must consider the
B. Transient (food or nest-site-dependent) "AE" scavengers. Scavengers occur in every
C. Sesonal (nest site and food dependent for part of year SOOS habtat Often their activities and
only) . coooan
~~~~~~~~~~~"c ,o:..3-y habitat. Often their activities and
~So~EamCS~ 0"~ ~presence go unnoticed or at least
IV. Habitat Restrietions "OmO.TONSTI�'
A. Rqire more than one habi tat their ecological functions go un-
0. Adaptto leone than one habitat appreciated. However, several- of
C. Reps tricted toa one habitat C e a d d x
C. .s.tndted to one habitat 01000 ... Sanibel's conspicuous scavengers are
v. Imtraspecific Interactions Yed, exceptions. The black vulture and the
A. Territorial breeding season only p�cn c area
A, ... Tertna redgsesnol 0015turkey vulture help to keep the road-
B. Territorial, low-density uitiy otres
C. Territorial. high-density Uity y .let 0 . 0... ways free of car kills. The ubiquitous
0.Gregarious. non-territofial 0000001el01ers0 0
E. StG.e.go h.oen.ins tj.oo.ca~lat gulls rapidly dispose of the constant
E.Strong homing instinct Msi ice x
A A M~~~~~~~~~~~~~~~~~ ~~osgaito 00110tche00s
-e........ .t.. 1..- and periodically large quantities of
VI. Interspecif in Interactions Canals - 0 0x
APoVI. dnt--esifioo I000.00 -oo sei0tifOrhbopce aCoo beach-cast fish, shellfish and other
A. P-ovid.. f..d ouc f- -C-habit- peis ~ r~iMplsLIXX
Brazilian pepper crass
B. Competes for food source with co-habitorpeies e carcasses.
C. Providee "housing" for co-habitor species SpEc-ES soTe
D. Competes for space with o-habitor specie o O- The following sections discuss
E. Preys upon o-habitrpi The following sections discuss
VII. Interactions with Man
~~Y�.VII. ItOtin 000 000important species and ecological sub-
~~~~~A. Vistiible . . . . . . .systems. Together and individually
N. Secretive vim
C8. Sertiiov~e mae-node foo noylts 0s0 s 0.00 00000I( 0 . .these sub-systems provide wildlife
C. utili- ........d od s-ppli.......
D. Utilizes man-made hasbitapts se0 habitat for a variety of important
S. utilfoesm 00-Code hohitato 0000000.1 NCo-
E. Food supply decreased or eliminated .y man A00 .O , C-.. species (Table 6) . Over many years
PF. Habitat decreased or eliminated by man speciesC hAUv
G. Adapts to disturbed habitats these species haveachieveda dynamic
Table 5 - Impact-response matrix of selected wildlife to man- equilibrium with Sanibel s biological
Table 4 - Ecological, behavioral and human value parameters and physical resources. This section
; ~~~~~~~~~~~~~~~~dominated environments of Sanibel Island,
involved in the evaluation of individual species of wildlife with has considered a few common species
respect to their conservation. black-and-white warbler, gray kingbird, whose presence and influence are
purple martin, Carolina wren and the island-wide. The discussion of
of the native vegetation, providing vireos, feed on practically any available trophic levels has emphasized the
fertilizer, pruning, seed dissemination insect within the size range they utilize. essential roles that several important
and planting. (One herbivore, the species play in keeping the island's
gopher tortoise, is an extremely Several mammals--shrews, moles, some natural-systems in balance.
important species that will be examined rodents, and all rats--feed almost ex-
as a member of the upland subsystem.) lusively oninsects. s than a fraction Subs tem
clusively on insects. s-ess than a f raction
of a percent of all insect species are The Beach Subsystem
Another set of wildlife Species inimical to man's interests. Numerous
operates at the next trophic level as insect species are predators or parasites The Gulf Beach Subsystem begins
second-order consumers. These are the on other insects, and perform an invaluable on the seaward side of the coastal
insectivores, carnivores, and omnivores. service in control of populations. strand, behind the primary dunes and
Again, their presence and abundance here includes: the primary beach sand
depends upon and reflects the status To maintain Sanibel's interesting and dunes, the backshore beach, the inter-
of herbivores on which they prey. unique diversity of birds and other wild- tidal foreshore beach, the inshore
The insectivores are well represented life, for human or ecological reasons, breaker zone that extends into the
island-wide by predacious insects, natural insect environments must be "nearshore" waters (300 feet to the
spiders, wasps, dragonflies, frogs, maintained. boundary of jurisdiction or city limits)
toads, lizards, mammals and birds. The ecology of this last zone (nearshore)
Insect-eating fish, amphibians, has been treated by Morrill and Byle (1976)
Many birds are obligate insectivores. reptiles, etc., support third order and is discussed here only as it related
Some, such as the pileated woodpecker and consumers in large part; these are to the wildlife ecology of the other zones.
the common nighthawk, are selective as the carnivores and omnivores, such as
to type of insect prey. Others, such herons, egrets, terns, opossum, armadillo, Physically, the five zones function
as the yellow throat, prairie warbler, and snakes. as a single system, a relatively narrow

Wildlife Ecology 263

zone of fluid sand that continuously
molds itself t- 0the daily, seasonal and Trophic Level
annual forces of the sea. Each zone is Representa-
a product of an reflects the various tives
degrees ofinweancurenin Reference Producers Consumers Consumers Consumers Consumers Consumers
affecting Sanibel's Gulf coast. Area (Native Plants) (Herbivores) (Insectivores) (Omnivores) (Dominant (Scavengers)
(Complex) Carnivore)
The relative harshness of this en-
vironment limits the number of species
~that can live: here to a compar~tive ISLAND Many Herbi- Spiders, Raccoon Peral Dogs & Bacteria,Ants
that can live here to a-comparative WIDE All vorous Dragonflies, Fish Crow Cats have Beetles,Turkey
handful of hardy, uniquely adapted plant SYSTEM Vegetation Insects and Frogs,Lizards, replaced & Black Vulture
and animal species. Some highly special- their larval Nighthawks, Bobcat, Fish Crow
ized species (i.e., ghost crabs, beach stages Woodpeckers Pather and
fleas, and coquinas) are permanent
residents, but most, like the shorebirds, Phytoplankton, ConchsWhelks,
diving birds, sea turtles, and raccoons Marine Sea- - Zooplankton Menhaen,Clams, er Shark
are visitors only. Over time, many grasses head, Pen- Egrets, System Shar-
GULF - - - - - - - Cockles, Pen- Egrets, System Scaven-
species have become dependent on the BEACH sporobores, shells Pelicans gers plus
beach complex in some way or another. COMPLEX Ipomoea -- Gulls, Ghost
All bury themselves in defense against Bay Cedar Grasshoppers Tiger beetles Crab, Ants
Terrestrial Marsh Elder Marsh Rabbit Spiders Raccoon Ferals
the crashing waves and being tumbled up Cocoplum Warblers Rats,Mice ral
and down the beach. Here, masses of Sea Oats
coquinas and beach'fleas occur 'and Cabbage Palm
attract flocks of dunlins, plovers, Sea Grape System Species Indigo,Racer Red Shoulder System
sanderlings, sandpipers �and other shore INTERIOR Buttonwood Insects & plus Wasps Rattlesnakes Hawk Scavengers
birds. The agile snowy egret and RIDGE Gumbo Limbo Larvae Other preda- Raccoons -- Ferals plus Ants
LouisIiana heron: are ofteni-found chasing COMPLEX Strangler Fig Tortoise ceous insects, Rats & Mice and Beetles
Louisiana heron are often found chasing COMPWild Lime,Cats Marsh Rabbit Warbers Armadillos
~minnowsbetweenthewaves.Warblers Armadillos
minnows be tween the waves. : : ~ '~ ClawMyrsine, Vireos,Quail Opossum
Stoppers,Erno-
In the near and inshore zones there Cactu,Wid Coffee
are many types of phytoplankton that ..
function'as producers. These in turn Phytoplankton
are fed upon by many macrofauna that Duckweed Mosquito Spiders Herons, Egrets Red shoulder System
exhibit special locomotory, respiratory, Widgeon grass Larvae Frogs Rail, Coot, Hawk Scavengers
and morphological adaptations that INTERIOR Charas, Cattail Snails,Grass- Toads Snakes Alligator plus
aolatWETLAND Sawgrass,Cord- hoppers Wizards Raccoon Otter Crabs
permit them to inhabit the shifting COMPLEX grass, Sedges, Caterpillars Dragonflies
sands while filtering out their food Grasses,Myrtle Marsh Rabbit Vireos
supply. They, in turn, provide fo Iod for Leather Fern Rats Warblers
supply. They, in turn, provide food for Buttonwood Killifish
predaceous molluscs, rays, and the Distichilis
loggerhead turtle. Here too live many
of the shellfish species whose shells Phytoplank- Mosquito Spiders, Anol Herons Cormorant System
wash ashore, and give Sanibel its great MANGROVE ton Larvae Warblers, Egrets Pelican Scavengers
reputation for shell hunting. ESTUARINE Algae Insects Cuckoo Spoonbill Osprey plus
COMPLEX Sesuvium Ducks Woodpeckers Ducks Eagle Gulls and
Philoxerus Mullet Killifish Coots Alligator Crabs
In the open water are surf minnows Batis Raccoon
(i.e., menhaden, anchovy; and fry), Mangroves Gamefish
commercial and sport fishes; all are
preyed upon by a variety of other fish,
birds (e.g., terns, skimmers, cormorants, Table 6 - Summary of important animals in the food-webs of the ecological subsystems of Sanibel Island.
pelicans, osprey) and man.

In view of the historically stable zone which extends to the base of the defense against the sea. Here, storm
nature of this zone on Sanibel (Missimer primary dune. The lower portion is waves lose much of their erosive energy
and Riggs, 1976), the greatest direct literally devoid of resident animal life on the gradual incline. Thus, the back-
threat to wildlife is from the growing and the upper portion boasts few shore beach protects the interior
numbers of beach walkers, waders, and permanent residents like the ghost crab habitats from destruction.
shell collectors. and a few insects. Its physical presence
is perhaps its most valuable feature. It is well known that the loggerhead
Above the tidal foreshore zone, The offshore bar and the back beach slope sea turtles (Caretta caretta) return to
occurs the familiar backshore beach function together as the island's first Sanibel Island each summer to lay their

264 Appendixes

eggs in shallow sand nests on the upper of families of raccoons eating turtle The complex- was historically an important
portion of the backbeach. The majority eggs as they were laid occur in the wildlife habitat and a reservoir for beach
of the nesting sites between 1971 literature. With the reduction in the sand, and is the front line of protection
and 1975 have occurred on the more raccoon population which also preyed for the island during storms.
isolated, undeveloped beaches west of on ghost crabs, the ghost crab popula-
Tarpon Bay Road to Blind Pass. Annual tion increased with an increase of The integrity of this subsystem
reports of Caretta Research, Inc., predation of turtle nests by the tunnel- depends on the maintenance of each of
indicate that lights from condominiums ing crabs. its interrelated and interdependent
and motels, and people with flashlights zones. Each of these zones requires
in the more developed areas east of Preservation of turtle nesting special and equal attention to insure
Tarpon Bay Road disturb the nesting grounds is needed also because the that the entire complex is permitted to
turtles and may cause "false crawls". loggerhead is a key figure throughout function as a system.
Turtle nesting is declining as the- marine ecosystem--both as an
evidenced by a decrease from 12 nests important predator (of clams, conches, Uplands Subsystem
in 1970 to 5 nests in 1975 at one nest- crabs and the dangerous Portuguese
ing area, Turner Beach near Blind Pass man-of-war jellyfish) and as prey (eggs
-(designated as the Turner Beach Logger- eaten by ghost crabs and raccoons; The interior ridge complex is
head Turtle Sanctuary by the Lee County young by marine birds and fish; adults made up of those lands in the island's
Board of Commissioners- in 1969). In by sharks and man). Their role as a interior not inundated by seasonal
June of 1974 a tropical storm altered reliable transport mechanism within high water. The lands were formed as
the beach profile and caused a number their extensive migratory range is a series of beach ridges in parallel
of Australian pines to fall into the absolutely unique whereby as many as sub-sets of between seven and twelve
Gulf waters of the beach. That fallen 100 different species of marine life (Missimer, 1973). Over most of the
trees on the beach interfere with nest- have been found on turtles' backs. island, these ridges reach an elevation
ing activities appears obvious. Less of three to six feet above sea level
obvious perhaps is the slope of the Protection of the backshore beach and are covered with a dense growth
foreshore and width of the beach between nesting habitat is critical, and should of sub-tropical trees and shrubs.
the high tide line and the beach grass take precedence over human use of this
zone. East-of Tarpon Bay, the intensive zone during the nesting season if the The habitats within this sub-
beachfront development complemented turtles are to survive. system vary from desert-like conditions
by a very low foreshore profile may on the-higher riages in the western
discourage successful nesting. West Immediately behiand to dense hbaocksh of
of Tarpon Bay Road, the 1975 nesting beach, lie the primary beach sand ridges West Indian vegetation scattered
census indicates certain sections of = (dunes). Here, salt-tolerant vegetation throughout the island at lower elevations.
the beach have more nests than others --sea oats, railroad vine and purslanes--
and that more turtles nested in 1975 trap the wind-blownsand. Physically,dge complex
than 1970 even though the human popu- the primary dune serves as a beach sand is heavily vegetated. Accordingly,
lation and beach activity had increased reservoir, releasing sand back to the wildlife have adapted to these con-
over the five year period. Accordingly, beach during severe storms. ditions. Woodpeckers frequent insect-
attention should be given to study of invaded trees seeking insect larvae
the factors involved in beach site Historically, some of the shorebirds and commonly create hollows in a cabbage
selection bynesting turtles, particu- --snowy plover, Wilson's plover, willett-- palm or strangler fig for their nests.
larly if sections of the beach are to nested and roosted in this zone, but In addition to providing a source of
be designated as turtle nesting construction, foot traffic, picnicking, food and a place for nesting or perch-
sanctuaries. sea oat seed collecting by humans and ing, the vegetation of these ridges
dense strands of Australian pines have provides important cover for species
A second aspect of turtle nesting seriously degraded wildlifehabitat on that must be waryof predators. The
success involves predation by humans, the primarydunes. In some places the - practice of clearing understory
raccoons and ghost crabs. LeBuff (1969) dunes have been completely destroyed vegetation from around trees in develop-
reported that of 168 nests on Sanibel and built upon. ments reduces habitat and protective
and Captiva Islands, humans excavated cover. Songbirds, and other wildlife
15, raccoons dug up 6', ghost crabs Adherence to the coastal construction species generally considered attractive
tunneled into 24, storm tides destroyed set-back line, construction of dunecross- in the residential environment, are
16, and erosion destroyed 4. Of the walks, and dune restoration where necessary among the first to be adversely affect-
estimated 6,215 hatchlings that may would be a valuable first step in ed by this practice.
have reached the Gulf from the surviving restoring the natural function of the
nests, perhaps only 15 would survive to primary dune system. Much of the wildlife of the interior
breed. Prior to 1964 the raccoon ridges is wide-ranging and can be found
population became rather large before In summary, the Gulf Beach complex is in the other subsystems at various times,
it was decimated by a virus. Reports far more than just a barren strip of sand. but the upland species are those that

Wildlife Ecology 265

have adapted life styles tying them in and mammals. Ground nesting birds on dredging, and introduced pesticides all
some manner to the upland habitat. the interior ridges are particularly appear to be lowering populations of
Burrowing animals, for example, may vulnerable. reptiles and amphibians. Excavations
range over the island, but must that allow salt water intrusion is
construct their burrows oh the ridge to Most of the future development of
construct their burrows on the ridge to Sanibel will occur in the interior ridges probably contributing to this decline.
-- of the islands because the least alter- Raising the water table and increasing
ation of the ecosystem is required in the storage capaity of the watertable
The most prerominr ent burrowmplex is the this subsystem to provide suitable aquifer will lower this salinity
gopher tortoise. Thisreresidences. The alteration of habitat extreme and probably boost reptile
gopher tortoise. This reptile grazes and amphibian populations. (Campbell,
on herbaceousplants of the ridges and pwill displace wildlife and undoubtedly
associated swales. It is particularlybb, 1975.)
important to the ridge wildlife complex The chief factors influencing bird
because itsburrows provide refuge for InteriorWetlands i populations appear to be vegetation and
a variety of species, including reptiles, food supply. Presumably if historic bird
amphibians, raccoon, opossum, and a host Subsystem habitats are to be preserved and population
of invertebrates (Campbell, 1975). numbers restored, exotic plants will have
to be controlled and "natural" wetland
Snakes are relatively abundant in Of the wildlife species that occur to be controlled and "natural" wetland
vegetation re-established. If the
the upland areas, though seldom seen. on Sanibel, most can be found in the wetlands are to remain viable with ample
Species like the endangered indigo snake habitat provided by the interior wet- forage fish populations, water levels
which feeds on rodents, may be observed lands complex (Campbell, 1975; Alexander, must be high and salinity low. However,
in residential areas seeking small 1975). It is in the low-lying interior the present mix of birds, mammals, reptiles
mammals commonly associated with human of the island that fresh water is reptiles, and amphibians shows an increase
habitations. Bird feeders generally collected in seasonally inundated in number of species able to tolerate
attract rodents that occupy the interior marshes and perennial channels and ponds. people developed land, and saline wat
ridges. This hydrologic system, as reported by conditions (Campbell 1975).
Missimer (1976), is unusual for a
Wildlife forms that have adapted barrier island and accounts for much of
particularly to the drier open ridges, the wildlife diversity found on Sanibel.
like the six-lined racerunner lizard, The interior wetlands complexETLANDS
The interior wetlands complex of
are being presented with an expanding Sanibel sets it apart from all other The interior wetlands complex includes
habitat. Development practices that
require removal of vegetation reduces that barrier islands. Yet, as the most about 1850 acres of marsh in the center of
require removal of vegetation reduce intricate and most fragile complex of the island (remaining of an original 3000-
moisture retention of the shallow soil, the island's natural system, it is also 4000 acres), connected by the Sanibel River
creating dry (xeric) conditions on the the most vulnerable to insenstive develop- and a network of tributary canals created
higher ridges. The racerunner population ment. Maintenance of the environmental for mosquito control purposes. Additionally,
has increased accordingly. integrity of the interior wetlands complex a number of borrow pits in the interior have
that supports a healthy wildlife population created fresh and brackish water ponds that,
The introduction and rampant growth means a healthful environment for people. for the purposes of wildlife assessment,
of exotic tree species that outcompete are included among the habitats discussed
native vegetation will ultimately The interior wetlands provide some here.
take its toll on the wildlife of the of the most productive and valuable wild-
ridges. Where established, Casaurina life habitat on the island. As reported In-its earlier unaltered state heavy
and Schinus crowd out native plants by Hewitt (1975) and Campbell (1975), summer rains inundated the island's interior
and prevent natural succession of a total of 84 species of reptiles, lowlands, creating vast areas of open water
(Alexander, 1975). While there is some amphibians, and mammals found on the and marsh. Surplus water was slow to drain
wildlife utilization of the invading island some 35 species and subspecies away, but when the water in the interior
trees, unless their destructive spread are dependent on the interior wetland was high enough to break through the beach
is brought under control, the diversity habitats. Almost 300 species of birds front sand ridge, so much water poured
of wildlife species on the ridges and have been recorded on Sanibel over the through the ridge into the ocean that the
in other affected habitats will years, many of these species occur only interior would remain relatively dry
certainly decline. occasionally, however, there are 16 through the winter to the next summer's
important species that are common in the rains.
Introductions of non-native species fresh-to-brackish water habitat of the During the annual dry period
are placing unnatural pressures on bther interior wetlands. (winter) wildlife populations were at
wildlife. Breeding populations of The existing interior wetlands must their lowest in the island interior,
feral cats are well established on the be protected and improved if they are to but increased dramatically as the next
island. The feral cat is a deadly continue to support present wildlife rainy season brough water back into
hunter feeding on reptiles, birds, population levels. Increasing salinity, the marshes.

266 Appendixes

wetlands through the dry season.
These modifications greatly reduced
14,000 mosquito production and reshaped
the rest of the interior wetlands wild-
life populations.

Wildlife observations and water
bird counts conducted annually by the
U.S. Fish and Wildlife Service in the
NUMBERS 01959 .1958 interior wetlands indicate a positive
OF BIRDS : - : relationship between wildlife popula-
tions and water levels. As shown in
Figure 1, the numbers of birds in
r 10,000 1955 annual counts from 1949 through 1973
were found to fluctuate directly with
:: 0: f : -I : 1953'. *1951 0 :; 0 0 0 \ 0 recorded rainfall (Shea, .1974). Early
1956. .1960 management efforts in the interior
*1963 wetlands to maintain higher water ,
8,000 1962 levels in the marsh increased water
; 1961 fowl and wading bird activity,
~~~~~~~1957 :~~attracted greater numbers of colonial
nesting birds, and caused a noticeable
'1950 increase in alligators, otters and
other wildlife (Shea, 1974).

These increased populations are
attributed to improved habitat and
increased food supply created by the
maintenance of a higher water table.
4,000 R f ; 0 7 | The mosquito larvae-eating fish, for
example, could be sustained in greater
numbers through the dry season. More-
over, the additional fish population
supported greater numbers of third
2,000 , order consumers, such as, herons,
1.0 2.0 3.0 4.0 5.0 6.0 7.0 egrets and anhinga. As the base
of the food chain broadened diversity
INCHES OF RAINFALL and numbers of wildlife increased

JANUARY-APRIL (1950-1963) accordingly.

ALLIGATORS

Of all the higher order consumers,
Fig. I - Estimated:numbers of birds occupying the Bailey Tract of the J.N. "Ding" Darling Wildlife Refuge (as estimated by the U.S. the creature most affected by modifi-
Fishand Wildlife Servicerefugestaff)andtotalrainfall (fromlocalraingauge). cations of the interior wetlands is
the American alligator. Before channel-
ization of the Sanibel River, the
major source of fresh water available
to wildlife during drought periods
was in holes excavated to the water table
by the alligator. These alligator holes
sustained minimal wildlife populations
through the dry season. The creation of
Mosquito populations provided a at 45,000 per square foot or two permanent water in the Sanibel River
noticeable indicator of biological billion to the acre (Provost, 1969). provided more habitat during dry periods,
production when seasonal rains re- Channelization of the Sanibel River and maintenance of higher water levels
filooded the mangroves. Salt marsh was completed in 1960. Control struc- reduced the need for alligator holes.
mosquito egg densities along the tures at the drainage outlets were
Sanibel Slough were measured in 1950 constructed to maintain water in the The alligator as well as other wild-

Wildlife Ecology 267

life responded to the expanded open water Manem middle, and higher carnivores). Among
habitat by an-increase in its population.grove Subsyst em the primary consumers are commercially
Borrow pits dredged for real- estate de- important species such as pink shrimp
velopment in the interior wetlands The mangrove subsystem is the and striped mullet. The majority of
created additional alligator habitat. transitional habitat that separates the the sport fish species, such as tarpon,
However, encroachment of such develop- land from estuarine waters. The spotted sea trout, red drum, and snook,
ments into the wetlands has contributed mangrove-estuarine complex includes occupy the middle and higher carnivore
to the lowering of water levels, degraded mangrove swamps, oyster bars, shallow levels."
water quality, and the siting of resident- embayments, the impounded tidal and
ial areas of the island in the midst of salt flat area in the "Ding" Darling Further, "Black mangroves-have
a major portion of the alligator popula- Wildlife Refuge, the tidal flats along been the subject of less intensive
tion. the northern side of Sanibel, Tarpon investigation. Again, their role
Bay, the mangrove-fringed bayous of may be determined by their geographic
the Blind Pass area, and the vegetated position in a Coastal system. Black
man-made canals. This complex consists mangrove communities which are within
VEGETATION of about 5,400 acres, nearly-one half the range of regular tides probably
the total area of the island. The play a similar role -to red mangroves
major portion of this subsystem is in
major portion of this subsystem is in with which they are closely associated.
Vegetation of the interior wetlands the "Ding" Darling Refuge. Black mangroves at slightly higher
subsystem provides food, cover, and elevations seem to be an integral part
nesting for the wildlife population. The mangrove subsystem now com- of the mosquito-killifish food chain.
Herons, egrets and anhingas nest in prises about 2,800 acres of an original In fact, they and associated plants
branches of trees overhanging the Sanibel historical inventory of more than 3,200 probably produce the major part of the
River. Rails, gallinules, and bitterns acres. More than 2,000 acres of man- detritus which fuels this chain. By
utilize cattails for cover and nesting. grove swamp is in the refuge. Other this pathway they presumably contri-
Seeds and fruit of various plants provide major mangrove swamps are at Wulfert bute to adjacent estuarine waters,
food for raccoons, rodents and songbirds. Point (416 acres) and in the vicinity provided that their function is not
Growth of food plants in the interior of Dixie Beach Boulevard--Woodring Point impeded by larvicide spraying, ditching,
wetlands is often stimulated by fires (339) acres. Although this complex is or impounding."
semi-isolated from the uplands and
in the Spartina marshes of Sanibel's semi-isolated from the uplands and
interior wetlands. These fires were interior wetlands of the island by dykes In relation to aquatic fauna, T-bb
once common and distinct increases in eand roads, squito control, drainage, et al (1976) report, "Forage fishes
wildlife use were noted in the-burnedd ditches and canals provide including Cyprinodon variegatus,
area following fires. - arterial connections (Morrill and Byle,
area following fires1 . Fundulus confluentus, and Poecilia
latipinna will dominate the oxygen
Alterations of the vegetation According to Tabb et al, (1976) poor areas of the mangrove system.
regime of the interior wetlands can "The role of red mangrove communities in Cyprinodon is perhaps the most salt
adversely affect wildlife populations. estuarine food chains is dependent to tolerant species, surviving from
The invasion of the exotic trees a large extent on their relationship 0.120 ppt and breeding from 1-80 ppt.
Schinus, Melaleuca, and Casuarina to tidal range and freshwater flow. Thisspecies is generally excluded from
represent a major threat. These trees These communities which are situated areas where primarily freshwater fishes
generally invade where there has been within the effective intertidal range, are abundant and from bays where
an elevation change or lowering of or which are in close contact with salinity, clarity and mixing permit
the water table. Their rapid growth, streams or freshwater sheet flow systems, dense growth of sea grasses. All three
crowding out native vegetation to are effective contributors of debris species are euryhaline and, in addition,
which-the wildlife is adapted, pre- and detrital material to adjacent are capable of using the surface film
cludes natural succession and threatens estuarine waters. Fallen red mangrove of water for respiration. Even if the
biological diversity, leaves, unestablished seedlings, and area were to dry out, Fundulus
probably bark, twigs, and root tissue, confluentus can defer hatching of eggs
are invaded by a succession of micro- and the eggs can withstand relatively
The lowering of the water table organisms that assist in tissue de- long periods of exposure to dry
on Sanibel has also permitted the composition and also produce a net conditions. These small fishes, to-
intrusion of salt water. This provides increase in nitrogen content. The gether with fiddler crabs, form the
a direct threat to most wildlife of the resultant particulate material, with major diet of herons, ibis, pelicans,
interior wetlands complex. Several its associated microbiota, is an roseate spoonbills, and mammals such
amphibians and reptiles are particularly important food source for primary as raccoons. Among the larger fishes
vulnerable to increasing salinities and consumer organisms composed of a few the tarpon, Megalops atlantica, an
may be declining in numbers as a result species but large populations. These, obligate air breather and euryhaline
of the intruding salt water (Campbell, in turn, are the prey of several form, and the ladyfish, Elops saurus,
1975). levels of secondary consumers (lower, are admirably suited to this environ-

268 Appendixes

ment. Mullet, Mugil curema and M. of South Florida. If this is true for
ceplhalus, can also be found here the Sanibel populations of these wading E. tid;fuge Cati isbtOns
utilizing the surface film for feeding birds, then the numbers of wading birds sept.- c BirdCot.
and respiration. Invertebrates will seen feeding in the mangrove embayments, 1963 1967 1972 1974
be dominated by the fiddler crabs, around the tidal inlets, and on the
Uca spp., mangrove crab, Aratus Sanibel Shoals could fluctuate with nooo1,500 230 396 338
pisonia, coffee snail, Melampus the abundance of top feeding minnows, ,orest Cotot 2,300 917 760 22
coffeus, and littorinids, Littorina killifish:, scaled sardines, and bay
angulif era, all of which depend on anchovy. The foods of these fish inua 60 65 72 61
air for breathing." turn are, to a large degree, flood water Grent lu0 eron 350 41 39 51
mosquito and chironomid larvae, amphipods, Littlelue BIeron 1200 600 a170 62
Tabb et al (1976) continue, and other microfauna (Odum, 1971) which Lon .is.ae Ae.n 500 700 124 64
"Wherever waters lead to the bay one are sensitive to pesticides and larva- G atE -t 360 I00 80 65
can expect to see mojarras, snappers, cides. S0 gret 800 600 157 209
snook, tarpon, needlefish and barracuda.attle Onet 2S0 600 135 9
The creek which drains a set of mosquito Similarly, the planktonic larvae
ditches between The Dunes tract and San of crabs, shrimp, molluscs, and marine K Whitebi 4.000 So 365 440
Carlos Bay has been an especially worms in the mangrove embayments are Wd Ibis 110 65 23 44
valuable tarpon nursery system. As one adversely affected by chemical mosquito . oseteobill 75 - 4
proceeds from the least flushed inner controls. The adults of these inverte-
bays toward the middle and outer bays , brates c onstitute a second major food ; Glls 6.000 1,220 2,008
tidal action becomes more significant, source of wading birds (Table 6) and ;, u T.n6.ln.ksboeors 6,00 - 773 870
salinities are moderated by seawater, several species of ducks. ,Finally, T S ho.re :k : 7,00 - 140,4
and oxygen is added via tidal mixing. diving ducks, pelicans, cormorants, u C 3.700 .100 21 1.202
A larger variety of estuarine fishes, -gulls, terns, skimmers and the osprey
including mojarra, Eucinostomus spp.; represent second and third order
silversides, Menidia and Membras; consumers or predators in the zoo- Table7 - Estimates of seasonal peak populations of water birds
sea trout, Cyocion nebulosus; drum, plankton-mosquito larvae-fish food on Sanibel Island. Compiled from annual reports of J.N.
Sciaenops ocellata; pinfish, Laqodon webs. "Ding" Darling Wildlife Refuge.
rhomboides; etc., are found and
eventually the marine complement of Data from the "Ding" Darling Refuge
fishes are encountered in the outer Annual Reports for 1963, 1967, 1974-75, the tidal flats of Sanibel Shoals and
bays and tidal-passes." and the 1972 and 1974 Audubon Christmas Tarpon Bay, the tidal inlets connecting
Bird Count of Sanibel-Captiva (Table 7) the shoals area and the mangrove embay-
suggest that the wintering populations ments of the "Ding" Darling Refuge, the
BIRDS of aquatic birds of the mangrove-estuarine tidal flats of the refuge and its
complex and the Gulf beaches of Sanibel impounded area, and the edges of the
Whether they feed in the open are declining. In particular, there is mangrove islands and swamps. Some
waters, the edges or interiors of the an apparent decline in the number of species are social feeders and some
wmangeroves mostof the wd ilrifof the : white ibis, brown pelicans, cormorants, solitary feeders. The seasonally
mangrove subsystem depend on fish, gulls, terns, and shore birds. We do present fish-eating ducks feed in the
not know whether this trend is due to open embayments of the refuge, Tarpon
crabs, shrimp, and molluscs for food. human developmental activities on Sanibel open embayments of the refuge Ta
Others, passerine birds and wood-ibel Bay, and adjoining waters of Pine Island
peckers in particular, feed on insects resulting in a decreasing food supply, Sound. In years when the salinity in
and spiders. The seasonally present or the loss of breeding habitats else- impounded areas of the refuge is low,
plant-eating d where, or to inadequate bird census weed-eating ducks congregate there;
grass, Ruppia maritima in the refugedata. However, a thorough analysis of when the salinity is high these ducks
impoundment. refuge bird records and the Audubon feed primarily in the Sanibel River and
impoundment. X : Xbird counts for Sanibel and other near- fresh water sloughs. In addition to
Table 6 shows that the major by bird count areas where the same species Tarpon Bay and other open waters around
wading birds eat a variety of animals of birds occur could reveal whether the Sanibel a prime fishing area for the
in the food web. Of the several species apparent decline in numbers of birds is brown pelican and double crested
of birds listed in this table, the a regional or local phenomenon. If such cormorant is in the vicinity of Blind
details of the feeding and behavioral an analysis showed that the decline for Pass where large numbers of fish occur
ecology are known only for the roseate certain species is local and not regional, in waters of the pass and the adjoining
spoonbill (Allen, 1942) and the white appropriate management programs are in bayous.
ibis (Kushlan, 1974). Nevertheless, order.
stomach content analyses of wading birds In this area the larger water birds--
show that top minnows and killifish are The principal feeding areas brown pelican, cormorant, herons, and
the major food component in other areas of the wading birds of Sanibel are egrets--may be seen resting in Australian

Wildlife Ecology 269

pines along the bayous. The osprey has tive nest sites for these two years were Cited
already adapted to nesting on certain located in tall mangrove trees within the Litra e C
utility poles on the island in lieu of refuge proper. Thus, continued human de-
suitable tall dead trees. North of velopment of the island will probably
Sanibel in Sarasota Bay, colonies of not directly affect the osprey population
snowy and great egrets are beginning nesting in the refuge, but may show an Allen, R.P., 1942, The Roseate Spoon--
to nest in Australian pines on a spoil effect at the nesting sites in the dead bill, National Audubon Society
island. In view of this, Silver Key and mangroves east of Dixie Beach Boulevard. Research Report No. 2, 142 pp.
shores of Old Blind Pass might possibly
evolve into a small rookery. Because the endangered osprey is Heald, E.J. and D.C. Tabb, 1975,
relatively tolerant of humans and their In: Tropical BioIndustries
This raises the question as to why activities (at least during the breed- Development Co., Report to the Con-
there are no major breeding rookeries -ing season) and its highly visible nest servation Foundation "Mangrove
of pelicans, cormorants, and wading sites are frequently used year after - Communities".
birds in the mangrove-estuarine complex year, it is becoming a popular tourist
on Sanibel Island, even though many of site comparable to that of Sanibel's Kushlon, J.A., 1974, The ecology of
these species occur throughout the year alligators or roseate spoonbills. the white ibis in southern
on the island. Whatever the reason, the Florida, a regional study, 129 pp.,.
island's mangrove-estuarine complex Among the relatively inconspicuous Ph.D.' diss't., University of Miami.
serves as a refuge and feeding area-for or shy wildlife restricted to the
numerous adult and juvenile aquatic birds mangrove swamps are the resident Morrill, J.B. and W.K. Byle Jr., 1975,
in the same way that it does for mangrove water snake which feeds Preliminary survey of the marine
juvenile marine fish and shellfish. primarily on fish, and the rare mangrove ecosystem surrounding Sanibel
Thus, while natural nesting colonies (Maynard's) cuckoo whose diet is almost Island, The Conversation Foundation.
of some birds (i.e. pelicans and exclusively caterpillars of various
cormorants) do not presently exist on sorts. -A number of migratory insecti- Odum. W.E., 1971, Pathways of energy
Sanibel, conservation programs should vorous songbirds (i.e. warblers and flow in a south Florida estuary,
focus on maintaining and improving black-whiskered vireos) and several University of Miami Sea Grant Pro-
feeding habitats and the foods there- species of woodpeckers also forage in gram Technical Bulletin No. 7.
in. 0 X - 0 0; \ the mangrove swamps. Of the insecti-
vorous. species of amphibians and Woolfenden, G.E. and R.W. Schreiber,
It is of considerable interest reptiles, the Florida cricket frog, 1973, The common birds of the sa-
that certain beach nesting birds (i.e. squirrel tree frog, and green anole line habitats of the eastern Gulf
least tern and black skimmer) that did are common in the mangroves. Again, of Mexico: their distribution,
nest on the undeveloped beaches recent- we have a group of wildlife whose seasonal status and feeding biology,
ly nested on the man-made open sandy up- presence on the island and in the In: Jones, J.I. et al. (eds.),
lands of The Dunes development east of mangroves depends on a food source A Summary of Knowledge of the
Dixie Beach Boulevard in 1975. Portions adversely affected by chemical mosquito Eastern Gulf of Mexico, State
of such areas created in major develop- control programs. University System of Florida,
ment projects might be set aside as III J-1.
open space and managed for the breeding Several species of wildlife such
of shore birds (Sots and Parnell, 1975). as the raccoon, opossum, alligator, Robertson, W.B. Jr. and J.A. Kushlan,
Such a program would conform with both otter and other mammals retreat or The southern Florida avifauna,
conservation and development interests. migrate-to the mangrove swamps when In: Gleason, P.J. (ed.), Environ-
Accordingly, the nesting areas on The their food or environmental space is ments of South Florida: Present
Dunes demand immediate ecological stressed or limited in other habitats and Past, Miami Geological Society
analyses. on the island. In one sense the mangrove Memoir 2, pp. 414-452.
swamps are potentially an open habitat
Because it nests on utility poles or community. As the environmental
and is a conspicuous and threatened space of other ecological zones on the
species, the osprey's environmental island is altered and dominated by man's
requirements are the object of concern activities, additional numbers of wild-
throughout the United States. In life may be forced to emigrate into that
Southwest Florida and on Sanibel Island 50 percent of the island dominated by
in particular its numbers are increasing. the mangrove community.
The osprey nest census records of the
"Ding" Darling Refuge show that the
number of active osprey nests (breeding
pairs) increased from 8 in 1975 to-
19 in 1976. Most of the active and inac-

271

APPENDIX

ESTUARINE ECOLOGY 273
The Physical Environment 273
Bioclimate 273
Circulation 274
Water Quality and Sediments 278
Biological-Ecological Considerations 283
Marine Resources 283
Assessment of Ecological Relationships 285
Point Ybel to Woodrings Point (Bay Beach) 285
Tarpon Bay 286
Ladyfinger Lake System 287
Mullet Lake-Mangrove Lake System 287
Tarpon Bay to Wulfert Channel 287
J.N. "Ding" Darling Refuge Bayous 287
Wulfert Bay 288
The Albright-Runyon Key Bights 288
Dinken Bayou 288
Clam Bayou and Old Blind Pass 288
The Gulf Beaches and Littoral Zone 288
Man-Made Canals and Waterways '288
Acknowledgments 291
Literature Cited 291

273

APPENDIX

ESTUARINE ECOLOGY

by John B. Morrill and William K. Byle, Jr.

This report represents the com- and snorkeling (freestyle and towed delineated by Hela (1952). The
bined findings of a literature search behind a boat) were employed for Sanibel Island Marine Ecosystem
on the marine ecology of Sanibel and closer analysis, sampling and col- (S.I.M.E.) experiences a comparatively
a two-week field study of Sanibel's lecting. Still further analysis mild climate having two significantly
marine ecosystem. The literature was made using old and new one to distinct seasons: a warm, rainy
search encompasses a wide variety of three-hundred scale County aerials, summer from May through October and a
published and unpublished reports other aerial photographs and maps, cool, dry winter from November through
collected from research libraries and by studying color and infrared 35 April (Figures 1 and 2 and Tables 1,
in Miami, Ft. Myers, Sanibel, Sarasota millimeter slides taken for the pro- 2 and 3).
and St. Petersburg, Florida; from pri- ject. One night trip was conducted -
vate libraries and collections, and with a local bait fisherman in order Inthe winter, waters are sig-
from engineering firms. Additional to observe what species were using nificantly (16OF) cooler than summer
background and historical information the Sanibel Shoals at night. rin waters (See University System of
was considered by interviewing se- Florida, 1973) and are characterized
lected residents. This report is a systematic pre- by higher salinities, lower nutrient
Thisreportist a systrecommenda- levels and increased clarity (reduced
sentation of the data and turbidity). Biologicallyo respira-
turbiditL. Biologically, reapira-
Field studies were conducted tions requested of this team by the tion, detrital decomposition and bio-
the second and third weeks of June Conservation Foundation. logical oxygen demand decrease with
1975 to provide firsthand visual a subsequent decrease in turbidity
observations of the major physical and primary productivity.
and biological resources. Daytime
studies were conducted from a small Physical The warmer summer waters (78-
boat used to map tidal patterns, 810F) aremixed with the seasonal
assess water quality, record depth runoff which produces lower sa-
and sediment characteristics, map BIOCLIMATE linities, higher nutrient levels and
benthic flora, inspect natural and decreased clarity (increased turbid-
man-made features, observe bird Sanibel Island falls within the ity). Biological respiration, de-
populations, etc. Walking, wading tropical savanna climatological zone trital decomposition and biological

274 Appendixes

CIRCULATION

/o- : X As one of the most prominent
barrier islands on the Florida coast
and lying both at the south end of
9-_ _ - Pine Island Sound and Matlacha Pass,
across from the mouth of the Caloosa-
hatchee River, the S.I.M.E. is sub-
a- jected to a complex combination of
circulatory mechanisms. It is well
known that circulation is the net
product of many factors other than
geographical location and tides, i.e.,
adjacent land forms, prevailing
winds, rainfall and runoff, tempera-
s' 0 0 :; f ; Ago000 :ft00 go 0 0 0 gotures and bathymetry.

5i; - X - D The following is a discussion of
only those mechanisms observed or
known to play an essential role in
- X ; ; R At f ; 2 : : : providing the basic character of
X - ; ~ : : S 0 * X 0 0 \ iSanibel's marine ecosystem and which
directly relate to the planning and
I .~ 0 0 [ 0 t: 0 $ | 0 0 0 0 0 0 _ X 0welfare of Sanibel's residents and
z _ As i ;B ; : visitors.

2 L - Littoral Currents: The littoral
ElE ; tX [ 01 ;|;; i t0|0f 7: i i rX~or longshore currents are t hose which
move parallel to the shore along the
E;/ $ll El i-i [1 | DR ; ;|; 00 3 00 0 r [ movbeaches of Sanibel's Gulf Coast.
While they m ay move in either direc-
tion, their net effect is expressed
_ c 0 e;973a8._ MSo'MAR.-I ~cnA; lR. 16M~r? N. J� POb 9: OCrK DoE f. J. F~ M AR. 7fin a predominantly southerly drift of
/974 sediments which is readily observed
U AVERAGE (BASED ON 1941i THRU 1970) in reviewing the evolution of Blind
Pass (Figure 3) that presently sep-
I ACTUAL arates Sanibel Island from Captiva
Island to the northwest.

Fig. I- Average and actual monthly precipitation from weather observations Page Field, Ft. Myers, Florida. (After Duane Hall and This current is largely respon-
Assocs., 1974) sible for many of the physical and
biological characteristics of the
Gulf shore and offshore environment.
Here we are concerned with three
oxygen demand increase with a sub- as they affect the associated up- aspects of the system:
sequent increase in turbidity and lands, temporarily changing both the
primary productivity. chemical and physical character of (a) Physically, these currents
the marine habitat. Overall, how- account for the structure of the
ever, the bioclimate of the S.I.M.E. beach itself, a problem that is
Directly and indirectly, the appears to be significantly more being considered by another phase
seasonal rainfall and fresh water stable than similar habitats, per- of this project and by the beach-
runoff induce rapid chemical and haps because of greater oceanic erosion association. Ecologically,
physical fluctuations in the char- influence. This important ecol'ogi- this phenomenon is important since
acter of the estuarine waters. cal consideration accounts for its it also maintains the substrate
Periodic tropical storms (hurricanes) unique ecological character and composition and water quality nec-
may affect the marine waters much resources. essary for the characteristic marine

Estuarine Ecology 275

species of this habitat (sand fleas, visually polluted canal and bayou
coquinas, sand dollars, etc. and waters are flushed out Blind Pass
their predators). Historically, and then along the public beaches of N
these currents have created the phys- Turner Beach and Bowman's Beach. The SLAE - 6
ical environment suitable for the potential for this to become a more
nesting of the now threatened sea serious problem is proportional to soND.
turtles. the continuous growth and development /
of the Blind Pass areas of Sanibel - c
(b) Biologically, the littoral and Captiva. A similar situation - 2 , it St J. . .
current maintains many of the marine exists at the east end -of Sanibel
adult populations via the transport where non-point sewage and pollutant
of their planktonic larval forms discharges from Tarpon Bay to the
from along the upper and lower Flor- Lighthouse have tidal access to the
ida coastlines and by carrying nu- public beaches.
trients to these species once they
establish residence.
The "outfall" from the City's
(c) In a negative-sense, the Water Treatment Plant empties into
littoral current is capable of the littoral beach current some 600 e
rapidly dispersing diseases and pol- feetoffshore near the south end of
lutants to the marine and human Rabbit Road. Whatever (if any) im-
populations using 'the beaches. The pact this may have on the local marine
opportunity for this to happen (if biota should be resolved before addi-
not already happening) was observed tional outfalls of this type are re- Fig. 2 - Salinity-temperature stations of Wang and Raney (1971)
at the west end of the island where quired. in lower Pine Island Sound and Matlacha Pass.

Tidal Currents play a major role
in shaping many aspects of the estu-
Station Jun Jul Auq Sep Oct Nov Dec Jan Feb Mar Apr May arine environment on the bay side of
21, Chino Isl . 22.2 16.3 22.1 25.6 30.3 28.8 31.l1 32.9 32.3 28.0 27.5 32.7 Sanibel, but have a. uesser effect on
the Gulf side. Tides are usually the
22 St. James City 22.2 16.9 22.1 26.9 29.7 29.3 30.0 28.8 32.1 25.6 28.9 32.7 dominant force in the circulation of
23 San Carlos Bay 16.9 11.5 21.5 28.1 27.6 24.8 28.0 30.0 31.0 17.4 30.2 32.7 Florida's estuaries. Theircircula-
tion capacity is largely a function
of the estuary's configuration,
depths and proximity to the sea or
major tidal inlets.
Redfish Pass Rainfall Record Jun 1968 - May 1969
(From Byle) X - 9 Sanibel's tides are a mixture of
14.35 10.20 8;81 4.43 6.0 2.50 0.01 0.70 1.60 4.53 0.70 2.3 diurnal (one high and one low per day)
and semi-diurnal (two highs and two
lows a day). The diurnal character
dominates during spring tides, while
the semi-diurnal character occurs
Averaged Monthly Air and Water Temperatures (�C) from Charlotte during neap tide perraster occurs
during neap tide periods. The mean
Harbor Area, June 1968 to May 1969 tidalrange in the Gulf is 1.8 feet
0> (From Wang and Raney, 1971) and the spring range is 2.4 feet
Air Temperature 28.4 29.8 29.6 28.4 25.5 20.0 20.5 18.7 17.5 19.3 25.2 28.1X (Coastal Engineering Lab., 1959).
Water Tempera- 29.1 30.9 31.0 29.5 25.8 20.8 18.1 17.8 17.3 20.2 24.4 27.4
It is ecologically significant
ture that the seasonally heavy rainfall
and runoff periods and hurricane
season coincide with the seasonally
high spring tides of summer and fall.
Provost (1974) explains: "We find
high marsh and upland mangrove flood-
Table I - Salinities from intracoastal waterway. June 1968-May 1969. (From Wang and Raney, 1971). See Fig. 2 for station locations. ing starting in June and persisting

276 Appendixes

through November for about nine years nutrient, and biotic transport, and
in a row and then lessening dramatic- allowed for the full development of o~= '
ally and lasting only through the several ecologically distinct marine ;
~~~~R~B
summer for about nine years." There- environments. However, a number of
fore, sections of these "higher" natural and man-made features appear
areas may not be flooded several to be affecting the S.I.M.E. Yearll
months of the year (Figure 4). At F an.,i and Fi.-.i 611 5-5 X
� At ~~~~~~~~~~~~~~~~~~~~~~~~~~~~Oraqovchad Fintune (6]) 57-59 xX a XX 3
the same time the mean sea level and Prior to 1961, San Carlos Bay Gunter and Hall 119651 53 X X 2
mean high water along this section was approximately 11,400 feet wide Redtide StdH 63-66 x Ix X x
od. ~~t 0 . ~ 52.55 0 X 2
of Florida have risen nearly six on a line from Punta Rassa to Point ld-(,,97 t 6 8 l.
Alberto et at. 115/01 68S
inches since 1929 (Figure 5) result- Ybel. The volume of tidal water Wang & aney (1911) 69-6 9 3
Hour Glas Cmnase 5 5-67 0
ing in continuous, but subtle his- passing this line probably circulates d Ch J 731 71
toric changes in current, sedimen- the S.I.M.E. from Point Ybel to the G. Hll&AsMaiates (74) 73-740 X X XX 899X 9 3
tary and floral and faunal patterns West Power Lines in Pine Island ,.P.c. 751 73 x 1 x x x x 9 x II
as well as changes in position and Sound. The S.I.M.E. west of the lines L. C.. n.Po.]. A.. 751 75 4
Woodburn (9) 59 X x I
definition of the Mean High Water is probably circulated by tidal flow Phillis ad Srn 6 59 2
Line. from Blind Pass, Redfish Pass and ancoc k (9) 69 X X 13
Upper Pine Island Sound. Construction P.oot 171) 71 , 7
Fla. DPCSWR (75) 74 X I x 9 x lO
of the Causeway islands and accesses la as 5 1
"elna" OarlinolRefuue 66-75 x) 5
AS a barrier island, most of have narrowed the effective width of
Sanibel 's estuarine complex histor- the inlet from 11,400 feet (not count- Table 3 - Summary of waterquality studies containing data rele-
ically enjoyed the maximum effects ing the bridge supports) to 7,200 vant to the inshore waters of Sanibel Island.
of the Gulf's tidal ranges and in- feet. Today the same quantity of
tensities, a situation that simul- water is "jetted" through a little south Channel can transport pol-
taneously promoted optimal circulation, over half the original inlet's width. lutants to the Dixie Beach and Point
We find catch evidence that the in- Ybel beaches. Pollutants of concern
creased tidal velocities eliminated encompass discharges from ditches,
Estimated Year the only low intensity access the canals, yards, eroding shorelines,
Development of Appearance scallops had to the S.I.M.E., Pine marinas and drainfield seepages re-
( ~. Caloosahatchee River ~Cl~ rIsland Sound, Matlacha Pass and pos- leased into estuarine areas. Fur-
I. Ca10osahatchee River Canal 1884
2. Caloosahatchee River Channeliati~n and locks 9935 sibly Charlotte Harbor. ther, these same tidal current
2. Celoosahatchee River Channelization and locks 1 930
patterns (with and without wind
3. Sanibel Estates canals and diversion of Sanibel River
discharge 1 95? Physically, the increased tidal assistance) are such that an oil
4. Castaway Estates dead end canal 1958 velocities through the South Channel spill almost anywhere in the Intra-
5. Lighthouse Point Development Canal 19605 have magnified the erosion of Sanibel's coastal Waterway paralleling Sanibel
6. Island Mosquito Ditching Program and Diversion of
SanibelRiver into Tarpon Bay 1960 Dixie Beach. The numerous seawalls would almost certainly be carried
7. Dixie Beach Boulevard diked road 1960? installed along the high tide line rapidly into Sanibel's delicate estu-
8. Intracoastal Waterway channelization 1962 to abate the erosion have induced arine system or channeled onto the
9. San CarTs Bay spoil island Causeway 1963 substrate scouring at the bases of Dixie Beach shoreline. (Note: At
10. Sanibel Isles Development canal system 1963 permanent structures such as sea- least one barge load of oil per day
11. "Ding" Darling Wildlife Refuge Impoundment 1966 walls and stressed the adjacent passes from Boca Grande to the
12. Caloosa Shores Waterfront Canal System 1969? marine grass beds. It is also clear Florida Power Light tanks east of Ft.
1 3. Dal Sega Development Canal System 1 969 ~ 1972
13.~ Sal Sega Development Caoal System 1969 - 1973 that the old concrete jetties at the Myers via the Intracoastal Waterway
14. Shell Harbor Development Canal System 1970 Lighthouse Point Condominiums, Point channel.
15. Canaled Development, southwest Shore, Tarpon Bay 1971 - 1972
16. Sanibel Harbor Development Canal 1972 Ybel, are incompatible with the new
17. Gumbo Limbo Development Tidal Canal 1973 -1974 Channel velocities. Here the strong Lack of circulation creates pro-
18. Island Water Association water treatment plant outfall 1973 ebb currents reflecting off the west blems, too. Many examples of poorly
19. The Dunes Development 1974 jetty are eroding the shoreline, designed and constructed tidal ditch-
20. Permanent closure of tide control gates at east end of The jetties are also preventing nat- es, canals, marinas and lagoons can
Sanibel River 1974 ural shoreline processes from main- be found in the S.I.M.E. The effects
21. Moonlight Bay Development Walfert Point 197 Proposed taining the beaches from Woodrings of poor tidal circulation are notable
22. Silver Key Proposed Bulkhead line 197D Proposed
22. Ser Key Proposed lkhead line 1970 Proposed Point to Point Ybel, as is the in the following systems which can be
23. Nationwide Realty Development Clam Bayou - Dinken Bayou,
Old Blind Pass. Development and Boat Basins 1975 Proposed Causeway bulkheaded approach ramp, considered in three groups according
24. Caba-Ybel Yacht Basin now Tarpon 3ay Maroina Pre 1960 the borrow pit just to the east of to similar characteristics.
the ramp and the channel into Shell
Harbor. The first group are internal
Table 2 - Partial chronology of human developments affecting wa- excavated canals and lagoons, includ-
ter quality and marine life in the shallowwater ecosystems of With respect to pollution pro- ing the Lighthouse Point Condominium
Sanibel Island. blems, the currents through the lagoon, the Shell Harbor canals,

Estuarine Ecology 277

extremities of the Sanibel Estates The third example of tidally de-
canal system, the Sanibel Harbor pressed areas are tidal mosquito con-
APPROXIMATE SCALE canal, the Sanibel Isles canals, the trol ditches. The two sets of ditches
0 000 2000 . north and south ends of the Dixie observed (those entering Tarpon Bay
0 0 \ 1859 : _ - - I I l Beach Boulevard canal, the Tarpon Bay west of Gumbo Limbo development and
METERS mosquito control canal, the Pool, the those entering the canoe trail to
Caloosa Shores lagoon, the Dinken Mullet Lake) were relatively deep
Bayou canal, the Del Sega canals and (5-6 feet below MLW) compared to the
especially the Castaways canal off lands they drain (from MSL to +2
Mud Pond. feet). Excavated material was piled
1883 along each side of the ditches and
The second group are tidally de- some ditches are cut well into the
prived areas due to artifical impound- uplands. They are poorly flushed by
ment and are reviewed as follows: tides most of the year, during which
time they act as sediment traps for
x _ w i -1928: ,~ ;materials that enter them via leaf
The "Dunes Preserve" is a 70-acre fall, runoff, erosion and tides, thus
tract of tidal mangroves that have decreasing the quantity of sediment
been isolated by the construction of and nutrients reaching estuarine areas.
Dixie Beach Blvd., an act which stress-' When these ditches are flushed, during
ed the system and set the stage for a storm runoff periods, the channelized
recent kill caused by the Dunes De- runoff may stress the sensitive estu-
1944 velopment dewatering program -- water ary system by injecting large quanti-
was pumped from excavations into the ties of sediment and nutrients in a
tract and caused a nearly complete sudden manner. In some cases the
kill of the mangrove. Although a ditch spoil may be impeding tidal sheet
' large culvert was installed early in flow among the transected mangroves.
1974 and forty acres were seeded Corrective action includes cutting the
i\ 1948 i_ L(22,000 seeds in July 1974), most of ditches off from the estuary and fill-
the tract is still effectively de- ing them in.
prived of adequate tidal circulation.
This situation will most likely in-
+hibit successful recovery of the
MARCH OCTOBER;
area and severely limit its biologi- MARCH OCTOBER
cal productivity potential with a
substantial loss to the Ladyfinger MSHW l nr
AdTialeu/v//t s1a111111 111 ///
Lake and Tarpon Bay subsystems. MHWtH- HIGH MARSH --
Additional large culverts, strate- MNHW111//1111111
gically located under Dixie Beach

restoring the historic tidal regime MSL ___ L :
1960 Nie and biological role of the preserve. Tn

The "Ding Darling Refuge Im-
poundment" is a similar situation on - J
a larger scale. Here, the sand-shell NEAP SPING
dike/road prevents tidal penetration . TV
: 1961 g _ : - from reaching what appears to have -2'. NEAP SPRING
been a productive marine nursery TIDES
habitat of mangroves and shallow
bayous. Seasonal rains appear to be
insufficient for maintaining a bal-
Fig. 3 - History of Blind Pass, Sanibel-Captiva Islands, 1859-1961 anced aquatic habitat. The area
(After Duane Hall and Assocs., 1975) appears as a highly unstable, arti- Fig. 4 - Diagram illustrating how, in Florida, the same tide inter-
ficial brackish habitat effectively vals can flood the high marsh or mangrove swamp continuously
isolated from the adjacent estuary. at onetime of the year and not at all at another. MSHW, mean
It seems that corrective measures spring high water; MHW, mean high water; MNHW, mean neap
taken soon could restore the area. high water; MSL, mean sea level. (After Provost, 1974)

278 Appendixes

Wind Factors: Daily and seasonal shorelines along the Sound. Sus- tion than erosion along the bay side.
winds play an important role in all tained northerly winds can hold the Occasionally more enduring southerly
aspects of the S.I.M.E. (See pIIA-12, Sound in a low tide phase for several winds will compound tidal intensities
Summary of E. Gulf of Mexico, 1973). days at a time, sporadically exposing and durations. These prolonged high
The importance of wind to the estuarine the shallow's marine biota to freezing tides may seasonally flood the more
biota is critical since shallow estu- air temperatures and other stresses "upland" mangroves and add their
aries are often poorly circulated by (See Storey and Gudger, 1936, for litter to the detrital food base of
tidal mechanisms alone. Wind is Mortality of Fishes Due to Cold at the estuaries.
often responsible for moving water Sanibel Island, Fla., 1886-1936; and
to and from the inlets and dispersing Storey, 1937). Two recommendations logically
nutrients and plankton. The stronger, come from such considerations:
northerly, winter winds annually gen- Conversely, the prevailing
erate wave patterns that can (and do) southerly winds of summer are compar- (1) Access channels should not
create steep-sloped, high energy itively gentle (except accompanying be permitted which cut across the
beaches along the Gulf beaches, and thunderstorms) and create low pro- shoals protecting the mangrove shore-
simultaneously create shoals while file, low energy beaches on the Gulf. line from wave generated erosion.
eroding the north-facing red mangrove These winds also promote more deposi-
(2) High rise construction
FebtMatiorJu Apr Mt should be discouraged along the bay
Staton Jn Ju AugSep ~OctNov Dec Jon Feb Mar 'Apr May
St~ation: Jun Jul Aug: Sep: Oct Nov: Dec -Jan: side where it could deflect winds
which would normally circulate the
5 34.0 25.9 28.9 22.8 29.9 30.6 29.2 31.3 32.3 31.5 32.8 33.6 adjacent estuarine waters, ii.e., the
west end of Sanibel near the bayous
4 3:2.3 '27.2 31.6 -25.7 30.8 33.3 31.9 32.4 32.8 31.5 35.1 32.3 and along Wulfert Bay.

~3 ' 34.9 30.7 33.I 33.8 34.3 34.0 32.4 34.4 34.2 32.1 36.4 36.2
WATER QUALITY AND SEDIMENTS
2 '31.2 25.8 28.8 30.4A 34.8 33.3 31.9 33.1 33.6 32.1 34.2 35.3

I 29.5 23.0 29.7 28.2 32.9 33.3 31.9 33.0 33.4 32.1 342 35.3 Historically, the water qulity
of the shallow water marine ecosys-
6 36.6 26.1 30.9 30.6 34.1 32.7 31.0 32.6 33.7 29.5 35.5 34.9 tems of Sanibel Island exhibited
seasonal and annual fluctuations un-
7 37.9 22.6 24.0 33.1 34B 35.5 30.5 32.6 33.6 31 5 35.5 38.9 der the interplay of waters from the
Gulf of Mexico; Pine Island Sound;
8 33.3 17.4 23.3 31.2 34.8 28.8 30.2 32.6 33.5 30.4 35.5 349 Matlacha Pass; the Caloosahatchee
River; and the upland surface runoff,
9 32.9 12.0 22.4 24.3 28.9 28.8 26.0 30.3 34.2 27.6 35.1 37.2 ground water seepage and mangrove
- - ~~~~ground water seepage and mangrove
16 : 27.3 22.0 28.0 27.7 29.3 29.9 30.5 33.3 32.7 25.4 33.8 2.3 bayous components of the Sanibel-
Captiva Island system. The quality
of the Island' s marine waters has been,
I 7 31.2 25.8 ?9.3 29.0 30. 31.2 31.8 33.2 33.4 26.7 34.2 34.9 of the Island's marine waters has been
affected (if not locally stressed) by
18 34.0 29.0 30.9 33.2 31B 31.1 30.5 34.6 33.3 33.2 35.1 36.2 a variety of human developments since
the flood control dams on the Caloosa-
19 34.0 21.5 26.9 30.8 29.9 29.9 298 30.7 32.8 29.3 33.8 34.9 hatchee River and the diversion of the
Sanibel River from its historical exit
20 29.9 21.7 29.4 35.1 33.6 30.7 31.3 33.0 33.6 33.2 328 34.9 on the Gulf side to Dixie Beach via
the Sanibel Estates shallow canal sys-
21 22.2 16.3 22.1 25.6 30.3 28.8 31.1 32.9 32.3 28.0 27.5 32.7 tem in the early 1940's. With the ex-
22 22.2 16.9 22.1 26.9 29.7 29.3 30.0 31.6 32.0 25.6 28.9 32.7 ception of septic tank development
along the Sanibel River and mosquito
23 1 6.9 11.5 21.5 28.1 27.6 248 28.0 30.0 31.0 17.4 30.2 32.7 ditches, the effects of various
developmental activities on water
quality are not easy to assess (Table
2).

Table 4 - Monthly surface salinities (0/00) at stations 21, 22, and 23 in Pine Island Sound and San Carlos Bay. (After Wang and Raney, At the present time, the marine
1971). See Fig. 2 for location of sampling stations. waters adjacent to Sanibel are class-
ified by the State as Class II waters

Estuarine Ecology 279

that are to be maintained as suitable and the "Ding" Darling Wildlife im- ity are desired for swimming, fishing
for shellfish harvesting, recreation poundment area are subject to greater and boating. However, Din the waters
and management of fish and wildlife. fluctuations than the waters around around the barrier islands of south-
The waters in the bayous in the vicin- the island. Indeed, the monthly sa- west Florida, one can rarely see the
ity of Blind Pass (now Class III wa- linity records (Table 5) from five bottom in water greater than six feet
ters) are characterized by the poor stations (Figure 8) for 1971 show that except in the vicinity of tidal passes.
circulation and septic tank seepage the salinity in the perimeter canal in In the waters around Sanibel Island
(which was observed in June 1975) in the impounded area (Stations 1, 3, 4 Secchi disk readings at Stations 1
the Castaway Estates dead end canal and 5) varies spatially and seasonally to 4 miles offshore in the Gulf may
off Dinken Bayou. as compared to that in East Sanibel only be 4.5 to 7.5 feet (Goodcharles
Bayou (Station 2). In this respect and Jaap, 1973). Turbidity values
Marine water quality data for the impoundment canal and flats form in Pine Island Sound over a twelve
the Sanibel Island area are contained a miniature tidal estuary with char- . month period (1973-74) varied from
in periodic investigations of fish acteristics of a hypersaline lagoon highs in-July, February and March
and:shellfish populations and red ecosystem. to lows in October and November
tides. Water quality sampling sta- (Table 6). Field observations June
tions have been primarily in the Recorded values for pH in the- 1975 on the north side of Sanibel in-
deeper, open waters. Table 3 sum- Pine Island Sound area range from 7.8 dicate that the waters of the mangrove
marizes the water quality: parameters to 8.2 (Figure 9), which is normal bayous, Ladyfinger Lake, and Tarpon
reported in eighteen investigations for inshore waters along this coast. Bay are moderately turbid. On the
between 1954 and 1975. Prior to grass flats bordering San Carlos
1954 the only water quality records (2) Water Clarity (Turbidity) Pass-Pine Island Sound, the waters
for the Island are those associated are less turbid and marine grasses
with water temperatures during From a human viewpoint, marine may grow at depths of three to four
winter freezes (Storey and Gudger, waters of high clarity and low turbid- feet MLW.
1936; Storey, 1937). Thus, in the
section that follows on individual
water quality parameters, we can
provide only a general picture.
-provide only agen-eral picture. . Station Jan. Feb. Mar. Apr. May June July Auq. Sept. Oct. Nov. Dec.
(1) Salinity - Temperature - pH
1 22.5 38.1 52.6 43.7 41.1 31.1 9.2 7.8 7.8 10.9 20.9 23.3
: The salinity of the inshore 2 31.4 34.1 38.9 40.7 41.5 32.2 22.6 18.9 21.6 26.4 32.8 34.3
waters on the Pine Island side of
Sanibel Island ranges from 11.5 to 3 18.7 24.3 32.9 36.8 38.9 29.6 10.7 5.3 6.3 7.2 10.3 11.6
39.0�/00 with a mean of 24.90/00
(Table 4, Figure 6)., The variation in 4 18.1 24.2 33.5 44.9 45.3 31.3 10.2 4.4 5.9 6.4 8.1 10.1
salinity is due to seasonal variation
in rainfall (Table 1 and Figure 1), 5 8.8 12.4 18.1 25.2 25.4 15.8 1.7 1.4 2.2 2.0 3.0 5.4
discharges from the Caloosahatchee
River where salinities at the River's
mouth range from 4.1-35.2'/00 (McNulty Rainfall 0.00 0.69 0.00 0.05 2.84 15.21 8.40 4.35 7.26 0.13 1.52 0.65
et al., 1972; Gunter and Hall, 1965) (Inches)
and shoreward indrafts of the high sa-
linity Florida West Coast cyclonic
eddy of the Gulf of Mexico. Reports
by Woodburn (1959), Phillips and Notes: 1) Salinities taken on the 1st and 15th each month.
Springer (1960) and Hancock (1969) in-
dicate that the salinity and tempera- 2) Complete monthly salinity data for all stations for 1971, 1972, 1973, 1974,
ture in Tarpon Bay is similar to that 1975. Scattered data back to 1966. Available at the Refugee Headquarters.
in the adjacent Pine Island Sound.
The surface water temperatures in the 3) Rainfall data from two main rain gauges (Refuge station and Refuge headquarters)
area are climatically influenced for 1971, 1972, 1973, 1974, 1975.
(Table 1) ranging from 35�C in summer
to b0lC on occasions in December to 4) Station 2 outside of impoundment area on East Sanibel
February. Bayou side of'dike.

Salinities and temperature in the Table 5 - Average monthly salinities ppt (%) at five stations in the impounded area of the J.N. "Ding" Darling Wildlife Refuge, Sanibel
shallow waters of the mangrove bayous Island during 1971. (See Fig. 10 for location of stations.)

280 Appendixes

However, there are three excep- sugar sand one to two feet deep. How- set Number 1 (Figure 11). This beach
tions to this general pattern of ever, in the adjoining tidal channel ridge set encompasses the shallow
turbidity. One is the grass flat near the marina at Wulfert a Secchi water bayou-mangrove ecosystem along
area off Coral Creek where marine disk reading of four feet was obtained. the north side of the island from
grasses were clearly visible in six Tarpon Bay to Blind Pass. In this
feet of water. The usual clarity of From our ten-day field survey the area the bottoms are covered by la-
the water in this area may be due in turbidity of waters around Sanibel may goonal muds containing varying amounts
part to its being the tidal node area be ranked as follows from worst to of detritus, quartz sand and decaying
between San Carlos Pass and Blind Pass. best: Dinken Bayou> Clam Bayou area> plant matter. The large low energy
The second area is Wulfert Bay be- Wulfert Bay> Tarpon Bay> Ladyfinger tidal flats in the Refuge Impoundment
tween Wulfert Point and Wulfert Keys. Lake and Sanibel Bayou areas> Gulf area contain mixtures of silts, clays
Here Secchi disk readings of 16 inches Beach> Pine Island Sound grass flats> and plant material averaging one foot
were recorded. Because of the fine grass flats off Coral Creek Inlet. In thick over the underlying sands.
sediments, the water was so turbid each area the degree of turbidity re-
that the turtle grass growing in 28 sults from a different combination of
inches of water was barely visible. composition of suspended materials
But in an adjoining backwater area (plankton, fine detritus, inorganic 4
between Runyon Key and Wulfert Point -silts and clays); bottom types; and43
the Secchi disk was not visible deeper wind, wave and tidal current gener-
than six inches. In this area and in ated turbulence. At the present
lower reaches of Dinken Bayou the sedi- time water clarity around Sanibel is A
ments consist of fine, marly muds and due primarily to natural factors or - ------
to man's activities in other parts /
YEAR - ABEITOSof the Pine Island Sound system.
o ~ ~~ ~~~~~~~ A B RVITONSo
9) RE RB m AS~~~~L MSL.-MeatS..aL-vtlNott2l e i et)
I _ _~~~~~~~~~~ MTL - M... Tide Le-n (N..e3) (1~
+. , , II (3) Sediments/
(N. ... 6)4
clMLW.=RMan Lowt WatertINoteR 6', / / -
0 SLD=S. L- Datum (N.. 4)
,~3]~~~ II ~ ~~~The physical character of super- '
-sij S sea Ltrnl atorr(NtoHie
~+1 .50 1.i!.~~~MH46 ficial bottom sediments in the waters /
+15 Iaround Sanibel Island not only affect
If ill water clarity patterns but also are
partial determinants of the diversity
~~+l ~ ~ ~ Mf.00 09 M' ]of benthic marine plant and animal
S, I ; communities. Although no detailed
Cr0169~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I tO 4I4A214 1461 I, I SOS i /S 1
studies of sediments in the S.I.M.E. , .
:+0.50 }A5fAL F p--have been completed, several reports
S~~EAn LEVEL Io ~J24Y ,.that touch on this subject merit re- '
SEA LEVEL. view.
-000OF 1929 1929 S.LD Fig. 6 - Specific conductance and salinities at water quality sta-
Sediments in the Gulf around
o ~ ~InP:Brt I Sedimibel ~nt~s ~in ~the Gulfn ~ ar~~oundf~ ~ tions 18, 19 and 20, Pine Island Sound - San Carlos Pass, 1973-
--- -- - -4) Sanibel consist of two zones of 1974. (After D. Hall and Associates, 1974) See F ig. 7 for station
6- 50...... ' 'quartz sand similar to sediments cur- locations.
MLo-06 MLW-64 t rently carried by local streams and
derived from coastal sands (Figure
~~-1.00 -~~~~~10) . Directly south and northwest
of Sanibel the quartz-shell sand:
I. This chart iS based on data furished by the U.S. Coast Guard and Geodetic Samvy, of Sanibel the quartz-shell sand
and oo "Shore and Sea Boundaries" by Shalowitz (published by U.S.C. & G. S.) zones provide habitat for the impor-
2. Local MSL should not be confused with sea level datum of1929 as listed under tant Sanibel pink shrimp fishing In a study on the ecology of
item 4 since it is an adjusted datum based on sea level observations at selected grounds The Pine Island Sound sedi- Sanibel mollusks, Haas (1940) briefly
locations.
3. M.T.L. isthe plane midway between M.H.W. and M.L.W. ments have a size distribution simi- described several habitats as follows:
4. Officialdesignation of the existing bench mark networkat 0.00 elevation is"Sea lar to various coastal lagoons along On the San Carlos Pass side of the
Level Datum of 1929."
5. Available data indicates that the sea level (represented above by change in M.T.L.) the extreme southwest Florida coast is-land at depths below five feet the
has risen about OA4 ft. in this area between 1929 and 1962, averaging about 0.012 (Scholl, 1963). bottomi contains fine shell fragments.
ft. (0.19 in.) per year. The grass flats along the Pass and
6, Prior to 1962U.S.C. & GS. computed tidal range as a "mixed tide," averaging all
6. Prigoorto92 U.S.C.&G.S.mputedtidalrasgeaa"miedssides"hragisgull In a recent study on the deposi- Pine Island Sound are s andy with a
highs for M.H.W. and all lows for M.L.W. U.S.C. & 0.S. now classifieRs this Gulf
Coast tidal area as dominantly diurnal, and computes M.H.W;.from only higher- tional history of Sanibel Island, surface layer of fine silt and organic
highsand M.LW.fromwer-lows. Missimer (1973) discusses the phys- matter (easily disturbed by prop wash and
Fig. 5- Tide levels at Sarasota Bay, 1929-1962. (After Smalley, ical character of the submerged beach waves). The intertidal shoals consist
Wellford and Nalven - Consulting Engineers, Sarasota, Florida, ridges of the Island's oldest beach of firm sand. The Tarpon Bay grass
1967)

Estuarine Ecology 281^-

flat areas grade from firm sand to feet thick. In thle various develop- month period (Figure 12) indicate that
sandy mud to soft, silty sand from the ment canal systems these sediments water quality in this region of the-
channel toward Prawn Key. South of are one to two feet thick. It has Sound and San Carlos Bay is good.
the channel the shore is boundedby been well documented in recent liter-
an intertidal, firm sand shoal. ature on canal systems that these This is reflected in the five-day
sediments support a few species of B.O.D. values from two of these stations
Historically, as recently as 1940, benthic organisms and lower water (Figure 13).
the innermost reaches of Clam Bayou quality.
and Old Blind Pass had a white sandy
bottom (Haas, 1940). Today this area, (4) Dissolved Oxygen and B.O.D. One may conclude that the wa-
as well as Mud Pond, is characterized ters entering the Sanibel enclosed
by, soft 12 to 18-inch deep lagoonal These two parameters are of major water "areas" (bays, creeks, etc.)
muds. The bottom of the lower reaches importance in judging water quality, on flood tides are of high quality.
of Dinken Bayou and the area south of but data for the Sanibel Island marine However, the waters leaving them may
Albright and Runyon Keys consist of a waters are sparse and limited primar- well be of lower quality due to -
unique soft, white-grey-marly sand ily to surface water sampling stations degradation processes in the inshore
mud up to two feet deep overlying firm along the Intracoastal Waterway (Fla. waters and man-made dead end canal
sand. Dept. Pollution Control, Oct.- Nov. systems. Studies on the east end of
1973, San Carlos Bridge; D. Hall & Sanibel River by the Florida Dept. of
Another unusual sedimentary area Associates, 1974. Maximum D.O. values Pollution Control (1974), the west
is the "rocksl" about 1.5 miles west of 8.0 and minimal values of 5.0 at end of the Sanibel River by a Windham
of Rabbit Road where there is an out- three stations off Sanibel over a 12 College study team (1975) and the ,
cropping of coquina limestone (or
"mussel bracchia") just off the beach \_s 'u ;
which is periodically exposed and-
covered by sand. Haas (1940) suggest-
ed that this would be a favorable area \: 20 !
to study the origin of such-limestones.
The rock is relatively soft and frag- '
mented by storm waves. Our field ob- - 2
servations showed that the rock con-
sists of sets of thin layers of rock rp/ I\

prime surf fishing area. Geologic-
ally, it may have played and may con- .
tinue to play a key role in the l it- a I ,
toral drift erosion and accretion
processes that have shaped the Gulf '
side of the Island.

A third unusual sedimentary area
is the fluid sandy shoal off of Point \
Ybel. Here the quartz-shell sand is --
constantly moving under the force of s
tidal currents. This was the one in-
shore subtidal area where we observed
populations of the sand dollar, Mellita ' \
quinquiperforata. \

A fourth unusual sedimentary
area is composed of material accumu-
lating in man-made canals and deep
tidal ditches along Dixie Beach Blvd.
and the dike of the Refuge Impound-
ment. In these areas, organic-rich, _ _
fluid sediments are accumulating an-
nually. In the canals along the
Refuge dike these sediments are two Fig. 7 - Water quality sampling stations, Jan. 1973 - Nov. 1974. (After Duane Hall and Assocs. 1974)

282 Appendixes

mosquito control canal in Tarpon Bay at the Ft. Myers pier. At the time Pine Island Sound (Figure 14). In
by Hancock (1969) indicate that wa- the Sanibel values were below the mean their 12-month study (1973-74) D. Hall
ter of low quality is entering Tarpon total phosphate of 0.044 ppm for estu- and Associates (1974) recorded monthly
Bay and possibly the Shell Harbor aries outside the phosphate district variations in total and ortho phos-
Canal system from the upland Sanibel of central-west Florida (Odum, 1953). phate at their China Island Station 18
River drainage basin. More recently Alberts et al (1970) near Sanibel (Figure 15, Table 7).
recorded similar total phosphate con- Total phosphate concentrations ranged
Given the current emphasis on centrations in the surface waters of from 0.02 mg/1 in February to 1.69
dissolved oxygen values in waters
around human developments as compared J.N."DING" DARLING NATIONAL WILDLIFE REFUGE
to "natural" conditions by regulatory ,.....r LEE COUNVY. FLORIDA . .
agencies, an extensive-water quality .2i. R21E. R22E. .V, R.22E. R23E.
monitoring program is required for ;-I 'ij ,,,,,1
the disturbed and natural portions of , --'1
the Sanibel Island inshore and estu- : ....
arine waters to establish a baseline. T : 45T
Such a program should include 24 toi 4.. :, ($T
36 hour sampling regimes at close in-
tervals (at least once/month) on T T .
appropriate ebb-flood tidessequences 46 ...
and under a variety of weather con- 5
ditions (i.e., following heavy rains). 9 P
,- 4*" .4
(5) Nutrient' and Nutrient Supply

The well-being of natural systems ,
on and around Sanibel Island is in
part dependent on the marine plants
(mangroves, grasses, macro-algae and F.i
phytoplankton) which, in turn, are i
nourished by dissolved inorganic min-
erals and bioorganic substances (i.e,- "
vitamins, amino acids, carbohydrates).
Nutrients for marine plants around 3
Sanibel are derived from the Gulf
waters, the mainland- rivers, the run- .
off from Sanibel Island, the metab- .s ./
olism and decomposition of marine :.
plants and other marine life, and the : 1 .--
release of nutrients from marine sed-
iments in and around the Island. At
the present time our knowledge of the i O
nutrient budget in the various seg- ' .M.. -n -
ments of the Sanibel ecosystem is M X END
fragmentary. Until recently the AQ ISON
thrust of nutrient studies in the BOUNDARY
Sanibel marine waters was directed to-
ward understanding the casual mecha-
nisms of "red tide;" now such studies
focus on compounds of nitrogen and :
phosphorus because of their general- 1'~' . n.....L L S MEI RA.2 1E.E R.22E R.23E
role in plant growth and eutrophica- .. ............. 5ij,,'� ..
tion. ::: 4R-FLA-400-405 '

In December 1953, H.T. Odum re-
corded total phosphate values of 0.025 Fig. 8 - Location of salinity stations in canal along impoundment road-dike of J.N. "Ding" Darling Natural Wildlife Refuge.
and 0.032 ppm at Sanibel Island and
0.073 ppm on the Caloosahatchee River

Estuarine Ecology 283

(1) Shells
Biological-Ecological

Considerations The romance of shelling has made
Sanibel famous. It has lured thou-
MARINE~ RESOURCES __sands of people to this island over
.....MARINE RESOURCES the years and with good reason.
-. j ,f~---~ ........ According to Perry and Schwengel
S: Shelling, fishing and birding (1955)rd "The bundance and variety
,3 _ ^\\ , / ;;S : rank high among the amenities that of the marinemolluscan fauna of
K~"/ 'Y '' attract visitors and residents to the Sanibel-Captiva region is un-
9 - Sanibel Island. However, today the excelled by any other in America,
islanders agree that shelling and and by few areas of like extent else-
fishing are not like in the "good where." This is due to the mosaic
old days" before the Causeway. Tour- nature of the bottom environments
ists, too, express disappointment in inshore, offshore and in the estu-
the monotony of the kinds of shells arne areas of Sanibel; current
along Sanibel's Gulf shores and in patterns; slight modifications of
the apparent small catches of sport salinity; and geographic location
salinity,- and geographic location
fishes. Since impressions are often where ranges of southernand north-
;~'3=~-_ = based on colored memories and hear- ern species overlap.
say, we introduce this section with
Fig. 9- Monthly pH values for stations 18, 19, 20 (1973-74) Pine brief comments on selected marine The number of species of mol-
Island Sound - San Carlos Pass. (After D. Hall and Assocs., resources. lusks living in the Sanibel area is
1974.) See Fig. 7 for station locations. truly impressive although the actual
number reported in the literature
mg/l in August. The complexity of 50 02. varies (Perry; Haas, 1940). The
interpreting the causes. of monthly variety of species in four major
variations in concentrations of total --T IBOTTOM CHARACTER classes of mollusks is as follows:
-phosphate is seen by comparing Figure i:BOTTOM CHARACTER
-phosphate is seen by comparing Figure 030 J >- '|-... OFF WEST COAST OF Amphineura - 3 species; Gastropoda
15 for total phosphate with Figure 16 . FLORIDA (snails) - 198 to 250 species;
for nitrogen, Figure 1 for rainfall CONT05 IN FATHOMS - Scaphopoda - 7 species; Pelecypoda
and Table 6 for turbidity. 0 0 SO (bivalves) - 120 to 152 species. In
4, :- ~il_:CJ STATUTE MILES:, spite of this variety the beginning
In this same study concentrations 29. - shell collector is likely to find no
of nitrate, ammonia and total nitrogen more than 24 kinds of living or dead
exhibited monthly variations (Figure iS! mollusks. In this study on the ecol-
16). It appears from this figure that . ogy of mollusks of Sanibel, Haas
nitrate presently is sufficiently low . _ (1940) pointed out that the "vast
in Pine Island Sound to limit the ex- -mortuary" of shells on -the beaches
cessive growth of marine algae and was 99.9 percent mussel shells with
phytoplankton around Sanibel. shells of snails making up the other
MX;'~;' . .:.i& ' 0.1 percent. Of the other bivalves
It is unfortunate that the avail- on the beaches most were ark and pen
able studies do not tell us whether - _ shells which normally live in the
Sanibel is significantly fouling its firm sand bottoms offshore in vast
inshore estuarine waters. Clearly _ numbers. One may appreciate the di-
septic tank leaching field seepage 27-- 27- mensions of these populations by the
along the developed shores and canals QUAoRTZ..s.E.LL SONSI,.-" , .. ';. numbers of pen shells that accumulate
and along the Sanibel River slough -51E SAND
and along the Sanibel River slough ' A &7) RTh7taoSoE 4 i' FORT on the beaches after storms (the best
system and mosquito ditches enters the ASHELGAL SAND 7,.__ORS time for shelling). In one instance
upper reaches of the marine system ALGAL SAND at the northwest corner of the island
thereby enriching these waters. But a fOLITE SAND1o
it is difficult ntot asesess the relative gl FORAM SAND a sfeet wide and 7 inches deep was es-
contribution of nutrients from upland timated to have one million shells
sources compared to nutrient release (Haas, 1940).
from organic s ed~im~ents in upland cap- Fig. 10- Sediment distribution on West Florida Shelf. (From
nals and mosquito ditches and to bird Rezak and Edwards, 1972) In a four day census of the Gulf
feces of the large waterfowl popula- beaches of Sanibel in March 1976,. pen-
tions of Sanibel. Fig. 1 -Appearsas Fig. 6 in Hydrology Appendix)shells were the most conspicuous. Other

284 Append ixes

Praw"n Key grass flats and a bait coastal shorelines not be disturbed
"o shrimp roller trawl operating in or developed. Where these areas are
Tarpon Bay. not already preserved, purchase and/
or strict regulation is needed. A
~�"~ \~/ / w x - If in the future the estuarine comprehensive beach nesting program
, G - ---_, fish resources around Pine Island should be developed for the open sand
* j% /K 0 --o.- ~ , j suffer depletion from urbanization, nesting species, as well as sea
a, 0 \ ' / , " a' the waters of Sanibel Island may turtles. Such a program might be
/rA v experience more intensive commer- aimed at developing nesting areas
'~ ;~ '~.~.....-/cial fishing activiti es. Such
A/'e \ 1_d \\ cdial fishing activities. Such (behind dunes at Turner's Beach) and
activities may compete with water- controlling public usage during the
go \ // 0 0 0ft And ; fowl and sport fisherman and conflict breeding and nesting seasons.
� \�'~~~~~~~ ,~with the esthetics of the Island's
residents living along the shore; The main threat to avian feeding
- accordingly, we recommend that some and nesting along the bay side are
i j j forethought be given to this po- projects which create steep tidal
...... ;I Is m s e m"ns ~ . ... tentially inflammable socio-economic slopes and remove the native vegeta-
problem. tion; i.e., waterfront developments
having-d~or-to-shore yards with sea-
Fig. 12- Dissolved oxygen, ntracoastal Waterway, 1973-1974. (3) Avian Resources walls and usually a boat channel or
(Note stations 18, 19, 20.) (After Duane Hall and Assocs., 1974) basin. Our first recommendations
See Fig. 7 for station locations. Sanibel can claim one of the would be to protect all remaining
longest bird checklists in the State. estuarine shorelines and their assoc-
common bivalves included-dead and live It is significant that many of these iated mangrove forest, however far
calico scallops, cockles (6 species), species depend directly on the marine they may extend inland, including
ponderous ark, cat's paw, broad- life of the surrounding waters. In possible strategic purchase through
ribbed cardita, chione (2 species), fact, the diversity and sheer num- the State's environmentally endangered
Venus (2 species), surf clams, -bers of these birds reflect the Land program. Specifically, the
Dosinca, and coquinas. Some 20 species abundance of the marine resources Ladyfinger Lake mangroves behind
of bivalves were common while only upon which they depend. -Protecting: Woodrings Point and the mangrove
three species of snails were common. the Island's bird populations neces- forests at the west end of the R
sarily involves identifying and Refuge (Kesson Bayou), along Wul-T
(2) ;Fishes i- 0 lD 0 0 0 0 0 protecting these resources; i.e., fert Point and as much of the west
what and where they eat; where they end bayou system as possible, in-
roost; and where they nest. cluding Runyon and Albright Keys
Over 70 species of marine fish should be protected
have been reported to inhabit coastal From our field observations
waters off Sanibel (Tables 8 and 9). alone, we can safely say that liter-
Most are shallow water species whose ally all of Sanibel':s surrounding
habitats and food preferences are as: waters and bay bottoms play a critical
varied as the habitats from which they role in supporting the resident and
are usually caught. As part of the transient marine bird life. Here we
Pine Island system, they are irreplace- discuss only those locations that -
able fish breeding and nursery grounds. involve conflicting interests and \V
The estuarine-waters of Sanibel are someday may require special pro- \ \
frequented by sports and commercially tection. \ - /
important species. This complex eco- \ \
system is important as a fishery re- Most of the marine birds feed
source not only for man, but also for along the shorelines and/or in the \ \ i
waterfowl. Such extraordinary shallow waters. In general, all of
species as the bottle nose dolphin the beach,' shoal and mangrove shore- /
and the manatee also depend on the lines are select feeding grounds for \ /-' \ ---
system. herons, egrets and the many different O x --_ \ / " -
shore birds. Further, several species
At the present time the only (notably the Little Green Heron and 2
commercial fishing activities around the Osprey on the bay side and the
the island are permit-regulated gill terns, skimmers, etc. on the beaches) Fig. 13- Five day B O D values for water quality stations 8and
netting in the bayous of the Refuge, prefer to nest along the coastline. 19. (After D. Hall and Assocs., 1974) See Fig. 7for station Ioca-
bait fish otter trawling around the Accordingly, we recommend that all tions.
: _ : - :~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~tcs

Estuarine Ecology 285

The shallow waters behind the Several major roosting areas .. ......
Sanibel Shoals and at the mouth of and a few osprey nests were ob-
practically every bayou inlet are served. These are within pro-
easily identified as major feeding tected areas and do not appear to
grounds. Here large numbers of herons, be under any present or future
egrets, spoonbills and shorebirds can threat. However, they have been
be observed feeding during a low tide. indicated on the major resource
(Many of these same areas have suf- map. MM .. o. .S afS 5n o0r ... LO. .... 04. LO.
ficient quantities of table foods
(clams and pen shells) and live .. ....
specimen shells in addition to ASSESSMENT OF ECOLOGICAL RELATIONSHIPS: .L. .AS .. L. L.. L.5 AM LS Law SS .O
the many small fish, shellfish
and marine worms sought by the The marine communities of . ASS S .. . A... - OS . .S /.. L.. H. ...
birds.) Once these resources are Sanibel Island include those fish,
"discovered," over-zealous harl- . plankton, macrobenthic- algae, sea
vesting and collecting: typi~cally grasses, non-vegetated benthic areas,
;follows , seriously disrupting ; ; algae mats, mangroves, oyster bars /... . . E. . .. 0.. OS 0.. Lo. 5. Lo. .5. a.. A.
feeding schedules and devastating and solid substrates such as The
the delicate: ecological balance E I-Rocks, pilings, seawalls and mangrove M. o .S .S L ...' ... ... ... .. .. .
of these areas.
prop roots. All relate to human
vested interests on the island and
Table 7- Monthly total phosphorous-concentrations (mg/I) at
C may be affected by human activities. Intracoastal Waterway stations, 1973-1974. (Note.stations 18 and
A complete plan of protection
is required. A possible approach The occurrenceof phytopanktoncs.,1974.) See Fig. 7 for station
is for the City to request the and their seasonal presence-abundance locatons.
State Department of Natural Re- in the waters adjoining Sanibel are
sources to declare the "Sanibel sketchily recorded in studies by supported by various published
Shoals Feeding Grounds" as a,-bird Davis (150), King (1950), and (Haas, 1940) iand unpublished reports
sanctuary and allow no harvesting Williams and Ingle (1972). General (Florida State Dept. Nat. Res.).
or shell collecting or power boat- seasonal distribution patterns of
ing in the shallows (in waters dinoflagellates and diatoms near
less than three feet below Mean Sanibel are presented in the 1963-66 POINT YBEL TO WOODRING POINT (BAYBEACH)
Low Water) the length of Sanibel. - Red Tide Symposium (F.B.C.M.L., 1967).
The shallow grass flat zone
/ f oi OA0~a,,s ; - The outstanding effect of the between Point Ybel and the Sanibel
plankton community on the island's Causeway is narrow and subjected to
human population involves periodic strong tidal currents. The bottom
..7. JAM . ....... 0. i... . /. . of. .... . red tides that result in fish kills. is of shelly sand. This is the
The accumulation of dead fish along only area where we found the sea
the island's shores during the fol- urchin, Lytechinus variegatus. In
APR..... 24 4 ... 2 lowing red tides and other environ- the intertidal sand zone patches of
mental perturbations like winter short blade Cuban shoal weed occur.
MAO' 41 4 25, /6 /6 /2 2 ' / / 2 freezes is an environmental nuisance In the slightly deeper zone are
with which the City and citizens mixed patches of manatee grass,
should be prepared to cope. Histori- Cuban shoal weed and turtle grass.
JL.. /.. . /,6 /3S. 8.0 S 5 0.2 26. 0.. 2 cally, accumulations of fish were This zonation is interrupted by the
used as fertilizers; today, most Lighthouse Point Development sea-
AU6- /..../76. / /. .S..../2....../.. . barrier island communities treat such walled canal, the entrance to Sanibel
accumulations as garbage. We recom- Estates marine canal system and the
mend the former as the more environ- Causeway.
oV . 0 25 / 0 2 0 ....0 0 o 0 omentally sound means of dealing with
this nuisance. Between the Causeway and Wood-
/074 000 -0/ 00 .00 2.0 0/ 00 Ac 2.7 115 3.0 3.0 'S rings Point, the intertidal sand
. .0 -/ ../ .. . /. 2.2 d,0.0 3.. 2..0 .. The description and assessment beach zone is bordered by a narrow
of the inshore-estuarine, benthic sandbar with patches of Cuban shoal
Table 6 - Monthly turbidity values at Intracoastal Waterway sta-
tions 18-19 (1973-1974). (After D. Hall & Assocs., 1974.) Se Fig. weed. Stands of turtle grass pre-
tions-19(973974) (AfterD.Hall& Assocs,1974.) eFig that follows are based on aerial dominate on a firm sand bottom in
7 for stations.
photos and a ten-day field survey slightly deeper water.

286 Appendixes

The beach dynamics along this
shore are such that seawalls even

~~~~~~~~~~~~~0.0234 headed upland canal entrances pro-
0.334a
mote the steepening and loss of
0.020
0020CHARLOTTE HARBOR beach and reduction in the narrow
. CALE32R 03 fringe of marine grasses along the
~0.016 00.326 0.348 channel. Piers, however, do not
SURFACE WATER PHOSPHOROUS AUG 1969 adversely affect the shoreline or
the intertidal shoals.
~~~~~~~~~~~~~~~~~~~~0.016 ~~~Nautical Miles
0 1 2 3 4 TARPON BAY

%.. 00.20564
Rounding Woodrings Point one
0.02o
enters Tarpon Bay with its natural
meandering clay bottom channel five
0.04 0.358 0.138 to ten feet deep. A series of long,
0.0~ '. ~
NTINUAION Of~ 0.496 narrow intertidal oyster bars par-
-~ P PEC r lVEr ,. 7 allel the upper reaches of the
6.0841 FiC $IE
0.8 'channel. North and south of the
I122 0.144 0.242 channel the bottoms shoal and are
0.132 0.160 -covered with a mixture of Cuban,
turtle and manatee grass. Popula-
0.313 tions of hard shell clams, pen
0.1824~~~~~~~~~~~ ~shells and sea squirts (Molgula
0.061 15 0.106 0.552 occidentalis and Styela partita)
0.061 ~~~~~0.184 ($%~0
:0 ~ 1 8 / 0.~460'~ ~reside in the grass beds in the
~,~Q~.079"~ 0.480' ~t~~n central parts of the bay. On the
57 .2o south side of the bay between Green
Point and the mosquito control ca-
*. '4~~~~ hIj~~~~~~~~ f~nal, the shore is bordered by an
0"'~~~~~~~~~~~.02 *Y intertidal sand bar. Cuban and
~~~~0.0249 ,op :=eh ~~~" turtle grass beds form dense mead-
'Ir~~~~~~~~~~.,, ows between the bar and the shore.
0.022 ~~~~~~~~~~~~.o ~Bayward of the bar the grasses are
patchy but drifting red algae
(i.e., Gracillaria sp.) are abun-
dant. Although the grass beds do
not extend beyond the four foot
contour line, the red algae do. Thus,
nearly the entire bottom of the bay
~- 0.071 is populated with macroflora and their
,0.033 associated fauna including juveniles
� o,~~~0 of pink shrimp, tarpon, snook, sea
<Aro�~~~~~~ trout, red fishes, snapperand a va-
,o'..~ ~ ,,*0.026 riety of micro and macro-epiphytic
'2 'C ...algae, protozoa and invertebrates.

N~~~C?~ 0.006 ~~~The north side of Tarpon Bay
f'.70./l lacks an intertidal sandbar. The
Co/r,~~~~~~~~~~~~ ~bottoms along the protected shores
are less densely vegetated and have
soft silt sediments. Nevertheless,
this region of the bay is highly
productive as evidenced by the pres-
ence of hard shell clams, young
-Ir I. sshrimp, blue crabs and twenty species
of fish collected in a preliminary
survey of Woodburn (1959).
Fig. 14 - Surface water phosphorus (ppm), Aug. 1969 in Pine Island Sound, adjacent to Sanibel Island. (After Alberts et al., 1970)

Estuarine Ecology *287

At the present time the only prop roots and aerial roots of the the densities of shoots. They contain
direct developmental intrusions upon red mangroves bordering sections of beds of hard shell clams and formerly
the bay are a tidal canal discharging this creek are festooned with oysters populations of the bay scallop. How-
from the Palm Ridge Development, the sponges, crabs and other inverte- ever, one section of this system is
Tarpon Bay Marina and the mosquito brates. The clarity of the water unique and that is the large deltoid
control canal. Intertidal oyster bars here is reminiscent of bygone times. grass flat at the entrance to Tarpon
have developed at the entrance to the Mullet, needle fish, sheephead, red- Bay. Only here did we observe an
marina. Other oyster bars are de- fish, snapper and other fishes are overt abundance of whelks, hard shell
veloping near the mosquito ditch exits readily seen by any visitor. The clams, pen shells and the sulfur
on the south side of the bay. creek extends into the interior of sponge (Cliona celata). This area
the mangrove forest and opens out is a prime educational as well as
into Mullet Lake and Mangrove Lake fisheries resource.
LADYFINGER LAKE SYSTEM whose bottoms are carpeted in June
with filamentous green algae and
South of the entrance to Tarpon drifting red algae. The tangled J.N. "DING" DARLING REFUGE BAYOUS
Bay one enters Ladyfinger Lake through masses of green algae contain several
a branching tidal channel between red species of mollusks of which the The bottoms of the several bay-
mangrove islands. The scoured bottoms striate bubble (Bulla striata) is ous are veQetated with stands of
of the channel support an epibenthic most abundant. At the southwest side turtle grass and Cuban shoal weed
community of algae and invertebrates of Mullet Lake widgeon grass is pres- from M.L.W. to two-three feet below
characteristic of clear tidal creeks. ent indicating that this region prob- M.L.W. Tidal channels meander through
Solitary and colonial tunicates, en- ably receives considerable quantities the bayous and exit into Pine Island
crusting bryozoa, the handsome coral- of fresh water on occasion via four Sound through cuts in the Sanibel
like, orange and purple bryozoan mosquito control ditches. Given the Shoals. These bayous support a vari-
(Schizoporella unicornis), market- variety of marine life in this sys- ety of resident vertebrates and in-
size oysters, crabs, the purple soft tem and its accessibility by canoe, vertebrates as well as being an im-
coral (Leptogorgia), sponges, and it represents a valuable educational portant breeding area and nursery
attached macro algae which are a resource for the Island's schools. for fishes, pink shrimp, horseshoe
delight to free divers inhabit these crabs and two species of sea hares.
channels. The benthos as well as the By and large, this region is now a
well-developed intertidal prop root TARPON BAY TO WULFERT CHANNEL relatively high saline estuary ex-
communities bordering these channels cept near the diked Sanctuary Drive
make the channels one of the island's On leaving Tarpon Bay one must in the Refuge. This dike has altered
unique marine educational resources circumnavigate a large grass flat the composition of marine life within
and also one of its most attractive delta before heading north to Wulfert the impoundment area and in so doing
fishing areas. Channel at the west end of Wulfert, may have eliminated an important
Keys. The grass flats along this
Ladyfinger Lake proper is of side of the Island are extensive and
sufficient depth and clarity to be are dominated by turtle grass beyond
vegetated primarily by "healthy" 1.5 feet M.L.W.- In general, the
stands and meadows of turtle grass. maximum depths-at which the grasses
Macro-red algae tend to accumulate occur here are three feet M.L.W. o \ ,
in depressions. At the west end of However, in the vicinity of the west ;L .os.
Ladyfinger Lake are a series of power lines off Coral Creek Inlet ' \
tidal lagoons in the mangrove for- where the water is unusually clear, /
est. Here, stands of turtle grass the grasses grow at depths of four I
and Cuban shoal weed yield to dense to six feet M.L.W. e.I
beds of green algae typical of \\
South Florida mangrove lagoons where Near the mangrove shoreline the 1 -
tidal circulation is sluggish. This grass beds are intercepted by the
region is navigable by power boat Sanibel Shoals, an intertidal sand- / '
only at high water. bar with patches of Cuban shoal weed. \ X
Between the Shoals and the shore . ...
there are grass beds and accumulations Us a . AI. sr v T
MULLET LAKE - MANGROVE LAKE SYSTEM of drifting red algae and the sea
lettuce (Ulva lactuca) . Fig. 15 - Monthly phosphorous values at water quality station 18,
Immediately west of the mosquito Pine Island Sound 1973-1974. (After Duane Hall and Assocs.,
control canal in Tarpon Bay is the These grass flats are extremely 1974)
entrance to a lovely tidal creek and "healthy" as evidenced by grass
the Canoe Trail of the Refuge. The blades 18 to 24 inches long and by

288 Append ixes

marine faunal breeding and nursery DINKEN BAYOU found. Today the soft sediments of
area. ' these bayous support a different
In the lower half of Dinken benthic fauna. As Haas (1940) points
WULFERT BAY Bayou the waters are milky. Yet out, the Blind Pass area is unique in
turtle grass stands are present and that it is intermediate between the
At the west end of the Pine sea squirts and oysters occur along Gulf and Pine Island Sound tidal
Island Sound side of Sanibel, the the shores on pilings as well as areas and receives its fauna from
Wulfert Keys form a natural group of red mangrove roots and submerged both sides of the Island. This alone
barrier islands that have created branches. The shallow vegetated is sufficient to consider conserving
the wind-protected Wulfert Bay which bottom of the bayou extends to Mud and managing this area as an educa-
is completely exposed at mean low Pond, whose soft bottom is vege- tional resource.
water. The soft bottom here is tated with Cuban shoal weed and is
sparsely vegetated with turtle grass exposed at low tides. While this We strongly recommend that seg-
and drifting red algae. The benthic system appears to have adequate ments of the Blind Pass area be pro-
invertebrate community is probably tidal flushing, the dead end Cast- tected from upland development and
dominated by species of worms. The away canal off of Mud Pond is not over-utilization by people. These
waters here are especially turbid well flushed as evidenced by floating segments include Runyon and Albright
because of the fine sediments-being debris (including one dead alligator Keys and their adjoining bights, the
easily disturbed by the wind. four feet long) and fluid sediments ' Old Blind Pass side of Silver Key,
six to twelve inches thick over firm Old Blind Pass and Turner Beach as
sand. Visible septic tank seepage far east'as the dead end of Old
THE-ALBRIGHT- RUNYON KEY BIGHTS along the margins of this canal in- Blind Pass.
dicate the canal's waters may be pol-
At Blind Pass between these two luting Mud Pond and Dinken Bayou. THE GULF BEACHES AND LITTORAL ZONE
keys and Sanibel proper are two
shallow backwater areas whose bottoms CLAM BAYOU AND OLD BLIND PASS At first glance the marine
represent a unique marine habitat. habitats along the
Here and extending into Dinken Bayou The waters in these two shallow, Sanibel merit little comment other
the shallow bottoms adjoining the narrow bayous are highly turbid. Yet than that they are attractive. How-
tidal channels are composed of marly- the soft bottoms are vegetated with ever,- their marine life-is periodi-
clay-sand and the waters are milky. Cuban shoal weed to the upper dead cally disturbed by short-term en-
It is here and maybe only here that ends of both bayous. Permit reports vironmental perturbations such as
large local populations of angel by the Florida Department of
wing clams and burrowing pistol Natural Resources (1975) state storms
shrimp occur in the island's marine that only the shallowest of navi- upon the upper beaches windrows of
pen shells; Chaetopterus worms and
environment. This area is important gable wateways should be permitted. ther tes us worms and
their tubes, surf clams (Spisula
as a unique natural habitat and as The lower reaches of these passes solidissima), coquinas, mussels,
an educational resource. near the north end of Sanibel's snails, sand fleas (Emeritia) and
Turner Beach are six feet deep, crabs Such an event jubilee
well scoured, full of schools of rs c an a uie
fish and are areas of active feeding for shersa
by the pelicans that roost at the for others.
tip of Silver Key and parade on the
ad-joining sandbar. In the not too distant future
\ /6 / \ 0 adjoining sandbar. 0 ; the people of Sanibel and the marine
Years ago Haas (1940) remarked life of the inshore waters and inter-
that the innermost part of Clam Bayoulf
/....'/ ' // \ =._.tu~o/A/ had a white sandy bottom populated by side may have to adapt to the threat
... . ] tim / \ fiddler crabs as well as the marsh of bilge effluents and oil spills
/ \ / \ clam, Polymesoda floridana, which offshore if the Charlotte Harbor deep
/\ / / also was numerous (10-16 per handful) water port is developed.
.. \ ~ / \ ,' at the inner ends of Old Blind Pass.
e AL---- . .-..- Even as early as 1940, however, the
. .<... .-... ..... marsh clam population appeared to have MAN-MADE CANALS AND WATERWAYS
� , " . . . . ................. ...... s r.... been decimated in Clam Bayou by rac-
Fig. 16 - Monthly nitrogen values (mg/I) at water quality station coons. At that time the sandy bottom The environmental aspects of
18, Pine Island Sound, 1973-1974. (After Duane Hall and Asso- of Old Blind Pass was the only place Sanibel's upland canal systems merit
ciates, 1974) on the Island that the pointed venus additional comments. The canals fall
clam, Anomalicardia cuneimenis, was into two categories: the shallow

Estuarine Ecology 289

Table 8 - Popular and scientific names of fishes reported killed by "freezes" at Sanibel, Florida, 1934. (After Storey and Gudger, 1936)

Names Common Local Names Common Local
Scientific Name Local Name Elsewhere Habitats collections Scientific Name Local Name Elsewhere Habitats Collections

Seriola sp. amberjack amberjack p G.B. Sciaenops ocellatus redfish channel bass s & m
Chaetodipterus faber angelfish, black spadefish m & d Caranx crysos runner, blue hard-tailed jack sf & ad
Spheroides spengleri - blowfish, puffer balloon fish m & d Orthopristis chrysopterus sailor's choice; pigfish, etc. d
Pomatomus saltatrix bluefish :bluefish p pigfish; grunt
Lactophyrys tricornis cowfish horned trunkfish ad Carcharinus sp; Carcharias sp. shark shark
Galeichthys milberti catfish sea catfish ad G.B. Sphyrna zygaena shark,hammerhead hammerhead shark
Felichthys felis catfish, catfish, m & d G.B. Scoliodon terrae-novae shark,sharp nose sharp-nosed shark
gaff-topsail gaff-topsail Sphyrna tiburo shark,shovel nose shovel-nosed;
Mystriophis intertinctus eel, brown snake eel s & m bonnet shark
spotted Echeneis naucrates shark sucker remora;shark-sucker
many sp., several families flounder flatfish,flounder Archosargus probatocephalus sheephead sheepshead;
Mycteroperca bonaci. grouper, black marbled rockfish m & d prisoner fish s & m T.B.
Epinephelus morio grouper, red red grouper d Synodus foetens snakefish lizard fish s & m T.B.,G.B.
Haemulon plumieri grunt, black common grunt d Lutianus griseus snapper,mangrove gray snapper ad
Hyporhamphus unifasciatus hound minnow halfbeak;ballyhoo sf Centropomis undecimalis snook rovalia; robalo s & m G.B.
Caranx hippos jack crevalle; cavally sf & ad Lutianus synagris spot, red spot snapper d T.B.,G.B.
Oligoplites saurus jack, yellow leatherjack sf, s & m G.B. (young Lane
leatherjack snapper)
Garrupa nigrita jewfish jewfish, giant m & d Tarpon atlanticus tarpon tarpon,tarpum ad T.B.
Elops sauris ladyfish bonyfish; sf G.B. Opsanus tau toadfish bulldog-fish;
ten pounder - corpion s T.B.
Scomberomorus maculatus mackerel spanish mackerel p G.B. Ogocephalus radiatus toad,rock batfish
Mugil cephalus - mullet striped mullet s G.B. Cynoscion nebulosus trout trout; spotted P.B.,T.B.,
Mugil curema mullet, silver white mullet B.P.,P.S.,T.B. sque-teague ad G.B.
Strongylura notata needlefish gar;needlefish sf B.P.,T.B.,G.B. Lactophyrs sp. trunk trunkfish
Menticirrhus sp. perch, sand sea mink;whiting G.B. Echeneis remora shark sucker ad
Trachinotus falcatus permit round pompano G.B.
Lagodon rhomboides pinfish bream;pinfish ad T.B.,G.B., P.S.
Trachinotus carolinus pompano pampano; pompano s & m
Chilomycterus schoepfi porcupine balloon fish;
spiny boxfish s & m T.B.

Habitats Code: surface - sf all depths - ad shallow - s - Local Collections Code: Gulf Beaches - G.B. Tarpon Bay - T.B.
medium - m deep - d Pine Island - P.S. Blind Pass Area - B.P.

(three to five feet deep) Sanibel not seawalled the banks are eroding is that mangroves. especially white
Estates canal system whose bottom is except where white and red mangroves mangroves, grow rapidly along non-
vegetated with turtle grass and Cuban have become established. seawalled canal margins leaning out
shoal weed except at its innermost It is common knowledge that man- over the water. In times of heavy
extremities and the deeper (six to groved margins of canals and water- rains these trees may promote ero-
twenty feet deep) post 1950 canals ways are desirable as a natural ma- sion and slumping of the canal banks.
that are for the most part seawalled rine resource and as a mechanism for Thus, in order to minimize the stress
and have steep slopes that grade from stabilizing and protecting these to canal banks, the mangroves and
the seawalls. Where such canals are margins. What is not common knowledge other trees should be pruned. On

290 Appendixes

TARPON BAY GULF BEACHES
Achirus lineatus Hogchoker Bairdiella chrysura Yellowtail
Adinia xenica Banded killifish Chloroscombrus chrysurus Bumper
Anchoa mitchilli Bay anchovy Emblemaria atlantica
Bairdiella chrysura Yellowtail,Silver perch Eucinostomus argenteus Spotfin mojarra
Chasmodes saburrae Blenny Eucinostomus gula Silver Jenny
Cyprinodon variegatus Sheepshead minnow Fundulus similis Longnose killifish
Eucinostomus gula Silver jenny Harengula humeralis Red ear sardine
Eucinostomus melanopterus Flagfin mojarra Harengula pensacolae Scaled or silver sardine
Floridichthys carpio Chub Mugil trichodon Fantail mullet
Gobiosoma robustum Goby Selene vomer Lookdown
Hippocampus zostecae Dwarf seahorse Syngnathus louisianae Louisiana pipefish
Lepisosteus platyrhicus Florida gar Trachinotus carolinus Pompano
Lucania parva Rainwater fish,Diamond killifish
Menidia beryllina Silversides
Syngnathus floridae Florida pipefish
Syngnathus louisianae Louisiana pipefish
Syngnathus scovelli Silverstriped pipefish
Ulaema lefroyi Mottled mojarra

BLIND PASS PINE ISLAND SOUND
Eucinostomus sp. Mojarra Eucinostomus melanopterus Flagfin mojarra
Harengula pensacolae Scaled or Silver sardine

Killifish - no genus given

MANGROVES & SANCTUARY
Archosargus probatocephalus Sheepshead
Lagodon rhomboides Pinfish
Menidia beryllina Silversides
Mollienesia latipinna Molly
Mugil sp. Mullet
Orthopristis sp. Pigfish
Tarpon atlanticus Tarpon

Killifish-no genus given

Table 9 - List of additional species of marine fishes in the Sanibel Island waters by habitat. (Compiled from Woodburn, 1959; Gunter & Hall, 1965; Hancock, 1969; Fla. Dept. Nat. Res., 1970; Erwin, 1975)

Sanibel the areas that need such a ter quality and marine life. The Sanibel River, thereby relieving
management program include Sanibel tidal flushing and circulation of the canals in this area of their
Estates, the Dixie Beach Blvd. ca- the Castaway Estates, Del Sega and sediments accumulated over a period
nal, and the waterways and canals of Sanibel Estates canals could be im- of 25 years. The aftermath of a
Dinken Bayou and Clam Bayou. proved. Indeed in the case of the similar breach on Siesta Key fol-
The soft organic rich sediments Sanibel Estates canals an "Act of lowing hurricane Agnes, June 1972,
of the canals, particularly the pre- God" storm may breach the low-lying indicates that the rejuvenation of
1970 dead end canals should be re- land adjacent to the Gulf and re- marine life in this canal system
moved in order to improve their wa- open the original mouth of the would be spectacular.

Estuarine Ecology 291

Acknowled-gmens Progress at the University of tions in the impounded area of
Acknowledgments : ; : ; : Florida 16(1). 77pp. the Refuge.

Byle, W.K., Jr. (Environmental Ser- J.N. "Ding" Darling Natural Wild-
vices Unlimited). Resourced Analy- life Refuge. 1966+. Narrative
We are indebted to Mrs. Marita sis of Bay Island. 4 pps. Reports - Includes data on weather,
Haymes for her excellent assistance Csalinity, migratory birds, bird
censuses for refuge and Pine Is-
as a research librarian. In addi- of Florida. 1959. Coastal engi-nu orre a e -
tion, we thank other-people who land Sound, Corretta:Research Re-
neering investigation at Captiva ports.
assisted in this study and helped Island. Prepared for County
in the preparation of the manuscript. Commissioners, Lee County, Florida. Dragovich, Alexander. March 1963.
These include Mrs. Ann Winterbotham, Unpublished report. Hydrology and Plankton of Coastal
Richard Workman, John Clark and the Waters at Naples, Florida (Re-
following students and secretaries: Cobb, S.P., C.R. Futch, and D.K. Camp. print) Quart, J. of the Fla. Acd.
Judy, Theresa, Madeline, Mary, Nancy, 1973. The Rock Shrimp. Sicyonia of Sci. 26 (1): 22-46.
Carol Ann, Rob and Steve. brevirostris. Stimpson, 1971
(Decapoda, penaeidae). Memoirs Dragovich, A. and J.H. Finuconi and
This study was supported in of the hourglass cruises, Fla. B.Z. May. 1961. Counts of red
part by a contract from the Conserva- Dept. Nat. Resources Mar. Res. Lab.; tide organisms, Gymnodunium breve,
tion Foundation and a gift from Mr. Vol. 3, part 1. and associated oceanographic data
M.Q. Peterson, Boca Grande, Florida from Florida West Coast, 1957-59.
to the New College Environmental Conover, Y.T. 1967. The Importance U.S. Fish and Wildlife Service
Studies Program. of Natural Diffusion Gradients and Spec. Scientific Report. Fisheries
Transport of Substances Related to No. 369.
Benthic Marine Plant Metabolism. Dragovich, A. and J.A. Kelly, Jr.
Literatu re Cited -Botanica Marina, 9, 1-9. 1967. Occurrence of the Squid,
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Woodburn, K.D., et al. 1957. The
U.S. Army Engineer Division. South The Live Bait Shrimp Industry of
Atlantic Corps of Engineers. the West Coast of Florida (Cedar
August 1971. National Shoreline Key to Naples). Fla. St. Board
Study: Regional Inventory Report- of Conf. Mar. Lab., Tech. Series
South Atlantic-Gulf Region, Puerto
Rico and the Virgin Islands.; Woodburn, K.D. 1959. Tarpon Bay,
Sanibel Island Bulkhead Survey
U.S. Army Engineer Division. South.
Atlantic Corps of Engineers. (Lee County). Unpubl. Rept.
Atlantic CGoraps ofAEngineers. No. 59-60. Fla. St. Bd. Conserv.
Atlanta, Georgia. August 1971. Mar. Lab.
National Shoreline Study: Lee
County. Islands. Passes. ; Woodburn, K.D., B. Eldred, E. Clark,
Charlotte County. Maps. Sanibel R..F. Hutton and R.M. Ingle.
Island. pps. d78-d86. May 21, 1957. The Live Bait
Shrimp Industry of the West Coast
U.S. Dept. of Commerce/Coast and of Florida. Tech. Series No. 21,
Geodetic Survey. 1962. U.S. Fla. State Board of Conservation
Coast Pilot 5 Atlantic Coast - Mar. Laboratory, St. Petersburg,
Gulf of Mexico, Puerto Rico and Fla.
Virgin Islands. Fifth edit.,
June 16, 1962. GPO Coast and Geo- Zieman, J.C., Jr. 1968. A Study of
detic Survey, pps. 61-67. the Growth and Decomposition of
the Sea Grass, Thalassia testudinum.
U.S. Dept. of the Interior. Fish and M.S. Thesis. Univ. of Miami, Miami,
Wildlife Service. Gulf of Mexico - Florida.

295

NATURAL ENERGY SYSTEMS 297
Land Use and Energetic Maps 298
Model of Main Components of Sanibel 298
Balance of Payments Diagram 298
Calculation of Carrying Capacity 298
Land Use and Land Use Maps 300
Model of Main Components of Sanibel 300
Energy Budget and Balance of Payments 301
Carrying Capacity of Man and Nature 302
Alternative Futures for Sanibel 303
Conclusions and Recommendations 304
Literature Cited 305

297

APPENDIX 6

NATURAL ENERGY SYSTEMS

by Mark Brown

As man's influence in any land- to maintain balance of payments. and now with the development of areas
scape becomes the major feature, A method of calculating carrying for commercial and residential use, addi-
planning for future alternatives of capacity as a basis for a vital tional energy flows in with electricity,
land, energy and water use becomes economy is suggested and demonstrated, oil, gas, and goods and materials. Some
increasingly important. The con- and, finally, suggestions for overall energy is of low quality (in its ability
cern becomes one of insuring long- well-being and a process for develop- to do work), such as incident sunlight
range values and high quality of ment that will insure long-range and wind; and some is of high quality,
life by insuring that lands are put values and enhance quality of life are such as water and the fuels that sup-
to their highest and best use, that presented. port man's activity. The effective
different land uses do not conflict, use of all the available energies in
that energy for productivity is Sanibel Island, an island of re- a partnership relationship of man and
available in the quantities needed, cent rapid growth-and urbanization pres- nature is believed to lead to maximum
and that there is sufficient high- sure, is shown in Figure 1. The pattern economic vitality.
quality water for the needs of the of ecosystem communities that developed
population as well as natural sys- throughout the island have changed from Current theory and understanding
tems of the area. the primitive condition with increased of systems suggests that the greater
activities of man. The patterns of man the energy flows generated from na-
This report is concerned with and nature that developed as a result tural systems, the more matching eco-
these things, and others; and their of abundant natural energies and inter- nomic activity based on outside fuel
influence on long-range values and face with the Gulf are shown in Figure 1. energies can be "attracted" and sus-
quality of life. Trends of land The purchased energies attracted as the tained. This is certainly the case
use are presented, the energy re- basis for economic vitality and the free of Sanibel Island, blessed, or
quirements of productivity are ana- resident energies of the region are sum- cursed as it may be, with abundant
lyzed, and trends in energy avail- marized in the regional model in Figure energies of winds, waves, tides,
ability discussed. The economy of 2 and balance of payments diagram in longshore currents, sunlight, and
Sanibel Island is analyzed, and the Figures 3 and 4. rainfall. Effective "energy trades"
exchanges of major exported and im- of exports (in Sanibel's case; ser-
ported goods and services are dis- Energy flows into the region from vices) for imports depend on the
cussed in light of future ability the sun, wind, and rain as in the past, amount of nature's free energies

298 Appendixes

that can be used to subsidize pro- this method producing the best accuracy.
duction processes. If, for ex- LAND USE AND ENERGETIC MAPS Accuracy of this method has been de-
ample, the purchased energy content termined within 1 percent in past applica-
of services produced is higher than tions. The areas measured are the basis
other competing regions, economic for energy value tables and alternative
competitiveness and ability to Land use maps were prepared, using management calculations.
eattractgm and purchase additional simplified ecosystem communities for
energy may suffer. Thusen the pur- natural systems and an energetic clas-
sification scheme developed over the MODEL OF MAIN COMPONENTS:OF SANIBEL
services exported may act as at past four years for the urban systems
limitin factor on economic acti- Brown 1971; Brown, 1973; Odum and To organize our understanding and show
ity sustained by the region. Bro 1975; Brown, 1975). relationships of the main contributions to
the value of the area, a simplified
diagram was prepared that included
The combination of inside and The co1975 map was drawn from photo the main work processes which con-
outside energies that best maxi- tribute value each year (Figure 2).
mizes the totalflow of high quality graphy on a base map redrawn from Main flows of energy, both bought
energy maximizes the economy of man and U.S.G.S. quad maps of Sanibel Island, and resident, the eflows of water and
scale 1:24 000 Newer photography a t f s o any nd
sets guidelines for interfacing sub-cale1:24000. Newer photography accompanying flows of nutrients are
systems of the total environment. Thus, (1975) at a scale of 1:9,600 was included. By putting the work of
t he best strategy for developing long original man and nature on the same diagram,
maps. izes the main processes,
term value and vital economic function- maps. one summarizes the main processess
ing recognizes the contribution of free that contribute to the vitality of
energy flows generated from natural sys- the island whether paid for with
tems and maximizes total flows and The classification scheme used for money or not. The symbols used and
higher quality purchased fuel energies. natural systems is a simplified com- a brief explanation of each are
munity scheme for overview of the given in Appendix A.
present and past conditions. No attempt
was made to delineate the difference
The value of energy flows in eco- between ridge and swale vegetation in
logical systems can be converted into the present condition for two reasons.
equivalents of energy whose ability to First, the island is in such a stage of A simple diagram that sum-
support work is familiar. The basis transition that no clear lines of de- marizes the exchanges of energy and
used is the fossil fuel equivalent marcation are evident on aerial photo- money was evaluated for 1975 (Figure
(FFE). In this manner the free natural graphs. Because of altered hydro- 4). Evaluation of balance of en-
work of ecological systems can be ex- periods, successional transition of ergy and money in this manner helps
pressed and compared directly to the once cleared lands, and invasion of to perceive major contributions to
work of the economic sector; and the exotic species, the once evident marsh the region's economy and sensitivi-
relative value of both sectors can be and ridge vegetation can no longer be ties to external change. Parameters
evaluated. delineated with any degree of accuracy. and coefficients for flows of energy
And, second, the minimum cell size, or were derived from previous studies of
minimum perceivable subsystem area south Florida and Lee County (Brown,
delineated was 1.5 acres; so while there 1973; Odum, Brown, et al., 1975).
were areas of "pure" swales of spartina All energy was converted to the same
An energy diagram of the many as-
pects of the systems of man and nature marsh discernable on the larger scale equivalent basis to support work--the
together shows their interplay in ways photographs, they were of such a size fossil fuel equivalent (FFE). A
not usually understood when examined Xas to preclude classification. table of conversion factors is in-
separately. Flows of money, materials, cluded as Table 3.
goods, and fuels can be converted to an Measurement of the areas of sub-
equivalent basis so that their true re- systems was done by cutting up a 7
lationships can be shown. The model mil mylar print of the maps and weighing CALCULATION OF CARRYING CAPACITY
can then be examined in relation to on an analytical balance accurate to
questions of resource protection and .001 grams and multiplying by a conver-
management, with suggestions made to- sion factor to transform weight into The total activity of man and na-
ward maximizing values and making good acreages. Many other methods, including ture that can be sustained depends on
interfaces between man-dominated and the use of a leaf area index machine the amount of outside controlling high
natural subsystems. and planimetering, have been tried, with quality energy that can be attracted

( Q 0 ; : Natural Energy Systems 299

186

3 6

2b M -wt V ,i Co ve 126 a

5 Mobile Hmes 16 Mangrove

6 Multi Family - Apts. - Condo 17 Mud Flat
7 M-tes 18 Neutral Embayment
L Commercial 19 Coastal PlanktQn
99 Utility
n oi l e o mae s 1Lae M. Can oea
6 M ulear-d 17 -u FBat

3LowDensty Rsidetia Coastalnland M to

Fig. 1 - Present condition (1975 vegetation and land use for energetion of Snibel Island. Compiled by M.T Brown, J Bartholomew and R Costanza).
-ANO~~~~~~~~~~~~1

Fi. -Pesntcndtin 175 vgtaio ndlad s fr nrgti ubysemcasifctin f aibl san. Cmple b .T BonJ.Brtolme ndR.Cstnz)

300 Appendixes

to add to and amplify energies. Sys- deepening the streams, altering stream MODEL OF MAINCOMPONENTS F SANIBEL
tems compete in attracting outside in- course, and increasing runoff. Energies
vestments. Those with lower investment that were once used to their fullest now
ratios (the rate of fossil fuel energies go relatively unused in their original
to resident energies) match outside en- locations and thus the amplifying values Figure 2 is a regional model of
ergies with more value from inside and of water in these locations are lost. Sanibel Island. The main components of
compete better in what they offer for the island system that add value each
exchange. year are included, as well as exchange
The-early development of lands for
agricultural purposes constitutes the pathways of materials, energies, and
money. Starting at the right and top of
Systems compete well so long as thmajorcause of changes in land use untilney. Starting at the ex ternal flows or
their investment ratio is less than that the recent past. Since that time, how- sou rces for mare the exterials, energies, and
which is characteristic of the larger ever, development of the island for com- sources for materials energies, and
system within which they operate. In mercial and residential use has had sig- money. The first and second components
system within which they operate. In are the beach and dune areas of the Gulf
974 the investment ratiofor southwest nificant effect, primarily because ofare the beachand dune areas of the Gulf
1974 the invest ment ratio for sou.9/1 the actual acreages developed and scoast where wave energies and coastal
Florida coastal communities was 1.9/1. ondaril y on the chanteshore-
That is to say, for every 1 kcal of na- ondarily because of the changes induced winds are high. Onthe front shore-
tural resident energy, 1.9 kcal of fos- to the'remaining land areas by drainage line (swash zone);that receives break-
and mosquito ditches and the introduc- ing waves, the surging waters are re-
slify theresident energyw . Investment tion of exotic species. ceived, filtered and returned to the
lify the resident energy. Investment
ratio for Sanibel was calculated and
compared to other competing regions.

LAND USE AND LAND USE MAPS. GO

-Given in Figure 1 is a land use: DOaX GG
map for the island,; showing the main
features of the landscape and man's W
land use patterns that had developed
by 1975.

In the primitive condition,
Sanibel Island is described as con-
sisting of a leeward shoreline of man- :
groves and ridge areas of grassland \
prairies, and palmetto jungie and mixed
woods (Cooley, 1955) with a lower basin I
through the center of the island of
ridges and swales of marshes and sea- l
sonal marshes or wet prairies. Wet , waL
season rains were collected in the
marshes and slowly passed to the cen-
tral basin of the Sanibel River and I
eventually, if the rains were of suf-
ficient duration and magnitude to
cause a breakout along the coast, pas- \ /
sed to the Gulf. Because the energy
qualities of water are high, greaterENT
potential for maximum work is derived - reWE
from using waters over a wider area /
where they generate greater value. / ..-N
Consequently, a pattern of broad
marshes and a slow meandering stream
had developed to take advantage of thisND o7 -
important energy source. Man's manipu-
lation of the landscape has changed Fig. 2 - Regional model of Sanibel Island showing main components that generate value and major flows of materials and energies that
this pattern by straightening meanders, generate vitality.

Natural Energy Systems 301

sea. A portion of the water's or- had their toll in changing the character, gradual decline of visitors and the
ganic load is deposited on the beach structure, and function of these in- income they bring to the island can
where it is trapped by the sand fil- terior ecosystems. Exotic species in- be the only result. As the ratio
ter. The organic material so trapped vasion is characteristic of disturbed of natural (resident) energy flow
provides the food base for many in- areas (Myers, 1975; Duever, 1974). ;to total flow of useful work dimin-
vertebrates. That portion not direct- Cleared areas, in the first stages of ishes, the price of services and
ly and immediately consumed undergoes regrowth, and areas with altered hydro- goods offered for sale must increase,
microbial decomposition and enters periods, are prime targets for invasion. ultimately causing a significant de-
local detrital food chains. Breaking cline in the net income to the is-
waves shift sands and carry sand and Development on the interior lands land.
shells from deeper waters, 0 imposes direct stress on the natural sys-
tems by the actual clearing of lands. Leaving the interior and moving
The same energy sources that aug- The indirect effects of increased run- toward the leeward side othe island,
mangrove communities are the predominant
ment beach accretion are also the off Which transports high nutrient
prime agents of beach depletion. In loads, increased sewage, increased inputs of energy and materials (sun-
the regional sand budget, however, de- pumpage of ground waters for ir- light, water nutrients) are shown. It
light, water, nutrients) are shown. It
pletion in one area means accretion rigation of lawns, and increased is important to note the overlandflow
and deposition iniother areas. use of the lands by increasing num- of water and nutrients from the higher
bers of people all contribute to lands' of the interior. It has been cal-
Adjacent to, and landward from the heavy stress, and continued change culated that this source of nutrients
swash zone are various types of dune of these lands.
ecosystems. Dunes are the most fragile total nutrients available to some man-
total nutrients available to some man-
of the terrestrial ecosystems. The Sanibel Island has no potable grove systems(Burns, 1975) but further
most important stresses affecting dune water supply. Thus, water is pump- that chloride content of soil water
ecosystems are the paucity of fresh- ed from the Hawthorn aquifer and plays a major role in suppression of
water, salt water spray, wind, and desalinated by electrodialysis. De- transpiration. The freshwater input from
their use by man. The dune is char- salination is an energy expensive upland sources is a vital component in
acterized by sparse vegetation that process (detailed calculations are al
serves the role of trapping and hold- included as Appendix B). As future maintaining ptions and that diversion
ing shifting sands. Wind, as an energy energy supplies become less avail-
of freshwater from the uplands to off-
source, regulates the amount of sand able and costs rise proportionally, shore regions may suppress natural
deposition. coupled with increased maintenance productivity of mangrove foests
costs and decreased efficiency of (Burns, 1975).
The component of urban development an older plant, the costs of water
labeled coastal development is a primary for the island can 'do nothing.but
aspect of the beach and dune system of rise.
source responsible for the transport
Sanibel. The quality of the beach, as of nutrients and detrital matter into
of nutrients and detrital matter into
well as development is important in at- The purchased energy to construct, and out of the tidally-influenced man-
tracting man. The shells of off-shore operate, and maintain the developed With eachrise and fall they
molluscs are brought to the beach by portions of the island flows through deliver an important food source to
wave action. The interaction of users the system with dollar payments flow- the estuarine bay food chain.. a food
and buildings may have positive effects ing in the opposite direction. Be- chain that eventually ends with com-
through increased nutrient flows, but cause the two flow in opposite di- mercial and sport fish caught by man,
in most cases there is stress to this al- rections, the consumer receives en- and another important income source
ready fragile system through overuse and ergy and pays out money. The main to the region.
development approaches that alter the contributions of income to the island
character of dune vegetation and cause are heavily dependent on a healthy na-
erosion of dune sands. tural environment. Tourist income as
ENERGY BUDGET AND BALANCE OF PAYMENTS
shown in the model is a result of
Inland from the beach and dune sys- tourists being "attracted" to Sanibel
tems are the interior "wetlands" or Island by its "image." The image is
ridge and swale systems and the upland a nonweighable storage of information, Figure 3 is a simplified model
vegetation systems. These systems are but is the product of the total pro- of energy flow and balance of pay-
undergoing extreme change as a result ductivity of all components of the ments. The region receives, as a
of actions by man. The direct actions island system. Thus, development of basis for its vitality, natural en-
of man in clearing lands, drainage for coastal and interior areas will at ergies inflowing that develop basic
fast removal of wet season rains, mos- first increase the image to outside resources of lands, beaches, ecosys-
quito control ditches, and the intro- visitors, but if development causes tems, and water. These resources
duction of exotic species, have all degradation of natural areas, a are used to attract incomes of money

302 Appendixes

which include tourist and retirement
dollars, and capital investment..
These incomes are then paid to buy
additional energy inflows in theGOODS TO FUELS TO GOODS TO FUELS TO GOODS TO FUELS TO
a oESIDENTIAL REENTINTIL OMMERCIAL COMMERCIAL MOTEL MOTEL
form of fuel~s, goodsN and services. RNPTIIO
form of fuels, goods, and services. SECTION SECTION SECTION SECTION SECTION SECTION TRANSPORTATION
The attraction of money from sales
and tourist dollars is in competi-
tion with other regions and, thus, 5.1 I\. 2. O.I 11.0 /4.6 7.0 0.3 2.4
the amount of money obtained and en- - --__-/
ergy eventually bought depend on the
region's ability to maintain a bal- . E x GD T ULST
ance of payments. This depends ul- , ir p A
timately on world-wide prices of fuels STATECT \ \ P
INVESTMENT TOURISTS TxES72 AND
and the availability of monies from 7
OUTIDE INCOME 'oAND O �-.,\ ,
external sources. If prices increase, IE PAYMENTS �96\ \\I
and incomes decrease (ultimately be- \\\
14.9 ~I 8.
cause of national energy shortages), .
the purchased energy available to the .-------
island will be less. In this way,
the diagram indicates the extent to
which the island's total vitality is
based on external energy availability
and effective maximization of free
resident energies.
102.9
NATURAL ENRES 102.9 SANIBEL ISLAND

~~~~~~~~~~~~~~~~OUTSIDE ~E in 169.7
R out 41.76
SERVICES,CiOD, ;:ol-i7
FUELS KCO XlOI
SXlO6 ....~

1~~~.69 ~ 141.~76 ~Fig. 4- Balance of payments diagram showing the main energy and money flows by source and exchanges that generate a vital economy.
ASSETS

Figure 4 is a breakdown of the CARRYING CAPACITY OF MAN AND NATURE
flows in Figure 3. Tabulated in Table
4 are the major components of Sanibel's
energy budget and the percentage of the Determining the carrying ca-
Dectefr maning mthe moreyn comle
total. Natural energies contribute ap-
phanityi for mane ispmucioes aomle
proximately 38 percent of the total en- than it is forother species, and
ergy that Sanibel Island consumes in in- as such, has to be treated as a com-
NAUATURAL ~~~~~direct ways, but are of great importance plex problem. Carrying capacity is
FREE direc t w a y s ~~~~~~~~~~~~~plex problem. Carrying capacity is
0~PEEREGYto the total vitality of the system. usually thought of as-the number of
individuals of a given species that
an area of a given size will sup-
port. When applied to industrial-
Tourist income contributes approxi- ized man, a better definition re-
mately 45 percent to the island economy, lates carrying capacity to energet-
the remainder coming from capital in- ics. Just as one can increase the
63.8 vestment and outside income. With an carrying capacity of a range for
BX106 economy so heavily geared to tourist cattle by the addition of energy
dollars, effective maintenance of na- (fertilizer, irrigation, etc.) the
Fig. 3- Aggregate energy flow diagram showing the interaction tural energies, and those natural sys- carrying capacity for man has in-
of bought energy with free resident energy and balance of tems they amplify, is of prime impor- creased with every increase in
payments. tance. fossil fuel utilization.

Natural Energy Systems 303

Carrying capacity for man, zation of free resident energies, The ratio of purchased energy
then, is in direct proportion to by amplifying them with small to resident natural energy is a meth-
the energy he has at his disposal. flows of bought energies. Ef- od of evaluating the relative eco-
Sanibel Island could conceivably fective energy trades are those nomic positions of regions. This ratio
hold 100,000 people if there were trades of exported goods and expresses the level whereby a region
energy enough to maintain order... services-for imported energies adds to and amplifies natural energies
energy enough to obtain potable where the result is a net gain. to do the work of producing goods and
water, treat sewage, incinerate In Figure 3, it is shown that services. The "investment ratio" of
garbage and build the roads, hos- Sanibel Island exports services areas similar to, and in competition
pitals, and government services with an energy content of with, Sanibel Island is 1.9 to 1. To
necessary, as well as defer the 104.4 x 1010 kcal, and imports remain in competition with these areas,
host of other "environmental" . energy totaling 169.7 x 1010 kcal, Sanibel Island should strive for an
problems that are a consequence or an energy trade of 1.6 to 1. equal or lower ratio. For, if the
of high densities. In other words, for every 1 kcal island's ratio is higher, sold services
of energy exported, Sanibel ob- will contain a higher portion of pur-
The problem of determining carrying tains in return 1.6 kcal of energy chased energy than competing regions,
capacity of environments becomes a prob- States exports 1 kcal of energy and prices by necessity will be higher.
lem of obtaining a sufficient supply of to the OPEC nations and get in
energy to support the population. In return 8 kcal; before the 1973 The investment ratio for Sanibel
1973 Hubbert estimated that the United price increases our energy trade is calculated in the following manner:
States had tapped the last of its easily was 24 to 1).
accessible cheap energy supplies, and total purchased energy investment
for the next century will see a decrease resident energy ratio
in the total reserves (Figure 5). Odum 10
(1975) calculates that the "net" energy 169.7 x 10 kcal 165/1
available to society, after the energy 102.9 x 010 kcal
costs of obtaining future supplies is 70
subtracted, has peaked and is decreasing.
In all, the energy picture for the fu- 60 The investment ratio for Sanibel
ture is not bright. Decreasing avail- _\ is lower than competing regions How-
abilities mean higher competition and is lower than competing regions. and the
ever, with growing populations and the
higher prices for the stocks'that re- increasing energy flows they require
main. Those regions within the total for control of the environment, the
economy that can maintain balance of 30 ratio is control of th e environment, the
ratio is changing. To equal'other com-
payments with effective "energy trades" petingregions' ratios,Sanibel need
will by that aspect alone guarant -need
will by that aspect alone guarantee 20 UNITED STATES only grow 15 percent at current energy
future energy supplies. i0 . consumption rates. Looking at it
--___~_~ ~ ] =another way, Sanibel's energy con-
Regions use purchased energy to 1850 1900 1950 2000 2050 2100 2150 200 2250 2300 2350 suption can ncrease by 15percent
add to and amplify free resident ener- YEAR and still remain competitive.
gies, combining them in many ways for Fig. 5 - Graph of world and United States remaining energy
export and sale to outside markets. reserves (crosshatched area is energy used to date). Estimate
Sanibel Island uses purchased energy of combined production cycle of crude oil and coal for the ALTERNATIVE FUTURES FOR SANIBEL
to provide, operate and maintain struc- world and United States. (Estimates as of 1971 and 1972).
ture that in essence amplifies the free Data from Hubbert, 1973. (Based on 2X 102 metric tons for energetic car-
resident energy of beaches, bays, man- gross energy). rying capacity estimate the total
rying capacity estimate the total
groves, and wildlife. The island "ex-
ports" a service to outside markets in "attract" and still maintain a vi-
the form of an excellent environment During times of cheap energy tal economy and competitive posi-
for vacationers to spend leisure time. prices and abundant supplies, ef- tion. This value (25.81 kcal/yr),
The purchase energy content of this fective energy trades have little when converted to population fig-
export determines the price; the consequence, but as prices rise ures using per capita energy fig-
more free resident energy that is with scarcity, competition and ures for the present condition,
utilized in providing the service, purchasing power play a larger shows that Sanibel could conceivably
the lower the asking price. role. The higher the energy allow a total average yearly oc-
trade, the greater dollar return, cupancy of 13,300 people to reside
Competitive position is en- and, thus, the greater the purchasing on the island. Using current ra-
hanced with the effective maximi- power. tios of permanent vs. tourist

304 Appendixes

population, this would mean ap- al 16,000 - 24,000 units. A me- Conclusions and
proximately 9,200 permanent resi- dium value, then, could be 20,000
dents and average yearly occupancy additional dwelling units; add to Recommendations
of seasonal visitors totaling this the-existing 4,000 units and
4,115 (or 125,000 tourists staying Sanibel Island could have as many
for 12 days).: as 24,000 occupied dwelling units. Sanibel Island should recognize
and work towards a leveled or steady
However, a cautionary note WMRT assumed occupancy rates of state economy. If there are general
should be included. There is in- 2.25 to 3.9 when computing popula- shortages of power developing in
creasing evidence that costs for tions. Lee County Planning Dept. data the United States, either because
services and increasing; population (1973) shows approximately 1.5 people/ fuels are unavailable or because
densities do not exhibit a linear dwelling unit; so, for the purpose of fuels are more expensive to get, the
relationship. The energy costs this calculation, 2.0 people/dwelling economy may enter an inflationary
associated with increasing popu- unit was used as an average. With state. With fuels costing more, the
lation densities may increase by this value, then, in the foresee- amount of work done for each unit of
some greater function, so that a able future there could be as many money spent is less, requiring an
15 percent increase in populations as 48,000 people living on Sanibel increase in costs for goods and ser-
may requirea 25 percent increase inX Island. Add to this figure an in- vices. Then the monies available to
energy consumption to provide neces- creased number of tourists (assuming tourism, retirement incomes, and
sary services. It is also important the same ratio as existed in 1974), investment will diminish. If there
iarenational levelini tendencies
to note that if per-capita consumption approximately 21,000, and the total are national leveling tendencies,
of fuels, goods, and services contin- average yearly occupancy of Sanibel they will have a sharply amplified
ues to increase, .population increases Island will reach approximately effect on Florida. If development
should be even less.. The carrying 69000 peopl economically favorable
times, when the costs of goods and
capacity for best economic development services are roatislofloods and
indicates the level of purchased ener- economic positionwhen goodsiandeser-
gies that may be attracted, for the is- 400 vices are more:expensive, ay make
land to maintain competitive position. nvironmntal
All increases in population must be environmental costs (water; electric
calculated against increases in per //300 ity, and sewage systems) too high,
.calculae ainst increases in per0 < 300 --thus lowering the carrying capacity
capita energy consumption the island.
*4~~~~~~ ; Be Xof the island.
It has been estimated that there M 2o0
By recognizing that leveling is re-
are about 4,000 additional dwelling quired eventually, the island maymake
units recorded and approved for Sanibel t te islandmay make
moves toward insuring economic stability
Island (WMRT, 1975). Calculations 1 loo
from the land use map, assuming three Z and maintaining a competitive condition
dwelling units per gross acre of cleared by keeping further growth related to
lands, confirm this. Four thousand addi-- 0 environmental resources and ability to
tional dwelling units would double 0 5. 10 15 20 30 3540450 pay. Borrowingtooheavily against fu-
~Sanibe's present population, at the S \ R 0; ture energy supplies to finance present
Sanibel's present population, at the POPULATION X103
same time more than doubling Sanibel's growth may lead to instability.
present purchased energy requirements. Fig. 6 - Graph-of per capita dollar costs of government vs. pop-.
The investment ratio or ratio of pur- ulation size. Source: 1972 Florida Census of Local Govern- As land becomes more scarce and
chased energy to resident energy would ment Finances. Commission on Local Government, 1973. costs per acre continue to rise, there
be 3.3 to 1, a ratio far exceeding that toward high-rise de-
of other competing regions, and equaling velopment. The resulting high concen-
almost that of the urbanized areas of trations of people, cars, energy use,
Ft. Myers and Naples! In other words, The graph in Figure 6 shows the and environmental loads may make for a
with current development trends, Sanibel nature of increased per capita gov- less secure economic status, if there is
can expect population densities, and the ernmental costs vs. population size a national recession in fuel and result-
associated decreases in a quality envi- for various cities throughout Flor- ing economic inflation.
ronment, that have been experienced by ida. It is interesting to note that
these mainland communities. the optimum city size according to To achieve a leveled or steady state
this data is roughly about 15,000 peo- economy there are several alternative
On another note, WMRT (1975) ple. But more important, the graph guidelines that could be implemented
estimates that the number of pos- indicates that should Sanibel increase through existing democratic processes.
sible dwelling units based on pro- its population size to 48,000 people,
jections using all zoned lands per capita government cost will rise (1) Provide limits to high power
could reach as high as an addition- about 40 percent. density usages such as high rises, high

Natural Energy Systems 305

density condominium developments and the and economy of a region is a difficult Costanza, Robert. 1975. Distribution of
concentrations of heavy industry. When task and can only be performed accurately incoming energy and energy use (in-
energy concepts are applied to urban after the fact, but trends indicate that cluding the high quality energy in
systems, we find that high energy con- future carrying capacities will be less water) in Carrying Capacity for Man and
centrations result in more energy loss than present values. In that light, any Nature in South Florida. H.T. Odum and
per unit of work than do lower concentra- decision to increase the population den- M.T. Brown, eds. Final report to U.S.
tions. sity of Sanibel Island should be made Dept. of Interior and State of Florida
only after presently committed lands have Division of State Planning.
(2) Maximize diversity of the re- been fully developed and their true impact
gion on the principle that added value - assessed. Duever, M. 1975. Oral presentation to
emerges from the interactions of a variety Center for Wetlands on subcontract
of land use types.in the same area. Large to National Audubon Society at Cork-
scale developments done on the mass Literature Cited screw Swamp. June, 1975.
production basis should be discouraged
since they work against this princi- Florida Resources and Environmental Analysis
ple. Since value or quality of life Center, Florida State Univ. 1975.
emerges from having a variety of Adley Associates. 1973. Technical Patterns of energy consumption in Florida,
human and natural activity available, memoranda to Lee County Board of 1960-1972. Prepared for Florida Energy
this principle applies within any County Commissioners. Committee.
scale system from the variety of activ-
ities of a park to the variety of land Brown, M.T. 1970. A study of the Hubbert, M. King. 1974. U.S. energy re-
use systems of a-region. power density of Gainesville, sources, a review as of 1972 (part 1).
Florida, in Complex Systems. A monograph prepared for the Committee
(3) Develop incentive to maintain John Day, ed. Cornell Univ. on Interior and Insular Affairs, United
and improve existing areas of develop- Press. States Senate Committee Print, U.S.
ment through higher taxes on new devel- Government Printing Office, Washington,
opment, lower taxes on non-developed Brown, M.T. 1971. Energy budget as D.C.
lands and extend municipal services to related to community structure in
existing systems before newly developed urban systems. Terminal thesis, Lee County Planning Dept. 1973.
areas. Department of Architecture, Univ. Housing and construction. Work-
of Florida, Gainesville, Florida. ing papers of Lee:County Planning
(4) Establish special incentives Dept. and Lee County Planning
for the development of low energy com- Brown, M.T., and Grant Genova. 1973. Commission.
munities and habitats that maximize Energy indices in the urban pat-
the available natural energies as well tern. Masters terminal thesis, Myers, R. 1975. Melaleuca in Carry-
as fossil fuel energies through a sym- Department of Architecture, Univ. ing Capacity for Man and Nature in
pathetic relationship with the surround- of Florida, Gainesville, Florida. South Florida. H.T. Odum and M.T.
ing environment. Brown, eds. Final report to U.S.
Brown, M.T. 1975. Lee County, an area Dept. of Interior and State of
(5) Reevaluate existing zoning of recent rapid growth in Carrying Florida Division of State Planning.
policies, established under rapid growth Capacity for Man and Nature in
conditions for controlling successional, South Florida. H.T. Odum and M.T.
low diversity interface problems of con- Brown, eds. Final report to U.Sss . (Manuscript)
centrated energy utilization. Present Dept. of Interior and State of
zoning techniques may work against the Florida Division of State Planning.
stability of the city by insuring a Odum, H.T. and M.T. Brown, eds. 1975.
low diversity, high energy system. Burns, Larry. 1975. Mangroves, part 3 Carrying Capacity for Man and
in Carrying Capacity for Man and Nature in South Florida. Final re-
(6) National leveling trends and Nature in South Florida. H.T. Odum port on contract #CX000130057 to
the amplified effect on Florida may de- and M.T. Brown, eds. Final report National Park Service, U.S. Dept.
crease demands for new housing, in which to U.S. Dept. of Interior and State of Interior and State of Florida
case lands cleared of natural vegeta- of Florida Division of State Planning. Division of State Planning.
tion in preparation of development that
never occurs lowers diversity, increases Commission on Local Government. 1973. Wallace, McHarg, Roberts and Todd,
runoff, reduces total energy flow through 1972 Florida census of local govern- Inc. 1975. A Summary of Phase
natural systems and in general stresses ment finances. Special report 73-9. 1 planning studies toward com-
natural systems needlessly. prehensive land use plan for
Cooley, George R. 1955. The vegetation city of Sanibel.
Assessing the impacts of increasing of Sanibel Island, Lee County, Florida.
populations on the man-dominated systems Reprint from Rhodora, 57:682.

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