Tucson, Arizona, flood of October 1983

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CoaStal Zone
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INFORMATION CENTER

The Tucson, Arizona, Flood
of October 1983

Committee on Natural Disasters
Commission on Engineering and Technical Systems
National,Research Council

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The Tucson, Arizona, Flood
of October 1983

Prepared by:

Thomas F. Saarinen (Team Leader), Department of Geography, University of
Arizona, Tucson

Victor R. Baker, Department of Geosciences, University of Arizona, Tucson

Robert Durrenberger, Scottsdale, Arizona

Thomas Maddock, Jr., Tucson, Arizona

For:

Committee on Natural Disasters
Commission on Engineering and Technical Systems
National Research Council

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COASTAL SERVICES CENTER
2234 SOUTH HOBSON AVENUE
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@NATIONAL ACADEMY PRESS
@.'!Washington, D.C. 1984

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NOTICE: The Committee on Natural Disasters project, under which this
report was prepared, was approved by the Governing Board of the National
Research Council, whose members are drawn from the councils of the
National Academy of Sciences, the National Academy of Engineering, and
the Institute of Medicine. The members of the committee responsible for
the report were chosen for their special competences and with regard for
appropriate balance.
This report has been reviewed by a group other than the authors
according to procedures approved by a Report Review Committee consisting
of members of the National Academy of Sciences, the National Academy of
Engineering, and the Institute of Medicine.

The National Research Council was established by the National Academy of
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and the Institute of Medicine. The National Academy of Engineering and
the Institute of Medicine were established in 1964 and 1970, respec-
tively, under the charter of the National Academy of Sciences.

This study was supported by the National Science Foundation under Grant
No. CEE-8219358 to the National Academy of Sciences. Any opinions,
findings, and conclusions or recommendations expressed in this report
are the authors' and do not necessarily reflect the views of the
National Science Foundation, the National Research Council, or the
authors' organizations.

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COMMITTEE ON NATURAL DISASTERS (1983-84)

Chairman

JOHN F. KENNEDY, Institute of Hydraulic Research, University of Iowa,
Iowa City

Vice Chairman

KISHOR C. MEHTA, Institute for Disaster Research, Texas Tech University,
Lubbock

Immediate Past Chairman

ANIL K. CHOPRA, Department of Civil Engineering, University of
California, Berkeley

Members

ROBERT G. DEAN, Department of Coastal and Oceanographic Engineering,
University of Florida, Gainesville
JOSEPH G. GOLDEN, Environmental Research Labs--NOAA, Boulder, Colorado
PAUL C. JENNINGS, Division of Engineering and Applied Sciences,
California Institute of Technology, Pasadena
T. WILLIAM LAMBE, Consultant, Longboat Key, Florida
RICHARD D. MARSHALL, Structural Engineering Group, Center for Building
Technology, National Bureau of Standards, Washington, D.C.
JAMES K. MITCHELL, Department of Geography, Rutgers University, New
Brunswick, New Jersey
LESLIE E. ROBERTSON, Robertson, Fowler & Associates P.C., New York,
New York
THOMAS F. SAARINEN, Department of Geography, University of Arizona,
Tucson
METE A. SOZEN, University of Illinois, Urbana, Illinois
T. LESLIE YOUD, Research Civil Engineer, U.S. Geological Survey,
Menlo Park, California

iii

Staf f

0. ALLEN ISRAELSEN, Executive Secretary
STEVE OLSON, Consultant Editor
LALLY ANNE ANDERSON, Secretary
JOANN CURRY, Secretary

Liaison Representatives

JOHN GOLDBERG, Program Director, Design Research, Division of Civil and
Environmental Engineering, National Science Foundation, Washington,
D.C. (to September 30, 1983)

WILLIAM A. ANDERSON, Program Director, Societal Response Research,
Division of Civil and Environmental Engineering, National Science
Foundation, Washington, D.C. (from October 1, 1983)

ACKNOWLEDGMENTS

The team members wish to acknowledge the time and information freely
provided by the large number of people they interviewed. These
include: Ron Asta, Frank Bangs, Frank Barrios, Bob Berge, Julio L.
Betancourt, Leslie A. Bond, Fred Boner, Al Carillo, Dick Casanova,
Mustafa Chudnoff, Major Douglas, Rob Emmett, David Eloy, Grace Evans
Bob Gall, Alex Garcia, Margot Garcia, Michael Goodrich, Tom Helfrich,
Katie Hirschboek, H. W. Hjalmarson, Ronald Imes, Bobby Jennings, Claire
Jensen, Jerry Jones, John Jones, Jim Koch, Mary Ann Lambert, Bob Le
Fever, Larry Mann, Ed McCullough, Bill Mosher, Marie S. Pearthree, David
Radcliffe, Brian M. Reich, K. G. Renard, Sol Resnick, Priscilla Robin-
son, Rod Roeske, Hugh Sheenan, Suzanne Shields, David Smutzer, Barbara
Tellman, Bill Vasko, Mike Walsh, Randy Weber, Joann Webster, Allen
Whear, Benny Young, Michael E. Zeller, and Tom Zickus.
University of Arizona geosciences students who performed field and
aerial photo analysis of inundation, channel changes, and flood erosion
in relation to bank protection works were: R. Scott Anderson, Jeanne
T. Brooks, Carl F. Dickason, Julia E. Fonseca, Ellen K. Gill, Andrea
Handler-Ruiz, William M. Kos, Jeffrey A. Leenhouts, Sandra L. McIntire,
Bradford H. Miller, Debra J. Novet, Stephen A. Smith, Kathryn Steinzig,
and Marybeth Vogel.
Photographs were supplied by: Victor R. Baker, Peter Kresan, Tad
Nichols, Thomas F. Saarinen, the Arizona Daily Star, the Arizona
Historical Society, and the University of Arizona Special Collections.
A special thank you is due to tho.-,e who read and commented on all or
part of the manuscript: Julio L. Betancourt, Leslie A. Bond, Robert
Ingram, Paul Kangieser, Edward A. Keller, Jonathan G. Taylor, Barbara
Tellman, Raymond M. Turner, and Michael E. Zeller. James L. Sell served
as a research assistant and Helen M. Horley typed the manuscript.

CONTENTS

1. INTRODUCTION 1

2. THE METEOROLOGICAL EVENT AND THE WARNING PROCESS 3

The Storm of September 28-October 3, 1983 4
Was This "The Storm of the Century"? 10
The Warning Process 15
Recommendations 19

3. GEOMORPHOLOGY AND HYDROLOGY DRAINAGES IN THE TUCSON BASIN 22

Geomorphic History of Tucson Drainage Courses 24
Hydrologic Aspects of the 1983 Flood 31
An Overview of Flood Erosion and Deposition 34
An Assessment of Bank Protection 42
Sand and Gravel Operations 51
Stream Channel Stability in the Tucson Basin 53
Types of Damage to Property 58
Recommendations for Future Studies 6b

4. THE HUMAN RESPONSE TO THE OCTOBER 1983 FLOOD IN TUCSON 64

The Emergency Response to the Tucson Flood of October 1983 64
Public Perception of the Flood Hazard 65
Community Attitudes Toward Long-Term Planning 68
Piecemeal Planning in Floodplains 71
Future Prospects for Enlightened Floodplain Planning in Tucson 76

5. CONCLUSIONS 84

REFERENCES 86

vii

APPENDIX A: WEATHER MAPS FOR SEPTEMBER 28-OCTOBER 3, 1983 91

APPENDIX B: MAPS OF POSTFLOOD BANK
EROSION IN THE TUCSON BASIN 101

NATIONAL RESEARCH COUNCIL REPORTS
OF POSTDISASTER STUDIES 1964-1983 109

viii

INTRODUCTION

"The 100-year flood has come and gone, so, by all rights, Tuc-
sonans should enjoy another century of great Southwest weather."

--postflood message sent to
national media by Metropolitan
Tucson Convention and Visitor's
Bureau

"This is a desert?" asked an October 2, 1983, headline of the Arizona
Daily Star above pictures of lateral erosion caused by desert streams
with huge standing waves. The Santa Cruz River, which is generally dry
300 or more days per year, had only one of its 18 bridges open for
service on the morning of Monday, October 3. Along the Rillito, a
tributary of the Santa Cruz, hundreds of area residents watched on
Sunday, October 2, as the river gradually eroded 100 ft from its bank
through a parking lot and undermined an office building, which collapsed
into the widened stream. The water from the combined streams overflowed
its banks beyond the Tucson metropolitan area to flood acres of farmland
and force the evacuation of the entire community of Marana, which was
situated in the stream's delta. Early estimates of the costs of repair-
ing public bridges and major roadways in the Tucson area ranged from $54
to $100 million.
The tropical weather pattern responsible for this flooding also
caused major floods along the Gila River and two of its tributaries, the
San Francisco River and the San Pedro River. A few days earlier another
storm caused floods in Prescott, Arizona. Particularly hard-hit were
Clifton (a mining community along the San Francisco River already
beleaguered by a bitter labor strike), Marana and Rillito (downstream
from Tucson along the Santa Cruz), and several communities along the
Gila River from Winkelman to Kelvin (Federal Emergency Management
Agency, 1983). So widespread and severe were the floods in Arizona
south of the Mogollon Rim that some regard them as the worst disaster in
Arizona since it became a state in 1912.
There are many aspects of the Arizona floods of October 1983 worthy
of further investigation. Some examples are the sociological effects of
the flood on the tension-ridden community of Clifton, where strikers
accused the Governor of a greater readiness to use the National Guard to
control the strikers than to deal with the flood emergency; the special

problem of great distances hampering flood relief efforts in a state
where the flooded communities were widely separated from each other and
from the disaster assistance center in Phoenix; the almost total col-
lapse of the road system in southern Arizona, where one bridge served as
the last remaining link between Tucson and Phoenix; or the problems of
places like Marana where desert rivers debouch beyond their deeply
incised channels. We do not attempt to address all these potentially
interesting topics but instead focus on metropolitan Tucson and on what
we regard as the most unique aspects of the event: the flood behavior
of desert streams, and the implications of recent rapid urban growth and
development for dealing with the flood hazard.
Tucson provides an excellent site for studying the problems of rapid
urban growth in the desert. It is one of several cities in the Sunbelt
that have for the past four decades had a rate of growth well beyond the
national average. The rapid growth In the Sunbelt is often attributed,
as the name indicates, to the climatic amenities of the region. The
long-sustained rapid growth has also attracted many people who are
interested in the economic climate. Rapid growth creates many economic
opportunities. This is especially true in places like Arizona, where
the prevailing opinion is that the use of private land should be free
from government interference. Newcomers see Arizona as a promising
place to work under fewer of the planning constraints imposed in many
other areas.
A perennial problem in this desert area of rapid growth stems from.
the newcomers' unfamiliarity with local environmental constraints.
Images, ideas, and institutions from outside are applied, however
inappropriate they may be. A prime example is floodplain zoning, in
which many provisions were designed for streams in humid areas. On
desert valley floors, true floodplains with overbank flows are rare
while lateral erosion of arroyo banks is common (Committee on Natural
Disasters, 1982). Basic understanding of such facts and of their
implications for wise planning is not widespread among professional
engineers or the general public. In part this stems from the current
limits of scientific knowledge of desert streams; in part It is a
natural result of the large influx of newcomers unaware of desert
conditions; it also results from general attitudes that tend to favor
growth rather than planning.
For all of the reasons just mentioned, Tucson provides an exciting
locale for studying human adaptation to a desert site. FurthermoreV a
long, detailed, and continuous record of arroyo cutting on the Santa
Cruz is available. This record documents past floods and the tremendous
changes in the river's landscape since Tucson became part of the United
States with the Gadsden Purchase of 1854.
In the remainder of this report we discuss the Tucson flood from the
perspective of these themes. We try to answer the question of what
happens during a major flood in a desert area that has undergone rapid
urban growth. As we do so we try to point out scientific research ques-
tions or public policy issues that could be addressed by more detailed
research. Chapter 2 discusses the meteorological event and the warning
process, Chapter 3 discusses the geomorphology and hydrology of the
Tucson Basin., Chapter 4 examines the human response to the flood, and
Chapter 5 offers our conclusions.

THE METEOROLOGICAL EVENT AND THE WARNING PROCESS

Episodes of heavy rainfall over extensive parts of northwestern Mexico
and the southwestern United States occur nearly every year in late
summer and early fall. The location of areas receiving maximum precip-
itation from the storms varies from one storm period to the next and
depends on the meteorological conditions prevailing at the time of the
event. Storms that produce the largest amounts of precipitation occur
when ocean temperatures in the southeastern part of the Pacific Ocean
are high, when moist air associated with the remnants of a tropical
cyclone in that region is drawn across Mexico into the American South-
west, and when this air then interacts with a significant frontal system
associated with an upper-level cold trough or low over the region.
This "tropical connection" has been examined by a number of scien-
tists, notably Douglas (1972), Pyke (1975), and Court (1980). They have
identified the significant events in the precipitation history of the
Southwest attributable to tropical storms. Their work has been analyzed
and amplified by Hansen and Schwarz (1981), who have established the
conditions under which a hypothetical storm would produce maximum con-
centrations of precipitation in Arizona. They suggest that the ideal
conditions are:

1. Antecedent synoptic-scale weather features that permit the
accumulation and transport of significant moisture into the Southwest
well ahead of a tropical cyclone circulation. This moisture is neces-
sary for the rainfall to be of long duration. The August 1951 storm
that gave the greatest long-duration rainfall of record had such an
antecedent weather feature. This feature allows for substantial rain-
fall prior to that associated with the hypothesized tropical cyclone
circulation.
2. The southward development of a midlatitude cold trough aloft to
help accelerate the storm as it turns northward or north-northeastward
and crosses Baja California's coast and mountainous backbone at its
lowest elevation (near 290N latitude). The accelerated speed de-
creases the time the storm spends over land and therefore minimizes loss
of intensity. In the optimum case the tropical cyclone should regain
some of its intensity as it moves over the small area of warmer waters
in the northern portion of the Gulf of California.

3. Maximum or near maximum sea surface temperature (SST) off the
west coast of Baja California. This permits an offshore tropical
cyclone to remain fully developed farther north than under normal SST
conditions. This apparently was the case with the September 24-26,
1939, storm. Tropical storm Joanne in October 1972 was also fed by
above-normal SST.
4. A well-formed tropical cyclone gaining intensity well south of
Baja California and moving slowly northwest or northward so as to permit
the optimum realization of the antecedent tropical cyclone rainfall.
5. A tropical cyclone track that, after reaching the latitude of
Baja California, parallels the coast at just the right distance offshore
so that, in addition to having a good supply of energy from Pacific
Ocean waters, the outer fringes of the massive storm circulation draw
from the very warm waters of the Gulf of California.
6. Entrance into southwestern Arizona with a circulation of great
strength, after which the remnant storm interacts with a significant
midlatitude frontal system associated with an extremely cold trough or
low pressure aloft, as occurred in the disastrous storm of September
1970.

The list of conditions established by Hansen and Schwarz was derived
by examining a large number of episodes of heavy rainfall that had
tropical origins and were associated with the remnants of tropical
storms that hit the American Southwest. Table 1 lists some of the most
significant tropical cyclones that have produced moisture in the area.

THE STORM OF SEPTEMBER 28-OCTOBER 3, 1983

The August before the storm of September 28-October 3, 1983, had been a
very wet month; so had September. In fact, it had rained almost every
other day at many climatological stations in Arizona. This, in the
normally dry fall season, was unusual. On September 28 the surface
weather map exhibited few unusual features. A thermal low lay over the
head of the Gulf of California, and the tail end of a weak cold front
appeared across the Great Basin to the north. (Weather maps may be
found in Appendix A.)
At the 500-mb level, however, an immense trough elongated in a
southwesterly to northeasterly direction had developed, bringing
tropical moisture into the area. At the same time, a tropical storm,
Octave, was gaining strength off the tip of Baja California. Winds at
virtually all levels above the surface were from the south to south-
west. Isobars at the 500-mb level trended in the same direction. The
National Weather Service (NWS) Forecast Office in Phoenix noted this and
forecast the renewal of summer monsoon-type showery weather.
Precipitation in Tucson began innocently enough at 5:00 p.m. on
Wednesday, September 28. Off and on until midnight, 0.07 in. of rain
fell. The rain then ceased until noon on September 29, when a shower
occurred. Rain then persisted until noon on September 30. The first
flash flood warning of the period was issued by the Tucson NWS Office on
September 29 for the period between 5:40 p.m. and 8:00 p.m. At 10:20

TABIE 1 Selected Storms that Have Affected the American Southwest

Tropical
Date Storm Affected Area

Sept. 24-26, 1939 Arizona/California/Nevada
Aug. 26-29, 1951 Charlie Northwest Mexico/California/Arizona
Aug. 17-19, 1960 Diana Baia California/Sonora
Sept. 15-19, 1963 Katherine Southern California
Sept. 23-26, 1965 Hazel Northwest Mexico
Aug. 29-Sept. 2, 1967 Katrina Southeast California/Southwest Arizona
Sept. 7-14, 1969 Glenda Central Arizona
Sept. 4-6, 1970 Norma Central Arizona
Aug. 27-Sept. 6, 1972 Hyacinth Southern California/Arizona
Sept. 30-Oct. 6, 1972 Joanne Southern, central, and eastern Arizona
Sept. 6-10, 1976 Kathleen Southern California/Arizona
Aug. 11-15, 1977 Doreen NW Mexico/California/Arizona
Oct. 6-11, 1977 Heather Mexico/Arizona
Sept. 28-Oct. 3, 1983 Octave Mexico/Arizona

p.m. a weather statement was issued indicating decreased rainfall and
thunderstorm activity. Furthermore, it added:

The Santa Cruz River is quite high--and persons living near
the river should be cautious--as there may still be localized
flooding of the lower banked areas . . . . Light to moderate
rain is still falling over eastern Pima County--and dips and
washes may still have some running water for the next few
hours. Motorists in the affected areas should continue to use
caution in eastern Pima County.

By Friday afternoon there were clues appearing that more heavy
precipitation was due. Moisture, in the form of clouds, could be seen
streaming northward from tropical storm Octave (Figure 1), and meteo-
rologists at the Phoenix NWS Office marked the location of several
embedded, precipitation-enhancing short waves rotating around the major
upper-level trough (Figure 2). As a consequence, the hydrologists with
the Joint Federal-State Flood Warning Office issued a statement:

Heavy rainfall during the past few days has caused signifi-
cant rises along many rivers and streams throughout the eastern
two thirds of Arizona.
Although no mainstream flooding has been reported, the
San Francisco River near Clifton remains near bankfull and
lowland overflow has been reported along the Santa Cruz River
near Marana today. Significant flows have also been reported

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FIGURE 1 Moisture from tropical storm Octave, located off the
west coast of Baja California, may be observed in the band of
clouds extending across northwest Mexico, Arizona, and New
Mexico. This photograph was taken at 6:15 p.m. GMT on October
2, 1983.

along portions of the Verde River and its tributaries and along
Tonto Creek.
The rains have saturated the ground and filled most streams
and rivers . . . . Any additional rainfall will run off rather
rapidly and could cause increased or renewed rises.

Thus, when it began raining shortly after midnight on Saturday,
October 1, the Phoenix NWS Office issued a flash flood watch for all
parts of central and southern Arizona and, in particular, south- and
west-facing mountain slopes. It said:

Many areas of central and southern Arizona have received from
2 to 4 inches or more of rainfall since Wednesday, September 28
. . . with lesser amounts elsewhere. The ground has now become

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FIGURE 2 National Weather Service 500-mb analysis for Friday
evening, September 30, 1983. Embedded short waves are shown by
dashed lines.

saturated in a large portion of the state. As a result . . .
additional rainfall in these areas now has a very high risk of
running off almost immediately.
Satellite photos during the predawn hours show heavy amounts
of moisture approaching Arizona from both the west and south.
Very strong southwesterly winds in the upper atmosphere will
cause this moist air to impinge upon the central mountains
and force the air to release its moisture. As a result
the potential for heavy rains exist for these south- and
west-facing slopes of the central mountains . . . as well as
those remaining portions of Arizona south and west of the
central mountains.
Persons in the watch area, particularly motorists
and those in known flood-prone areas or in areas which have
flooded recently. . . . should use extreme caution today. Check
preparedness requirements and be ready to move to higher ground

immediately if threatening clouds approach or if water levels in
your area begin to rise.
Motorists should not attempt to cross flooded roadways
. as water depths and currents are frequently misjudged.

The heaviest precipitation associated with the storm occurred
shortly thereafter and was reported by personnel at the Tucson NWS
Office. Their comments appear below:

At 9:10 a.m. MST Tucson local radar is showing a heavy shower
activity throughout eastern Pima, - - . northern Santa Cruz, and
northwestern Cochise counties. Most of Pinal County is also
affected. An inch and a quarter of rain has fallen at the
airport here in Tucson in the last two hours and there have been
numerous reports of one and a half inches or more throughout the
city and outlying areas.
All rivers, . . . washes, dips, and other low-lying
areas are reported running full. Motorists and persons in af-
fected areas are advised to take extreme caution and not enter
any flooded areas.

Heavy rains continued over much of Arizona during the morning.
Rates of over 1/2 in./h were reported from a number of sites in the
southeastern part of the state. By noon the Tucson NWS Office could
report a lessening of precipitation, but flooding was widely reported in
the metropolitan area.
The 2:50 p.m. statement from the Phoenix NWS Office on Saturday
afternoon did not give much hope for relief. It read:

[There is a] flash flood watch for south-central and
southeast Arizona until 5 a.m. MST. . . . The watch area
includes Pima, Pinal, - . . Santa Cruz, . . - Cochise,
. . . Maricopa, Southern Yavapai, Gila,
Graham, and Greenlee counties.
A steady stream of subtropical moisture is moving into
Arizona from the south. This will continue to bring numerous
and locally heavy showers over all but the far west portions of
the state. For tonight the areas most vulnerable to heavy rain
are the central and east-central mountains southward.
Heavy rains have continued to fall in the Tucson area through
early afternoon. Satellite pictures indicate that much of Pima,
. . . Pinal, and Graham counties are continuing to get heavy
showers.
A flash flood watch means flash flooding is possible.
Motorists should stay out of flooded stream crossings and
highway dips and avoid narrow . . . steep-walled canyons.
Heavy rains of the past few days and again today have already
brought considerable flooding problems. All persons with
property subject to flash flooding should take immediate action
for protection if possible.

During Saturday evening, continued runoff and the possibility of
additional precipitation brought this flood statement from the Joint
Federal-State Flood Warning Office:

Continuing rains during the past several days and especially
today have caused significant rises throughout the Santa Cruz
Basin and its tributaries. Water levels throughout the river
are extremely high with lowland overflows occurring in the
Continental and Marana areas.
Riverbottom road crossings throughout the Tucson area are
closed because of the high water. Possible additional rains
could cause further increases in river level or renewed rises
with some additional overflow.
Persons located near the river should remain alert to current
conditions and the possibility of the sudden increases in river
levels through Sunday.

The air flowing across Arizona continued to be warm and unstable,
and satellite pictures and radar echoes continued to show large thun-
derstorms over northwestern Mexico. At 9:50 p.m. local radar showed
mostly light showers in the Tucson metropolitan area moving toward the
northeast. However, at 1:25 a.m. on October 2 the radar picked up a
line of showers that extended from Redrock, north of Tucson, to a point
just west of Sasabe. These cloud cells were moving toward Tucson at
about 20 mph and were forecast to reach the area around 3:00 a.m.
Satellite photographs had shown them to be increasing in intensity.

Local inflow from very heavy and persistent showers and
thunderstorms in the Tucson area has also dramatically increased
the flow in the Santa Cruz River. The flow in the river has
increased between Continental and Tucson. This flow is still
far short of that which is needed to cause the river to leave
its channel at Tucson. However, . . . local inflow into the
Santa Cruz in the Tucson area from these heavy showers and
thunder-storms has caused a sharp rise in the river. While the
river is still well within its channel, . . . heavy lateral
erosion of the river banks has . . . and will continue to.take
place through at least 9 a.m. this Sunday morning. Those
persons affected by this erosion should move to a place of
safety immediately.

At the same time, numerous law enforcement agencies were indicating
that all dips, washes, rivers, and low-lying areas in the Tucson metro-
politan area were full of water. The Rillito at North Country Club Road
was overflowing its banks, and there was water in the surrounding
streets. Considerable lowland flooding had occurred near Marana and
northward along the Santa Cruz. The overflow of the Santa Cruz at
Continental continued.
However, the worst of the heavy precipitation was over. Spor-
adic showers continued in the Tucson area through noon on October 3.

However, continued runoff on major watersheds contributed to severe
flooding at Clifton on the San Francisco River, at Safford and Duncan on
the Gila River, and on the San Pedro and Santa Cruz rivers. Most of
these streams crested before noon on the third, but additional
precipitation could have caused additional problems.
By 6:30 p.m. on October 3, showers and thunderstorms in the affected
area had decreased markedly. The Phoenix NWS Office issued a flash
flood statement that canceled the flash flood watch still in effect.
The storm was over--the task of recovery had begun.

WAS THIS "THE STORM OF THE CENTURY"?

Suggestions that Tucson has seen its 100-year storm and need not worry
about another one for another century are simplistic and false. Even if
it were a 100-year storm, there would still be a one percent chance of
another next year or any other year. A review of the probable maximum
precipitation (PMP) conditions given above reveals that one ingredient
in the maximum storm event was missing. Tropical hurricane Octave, like
Norma in 1970, expired quietly at sea and did not penetrate Arizona.
However, the copious and continuous precipitation associated with this
particular event may be attributed to the presence of the other factors
listed in the first part of this section. Ocean temperatures off the
west coast of Mexico were above normal (Figure 3), and an elongated
upper-level trough that penetrated to the tropics brought warm, moist,
unstable air into the region. Also, cold air had been advected into the
region on the back side of the trough.
The significant and unusual features of this storm period were the
amounts of precipitation that occurred prior to September 28 and the
duration of the precipitation in the five days that followed. August
and September had been extremely wet over much of the central and
eastern part of the state. September was the wettest September of
record at a number of locations in Arizona. Then, once it began to rain
on September 28, there were only brief respites from precipitation in
the days that followed. At the Tucson NWS Office there were 26 dif-
ferent hourly observations in which precipitation was reported on
September 28, 29, and 30. After the rain began again between 1:00 and
2:00 a.m. on October 1, it lasted for almost 42 hours with brief pauses
between showers (Figure 4). Most of the severe flooding was associated
with the persistent rains in the morning hours of October I and October
2. But, in comparison to precipitation from a large August thunder-
storm, the amounts were small (Table 2), and the return periods for time
durations of less than three hours were three years or less (Figure 5).
However, the rain that began falling shortly after 6:00 a.m. in
western Tucson on October I culminated in a heavy shower of 0.78 in.
between 3:00 a.m. and 4:00 a.m. on October 2, bringing a 24-hour total
of 3.58 in. Values derived by Paul Kangieser, former State Climatolo-
gist for the National Weather Service, from the Precipitation-Frequency
Atlas of the Western United States (National Weather Service, 1973),

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4ON Y 40N

Vpj@:i

30N 30N

ZOM %Wm .0 ZON
lr.

i ON C 1ON

0
'f--I ' * I * * * ' ' * ' -) -, 0
. . . . . . . . . . . . . . . . . . .
C . . . . . . . .

1OS
1OS

20S 20S

. . . . . . . . . . . .
30S
30S

170W 16OW 150W 140W 130W 12OW 11OW 10OW 90W BOW 70W

FIGURE 3 Mean sea surface temperature anomalies for September
1983. Note the pool of warm ocean water off the coast of Baja
California where tropical storm Octave formed. The monthly
anomaly is the difference between the monthly mean sea surface
temperature and the climatological monthly mean value. Shading
shows where the monthly mean is colder than climatology. The
contour line interval is 0.50. Source: Oceanographic Monthly
Summary, 1983.

12
1.2 6.71 6

.5 1.0 z
z
Q

4 F-
0.8

Uj
0.6 3 cL

Cr
:D 0.4 2
0

0
0.2 1

0 9/28 9 1 9/ 10/1 10/2 10/

DATE
FIGURE 4 Precipitation at the Tucson NWS Office between Sept-
ember 28 and October 3, 1983. Bars show hourly totals; the
solid line shows cumulative totals.

TABLE 2 Maximum Precipitation at Tucson from the
Storm of September 28-October 3, 1983

Precipi- Date at Time at
Period tation (in.) End End

5min 0.27 Oct. 2 3:20 a.m.
10 min 0.40 Oct. 2 3:22 a.m.
15 min 0.42 Oct. 2 3:22 a.m.
20 min 0.44 Oct. 2 3:22 a.m.
30 min 0.65 Oct. 2 3:22 a.m.
45 min 0.69 Oct. 2 3:22 a.m.
60 min 0.77 Oct. 2 4:01 a.m.
80 min 0.83 Oct. 2 4:16 a.m.
100 min 0.99 Oct. 1 8:55 a.m.
6129

120 min 1.23 Oct. 1 9:15 a.m.
150 min 1.32 Oct. 1 9:45 a.m.
180 min 1.37 Oct. 1 10:15 a.m.
6h 2.04 Oct. 1 12:00 p.m.
12 h 2.45 Oct. 1 3:00 p.m.
29 h 3.58 Oct. 2 4:00 a.m.

HOURS
0.5 1 2 3 6 12 24
10

N.
C X
0.7-

z
0 0.5-

t: 0.3-

0.2- 100
W
at 50
IL 25 0
10 Cr
W
0.1- 5
2 Z
0.07-

0.05- W
0.021

FIGURE 5 Rainfall intensity-frequency distributions at the Tuc-
son NWS Office.

appear as Table 3. It can be seen from the table that precipitation
occurring during the period of greatest intensity did not exceed values
for a 25-year return period at the weather station located at Tucson
International Airport.
There have been a number of differences of opinion as to the inten-
sity of this storm. If one adopts techniques other than those used by
Kangieser, including the Pearson III distribution, a return period of
nearly 50 years can be derived. However, Kangieser argues that the
Pearson III distribution overestimates return periods for rainfall
durations longer than 6 hours. A more accurate estimate, he contends,
can be made using smoothed regional values of the kind found in the
Precipitation-Frequency Atlas of the Western United States (P. Kan-
gieser, personal communication, 1983). F-i-gure 6 compares return periods
calculated on the basis of these two techniques.

TABLE 3 Estimated Return Periods for Precipitation
in Tucson

Return Period (yr)
Duration 1 2 5 10 25 50 100

5min 0.27 0.34 0.44 0.50 0.61 0.68 0.77
10 min 0.41 0.52 0.68 0.78 0.94 1.06 1.19
15 min 0.53 0.66 0.86 0.99 1.19 1.34 1.50
30 min 0.73 0.92 1.19 1.37 1.65 1.86 2.09
1h 0.92 1.16 1.50 1.73 2.09 2.35 2.64
2h 0.95 1.28 1.67 1.94 2.35 2.64 2.96
3h 1.06 1.35 1.78 2.08 2.52 2.84 3.18
6h 1.17 1.50 2.00 2.34 2.84 3.21 3.59
12h 1.26 1.65 2.24 2.62 3.19 3.62 4.06
24h 1.37 1.81 2.48 2.92 3.55 4.05 4.54

RETURN PERIOD (YEARS)
1.01 1.1 1.5 2 5 10 25 50 100 200 500 1000
I I I I i I I I I T
-FISHER-TIPPETT TYPE I ez?@ HR
(BASED ON NOAA ATLAS 2 DATA)

-GOODRIDGE ANALYSIS
4- (BASED ON PEARSON TYPE M) 24 HR 6 HR

3 - 0
1 HR

z
2

I-

0
1.0 18 5'0 80 90 96 98 99 99.5 99.9
PROBABILITY M

FIGURE 6 Return periods calculated on the basis of a Pearson
III distribution and data from the Precipitation-Frequency Atlas
of the Western United States (NOAA Atlas 2).

But how unusual was the meteorological event itself? On September
23, just prior to this episode in Sonora and eastern Arizona, the area
around Prescott in central Arizona was drenched with rainfall from a
tropical air mass. Shortly after October 3 another tropical storm
entered the coast of western Mexico, and moisture from the storm con-
tributed to flooding in Mexico and Texas. Some of the other periods
when surges of tropical air from the eastern Pacific Ocean affected
northwestern Mexico and the southwestern United States were listed in
Table 1.
One of the largest and most severe storms with a tropical connection
was the Labor Day Storm of 1970, which is generally used as a model of
what can happen in Arizona. The isobyetal map for this storm appears in
Figure 7. As can be seen, the areal extent of this storm and the
amounts of precipitation dropped on the state were comparable to the
present event. Intensities during the 1970 storm were higher, and the
meteorological conditions were somewhat different, but the results were
similar, although the area affected was farther north and west.
However, not too many of these persistent tropical surges have
passed over the Tucson area and into the White Mountain region to the
northeast. In this case, the flow of air at all levels directed a
stream of moisture from off the coast of Baja California toward the
northeast. It was the persistence of this flow that was unusual and not
the intensity of the precipitation associated with any particular part
of it. Much of the precipitation was orographic in nature. Maximum
amounts occurred on the south and west slopes of the mountains, and the
highest values were recorded at high elevations. Mount Lemmon reported
over 10 in.; Blue, farther northeast, in the White Mountains, nearly 11
in. The location of the stream of moist air can be seen by looking at
the map of total storm precipitation (Figure 8) and by examining the
500-mb charts in Appendix A.
Thus, although Tucson did not experience its "storm of the century"
during September and October of 1983, it is possible that a future surge
of tropical moisture across this area will cause such an event for the
Tucson metropolitan region. Given the consequences of the 1983 storm,
the result will be devastating.

THE WARNING PROCESS

The process of providing the public with timely warnings of impending
weather-related disasters involves a number of groups that need to work
in unity at the time of the event. To do so effectively requires work-
ing and planning together prior to the event. Lack of an adequate ob-
servational network, lack of adequate communication facilities, limited
cooperation amofig agencies charged with serving the public, and a lack
of understanding among governmental officials about the nature of dis-
asters and about the available warning systems often result in a poor
set of responses when an emergency situation exists. The situation In
Pima County in early October 1983 was no exception.
During any major flood event, hydrologists and meteorologists need
timely reports of precipitation and runoff. During the Tucson flood the

FLAGSTAFF

4
41
PRESCOT T
% 5 6 _4 if.
P
ON
11 YS'
0
a to.. a-
b S@6 RIO 134*
4 a 11.4

10
4 a
RIVE

4
5 GLOBE

It, RIVE

1P 6

0
@IJCSON
8.1 32*

12*

III, Ito*

SCALE
MILES 2P ? 25 50 75
KM 2p- 9 25 50 75

FIGURE 7 Rainfall in southern and central Arizona from the La-
bor Day Storm of September 4-6, 1970, in inches.

DARDC (Device for Automatic Remote Data Collection) Network of rainfall
reporting stations worked reasonably well when queried locally by the
Phoenix NWS Office's NOVA 4 computer. However, reports from the same
network, when queried by the national Central Area DARDC Automated
System (CADAS) failed to respond. Thus the only other precipitation
data available to weather forecasters and hydrologists during the storm
period were the routine morning and late afternoon reports from regu-
larly reporting climatological substations and other agencies. Col-
lection of reports from these stations and others was hampered in some

L TAFF

Ok,,RAO@
35*

RESCOTT

PAYSON 40"
6
'944f 30

S I L
RIVER 9 10-

GLOBE
PHO Nix

RIVER

6 33

32*
113* 0 4
/C

112* 9.T2

110*

SCALE
MILES 2 9 25 50 175
25 0 25 so 7@5
KM _ .

FIGURE 8 Rainfall in Arizona from the storm of September 28-
October 3, 1983, in inches.

instances by telephone outages. However, in Tucson the local network of
cooperating observers provided valuable information to the Tucson NWS
Office.
The system to acquire real-time hydrologic data did not function
effectively during the storm period. All stations in the network report
at OOZ and every three hours thereafter via satellite to the downlinks
at NOAA's Wallops Island facility in Virginia and at the Salt River
Project office in Phoenix. Additionally, the stations report every 15
minutes to the Salt River Project after certain specific criteria are

met. During the critical period of the storm on October 1, the Salt
River Project downlink was out of service from 7:00 a.m. to about 8:30
p.m. due to computer problems. Valuable data were lost and not avail-
able to hydrologists concerned with problems of river flooding.
In addition to problems of acquiring data and information on precip-
itation and flood flows, there existed problems of communication and
understanding. In evaluating their performance during the emergency,
officials of Pima County admitted that their efforts could not be given
superior grades but blamed part of the problem on inconsistent state-
ments from the National Weather Service. As can be seen from the
excerpts in the preceding text, this "passing of blame" was unjusti-
fied. From 6:00 p.m. on September 29 until midnight on October 5, the
Tucson NWS Office issued 20 warnings and statements, of which 13 were
radar-generated updates. In the same period the Phoenix NWS Office
issued 28 warnings, watches, and statements, of which nine were flood
warnings generated by the Joint Federal-State Flood Warning Office.
Weather statements and radar updates reflect observed conditions and
vary with those conditions. Watches and warnings are subjective evalua-
tions of meteorologic and hydrologic conditions occurring during the
event. The consistency of such issuances depends on the available data
and on the timing of their release. Use of weather watches and warnings
by the public and by public officials requires that they understand them
and that they understand reasons for what seem to be inconsistent state-
ments and warnings.
All statements and forecasts of the National Weather Service are
transmitted to users by the NOAA Weather Wire and by NAWAS (the National
Warning System). The former is a statewide hardcopy teletype system to
users. At the time of the Tucson storm, it included only three of five
TV stations and none of the radio stations in the Tucson area. However,
the Weather Wire was relayed to the two Tucson newspapers (the Tucson
Citizen and the Arizona Daily_Star) by the press-wire facilities of the
Phoenix offices of the Associated Press and United Press International
(incidentally, these organizations relay such issuances to subscribers
of their radio services). The NAWAS voice transmissions went to all
sheriffs' offices and other public safety agencies in the state. Thus
the amount of information transmitted appears to have been sufficient
for the public and the officials appointed and elected to care for their
safety to have been well aware of the scope and extent of the disaster.
There is a national program to provide warning of impending dis-
asters--the Emergency Broadcast System (EBS). However, activating this
system was not possible because no primary EBS station had been desig-
nated in the Tucson metropolitan area and the only radio station that
had volunteered to fill this gap was not on the Weather Wire and so did
not receive EBS activation requests. Although several flood warnings
from the Phoenix NWS Office were headlined EBS REQUESTED, they were not
implemented. The Pima County Emergency Services Director was quoted in
Tucson's Arizona Daily Star of October 12, 1983, as saying, "We just
didn't see the need for activating the EBS system."
NOAA Weather Radio provided the best source of information about the
progress of the storm to the agencies in the Tucson area that used it to

monitor the weather conditions affecting their operations. According to
Dave Williams in Tucson's Arizona Daily Star of October 7, 1983, "On
Saturday, the best electronic sources of information about the flooding
were the NOAA weather broadcasts."
Although the forecasts issued by the National Weather Service in
Tucson during this storm episode were accurate and timely, problems did
occur within the agency. Once the storm was in progress, many of the
systems and networks used to measure precipitation and runoff malfunc-
tioned, making it impossible to have a clear picture of the series of
events that occurred during the storm. In addition, it is difficult for
a National Weather Service Office such as that at Tucson, which had only
one or two individuals answering the phones, making observations, and
handling other station duties, to respond to all of the demands placed
on it during an emergency period. Reasons for this are not entirely
clear, but some of the problems clearly relate to a lack of manpower.
In addition, there evidently were no policies on the retention and
analysis of data during and after the storm. In the past it has been
customary for both the Corps of Engineers and the National Weather
Service to investigate weather events of this magnitude. Only the
Bureau of Reclamation Flood Office out of the Denver Federal Center was
critically interested and involved in meteorological analysis of this
storm episode.
As the events associated with this storm and flood show, the
responsibility for particular kinds of analysis of events during and
after weather-related disasters needs to be clearly defined. Lack of
understanding of interagency responsibilities is a continuing problem.
For example, at 4:30 p.m. on Monday, October 3, the Phoenix NWS Office
stated, "The [San Carlos] reservoir is expected to begin spilling later
Tuesday afternoon." In fact, spilling began about 1:30 p.m. that Tues-
day. However, officials of the Arizona State Division of Emergency Ser-
vices said in a press release issued Monday evening that they expected
San Carlos to spill about midnight that night based on estimates of the
State Department of Water Resources. When questioned about this dif-
ference of opinion, State Emergency Services personnel said that because
people would have to be evacuated, they preferred to take the sooner
rather than the later time--a difference of about 18 hours!
It would seem that these two forecasts (the former official and the
latter not official) did not lend credence to public releases.

RECOMMENDATIONS

Additional efforts are needed to coordinate the work of the various
agencies involved with disasters before, during, and after the events.
Both state and federal agencies charged with coordinating the acquisi-
tion and analysis of meteorological and hydrological data must exert
stronger leadership to ensure cooperation of all existing agencies
within the affected areas. Some other topics that need attention are
listed below.

1. Safeguardi g Flood Data and Information

If the Federal Emergency Management Agency is to continue to be the lead
agency in disaster mitigation efforts, there needs to be a clearer
statement of the duties and responsibilities of NWS personnel during and
after severe weather events so that the National Weather Service's
contribution to the.analysis of events can be clearly defined. During
an event, efforts should be made to acquire and retain all data and
information essential to understanding and analyzing it. These mater-
ials should be retained until needed by hazard investigators. The
originals could be kept by the cognizant NWS office for a specified
period of time, such as five years, after which they should be appro-
priately archived.

2. Investigation of Meteorological Conditions

Each major severe meteorological event should be investigated thoroughly
by the cognizant local forecast office of the National Weather Service.
These investigators should be assisted by such additional experts as are
needed from the regional forecast offices. This analysis should be the
basis for reports used by other local and federal agencies. It is an
inefficient use of tax dollars to have each event handled on an ad hoc
basis, with many federal agencies conducting an analysis of the meteoro-
logical conditions contributing to a natural disaster.

3. Issuance of Disaster Warnings

If the disaster or potential disaster is related to weather., then the
National Weather Service should have sole responsibility for issuance of
watches, warnings, and statements about existing and expected conditions
to the public. This is true even in gray areas such as the collapse of
dams weakened by rains or overtopping of dams because of excessive river
flow.

4. Acquisition of Meteorological Data During Events

Local offices of the National Weather Service should encourage coopera-
tive observers to report more faithfully on weather conditions during
severe storm events. Also, ways need to be found to ensure redundancy
in automatic systems so that data can be obtained under inclement
weather conditions.

5. Communication of Warnings to the Public

Although NOAA Weather Radio appeared to operate effectively during the
Tucson flood episode, too few people are aware of this service. During
severe weather episodes it is essential that all electronic media make

full use of all available information. Local radio stations could, for
example, retransmit NOAA Weather Radio broadcasts. Additionally, local
television stations, staffed with professional meteorologists, could
rebroadcast NWS radar pictures and explain them to the public at the
same time that they are presenting verbatim the latest NWS advisories on
the air.

6. The Tropical Connection

Episodes of extensive, heavy precipitation have their origins south of
the U.S.-Mexico border. To give American citizens adequate warning of
these events, better cooperative programs should be developed with the
states of northwestern Mexico to monitor and record weather events. Two
specific suggestions are (1) the extension of the Automatic Hydrologic
Observation System (AHOS) managed by the U.S. Geological Survey and (2)
the establishment of a cooperative surface observation program with the
state of Sonora or the government of Mexico so that severe storms may be
monitored on their way across Sonora.

7. Cooperation Among Local, State, and Federal Agencies

During a major weather-related disaster, officials charged with public
safety and emergency services should have coordination representatives
of their agencies at the local offices of the National Weather Service.
These representatives should be trained and knowledgeable in the opera-
tions of the National Weather Service and understand the significance
and degree of reliability of the various forecasts issued by the local
forecast office. They should be able to translate the various issuances
of the National Weather Service into statements about the potential
impact of severe weather events on their operations.

GEOMORPHOLOGY AND HYDROLOGY DRAINAGES IN THE TUCSON BASIN

Tucson is located in a topographic basin bounded by the Santa Catalina
and Tortolita Mountains to the north, the Rincon Mountains to the east,
the Santa Rita Mountains to the south, and the Tucson Mountains to the
west (Figure 9). The principal watercourses in this basin collect
drainage from and flow between these ranges. Like many desert mountain
masses, those near Tucson have broad piedmont surfaces extending at
fairly uniform slopes of 10 to 30 m/km away from much steeper mountain
fronts. These piedmont surfaces may be erosional bedrock surfaces,
called pediments, or they may be mantled by fan gravels and dissected by
deep washes. The ephemeral streams of the piedmont areas convey water
and sediment from the mountain fronts to the valley floors in the basin
during occasional rainstorms. Coarser gravel and boulders are deposited
mainly on the piedmont, while the finer fraction of the load, including
sand, silt, and clay, are conveyed to the valley floors.
The Santa Cruz River begins in the San Raphael Valley along the
border with Mexico. The river flows south into Sonora and turns
abruptly west and north to reenter the United States east of Nogales.
The channel extends northward through Tubac and Green Valley to reach
the downtown portion of Tucson. Through much of Tucson the Santa Cruz
is deeply entrenched into the sediments of the valley floor. The Santa
Cruz drains about 5,800 km2 to the south of Tucson, including large
piedmont surfaces extending from mountains on the east and west sides of
its valley. Sediments transported to Tucson are mostly fine sand and
silt.
Northwest of downtown Tucson the Santa Cruz River is joined by the
Rillito system, which drains about 2,400 km2 to the north and east of
Tucson. The Rillito flows about 20 km along the northern boundary of
the city at the base of an extensive piedmont extending from the Cata-
lina Mountains. In northeast Tucson the Rillito is split into two major
tributaries, Tanque Verde Creek and Pantano Wash (Figure 10). Pantano
Wash collects drainage from extensive areas to the southeast and tra-
verses a long section of basin floor. Because of its length, sediment
sizes become relatively fine where Pantano Wash reaches Tucson. In
contrast, Tanque Verde Creek transports a relatively coarse load from
the nearby Santa Catalina and Rincon Mountains. The coarse sand of
Tanque Verde Creek mixes with the finer Pantano sediments to give the

MARANA TORTOLITA
/0 MTNS SANTA CATALINA MTNS

Z ORTARO

INA RD

CW ro

UE ROE
SPEEDWAY BLV'D\
TUCSON'l
MTNS

RINCON MTNS

SAN XAVIER MISSIONO '@'M, RTINEZ HILL

SIERRITA SANTA
MTNS RITA
GREEN Z' MTNS
VALLEY
*CONTINENTAL

/110

N
Ce,
100
RhjEo?

SCALE 0
0
MILES PHO NIX kt
SP'LT 0
5 10 25
15 20 R
KILOMETERS GILA

TUCSO

NOGALES
FIGURE 9 Index map of the Tucson Basin showing the principal
watercourses, mountain ranges, and transportation routes.
L4'VQUEVCROE

'W"
A
-A
g, T
'yt x4i'
"A "f
T@'
e, 2 A @i

FIGURE 10 Aerial view of the eastern Tucson Basin on October 9,
1983, showing Pantano Wash in the foreground and the Santa Cata-
lina Mountains on the skyline. Flood damage to the Rincon Coun-
try mobile home development (bottom center) is shown in Figures
26 and 38. Photograph by Peter Kresan.

Rillito an intermediately coarse sand load, which is then conveyed to
the Santa Cruz River, which transports fine sediments. These sediment
load characteristics play an important role in the adjustment of the
different streams to changing flow conditions.
About 2 km north of the confluence of the Rillito, the Santa Cruz is
joined by the Canada del Oro. This stream drains about 660 km2 from
the western slopes of the Santa Catalina Mountains and eastern slope of
the Tortolita Mountains.

GEOMORPHIC HISTORY OF TUCSON DRAINAGE COURSES

Floods are usually defined by the damage they do. The flow of water in
a stream channel, as studied by hydrologists, is not considered a flood
unless it rises sufficiently to cause damage and disruption. In gen-

eral, flood hazard management emphasizes the economic consequences of
rising water levels.
Another view of floods emphasizes their association with the river,
the valley, and the valley lands adjacent to the river. This geologic
perspective on floods (Moss et al., 1978) is not often incorporated into
flood hazard management. In the humid temperate portions of the United
States, river channels generally occur within a bottomland surface that
is created by the river itself. The river occasionally overtops its
banks, carrying and depositing sediment on that surface. This surface
is the geologic floodplain of the river. The hazard zones of such
rivers show close correlation to this geologic floodplain, since it is
inundated relatively frequently. Shallow water might cover it with a 50
percent chance each year, and deep flows with a depth roughly equal to
twice the channel bank heights might occur with a 2 percent chance per
year (Moss et al., 1978).
The above experience has little applicability to ephemeral sand-bed
streams in valley bottomlands of the arid and semiarid West. Streams in
that environment may flow directly on broad, low valley floors with
little or no channel. In that case every flow event could cause damage,
especially as the threads of flow shift on a depositional surface. The
contrasting extreme is the incised channel, where the stream has cut
through the former bottomlands so deeply that even very rare high flows
will not spill out of the incised banks. Both the above conditions may
occur on the same stream, either at different localities at a given time
or at different times at the same locality. The management of flows in
such an environment cannot ignore the geologic complexities of the
system. Experience gained in the Tucson flood of 1983 will illustrate
this conclusion.
The general channel configurations and cross-sectional shapes on
valley floors in the Tucson area today derive from a history of arroyo
cutting in the late 1800s and early 1900s. Similar histories are
prevalent throughout the southwestern United States, and considerable
controversy surrounds attempts to provide a general explanation of the
phenomenon (Cooke and Reeves, 1976). At Tucson an extensive historical
record allows a precise reconstruction of events associated with the
transition of the Santa Cruz from an alluviated valley floor to a
narrow,, steep-sided channel (Betancourt and Turner, in press).
Prior to the major flood of August 1890, the.Santa Cruz River
exhibited perennial flow at several reaches near Tucson (Figure 11).
The generally high water table intersected the valley floor at these
locations and maintained the flow through perennial springs. Two
springs upstream of San Xavier Mission, Agua de la Mision and Punta de
Agua, served to irrigate fields at the mission. Near such springs small
marshes, or cienegas, developed, with lush vegetation, fish, and beaver
locally. Reaches between the spring outflows, amounting to 75 percent
of the river course in the Tucson Basin, were ephemeral because of
infiltration into the dry, sandy riverbed. These reaches were generally
marked by shallow swales. However, local sections did have short dis-
continuous gullies with vertical banks up to 3 m high and 20 m apart.
During the 1880s this system began to reflect a profound human im-
pact. Various impoundment and diversion structures were introduced to

EXPLANATION :R.13E.JR.l4E.':::::

0- Pre- 1900 spring, now dry ......

Headcut
F -@l ..' ...... 1889 headcut::.:::
ditch ::: :: :::
Pre-1900 morsh,now dry from.,Hughes@
:ST MARYS ROAD
Present main5tem channel of
A the Santo Cruz River .-CONGRESS ST
A- Perennial reaches in ... ...
13 Wo 7-.
rners
q::
1890, now dry TUMAMOC I) Mill
B 6- Intermittent reaches HILL@
in 1890 "A MOUNTAIN ... ...
Worner-@:':
Modern Tucson urbanized area I ake:

S17ver
Lol(e

.............

::F: 1:

T 14 S.
Ki lometers T 15 S@
t
0 1 2 3 4 5

Miles
N
0 1 2 3 . ..... ...

Contour interval 30 meters
Q
Dry pre-Wl hebc1c6t(bose:. ...
Of headcut intersect
watertable by. 1882)
VALENCIA ROAD
Compiled from U-S G S
base map 1:62,500

IUD

i'?er

MARTINEZ
Son Xavier HILL

Q.
ARIZONA

BLACK ry
MOUNTAIN LU

M
Pre-1187 0
V)
so, u t\ . " ,
Phoenix 0 , il ( headc Agua de /0
misi6n
T 15 S.
Tucson Punto Artificial Channel T 16 S.
de Aguo
MAP OF Pre-1910 course of built in 1913 to
STuDY AREA '0 Sonto Cruz Rivi9r join west and
east arroyos

FIGURE 11 Map of a portion of the Santa Cruz valley near Tuc-
son showing the present mainstem channel, perennial and inter-
mittent reaches in 1890P and the location of headcuts and
190

marshes (cienegas) in the late nineteenth century. Source:
Betancourt and Turner, in.press.

facilitate irrigation on the alluvial valley floor. In 1888 a major
ditch was constructed by Sam Hughes near the present St. Mary's Road to
intercept underflow in the Santa Cruz alluvium. In October 1889 a
relatively small flood cascaded into Hughes' ditch, forming a headcut,
or nickpoint. A major flood in July-August 1890 caused this headcut to
work its way upstream approximately 4 km to a small impoundment at a
former cienega called Silver Lake (Figure 11). The valley floor of the
Santa Cruz was now incised with an arroyo about 30 m wide. The headcut
continued to recede with each flow event until by 1910 it had reached
Martinez Hill.
In the winter of 1914-15 the Santa Cruz experienced several pro-
longed floods that significantly widened the channel through bank
erosion. The Arizona Daily Star on February 1, 1915, recorded the
erosion of the east abutment to the Congress Street bridge by bank
erosion through meander migration (Figure 12):

Sudden destructive tendencies developed in the flood that
swept down the Santa Cruz River yesterday morning and from 10
o1clock until noon the river rapidly washed away a large section
of valuable land enclosed within a wide curve on the east side
of the stream just south of the Congress Street road and con-
taining five or more acres, finally about noon destroying more
than a hundred and fifty feet [45 m] of embankment that con-
nected Congress Street with the east approach to the bridge.
. . . The work of destruction was continued steadily, but
more slowly throughout the afternoon and by midnight the rushing
water was creeping at the outside of the curve close to the row
of cottages just east of the big concrete irrigation ditch and
threatening to include the houses in the ruin.
While the river did not rise any higher, it developed a
terrific boring power that rapidly crumbled the soft dirt into
the swirling current of the muddy Santa Cruz. The current
worked with telling effect on the sandy subsoil of the rich
arable land of the bottom and the total damage is estimated to
be not less than $50,000 at midnight. The east approach to the
bridge was swept away leaving 200 feet [60 m] of water between
the road and the bridge. The piers of the bridge itself also
sank. . . . The sudden driving force that the stream acquired
in the morning rendered useless the protective measures taken
and there was little that could be done through the day to
protect the embankment.. Foot after foot went out and by mid-
night it was estimated that the gap between the bridge and the
east end of the road was more than 200 feet [60 m).

With minor changes this description could apply to damage at bridges
in the flood of October 1983.
After the floods of 1914-15 the Santa Cruz continued to incise
upstream of Martinez Hill (Figure 11). By the 1930s a headcut had
migrated from Agua de la Mision up an artificial channel built in 1913
to join the west and east branches of the,stream. During the 1920s and
the 1930s the incised river near Congress Street began to aggrade. The

@'4

FIGURE 12 Erosion damage to the east abutment of the Congress Street bridge
on February 1, 1915. The view is upstream (south), and Sentinel Peak ("A"
Mountain) is visible at right. The gap of 60 m from the bridge to the east
bank (left in picture) resulted from the downstream migration of a meander
bend on that bank. This meander bend was visible in a 1902 photograph
(Betancourt and Turner, in press). Source: Arizona Historical Society,
Tucson.

aggradation probably resulted from the decreased velocities achieved by
the channel widening in 1914-15, from the stabilizing effect of cotton-
woods and other riparian vegetation, and from the lack of major winter
floods in this period. Because of their relatively low sediment loads
(in contrast to summer floods), winter floods are particularly erosive
for the sand-bed streams of southern Arizona.
Starting in 1950 the Santa Cruz through Tucson was modified by
artificial narrowing through landfill operations and by highway con-
struction. The reach from Martinez Hill to Congress Street had been
straightened in 1935 by the efforts of the Works Progress Administra-
tion. Flows were deflected from severe bends by means of revetments.
The result of these changes was renewed downcutting by higher-velocity
flows through the straightened and constricted channel. The zone of
aggradation moved downstream, past all the urbanized reaches, to the far
northern end of the Tucson Basin.
The Rillito system had an early history similar to that of the Santa
Cruz. From a condition in 1858 that included beaver dams along a broad

-valley floor, the stream had incised to a wide channel with vertical
banks by 1890. The change was attributed by Smith (1910) to cutting of
vegetation, overgrazing by cattle, and flood erosion. Channel incision
continued into the twentieth century as excessive withdrawal of ground
water eliminated riparian vegetation along stream banks and bars.
Studies of aerial photographs since 1941 show that the Rillito-
Pantano-Tanque Verde system has been characterized by prolonged periods
of channel narrowing locally interrupted by abrupt periods of widening
with attendant bank erosion (Figure 13; Pearthree, 1982). Narrowing
from 1941 until 1965 occurred during an interval dominated by short-
duration floods with peaks less than 300 m3/s. Most of these flows
occurred in the summer and early fall, and they probably transported
very high sediment loads. In 1965 a large winter storm produced a
prolonged flood that peaked at about 350 m3/s for Tanque Verde Creek
and the Rillito. This flood carried a relatively low sediment load and
generated extensive bank erosion for both stream channels. In contrast,
Pantano Wash did not experience this flood and continued to narrow.
After the 1965 event both Tanque Verde Creek and the Rillito dis-
played either natural recovery or local artificial stabilization. In
December 1978 another major winter storm affected these streams. As in
1965, this event, which peaked at 464 m3/s in the Rillito, was char-
acterized by prolonged duration and a relatively low sediment load. In
addition, a flow in March 1978 had removed much of the sediment that
had accumulated in the stream channels during the preceding recovery
period. Extensive bank erosion occurred during a three-day period of
flow. Channel realignment, bank protection, and bridge repair after the
1978 flood led to the general condition of the Rillito-Tanque Verde-
Pantano system immediately prior to the 1983 flood.

Jak A6"aL wS limp 11 -111

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FIGURE 13 View upstream (east) from the Campbell Avenue bridge
on October 1, 1983, showing erosion of the north (left) bank by
meander flow. Note the dark thread of high-velocity water fol-
lowing the meander thalweg from the next bend upstream. Also
note the utility lines in the stream channel. Photograph by
Peter Kresan.

It is clear that the streams of the Tucson Basin have been irrevers-
ibly altered from conditions that prevailed prior to large-scale human
intervention. A return to the channel characteristics of the 1800s is
impossible for the following reasons: (1) groundwater overdraft has so
lowered the water table that the stabilizing influence of riparian vege-
tation has been lost, (2) the urbanization process has reduced the in-
flux of sediments from tributaries into the main channels while in-
creasing the influx of water from individual storms, and (3) channels
have been constricted by bridges, filling on banks, and revetment works.

HYDROLOGIC ASPECTS'OF THE 1983 FLOOD

The flood peak on the Santa Cruz River at Cortaro occurred between 8:00
p.m. on Saturday, October 1, and 9:00'a.m. on Sunday, October 2 (H. W.
Hjalmarson, U.S. Geological Survey, personal communication, 1983). Peak
flood discharges have been provisionally estimated for several local-
ities in the Tucson Basin (Table 4). Extensive bank erosion resulted in
the losses of gages on major watercourses, but postflood hydraulic
calculations are being used to determine flood peaks. Final estimates,
hydrographs from undamaged gages, and detailed interpretation are still
being generated by the U.S. Geological Survey. However, several con-
clusions concerning 'flood frequency seem warranted at this preliminary
point.
The Santa Cruz River peaked at 1,490 m3/s (52,700 cfs) at Congress
Street. This event exceeds by more than a factor of two any other flood
recorded at that station. It exceeds by a factor of 1.75 the magnitude
of the 100-year flood designated in the Federal Emergency Management
Agency (FEMA) Flood Insurance Study (Federal Emergency Management
Agency, 1982). Even more important is the fact that the FEMA flood
magnitudes were adjusted upward from the standard procedures. The
problem of estimating a true recurrence interval for this event will be
treated below. The Rillito also had an extreme flood (Figure 13), esti-
mated at 840 m3/s (29,700 cfs). The FEMA-determined return period for
this event would be between 50 and 100 years.
In contrast to the Santa Cruz and Rillito, other streams in the
Tucson area had floods that were much less extreme in relation to past
experience. The Canada del Oro at Overton Road had a peak flow of 185
m3/s (6,600 cfs), as estimated by the U.S *Geological Survey. This
compares with the 10-year flood estimate of 280 m3/s (10,000 cfs),
which the federal Flood Insurance Study for the Pima County Department
of Transportation and Flood Control District used as the regulatory
flood. Pantano Wash peaked at 310 m3/s (11,000 cfs), which is between
the 10-year discharge of 250 m3/s (9,000 cfs) and the 25-year dis-
charge of 400 m3/s (14,000 cfs). The record flow of Pantano Wash at
Broadway was 570 m3/s (20,000 cfs) in 1958.
The annual flood.peaks of the Santa Cruz River have been recorded at
the Congress.Street bridgesince 1915. @In the period 1915 to 1981
(Figure 14), 73 percent of all annual peaks occurred during July and
August, 18 percent occurred.dur,ing September and October, and 9 p@rcent
occurred during November through February. No annual peak flows have
been recorded,in March, April,.May,,,or June. A standard log-Pearson III
analysis of this record is,,shown.in@Figure 15., This plot was derived
according to standard.procedureg,followed throughout the United States
(U.-S. Water R6sources-Council,1981). Thi.s plot estimates the 100-year
flood as about 650 m3/s (23,000 cfs), only half the magnitude of the
1983 flood. By this analysis the return period of the 1983 flood would
be more than 1,000 years. This is beyond the frequency of events that
are considered in usual hazard management.

TABLE 4 Estimated Flood Peak Discharges and Recurrence Intervals for
the 1983 Tucson Flood

Provisionally Estimated Dischargea 100-year Flood Dischargeb
Locality cfs m3/s cfs M-3/s

Santa Cruz at
Congress Street 52,700 1,490 30,000 850
Santa Cruz at
Cortaro 65,000 1,840 40,000 1,130
Rillito at
Flowing Wells 29,700 840 32,000 900
Canada del Oro
at Overton Road 6,600 185 28,000 800
Pantano Wash
at Broadway 11,000 310 25,000 700

aH. W. Hjalmarson, U.S. Geological Survey, personal communication, 1984.
1pFederal Emergency Management Agency Flood Insurance Study.

- July, September, November, December, -600
20,000- Au October January, February

500

V)
LL 15,000-
-400

< Z5

U)
E 6U()
y 10,000-

Ld -
CL

200

5000-

1co
io
1910 1920 1930 1940 1950 1960 1970 1980
WATER YEAR
FIGURE 14 Annual peak discharge for the Santa Cruz River at
Congress Street between the water years 1915 and 1981. The gage
was removed late in 198 '1. Note the months of peak discharge.
Newspaper accounts for the period between 1902 and 1914 also in-
clude several major storms in winter. Source: Betancourt and
Turner, in press.

105

103

10
1.005 1.05 1.25 2.0 5.0 10 100 500
RECURRENCE INTERVAL IN YEARS

FIGURE 15 Flood-frequency analysis of the 1915-81 annual flood
peaks of the Santa Cruz River at Congress Street. The plot was
derived according to the nationally mandated procedure (UoS. Wa-
ter Resources Council, 1981).

Most standard techniques for estimating the recurrence probabilities
of flood events assume a stationary mean (U.S. Water Resources Council,
1981). This means that the methods presume a flood history has been
extracted from a river whose hydrologic characteristics have not changed
over the period of measuremento Clearly this assumption does not apply
to the Santa Cruz flood record (Figure 14). From 1915 to 1960 no flood
occurred that exceeded 340 m3/s (12,000 cfs), but since 1960 there
have been six such events (including the 1983 flood). Moreover, this
change in flood behavior has occurred on a river whose channel has
experienced profound morphological change since about 1890. Even more
important are probable climatic factors. Note that the big floods since
1960 are predominantly fall and winter events (September through Feb-
ruary), as they were in the period 1915 to 1929. However, the smaller
annual peaks of 1916 to 1960 are nearly all summer events (July and
August). The nature of the storm systems responsible for the flood
peaks are clearly different during the latter period of recordo
Accelerated channel change and,climatic shifts are probable factors
in many watersheds throughout the arid and semiarid western United

States. This invalidates the assumption of a stationary mean that is
almost universally applied to flood-frequency analyses in these water-
sheds. It follows that this also invalidates land-use zoning based on
nationally mandated flood-frequency-analytical procedures that are
indiscriminately applied to the arid and semiarid West.
As shown in the next section, the most important geomorphic aspect
of the streams in the Tucson Basin is their tendency to alter their
cross-sectional shape in response to changes in water and sediment
influxes. The streams experience such rapid and large responses to
changing conditions that erroneous hazard zonation can arise from
conventional engineering hydraulic-hydrologic calculation procedures.
For example, these procedures predict the water surface elevation of the
100-year flood in a particular stream channel by assuming that the
geometry or position of the channel does not change significantly prior
to, during, or after the flood. This assumption is almost always
incorrect'for the ephemeral stream channels in alluvial basins of
semiarid regions. Indeed, the bank erosion of such streams generally
presents a hazard to property that exceeds the hazard of damage from
floodwater alone.

AN OVERVIEW OF FLOOD EROSION AND DEPOSITION

To assess the regional effects of the Tucson flood, a team of University
of Arizona geosciences students surveyed the postflood changes in water-
courses throughout the Tucson Basin (Figure 16). The detailed maps of
their results are presented in Appendix B. This section briefly sum-
marizes those observations.' Because incomplete bank protection was
found to be a major factor in localizing bank erosion, a separate
section is devoted to that issue.
At Martinez Hill the incised meander train of the Santa Cruz River
encounters a bedrock obstruction (Figure 17). Flow is deflected by the
obstruction, inducing pronounced bank erosion. Despite extensive riprap
revetments, two bridges were lost at this site (Figure 17). The west-
ward meander migration along San Xavier Road was a direct result..of the
natural deflection of flow by Martinez Hill.
Approximately 2 km downstream of Martinez Hill, at the junction with
Santa Clara (Hughes') Wash, the Santa Cruz.was modified by a meander
cutoff in 1935. This improvement attempted to prevent bank recession by
meander migration. The 1983 flood produced extensive erosion in the
vicinity of the island created by this cutoff (see Map 1, Appendix B).
About 30 m of bank recession occurred on both sides of the artificial
cutoff channel. Erosion upstream of the cutoff threatened a city sewer
line crossing. After the flood a levee was constructed in the channel
to divert flows into the original Santa Cruz meander to lessen the rate
of future bank recession near the sewer line.
Downstream of Santa Clara Wash in the vicinity of Valencia Road, the
character of the Santa Cruz changes from a broad shallow arroyo, about
200 to 400 m wide, to a deep narrow arroyo about 100 m wide. Bank ero-
sion was less here because mature mesquite vegetation added stability
with its deep root systems. The response.ofthe stream through this

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KILOMETERS
FIGURE 16 Location map of watercourses near Tucson with an in-
dex to detailed maps shown in Appendix B of erosion, bank pro-
tection, and related flood effects for the October 1983 flood.

reach was mainly by channel scour. Scour of 2 to 3 m can be documented
by referring to the preflood footings of high-voltage transmission
towers in the channel.
Two prominent meander bends between Valencia Road and Drexel Road
0
L L I TO

CORT

illustrate important erosional effects. The cutbank of the upstream

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77"

A-,

FIGURE 17 The Santa Cruz River at Martinez Hill (lower right)
on October 9, 1983. Damage to the north abutment.of the north-
bound lane bridge of Interstate 19 is visible at center. As the
flow meandered to the west'bank, it eroded the west abutment of
the San Xavier Road bridge (top center). Bank erosion extended
through the former intersection of San Xavier Road and the ac-
cess road to Interstate 19 at left center. Note the blocks of
collapsed bank material on this bank. Riprap placed along this
bank failed to prevent meander migration in the 1983 flood.
Photograph by Peter Kresan.

meander bend was protected by 100 m of riprap revetment. Nearly all of
this was destroyed during the flood because bed scour undermined the
revetment. Approximately 3 m of bank erosion occurred at the,bend.
Immediately downstream of the protected meander bend, an unprotected
bend experienced approximately 40 m of bank recession on its cutbank.
The increased erosion at this site is directly related to the protected
banks upstream.
Approximately 400 m downstream of Irvington Road, the diversion
channel of the West Branch of the Santa Cruz River joins the Santa Cruz@
main channel. The diversion channel was constructed to lower flood

stages at the Midvale Farms subdivision, which lies immediately west of'
the Santa Cruz River between Drexel and Irvington roads. A concrete
drop structure on the West Branch is used to control the gradient change
at the confluence, and soil-cement revetments were used to protect chan-
nel banks at the confluence. the flood peak in the West Branch is
estimated at 85 m3/s (Brian Reich, City of Tucson, personal communi-
cation, 1983). Bank erosion opposite and downstream from these revet-
ments was especially pronounced, averaging about 30 m of recession
(Figure 18).
North of Ajo Way an alternating pattern of meander bend erosion
continued through an unprotected reach to 29th Street (see Map 2,
Appendix B). Between 29th Street and 22nd Street, former meander bends
of the Santa Cruz are protected by unsorted debris and/or riprap. Bank
erosion occurred at all these bends during the 1983 flood. It was most
pronounced where unsorted debris was undermined by scour.
North of 22nd Street to St. Mary's Road the Santa Cruz River is
nearly completely confined within artificial banks. The landfill
operations near downtown Tucson (Betancourt and Turner, in press) have
reduced the stream to a relatively straight channel averaging 50 m in
width. This reach is channelized with soil-cement revetment on both
banks. Flood discharges through this reach were confined within these
artificial banks. Where protected by soil cement, banks were generally
unaffected by the flood flows (Figures 19A and 19B). Confinement of
flooding to a narrow cross section and reduction of sediment load in the
flow because of the protected banks resulted in general bed degradation
throughout this reach.
Downstream of Speedway Boulevard the Santa Cruz River channel widens
and becomes more sinuous. The 1983 flood caused considerable erosion on
the cutbanks of meander bends. Near Grant Road an old sanitary landfill
was intercepted by bank recession, spilling refuse into the active
streambed. The piecemeal bank protection in this reach showed consid-
erable failure, in contrast with the reach of continuous bank protection
lining the channel upstream of St. Mary's Road.
At Fort Lowell Road the sinuosity of the Santa Cruz decreases, and
bank erosion by the 1983 flood was less severe than immediately upstream
(see Map 3, Appendix B). Some of the stability of this reach can be
attributed to riparian vegetation in the channel. Growth of the vege-
tation was facilitated by an influx of sewage effluent from a treatment
plant. Shallow overbank flooding and deposition occurred in this reach.
Downstream of Ruthrauff Road the Santa.Cruz showed a major change in
character. The channel banks were so stabilized by vegetation that they
were unable to enlarge to convey the floodflows. Floodwater spilled on
to the adjacent floodplain surface. A secondary channel with a headcut
developed on this surface. The width of inundation near Sunset Road was
approximately 400 m (Figure 20).
Even greater spreading of the floodflows occurred downstream of the
Rillito confluence (see Map 4, Appendix B). Large sand and gravel pits
and the Pima County sewage treatment-facility are immediately adjacent
to the channel. Most of these facilities are along the east banks, with
various types of revetments serving to protect that bank. Erosion from
the 1983 flood was concentrated on the unprotected west banks.

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FIGURE 19A View of Santa Cruz River upstream (south) from St.
Mary's Road bridge on October 2, 1983. Note confinement of flow
within artificial banks composed of soil cement. Photograph by
Peter Kresan.

Nt
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FIGURE 19B View from approximately the same position in late
October 1983. Note incision at base of soil-cement slope and
meandering thalweg of low-flow channel that developed during
waning flow. Photograph by Peter Kresan.

W- SUNSET

LEGEND:
SANTA CRUZ RIVER-
NOVEMBER 12, 1982

SANTA CRUZ RIVER-
OCTOBER 3,1983

100-YEAR FLOODPLAIN

500-YEAR FLOODPLAIN
(FEMA)

LIMITS OF OVERBANK
FLOODING

SCALE

0
0 100 FEET 200 300
I. ow- ==NEI . . . . . .
METERS

FIGURE 20 Map showing channel changes and FEMA floodplain
designations along the Santa Cruz River near West Sunset Road.

At Ina Road spectacular erosion on the west abutment resulted in
bank recession that exceeded the original channel width spanned by the
Ina Road bridge (Figure 21). Extensive overbank flooding and deposition
occurred downstream of this point. Much of Cortaro Road between the
Santa Cruz and Interstate 10 was buried by overbank deposition.
A relatively sinuous reach downstream of Cortaro Road was lined with
riparian vegetation maintained by sewage effluent. The 1983 flood cut a
straight channel through this section and deposited thick overbank sedi-
ments to either side of the channel (Figure 22). Note that the Santa
Cruz gradually changed to this behavior from an incised, eroding channel
near Speedway Boulevard in which the 1983 floodflows were confined.
At Marana (Figure 23) the flooding of the Santa Cruz became a broad
shallow inundation over extensive valley floors. Damages to farmland in
this region are not described in this report. Significantly, the char-
acter of flooding downstream of this point was depositional (Figure
24). Sediment transported from the extensive areas of erosion upstream
contributed to aggradation in this area. The aggradation, in turn, led
to more extensive inundation. The buildup of sediment from past floods
may have so increased slopes in this reach that a new headcut was
initiated in the Santa Cruz valley near Picacho Peak (Figure 25).
The postflood erosion survey also documented the behavior of the
Rillito-Pantano-Tanque Verde system during the 1983 flood. Pantano Wash
was quite interesting because a large drop structure at Broadway sepa-
rates the system into an incised reach downstream, to the north of
Broadway, and a less incised reach upstream, to the south of Broadway
(see Maps 5 and 6. Appendix B). Bank erosion from the 1983 flood was
minimal upstream of the drop structure. Exceptions were at a prominent
meander bend (Figure 26) and at a sand pit north of Golf Links Road.
Downstream of the Broadway drop structure, Pantano Wash is deeply
incised. It responded to the 1983 flood by the alternating pattern of
bank erosion described above for the Santa Cruz River system. Local
areas of bank protection from riprap and wire fence revetment were
effective in-shifting the concentration of this erosion to unprotected
banks. At the downstream end of revetment works around the Tanque Verde
Road bridge, a major zone of bank recession caused the loss of resi@
dential property.
The upper reaches of Tanque Verde Creek, as with upper Pantano Wash,
showed much less bank erosion in the 1983 flood than did entrenched
reaches of the Rillito and the Santa Cruz River. Banks were suffi-
ciently low that overbank flooding occurred at the Forty-Niners Country
Club Estates. Major bank erosion appeared at the confluence of Sabino
Canyon Creek and Tanque Verde Creek. This occurred because of (1) the
angle of the stream juncture, which directed flows at an unprotected
bank, and (2) changes in sediment loading that occurred as the two flows
mixedo The second factor probably also explains the increased erosion
that occurred immediately downstream of the confluence of Tanque Verde
Creek and Pantano Washo

FIGURE 21 The Ina Road bridge over the Santa Cruz River on
October 8, 1983, showing extensive erosion of its west abut-
ment. Channel shifting to the west resulted in deposition at
the former bridge cross section. Water spilling into the
flooded gravel pit (right center) eroded large sections of
the eastern approach road. Photograph by V. R. Baker.

The Rillito from Craycroft Road to the Santa Cruz River is an
entrenched system. _It responded to the 1983 flood by pronounced bank
erosion following a pattern of meander bends, as allowed by piecemeal
bank protection (see Map 7, Appendix B). From Swan Road to Dodge Road
this erosion occurred in a reach that had little bank protection (Figure
27). A major bend at Prince Road resulted in migration of a meander
cutbank during the 1983 flood-that undermined several houses and town-
homes. The bridges at Campeell Avenue and First Avenue (Figure 28)
suffered erosion of their northern abutments by meander migration. Many
of these effects repeated the experience of floods in 1965 and 1978
(Pearthree, 1983).

AN ASSESSMENT OF BANK PROTECTION

It is clear that unprotected banks in the Tucson area suffered phenom-
enal erosion during the flood of October 1983 (Figure 29). This hazard
has been recognized for many years, and several types of bank protective
works were in place at the time of the flood*(Table 5). Thus the flood

41:t@i

417

FIGURE 22 View downstream (north) along the Santa Cruz River
north of Pima Farms Road (foreground) on October 8, 1983. The
sinuous bends lined with riparian vegetation developed from
relatively continuous low discharges from a sewage treatment
plant located approximately 5 km upstream of this point. The
flood discharge carved a straighter course along the center of
the low-flow meander trend. Also note the extensive sedimenta-
tion in splay patterns to either side of the central flood
channel. Interstate 10 runs diagonally across the top half of
the photo,-and the Tortolita Mountains are visible on the
skyline. Photograph by V. R. Baker.

provided an excellent test of the performance of this protection. The
maps of Appendix B document the spatial distribution of this protection
in relation to bank erosion.
The experience of the 1983 flood has shown that bank erosion was the
most severe hazard encountered on the incised sections of stream chan-
nels through the Tucson Basin. To assess the bank protection as a
factor in reducing this hazard, two questions can be asked: (1) What
was the engineering performance of different bank protection designs--
i.e., which designs effectively prevented bank erosion? (2) What was
the overall effect of bank protection on the fluvial system? Both
questions must be addressed, because.piecemeal bank protection can meet
the needs of some individuals in protecting their property from bank
erosion while the stream system as a whole requires consideration of
comprehensive bank protection.

FIGURE 23 View of Marana (center) looking south toward the
Tucson Mountains on October 9, 1983. Floodflows in this area
spread over extensive agricultural land and caused considerable
damage. The prominent meander bend at Marana experienced severe
erosion during the prolonged winter flood of 1978. In contrast,
the much larger 1983 flood peak resulted in relatively little
erosion on this bend. Photograph by Peter Kresan.

Since 1974, the design of bank protective works in Pima County has
required the approval of the Floodplain Management Section of the Pima
County Department of Transportation and Flood Control District. Non-
standard protective works, including cable-tied automobile bodies and
rail, wire, and rock revetment, probably predate 1974 in most cases.
The local effectiveness of the three types of bank protection
involving engineering design can be seen by observing the banks of the
Santa Cruz River along the 12.8-km reach from Speedway Boulevard to the
junction of the Rillito. Riprap revetment was used to protect 2.6 km of
bank; wire-fence revetment (with rock fill) was used for 0.5 km. Damage
to riprap was more extensive during the 1983 flood. Scour into the
streambed is facilitated at the junction between the riprap and the
unprotected bed. The rock falls into the scour hole and is either
transported downstream or buried in scour holes that develop downstream
of individual riprap clasts. Over 80 percent of the study reach pro-
tected by riprap showed at least some undercutting and bank recession.
In contrast, the wire-fence revetment generally showed damage only on
the upstream and downstream ends of protected banks. Scour at those
sites caused banks to recede behind the revetments. The soil-cement

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FIGURE 24 Depositional patterns on October 8, 1983, produced by
the flooding of the Santa Cruz River immediately downstream of
Marana. Photograph by V. R. Baker.

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FIGURE 25 Headcut on the Santa Cruz valley floor immediately
south of Picacho Peak, 15 km northwest of Marana, on October 8,
1983. Photograph by V. R. Baker.

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FIGURE 26 Pantano Wash at the Rincon Country mobile home
development (upper right) on October 9, 1983. Escalante Road
runs along the top (south) end of the photograph. The prominent
bend of Pantano Wash at the top center undermined several mobile
homes, which can be seen in the channel at the center and bottom
of the photograph. Several automobiles were also incorporated
into the northward flow of Pantano Wash. A ground view of the
channel at this location is shown in Figure 38. Photograph by
Peter Kresan.

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FIGURE 27 The Dodge Road bridge over the Rillito on October 9,
1983. Damage to the north (left) abutment was caused by meander
migration. Note the prominent cutbank on the north side and
corresponding point bar on the south (right) side of the
stream. The meander bend immediately downstream (bottom right)
is threatening an electric utility station. The anomalously
wide section of channel at the top center was the site of a
preflood channel sand-mining operation. Photograph by Peter
Kresan.

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FIGURE 28 The Rillito at the First Avenue bridge on October 9,
1983, showing meander migration on the south (left) bank, which
undermined the office building complex in the upper left of the
photograph. The return flow to the opposite bank at the upper
right damaged the north (right) abutment of the bridge.
Temporary repair had been effected at the time of this
photograph. Figures 35 and 36 show damage to the office
buildings. Photograph by Peter Kresan.

FIGURE 29 Bank erosion along the Rillito at the Dodge Road
bridge on October 10, 1983. Photograph by Thomas F. Saarinen.

revetments were undamaged, although prominent erosion of banks occurred
immediately downstream of the protection.
The mode of destruction for wire-fence revetments was generally not
by scour, as for unconfined riprap. Rather, progressive erosion at the
upstream or downstream end of the revetment would scour behind the
protected bank. In-extreme cases the former bank facing would be
isolated in midchannel as the bank receded Away from it (Figure-30).
Failure of soil-cement revetment: was observed at several local-
ities. Inadequate keying of the soil cement to the upstream or down-
stream terminus of the protection was the major cause of failure. At
Prince Road and the Rillito, a prominent meander bend scoured behind the
upstream end of a soil-cement revetment, resulting in major damage to a
complex of townhouses (Figure 31).
An example of a properly keyed revetment is the protection for the
southeast abutment of the Sabino Canyon Road bridge over Tanque Verde
Creek (Figure 32). The pronounced channel widening upstream of the
revetment terminates abruptly at this key.
Major bank erosion occurred immediately downstream of reaches that
had been extensively protected with soil cement on both banks. An
example is the reach of the Santa Cruz immediately downstream (north) of
St.-Mary's Road.- Soil-cement revetments continuously line both banks of
the Santa Cruz for nearly 2 km upstream of this point. Erosion appeared

TABLE 5 Types of Stream Bank Protection Observed in Watercourses of the
Tucson Basin

Type of
Protection Description

Soil-cement Embankment facing composed of 8 to 15 percent
revetment portland cement mixed with natural bank material.
Soil is removed, mixed with cement, and laid on
the prepared bank surface in thin layers. The
revetment extends to below the level of channel
scour and is keyed into the banks at the upstream
and downstream termini.

Wire-fence Wire enclosures held by vertical steel members
revetment (often rails) and filled with boulders. A variety
of this revetment consists of wire baskets of rock
called gabions.

Riprap A blanket of boulders that exceed the competence
of:the largest floodflows. The material is used
as facing for the bank.

Unsorted debris Any material dumped directly on stream banks to
prevent erosion. Commonly used materials are
automobile bodies, concrete blocks, demolitions
waste, crushed rock, poured concrete, and rubbish.

immediately at the terminus of this protection (Figures 33A and 33B).
It was sufficiently intense to scour,the terminus of the soil-cement
bank itself (Figure 34). The postflood erosion survey (Appendix B)
found that severe erosion occurred at the downstream terminus of every
protected bank along deeply incised reaches of the Santa Cruz and the
Rillito. Clearly, piecemeal bank protective works concentrate areas of
eroded as well as protected banks, and the erosive consequences of such
protection should be considered in the overall management of the river
system.
The necessity of protecting bridges from loss during floods unavoid-
ably generates a need for localized bank protection. As observed in the
1983 flood, the loss of a bridge most often occurs by bank recession at
one abutment. The recession is generally associated with meandermigra-
tion during the flood. To protect the bridge abutments, a reach both
upstream and downstream must be lined with bank protection. The natural
tendency of the stream in flood to widen its channel and incorporate
added sediment load is thus impeded in the bridge reach. The stream
will therefore attempt to scour the streambed at the bridge section,

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FIGURE 30 Erosion of bank protected by wire-fence revetment
along the Rillito at Craycroft on October 10, 1983. Photograph
by Thomas F. Saarinen.

leading to failure by an undermining of the bridge piers. If degrada-
tion control structures are placed on the bed to prevent scour, the
bridge reach is transformed into a rigid-walled flume. High-velocity,
sediment-impoverished floodwater passing through the protected bridge
reach will be erosive in the reach immediately downstream. As in other
examples, given several floodflow events, partial bank protection will
beget the need for more bank protection.

SAND AND GRAVEL OPERATIONS

In southern Arizona it is a common practice to mine sand and gravel from
active channels by excavating shallow pits in their beds (Bull and
Scott, 1974). These operations move from place to place as local areas
are depleted and flow events modify older workings. The effects of such
gravel mining are extensive along the Rillito-Pantano-Tanque Verde
system.
The responses of a stream to the lowering of the bed at sand and
gravel pits include the following: (1) upstream bed degradation, (2)
bank sloughing near the pits, (3) bank erosion caused by temporary water
diversion structures used to protect mining operations, and (4) down-
stream bank erosion caused by the "sediment trap" action of some pits.

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FIG'URE 31 The Rillito near Prince Road (lower left) on October
8, 1983. Damage to the Pima Park Townhomes (center) occurred
when the prominent meander bend at the bottom center migrated
west (left) into the vacant property immediately upstream of the
townhouses. This allowed erosion to occur behind the soil-
cement bank protection lining the stream at the townhome pro-
perty. The prominent point bar at the bottom center developed
as the meander migrated westward. Photograph by V. R. Baker.

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FIGURE 32 Soil-cement revetment works lining both banks of the
Tanque Verde Creek immediately east of the Sabino Canyon Road
bridge (top left) on October 8, 1983. Photograph by V. R. Baker.

The latter problem arises when a pit traps enough sediment entering its
upstream end that the outflow from the pit is sediment impoverished and
therefore erosive immediately downstream of the pit.
Along the Santa Cruz River, extensive sand and gravel pits have been
developed on the surface of the valley floor immediately adjacent to the
entrenched channel of the river. At Ina Road a major pit contributed to
the undermining of the approach road to the Santa Cruz bridge (Figure
21). A large abandoned sand pit on the Rillito occurs midway between
Swan Road and Dodge Road (see Map 7 in Appendix B). The pronounced
meander bend erosion downstream of this point, including the erosion of
the nQrth abutment of the Dodge Road bridge, may be at least partly
related to this sand pit (Figure 27).
The specific changes in the river system described above for the
Tucson flood of October 1983 are in keeping with the general long-term
characteristics of southwestern streams, as outlined in the next section.

STREAM CHANNEL STABILITY IN THE TUCSON BASIN

Reports of the U.S. Geological Survey in the 1890s note that while
runoff in Arizona is very low, at times floods occur whose violence and
duration are phenomenal. This is still true. It is also true that no
stream flowing north to the Gila River in Arizona or New Mexico has a
permanent discharge at its confluence with the main channel.

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FIGURE 33A View downstream (north) along the Santa Cruz River
from the St. Mary's Road bridge on October 2, 1983. Note that
the soil-cement banks confine the flow for approximately 100 m
beyond the bridge. Pronounced bank erosion occurs at the di9tal
end of this protection, especially on the west (left) bank,
toward which the flow is directed. The high-velocity thread of
the flow is marked by antidunes and standing waves. Photograph
by Peter Kresan.

West of the San Pedro River, even floodflows rarely reach the-Gila
River. East of the San Pedro River, streams frequently flow to the main
stream. Because the transported sediment has to be deposited as dis-
charge declines, western streams are aggrading, but irregularly so.
Water spreads widely among areas of deposition and flows over relatively
small intermittent channels. Head cutting may be present at high dis-
charges. Under pristine conditions of a high water table, some local
permanent water may occur.
Upstream from areas of deposition, river channels are well defined.,
but again the characteristics of the channel are determined by the
discharges of water and sediment. Under natural conditions upstream
from the junction of the Santa Cruz and Rillito, the channels were

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FIGURE 33B View from approximately the same position on October
16, 1983. Note that the west.bank has receded further from its
position on October 2. Damage to the distal end of the soil-
cement bank protection on the east (right) bank is shown in more
detail in Figure 34. Photograph by Peter Kresan.

alternate reaches of incision and deposition, depending on the relative
inflow of water and sediment from tributary streams. on a larger scale
this is equivalent to the discontinuous gully system.
The stability of this system, such as it is, depends on a supply of
sediment that increases with increasing discharge, on vegetative protec-
tion of stream banks, or on valley fill. Because the various tribu-
taries to a stream system do not have equal ratios of transported
sediment to water discharge, the stability of a system will vary in
different reaches of the stream. Also, because sediment transport
increases with increasing intensity of rainfall, the ratio between water
and sediment varies seasonally. Because sediment moves as slugs, the
ratio of water to sediment decreases with succeeding years of high dis-
charge. Eventually the duration of above-normal discharges probably
exerts more influence on stream behavior than do peak flows.
The City of Tucson has been built on this unstable system. The

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FIGURE 34 View downstream (north) along the Santa Cruz River
between the St. Mary's Road bridge and the Speedway Boulevard
bridge (visible at top center) on October 10, 1983. The distal
terminus of the soil-cement bank protection has been eroded by
the flows shown in Figure 33A. Photograph by Thomas F. Saarinen.

increasing demand for water by this growing city can be! met only by
tapping groundwater in larger and larger amounts. The result has been a
lowering of water tables and the disappearance of streamflow at low
rates. Downstream of the city, sewage effluent has increased and
currently flows as far as Red Rock. The result has been the almost
complete disappearance of riparian vegetation within the city. Except
where controlled by structures, the streams have become incised, perhaps
by as much as 6 ft, over the last 50 years. Cook and Reeves (1976) and,
Betancourt and Turner (in press) have documented the effects of man's
activities on the Santa Cruz River through Tucson.
The city and its built-up environs now cover over 100 square miles.
As a result, storm runoff with a low concentration of sediment has
increased. Over the last six years there have been more than average
winter floods, each finding smaller amounts of sediment to move.
Normally, degradation of the main stream increases the sediment
discharge from tributary streams, but the construction of roads and
other developments paralleling the river has prevented this.
The result has been increasing bank erosion at different points on
the streams. If, over a period of the next few years, winter runoff

declines while summer thunderstorms increase, the amount of sediment
available for transport in winter storms will increase, improving stream
stability. If not, bank erosion associated with channel meandering is
to be expected. Over time, however, the incised streams in the Tucson
Basin will probably become wider and deeper.
The widespread flooding below the junction of the Santa Cruz and
Rillito was caused by the magnitude and duration of the stream discharge
during the October 1983 flood. While such flooding could be controlled
by levees, it is questionable if this is desirable. Control of flooding
would push the locus of spreading downstream and could possibly cause
incision of the channels. Levees might also interfere with the use of
sewage effluent for irrigation. Most important, levees would reduce the
area of groundwater recharge in the area of heaviest pumping.
Whatever is done, it should be realized that an area of deposition
will constantly grow and that it is basically unstable from either small
or large floods.
Because of the expanding developed area in the Tucson Basin, there
is no reason to presume that the present problems of bank stability can
be reversed naturally. As long as sediment transport is small in terms
of discharge and stream gradient, there will be problems of bank ero-
sion. Many reaches of the stream have been protected, at least on one
side, by different types of revetments. Most have worked reasonably
well. But, in all locations noted, excessive bank erosion has resulted
downstream of the revetted area. Bridges pin the location of the stream
and limit the possible variation in bank position and river slope. If
the stream is fully revetted, the stream can be expected to degrade its
channel in some areas and thus undermine the revetments.
No program for the prompt construction of channel revetments through
the built-up area can be expected. Such construction will likely be on
a piecemeal basis and simply shift the areas of intense erosion. With-
out bank protection, erosion will continue until a new equilibrium is
reached. The state of the art cannot predict what such an equilibrium
will be.
One major grade control structure has been built on Pantano Wash.
Theoretically, a reduction in slope should result in a narrower
channel. The behavior of this stream should be closely observed,
because its sediment transport is reduced when the stream flows into
pits excavated for sand and gravel. This should result in a wider
channel downstream and might cause degradation below the structure.
Little information is available about the hydraulics of the rivers
in the Tucson Basin. There are no sediment sampling programs and few if
any actual discharge measurements at high flows, and the county has
abandoned its regular measurement of stream discharge. Because any
available method of calculating discharge at high flows has a probable
error of +40 percent, the effectiveness of any design is uncertain.
This situation is not unique to the Tucson Basin. It exists every-
where. John F. Kennedy's 1983 paper, "Reflections on Rivers, Research,
and Rouse," should be required reading for anyone working with fluvial
hydraulics.

TYPES OF DAMAGE TO PROPERTY

An exhaustive survey of property damage is beyond the scope of this
report. Other flood studies have documented damage to property by
inundation (Beal, 1983). The focus here is on damage associated with
pronounced channel erosion. Damage to various bank protective works was
described in an earlier section of the report. Figures 30, 31,and 34
illustrate the types of damage incurred.
Damage to buildings was predominantly from undermining of founda-
tions by bank recession. The office building complex immediately
southeast of the First Avenue bridge was undermined by the migration of
a meander bend upstream of that bridge (Figure 35). Collapse of the
structure progressed as flows continued to erode unprotected banks
(Figure 36). The Pima Park Townhomes (Figure 37) were undermined
despite protection by a soil-cement revetment. Although the damage can
be traced to improper keying of that revetment, the experience shows
that even the best type of bank protection will not necessarily provide
100 percent control of the hazard. Mobile homes and vehicles were
introduced into the flooded stream channels either by undermining
(Figure 38) or by floating in overbank flows. In a major flood, these
large pieces of debris can pose a hazard by blocking narrow channel
reaches, such as bridge underpasses.
Other sections of this report have summarized the failures of
bridges (see Figures 17, 21, 27, and 28). Table 6 summarizes these
failures. In most cases, failure was by the erosion of one abutment
(Figure 39), generally by the migration of a meander loop at that
point. Careful study of the flood erosion and sedimentation survey
(Appendix B) reveals a systematic pattern of erosion at meander loops,
much of it directed or otherwise facilitated by the extant piecemeal
bank protection. Eroded abutments left breaches in the roadways (Figure
40) that closed many highways during and after the floods.
Power lines along both the Santa Cruz River and the Rillito were
severely damaged. Power line poles near channel banks were toppled when
bank recession undermined their support pads. Other poles and towers
had deep footings in bed or bank materials that were exhumed by channel
bed scour, causing some towers to topple and others to be severely
imperiled by subsequent flows. Along the utility right-of-way for the
Santa Cruz River from Valencia Road to the confluence of the Rillito,
the postflood erosion survey counted 28 high-voltage electric towers
that were severely damaged or destroyed. Another 13 low-voltage poles
were twisted or toppled in the reach of the Santa Cruz from Grant Road
to the confluence of the Rillito. One hundred meters west of the Dodge
Road bridge, a Tucson Electric power station was threatened by 15 to 25
m of bank recession on the Rillito (Figure 27). As shown in Figure 27,
bank erosion ceased prior to undermining structures at the power sta-
tion. The many damaged high-voltage poles in the Rillito utility
right-of-way were not counted in the survey.
Damage to sewer line crossings of the major washes is a major
concern, since considerablerecharge to the principal aquifers occurs
through the sandy streambeds. A municipal sewage line was threatened on
the Santa Cruz approximately 1.6 km north of Martinez Hill. A levee was

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FIGURE 35 Damage to an office building complex caused by the
undermining of the bank of the Rillito at First Avenue. An
aerial view of this site is provided in Figure 28. Photograph
by Tad Nichols.

FIGURE 36 Damage to an office building adjacent to unprotected
channel banks along the Rillito immediately upstream (east) of
the First Avenue bridge. Photograph by Thomas F. Saarinen.

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FIGURE 37 View downstream (northwest) along the Rillito from
the terminus of Prince Road (lower left) on October 8, 1983.
Compare this picture with the aerial view that includes the same
reach (Figure 31). The house in the left foreground has toppled
into the active meander cut slope. Damage to the Pima Park.
Townhomes is visible in the right background. Photograph by
Thomas F. Saarinen.

constructed in the channel after the flood from channel sediments to
divert relatively small postflood discharges from an active cutbank on
the east abutment of the sewer line crossing.

RECOMMENDATIONS FOR FUTURE STUDIES

The geomorphic and hydrologic complexity of stream systems In the
semiarid West does not lend itself to the flood hazard regulatory
practices established at the national level. The nature and pat tern of
damages in the 1983 flood confirm this conclusion. We recommend the
following areas of research to improve the scientific basis for flood
hazard regulation in these regions:

1. A method of flood-frequency analysis must be developed for a
statistical series of peak flow records that violate assumption of a
stationary mean. Regional hydroclimatological studies and paleohydro-
logical studies of recent flood deposits may be promising approaches in
this research.

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FIGURE 38 Flood debris in the channel of Pantano Wash from the
Rincon Country mobile home development (see Figure 26) in late
October 1983. The view is downstream (north). Photograph by
Peter Kresan.

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FIGURE 39 Dodge Road bridge on October 8, 1983, showing erosion
of its north abutment by the Rillito. A ground photograph of
the bridge is shown in Figure 40. Photograph by V. R. Baker.

TABLE 6 Selected Observations of Bridge Damages from the 1983
Tucson Flood

Stream Bridge Observations

Santa Cruz Northbound Inter- Riprap bank protection failed to prevent
state 19 erosion of north abutment, resulting in
the loss of about 60 m of the northbound
approach lane (Figure 17).

Santa Cruz San Xavier Road bridge About 200 m of preflood riprap
at Martinez Hill revetment on the west bank failed to
prevent erosion of the west bridge
abutment. Approximately 30 m of bank
recession occurred in an active meander
bend (Figure 17).

Santa Cruz Valencia Road Bank erosion of 10 m threatened to destroy
the west abutment, but artificial filling
during the flood prevented this. Bank
erosion occurred despite a riprap
revetment because scour undermined this
protection.

Santa Cruz Grant Road bridge The west abutment was'damaged by the
westward migration of a meander cut
slope. An old landfill upstream of the
bridge was also exposed in this meander
bend.

Santa Cruz Sunset Road bridge Total destruction.

Santa Cruz Ina Road bridge The west abutment was scoured despite
preflood protection with a riprap
revetment (Figure 21).

Santa Cruz Cortaro Road bridge Total destruction despite preflood
protection with a wire-fence revetment.

Rillito Swan Road The north abutment was eroded by the
cutbank of a meander.

Rillito Dodge Road The north abutment was eroded by the
cutbank of a meander (Figures 27, 39, and
40).

Rillito Campbell Avenue Damage to the north abutment occurred
despite a wire-fence and riprap revetment.

Rillito First Avenue The north abutment was eroded by the
cutbank of a meander (Figure 28).

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FIGURE 40 The Rillito at Dodge Road on October 5, 1983, show-
ing the erosion of the north abutment. Photograph by Peter
Kresan.

2. The complex regime behavior of semiarid streams must be incor-
porated into the analysis of channel behavior during flood events. This
involves an appreciation, through geamorphic research, of the channel
changes that occur in semiarid streams over a time scale of decades to
centuries.
3. A total-system approach needs to be developed for the management
of ephemeral stream courses in urban areas. This approach needs to
establish the sediment budget responsible for regime adjustments. It
also needs to establish the influence of urban land-use changes on both
runoff and sediment yield to the stream courses.
4. Bank protective works, either piecemeal or continuous, need to
be evaluated for their effects on the total stream system.

THE HUMAN RESPONSE TO THE OCTOBER 1983 FLOOD IN TUCSON

When the October 1983 flood hit Tucson, it caught local officials by
surprise. Many of those with responsibilities in an emergency were out
of town that first weekend of October. Those present soon found them-
selves in a chaotic disaster situation for which they were poo rly pre-
pared. Although individuals and groups responded well, there was an
overall lack of coordination and communication that indicated a want of
emergency planning and practice.
This chapter briefly describes the emergency response and attempts
to explain why the community was caught off-guard. The explanation in
turn examines two major factors: the public perception of the flood
hazard, and community attitudes toward long-term planning. These per-
ceptions and attitudes arise from the unique qualities of the desert
environment and the atmosphere of rapid growth that has marked Tucson
for the past several decades. Whether the flood of October 1983 will
result in better emergency responses and more enlightened long-term
planning is the subject of the final section.

THE EMERGENCY RESPONSE TO THE TUCSON FLOOD OF OCTOBER 1983

The emergency response to the Tucson flood of October 1983 showed the
familiar signs of a lack of thorough emergency preparation. The flood
arrived before most people realized its magnitude; timely warnings to
the public were often not forthcoming; communication channels became
jammed; good contact with the field was often unavailable; there was a
lack of coordination among the various agencies involved; and a lack of
trained emergency personnel to relieve regular staff soon became appar-
ent (Pima County Manager's Office, 1983).
A major part of the problem can be attributed to a failure to take
the flood hazard seriously. There was little or no regular practice of
emergency procedures before the flood. Therefore problems were not
anticipated or prepared for, proper equipment was not available, and
tasks were not assigned to particular individuals or agencies.
Pima County Emergency Services is an organization with a tiny staff
and small budget. Since the agency's main emphasis is on nuclear pre-
paredness or chemical spills on Interstate 10, it devoted little time or
energy to preparing for floods. Sporadic efforts in the past to organ-

ize meetings to discuss flood preparedness had failed because of a lack
of interest, a lack of high priority, and a lack of leadership. The
agency's Emergency Operating Center did not become the focus of the
flood emergency response because other local and state agencies worked
independently, using their own facilities with no apparent awareness of
the great advantages in dealing with a disaster through a single emer-
gency operating center. The lack of preparedness drills left each local
agency without a clear idea of the roles of other agencies and of how to
properly coordinate emergency response efforts.
The Pima County Sheriff's Department, which has major emergency
responsibilities, is an example. The department worked independently
out of their own facilities, which are far removed from the Emergency
Operating Center. Each of the department's rural and urban districts
also worked independently under a lieutenant. They did the tasks that
they have been trained to do, such as getting barriers on bridges and
highways, search and rescue, crowd control on arroyos, and evacuation as
the need for it became apparent. A major concern of the Sheriff's
Department was looting. The department was surprised to learn that very
little took place. As in many previous disasters, much looting was
expected and it turned out to be very rare in the emergency period.
Coordination and communication of information became a problem.
Well-organized and experienced volunteer agencies such as the Red Cross
were handicapped by a lack of good information. As Chapter 2 notes, the
National Weather Service provided good information, but it was not used
effectively at the local level. For example, in spite of the flood
disaster, the Emergency Broadcast System was not activated, and thus, as
Williams (1983) observes, "On Saturday, as the rivers rose and buildings
fell, recorded music, network talk shows, sports events, and cartoons
played on as if nothing was wrong."
This largely negative assessment of the local emergency response
should be balanced by acknowledging that Tucsonans, like most people in
disaster situations, did respond well as individuals and in agencies or
departments. There was great willingness to pitch in and help, and many
individuals and groups participated courageously and steadfastly. Two
rescuers died in the line of duty when their helicopter crashed during
rescue operations. The Red Cross did an excellent job of setting up
emergency shelters for flood victims and coordinating the flow of
blankets, clothing, and food. Many local government employees worked
long hours at necessary tasks, and hordes of volunteers showed up to
help. The major problem was the lack of overall coordination to use
these energies effectively and of timely action to ensure a prompt
response to all problems wherever they might be. The following two
sections examine the reasons for this lack of a well-coordinated
response.

PUBLIC PERCEPTION OF THE FLOOD HAZARD

Large, rare flood events are difficult to deal with anywhere. People
find it hard to imagine the volume of water that will fill their local
stream in a 50-, 100-, or 200-year flood because it is so far beyond the

normal events they have personally experienced. In Tucson this general
tendency to discount the possibility of large floods seems even more
extreme. The arroyos, dry washes, and riverbeds in Tucson are dry over
300 days per year. Also, most Tudsonans are newcomers. Since the Santa
Cruz has had fewer large flows over the past couple decades than have
most nearby comparable basins, most Tucsonans have had little direct
local flood experience.
The dry and sunny daily weather and dry washes in Tucson apparently
lead newcomers and oldtimers alike to discount the flood hazard. On the
few days each year when water flows, it is often only a few feet deep,
hardly menacing at the bottom of the deeply entrenched steep-walled
channels. Flash floods are typical. They rise quickly, recede quickly,
and are quickly forgotten. "The floods are forgotten as soon as the sun
comes out," said one county deputy sheriff to explain why the size and
persistence of the October 1983 flood caught them by surprise. The
rivers are so dry that local folklore has a category of "dry river
jokes." This is exemplified by the recently established, annual
"Rillito River Regatta," which features a parade of sand vehicles
dressed up to look like watercraft (Hatfield, 1982).
Tucson has suffered many severe floods since being founded, and
human intervention in the landscape has led to enormous changes in the
river bottoms (Dobyns, 1981; Betancourt and Turner, in press). The
irrigated agricultural landscape of the late Mexican and early Anglo
period was totally transformed during floods in the 1890s, when the
channel of the Santa Cruz at Tucson was entrenched. About 25 years
later another devastating flood destroyed the Congress Street bridge,
with lateral erosion there widening the channel to twice its former
width. Photographs such as that in Figure 41 show huge crowds watching
the flood. The convergence phenomenon was evident then just as in 1983,
when huge crowds watched the turbulent water.
The flood of 1914-15 was not exceeded until the 1960s, so it is not
surprising that the community's memory of major floods faded. People
who were 20 or older when they saw that flood would be past retirement
age before another flood of equal magnitude occurred. Even if they
remained in the community, their numbers would have been swamped by the
hundreds of thousands who arrived later with no knowledge of such large
local floods.
The rapid growth of Tucson over the past four decades (Bufkin,
1981) has produced a population largely inexperienced with the desert
(Saarinen, 1983) and local flooding conditions. Their images of
floodplains derived from more humid parts of the country do not ade-
quately describe the behavior of desert streams. Even professionals who
are well informed about local hydrologic conditions are outnumbered by
new arrivals who apply principles derived from other places. A shortage
of well-trained personnel is evident and understandable, since even
current hydrologic textbooks devote very little space to desert streams.
The first floodplain zoning ordinance applied in Tucson was based on
the standard U.S. model, which is based primarily on overbank floods
rather than lateral erosion. (See Bond (1984) for other problems
related to use of national models in the Arizona context.) It took
another decade of struggle before lateral erosion provisions were

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FIGURE 41 Huge crowds watch 1914-15 flood. Source: Special
Collections, University of Arizona Library.

included in local floodplain zoning ordinances. Many individuals and
groups made concerted efforts, against strong resistance, to raise the
level of concern about the flood hazard (Tellman et al., 1980).
Local newspaper coverage of pertinent past flood events could
partially remedy the lack of direct local experience with floods. At
the time of the floods in the 1890s and in 1914-15, the newspaper
offices were within a few blocks of the river. Reporters, editors, and
all other newspaper personnel had direct contact with the natural
events. The coverage was extensive. Today's newspaper offices are much
farther from the river, and writers or editors are little aware of the
rich archival sources in their own files that could provide perspectives
on flooding for the public. The special report on "The Flood of '83"
put out by the Arizona Daily Star on October 17, 1983 (Beal, 1983), did
a good job of documenting some of the damages from the flood. But it
failed to provide the public with any perspective on how often such
floods might occur or what the community should do to prepare for them.
Occasional editorials (Arizona Daily Star, 1981) or articles
(Emerine, 1983) take a long-term planning perspective toward floodplain
development. These are offset by others that strongly oppose floodplain
planning measures. The prodevelopment stance of one newspaper editor
was carried to extreme lengths in an editorial entitled "City Flood Plan
More Dangerous Than Flood Threat" (Tucson Daily Citizen, 1976). The
editorial downplayed the possibility of a severe storm, advocated a more

flexible ordinance, and raised the fear that Tucsonans might be "flood
proofed into the poorhouse." The quotation at the beginning of Chapter
I of this report by the Metropolitan Tucson Convention and Visitor's
Bureau (1983) provides another negative example of community leadership
with respect to the flood hazard.
Public awareness and concern about the flood hazard in Tucson are
very low. A study carried out by McPherson and Saarinen (1977) docu-
mented this low level of awareness and concern through interviews with
residents living in the floodplain. The interviews revealed that over
60 percent of these floodplain dwellers did not realize that their areas
were in a flood danger zone. Only 38 percent felt that they would be
personally affected by a major flood. In 1978, shortly after the
McPherson and Saarinen study was published, a major flood occurred on
the Santa Cruz River. The U.S. Army Corps of Engineers was then carry-
ing out some studies in Tucson, and the Corps supported a study to
interview residents in the Santa Cruz floodplain using the McPherson and
Saarinen questionnaire (Kemmeries, 1978). This provided a direct test
of the effect of the 1978 flood on people's perceptions of personal
risk. In the Kemmeries study only 9 percent perceived a personal risk,
compared with 38 percent in the previous study. Since most people were
spared any direct damage, they apparently felt this meant that they
would be spared again in the future. Similar comments were elicited in
informal interviewing of floodplain residents by a reporter from the
Tucson Citizen just after the October 1983 flood (Davis, 1983). The
findings of these studies are corroborated by the small number of flood
insurance policies that have been purchased in areas of risk (Arizona
Daily Star, 1983).
The local lack of awareness and concern about the flood hazard helps
explain why Tucson was unprepared for the October 1983 flood. But to
fully understand the local adaptation to the flood hazard, one must also
take into account general community attitudes toward long-term planning.

COMMUNITY ATTITUDES TOWARD LONG-TERM PLANNING

The phenomenal growth of Tucson during the past four decades has pro-
duced a prosperous economic climate and has attracted many people who
wish to profit from that climate. It has also led to some concern
regarding the deleterious social and environmental consequences of rapid
growth. A recent study (Planning and Management Consultants, 1980)
based on interviews of Tucson community leaders concluded that "the
dominant ideology in the community remains the traditional Arizona one
of unfettered growth; it is equated with freedom and the American way
(p. E-10)." Although seen as the dominant ideology, this view has never
been totally accepted and continues to be challenged (Abbey, 1984).
In the early 1970s Tucson went through a strong local debate on the
merits of controlled or managed growth. Many environmental activists
were linked with the controlled-growth side of the issue, and for a time
local politics were dominated by people with this view. The Tucson
Comprehensive Plan of 1975 (City of Tucson, 1975) clearly reflects the
controlled-growth view. It is interesting to note that a series of

volumes published by the Urban Land Institute in 1975 under the title
Management and Control of Growth includes both pro and con positions
taken by Tucsonans at the time (Finkler, 1975; Drachman, 1975).
Local developers vigorously opposed growth management. Most of the
environmentally oriented city council was voted out of office in a
recall election for the political mistake of raising the water rates
during the summer when water use was at a peak, and their views were
discredited. Currently, the progrowth forces, which are led by devel-
opers who have an obvious stake in this position, have the ascendancy.
In the recent mayoralty contest, the progrowth, prodevelopment incumbent
won a fourth successive four-year term, but ironically the majority of
the council is of the opposing party. The strength of feelings on both
sides has impeded discussion that could lead to wise decision making.
It is a local dilemma that stymies initiatives by either side.
The history of flobdplain zoning in Tucson clearly illustrates the
strong resistance of local landowners and developers to land-use con-
trols, as well as the general lack of awareness of flood-related issues
by the population. It is not simply a matter of people not realizing
that building in floodplains can be dangerous and expensive. Throughout
its history there have been Tucsonans who have learned by experiencing
floods. Before the entrenchment of the Santa Cruz, even minor floods
would cover much of the low@lying land in the valley, and a newspaper
report of 1886 stated that "the bottom of the Santa Cruz Valley is an
unsafe place for dwelling houses" (Betancourt and Turner, in press).
Presumably, others shared this view, since most development was on the
terraces above the valley floor. Still, even then there were some who
built houses in the valley bottom.
The earliest attempt to regulate development on the floodplain
aroused considerable wrath among local landowners. The two planners who
suggested it were hanged in effigy in 1963 in front of the Elks' Club
where a public hearing was to take place. The first paragraph of a
report in the Tucson Daily Citizen (Cooper, 1963) described the scene:

Some 400 irate landowners and residents along the Rillito River
today swarmed over a floodplain ordinance hearing, hanged two'
city-county officials in effigy and made one common point
clear: They are violently opposed to restrictive zoning.

There were threats of even worse treatment (Faure, 1981).
Real progress in developing floodplain zoning did not occur in
Tucson until the federal government exerted pressure at the state and
local levels. For many decades the federal government had pursued the
policy of building dams and levees to protect the public from floods.
This policy was not successful, as flood losses continued to grow
despite billions of dollars spent on flood protective structures.
Ironically, the building of large, expensive protective works often
helped to increase the damages of the large, rare floods, because of
what has been termed the "levee effect." Once levees were built, people
assumed that formerly risky areas were now safe and moved into them.
Thus when a large, rare flood brought waters beyond the capacity of the
flood protective works, floodwaters wreaked havoc on a much larger
population.

The new federal policy involved the carrot of flood insurance and
the stick of floodplain regulation. Flood insurance would be available
for any community that adopted floodplain regulations. These policies
reached Tucson in 1972, when the State of Arizona began passing flood
control legislation. The local government felt obligated to act,
because by making it impossible to obtain the needed insurance, the city
could be sued by someone suffering flood damages on the grounds that the
city failed to act.
As a result of state and federal pressure, both the City of Tucson
and Pima County developed floodplain zoning ordinances. Pima County's
ordinance was regarded as a weak one with many loopholes and no real
teeth. It was adopted in 1974. The City of Tucson, with its environ-
mentally oriented city council, was developing a much stronger ordi-
nance, which many people expected might later be adopted by the county
(City of Tucson Department of Planning, 1976). This proposed ordinance,
which contained provisions to deal with bank erosion on meanders, got
through the Citizen's Advisory Planning Commission. But it was never
adopted by the city council after most of the council's members were
ousted from office through the recall election. The city did not adopt
a strong floodplain ordinance. In fact, it did not adopt any floodplain
ordinance until federal pressure was once again applied.
The new federal pressure came from the completion of the local
floodplain mapping based on fixed bed models. At this point the city
was no longer eligible for flood insurance with only the intention of
adopting an ordinance. It now had to adopt an ordinance to remain
eligible for flood insurance. The state, too, which was providing funds
for the downtown Rio Nuevo project, required that the city have an
ordinance. In July 1980 the city therefore adopted a floodplain
ordinance much like the weak version adopted earlier by Pima County.
Even as it was adopted, the ordinance was seen as inadequate, and a
committee was set up to develop a better one. However, it should be
noted that the Pima County and City of Tucson ordinances, although not
ideal, are considered the best and most strictly enforced floodplain
ordinances in Arizona (Leslie A. Bond, personal communication, 1984).
The committee that was convened to develop a better floodplain
ordinance consisted of a variety of citizens, from laymen to experts.
Various city agencies were represented, as were the Southern Arizona
Home Builders Association and the Tucson Board of Realtors. It soon
became clear that the main battle was between the hydrologic experts
(from the University of Arizona and Pima College, the U.S. Geological
Survey, and the Corps of Engineers) and the home builders' representa-
tive. A compromise document was passed on to the council. The council
sent it back for further revisions due to strong pressure from builders
and real estate agents. When a less restrictive version returned from
the committee, the builders and realtors still objected. In a newspaper
article entitled "Diluted Flood Plain Law Likely," Burchell (1983)
stated that, "In the two most recent council discussions of the pro-
posal, it was amended four times at the request of the development
industry."
A measure of the degree of dilution of the original proposals may be
seen in the fate of the setback provision. One committee member felt

that no building should be allowed within 1,000 ft of the banks because
lateral erosion of that magnitude had occurred in the past. The devel-
opers wanted no setback. Getting a lateral erosion provision was an
accomplishment in itself. But by the time the provision appeared in the
ordinance adopted in 1982, the limit was only 300 ft for residential
buildings and 100 ft for commercial and'industrial developments. One
person interviewed pointed out that such compromises were a great step
forward from previous periods when only two extreme viewpoints existed:
those who advocated no building whatever in floodplains, and those who
said that the government should stay clear of the floodway and let the
buyer beware.

PIECEMEAL PLANNING IN FLOOD PLAINS

Past planning for floodplains in Tucson can best be described as piece-
meal. The history of floodplain zoning indicates that different juris-
dictions have used different design standards at different times. The
design standards of the 1960s differed from those of the 1970s, which
also differed from those of the 1980s.
Many of the areas of major damage in the October flood were devel-
oped in conformance with past codes. The Lamar Heights area was built
up before floodplain zoning was established (Figures 18 and 42). The
Pima Park Townhomes (Figure 31) on the Rillito near Prince Road were
built with densities derived from earlier zoning.
An exception was the damaged Riverfront Village executive offices on
North First Avenue (Figures 35 and 36), which were built at the in-
sistence of the developer despite their nonconformance with zoning
standards and the danger from floods. The developer was allowed to
build them after signing the following release statement (Pima County
Recorder, 1983):

We, the undersigned, our successors and assigns, do hereby save
Pima County and the City of Tucson, their successors and
assigns, their employees, officers, and agents, harmless from
any and all claims for damages related to the use of said lands
now and in the future by reason of flooding, flowage, erosion or
damage caused by water, whether surface, flood or rainfall.

A major difficulty in planning for the river as a system is that
most of the floodplain land in the Pima County portions of Tucson is
privately owned. The threat of suits by property owners may be enough
to gain them some variance. This does not mean that the city and county
cannot legislate the land use, but it does leave open the possibility of
suits that would leave the interpretation to the courts. National deci-
sions on environmental issues and a recent local court case involving a
streambed gravel pit mining operation (Pima County v. John Cardi, 1979).
indicate that the owners' wishes may not prevail when a hazard to life
and property is involved.
Private ownership of the river leads to decisions being made on a
plot-by-plot basis. Developers, who are engaged in a risky business

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FIGURE 42 Aerial view of Lamar Heights"on October 2) 1983.
Notice that the junction of Michigan and Koster avenues has been
eroded away along with several houses. Photograph by Peter
Kresan.

with a rather short-term time horizon, are inclined to disregard such
long-term hazards as floods, which may occur long after they have left
the scene. They prefer to avoid the extra costs of flood-proofing or
flood-protection and are likely to discount the flood hazard, as the
case of the Riverfront Village offices demonstrates. Furthermore, even
if individual developments did provide bank protection, these would only
enhance erosion immediately downstream (as demonstrated in Chapter.3 and
shown in Figure 43).
Another factor contributing to the piecemeal planning of the past is
a holdover of small-town attitudes toward dealing with desert floods and
rainfall. A casual attitude toward floods and rainstorms is evident in
the public works designed to handle flows of water. Dip crossings are
.common (Figure 44), and in spite of warning signs people try to ford
them during floods, sometimes paying for the mistake with their lives.
One substandard road crossing the bed of the Santa Cruz River was closed
by the October 1983 flood, isolating a subdivision south of Tucson for
five days. In the absence of storm sewers, certain streets handle the

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FIGURE 43 Aerial view of Santa Cruz River showing the sudden
widening of the stream banks at a point with no bank protec-
tion. Photograph by Peter Kresan.

runoff and become, in effect, tributaries of major streams when enough
rain falls. Each year after a major storm, pictures appear in the paper
joking about how people adapt to these conditions by pulling out their
water skis, inner tubes, or boats (Figure 45).

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FIGURE 44 Dip crossing showing common practice of roads cross-
ing at streambed level. Photograph by Thomas F. Saarinen.

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FIGURE 45 Youths on water skis after a rainstorm. Source:
Arizona Daily Star-.

This small-town atmosphere is not "as acceptable today as it once
was. Higher road and runoff standards are being demanded by the public
and are necessary in a city rapidly approaching a population of a half
million. The costly delays of tens of thousands of people by runoff or
increased chances of accidents can no longer be laughed off as minor
inconveniences. Sheriffs, police officers, and others often find the
problems of high flows in streets frustrating, inconvenient, and un-
safe. A channel more than a foot deep may force lengthy detours. As
more and more people arrive, the need for a more sensitive adaptation to
the desert environment'intensifies, not just with respect to the main
streams but throughout the newly urbanized environment.
As noted in Chapter 3, the ecosystem around Tucson has undergone
dramatic physical changes. Since the 1950s, the rate of removal of
groundwater (the sole water supply for Tucson) has exceeded the natural
rate of replenishment (Barr and Pingery, 1976). As a result, the water
table has been dropping at a rate that accelerates each year as the base
population continues to grow rapidly. The falling water table has
adversely affected the amount of riparian vegetation, which if present
would slow floodflows somewhat and contribute to the deposition of
sediments. The vast stretches of formerly open desert that are now
covered by houses, buildings, streets, roads, and other paved areas
leads to more rapid runoff with less sediment, thus enhancing the ero-
sive power of the rivers. Gravel, sand, and other sediment have been
mined for construction materials to build homes, roads, and other
buildings, as well as to provide fill for the major freeway, which
parallels the river's course for many miles through the city. Further-
more, major streets like River Road and Mission Lane trap most of the
sediment that formerly would wash down from the mountains to replenish
the sediment carried away by the rivers.
These human-induced changes to the ecosystem have occurred with
little heed to their potential consequences. Yet in a river or any
natural system, a change anywhere will reverberate throughout the
system. It is therefore important to try to elucidate some of the
repercussions caused by human alterations of the natural landscape.
This can make it easier to avoid the unforeseen deleterious effects that
occurred in the Tucson flood of October 1983 and will occur in future
flood events.
Adaptation to the local ecosystem is not needed only in the main
streams. It is necessary through the entire system of tributary
washes. Table 7 lists the probabilities of storms of various sizes
centering on small areas anywhere in Tucson's urbanized areas. These
can and do have devastating effects on small localities if the infra@
structure of pipes, conduits, and stream channels is inadequate (Reich,
1982). Therefore local adaptations to the ecosystem, such as a
detention-retention provision in the zoning ordinance designed to slow
runoff and enhance on-site infiltration, should be sought and welcomed.
Unfortunately, adoption of such innovations may take place only after a
protracted struggle, and the longer they are delayed the more costly
will be their implementation.

TABLE 7 Chance That Rainstorms Will
Strike a City of 100 Square Miles

Size of Storm Average Number of Strikes

200-year storm 2 strike's in 25 years
100-year storm 2 strikes in 10 years
50-year storm 2 strikes in 5 years
10-year storm 2 strikes in 1 year
5-year storm 4 strikes In I year
2-year storm 10 strikes in 1 year

Source: Reich, 1982.

FUTURE PROSPECTS FOR ENLIGHTENED FLOODPLAIN PLANNING IN TUCSON

Research on natural hazards often notes the tendency for people to adopt
mitigation measures immediately after a major disaster. If not adopted
then, the likelihood of adoption diminishes rapidly as the memory of the
event fades. There was a willingness to do something about floodplain
planning immediately after the Tucson flood of October 1983. The local
floodplain managers were astute enough to take advantage of this short
period of grace. As a result, on October 11, within a week of the
flood, the Pima County Board of Supervisors voted to amend the flood-
plain ordinance, placing an 18-month moratorium on rezonings and
construction in floodplains. Such an amendment would not have had a
chance of passing earlier, according to the head of the Pima County
Department of Transportation and Flood Control District (Bual, 1983).
The moratorium on rezonings and construction in floodplains gives
Tucson officials and citizens an opportunity to once more think through
the issue of floodplain management. The piecemeal planning of the past
does not work, as the pattern of enhanced erosion just beyond protected
areas demonstrates. The damage to public and private property along
stream banks was great, but it is minor compared with what it could be
given current construction plans in Tucson, particularly along the
Rillito.
The Rillito corridor has been one of the most active areas of land
speculation and development in the Tucson metropolitan area over the
past several years. This is especially the case along the north bank,
which is immediately adjacent to the Catalina foothills. This foothills
area is widely perceived as the most attractive and prestigious location
in Tucson. It has a spectacular mountain backdrop, wide vistas across
the valley, rolling terrain, and large and dense stands of saguaro-palo
verde desert vegetation. The desirability of the area has led to much
development pressure and rising land values. Land at Campbell Avenue

and River Road has the highest value in the corridor, but the entire
area from Country Club Avenue to Oracle Ro'ad has been bid up very high.
High land costs lead to high-density use. So the Rillito corridor,,
formerly notable for its rural ambience with stables, ranches, the
Rillito Race Track, and winding River Road (Figure 46), is now being
transformed by high-density residential development (Figure 47). Over a
thousand building units have been platted, and many would probably be
under construction were it not for the moratorium. Locations adjacent
to the river are reflected in such names as Haciendas de Rios, Rio
Cancion, Riverside Apartments, River Grove Estates, Rio Vista, and Lazy
Creek. Obviously the potential for flood damage will be much greater in
the future as these and other projects are completed.
The success of soil-cement bank protection has been praised and
seen by some as a solution to future flood erosion problems in Tucson
(Cornelius, 1983). The most notable use of soil-cement bank protection
was in the Rio Nuevo project west of downtown Tucson on the Santa Cruz
River, where close to 2 miles of bank protection were in place prior to
the October flood. But the cost of this project could be justified on a
benefit-cost ratio because of its special character. It is a very
large, long-term project designed to dovetail with downtown redevelop-
ment and the Santa Cruz River Park (Figure 48). Major important bridges
were already in place, and former landfill areas posed potential prob-
lems without adequate protection (Figure 49). Most projects would not
have as compelling a set of reasons for such substantial public and
private investment in bank protection and grade control structures. The
Rio Nuevo project was also designed to meet FEMA design standards for
the 100-year flood (850 m3/s or 30,000 cfs). During the October flood
the limits of its capacity were strained (Figure 50) and areas imme-
diately downstream were severely eroded (Figure 51). To build protec-
tive works beyond this standard is enormously expensive.
Since piecemeal planning will not work, the question becomes whether
to fully protect the river system or to leave it alone. Clearly it will
be hard to leave it alone given the bridges already in place and current
pressure toward development. In their recent studies, the Corps of
Engineers essentially concluded that the value of current development in
Tucson's floodplains did not warrant the costs of full bank protection,
which, including land acquisition costs, may amount to $3 million per
mile.
If Tucsonans insist on developing the floodplain, some hard thinking
should be devoted to the question of who pays. One view expressed is
that harvesting the floodplain should not be charged to people who
locate elsewhere. Presumably those who benefit should share in the
costs. It would be worthwhile to study carefully what the most
equitable arrangement of cost sharing between public and private
interests might be before proceeding further.
Meanwhile, as the memory of the October 1983 flood fades, the like-
lihood that appropriate mitigation measures will be adopted continues to
diminish. Less than two months after the Tucson flood, a meeting to
discuss its implications was organized by the Environment and Behavior
Committee of the University of Arizona. Speaking at the meeting were
the two top floodplain managers for the city and the county. A local

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FIGURE 46 Low-density rural ambiance formerly characteristic of
the entire Rillito corridor. On the left are homes, stables,
and open fields. On the right is a tennis club; in the upper
right background are the Pima Park Townhouses (see Figure 37).
Photograph by Peter Kresan.

expert from the university was also there with slides of the changes in
the river, as was the study team's leader with the team's preliminary
findings. One might imagine that less than two months after the largest
flood in the city's history, this meeting might have had great local
interest, particularly when calculations on the recurrence interval of

FIGURE 47 New construction now characteristic of many portions
of the Rillito corridor. Notice the Rillito Race Track in the
background. Photograph by Thomas F. Saarinen.

the flood were being presented. Not so. Both local newspapers men-
tioned the event, but it merited only a tiny interior article in each.
The head of the Pima County Flood Control District, in his speech at
this meeting, discussed the cycle of concern about floods. He said that
the community was now in the postflood stage, meaning back to normal.
As the newspaper coverage so clearly implied, the brief awakening to a
perceived need for floodplain management was over.
On February 21, 1984, the voters of Pima County approved a W-8
million bond election to repair flood damages. This indicated that the
community was willing to pay for damages from the October flood. To
what extent the community will support long-term future floodplain
management remains an open question.

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FIGURE 49 View looking south along the Santa Cruz with Inter-
state 10 on the left. The open, yet-to-be developed lands of
the Rio Nuevo project are west of the Santa Cruz between the
neighborhood of Menlo Park and the river. In the middle back-
ground is the Congress Street bridge. South of Congress is 'a
large area of sanitary landfill. Just above the bottom edge of
the photograph may be seen new construction of the first stage
of the Rio Nuevo project at St. Mary's Road (also see Figure
50). Photograph by Peter Kresan.

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FIGURE 50 The St. Mary's bridge during the flood of the Santa
Cruz,on October 2. 1983. Notice the waves above the level of
the riverside walk. The new construction in the background is
the first residential portion of the Rio Nuevo project. Photo-
graph by Peter Kresan.

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FIGURE 51 Point on the west bank of the Santa Cruz just beyond
the bank protection of the Rio Nuevo project. The top photo-
graph, taken during the flood on October 2, 1983, shows people
watching the undermining of the bank below the shed. The bottom
photograph, taken later in the month, shows that the portion of
the bank on which the shed stood is no longer present. The view
of the house is no longer obscured by the shed and the roots of
the tree at right are exposed. Photograph by Peter Kresan.

CONCLUSIONS

The study team limited its study to the Tucson metropolitan area to
focus on what it regarded as two important aspects of the event. The
first was the way in which floods of desert streams differ from floods
in humid areas, for which most floodplain legislation has been devel-
oped. The second was the implications of Tucson's rapid growth for
dealing with the flood hazard.
The storm that caused the Tucson flood of October 1983 had a recur-
rence interval for a 24-hour period of 30 to 50 years. Soils were
saturated prior to the flood by the third wettest August and the second
wettest September of record. Problems arose in the gathering and com-
munication of hydrologic information during the storm, and the dissemi-
nation of weather-related information to the public and emergency
agencies was often inadequate. Agencies involved in disasters need to
work together before, during, and after the event to coordinate their
efforts, and the role of the National Weather Service in analyzing the
event needs to be clearly defined.
The stream flows on the Santa Cruz River and the Rillito were the
largest of record, though those on the Canada del Oro and Pantano were
not. The record flow on the Santa Cruz was one of a series of high
flows since the early 1960s. These can be interpreted as the result of
an unusually wet series of years and human-induced changes in the
natural system that have accentuated runoff. Certainly, within the
Tucson metropolitan area, the desert has been significantly altered in
ways that enhance stream flow. To be on the safe side, the community
should design as if more high flows will be forthcoming.
The nature and pattern of damages and channel change during the 1983
flood demonstrate the profound geomorphic and hydrologic complexity of
stream systems in the semiarid West. Nationally standardized procedures
for flood-hazard evaluation proved inadequate for anticipating the dam-
ages. When the method developed by the U.S. Water Resources Council
(1981) of determining floodflow frequency is applied to the Santa Cruz
River for the period 1915-81, the 1983 flood discharge is predicted to
have a return period greater than 1,000 years. The 1983 flood exceeded
the 100-year flood magnitude of the Federal Emergency Management Agency
(FEMA) by a factor of 1.75. However, these flood-frequency analyses
appear to violate the assumption of a stationary mean, since the largest

floods on the Santa Cruz occur in the most recent part of the flood
series.
Even more problematic is the use of standard step-backwater calcula-
tions to route flood discharges obtained from the standard flood-
frequency analyses. This procedure, as used in FEMA's 1982 Flood
Insurance Study, assumes a static channel and valley floor geometry.
So much channel enlargement occurred during the flooding that the FEMA
study greatly overestimated areas of overbank flooding along many seg-
ments of the Santa Cruz. Standard hydraulic procedures simply do not
apply to the complex sediment-charged stream systems of the semiarid
West. The regime behavior of such streams must be incorporated into the
analysis of channel behavior during flood events.
Within Tucson there was little overbank flow. The greatest flood
damage was caused by lateral erosion of arroyo walls. This provides
strong justification for the lateral erosion provision recently added to
the local floodplain zoning ordinances. Lateral erosion severely dam-
aged buildings adjacent to the streams and bridges, causing transporta-
tion problems and creating large expenses for the community.
Soil-cement bank protection, which has been used in several sections
of the river system, held up well, but aerial photographs of flood
damage reveal that this was at some expense to adjacent areas. A
consistent location of lateral erosion was immediately downstream from
places with strong bank protection. Piecemeal bank protection does not
work. Clearly the rivers must be treated as a system. The areas along
streams should either be left alone or completely protected.
Downstream from Tucson stream channels disappear. In this area of
deposition from ephemeral streams, floodwaters spread over a wide area,
moving as sheet flow with no permanent channel. Here the flood damaged
agricultural land and human settlements, with the usual associated
problems.
The Tucson flood has provided the community with a strong impetus to
think carefully about future floodplain development. So far, only a
limited amount of development has occurred in the flood-prone areas.
But as open space close to the city has become more scarce due to rapid
urban growth, pressure has built to develop the floodplain land, which
is largely privately owned. In a community dominated by positive atti-
tudes toward growth and development, it will be difficult to resist this
pressure. Yet the costs of complete bank protection are prohibitive.
Unless private developers in conjunction with public authorities can
organize some sort of improvement district to pay the costs of protect-
ing the entire river, it would be unwise for the community to allow them
to proceed. Furthermore, if complete bank protection is provided, grade
control structures will be needed to prevent downcutting that would
undermine the protective works. The costs of these grade control struc-
tures might equal or exceed the cost of bank protection. But even if
these enormous costs could be met, and Tucson were completely protected,
what would happen to the areas downstream?

RE FERENCES

Abbey, Edward, (1984) "Arizona's Future: How Big is Big Enough?" Arizona
Daily Star, January 29.

Arizona Daily Star (1981) "Flood Precautions Wise," editorial, November
8.

Barnes, Peggy (1983) "Only 5 Percent of City Homeowners Insured for
Floods, Experts Say," Arizona Daily Star, October 4.

Barr, James L., and David E. Pingery (1976) "Rational Water Pricing in
the Tucson Basin," Arizona Review 25(10):1-10.

Beal, Tom, (1983) "The Flood of '83: A Special Report," Arizona Daily
Star, October 17.

Betancourt, Julio L., and Raymond M. Turner (in press) "Historic Arroyo-
Cutting and Subsequent Channel Changes at the Congress Street Cross-
ing, Santa Cruz River, Tucson, Arizona," Water Supply Series, U.S.
Geological Survey, Tucson, Arizona.

Bond, Leslie A. (1984) "Floodplain Management and Unique Hazards In
Arizona," paper presented at the Western States Invitational
Workshop on Enhancing State Capability for Mapping and Managing
Unique Flood Hazard Areas, February 15-16, 1984, Palm Springs,
California.

Bual, Bobbie Jo, (1983) "Floodplain Rules Were Dead Till Storms,
Huckleberry Says," Arizona Daily Star, October 15.

Bufkin, Don, (1981) "From Mud Village to Modern Metropolis: The
Urbanization of Tucson," The Journal of Arizona History 22(2):63-98.

Bull, William B., and K. M. Scott (1974) "Impact of Mining Gravel from
Urban Stream Beds in the Southwestern United States," Geology
2(4):171-174.

Burchell, Joe, (1982) "Diluted Flood Plain Law Likely," Arizona Daily
Star, March 22.

City of Tucson (1975) The Comprehensive Plan for the City of Tucson,
Pima County, the City of South Tucson, and Pima Association,of
Governments.

City of Tucson Department of Planning (1976) Floodplain Regulation: A
Report to Accompany the Proposed Floodplain Ordinance, City of
Tucson.

Committee on Natural Disasters (1982) Storms, Floods, and Debris Flows
in Southern California and Arizona, 1978 and 1980, National Academy
Press, Washington, D.C.

Cooke, Ronald U., and Richard W. Reeves (1976) Arroyos and Environmental
Change in the American South-West, Clarendon Press, Oxford.

Cooper, Jim (1963) "Flood Plain Foes Erupt at Meeting," Tucson
Citizen, May 23, 1963.

Cornelius, Terry, (1983) "Soil Cement Praised as Flood Fighter," Tucson
Citizen, October 5.

Court, Arnold (1980) Tropical Cyclone Effects on California, Technical
Memorandum NWS-WR-159, National Oceanic and Atmospheric Administra-
tion, Salt Lake City.

Davis, Tony (1983) "Buy Riverfront Property, Break Flood/Rebuild
Pattern," Tucson Citizen, December 2.

Dobyns, Henry F. (1981) From Fire to Flood: Historic Human Destruction
of Sonoran Desert Riverine Oases, Anthropological Paper No. 20,
Ballena Press, Socorro, New Mexico.

Douglas, Arthur V. (1972) "The Climatology of Northeastern Pacific
Tropical Storms and Hurricanes," First Progress Report, NOAA
Contract 1-35241, Laboratory of Tree-Ring Research, Tucson.

Drachman, Roy P. (1975) "Land Use Under Restraints: A View of/from
'the Industry,"' pp. 501-508 in Management and Control of Growth,
Randall W. Scott, David J. Brower, and Dallas D. Miner T-eds.), Urban
Land Institute, Washington, D.C.

Emerine, Steve (1983) "Floods Resurrect Issue of Rampant Tucson Growth,"
Arizona Daily Star, October 12.

Faure, Andre M. (1981) Arizona Daily Star, letter to the editor,
November 30.

Federal Emergency Management Agency (1982) Flood Insurance Study, City of
Tucson, Arizona, Pima County, Federal Emergency Management Agency,
Washington, D.C.

Federal Emergency Management Agency (1983) briefing paper for the
Interagency Hazard Mitigation Team meeting commencing October 17,
1983, at 1:00 p.m., Federal Emergency Management Agency, Washington,
D.C.

Finkler, Earl (1983) "Nongrowth As A Planning Alternative: A Preliminary
Examination of an Emerging Issue," pp. 118-135 in Management and
Control of Growth, Randall W. Scott, David J. Brower, and Dallas D.
Miner (eds.), Urban Land Institute, Washington, D.C.

Hansen, E. Marshall, and Francis K. Schwarz (1981) Meteorology of
Important Rainstorms in the Colorado and Great Basin Drainages,
Hydrometeorological Report No. 50, U.S. Corps of Engineers, Silver
Spring, Maryland.

Hansen, E. Marshall, Francis K. Schwarz, and John T. Riedel (1977)
Probable Maximum Precipitation Estimates, Colorado River and Great
Basin Drainages, Hydrometeorological Report No. 49, U.S. Corps of
Engineers, Silver Spring, Maryland.

Hatfield, David (1982) "Rillito Regatta No Ordinary Stunt," Arizona
Daily Star, May 26.

Kemmeries, Nancy (1978) "Flood Hazard Perception in Tucson, Arizona,"
Tucson Urban Study, U.S. Army Corps of Engineers, Los Angeles
District, Los Angeles.

Kennedy, John F. (1983) "Reflections on Rivers, Research, and Rouse,"
Journal of Hydrological Engineering, ASCE 109(10):1258-1260.

McPherson, Harold J4, and Thomas F. Saarinen (1977) "Flood Plain
Dwellers' Perception of Flood Hazard," The Annals of Regional
Science 9(2):25-40. Reprinted in Arizona Review 26(12):l:, TO.

Metropolitan Tucson Convention and Visitor's Bureau (1983) Public
Service Announcement 3011, Tucson.

Moss, J. H., V. R. Baker, D. 0. Doehring, P. C. Patton, and M.. G. Wolman
(1978) Floods and People: A Geological Perspective, Report of the
Committee on Geology and Public Policy, Geological Society of
America, Boulder, Colorado.

National Weather Service (1973) Precipitation-Frequency Atlas of the
Western United States, Vol. 8: Arizona, National Oceanic and
Atmospheric Administration, Silver Spring, Maryland.

Oceanographic Monthly Summary (1983) Vol. 3(9).

Pearthree, M. S. (1982) Channel Change in the Rillito Creek System;
Southeastern Arizona, unpublished, University of Arizona, Tucson.

Pima County Manager's Office (1983) Administrative Review of Emergency
Operations During the Flood Disaster of October I-October 5, 1983,
November 15, Pima County.

Pima County Recorder (1983) Plat for Riverfront Village and Riverfront
Condominiums, book 36, page 10 of maps and plats, April 21.

Pima County v. John Cardi (1979) Arizona Reports, June 5.

Planning and Management Consultants (1980) The Evaluation of Water
Conservation for Municipal and Industrial Water Supply, Vol. II:
Illustrative Examples, U.S. Army Engineer Institute for Water
Resources, Fort Belvoir, Virginia.

Pyke, Charles B. (1975) Some Aspects of the Influence of Abnormal Eastern
Pacific Ocean Temperatures upon Weather Patterns in the Southwestern
United States, NR 083-287, Vol. II, Department of Meteorology,
University of California, Los Angeles.

Reich, Brian M. (1982) Memorandum of September 2 to City Engineer
reporting on drainage complaints from the storm of 14:30/15:30,
August 23, 1982, Deputy City Engineer, Floodplain Section, City of
Tucson.

Saarinen, Thomas F. (1983) "Public Perception of the Desert in Tucson,
Arizona," paper presented at Social Implications of Environmental
Problems: A Mexico/United States Research Workshop, March 9-11,
1983, Rio Rico, Arizona.

Smith, G. E. P. (1910) Groundwater Supply and Irrigation in the Rillito
Valley, University of Arizona College of Agriculture, Agricultural
Experiment Station Technical Bulletin 64, Tucson, Arizona.

Tellman, Barbara, Edgar McCullough, and Priscilla Robinson (1980) Flood
and Erosion Hazards in Tucson, Southwest Environmental Service,
Tucson.

Tselentis, Tony (1976) "Beware 'Freak' Storms," Tucson Citizen, August 7.

Tucson Citizen (1976) "City Flood Plan More Dangerous Than Flood Threat,"
editorial, May 25.

U.S. Water Resources Council (1981) Guidelines for Determining Flood Flow
Frequency, Bulletin 178, U.S. Water Resources Council, Washington,
D.C.

Weaver, Robert L. (1962) Meteorology of Hydrologically Critical Storms in
California, Hydrometeorological Report No. 37, U.S. Weather Bureau,
Washington, D.C.

Williams, David (1983) "Local Radio, TV Dropped the Ball on Flood
Warning," Arizona Daily Star, October 7.

APPENDIX A:

WEATHER MAPS FOR SEPTEMBER 28-OCTOBER 3, 1983

1@"O 1012 IW4 low "1012 low low 608 W12 wo fQ4
di, lilt
12
ftlN,

14,
4;;
17

76%,
mok,

V.
Ne A- 5, -v, z 1- " -1
!4
51
'W2 T
-j!
55

52
so
51,

51.

lot

"of
7 ltt@
"WAC1, "KA:11111 '1,11' 1
&7A-t), v 4n tI.
IN11r, 1016
[A
Ai toj

'7-@ -,--m 777-@ w
7,1
A\
''u"40-

110*

10
14 P-MMUWAR @@i WT 1@, :IN To u fil

FIGURE Al Meteorological conditions on Monday, September 26,
1983.

7737V
"R @ I , -" " - @ " @' -, "!'jl. low
400'10 2
1016

'@x
'23 "fli
46,5
q
TZ -
, 5 . -11 ;' 'A' _@'

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15
swu v,
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77,
Sal

1016

"I M@
Wr- @X
A
j"7

-4-

T-.
'k, /Tf

14,1

FIGURE A2 Meteorological conditions on Tuesday, September 27,
1983.

7
3?v 1020 1024 1 16" too; 1040 toloz,
10 , ,. [email protected]

"k
NO,

4@
s@. I

44T
I I-, u@ - -1_@ 11@ 1i "It
41 1 1 .N
IS

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+

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P
vt

-tf
@7 wh@

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IT 7.10 E,IrKtr@g
AND 1,7ATIO@ lott"I

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ZVI
V

to",

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-7-7

FIGURE A3 Meteorological conditions on Wednesday, September 28,
1983.
lil, I Olt)

* C86T
'6Z jaqmaidaS Ifupsanqj, uo SUOT3TPU03 Tv'aT!@OTOaO93aW i7V HHMId

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Item

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-t 71
48

17"
IM, @,A
"40

IL
511

J,
ZO

1012
7-- VN r

n`a@,, 1- 1-11 ,
77

FIGURE A5 Meteorological conditions on Friday, September 30,
1983.

IW4 0
31 p
V

31
"50

A
MGM g
n
4@
-4;, YW,"7,
r, 5@4
"V M Alt
Boy 20'
IT

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,j@ g&
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Ij

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LOW

ZA,

3
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twy

"L I' i Y11 1016
11 C@j

Nj
t4
n W
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C04 uw,
7'@;o A 0A, i-A

FIGURE A6 Meteorological conditions on Saturday, October 1,
1983.

I IOU
4012-3r- Z' z:1

I@01

Well-
5!2 r@

Rion

"A'
AI

A f

77-77-111
Thf-ri-

z -t It,

:,4 z

I to
7", -'7,,' i7-

FIGURE A7 Meteorological conditions on Sunday, October 2,
1983.

t to" "IC0 IOU j6,V,! 1000
cis- 10rt2 1008 004
"St-

/0"
'Sa
41

vol "t-E
au
m2pi,
91

IP, "W f

I&
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co,
419T
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2

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vj
- V*t
0 -1t
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@7
z 7 ": - - 11 --,
W- v q

A
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,

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t
-77- 7

Z t
WWI'

@4
A, M,
7@

FIGURE A8 Meteorological conditions on Monday, October 3,
1983.

APPENDIX B:

MAPS OF POSTFLOOD BANK EROSION IN THE TUCSON BASIN

M
\\@A
AARA

RILLITO

ORTARO

INA RD

W
0
z cc
0 FL
U

P INCE

W
GRANT 0
C
/@'T MA WS J OA WAY SPEEDWAY
\J

22ND ST
0 51
v
GOLF LIN@XS
AFB ESCALANTE
IRVINGTON

"30

LIVIARTINEZ HILL

SCALE
0 10
5

MILES
01 5 10 115
KILOMETERS
4S'P '@'.W@A-1@1

Watercourses near Tucson with an index to the following maps
showing erosion, bank protection, and related flood effects from
the October 1983 flood.

101

102

AJO WAY

CONCRETE DROP
STRUCTURE

IRVINGTON ROAD

LEGEND:
PREFLOOD BANK
BANK EROSION
SAND/GRAVEL PIT
BANK PROTECTION
DREXEL ROAD
-SOIL-CEMENT REVETMENT
WIRE-FENCE REVETMENT
N ... RIPRAP
f -UNSORTED DEBRIS
--UNCLASSIFIED REVETMENT

SCALE
1/2 0 1/2 1
VALENCIA ROAD ==low
MILES
0
==mold
KILOMETERS

so,

MAP 1 The Santa Cruz River from.Martinez Hill to Ajo Way.
CON
' N S
DROP
'R @E
ROAD
@'R 0,

103

SPEEDWAY LVD

ST MARY RD
LEGEND:
PREFLOOD BANK
BANK EROSION
SAND/GRAVEL PIT
BANK PROTECTION
W ST
-SOIL -CEMENT REVETMENT CONGRESS
WIRE-FENCE REVETMENT N
RIPRAP
---UNSORTED DEBRIS
---UNCLASSIFIED REVETMENT

SCALE
1/2 0 1/2 1

MILES 22ND ST
0 1
.1
KILOMETERS

29 TH T

f
I
AJO WAY

MAP 2 The Santa Cruz River from Ajo Way to Speedway Boulevard.

104

SUNSET RD

7r-O

AREA OF
OVERBANK
FLOODING

RUTHRAUF RD 0

SWEETWATER RD

PRINCE RD

FT LOWELL RD

LEGEND:
PREFLOOD BANK
BANK EROSION
SAND/GRAVEL PIT
BANK PROTECTION
-SOIL-CEMENT REVETMENT
WIRE-FENCE REVETMENT
RIPRAP N
... UNSORTED DEBRIS
---UNCLASSIFIED REVETMENT

SCALE
1/2 0 1/2 1

MILES
i 0 1

KILOMETERS

SPEEDWAY BLVD

MAP 3 The Santa Cruz River from Speedway Boulevard and the
Rillitc, from La Canada DrIve to their confluence.

105

CHANNEL CARVED
BY FLOOD

OAI-

ROCKS RD

MAP 4 The Santa Cruz River from its confluence with the Rillito
to Valley Road.

106

BROADWAY BLVD

22ND ST

GOLF LINKS RD

LAKESIDE
PARK

z z

MAP 5 Pantano Wash from Houghton Road to Broadway Boulevard.

107

"I'D
WASS
3

REACH
NOT
MAPPED

GRANT RD

LEGEND:
PREFLOOD BANK
BANK EROSION
SAND/GRAVEL PIT
BANK PROTECTION
-SOIL-CEMENT REVETMENT
WIRE-FENCE REVETMENT N
... RIPRAP
... UNSORTED DEBRIS @PEMWAY .-D
---UNCLASSIFIED REVETMENT

SCALE
1/2 0 1/2 1

MILES
0 1
I'_
KILOMETERS

BROADWAY BLVD

DROP STRUCTURE

MAP 6 Pantano Wash from Broadway Boulevard and Tanque Verde
Creek at their confluence.
k,

108

ORACLE RD

FIRST AVE

CAMPBELL AVE

No z
COUNTRY CLUB AVE

_____20DGE RD

SWAN RD

MAP 7 The Rillito from Swan Road to Oracle Road.

NATIONAL RESEARCH COUNCIL REPORTS OF POSTDISASTER STUDIES, 1964-1983

Copies available from sources given in footnotes a, b, and c.

EARTHQUAKES

The Great Alaska Earthquake of 1964:a

Biology, 0-309-01604-5/1971, 287 pp.
Engineering, 0-309-01606-1/1973, 1198 pp.
Geology, 0-309-01601-0/1971, 834 pp.
Human Ecology, 0-309-01607-X/1970, 510 pp.
Hydrology, 0-309-01603-7/1968, 446 pp.
Oceanography and Coastal Engineering, 0-309-01605-3/1972, 556 pp.
Seismology and Geodesy, 0-309-01602-9/1972, 598 pp.,
PB 212 981.a,c
Summary and Recommendations, 0-309-01608-8/1973, 291 pp.

Engineering Report on the Caracas Eartbquake of 29 July 1967 (1968) by M.
A. Sozen, P. C. Jennings, R. B. Matthiesen, G. W. Housner, and N. M.
Newmark, 233 pp., PB 180 548.c

The Western Sicily Earthquake of 1968 (1969) by J. Eugene Haas and Robert
S. Ayre, 70 pp., PB 188 475.c

The Gediz, Turkey, Earthquake of 1970 (1970) by Joseph Penzien and Robert
D. Hanson, 88 pp., PB 193 glg.b,c

cl'National Academy Press, 2101 Constitution Avenue, N.W., Washington,
D.C. 20418.

bCommittee on Natural Disasters, National Academy of Sciences, 2101
Constitution Avenue, N.W., Washington, D.C. 20418.

cNational Technical Information Service, 5285 Port Royal Road,
Springfield, Virginia 22161.

109

110

Destructive Earthquakes in Burdur and Bingol, Turkey, May 1971 (1975) by
W. 0. Keightley, 89 pp., PB 82 224 007 (A05).b,c

The San Fernando Earthquake of February 9, 1971 (1971) by a Joint Panel on
the San Fernando Earthquake, Clarence Allen, Chairman, 31 pp., PB 82 224
262 (A03).b,c

The Engineering Aspects of the QIR Earthquake of April 10, 1972, in
Southern Iran (1973) by R. Razani and K. L. Lee, 160 pp., PB 223 599.c

Engineering Report on the Managua Earthquake of 23 December 1972 (1975) by
M. A. Sozen and R. B. Matthiesen, 122 pp., PB 293 557 (A06).b,c

The Honomu, Hawaii, Earthquake (1977) by N. Nielson, A. Furumoto, W. Lum,
and B. Morrill, 95 pp., PB 293 025 (A05).c

Engineering Report on the Muradiye-Caldiran, Turkey, Earthquake of 24
November 1976 (1978) by P. Gulkan, A. Gurtinar, M. Celebi, E. Arpat, and
S. Gencoglu, 67 pp., PB 82 225 020 (A04). c

Earthquake in Romania March 4, 1977, An Engineering Report, National
Research Council and Earthquake Engineering Research Institute (1980) by
Glen V. Berg, Bruce A. Bolt, Mete A. Sozen, and Christopher Rojahn, 39
pp., PB 82 163 114 (A04).b,c

El-Asnam, Algeria Earthquake of October 10, 1980, A Reconnaissance and
Engineering Report, National Research Council and Earthquake Engineering
Research Institute (1983) by Vitelmo Bertero et al., 195 pp.b,c

Earthquake in Campania-Basilicata, Italy, November 23, 1980, A
Reconnaissance Report, National Research Council and Earthquake
Engineering Research Institute (1981) by James L. Stratta,Luis E.
Escalante, Ellis L. Krinitzsky, and Ugo Morelli, 100 pp., PB 82 162 967
(A06).b,c

The Central Greece Earthquakes of February-March 1981, A Reconnaissance
and Engineering Report, National Research Council and Earthquake Engi-
neering Research Institute (1982) by Panayotis G. Carydis, Norman R.
Tilford, James 0. Jirsa, and Gregg E. Brandow, 160 pp., PB 83 171199
(A08).b,c

The Japan Sea Central Region Tsunami of May 26, 1983, A Reconnaissance
Report (1984) by Li-San Hwang and Joseph Hammack, 19 pp., PB 84 194 703
(A03).b,c

FLOODS

Flood of July 1976 in Big.Thompson Canyon, Colorado (1978) by D. Simons,
J. Nelson, E. Reiter, and R. Barkau, 96 pp., PB 82 223 959 (A05).b,c

Storms, Floods, and Debris Flows in Southern California and Arizona--1978
and 1980, Proceedings of a Symposium, September 17-18, 1980, National
Research Council and California Institute of Technology (1982) by Norman
H. Brooks et al., 487 pp., PB 82 224 239 (A21).c

Storms, Floods, and Debris Flows in Southern California and Arizona--1978
and 1980, Overview and Summary of a Symposium, September 17-18, 1980,
National Research Council and California Institute of Technology (1982) by
Norman H. Brooks, 47 pp., PB 82 224 221 (A04).b,c

The Austin, Texas, Flood of May 24-25, 1981 (1982) by Walter L. Moore,
Earl Cook, Robert S. Gooch, and Carl F. Nordin, Jr., 54 pp., PB 83 139 352
(A04).b,c

Debris Flows, Landslides, and Floods in the San Francisco Bay Region,
January 1982, Overview and Summary of a Conference Held at Stanford
University, August 23-26, 1982, National Research Council and U.S.
Geological Survey (1984) by William M. Brown III, Nicholas Sitar, Thomas
F. Saarinen, and Martha Blair, 83 pp., PB 84 194 737 (A05).b,c

DAM FAILURES

Failure of Dam No. 3 on the Middle Fork of Buffalo Creek Near Saunders,
West Virginia, on February 26, 1972 (1972 by R. Seals, W. Marr, Jr., and
T. W. Lambe, 33 pp.,,PB 82 223 918 (A03).0

Reconnaissance Report on the Failure of Kelly Barnes Lake Dam, Toccoa
Falls, Georgia (1978) by G. Sowers, 22 pp., PB 82 223 975 (A02).b,c

LANDSLIDES

Landslide of April 25, 1974, on the Mantaro River, Peru (1975) by Kenneth
L. Lee and J. M. Duncan, 79 pp., PB 297 287 (AO5).b,c

The Landslide at Tuve, Near Goteborg, Sweden on November 30, 1977 (1980)
by J. M. Duncan, G. Lefebvre, and P. Lade, 25 pp., PB 82 233 693 (A03).c

The Utah Landslides, Debris Flows, and Floods of May and June 1983 (1984)
by Loren R. Anderson, Jeffrey R. Keaton, Thomas Saarinen, and Wade G.
Wells 11, 96 pp. (A06).

TORNADOES

Lubbock Storm of May 11, 1970 (1970) by J. Neils Thompson, Ernest W.
Kiesling, Joseph L. Goldman, Kishor C. Mehta, John Wittman, Jr., and
Franklin B. Johnson, 81 pp., PB 198 377.c

112

Engineering Aspects of the Tornadoes of April 3-4, 1974 (1975) by K.
Mehta, J. Minor, J. McDonald, B. Manning, J. Abernathy, and U. Koehler,
124 pp., PB 252 419.c

The Kalamazoo Tornado of May 13, 1980 (1981) by Kishor C. Mehta, James R.
McDonald, Richard C. Marshall, James J. Abernathy, and Daryl Boggs, 54
pp., PB 82 162 454 (A04).b,c

HURRICANES

Hurricane Iwa, Hawaii, November 23, 1982 (1983) by Arthur N. L. Chiu, Luis
E. Escalante, J. Kenneth Mitchell, Dale C. Perry, Thomas Schroeder, and
Todd Walton, 129 pp., PB 84 119 254 (A07).c

Hurricane Alicia, Galveston and Houston, Texas, August 17-18, 1983 (1984)
by Rudolph P. Savage, Jay Baker, Joseph H. Golden, Ahsan Kareem, and Billy
R. Manning, 158 pp., PB 84 237 056 (A08).b,c

NationaC Acadcy@y Press
The National Academy Press was created by the National Academy of
Sciences to publish the reports issued by the Academy and by the
National Academy of Engineering, the Institute of Medicine, and the
National Research Council, all operating under the charter granted to
the National Academy of Sciences by the Congress of the United States.

3 6668 00002 2758