Georgetown County shorefront management plan from Garden City to North Inlet

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

''GEORGETOWN COUNTY

SHOREFRONT- MANAGEMENT PLAN

From Garden City to North Inlet

ftOP 1011 oo Sale

U..DEPARTMENT OF COMMERCE NOA~
COASTAL SERVICE CENTER
Prepared for: ~~~~~2234 SOUTH HOBSON AVENUE
V SOUTH CAROLINA COASTAL COUN~~ CIALESO C2452

Prepared by:
APPLIED TECHNOLOGY AND MANAGEMENT, INC.
and.
OLSEN ASSOCIATES,. INC.

July 1986

EN.
333iMULL fill~~~~~~~~~~~~~~~~-S.

.G46 2
1 ____98 6__ ___

1.0 INTRODUCTION
1.1 PURPOSE
In 1979, the South Carolina Coastal Council completed a
comprehensive management program for the eight-county
coastal zone within the State. The program was approved by
the General Assembly on.February 14, 1979 and by the Federal
government on September 29, 1979.

Accordingly, the Shorefront Management Plan included within
this report specifically addresses the following two major
goals formulated in the State plan:

1. The development of a program that will achieve a
rational balance between economic development and
environmental conservation of natural resources
within the shorefront portion of the coastal zone
of South Carolina.

2. The development of a permitting system for
activities within the dynamic shorefront portion of
the coastal zone that will serve to implement the
goals and objectives of the management program and
promote the best interest of all citizens of South
Carolina.

� The purpose of the Shorefront Management Plan is to make
recommendations suitable for adoption by local government
necessary for the protection of beach/dune resources, as
well as both future and existing adjacent upland
development. Accordingly, this study will address the

v . following three major areas of coastal regulation:

1. Setbacks or similar controls necessary to both
insure the long-term integrity of the dynamic
beach/dune system and to prevent future development
from ultimately being located on the active beach
L 1

face as a result of chronic or persistent beach
erosion and shoreline recession. In addition,
setbacks associated with storm related impacts to
the beach/dune system will be discussed.

2. Coastal construction zones within which minimum
building standards should be implemented to insure-
that future major habitable structures are designed
to properly accommodate the impacts associated with
a 100-year storm event.

3. General erosion control policy guidelines dealing
with the consideration of future permits requesting
armoring, groins, beach restoration, bulkheads, and
other coastal protection structures.

Within the Garden City section of the Georgetown County
coastline, the methodologies utilized by this study to
recommend building setbacks were similar to the formats
developed for comparable studies performed by previous
investigators for both Myrtle Beach and North Myrtle Beach.
The methodology involves the determination of the ideal
present shoreline (IPS) and the identification of the 25-
and 50-year future dune crest based upon both the IPS and
known rates of erosion or accretion (Kana, et al). This
technique is based upon the long-term extrapolation of
average annual rates of volume change in the beach face.
South of Murrells Inlet within the remainder of the study
area, long-term recession predictions were made on the basis
of comparisons of historical beach profile surveys and/or
shoreline and inlet change maps available from reliable
sources.

Neither of these two approaches, however, account for short-
term and typically more severe erosional effects associated
with low-frequency storm events (i.e. severe northeasters,

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tropical storms and hurricanes). For that reason, a
separate computer analysis has been included which simulates
the erosion of the ideal present profile (IPP) during the
occurrence of the 25- and 50-year storm. The latter can be
expected to have an annual probability of occurrence of .04
and .02, respectively. A 25-year storm, for example, is an
event that statistically would be expected to occur once in
25 years, on the average.
F
1.2 STUDY AREA
Located within the Grand Strand, the study area along the
Georgetown County Coastline extends from a point 3.4 miles
north of Murrells Inlet south to North Inlet, a total
shoreline length of approximately 18 miles. From north to
south, the areas investigated include a portion of Garden
City, all of Litchfield Beach and Huntington Beach State
Park, Pawley's Island and Debidue Beach. These four areas
are each separated by a tidal' inlet. Figure 1.2-1 shows the
general location of the study area. Located between Garden
City and Huntington Beach State Park, Murrells Inlet was
structurally stabilized by the COE in 1979. Midway Inlet,
Pawley's Inlet and North Inlet are located along the
southern limits of Litchfield Beach, Pawley's Island and
Debidue Beach, respectively. From Little River Inlet, the
Grand Strand coastline follows a general arc to North Inlet
at the southernmost point.

Extreme variability in development pressures, including both
development patterns and density, exists between Garden City
and Debidue Island. As the coastline population has grown,
the worth of South Carolina's beaches to the local and state
economy has become considerable. It should continue to
increase as long as adequate sandy beaches suitable for
recreation are preserved and maintained.

Specific stretches of Georgetown County's shoreline are

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Little R&J7,

STDY AREA

~ t. Helena Sdl.

- Pt. Royal Sd.

0 ~ 30 KM

FIGURE 1.2-1
STUDY AREA LOCATION MAP

migrating as the result of long- and short-term local
variations in sand supply, shoreline orientation and the
proximity to inlets and shoreline structures. The effects
of sea-level rise on shoreline recession is relatively
uniform along the coastline and is a cause of irreversable
net offshore sediment transport. Long-term shoreline
recession trends indicate the shoreline within the study
area has experienced a net average landward movement.

Clearly, the greatest man-induced causes of shoreline
instability are the results of shoreline hardening and inlet
improvement and stabilization projects. Problems associzated
with the dynamic state of natural inlet channels are
commonly magnified by dredge spoil disposal practices and
the construction of inlet jetties. The Murrells Inlet
stabilization project, completed in 1980, has substantially
altered sediment transport in the nearshore area along
adjacent beaches. The Georgetown County areas of Litchfield
Beach and Huntington Beach State Park, extending 6.8 miles
south of the Murrells Inlet jetties, have experienced
significant shoreline accretion and erosion at various
locations following the jetties' construction.

Beach and offshore erosion is a condition that occurs along
the majority of Georgetown County's coastal areas.
Erosional impacts on shoreline development are most directly
related to the demand for shoreline armoring. In general,
this area has had moderate increases in both soft and hard
shoreline protection measures such as seawalls, groins, rip-
rap, sand bags, beach scraping, dune restoration and
revegetation, sand fences and limited beach renourishment.

Groins, piers and jetties are manmade structural barriers,
each of which interrupts the natural sand transport across
the nearshore littoral zone. Net sediment transport along

the county's coastline is generally southward, with periods
of large reversals toward the north caused by variations in
wave climate. The magnitude and direction of the longshore
currents, created by waves breaking at an angle to the
coast, determine sand transport along the coastline.

1.3 PREVIOUS STUDIES
Recent investigations of the Georgetown County shoreline
have focused on the Pawley's Island and Debidue Beach
shorefront developments. Erosional impacts on the county's
coastal population is of considerable concern when
developing and implementing viable shorefront management-
policies. Accordingly, shoreline data representing all
coastal areas were collected, compiled, and reviewed with
regard to quality and quantity to identify the needs for
additional data. Previous data collection efforts and a
review of Georgetown County's earlier shoreline studies are
summarized below.

An early field investigation that included the Garden City
shoreline area was conducted in 1955 by the Corps of
Engineers (Charleston District) to document post-hurricane
beach profile response. Beach profiles were established and
surveyed to approximately 2.0 feet below MSL (1929 NGVD).
The COE estimated erosion rates following the occurrence of
Hurricane Hazel as great as 52 cubic meters per meter at
Myrtle Beach (COE Reconnaissance Report, 19.83). In a 1983-
84 field reconnaissance effort for a report of recommended
beach erosion control and hurricane protection measures
(March 1984), the COE resurveyed the shoreline areas from
North Myrtle Beach to Garden City and established additional
transects along this shoreline.

In another beach erosion study (Hubbard et al, 1977), both
navigation charts and aerial shoreline photography were

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analyzed to estimate linear short- and long-term erosion
rates. Based on 25 to 100 years of successive shoreline
data, they concluded that long-term erosion rates are in the
range of 1-3 feet/year with the exception of areas adjacent
to tidal inlets and shoreline stabilization structures.
* They qualitatively described short-term stability as
directly dependent on the number and intensity of
extratropical and tropical storms occurring for a particular
Fr number of years.

After construction of two jetties at Murrells Inlet in 1977,
the Corps of Engineer's Coastal Engineering Research Center
(CERC) began a formal study to monitor the effect of the
Murrells Inlet navigation project on both the inlet and the
adjacent beaches. The Phase I monitoring program provided
for quarterly surveys along 43 transect lines between 1979
and 1982. IThe scope was then reduced to Phase II field
surveys to monitor 18 transects semi-annually through
October 1987.

The Murrells Inlet Monitoring Study provides valuable data
v0,- to assess the effects of inlet stabilization on long- and
short-term shoreline fluctuations. for the Garden City and
Huntington Beach/Litchfield Beach areas. This investigation
is the most comprehensive study conducted within the study
area, which includes a 10-year program for the continuous
collection of coastal data. CERC's digitized survey data
was acquired for comparative shoreline analysis in the
r- Georgetown County study area.

The COE published an interim report (March 1985) to
highlight and summarize their findings, particularly
detailing those areas that are presently experiencing the
greatest change. The following shoreline changes were
noted:

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of

1. Significant growth of the ebb tidal shoal extending
seaward of the approximately 3400 foot long
jetties.

2. Extreme erosion rates in a region between 2.5 and
3.5 miles south from the jetties.

3. The accretion of large volumes of sand on the south
shoreline adjacent to the south jetty.

Preliminary results from the analysis of wave and
directional current data suggest the directions of longshore
sediment transport are variable in the vicinity of the
i-
jetties, while the sheltering effects of the jetties allow
minimal southerly transport within an area 2.0 miles south
from the jetties.

Cubit Engineering (1981) conducted a study of limited scope
for Pawley's Island which addressed general coastal
processes, shoreline variability specific to Pawley's Island
and recommendations for potential alternatives to shoreline
maintenance. In this study, 12 beach profiles were surveyed
over some three miles of island shoreline. Field notes
providing station documentation and actual profile data were
obtained from Cubit for replication in this study.
Conclusions presented by the Cubit study acknowledged
Pawley's Island has experienced a high degree of shoreline
L variability adjacent to both inlets. A chronological
analysis of inlet migration indicates that Midway Inlet
migrated south between 1872 and 1934, after which this trend
reversed to the position of the entrance channel at its
present position. A terminal groin (685 ft) was constructed
on the south bank along the inlet in the 1950s and has been
effective in preventing further migration of the inlet
entrance channel. Deposition of southerly littoral drift
appears to have resulted in the cyclic migration of both the

Pawley's and Midway Inlet channels to the south, with
subsequent recutting to the north or breaching during
storms. Analysis of shoreline movement at Pawley's Inlet
for the period from 1872 to the mid-1960's indicate that
this inlet had migrated south a nominal 6500 feet. Barrier
crest elevations are generally low (8-15 feet) with
significant probability for flooding during low-frequency
storms.

In a 1976 investigation, the Clemson University Department
of Forestry measured shoreline fluctuations using aerial
photographs for approximately 10-year intervals between 1939
and 1975. Six stations were established along the southern
end of Debidue Island adjacent to North Inlet to measure
historical shoreline movements. Based on these maps, they
summarized that the southern spit migrated south, accreting
1800 meters between 1872 and 1939 and is presently eroding.
These erosion rates vary between 6 and 11 feet/year over the
period from 1963 to 1975.

A 1975-76 investigation of North Inlet was conducted by the
COE-CERC to evaluate the hydraulics and dynamics of a
natural tidal inlet. Over a two-year period from July 1974
to June 1976, intensive field studies were undertaken to
collect a wide range of physical data.

Channel hydrography data, longshore current velocities, wind
data, visual wave data and bathymetric and beach profile
data were collected to evaluate inlet dynamics. In
addition, three tide gages were installed to provide
continuous water surface records in the vicinity of the
inlet. The study focused on the analysis of 1) inlet
hydraulics, 2) longshore currents adjacent to the inlet, and
3) seasonal morphology of North Inlet's tidal shoals and
adjacent beaches.

The authors concluded North Inlet is hydraulically ebb-tidal
dominant, longshore currents are primarily controlled by
wind-stress, and the exchange of sediments between the inlet
channels and adjacent beaches suggests a distinct seasonal
pattern in response to both high-energy conditions and
seasonal changes in MSL.

In 1985, Research Planning Institute (RPI) conducted a
preliminary assessment of three development tracts along
Debidue Island. The scope of this study included an
analysis of historical shoreline movement, estimates of
long-term shoreline trends based on historical shoreline.
maps, identification of environmentally sensitive areas, and
a review of state and federal development restrictions with
recommendations for areas of preservation and development.
Conclusions of the RPI study acknowledged the extreme
shoreline variability along the southern reaches of Debidue
and the relative shoreline stability of the beach segment
north of the Debidue Colony Seawall.

Maps of historical shoreline changes in the Georgetown
County area are based on shoreline field surveys and
vertically controlled photography compiled in a cooperative
shoreline movement study by the National Ocean Service (NOS)
and the Corps of Engineers Coastal Engineering Research
Center (CERC). Shoreline positions were mapped beginning in
1872 and are compared with subsequent survey data of 1926,
1934, 1962-63 and 1983.

1.4 PRESENT STUDY
The objective of the present study is to formulate a
comprehensive shorefront management plan based on an
understanding of existing Shoreline conditions specific to

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each coastal area. To provide background information, data
collection efforts include the following control data:

1. Land use data,
2. Tide data,
3. Wind data,
4. Storm data,
5. Wave-data,
6. Aerial photographs.,
7. Historical shoreline movement data,
8. Inventory of major coastal structures and beach
nourishments,
9. Sediment data,
10. Beach profile data,
11. Floodplane maps, and
12. Existing coastal management practices in the study
area.

Shoreline data were evaluated in depth and the need for
further data acquisition were identified. The present
project initiated a comprehensive shorefront monitoring
program to address the need for additional data. The
monitoring efforts included:

1. Establishing fifty-six survey stations along the
Georgetown County shoreline; each station control
point consisted of a permanent benchmark and a
survey monument. Vertical elevations of these
benchmarks were surveyed by professional surveyors,
and carefully documented so that the data from
future surveys can be replicated with confidence
using the new control reference points.

2. Beach profiles were measured at each monitoring
station in April 1986. The profile transects
commenced landward of the primary dune and offshore

to the -3 ft (mean sea level datum) wherever
possible.

3. Sediment data were collected at 21 monitoring
stations.

4. An extensive field investigation was conducted to
document the existing shorefront condition and
coastal structures including seawalls, bulkheads,
rip-rap, groins, jetties, and stormwater discharge
structures.

Using the historical information and the recently collected
site specific data, the following analysis was conducted:

1. Development patterns were evaluated.

2. Sediment grain size analysis was conducted to
provide sediment statistical parameters to provide
essential information for estimating littoral
processes and future beach nourishment design.

3. Volumetric changes of beach sand were computed
using comparative beach profile data.

4. Short-term erosion rates were computed based on the
mean high water contour movement derived from
comparative beach surveys.

5. Long-term erosion rates were estimated using the
historical shoreline maps. This shoreline
recession rates, were subsequently used to predict
25 and 50 year future shoreline.

6. Ideal present profiles were established.

7. The storm impact zones were calculated by computer
model simulation.

8. The inlet dynamics were assessed for Murrells
Inlet, Midway Inlet, Pawley's Inlet, and North
Inlet.

Upon examining-the pertinent information and the results of
the analyses, a comprehensive shorefront management plan was
recommended. A similar study was conducted for Horry County
shoreline concurrently with the present study for Georgetown
County.

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2.0 LAND USE
2.1 EXISTING LAND USE
The study area covers most of the coastal region of
Georgetown County except North, South and Cedar Islands. It
lies within the Waccamaw Neck, a region delineated as one of
the six major-planning areas in Georgetown County. The
Waccamaw Neck is bordered on the north by Horry County, on
the west by the Waccamaw River/Intracoastal Waterway, on the
south by Winyah Bay and on the east by the Atlantic Ocean.
The following presentation of the land use data is extracted
from the land use plan prepared for the Waccamaw Neck by the
Georgetown County Planning Commission (1985). It closely
represents the development in the study area as most of the
development in the Waccamaw Neck is concentrated within the
immediate coastal area.

The first attempted Spanish settlement on this continent was
made on Waccamaw Neck in 1526 near the Bellefield House
within the Hobcaw Barony. In the nineteenth century, rice
plantations dominated the land use in the Waccamaw Neck. In
the 1840's almost half of the rice produced in the United
States was grown on the plantations in Georgetown County.
By the turn of the twentieth century, however, commercial
production of the rice in the county had nearly ceased due
to the loss of slave labor and the competition from
mechanized farms in the southwest. Rice production was
replaced by the timber industry which has dominated land use
in Waccamaw Neck for several decades.

Presently, Waccamaw Neck plantations are being transformed
into residential communities for permanent and seasonal
residents.' Because of the abundant natural amenities,
tourism has assumed a major role in the economy of the area.
The tourist attractions include Brookgreen Gardens, Pawley's
Island, Huntington Beach State Park, and numerous resort
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developments in the area. Murrells Inlet has become one of
the favorite places to enjoy seafood along the Carolina
coast.

Population
While most of Georgetown County has experienced a modest
increase in population, that of the Waccamaw County Census
Division (CCD) has grown at a much faster rate -- at least
three times faster than the other CCD's. Table 2.1-1
presents the population and socio-economic data for the
Waccamaw Neck. A unique characteristic of the Waccamaw Neck
population, as illustrated by Table 2.1-1, is its
variability. Because the area is a popular summer resort,
the peak population during summer season can be 4 to 5 times
larger than the permanent population. These seasonal
influxes causes severe strains on service delivery systems
such as potable water, sewer and electricity.

The 1980 Waccamaw Neck population was 6,513 people. Of this
total, 70% were white and 53% were male. The mean family
size was 3.6 persons/family. The average household size was
2.7 persons. Median household income was $14,938 and per
capita income was $7,343. The retail trade, professional
services and entertainment provide the bulk of the
employment opportunities in the Waccamaw Neck.

Land Use
The Waccamaw Neck consists of approximately 51,504 acres and
only 7% of it was developed as of 1985. Considering the
existing development, land held in public trusteeship
(Brookgreen Garden, Huntington Beach State Park, etc.), and
wetlands unsuitable for development, only 17,467 aqres are
available for future development. For the purposes of land
use survey, the Waccamaw Neck can be divided into four
areas: Murrells Inlet/Garden City Point, Litchfield,
Pawley's Island, and Arcadia/Hobcaw. Table 2.1-2 summarizes

Table 2.1-1. Waccamaw Neck Socio-Economic Data, 1980-2005.

1980 1985 1990 1995 2000 2005

Permanent Population 6,523 9,138 11,913 14,024 16,295 18,910

Employment 2,838 3,976 5,184 6,103 7,091 8,229

Dwelling Units 4,792 6,713 8,752 10,303 11,971 13,892

School Enrollment 1,625 2,276 2,967 3,493 4,058 4,709

Auto Registration 3,480 4,875 6,356 7,482 8,693 10,088

Peak Population* 30,156 38,985 51,725 64,902 78,969 93,385

*Includes permanent population, seasonal overnight tourists and day
visitors.

Source: Waccamaw Regional Planning and Development Council, Horry and
Georcetown Counties Socio-Economic Data by Study Periods Each Five
Years. 1980-2005

Table 2.1-2. Existing Land Use for Waccamaw Neck.

Murrells Inlet Pawley's Arcadia
Land Use Category Garden City Point Litchfield Island Hobcaw

Single-Family Residential 623 379 679 89 1,770

Multi-Family Residential 40 91 19 20 170
Residential Subtotal 663 970 698 109 1,940

Commercial 88 62 81 0 231

Public/Semi-Public 34 46 76 2. 158

Golf Courses 139 -349 326 101 915

Other Public Uses 7,664 276 0. 15,671 23,611

Streets 325 249 300 54 928

Wetlands 2,960 1,589 1,593 13,155 19,297

Vacant or Undeveloped Land 3,342 3,072 4,314 6,739 17,467

TOTAL ACERAGE 13,575 6,105 7,387 24,437 51,504

Source: Waccamaw Regional Planning and Development Council, Field Survey, June, 1985.

the existing land use in each area under nine categories:
single family residential, multi-family residential,
commercial, public/semi-public, golf courses, other public
uses, street, wetlands, and undeveloped land.

Murrells Inlet/Garden City Point
Garden City Point is a long and narrow peninsula, about 3.7
miles in length surrounded by the ocean and tidal marshes.
It has been developed to the point that, as of 1985, less
than 9% of the developable land was vacant in Garden City,
Point. Major problems currently associated with development
in Garden City Point are access and sewer capacity.
Waccamaw Drive is the only access road running the entire
length of the Point, and the closest access from U.S. 17 is
via Atlantic Avenue, about 3 miles north of the southern tip
of the peninsula. The nearest fire station in Murrells
Inlet is about 6 miles from the peninsula tip.
t~~~~~
Litchfield
Huntington Beach State Park occupies the northern portion of
the area between Murrells Inlet and Midway Inlet. The rest
of the coastal area consists of three major developments:
North Litchfield; Litchfield By The Sea; and South
Litchfield. The principal land uses in this area are
single-family residential and low-density multi-family
resort development. Similar to Garden City Point, the
access to the coastal area is also limited.

Pawlev's Island
Pawley's Island has only 5 acres of vacant land available
for future development which is about 3% of the total
developable land. The primary problem associated with
development in this area is the lack of a central sewage
collection system.

Arcadia/Hobcaw
The Belle W. Baruch Nature Preserve, donated to the State of
South Carolina for wildlife and marine research, is located
at the southern end of Debidue Island. Immediately north of
the Belle W. Baruch Nature Preserve is a low-density
residential development, the DeBordieu Colony. The northern
portion of Debidue Beach is occupied by the Arcadia
Plantation and is presently undeveloped.

2.2 RUTURE LAND USE
As the population of the Waccamaw Neck increases, additional
land will be needed for residential, commercial,
public/semi-public and other various uses. According to the
development growth trend, a future land use was projected by
the Waccamaw Regional Planning and Development Council in
accordance with zoning ordinances and development standards
established byl!Georgetown County. The future land use
projection is shown in Table 2.2-1.

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Table 2.2-1. Future Land Use - Waccamaw Neck Totals.
Acerage Needed

Land Use Category 1990 1995 2000 2005 TOTAL

Residential

Single-Family 618 451 451 590 2,110
Multi-Family 86 88 131 160 465

TOTAL 704 539 582 750 2,575

Commercial 70 53 57 66 246

Public/Semi-Public 48 37 39 45 169

Streets* 123 94 102 129 448

TOTAL ACERAGE 945 723 780 990 3,438

*Assumed average for streets was 15% of projected developed acerage

Source: Waccamaw Regional Planning and Development Council, 1985.

� (9 � (9 � �~~~~~~~~~

3.0 BACKGROUND INFORMATION AND DATA COLLECTION
3.1 TIDES
Tidal data have been collected by the National Ocean Survey
(NOS) at four open-coast gages in the vicinity of the study
area over the last 30 years. North to south, these
locations include Hog Inlet Pier, Myrtle Beach Pier,
Springmaid Pier and Pawley's Island Pier. The gage at
Myrtle Beach Pier was operational between 1957 and 1978,
with subsequent installation at Springmaid Pier for the
period 1978 through 1982. The longest continuous tidal
records are for the primary gage at Charleston and cover the
period from 1920 to the present. Using spectral and
harmonic analyses, these tidal data obtained at the
Charleston and local gage locations require correlation for
the computation of statistical parameters such as local
daily MHW, MLW, tidal variation along the coastline (phase
lag) and the rise in mean sea level.

Analyses of tidal data is completed on a periodic 19-year
cycle, termed a Tidal Epoch. The tide gage installed at the
Myrtle Beach Pier measured a rise in mean sea level equal to
0.'34 feet between 1929 (NGVD-MSL) and the 1941-59 Tidal
Epoch. Mean sea level increased an additional 0.13 feet
between the 1941-59 and the 1960-78 Tidal Epoch along the
gage stations adjacent to both Georgetown and Horry
Counties. This translates into a 5.6-inch rise in sea level
for the last 49 years in this coastal location.

A recent study conducted by the U.S. Environmental
Protection Agency (EPA,1983) predicts a possible sea-level
rise of 1 foot over th& next 30 to 40 years and 3 to 5 feet
over the next .100 years (Figure 3.1-1). This rise in sea-
level will subject areas currently flooded in a 100-year
storm event to extreme flooding during higher frequency
events, particularly in coastal areas characterized by low
barrier-crest elevations.

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Ikl
Ea I
E 3- S
J
'> eq Results from
-J2- - @., EPA Study
2-<1~~~~~~~~ I mzV (1984)

I - i_ Post 0
Century /Projection of
7;,;g Present Trend
t _J----.--~ ~'--"- -
o
1700 1800 1900 2000 2100
YEAR

FIGURE. 3.1-1
SEA-LEVEL RISE OVER THE LAST CENTURY
AND PROJECTIONS BASED ON A RECENT EPA
STUDY (EPA, 1983)

Records of water-level variation obtained from tide gages
often include water elevations associated with storm tides,
which are valuable for predicting flood elevations. Extreme
storm-generated fluctuations in water-surface elevations
over the last Tidal Epoch (1951-1978), including
astronomical tides, are shown in Table 3.1-1. These are
derived using data obtained at the Charleston gage and
corrected for estimates of water-surface levels at the local
gages within the study area.

3.2 WIND
A wind-rose diagram, indicating average annual occurrence of
both wind speed and direction, is shown in Figure 3.2-1.
This diagram was derived from wind information for the
period 1942-1972 as observed at the U. S. Air Force Base at
Myrtle Beach (U.S. Air Force, 1975) and may be considered
representative of conditions throughout the study area. In-
depth analysis of similar data presented for each month over
the period 1942-1972 indicates the predominance of NNE winds
during the fall months (October-December). This corresponds
to the more frequent occurrence of northeasters and
associated higher levels of wave energy resulting in net
southerly sediment transport, as well as more noticeable
beach erosion observed during this period.

Similar analysis indicates the predominance of southerly
winds during the summer months (April-August) corresponding
to net northerly sediment transport and a gradual re-
building of the beach by the longer, lower frequency summer
waves. The months of October and November have the lowest
average wind speeds (5.2 ft/sec) and the greatest occurrence
(over 20%) of calm periods (winds less than one knot).
Table 3.2-1 lists average wind speeds and directions on a
seasonal basis as measured at the Myrtle Beach Air Force
Base. The shoreline orientation of the study area varies

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TABLE 3.1-1. Tidal Elevation Along Horry And Georgetown County Coast

TIDAL ELEVATION (FEET)

Location MHW MLW MSL HHW. LLW ..--

Hog Inlet Pier 5.00 0.00 2.50 10.00 MLW -3.5 MLW

Myrtle Beach 5.10 0.00 2.55 14.00 MLW -2.5 MLW

Springmaid Pier 5.25 0.20 2.72 8.50 MLLW -3.0 MLLW

Pawley's Island Pier 4.91 0.00 2.45 10.00 MLW -3.5 MLW

*Estimated highest high water observed based on extreme water levels
at Charleston, SC..
**Estimated lowest low water observed.
Source: NOAA-NOS, 1986

l l l~~~~~~~~~~

AVERAGE WIND ROSE FOR 1942-1947
&1949-1972 AT MYRTLE BEACH, SOUTH CAROLINA

NNW ' :NE

WNW NE

SSW E _ SSE

S 0%

FIGURE 3.2-1
WIND ROSE AT MYRTLE BEACH, SOUTH
CAROLINA

Table 3.2-1. Seasonal Mean Local Wind Speed Versus Wind
Direction Given in Miles Per Hour (Measured at
the Myrtle Beach Air Force Base).

Wind Direction
Season ENE E ESE SE SSE S SSW

Jan-Mar 8.77 8.60 8.06 7.23 7.76 9.04 10.26
Apr-Jun 8.79 9.12 8.63 8.09 8.52 9.77 10.37
Jul-Aug 7.82 8.08 8.09 7.35 7.99 9.23 9.67
Sep-Dec 7.73 7.68 7.25 6.53 6.96 7.83 8.87

l l l~~~~~~~~

l ., l~~~~~~~~~~

approximately 450 from an ENE-WSW orientation at the north
end to a NNE-SSW orientation at the south end. As a result,
wind from a particular direction will have a different
bearing relative to the shoreline at different locations
over the study area.

3.3 STORM DATA
The most severe hurricanes-of-record to affect Georgetown
County struck the coast in 1822, 1854, and 1954. Hurricane
Hazel (1954), characterized as a low-frequency storm
produced peak storm tides of 6.0 to 10.0 feet along portions
of the Georgetown County shoreline. Horry County was
severely impacted by Hazel's 15.5 ft storm tides along
Myrtle Beach and it was classified as a low-frequency 100-
year return-interval storm event (COE, 1983).

Horry and Georgetown County have been adversely affected by
significantly less severe hurricanes, the most recent being
Hurricane David in 1979. The most recent significant
hurricanes which made landfall along the South Carolina
Coast are presented in Figure 3.3-1. High-frequency storms,
referred to as northeasters, also produce a storm tide or
super-elevation of the ocean that allows the propagation of
greater wave heights onto the beach-dune face, often
resulting in significant beach-dune erosion, vegetation loss
and- structural damage.

Often these more-frequent storms, which can severely impact
the beach-dune system, are not well documented. During
hurricanes, tropical storms and northeasters, the
characteristic physical processes (current magnitude and
direction, wave conditions, and sediment transport) in the
nearshore zone may be drastically altered, resulting in the
transport of large quantities of sand both offshore and
along the coast. In addition, unstabilized inlets can be
expected to undergo accelerated migration.

-27-

KEY:
I-"n TROPICAL STORM STAGE
HURRICANE STAGE

4 -. ,,,, I-j.

~~/

* I~..

FIGURE 3.3-1
HURRICANE TRACKS FOR STORMS
IMPACTING THE SOUTH CAROLINA COAST
FROM 1952 TO 1979

Historically significant hurricanes that have tracked in
relatively close proximity to the northern portion of the
South Carolina coast have been analyzed by FENA to determine
site-specific hurricane characteristics. These historical
storm parameters were applied for the estimation of future
probabilities of the recurrence of flood conditions for the
purpose of issuing flood insurance.

A statistical analysis of historical hurricane records along
the Horry and Georgetown County and adjacent coastline areas
was interpreted in a 1983 FEMA study to forecast the
probable future incidence of a hurricane event. Relative to
the Horry and Georgetown County shoreline orientation, 330
east of north, hurricanes were classified by their
landfalling characteristics. Based on this analysis of
documented tropical storms and hurricanes, the FEMA study
(1983) estimates that 136 landfalling, exiting and
alongshore storms can be expected to track within 150 nm of
a point along the Georgetown County coast every 100 years.
Figures 3.3-2 and 3.3-3 present-storm tracks for hurricanes
impacting the South Carolina coastline between 1883 and
1920.

A circle of radius equal to approximately 150 nm., whose
locus is the center of Georgetown and Horry counties coastal
segment defines the area where hurricane crossings could
impact the Georgetown County coastal areas (Figure 3.3-4).
Hurricanes tracking within 150 nm. of the coastline are
designated as alongshore. Table 3.3-1 is a summary of the
probability of occurrence of storm. orientation reported in
the 1983 FEMA study, using historical hurricane tracks for a
150-nm radius of the study area.

-29-

KEY:
"= = TROPICAL STORM STAGE
HURRICANE STAGE

.1 0

FIGURE 3.3-2
HURRICANE TRACKS FOR STORMS
IMPACTING THE SOUTH CAROLINA COAST
FROM 1883 TO 1906
/ [~~~~~~~.'.

KEY:
- - TROPICAL STORM STAGE
HURRICANE STAGE

THE SOUTH CAROLINA COAST FROM 1887 TO.

1920
FIGURE 3.3-3
HURRICANE TRACKS OF STORMS IMPACTING
THE SOUTH CAROLINA COAST FROM 1887 TO
1920

400~~~~~

=^LE 1,5.702.4

~~~~~~SCLINATIAMIE

76 0 39 78 117 15

GULF OF MEXICO~~~~~~

FIGURE 3.3- 4 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 0

CROSSING AXS AND CIRCE FOR STOR

CRSTTSTICAL ANAXIS -HRYAND CRL O TR
GEORGETOWN COUNTIES (FEMA, 1983)

TABLE 3.3-1

Landfalling storms 18.4%
Exiting storms 37.5%
Alongshore storms 44.1%

Predicted peak combined total storm tides for varying return
intervals are presented in Figure 3.3-5 whereas Figure 3.3-6
presents the same for specific locations along the open
coast.

An earlier study, done to determine maximum tide elevations
for the entire coast of South Carolina, was conducted for
the Federal Insurance Administration. Using the National
Weather Service (NWS) SPLASH hydrodynamic model to calculate
peak storm tides, Meyers (Meyers, 1975) predicted Hurricane
Hazel's storm tide variation along the coast from Georgia to
the SouthlCarolina/North Carolina border (Figure 3 3-7).
This particular hurricane struck the Myrtle Beach area at a
time that coincided with that of the astronomical high tide.
High water marks (which include wave effects) were
documented as 15.5 feet at Myrtle Beach.

During a hurricane event, onshore winds displace the ocean
water onto the local coastline. In the vicinity of an inlet
along the adjacent low-lying shorelines, storm surge
flooding with wave effects superimposed will erode the
foreshore and, in some places, overtop the primary dunes.
As an example, Hurricane Hazel caused seaside overtopping
and breach of the spit extending south from Pawley's Island.

Hurricanes Grace (1959) and David (1979) are the most recent
(since 1954) hurricanes to have directly impacted the Horry
and Georgetown County shoreline. These storms were
relatively moderate storms, characterized as high frequency
10-year return period events.

-33-

FREQUENCY
0.10 0.05 0.04 0.02 0.01
22 I I

21
TIDE FREQUENCIES
20

17
GEORGETOWN COUN
16

')14- //" HORRY COUNTY
I3 14

11 ,'

6
10 25 50 100 500
RETURN PERIOD (years)

FIGURE 3.3-5
PREDICTED PEAK TOTAL COMBINED STORM
TIDES FOR VARYING RETURN INTERVALS

j-'----GEORGETOWN COUNTY -1_ HORRY COUNTY-
20
500-YEAR RETURN PERIOD
17.8 17.8 17.8 178 17.9 17.9 17.9
17.4 17.4 A
17.9 - -

100-YEAR RETURN PERIOD
t15 - 14. 3 14.3 14. 3 14. 3 14. 3 143
E 14.3
.4-. 13.0- 13. 0

50-YEAR RETURN PERIOD 113 1' 11.2 110
(.~ 10.6 10-
;';;W~~~~~~~~M - - .4
I 10- - 10.3

aC 10-YEAR RETURN PERIOD
' - 7.17 7.t7.1 71 7.3 7.3 7.3
-7-17- 7-.71 71 - 6.5 6.5
7.1 7.1
o

0 5 10 5 20 25 30 35 40 45 50 55 60 65 70 75
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

DISTANCE ALONG SHORELINE (miles)

FIGURE 3.3-6
PREDICTED PEAK COMBINED TOTAL STORM
TIDES ALONG THE HORRY AND
GEORGETOWN COUNTY SHORELINE (FEMA,
1983)

.. BEAUFORT __ _i_ CHARELSTON GGEORGETOWNS HORRY
COUNTY -I - COUNTY COUNTY COUNTY

GA SC COLUNTY SC INC

20 -

100-YEAR RETURN PERIOD
10- /
I- /

HURRICANE HAZEL
0 i l l l I lm I 1 o

0 20 40 60 80 100 120 140 160 180

DISTANCE FROM GAISC BORDER (nm)

FIGURE 3.3-7
SPLASH SIMULATION OF HURRICANE
HAZEL'S TOTAL COMBINED STORM TIDES
ALONG THE SOUTH CAROLINA COAST
(MEYERS, 1975)

a 0 0 0 0 0 0 0' Ill lU0

3.4 WAVES
The Waterways Experiment Station (WES) of the U.S. Army
Corps of engineers (USCOE) has compiled detailed hindcast
wave statistics from a Wave Information Study (WIS) for the
Atlantic Coast (USCOE, 1984). The data consists of wave
height, period and direction computed for three-hour
intervals, excluding tropical storms, over a 20-year period
(1956-1975) at various stations located offshore along the
coast. The data are presented in three phases:

Phase I consists of large-scale numerical hindcast of
deep water wave data from historical surface pressure
and wind data.
Phase II consists of numerical hindcasts at a finer
scale to better resolve the sheltering effects of the
continental geometry. Phase I data serve as the
boundary conditions at the seaward edge of the Phase II
grid.
Phase III consists of transformation of Phase II wave
data into shallow water and includes long waves.

Phase III wave data are not yet available for the stations
appropriate to the study area; however, shallow water wave
calculations have been made for Myrtle Beach by means of a
wave-refraction computer model (Siah et al. 1984) utilizing
the Phase II data. The results of these calculations are
included as a general representation of shallow-water wave
conditions typical of the study area.

WIS station 47, located at latitude 33.64� north and
longitude 78.13� west, or approximately 40 miles due east of
Myrtle Beach, is the closest station with available wave
data for the study area. Accordingly, Phase II data from
this station were summarized and input into the
aformentioned wave refraction model to obtain shallow water
wave data. Figure 3.4-1 presents a seasonal summary of this

-37-

STATION 47
JAN. - DEC.

OVER 2.99 H

2.00-2.49 nH ||

1.60-1.99 i

0.60-0.99 I

0.00-0.49 H

FIGURE 3.4-1
WAVE ROSE OFFSHORE OF MYRTLE BEACH

Phase II data in the form of a wave rose for waves refracted
landward from deep water. Table 3.4-1 presents a seasonal
summary of onshore wave conditions calculated by refracting
the Phase 11 data over the nearshore bathymetry in the
Myrtle Beach area. It should be noted that the onshore wave
conditions depicted in Table 3.4-1 occurred only when
weather conditions were conducive to their formation and
therefore do not represent an annual average. Rather, they
represent average conditions when waves actually 'occur from
this direction window, during 49% of the year. The
remaining 51% of the year may be considered as either calm
or lacking any significant onshore wave energy component.
Inclusion of these periods in the calculation of average
wave conditions will result in lower average wave heights
than presented in Table 3.4-1. It should also be noted that
the approximately 450 shoreline variation over the study
area, as well as localized refraction and shoaling in the
vicinity of inlets will result in significant variations in
wave orientation relative to the shoreline over the entire
study area.

3.5 LITTORAL DRIFT ESTIMATESi
Alongshore sediment transport, or littoral drift, is driven
by the shore-parallel component of current velocities in the
surf zone. In concurrence with onshore/offshore sediment
transport, littoral drift is the primary factor that
determines long-term changes in beach morphology.
Unnoticeable on a day to day basis except during storms,
this form of sediment transport becomes significant when
interrupted by a shore normal structure such as a groin or
jetty. The currents driving this littoral drift result
primarily from the transfer of momentum by wave forces and
secondarily from wind, tidal and Coriolis forces.
Frictional forces near the bottom and turbulence resulting
from velocity gradients across the surf zone act to reduce
the current velocity.

-39-

Table 3.4-1. Average Occurring Wave Heights (ft) by
Direction and Season for the Myrtle Beach Area
(Siah et al,1984).

Wave Direction

Season ENE E ESE SE SSE S SSW

Jan-Mar 4.4 --4.8 4.4 4.5 4.3 4.2 4.4
Apr-Jun 3.1 3.2 3.1 3.2 3.1 3.0 2.9
Jul-Sep 2.9 3.3 2.8 2.2 2.4 2.1 2.4
Oct-Dec 4.1 4.3 4.0 3.8 4.1 3.9 3.8

The direction of littoral drift varies with the direction of
longshore currents. Seasonal trends within the study area
indicate southerly-transport in the fall, winter, and early
spring months and northerly transport in the summer. These
trends, however, vary annually as well. As a result, annual
gross transport volumes often far exceed annual net
transport volum'es. The direction and quantity of net
transport depends primarily on the wave climate over the
time period and the shoreline location. It should be noted
that the largest percentage of the gross and net annual
littoral transport occurs during storm events.

Many methodologies and associated formulas have been
presented to quantitatively predict magnitudes of alongshore
sediment transport. Generally, these formulas become quite
complicated while the accuracy of their predictions often
remains questionable. Rather than derive a new methodology
or assess the validity of existing ones, Table 3.5-1
presents predictions of sediment transport rates made in
previous studies of the northern reach of the South Carolina
coast. From this table, a qualitative assessment of
littoral drift rates may be made. It is important to note
that the presence of groin fields, natural inlets as well as
stabilized inlets, and the approximately 450 difference in
shoreline orientation will result in significant localized
variation in sediment transport rates over the study area.

3.6 HISTORICAL AERIAL PHOTOGRAPHS
The most comprehensive aerial photographic records of the
South Carolina coastline, of reasonable resolution
(1:20000), are available from the Agricultural Stabilization
and Conservation Service (ASCS) and NOS. A detailed listing
of aerial photographic records is available through the
South Carolina Cartographic Information Center, Columbia,
South Carolina.

-41-

Table 3.5-1 Previous Estimates of Net Littoral Drift Rates in the Myrtle Beach Vicinity

Source Region Net Drift Rate - Direction

CSE/OA (1985) Myrtle Beach 3.4 X 105 yd3/yr. - Southerly

Finely (1976) & Debidue, North Islands 0.72 - 3.21 X 105 yd3/yr* - Southerly
Nummendahl & Humphries
(1977)

Kana (1976)- Capers Island 0.82 - 2.72 X 105 yd3/yr* - Southerly

Kana (1976) Bull Island 1.67 X 105 yd3/yr - Southerly

Knoth & Nummendahl (1977) Bear Island 0.74 - 1.89 X 105 yd3/yr* - Northerly

USACE, Charleston (1975) Murrell's Inlet 1.32 X 105 yd3/yr - Southerly

Hubbard, et al. (1977) Murrell's Inlet 2.28 X 105 yd3/yr - Southerly

*Converted from tons/yr assuming a specific weight of 90 lbs/ft3.

0� 0 0 0 0 0 0 00

Aerial photographs are useful in assessing historical
shoreline changes in order to distinguish between long-term
trends and short-term trends. After corrections for true
scale and camera tilt are included, limitations and errors
in calculating shoreline movement are primarily due to water
level corrections and locating the still water line
excluding the effects of wave motion.

Aerial photos of Murrells Inlet and the adjacent shorelines
were taken by the COE between 1977 and 1981 on a monthly
basis. Extending over 14 miles of shoreline from the
Surfside Holiday Inn area south to Midway Inlet, flights
were continued through October 1982 on a quarterly basis.

Qualitative analysis along the entire Georgetown County
shoreline using photographs from 1872 to 1973 (Hubbard,
1977) provides data to assess long-term shoreline
variability. The summations of individual measurements were
used to calculate the 25-, 50- and 100-year net accretion
and erosion trends.

Using NOS-COE shoreline movement maps for Georgetown County
from 1873, 1925-26, 1934, 1962-63, 1969-70, and 1983,
shoreline changes were depicted for each of the inlet areas
and described in more detail in Section 7.0.

In addition, assessment of both shoreline movement changes
and shorefront development patterns relied upon historical
aerial photographs provided by ASCS, NOS and SCCC. These
data cover an extensive period of records beginning in 1939
with more frequent flights in later years.

3.7 SHORELINE DATA
Historical shoreline changes are one of the best indications
of erosion trends and littoral processes. Qualitative

-43-

depiction of the shoreline changes can be obtained from the
comparison of aerial photographs. Section 3.6 lists the
available aerial photographs within the study area. These
photographs were usually taken at different tidal phases,
therefore, they may not be adequate to represent short-term
changes because of the resolution and accuracy. However,
they can represent the long-term shoreline changes
reasonably well.

To qualitatively depict shoreline changes, the National
Ocean Service (NOS) and Coastal Engineering Research Center
have compiled aerial photographs, historical shoreline
surveys, and U.S. Geological Survey base maps to construct a
series of shoreline movement maps from Cape Henlopen,
Delaware to Tybee Island, Georgia. These maps were
horizontally controlled according to the 1927 North American
datum. These shorelines indicate the location of local mean
high water line relative to 1929 NGVD. Shoreline movement
maps covering the study area were complied from the January
1983 NOS aerial photography and field surveys performed in
1969-70, 1962-63, 1934, 1925-26, and 1872. Since these maps
were both horizontally and vertically controlled, they were
used as the primary data source to estimate the long-term
erosion rate in the study area.

3.8 BEACH PROFILE DATA
Comparative beach-dune profiles derived from periodic field
surveys relative to permanent vertically controlled stations
provide a high quality future data base. Initially these
data collected for specific time intervals (5 to 10 year
period). allow valuable estimates of short-term shoreline
fluctuations. In future years (20 to 30 years), these data
will be useful to predict local long-term erosion rates. In
addition, the shoreline recession associated with sea-level
rise and storm effects can be more accurately quantified
with a consistent, reliable data base.

-44-

During a 1955-1958 COE post-hurricane reconnaissance study
for Horry and Georgetown Counties (COE,1983), surveys were
conducted within Georgetown County along the Garden City
shoreline areas. In April 1958, 12 profile stations were
established and surveyed, five of which were located and
replicated in the-present study for comparative analysis.
The seaward limit of these profiles was approximately -2.0
feet MSL (1929 NGVD). Subsequently, between November 1983
and March 1984 the COE resurveyed the stations established
during the previous 1955-58 erosion study.

Comprehensive monitoring to evaluate both the effects of the
Murrells Inlet jetties on the adjacent shorelines and the
hydraulic performance of the jetties on sediment transport
processes began in September of 1979. The COE has
established brass-capped concrete monuments and documented
bench marks extending north 7 miles to the northern limit of
Surfside Beach (station #5135) and south 7 miles to Midway
Inlet. Monitoring stations, extending both north and south,
were located at greater spacing intervals with increasing
distance from the inlet.

Along the Huntington State Park shoreline adjacent to the
Murrells's Inlet jetties, these profiles were spaced at 500
ft intervals. Between 0.75 and 2 miles, spacing was
increased to 1000 ft. In the remaining area to Midway
Inlet, these profiles were located at 5000-ft intervals.
Profile locations and transect lines were perpendicular to
the 1977 shoreline as shown in Figure 3.8-1.

A total of 43 offshore profiles were surveyed quarterly by
the Charleston District COE over a 5-year period ending in
1982. Subsequently, 18 profiles are to be surveyed on a
semi-annual basis through 1987. Profiles were surveyed from
the sand dunes offshore to the -18.0 contour for all

-45-

SURFSIDE BEACH

a~~~~

GARDEN CITY BEACH

4 � 0

MURRELLS INLET

t I6MURRELLB INLET

MAGNNOLIA BEAC14

LI'TCHFIELD BEAC14

MIDWAY INLET

FIGURE 3.8-1
SURVEY PROFILE LOCATION MAP FOR
MURRELLS INLET MONITORING PROGRAM

profiles, using a fathometer at high tide to overlap points
surveyed on land using rod and level.

A 1981 shoreline management study (Cubit, 1981) established
12 stations along the approximately 3.6 miles fronting
Pawley's Island. These stations were non-uniformly spaced
with 7 stations located on the north half of the island and
the remaining 5'stations south to Pawley's Inlet. Original
reference control points established during this study were
not located although the central points for comparative
analysis purposes were replicated based on documentation
from the previous baseline. Insufficient documentation and
significant profile disparities between the 1981 and 1986
surveys deemed these comparisons questionable and therefore
invalid.

A beach profile survey program was conducted by th~ project
team in April 1986. After reviewing the historical beach
profile data collected by the U.S. COE and other
investigators between 1958 and 1984, 56 survey stations were
established in the Georgetown County study area. The
spacing between the stations was generally 1/3 mile. Of
these stations, 29 coincided with historical survey stations
which were either recovered or replicated according to
available historical survey field notes. The remaining 27
stations were "new" stations established during the present
study. There were 12 stations established in Garden City,
18 in the Litchfield area, 12 in Pawley's Island, and 14 in
Debidue Beach. Figure 3.8-2 shows the location of each
survey station.

Each survey station consisted of a survey monument and
corresponding benchmark (BM). The survey monument provides
permanent demarcation of the station location as well as a
reference point from which to conduct beach profiles. The
location of the monuments were carefully documented with

-47-

9'~~~~~~~':~~~ Y

26~~~~~~~~~~~~~~~~~~~~~~~~~~~~46

C' ~~~~~~~~~~~~~~~~~~ILT A 5
PI~~~~~nt~~~~tion~CMO 4620(SN .

4610~

456~~~0

BEACH PROFILE SURVEY AND SEDIMBENT

10~~~~~~

survey notes which include general location descriptions,
monument descriptions and tie-in distances to nearby
landmarks, profile azimuths and relative offsets. This
documentation should allow survey replication on a later
date even though the monument may be destroyed. Newly
established or replicated survey monuments consisted of a
P,K. nail and brass cap on which a 4-digit SCCC station
number was inscribed, attached to either a permanent
structure of an eight foot section of 4 in. by 4 in. wood
post embedded near the sand dune in more remote areas. The
associated BM, a vertically controlled reference point with
elevation surveyed in relation to MSL, usually took the form
of a railroad spike in a 4 in. by 4 in. post or a power
pole, a P.K. Table 3.8-1 shows a list of the SCCC station
numbers, the transect bearings, and the associated COE
station number.

Profile azimuths were generally perpendicular to the
shoreline orientation. Wherever possible, surveys commenced
well landward of the actual beach foreshore in order to
include all relevant portions of-the active dune system or
characteristic upland at each station. The profile surveys
extended seaward to MLW at the majority of the stations.
Sediment samples were taken from three locations at each of
21 survey stations for grain size analysis. The three
sample locations corresponded to the toe of dune or existing
� seawall, MHW and MLW. Sediment sample stations are
presented in Figure 3.8-2 and Table 3.8-1

Nine out of 12 Cubit Engineering (1981) monuments were
replicated. The remaining three stations could not be
located because of insufficient documentation.

It is important to note that beach profile data were
effected by beach fills near Murrells Inlet. Between
December 1978 and June 1980, 633,497 cubic yards of dredged

-49-

Table 3.8-1. Survey Stations Cross-Reference Table.

CERC # COE # Sediment
Area SCCC # (1979-82) (1983-84) Bearing Sample

Garden City 4660 -- 206+28 S56E
4655 144+25 x
4650 -- 239+00 S54E
4645 120+80 -- S60E
4640 -- 270+00 S54E
4635 81+50 -- S60E
4630 -- 300+00 S58E x
4625 51+50 -- S72E
4620 31+61 -- S72E x
4615 21+61 -- S72E
4610 11+46 -- S45E
4605 1+31 -- S45E x

Litchfield 4590 59+62 -- S45E x
4585 72+31 -- S45E
4580 92+00 -- S52E
4575 122+00 -- S46E
4570 142+00 -- S46E
4565 162+00 -- S46E x
4560 182+00 S42E
4555 202+00 -- S48E
4550 222+00 -- S44E
4545 242+00 -- S43E x
4540 252+00 -- S52E
4535 -- -- S44E
4530 -- -- S46E x
4525 302+00 -- S59E
4520 -- -- S48E
4515 352+00 -- S61E x
4510 374+45 -- S54E
4505 402+00 -- S50E x

Pawley's
Island 4460 -- -- S50E x
4455 -- -- S58E
4450 - -- S66E
4445 -- -- S66E x
4440 . - -- S62E
'4435 . - -- S62E
4430 -- -- S64E x
4425 -- -- S60E
4420 -- -- S60E x
4416 -- -- S60E
4410 -- -- S60E
4405 -- -- S60E x

Table 3.8-1. (Continue)

CERC # COE # Sediment
Area SCCC # (1979-82) (1983-84) Bearing Sample

Debidue 4370 -- -- S84E x
4365 -- -- S64E
4360 -- -- S66E
4355 . -- -- S64E x
4350- -- -- S66E
4345 -- -- S80E x
4340 -- -- S82E
4335 -- -- S78E x
4330 -- -- S80E
4325 -- -- S78E
4320 -- -- S78E x
4315 -- -- S78E
4310 -- -- S78E
4305 -- -- S76E x

spoil material from the Murrells Inlet entrance channel was
placed north of the inlet (stations 4615 to 4625) and
542,944 cubic yards of dredged material was placed south of
Murrells Inlet (stations 4575 and 4580).

3.9 SEDIMENT DATA
Previous studies to evaluate the native beach sand on
Georgetown County's shoreline for grain size characteristics
and statistics do not exist in a documented form.
References to beach and dune sediments were described
qualitatively in the geomorphology sections of recent
shoreline studies (Cubit, 1981 and RPI, 1985).

To provide basic sediment grain size statistical parameters
such as mean phi, median phi and the relative grain size
distributions (phi84 and phi86), a summary of data collected
in a 1955 COE study along the Myrtle Beach shoreline is
presented. Surface sand samples were taken at Myrtle Beach
during September and October field reconnaissance surveys
and analyzed for grain size distributions. Samples were
taken at 16 locations along the foreshore area at mid-tide.
Table 3.9-1 presents a summary of these data averaged for
all locations.

In 1972, sand samples were taken by the COE at three
locations along Garden City and analyzed for grain size
distribution. The average mean grain diameter of these
samples was 0.33 mm for a composite representing sediments
sampled at the toe of the dune, mid berm and "at the water's
edge".

Beach sediment samples along North Myrtle Beach were
collected in a 1985 study to determine the distribution of
sediment characteristics along the beach foreshore area.
Mean grain size, standard deviation, skewness and size-
fractions were computed at 3 locations along eight stations.

-52-

Table 3.9-1. Summary of Sediment Characteristics

NATIVE BEACH SAND AT.THE MID-TIDE LEVEL

AVERAGE Phi8 Phil6 / Phi Mean/ Phi sorting Median Dia (mm)5/

15 surface
samples 2.50 (0.18mm) 1.45 (0.37mm) 1.98 (0.26mm) 0.53 0.23

13 samples from
1 ft below
surface 1.55 (0.17mm) 0.65 (0.64mm) 1.10 (0.31mm) 0.43 0.27

28 samples
(both types) 2.53 (0.17mm) 1.18 (0.44mm) 1.86 (0.28mm) 0.68 0.24

2/ 84% of the sand has a diameter greater than that shown.
/ 16% of the sand has a diameter greater than that shown.
/ Average of Phisd and Phil6.
4/ One-half the difference between Phi and Phi
-/Half the sand is larger and half smaller than the indicated size.

GARDEN CITY BEACH NATIVE BEACH SAND SAMPLES

PROFILE LOCATION 16 PHI 84 PHI MEAN PHI S.D. PHI MEDIAN DIAM SHELL
SECTION ON PROFILE UNITS UNITS UNITS UNITS PHI UNITS mm CONTENT

70 + 00 Toe of Dune 1.89 2.32 2.11 .22 2.12 .23 1%
Mid Berm 1.94 3.06 2.50 .56 2.32 .20 1%
196 + 05 Toe of Dune .32 2.32 1.32 1.00 1.84 .28 21%
Mid Berm 1.43 2.47 1.95 .52 1.19 .27 1%
Water's Edge .80 2.40 1.60 .80 1.74 .30 1%
255 + 00. Toe of Dune 0.0 2.25 1.13 1.13 1.36 .39 32%
Mid Berm -.07 2.40 --- 1.17 1.24 1.51 .35 34%
Water's Edge -.14 2.40 1.13 1.27 1.79 .29 39%

Composite 0.77 2.45 1.61 0.84

Source: COE Reconnaissance Report, 1983

The samples were described as well-sorted fine sands (2.0 to
3.0 phi, or 0.25 to 0.125 mm) with average mean grain-size
equal to 2.64 phi or 0.16 mm. Variation along the length of
shoreline represented by these samples was found to be
negligible and uniform across the profile. It should be
noted that the sediments were collected at +6.0, +2.5 and
-2.5 feet (MSL) elevations along the profile.

From a comparison of sand from Garden City, North Myrtle
Beach and Myrtle Beach, sand sizes vary consistently along
the length of the shoreline. The average mean grain size
for North Myrtle Beach, Myrtle Beach and Garden City were
computed to be 0.16, 0.20 and 0.33mm, respectively. As part
of the present study, sediment samples were taken from 21
survey stations. At each station, three samples were
collected at the toe of the dune, MHW and MLW results of the
sediment analysis are presented in Section 5.0. The
sampling stations are depicted in Figure 3.8-2 and Table
3.8-1.

3.10 BEACH MORPHOLOGY
Beach morphology varies considerably over the study area and
an area-wide classification can only be given in general
terms. Factors contributing to this overall variation
include the proximity of tidal inlets and swashes, the
amount and type of development along a particular reach,
shoreline orientation, the existence of shoreline erosion
control structures and the quantity of sediment supply
available to the reach, in particular, local variations in
sand supply.

The intertidal portion of the beaches in the study area may,,
in general, be classified as mildly sloping beach of low
elevation. This combination results in a relatively wide
low-tide beach and very little to no high-tide beach at many
places. This characteristic is a result of the considerable

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tide range combined with the relatively small grain size of
the natural beach sediments that maintain a mild beach
slope. Occasionally along the study area, this flat face is
interrupted by an upper beach berm above the mean high water
line (MHWL). This berm extends to the dunes or to the
immediate upland if the dunes have been removed or
destroyed. At several locations along the study area, beach
surveys showed'evidence of active ridge and runnel, and
associated swash-trough systems indicating seasonal onshore
transport that would be expected during the month of the
survey, i.e. April.

In general, the southernmost ends of the barrier islands
within the study area exhibit southerly migration trends in
the form of migrating spits. Accordingly, the shorelines
adjacent to unstabilized inlets typically exhibit
accretional tendencies as a result of sediment storage and
sand bypassing at thel inlet 4ia inlet shoal migration.
Therefore, the shorelines in the immediate vicinity of
inlets should be considered quite unstable and subject to
severe short-term and large-scale variations in morphology,
particularly in response to storm events. This phenomenon
has resulted in various forms of inlet stabilization via
structures at several of the developed sections of shoreline
within the study area. A discussion of typical beach
profile characteristics for each of the reaches of the study
area is presented in the following sections.

Garden Citv Beach
Approximately 3.4 miles of Garden City Beach shoreline lie
within Georgetown County. When comparing the shoreline
characteristics of developed areas that indlude bulkheads
and gr6ins, to the unaltered, natural shoreline sections, a
distinct variation in beach morphology becomes apparent.
The back beach system along the armored sections of
shoreline, which are located at the immediate north and

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south ends of the Garden City reach, is characterized by a
relatively flat plateau at elevation 10-12 ft. Any dunes
that may have once existed appear to have been leveled.
Natural vegetation has been severely depleted, particularly
along areas where buildings lie within 10-20 ft of the
bulkhead. The beach face itself extends from the bulkhead
at an average elevation of +8 ft (NGVD) and drops sharply to
the apparentlimit of wave uprush where it then begins to
flatten out. This steep buildup of sand landward of the
limit of wave uprush is characteristic of the sand-trapping
effects of the existing groin system. Figure 3.10-1a
presents a typical beach profile along the armored stretches
of Garden City Beach (station 4620).

The apparently unaltered back beach system along the central
portion of this shoreline exhibits one or two well-developed
and well-vegetated dune ridges with crest elevation of up to
15 ft. Houses in this area are generally located further
landward from the beach, thereby better maintaining the
overall integrity of the natural dune system and its
stabilizing natural vegetation. Seaward of the dunes lies a
characteristic berm varying between 15 ft to 30 ft in width
and averaging 8 ft-9 ft elevation. The intertidal beach
advances seaward at a more gradual slope at this location
that along the armored sections of shore both to the north
and the south. Figure 3.10-lb is typical of the beach
profile along the central section of Garden City Beach as
surveyed during April 1986 at station 4635.

Litchfield - Huntinaton Beach
The 7.1-mile stretch of shoreline between Midway Inlet and
Murrells inlet consists of Litchfield Beach to the south and
Huntington Beach State Park to the north. This stretch of
shoreline may also be divided into two sections when
evaluating beach characteristics. Distinct variations in
beach morphology are apparent between the shoreline of

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25 PrPfile Line 620

10 5o to 15o 00 250 300 350 400 450 500 550
Distance. F

25 Pr-Ofile Line 63S

0 p2
i~10

-5
-�0

O0 100 I , 200 25 0 3001 350 40C 50 452 5e00 50

FIGURE 3.10-1
A) TYPICAL BEACH 'PROFILE AT GARDEN
CITY POINT
B) TYPICAL BEACH PROFILE NEAR INLET
HARBOR
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~150

Litchfield Beach and Huntington Beach State Park.

The southernmost 1,500 ft of South Litchfield Beach north of
Midway Inlet exhibits features characteristic of an actively
migrating and dynamic recurved sand spit. Land elevations
rarely exceed +8 ft and vegetation is sparse. The spit
averages 300 ft in width, and increases to 700 ft at its
southernmost end. Along the remaining approximately 3.3
miles of South Litchfield Beach, the back beach system
becomes increasingly extensive while the beach face system
maintains a consistent profile. The relatively stable dune
system at this location is both well developed and well
vegetated, and often exceeds +20 ft in elevation. The
number of distinct dune ridges increases from one to three
in a northward direction. A berm, 30 ft to 40 ft in width,
extends from the seawardmost toe of the dune system at an
average elevation of +7.5 ft. This berm is also well
vegetated and undergoes a gradual transition to a mildly
sloping dry beach face that extends to the approximate mean
high water line where the intertidal beach flattens out
considerably. A dry beach of 60 ft to 80 ft in width exists
at high tide along this shoreline. These morphological
characteristics and the absence of any evidence of scarping
are indicative of a stable beach system. Figure 3.10-2a
(station 4530) is representative of beach conditions along
the majority of the South Litchfield Beach and Litchfield By
the Sea shoreline during the period of the survey.

Beach morphology along the northernmost 2,000 ft of
Litchfield Beach and the entire 3.5-mile stretch of the
Huntington Beach State Park shoreline has been significantly
affected by the Murrells Inlet Navigation Project which
included the construction of, jetties at the inlet for
purposes of stabilization. The 4,000 ft of shoreline
immediately south'of Murrells Inlet has undergone localized
accretion resulting from the landward migration of the

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25 - Profile Line 530 2S Profile Line 555

BO4A , 14APR 04 86 .1500

-5 -

-5 - -5

-10 - O1-

-150 -100 -50 0 50 100 15o 200 250 300 350 400 -150 -ICC -50 0 50 10 0 2C e.C 25: _32 350 400

Dietance. FT Distance. FT

25 - Profile Line 570 25 Profile Line 575
-11 APR f6 1715 -11 APR9 6 1645
20 D
20- 'D 20

15 - 15

5 5

eB --- - �

-5 _ -5

-10
- -10

-150 -100 -50 0 50 oo00 150 200 250 300 350 400 50 lC0 10 200 2S0 300 350 400 450 500 550 600

Distance. FT Distance, FT

FIGURE 3.10-2
A) TYPICAL BEACH PROFILE NEAR C) TYPICAL BEACH PROFILE AT
LITCHFIELD BY THE SEA HUNTINGTON BEACH STATE PARK
B) TYPICAL BEACH PROFILE NEAR NORTH D) BEACH PROFILE AT NORTHERN

LITCHFIELD BEACH HUNTINGTON BEACH STATE PARK

southern portion of the inlet ebb tidal shoal system
subsequent to construction of the jetties. This is a
typical phenomenon generally associated with inlet
stabilization and is not expected to abate in the near
future.

Typically, the back beach dune system along the northernmost
2,000 ft of Litchfield Beach and the southern half of
Huntington Beach State Park is narrower than that to the
south and consists of a single dune ridge. The elevation of
this ridge decreases progressing northward from
approximately 18 ft to 8 ft in elevation. Accordingly, the
dune to the south presently exhibits severe scarping as
indicated in Figure 10-2b which is located in front of the
northernmost house at North Litchfield Beach (station 4555),
while the beach along the southern half of the State Park
exhibits lower overall elevations and a veryimild beach face
slope as depicted in Figure 3.10-2c (station 4570).
Vegetation along the back beach system is fairly abundant.
The high tide beach along this entire stretch of shoreline
is narrow to nonexistent at some locations.'

Along the northern half of Huntington Beach State Park, the
shoreline begins to exhibit a wider beach face and the re-
emergence of a dune system located some distance from the
actual beach face. This is due to the landward migration of
the southern portion of the Murrells Inlet ebb tidal shoal
and corresponding accretion of new beach immediately south
of the navigation project. The present dune system consists
primarily of a well-vegetated single dune ridge of elevation
10 ft-12 ft. An upper berm system interspersed with small
dune mounds extends seaward of this major dune ridge to the
beach face at approximately the 5 ft contour. The width of
this upper berm system increases northward from a point 200
ft north of the north park beach access to about 900 ft from
Murrells Inlet. The width of high tide beach likewise from

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increases northward. Figure 3.10-2d (station 4575)
presents the present day characteristic features of the
northern Huntington Beach State Park shoreline.

Pawlev's Island
Beach morphology over the 3.6 mile stretch of Pawley's
Island shoreline is significantly affected by shoreline
armoring, inlet-migration and inlet shoals. In general, the
island can be divided into three sections, each with
distinct morphological characteristics. These
morphologically similar areas include the southern spit
section, the central island section and the northern island
section.

The southern spit section is designated by a narrow land
formation extending northward approximately 0.8 miles from
Pawley's Inlet. This spit, formed during, the southerly
migration of Pawley's Inlet, is approximately 200 ft wide
from its bay shoreline to the open coast mean high water
line. Most of this shoreline reach has been bulkheaded
although in many places the bulkhead is presently buried by
wind blown sand. An extensive groin field is also present
along this entire shoreline reach and appears to be
retaining sand above the mean high water line. A sparsely
vegetated, narrow dune system with a maximum elevation of +8
ft to +10 ft exists along the northern two-thirds of this
stretch but is absent along the southern third. The beach
face starts at approximately the +6 ft to +7 ft contour and
maintains a relatively mild slope. Analysis of profiles and
field observations indicate very little high tide beach,
typically 20 ft-25 ft wide but as narrow as 5 ft-10 ft at
some locations. The narrow width and low elevation of this
southern spit section make it vulnerable to wave overtopping
in the event of a storm. Combined with a large volume of
runoff from the mainland that could be routed through
Pawley's Creek during the occurrence of a major storm, these

Profile Line 410
-15 APR SE -34E
A 200

5 50

J O

-5

50 100 150 200 250 300 350 400 450 500 550 600

ODtlaenc, FT

25 Profile Line 430
-15 APR 8 1140
B ao

- 5-

-5

- -0

51 :.0 150 200 250 300 35C 40C 45^ 50c0 55 6P;

Distance. FT

-5 -
5 PrOfle Line 440
-- 5 AP BE 1020

15' -

-5

-t10

50 o00 150 200 250 300 350 400 450 500 550 600

Distance. FT

FIGURE 3.10-3
A) BEACH PROFILE AT SOUTHERN PAWLEY'S
ISLAND, B) BEACH PROFILE AT CENTRAL
PAWLEY'S ISLAND, C) BEACH PROFILE AT

NORTHERN PAWLEY'S

conditions could be conducive to a breach of the island in
this southern spit section. Figure 3.10-3a is a typical
profile of the beach along this southern section.

The central island section extends approximately 1.9 miles
from a point along the northern reach of the southern spit
section to Pawley's Island Pier. The widest portion of
Pawley's Island is located along this section as are the
highest dunes, ranging as high as 25 feet in some locations.
In general, the dune system is better developed and supports
a greater abundance of natural vegetation than the dune
system along the southern spit section. The existing groin
system along the central section has resulted in sand
trapping in the immediate vicinity of these groins. Old
timber bulkheads located at the very southern extent of this
reach appear to have little effect on the overall beach
morphology and are at present buried by sand in man, places.
The beach face starts at approximately the 7 ft-8 ft contour
and extends seaward at a considerably steeper slope than do
the beaches to the north or south. The high tide beach
remains very narrow, averaging about 30 ft in width. Figure
3.10-3b (station 5430) depicts a representative profile of a
beach segment along the central island shoreline.

The northern island section consists of approximately 0.9
miles of shoreline from Pawley's Island Pier to Midway
Inlet. The majority of homes along this section are set
back from the beach and the shoreline is almost entirely
unarmored. The combination of these factors results in a
dune system that has retained its natural morphology. This
morphology is characterized by a single, well-developed dune
ridge ranging from 12 ft to 15 ft in elevation and extending
landward to a back beach plateau at the approximate 8 ft
elevation. With few exceptions, this entire system beach-
dune systems remains well vegetated. The beach system along
this section-has been significantly affected by its

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proximity to Midway Inlet. As a result of inlet migration
and shoaling processes the beach along this north section is
among the widest in the entire study area. Extending from
the dune system at approximately the 7 ft-8 ft contour, the
beach face slopes seaward at a very gradual rate. At least
80 ft to 100 ft of dry beach presently exists at high tide
on the extreme north end of the island. This width
decreases southward to the Pawley's Island Pier where it
returns to a typical 30-40 ft width. Figure 3.10-3c
(station 5440) is a representation of beach profile
characteristics along the northern section of Pawley's
Island.

Debidue Island

Similar to Pawley's Island, beach morphology over the 4.6
miles of Debidue Island shoreline is affected by seawalls,
inlet migration and inlet shoaling. Accordingly; Debidue
Island can likewise be divided into three general shoreline
areas when discussing beach morphology, each typified by
distinct physiographic characteristics. For discussion
purposes, these sections will be designated as the
undeveloped southern spit section, the wider central island
section, and the undeveloped northern section.

The undeveloped southern spit section of the Debidue Island
shoreline extends approximately 1.2 miles north from North
Inlet. The majority of this spit has formed over the last
100 years. Beach morphology here is typical of a relatively
young spit and is significantly affected by the shoaling and
migration cycles of North Inlet. This reach is moderately
vegetated with sea'grasses that lend stability to the back
beach dune system. This system consists of two distinct
dune ridges along the southern end of the spit forming one
dune ridge towards the northern end where the spit narrows.
Dune elevations average about +12 to +15 ft. A mildly

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25 ' Profile Line 315 25 Profile Line 325
-- 17 APR 86 1225 2017 APFR E6 1150
A 20 B

i5 - -5 -

o .o
tO- 5.

Wo 0 __ 0---------------------C------ 4- o

-5 - -5 - ..

-10 - -.0

-150 -100 -50 0 50 100 150 200 250 300 350 400 -50 0 S0 100 150 200 250 300 350 400 450 500
Distance. FT Dlstence. FT

25 profile Line 335 25 - Profile Line 360
17 APR6 l110 --17 APA E 915
C 20 D 2o /20

,,. ,5. / \ \

� 5 - 55

O-5 o .

-5 -10 -

-IO . -tO '

-150 -ICO -50 0 50 t00 15E 200 25C -OC 355 4:C -150 -100 -50 0 50 to100 150 200 250 300 350 400
Distance. FT Distancea. FT

FIGURE 3.10-4
A) BEACH PROFILE AT DEBIDUE BEACH C) BEACH PROFILE AT DEBORDIEU
NEAR NORTH ISLAND COLONY
B) BEACH PROFILE AT CENTRAL DEBIDUE D) BEACH PROFILE AT NORTHERN
BEACH DEBIDUE BEACH

sloping berm, heavily vegetated with wax myrtle, extends 30
ft-40 ft from the toe of the dune at elevation +6 ft to a
steeper beach face at the 5 ft contour. During the April
1986 field survey, the beach face characteristically
extended to a swash-trough at about elevation +2 ft, then
rose to a 30-40-ft wide plateau at approximately +3 ft
before gently sloping offshore. Figure 3.10-4a (station
4315) illustrates the characteristics of the southern spit
profile.

Although these characteristics are typically associated with
an accreting beach, in this case they are primarily
attributable to the effects of the North Inlet shoal system.
The high tide beach at this location during the April survey
was virtually non-existent. Observations of wave run-up
into the seaiardmost extent of the older wax myrtle
vegetation would indicate a trend of chronic shoreward
migration of the shoreline. Such apparent contrasts serve
as evidence of the highly unstable shoreline conditions
along this southern section of Debidue Island.

The central island section consists of 1.7 miles of
shoreline beginning at the north extent of the Debidue
Island spit and continuing to the northern extent of the
Debordieu Tract development. The southern half of this
shoreline reach remains in its natural state although it has
undergone accelerated erosion in the recent past. The
landward location of the back beach relative to the seawall
constructed along the northern half of the reach is
significant. The natural dune system here consists of a
well-defined ridge rarely exceeding 10 ft in elevation.
Vegetation in the form of beach grasses is sparse due to
shoreline recession, whereas wax myrtle and shrubs are
abundant. The latter, however, do little to maintain the
integrity of the dune system. The transition from dune to
beach face takes place at approximately the 6 ft contour and

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the beach maintains a gradual, mild slope towards the ocean.
The observed high tide beach is approximately 30-40 ft in
width. Figure 3.10-4b (station 4325) is a representative
profile of the unarmored reach of the central island
shoreline.

The northern half -of the central island section has been
armored by a wooden seawall landward of which an artificial
dune line has been constructed to elevations of 20 ft and
vegetated with native seagrasses. During the period of
survey, the beach elevation immediately seaward of the
seawall averaged +3 ft on the south end, rising to
approximately +6 ft at the north end. Accordingly, the
seawall at the south end is exposed to wave uprush on a
daily basis. Figure 3.10-4c presents a typical profile
along the seawalled portion of the central Debidue Island
,shoreline.

The undeveloped northern section of the Debidue Island
shoreline extends north from the northern limit of
development along DeBordieu Tract approximately 1.9 miles to
Pawley's Inlet. The back beach system along this section of
shoreline is typified by a well-developed and well-vegetated
dune system consisting of 2 or 3 distinct dune ridges at
elevations often greater than 20 ft. The beach face meets
the seawardmogt dune at an average elevation of 7.5 ft and
maintains a relatively mild slope towards the ocean. The
high tide beach is approximately 40 ft to 50 ft wide. The
northernmost end of the island exhibits an even wider beach
face due to the influence of the Pawley's Inlet shoal
system. Figure 3.10-4d (station 4360) is a typical profile
of the undeveloped northern section of Debidue Island

3.11 COASTAL STRUCTURE INVENTORY
A wide variety of coastal structures exist throughout the
study area. These structures vary greatly as to their type,

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function, condition, composition, and frequency of
occurrence along the specific reaches of shoreline that
comprise the study area. Types of structures include
seawalls, bulkheads, sandbagging, revetments, groins,
jetties and artificial dunes that are often referred to as a
soft structure. These structures are designed for
reclamation and retention of uplands, shoreline
stabilization, inlet stabilization, dune and upland
armoring, and beach enhancement. The condition of
structures is widely varied and can generally be considered
to be a function of age and original design. The U.S. Army
Corps of Engineers, in a 1983 report assessing shoreline
structural conditions north of Murrells Inlet asserted that
the majority would not be able to withstand a major
hurricane. Structural composition varies between concrete,
timber, rock, gravel, filter cloth and beach sand.
Frequency of occurrence ranges from the heavily armored
shoreline reaches of Pawley's Island to the virtually
structure-free beach along the Litchfield-Huntington
shoreline.

The inventory maps included as Appendix D provide a detailed
depiction of the type, composition and frequency of
structures presently existing along the entire study area.
The following paragraphs include additional discussion on
the background, condition, function and apparent present day
effectiveness of these structures over the specific
shoreline reaches comprising the study area. Revegetation,
sand fences, dune walkovers, and other "minor" structures
are not included in this shoreline inventory.

Debidue Island
Approximately 82% of the Debidue Island shoreline remains
devoid of any shoreline structures. The primary exception
to this is the approximately 4,100 ft wooden seawall along
the central developed portion of the island known as the

Debordieu Tract. This seawall was constructed of pressure-
treated timber with an approximate top elevation of +8.5 ft
MSL. It currently serves the dual purpose of protecting the
upland residential development from the storm surges and
waves associated with moderate storms, as well as daily wave
run-up while retaining backfill that was artificially placed
on its landward side during the development of the Debordieu
Tract.

In response to accelerated erosion south of the developed
portion of the DeBordieu Tract, an artificial dune extending
1500 ft south of the seawall was constructed in early 1986.
Averaging 13-15 ft in elevation, the dune is set well
landward of the natural dune ridge and has also been
vegetated. The dune should provide a valuable upland buffer
in the event of a severe storm as well as an additional
reservoir of sand to supplement natural beach-building
processes.

The remnants of two derelict timber groins are located on
the beach face approximately 0.7 miles south of the southern
end of the DeBordieu Tract seawall. The groins were built
in 1971 by the Belle W. Baruch Plantation Institute in an
attempt to stabilize the receding beach at that location.
The groins were unsuccessful and only remnant piles and a
few sheet sections presently remain. A timber groin also
exists at the northern end of Debidue Island approximately
0.4 miles south of Pawley's Inlet. The groin was built
around 1970 by the Arcadian Plantation. The groin remains
in a good state of repair above the mean high water line but
has lost its panels seaward of this line. As a result,
although there is an observable buildup of sand along its
updrift side, the groin poses no significant'littoral
barrier.

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Pawlev's Island
The most predominant structures along the Pawley's Island
shoreline are a system of groins of various lengths and
spacings, extending from the southern tip of the island
north to the Pawley's Island fishing pier. Originally,
groins were constructed of palmetto logs in the late 1940's
by the South Carolina State Highway Department (SCSHD).
These groins have since been replaced and additional ones
built by the SCSHD so that, at present, a system of 23
groins of creosote timber construction exists along the
shoreline. Many of these groins have been extended and/or
armored with stone at their seaward ends. In many cases the
rock has settled substantially thereby decreasing its
effectiveness. The existing groins are in various states of
repair and, as a result, exhibit varied degrees of
effectiveness. Generally, the groins seem to be effective
in trapping wind-blown sand above the mean high water line,
however, their relatively short length precludes potential
for trapping significant quantities of alongshore littoral
drift. It should be noted that the groin field could
potentially be useful in retaining future beach fill
constructed at this location, although their relationship to
beach restoration should be evaluated.

A large terminal training groin, approximately 685 feet in
length, was constructed at the north end of the island by
the SCSHD in the late 1950's. This groin, constructed of
creosote timber and armored with stone, was intended to
prevent further southerly migration of the Midway Inlet
channel and corresponding erosion of Pawley's Island. In
this sense the groin has been effective in stabilizing the
inlet.

Both the northern and southern ends of Pawley's Island have
been armored with rock revetments that appear to have been
successful in retarding upland erosion associated with inlet

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migration. Wooden bulkheads at the landward extent of many
of the groins were observed at intermittent locations along
the central anid southern reaches of the island shoreline.
At several of the locations, the bulkheads had become buried
by sand, thereby precluding an accurate assessment of both
their condition and linear extent. The length of the
bulkhead was estimated to be at least 2,500 ft and general
observations indicate fairly gbod overall conditions.

Pawley's Island Pier was originally built by a Mr. Arthur.
Erick in the late 1940's. The pier was destroyed in 1954 by
Hurricane Hazel and rebuilt to its current 680 ft length in
the spring of 1955. Around 1970 the pier was sold to
Pawley's Island developers and in 1971, ownership was passed
onto the Pawley's Island Pier Village Association, who
remain its current owners. (Personal communication - Doc
Lanchicotte).

Litchfield-Huntinaton Beach
With the exception of approximately 920 ft of concrete block
bulkhead fronting the Litchfield Inn, this entire stretch of
shoreline is structure-free. The bulkhead at the Litchfield
Inn was constructed to retain backfill for the swimming
pool, patio and other upland amenities. The bulkhead
appears to be performing well as no indication of lost
backfill, fissures in the wall, nor flanking was observed
upon visual inspection. The north tip of this shoreline
reach is bounded by the south jetty at Murrells Inlet.

Murrells Inlet Naviaation Prolect
In 1971, Congress authorized a navigation improvement
project for Murrells Inlet under the provisions of Section
201 of the Flood Control Act of 1965. Construction of the
project began in 1977 and was completed in 1980. Primary
design features of the project included jetties north and
south of the inlet, a weir section, the creation of a

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navigation channel and the option for construction of a
deflector dike in the event that the navigation channel
migrated into the deposition basin (see Figure 3.11-1).
The south jetty is 3,319 ft long, of typical rubble-mound
construction and capped with an asphalt walkway at an
elevation of +9 ft MLW. The north jetty is 3,445 ft long
and is also built of rubble-mound construction to an
elevation of +9 ft MLW. A 1,315 ft weir section of the
north jetty was built to an elevation of +2.2 MLW to allow
sand to pass over it into the deposition basin during
periods of southerly sediment transport. As the basin
becomes filled with sand, a dredge can remove the sand and
deposit it on nearby beaches. The deposition basin was
originally dredged to a depth of -20 ft MLW and the
navigation channel to a depth of -10 ftMLW, resulting in
more than a million cubic yards of sand being pumped to
beaches of Garden City to the north and Huntington Beach
State Park to the south. The deflector dike has not been
constructed because to date, the navigation channel has not
shown a tendency to migrate into the deposition basin
(Douglass, USACE - 1985).

Garden Citv Beach
North of Murrells Inlet, the shoreline along Garden City
Beach is armored by a system of groins and seawalls at both
its north and south ends. Commencing 2,250 ft north of the
north jetty, a 2,670 ft timber seawall varying in elevation
from +9 ft to +11 ft serves to retain backfill and protect
the upland residential properties from wave run-up as well
as storm surges and waves associated with moderate storms.
Two groins were constructed along the southern half of this
seawall in 1968 and two others were constructed along the
northern half in 1970. All four groins are 270 ft in length
and were constructed of creosote timber and stone by the
South Carolina State Highway Department.

-72-

U.S. I7

BUS. I? MURRELLS INUCT

0~~~~~~~~~~~~~~~~U.1

HUNTINGTO B CEACH

NAV~~~~~~~~~~~~~IOAIN CRANEEK

DEPOSITION~~~~~~~~~EFEOO DSINEaa a c

FIGURE~~~~~~~ 3.11-1

MURRELLS INLET NAVIGATION
IMPROVEMENT PROJECT

Another timber seawall is located approximately 3,900 ft
south of the Georgetown-Horry County Line; it varies in
elevation from +9 to +11 ft. The seawall serves to retain
backfill and protect upland residential property from wave
impacts. Three groins were constructed along the northern
half of this seawall in 1970 and three others were
constructed along the southern half in 1974. All six groins
are 200 ft in length and were constructed of stone by the
South Carolina State Highway Department.

-73-

--4.0 SHOREFRONT DEVELOPMENT PATTERNS
Shorefront development along the section of Georgetown
County shoreline encompassed in this study may be generally
classified as residential in nature. Over virtually the
entire study area, buildings along the coast are either
single family residences, relatively low-density multi-
family comdominiums, or resort complexes. This is in
contrast to the Horry County shoreline where the majority of
the coastal development is higher-density commercial
structures consisting of high-rise hotels, older low-rise
motels, campgrounds and mobile home parks. Also in contrast
to Horry County is the fact that approximately 48% of the
Georgetown County study area is still undeveloped, while
barely 20% of the Horry County study area has escaped
development. The following paragraphs present a more-
detailed breakdown ofishoreline development patterns along
the Georgetown County study area.

Debidue Island
Development along the Debidue Island shoreline has been
limited to the construction of primarily single-family and a
few multi-family residences along the DeBordieu Tract. this
development has been taking place over the past 15-20 years
and has included canalization of tidal creeks and
construction of dykes, causeways, impoundments and other
alteration of wetlands immediately upland of the DeBordieu
Tract (Kana et al, 1985).

South of the Debidue Tract lies the Belle W. Baruch
Plantation, consisting of more than 16,000 acres that were
set aside in 1964 by the late Belle w. Baruch to be held in
trust for marine science and related research. It is not
likely that this stretch of shoreline will ever be
developed. North of the Debidue Tract are two plots of land
referred to as Arcadia I and II. Both plots are privately
owned and, more than likely, will be subject to development
-74-

plans in the near future. No public access to the b3beaches
of Debidue Island is provided through the island uplands.
In all, approximately 20% of Debidue Island has been
developed as either single-or multi-family construction
while 80% remains undeveloped. It should be noted that
several sections of Debidue island have been designated by
the Coastal Barriers Resources ACT (CBRA) as being
"undeveloped coastal barriers" and therefore ineligible for
federal subsidiary for flood insurance as well as certain
infrastructure.

Pawlev's Island
Pawley's Island was first settled in the late 1700's as a
summer retreat from the hot, malaria-infested lowland
plantations located. More recently, the island has been
extensively developed as a summer resort community. All
beachfront property is privately owned and, with the
exception of several condominiums in the vicinity of
Pawley's Island Pier, the island consists entirely of single
family residence. Public access to the beach is made
available from a small public parking lot at the southern
tip of the island and at various street ends along the
island (Cubit-1981). Very few undeveloped shorefront tracts
remain on Pawley's Island.

Litchfield - Huntinaton
The southernmost 5000' of Litchfield Beach is presently
undeveloped. Commencing north from this point, however,
development in the form of multi-family condominiums and
single family residences line the shore. In general, the
multi-family developments have gone up in the last 10-15
years, whereas most of the single-family residences are
somewhat older. Approximately 1.3 miles of shoreline
immediately south of Myrtle Beach State park, denoted
primarily as North Litchfield Beach, consists entirely of
single-family residences. The Myrtle Beach State

-75-

Park,shoreline, extending from this point north to Murrell's
Inletis entirely undeveloped. Public access to the beach
is available via the State Park and at a few locations south
to Midway Inlet. In all, approximately 63% of the
Litchfield-Huntington shoreline may be classified as
undeveloped, 10% as multi-family/commercial and 27% as
single-family residences.

Garden City Beach
Approximately 80% of that portion of Garden City Beach
shoreline that lies within Georgetown County is developed
with single family residences. The remaining shoreline may
be classified as 11% multi-family residence and 9%
undeveloped. Public beach access is very limited as
virtually the entire beachfront is privately owned and
fronted by private homes or condominiums. Exhibits
presented' as Appendix E provide a graphic chronological
history of development trends along the entire Garden City
shoreline. A discussion of these trends follows.

Garden City Beach Development History
Of specific interest to the South Carolina Coastal Council,
as outlined in the contract to perform this study, was the
development trend of the entire Garden City shoreline.
Accordingly, in-depth research was performed that resulted
in a chronology of development patterns within the immediate
vicinity of the shoreline of both the Georgetown (3.4 mile)
and Horry County (1.8) mile segments of Garden City.

This research consisted of acquiring historical aerial
photography of the Garden City area for as many different
years as possible and then analyzing the photography to
determine periods of construction for all discernible
buildings. Aerial photography was obtained from more than a
half-dozen sources and was usually taken from high
altitudes, thereby requiring a magnifying glass, or in some

-76-

cases photo enlargements, in order to accurately identify
individual structures. The final product, included as
Appendix E, consists of a series of exhibits reduced from
I" = 200' aerial photo-maps (flown in 1982) coded to depict
the oldest known date that each structure has been in
existence. These maps do not necessarily depict buildings0
that were razed to make room for newer structures, however,
the majority of those buildings erected along the coastline
after 1982 have been included. Figure 4.0-1 and 4.0-2 show
the example of the development pattern between 1939 and0
1975.

Examination of the various sources of photography indicates
that in 1939, only seven houses had been built in the Garden
City area. These houses were located in the immediate
vicinity of the present day Georgetown-Horry County line,
presumably convenient to the nearest form of transportation
to the mainland. development obviously continued from this
point forward, but the occurrence of Hurricane Hazel in 1954
destroyed or severely damaged much of the construction to
t*. ~that time. For example, post-storm photography indicates
that approximately 75 homes within a one-mile radius of the0
county line successfully survived the hurricane. this
included a building that is now the Kingfisher Inn.
analysis of the same photography, however, indicates that
approximately 100 homes were blown or floated off their0
foundations, some all the way into the westward-lying marsh.

By 1957, the Garden City area appears to have recovered from
the damage caused by Hurricane Hazel and development began
to resurge. Approximately 200 homes existed at that time in
the area and construction was beginning to spread both
farther north and south of the county line. Development
accelerated to the point that by 1963, several hundred homes
extended as far as 1.75 miles south of the county line and
all the way to the north end of the present-day Garden City

-77-

f S

1939

Ur U- - U

IJ.54~~~~~~~~~~~~~~~~~~~~~~~~~~~

m~~~~~~~~~~~~~~~~~~~~~~~~~~an

r957

a~~~~~~a. ~Mao mge a 1.~ in ~
uS.~~~~ ~~~~~~~a Ros aft-- 11 a old

Au~ ~~~ ~ ~~~~~~~~~~~~~` ' a - Mi ue
aesmema * mmml *EU~~~*a d s a Csi aUU

No am* *g N Imago a.5 S.;hiaid a :4 s msml .*M
~~~~~~~~~~~a. . - lUUIU *3 Gamemosn a gas as a as

~~~~~~~~aneum anMaei Bongoes va 0 a Safi mmma$ Nose so am go a * *
M. a SN oSws a ma aiga
u~~~~~~~~~de Gom uneun. a Ifilgavou4*g somas goa aii 112o a. ago11110 a I'm a '!

1975 -

limit. In addition, several large commercial buildings in
the vicinity of the Kingfisher Inn had also been
constructed. The period 1963 to 1973 was one of continual
rapid growth and'development throughout Garden City. Of
particular note was the large number of single-family
residences constructed to the south, extending to what is
now the Garden City Point area adjacent to Murrell's Inlet.

By the mid-1970's Garden City consisted of well over 1,500
homes, condominiums and commercial buildings. Further
development took place primarily along the northern and
southern extremities of the city and on the remaining vacant
parcels within the already developed area. From the late
1970's to 1984, residential development of Garden City Point
and multi-family/commercial development towards the north
end of Garden city continued. In addition, a relatively new
form of construction, best described as multi-family low
rise condominiums, came into the area. In some instances,
older private homes were demolished to provide available
land for this type of construction. since 1984, development
trends have consisted typically of single-family residence
in the Garden City Point region and multi-family
condominiums and hightrises in northern Garden City.

5.0 SEDIMENT ANALYSIS
Beach sediment data were collected at 21 stations within the
Georgetown County study area. Surface sediment samples were
collected at the following three locations along the
profile; 1) toe of the primary dune or seawall, 2)locations
of MHW or approximately +2.5 ft MSL, and 3) location of MLW
or approximately -2.5 ft MSL. Sediment samples were
selected at approximately every third station and at
stations adjacent to inlets to provide information on
sediment statistics and grain size distribution. Selection
of sample stations was in consideration of the proximity to
inlets, piers and shorefront structures to accurately
represent the sand characteristics along specific shoreline
reaches. Representative samples containing at least 200
grams were collected, labeled and analyzed for size
frequency distributions.

Sediment sizes are generally expressed by the grain diameter
(mm) or using phi (0) units which are related to grain
diameter by the expression: = -log2 (mm). Figure 5-1
presents grain size scales with conversions tables and
Wentworth size class descriptions. For all samples, grain
sizes were expected to range-between coarse sand (0.75 phi
or 0.60 mm) and very fine sand (4.00 phi and 0.06 mm) which
for unconsolidated sand required sieve analysis methods. As
an extremely small fraction (<1%) of the sample is in the
silt range, requiring pipette or hydrometer analytical
methods, analysis for this fraction of sediment grain sizes
was not justified. Particle sizes equal to or greater than
0.75 phi were dried and weighed and a brief description of
the visual characteristics of the remaining pan fraction
noted. Although the majority of the samples were comprised
of grains smaller than 0.75 phi, a few samples contained an
unusually large fraction of very coarse sand sizes with
shell fragments.

Millimeters Microns Phi (~) Wentworth Size Class
( Kilometer)
-20
4096- ' - 12
1024 - -10 Boulder (-8 to -1 2~)
-256 -8
64 -6 Cobble (-6 to -84) u
- 16 -4 Pebble (-2 to -6f) >
- 4 -2
3.36 -1.75
2.83 -1.5 Granule
2.38 -1.25
----- 2.00 -1.0
1.68 -0.75
1.41 -0.5 Very coarse sand
1.19 -0.25
- 1.00 0.0
0.84 0.25
0.71 0.5 Coarse sand
0.59 0.75
- 0.50 500 1.0
0.42 420 1.25
0.35 350 1.5 Medium sand
0.30 300 1.75 Z
- 0.25 250 2.0 .
0.210 210 2.25 1
0.177 -177 2.5 Fine sand
0.149 149 2.75
0.125 125 3.0
0.105 105 3.25
0.088 88 3.5 Very fine sand
0.074 74 3.75
--- 0.0625- 62.5 4.0
0.053 53 4.25 -
0.044 44 4.5 Coarse silt
0.037 37 4.75
0.031 31 5.0 Q
0.0156 15.6 6.0 Medium silt
0.0078 7.8 7.0 Fine silt
0.0039 3.9 8.0 Very fine silt
0.0020 2.0 9.0
0.00098 0.98 10.0 Clay
0.00049 0.49 11.0 (Some use 2~ or
0.00024 0.24 12.0 9~ as the clay
0.00012 0.12 13.0 boundry)
0.00006 0.06 14.0

FIGURE 5-1
GRAIN SIZE SCALES AND WENTWORTH SIZE
CLASS DESCRIPTIONS (Folk and Ward 1957)

Grain size data were entered into a computer data base and
statistically analyzed according to the graphic methods
described by Folk and Ward (1957). Statistical methodology
developed by Folk and Ward includes a greater portion of the
grain size distribution (90%) for determining sediment
characteristics as opposed to alternative methods (Inman,
1952) which include only the distribution of sizes within
the first standard deviation (68%). The methods of Folk and
Ward (1957) adequately analyze data which are skewed or
demonstrate a bi-modal distribution.

Mean grain size, median grain size, standard deviation of
the grain size frequency distribution, skewness and kurtosis
are the statistical parameters computed for evaluation of
the sample data. Cumulative frequency plots of grain size
distributions and a table summarizing phi, weight retained,
cumulative weight, weight percent' and cumulative percent are
presented for each sample in Appendix B. Most commonly, to
characterize a sample, the average grain size (mean) and the
standard deviation or degree of sorting are discussed. The
greater the standard deviation, the less the degree of
sorting and greater the variability of sediment sizes.

For more specific analysis,, skewness (a~) is computed as a
measure of the degree of departure from a normal
distribution of grain sizes. A positive value is skewed to0
the right (contains ,a greater range of sediment sizes) and a
negative value (excess coarse grains) is skewed to the left.
Kurtosis (O3) is a measure of the peakedness of the
distribution of sediment sizes, where f3=1.O is associated0
with a normal distribution.

Table 5.1 presents a summary of sediment statistical
parameters for sample data collected along Garden City
Beaches, Litchfield/Huntington Beaches, Pawley's island and
Debidue Beach shorelines. These samples, listed from north

-83-

Table 5.0-1. Summary of Sediment Statistical Parameters Along Georgetown County

TOD MH. MLW
Station PS0 mm O a a 950 mm O a P50 mm a a

4655 1.2* .44 1.4* .38 1.9 .27 0.9 -0.3

4635 1.9 .27 0.6 -0.1 1.9 .27 0.8 -0.4 2.0 .25 0.9 -0.4

4620 2.1 .23 0.5 -0.2 2.2 .22 0.5 -0.2 1.7' .31

4605 2.1 .23 0.7 -0.5 1.7 .31 0.9 -0.2 ** ** **

Murrells
Inlet
Avg m 1.8 .29 ' Avg - 1.8 .29 Avg - 1.9 .27

4590 2.5 .18 0.5 -0.4 2.5 .18 0.4 -0.2 2.0 .25 0.7 -0.3

4565 1.8 .29 0.5 0.0 2.2 .22 0.5 -0.2 2.3 .20 0.5 -0.3

4545 2.5 .18 0.4 -0.4 2.5 .18 0.4 -0.3 2.3 .20 0.6 -0.3

4530 2.3 .20 0.4 -0.3 2.3 .20 0.8 -0.4 1.6 .33 0.8 0.2

4515 2.2 .22 0.4 -0.2 2.4 .19 0.6 -0.4 2.0 .25 0.7 -0.3

4505 2.3 .20 0.5 -0.2 2.0 .25 0.7 -0.4 1.9 .27 0.8 -0.4

Midway
Inlet
Avg - 2.3 .20 Avg - 2.3 .20 Avg - 2.0 .25

*Large portion of coarse sand fraction
**Sample with grain size analysis insufficient

P - grain size in phi units
a - standard deviation in phi units
-a skewness

Table 5.0-1 (ContinUed)

station 'P50 1 o o r o mm am Cy Pof MLW aF 1Po

4460 1.9 p.27 9.05 -0.3. 1.7 .31. 0.6 0.0 1.6 - 33 0.7 0.1

4445 1.9 .27 0.7 -0.4 2.4 .19 0.4 -0.4 2.3. ..23 0.7 -0.4

4430 1.9 .27 0.5 0.0 2.0 .25 0.6 -0.2 1.3* .43.

4420 2.1 .23 0.5 -0.3 2.2 .22 0.5 -0.2 2.4 '.19 0.6 -0.4

4405 2.3 .20 0.4 -0.2 2.6 .3.6 0.2 -0.3. 1.8 .29 0.8 -0.3.

Pawley's
Inlet
Avg -2.0 .25 Avg -2.2 .22 Avg -1.8 .29

4370 2.0 .25 0.5- -0.2 1.5* .35 2.2 .22 0.5 -0.3

4335 1.81 .29 0.6, -0.2. 2.2 .22 -0.9 -0.5 2.2 622 0.9 -0.5

4345 Los .29 0.6 -0.2 2.6 .3.6 0.4 -0.1 2.0 .25 0.9 -0.5

4335 1.1 .29 0.6 -0.2. 2.4 .19 0.4 -0.3 2.3 .20 0.8 -0.4

4320 2.4 .39 0.4 -0.2 1.9 .27 0.7 -0.2 1.8 .29 0.3 -0.3

4305 2.1. .23 0.4 -0.2 2.0 .25 0.6 -0.2 2.3 .20 0.6 -0.5

North
Inlet
Avg - 2.0 .25 Avg -2.1. .23 Avg 2.1 .23

:Large Portion of coarse sand fraction
*SaRPiLe with grain size analysis instatficiont

Souxce: Applied Technology and management, Inc. and
Olson Associates, Inc., 1986i

to south, indicate a high-degree of variability for the
entire shoreline fronting Garden City. This data set was
biased by the recent placement of artificial fill along the
Myrtle Beach shoreline immediately north of Garden City
combined with the beach nourishment project which placed
633,497 cubic yards of Murrells Inlet dredge material along
the Garden City shoreline in Georgetown County during the
period 1978 to''1980. Of the 12 samples collected along this
shoreline 4contain a large fraction of coarse sand grains
as presented in Figure 5-1. Recognizing this possible bias,
grain sizes along Garden City Beaches ranged between 1.2 and
2.1 phi, or 0.44 and 0.23 mm. The average standard
deviation of the distribution of grain sizes, i.e. a measure
of sorting, was found to be moderate (GrU/) = 0.7).
specific conclusions drawn from these sediment statistics
are only applicable in a temporal sense and will be expected
to vary as the natural shoreline processes (waves
conditions, shoreline orientation, nearshore slope and
normal sediment population) sort and redistribute the non-
native beach nourishment material.

* ~~~Mean grain sizes for sediment samples collected at six
stations along the Huntington Beach State Park and
Litchfield Beach shorelines were relatively uniform,
averaging 2.3 phi, and represented a higher degree of
* ~~~sorting then the Garden City Beaches. The average standard
deviation, including samples across the profile and along
the shoreline, is equal to 0.5 phi. Characteristically,
samples were found to have higher variability (less sorted)
* ~~~across the profile than along the length of local shoreline
and generally coarser towards the location of mean low
water.

* ~~~Sediment samples were collected at 5 stations along Pawley's
Island. Mean grain sizes ranged from 1.6 to 2.6 phi, or
0.33 to 0.16 mm, and exhibited a moderately sorted

-86-

distribution with an average standard deviation of 0.6 phi.
The grain size distributions varied along the entire
shoreline and across the individual profile stations. An
average grain size for this area was calculated as 2.1 phi
neglecting the extreme value of 1.3 phi found for sample
4430 MLW.

Debidue Beach sand characteristics were found to be slightly
coarser with all samples negatively skewed and containing a
greater fraction of coarse grains. Mean grain sizes ranged
between 1.5 and 2.6 phi with an overall average mean grain
size equal to 2.1 phi. Again, these sand samples variedz as
to the degree of sorting. Standard deviations ranged from
0.4 to 0.9 phi and averaged 0.6 phi. Figure 5-2 presents
typical sediment statistical parameters for a station
located along the seawall adjacent to DeBordieu Colony
(#4335).
i~~~~~

North to south, the average grain size increase slightly
between Huntington Beach and North Inlet.

-87-

r rO,��I

i---- ~ ~ -

CUMULATIVE FREQUENCY CURVE OF SAMPLE: 4335 TOD CUMULATIVE FREQUENCY CURVE OF SAMPLE: 4335 Nh11W

0~~~~~~~~~~~~~~~~
o~~~~~~~~~~~~~~~~~~~~O
0.

o 0

=-~~~~~~~~~~~

-I -I

.n.

8.00 ,'� oo 2'. 00 31.'00 ~'� 00 0.00 1.00 2. 00 3. 00 4. 00

GRAIN SIZE (MM) GRAIN SIZE (MM1)
SAMPLE. 4335TOD DATEi 19603514 STATIONs 4335 SALEs 4335H1MM DATE. 19860604 STATION, 4335
PROJECTS SCCC SAMPLE WEIGHT. 179.00 GRAMS PROJECT,*SCCC SAMPLE WEIGHT, 232.70 GRAtS

PHI WEIGHT CUISJLATIVE WEIGHT CUMULATIVE PHI WEIGHT CUMULATIVE WEIGHT CUMULATIVE
RETaffi3 WEIGHT (t) PERCENT PERCENT RET. (O) WEIGHT (6) PERCENr PERCENT
8.7! 9.00 9.00 5.0 5.01 0.75 0.40 0.40 0.2 0.17
1.25 25.60 34.610 14.2 19.24 125 1.90 2.30 0.0 0.99
2.00 75.40 110.60 41.9 61.10 2.00 34.hl0 36.90 (4.9 15.8B.
2.50 53.00 163.00 29.5 90.61. 2.50 94.70 131.60 40.7 56.55
2.75 i4.50 177.50 8.1 90.12 2.75 B0.00 211.0 3 4.4 90.93
3.00 : .9 170.70 0.7 99 39 3.00 (6.10 227.70 6.9 97.65
3.25 0.70 979.40 0.4 99.70 3.25 4.10 231.80 I.0 99.61
3.75 0.30 179.70 0.2 99.94 3.75 0.80 232.60 0.3 99.96
PAN 0.00 GRAMS PAN 0.00 GRAMS

STATISTI CAL PARAMETERS
MEDIAN. I.a MEDIAN- 2.4
GRAPHIC MEAN- 1.8 GRAPHIC MEAN- 2.4
INCLUSIVE GRAPHIC STANDARD DEVIATION- 0.6 INCLUSIVE GRAPHIC STANDARD DEVIATION- 0.4
INCLUSIVE GRAPHIC SKEWNESS- -0.3 INCLUSIVE GRAPHIC SKEWNESS- -0.3
GRAPHIC FURTOSIS- 0.9 GRAPHIC &URTOSIS- 1.1
NOT ENOUGH DATA POINTS ENTERED. RINM-4

FIGURE 5-2
SEDIMENT STATISTICAL ANALYSIS AT

DEBORDIEU COLONY

6.0 BEACH PROFILE AND EROSION ANALYSIS
6.1 COMPARATIVE BEACH PROFILES
Previously surveyed beach-dune profiles, replicated by this
study, were assembled for comparative analysis. Data were
analyzed using 3 profile surveys conducted in 1958, 14 new
profiles established in.1979 by the USCOE, Coastal
Engineering Research.-Center, and 12 stations established in
1981 along Pawiey's Island. Shoreline response associated
with the construction of the Murrells Inlet jetties
necessitated monitoring of adjacent beaches that provided
yearly data from 1979 to 1982.

All available data, including field-survey notes, were
collected and digitized. Profiles were entered into a
common data base along specific shoreline segments and
adjusted horizontally and vertically using both field survey
notes and reference control point information. Comparative
beach-profile survey data recovery is summarized in
Table 6.1-1. Where vertical or horizontal control of
comparative surveys could not be established, the data were
flagged accordingly or deleted.

Qualitatively, successive surveys were reviewed for both
consistency and quality. Comparative survey records
covering the period 1958 to 1986 were considered for 'long-
term erosion analysis. Profile data along Garden City and
Huntington-Litchfield Beaches, collected between 1979 and
1986, were surveyed to monitor the effects of the Murrells
Inlet jetties and represented short-term profile data.
Comparisons of Pawley's Island survey data between February-
March 1981 and April 1986 represent short-term shoreline
variation.

Analysis of volumetric changes and shoreline movement using
these comparative profile data were encumbered by the
limited data base. Accordingly, long-term erosion and
-89-

Table 6.1-1. Inventory of Comparative survey data

YEAR OF COMPARATIVE COMPARATIVE DATA
AREA PROFILE # SURVEY DATA TOTAL NO. SURVEYS

GARDEN CITY 4605 1979, 1980, 1981, 1982, 1986 5
...- ....... - 4610 1980, 1981, 1982, 1986 4
[i -._- 4615 1979, 1980, 1981, 1982, 1986 5
4620 1979, 1980, 1981, 1982, 1986 5
4625 1979, 1980, 1981, 1982, 1986 5
4630 1958, 1984, 1986 6
4635. 1979, 1980, 1981, 1982, 1986 5
4640 1958, 1984, 1986 6
4645 1958*,1983*, 1986 6
4650 1958, 1984 5
*- 4660 1958, 1984, 1986 5

LITCHFIELD
HUNTINGTON 4505 1979*, 1981*, 1982*, 1986,
1980* 4
i~ ~ 4510 1986 1
4515 1979, 1981, 1982, 1986, 1980 4
4520 1986 1
4525 1979, 1981, 1982, 1986, 1980 4
t 4530 1986 1
4535 1986 1
� - 4540 1979, 1981, 1982, 1986, 1980 4
4545 1986 1
4550 1986 1
4555 1979, 1981, 1982, 1986, 1980 4
4560 1986 1
4565 1986 1

4570 1979, 1981, 1982, 1986, 1980 4
4575 1979, 1981, 1982, 1986, 1980 4
4580 1979,-1981, 1982, 1986, 1980 4
4585 1986 1
4590 1979, 1981, 1982, 1986, 1980 4

PAWLEY'S
l ISLAND 4405 1981, 1986 2
4410 1981, 1986 2
4416 1981, 1986 2
4420 1981, 1986 2
4425 1981, 1986 2
4430 1981, 1986 2
4435 1981, 1986 2
4440 1981*, 1986* 2
4445 1981, 1986 2
�0 4450 1981, 1986 2
4455 1981*, 1986 2
4460 1981*, 1986 2

*Profiles excluded where survey comparisons were not valid

Table 6.1-1. (continued)

YEAR OF COMPARATIVE COMPARATIVE DATA
AREA PROFILE # SURVEY DATA TOTAL NO. SURVEYS

DEBORDIEU 4305 1986 1
4310 1986 1
4316 .1986 1
4320. 1986 1
4325 1986 1
4330 1986 1
4335 1986 1
4340 1986 1
4345 1986 1
4350 1986 1
4355 1986 1
4360 1986 1
4365 1986 1
4370 1986 1

accretion rates were limited to 3 stations within the entire
Georgetown County study area. To supplement this limited
data set, 23 new profiles were established at approximately
-2,000-ft intervals -along the Huntington-Litchfield Beach----
shoreline and Debidue Beach.* The survey profile locations
are shown in Figure 3.8-2

6.2 VOLUMETRIC ANALYSIS
* ~~~Comparative beach-dune profiles were analyzed along
Georgetown County's shoreline to determine the rates of
long-term and short-term volume changes. Individual
comparative profiles were examined to compute changes in
* ~~~profile volume where volume is defined as cross-sectional
area multiplied by a unit width. As discussed in Section
6.1, data records representing 25 or more years (i.e. 1958
surveys) allowed an estimate of long-term profile volume
changes, whereas the remaining data base (1979 to present)
would allow only for estimating short-term volume
variability.

* ~~~Short-term profile changes are caused by severe storms or
structural shoreline modifications, such as jetties,
shorefront structures and dredging. Seasonal storms, i..e.
northeasters and hurricanes or tropical storms, cause the
* ~~~beach to erode and the shoreline to fluctuate. Over a
relatively short period-of time, several days to many years,
L ~~sand will be transported shoreward and the beach recovers by
accretion or onshore sediment transport. In contrast,
profile changes which maintain a consistent trend over a
long period of time (generally greater than 25 years) are
catagorized as long-term changes or trends. In response to
the pervasive rise in mean sea level, the beach profile
* ~~~shifts landward to maintain a natural equilibrium state.

-92-

Two methods were used to compute volume changes, the first
method follows a prescribed control-volume approach and the
second method computes volume changes across the profile for
the limits of the region in common comparison. Figures
6.2-1 and 6.2-2 define the width of the profile over which
volume changes are computed using the l)control volume and
2) comparative profile segment approach, respectively.

In the control-volume method, volume changes were computed
between the +10.0' and -3.0' contour wherever possible. .
When low dune-crest elevations and seawalls precluded using
the +10.0' contour, an alternative maximum contour elevation
was chosen.' Unit control volumes, average annual volume
changes and net volume changes are presented in Tables 6.2-
1, 6.2-2, and 6.2-3 for all comparative profiles. Negative
volume changes represent erosion. The control volume,
representing the portion of the profile used to determine
volume changes, is limited by the initial position (Xmin and
:max in Figure 6.2-1) of the earliest survey date. The
control volume method analyzes only part of the dynamic
portion of the beach profile, which includes the entire
primary dune seaward to the point of limiting depth, or
depth of closure, which is defined as the shoreward depth
which experiences seasonal profile variations. Volume
changes calculated using the landward and seaward limits
established by the initial control volume may not and often
do not represent the actual magnitude of the volumetric
change over the active profile. To demonstrate this
analysis flaw, Figure 6.2-2 shows serious erosion at Station
4555 between 1979 and 1968, however, the control volume
method, shown in Figure 6.2-1, indicates only small changes.
The control volume method is used in this report because it
is required to establish the ideal present profile.

The purpose of the profile data collected along the
shoreline by the USCOE, both north and south of Hurrells

-93-

CONTROL VOLUME METHOD

25
Profile Line 555
0- APR 79 0

20-
:.'I '~ iO- ~ ' 0to
--CONTROL
. - I 5, - VOLUME #1 (CV1) .
DEFINES ACTIVE .
Sc - ~PROFILE SEGMENT

w-5 - CONTROL.
Lu r- VOLUME rl_
Xmin Xmax
-to

-t5 -

-20 -

I . I . . . . . .
-200 -100 0 100 200 300 400 500 600

Distance, FT

25
Profile Line 555
- 20 i APR 86 1500
20 -

15O -
10

. 5- CONTROL
. . VOLUME #2 (CV2) .

-5 -

-15 -
DEFINCVII - CV2
* -20 - AVERAGE VOLUME CHANGE (1979-1986) =USING THE

-200 -100 0 too 200 300 400 500 500

Oistance. FT

DEFINITION SKETCH FOR COMPUTING
AVERAGE VOLUME CHANGES USING THE
CONTROL VOLUME METHOD AT PROFILE
#4555

-COMPARATIVE PROFILE SEGMENT METHOD

25
Profile Line 555
- i2 APR 86 �500
20 -__ 0 APR 79 0

15 -A

10- ERODED VOLUME

U. .
c ' A_ ~~~~~~~~~DEPOSITED VOLUME
0
0----------------------

- - COMPARATIVE
Wj I PROFILE SEGMENT - .

-to ~~~~~~~~~~~~~~~~~~~~~N.
-10-

-15-

AVERAGE VOLUME CHANGE (1979986) DEPOSITED VOLUME - ERODED VOLUME
-2~0 AVERAGE VOLUME CHANGE (1979-198)'=ME O ER
-20 - ~~~~~~~~~NUMBER OF YEARS

) I I I I I I . I
-200 -100 0 100 200 300 400 500 600

Distance. FT

FIGURE 6.2-2
DEFINITION SKETCH FOR COMPUTING
AVERAGE VOLUME CHANGES USING THE
COMPARATIVE PROFILE SEGMENT METHOD
AT PROFILE #4555

Table 6.2-1. Average, Net and Unit-width Volume Changes between 10.0 ft
and -3.0 ft MSL (Garden City)
Average Volumetric Net Volumetric
Change (yd /ft/yr) Changes (cy /ft)

Station 1958-84 1979-80 1980-81 1981-82 1982-86 1984-86 1979-86 1958-86
(26 yrs) (1 yr) (1 yr) (1 yr) (4 yrs) (2 yrs) (7 yrs) (28 yrs)

Garden City

4605 8.2 7.0 4.2 0.1 20.0

4610 18.1 -0.8 -5.3 -3.8

4615 32.2 -13.9 -7.3 -3.3 -2.2

4620 13.0 14.2 -10.9 -0.2 16.1

4625 2.3 27.0 -17.2 0.2 12.7

4630 2.8 3.9 81.4

4635 3.6 -1.9 2.0 1.8 10.9

4640 1.0 2.9 21.5

-- 4660 - 0.6 -1.0 13.2

Unit-W3dth Volume
(yd /ft)

Station January Sept Sept Sept Sept March April
1958 1979 1980 1981 1982 1984 1986

i. Garden City

4605 60.2 68.4 75.4 79.6 80.2

4610 47.8 65.9 65.1 44.0

4615 46.4 78.6 64.8 57.5 44.2

4620 20.2 33.5 47.5 36.7 35.9

4625 42.1 44.4 71.4 54.2 54.8

4630 54.7 128.3 144.2

4635 30.8 34.4 32.5 34.4 41.7 41.7

4640 39.6 66.9 61.1

4645 33.5 23.6 96.8

4660 30.9 46.0 44.1

Table 6.2-2. Average, Net and Unit-Width Volume Changes Between 10.0 ft and -3.0 ft
(Huntington/Litchfield)

Average Voumaetric Net Volumetric
Change (yd /ft/yr) Changes (yd /ft)

Station 1979-80 1980-81 1981-82 1982-86 1979-86
(1 yr) (1 yr) (1 yr) (4 yrs) (7 yrs)

Huntinoton and Litchfield Beach

4515 1.5 -5.9 1.9 0.7 0.3

4525 3.1 -5.4 -3.7 0.7 -3.1

4540 -20.6 -1.9 2.3 -0.3 -21.6

4555 -6.3 0.5 -4.0 1.6 0.5

4570 -12.4 9.7 12.6 0.6 12.4

4575 -2.6 30.1 2.4 1.1 34.4

4580 7.9 17.4 2.1 3.5 40.3

4590 9.0 -1.8 MD 10.6 60.4

Unit-Wdth Volume
iyd /ft)

Station Sept Sept Sept Sept April
1979 1980 1981 1982 1986

Huntinaton and Litchfield Beach

4515 46.9 48.3 42.5 44.4 47.2

4525 40.9 44.0 38.6 35.0 37.9

4540 56.3 35.7 33.8 36.1 34.7

4555 55.1 31.5 32.0 28.1 34.6

4570 42.6 30.3 40.0 52.5 55.1

4575 44.4 41.7 71.9 74.2 78.8

4580 139.0 146.0 163.4 165.5 179.3

4590 101.8 110.8 109.0 162.2

*Table 6.2-3. Average, Net and Unit-Width Volume Changes Between 10.0 rt and -3.O t
(Pawley's Island)

Average Vo umetric Net Volumet~ic Unit-Width Volume
Change (yd /ft/yr) Changes (ydJ/ft) (yd3/ft)

Station 1981-86 1981-86 Feb-Mfar April
(5 yr.) (5 yrs) (1981) (1986)

Pawlev's Island

4405 1.2 5.8 40.5 46.3

4410 0.0 0.0 44.8 44.8

4416 -0.2 -1.2 35.2 34.0

4420 -3.0 -14.9 41.4 26.5

* 4425 -0.1 -0.6 33.7 33.1

4430 1.0 5.2 32.7 37.9

4435 -1.1 -5.7 43.5 37.8

4445 1.6 7.9 33.5 41.4

4450 1.2 6.1 36.2 42.2

Inlet, was to monitor the effects on shoreline planeform
changes caused by jetty construction. The Murrells inlet
monitoring study was designed to study this major
perturbation. The effects of these jetties and inlet
dredging have caused substantial volumetric changes along
several profiles.

The nature of seasonal variation in profile cross-section is
well-documented and accepted. Winter profiles result from
offshore sand transport, with sand stored in a bar. During
summer months the beach recovers as moderate wave conditions
transport this bar onshore, resulting in a more gentle
(summer) profile. Accordingly, the short-term volume
changes presented in Tables 6.2-1 and 6.2-2 for the 1980-
1981 surveys along the Garden City and Huntington-Litchfield
Beach shoreline represent seasonal shoreline variation, and
must be regarded as a short-term, seasonal shoreline change.
Figure 6.2-3 represents the sea sonal profile variations of a
hypothetical survey depicting volume changes which result
from winter and summer wave conditions.

A second approach, the comparative profile segment method,
examines volume changes over a greater portion of the active
profile. This method will attempt to qualify and
substantiate the control volume methodology which may
inaccurately represent the magnitude of erosion or accretion
for profiles which experience a high degree of variability.
Using the comparative profile segment approach, Table 6.2-4
and 6.2-5 presents the average annual volume changes and the
net volume changes including notes to depict locations of
man-induced profile modifications. A comparison of profile
surveys analyzed using both methods to compute volume
changes revealed that the nature of the variability, either
erosion or deposition, was generally consistent between the
control volume and the comparative profile segment approach
for Georgetown County profile data.

-99-

SUMMER PROFILE

BERM DUNE
MEAN SEA LEVEL

WINTER OR STORM PROFILE

STORM WATER LEVEL
MEAN SEA LEVEL ,g'

'- ..

VOLUME CHANGES FOR STORM PROFILE

STORM WATER LEVEL -
MEAN SEA LEVEL

~~~L~~ _~ v ROSION

:'":,'.- '.. L. DEPOSiTION

FIGURE 6.2-3
IDEALIZED SEASONAL PROFILE VARIATION
AND THE ASSOCIATED VOLUME CHANGES

Table 6.2-4. Average and Net Volume Changes between
Comparative Profile Surveys

Average Volumetric Net Volumetric
Change (yd /ft/yr) Changes (ydF/ft) Notes

Station 1958-86 1979-86 1979-86 1958-86 Shoreline
(28 yrs) (7 yrs) (7 yrs) (28 yrs) Structures,
Nourishment,etc

Garden City

4605 2.9 20.2

4610 0.0 -0.1 1500' North
of Murrells
Inlet Jetties

4615 -4.0 -2.5 Beach Nourish-
ment
4620 3.0 20.8 12/78-6/80

4625 1.6 11.2

4630 2.6 72.2

4635 5.1 35.7

4640 0.3 9.1

4660 0.6 16.9

Average Vo umetric Net Volumetric
Change (yd /ft/yr) Changes (yd /ft) Notes

Station 1979-86 1979-86 Shoreline
(1 yr) - (7 yrs) Structures,
Nourishment, etc

Huntinaton and Litchfield Beach

4515 0.9 6.1

4525 1.7 8.9

4540 -3.4 -23.8

4555 -1.8 -12.2

4570 4.9 34.0

4575 13.8 96.3 Beach Nourish-
ment 11/80-
12/80
4580 6.7 46.9 "

4590 31.5 220.7 500 ft South
from Murrells
Inlet South
Jetty

Table 6.2-5. Average and Net Volume Changes Between Comparative
Profile Surveys (Pawley's Island)

Average Voiumetric Net Volumetric
Change (yd /ft/yr) Changes (yd /ft) Notes

Station 1981-86 1981-86 Shoreline
(5 yrs) (5 yrs) Structures,
Nourishment, etc

Pawlev's Island

4405 1.2 5.8

4410 -0.1 -0.5

4416 -0.9 -4.6

4420 -3.3 -16.4

4425 -1.6 -8.2

4430 1.6 7.9

4435 -1.6 -7.8 South 300' from
Pawley's Island
Pier

4445 -2.3 -11.4

4450 -1.4 -6.7

9~i

Garden City
Profile variability, based on average annual volume changes
along the shoreline segment south from Kingfisher Pier to
Murrells Inlet, was greatest for stations fronting Inlet
Harbor. Net accretion occurred at the five beach profiles
extending south from Kingfisher Pier along 2 miles of Garden
City shorelinewithin Georgetown County. Erosional trends
were observed at profiles immediately north of the Murrells
Inlet north jetty where the beach was nourished between 1978
and 1980.

Long-term volumetric changes were computed at 3 stations
along the Garden City shoreline. These trends indicate
erosion at stations #4640 and #4660, where long-term erosion
rates ranged from -0.3 to -0.6 yd3/ft for the last 28
years.

Profiles along the shoreline immediately north of Murrells
Inlet (2000 ft) eroded from 1981 to 1986. Beach nourishment
along this shoreline segment (12/78 to 6/80) has resulted in
a beach planeform out of equilibrium with the natural
shoreline processes.

Huntinaton-Litchfield Beach
Analyses of volume changes for Huntington-Litchfield Beach
profiles indicate a short-term depositional trend over the
northern and southern shorelines. Beach profiles for
stations #4540 and #4555 consistently eroded from 1979 to
1986. This shoreline has experienced a sediment deficit
which is a direct result of Murrells Inlet jetties.
Longshore currents fail to transport sufficient sand to this
reach of shoreline so that there is a net deficit in
southerly sediment transport to these beaches. The
sheltering effects of an extensive ebb tidal shoal and the
0.6 mile long jetties have caused northerly longshore

-103-

currents to predominate along the northern reaches on
Huntington Beach.

Pawlev's Island
Pawley's Island has accreted at the southernmost beach
profile station (#4405) during the period of February-March
1981 to April 1986, and eroded along the shoreline reach
between station #4410 and #4425, a shore distance of
approximately 6000 feet. Erosion along the northern
shoreline of Pawley's Island is evident on the comparative
profiles seen in Figure 6.2-4. Applying a control volume
extending across the foreshore area of the dune-beach
profile, to compute volume changes at stations #4445 and
#4450 resulted in a net depositional trend. A visual
comparison of the 1981 survey data with 1986 surveys for
profiles at stations #4445 and #4450 depict erosion along
the primary dune. The most significant volume changes for
this profile occurred along the primary dune portion of the
profile and are more accurately represented using the
comparative profile segment methodology.
L
Analysis of volume changes for beach profiles at stations
#4555 and #4450 are better represented using a greater
region along the profile for computing volume changes. The
control volume does not account for erosion landward or
seaward of the original control points (Xmin and Xmax)
established using the foreshore region of the earliest
survey. Short-term beach profile variations in the region
of the primary dune may be described by the elevation of the
dune crest and the width of the dune. These characteristics
of the primary dune represent the first line of defense
against wave and high-frequency storm tide impacts on the
beach-dune system.

Volume changes for shoreline areas that are characterized by
large profile fluctuations or for cases where early survey

-104-

20 - Profile Line 445
-14 FEB 8S 0
_ 15 APR 86 950

to -....
=.

0 O ------------------------------_--_-__ -_--_-
a

tu
0i --
U.

t-o
-20 -

Profile Line 450
- i4 FEB 8 0
STAIOS-i5 APR 86 930

109- / / SAN

IL ~ ~ ~ / '',\
f~~~~~~~~~~~~~~~~~~..

0 - . ... .._

W
1.4
'U

-1O -

I , I. I , I . I , I . I

0 io0 200 300 400 500 600

Distance. FT

FIGURE 6.2-4
COMPARATIVE BEACH PROFILE SURVEYS FOR
STATIONS 4445 AND 4450 BETWEEN 1981 AND
1986 ALONG PAWLEY'S ISLAND

data represent a steeper winter storm profile, the actual
volume change may be underestimated or inaccurately
assessed. Also, the dynamic portion of the profile
extending to the depth of closure, or the limiting depth
associated with an active profile, is not considered in
these results.

6.3 SHORT-TERM SHORELINE EROSION RATE
Shoreline changes or beach erosion can be characterized
using the following categories:
1. Initial volume changes can be caused by a discrete
event such as a storm or beach nourishment. These
sudden shoreline perturbations can occur within
several days or overnight.
2. In response to sudden shoreline perturbations, beach
profile will undergo a period of recovery. As an
example, immediately following storm erosion, beach
fill, or coastal structure construction, the beach
profile will re-adjust as it reaches a new state of
equilibrium. The rate of changes is greater at the
initial stage of recovery, and decreases as it
approaches equilibrium. The period of recovery
normally is less than 10 years except for unusually
large disturbances.
3. Beach profiles will experience periodic changes as
it adjusts to differences in seasonal wave climate.
The lower frequency summer waves will cause onshore
sediment transport, resulting in a mild beach slope
and wide beach face. The high energy winter wave
climate results in offshore sediment transport and
formation of offshore bars which characterize the
winter profile. A mature stable shoreline will
endure seasonal erosion/accretion and yet maintain
long-term stability.
4. Long-term changes are caused by sea level rise, wind
and wave climate, shoreline orientation, offshore

-106-

bathymetry, inlet dynamics, and other geological
features. Long-term variation is typically much
smaller than the short-term changes. A stable
shoreline with negligible long-term erosion trends
may have substantial seasonal variation. Therefore
large quantity of time series data will be required
to filter out short-term changes and accurately
quantify long-term trends.

The first three categories are considered short-term changes
and are evaluated according to contour movement based on
comparative beach profile data.

In general, comparative beach survey data were available
between 1979 and 1986, although few stations also had 1958
data. No greater than 5 sets of survey data were available
at individual stations where the timelperiod between
consecutive surveys ranged from 1 year to 5 years, excluding
the 1958 data. Comparisons between consecutive surveys are
presented in Appendix B.

Shoreline changes, or contour movement of the beach
topography, can be interpreted using shoreline recession/
accretion rates. However, appropriate contour elevations
should be selected to obtain meaningful results. The beach
face near MSL usually has a mild slope (approximately 2 to
3% along the study area), consequently, the MSL contour
position is very sensitive to profile changes. For example,
when the dune erodes, the material may be deposited to the
foreshore area. Accordingly, the XSL contour is moved
offshore. The MSL contour would appear to be the result of
beach accretion, but in reality it may be the result of dune
erosion. Therefore, the movement of a contour in a dynamic
zone below MSL can yield misleading results. The mean high
water line (about 2.98' NGVD) is located along a steeper
beach slope (about 5 to 8% within the study area), and as a

-107-

result was less sensitive to the spacial redistribution of
the beach material and more accurately reflects both erosion
or accretion.

Table 6.3-1-presents the MHW contour locations and recession
rate in the Pawley'S Island area. Tables 6.3-2 and 6.3-3
show MHW contour movement in the Litchfield area. Table
6.3-4 and 6.3-5 present contour movement on Pawley's Island.
Comparative profile data is not available for Debidue Beach,
therefore the short-term changes can not be computed.

The short-term shoreline recession rate calculated using the
available beach-profile database indicates considerable
variation for shoreline changes, from 235 ft/yr accretion to
173 ft/yr erosion. The majority of extreme erosion/
accretion rates were derived from comparative data covering
a short time period (about 1 year) and reflected the effects
of seasonal changes and storm events.

Although the seasonal and yearly shoreline changes were
substantial (from 33 ft/yr accretion to 41 ft/yr erosion),
the average recession rates over 2 to 7 years were much
smaller. Table 6.3-6 summarizes the short-term shoreline
recession rates for each area indicate a highdegree of
variability within the data as summarized in Table 6.3-6.
Since the temporal database is small (5 profiles or less),
it is difficult to make conclusive predictions about the
short-term -erosion rates. As an example, the 1982-86 data
showed mostly erosion in the Garden City area, but 1979-86
data showed mostly accretion in the same area.

Pawlev's Island
There were only two surveys conducted for Pawley's Island
beach profiles (1981 and 1986). Table 6.3-1 presents the
changes for the northern portion of the island where erosion
occurred between survey dates and the southern reach which

-108-

Table 6.3-1 Mean High Water Contour Position
(Pawley's Island)

MHW Position (ft)

Rate of change*
Station 3/1981 4/1986 (ft/year)

4405 155 155 0.0

4410 172 166 -1.2

4416 206 199 -1.4

4420 389 354 -6.9

4425 353 345 -1.6

4430 340 341 0.2

4435 718 703 -3.0

4445 336 355 3.7

4450 360 380 3.9

4460 625 653 5.5

* Negative number indicates erosion.

Table 6.3-2. Mean High Water Contour Position (Litchfield Area)

Mean High Water Contour Position (feet from baseline)

Station 4/1979 4/1980 9/1981 4/1982 4/1986

4505 341 191 124 -- - 127 114

4515 130 142 142 99 103

4525 165 181 177 136 141

4540 187 138 151 94 94

4555 112 96 74 66 78

4570 143 18 114 173 179

4575 207 149 431 330 347

4580 421 394 502 533 528

4590 826 891 858 809

Table 6.3-3. Mean High Water Contour Movement (Litchfield Area)

Mean High Water Contour Movement Rate (ft/year)
(Negative number indicates erosion)

Station 1979-80 1980-81 1981-82 1982-86 1979-86 1980-86

4505 -150.0 -47.3 5.1 -3.3 -32.4 -12.81

4515 12.0 0.0, -73.7 1.0 -3.9 -6.5

4525 16.0 -2.8 -70.3 1.3 -3.4 -6.7

4540 -49.0 9.2 -97.7 0.0 -13.3 -7.3

4555 -16.0 -15.5 -13.7 3.0 -4.9 -3.0

4570 -125.0 67.7 101.1 1.5 5.1 26.8

4575 -58.0 199.0 -173.2 4.3 20.0 33.0

4580 -27.0 76.2 53.1 -1.3 15.3 22.3

4590 65.0 -23.3 -2.4 -13.7

4~I 0

Table 6.3-4 Mean High Water Contour Position (Garden City)

Mean High Water Contour Position (feet from baseline)

Station 1/1958 4/1979 4/1980 9/1981 4/1982 3/1984 4/1986

4605 410 436 453 466 448

4610 362 396 401 368

4615 315 550 401 328 303

4620 173 154 227 286

4625 237 253 363 300 286

4630 208 373 398

4635 340 353 363 355 359

4640 245 297 267

4650 218 174

4660 151 203 177

Table 6.3-5 Mean High Water Contour Movement (Garden City)

Mean High Water Contour Movement Rate (ft/year)
(Negative number indicates erosion)

Station 1979-80 1980-81 1981-82 1982-86 1984-86 1979-86 1980-86 1958-84 1984-86

4605 26.0 12.0 22.3 -4.5 5.4 2.0

4610 24.0 , 8.6 -8.3 1.0

4615 235.0 -105.2 -125.2 -6.3 -1.7 -41.2

4620 -19.0 14.8 16.1 22.0

4625 11.3 188.6 -15.8 10.5 5.5

4630 6.3 12.0

4635 9.2 17.1 -2.0 2.5 1.0

4640 2.0 -14.4

4650 -1.7

4660 2.0 -12.5

.R~ 0 9 00

Table 6.3-6 Summary of Short-Term MHW Contour Movement

Average MHW Contour Movement (ft/yr)*

Garden City Litchfield Beach Pawlev's Island

4 yr maximum 14.8 4.3
4 yr minimum ..: -15.8 -3.3
4 yr average.�' -3.7 0.8

5 yr maximum 5.5
5 yr minimum -6.9
5 yr average -0.1

6 yr maximum 22.0 33.0
6 yr minimum -41.2 -13.7
6 yr average -1.6 3.6

7 yr maximum 16.1 20.0
7 yr minimum -1.7 -32.4
7 yr average 6.6 -2.2

*Negative value indicates erosion

has experienced accretion. The rate of accretion increased
when approaching Pawley's Inlet.

Litchfield/Huntinaton Beach
In general, the shoreline between Murrells Inlet and Midway
Inlet had the highest degree variability within the study
area. Large erosion rates, as high as 150 ft/year, were
indicated by the April 1979 and April 1980 data, except near
the Murrells Inlet where the south jetty caused substantial
accretion. The April 1980 and September 1981 data indicates
accretion along this beach segment although this may be the
result of a transformation from a winter to summer profile.
Similarly, the September 1981 and April 1982 data indicate
mostly erosion. The changes in the position of the MHW
contour were less significant (from 4.3 ft/year accretion to
3.3 ft/year erosion) between April 1982 and April 1986,
which may indicate that the planeform changes are adjusting
to the effects of the Murrells Inlet jetties. The greatest
temporal variability occurred between station 4540 and 4575.
The spatial average of the MHW changes between April 1982
and April 1986 was about 2.2 ft/year erosion.

Garden City
With the exception of recent changes measured between 1982
and 1986, the area near Murrells Inlet north jetty (Station
4605 and 4610) has shown consistant accretion. Station 4615
experienced a high erosion rate as indicated in Table 6.3-5,
whereas the shoreline north from station 4615 was
predominantly accretional. The spatial average of the MHW
changes between April 1979 and April 1986 was about 6.6
ft/year accretion.

6.4 LONG TERM SHORELINE EROSION RATE
NOS shoreline movement maps described in Section 3.7, were
used to estimate long term erosion rate. The survey
stations were located on the shoreline movement maps, and

lateral changes of the shoreline position were measured
relative to the 1983 shoreline. With the assistance of
magnifying devices, the accuracy of the shoreline position
is about 7 feet. Since the time periods between shoreline
surveys were 9, 21, 28, and 50 years, the accuracy of the
long term shoreline recession rate is about 0.3 ft/year.
The time series of the shoreline position at each station is
shown in Figures 6.4-1 to 6.4-3 for different section of the
study area.

Figure 6.4-1, presents the shoreline changes along Debidue
Beach and indicates that there was distinct shoreline
movement trends between 1857 and 1925 when the sand spit at
the southern end of the island grew rapidly. During this
period of time, New Inlet, a previously existing inlet, was
closed by the Debidue Spit. In the process of inlet
closure, the southern Debidue Beach accreted and the
northern Debidue Beach eroded. After the inlet closure, the
southern island experienced heavy erosion, while the
northern island was accretional. This trend reversal is
typical when the shoreline recovers from a major
disturbance. Since 1925, North Inlet continuously migrated
toward the south with an average rate of about 100 ft per
year. The migration and erosion slowed in an exponential
fashion which is clearly shown in Figure 6.4-1.

Figure 6.4-2 shows the shoreline changes on Pawley's Island.
The variability of shoreline recession was greatest at
northern end of the island near Midway Inlet where the
southerly migration of the inlet has caused erosion at
northern end of Pawley's Island. At present, the southern
portion of the island appears to be relatively stable except
in the immediate vicinity of Pawley's Inlet.

The shoreline movement along Litchfield/Huntington Beach
State Park area (Figure 6.4-3) had greater variability than

-116-

QI~~~~- ~ ~432

/' /

' -

J i i B I I ; I * ! B S I * ~ I 1 l, * * . .

- 7YEAR

FIGURE 6.4-1
SHORELINE MOVEMENT AT MONITORING
STATIONS ALONG DEBIDUE BEACH

8 -
o-
4420

a-
4J -

445
0 ..- 44215 341
4 - - ---%

- 44o- 44102. _ / . /f
of- < i\ 8- O \

o0 -
o 8:

?850 1875 1900 t925 1950 1975 2WO 850 1875 1900 1925 1950 1975 2000
YEAR YEAR

FIGURE 6.4-2
SHORELINE MOVEMENT AT MONITORING
STATIONS ALONG PAWLEY'S ISLAND
STATIONS ALONG PAWLEY'S ISLAND

0 -

0 I455-
C_ :_

457K

o
8- 0-

STATIONS ALONG LITCHFIELD BEACH AND
__0,~~~0 :

~~HNIGOBECH~ STT PR

Pawley's Island. Similar to Debidue Beach, the pattern of
the shoreline movement was reversed around 1926-1934. In
the last two decades, the beach in this area has generally
experienced erosion except the northern end near Huntington
Beach State Park. The recent survey has shown significant
accretion on the south side of the Murrells Inlet south
jetty.

Shoreline changes along Garden City Point/Garden City, as
shown in Figure-6.4-4, were gradual except along the reach
between stations 4615 through 4630.

To quantify the long term shoreline recession rate,
shoreline data from 1962 to 1983 were used to determine
local trends. A linear regression analysis was done for
each station using data in the last 21 years. The slopes
resulting from the regression analysis was used to assess
long term erosion rates. These erosion rates for each area
were tabulated in Table 6.4-1 and 6.4-2, and also depicted
in Figures 6.4-5 and 6.4-6.

Shoreline recession rates along Debidue Beach followed a
distinctive linear trend, ranging from 11.4 ft/year erosion
near North Inlet to 2.'4 ft/year-accretion near Pawleys
Inlet. Pawley's Island showed moderate erosion (about 1 to
2 ft/year) except the northern portion near Midway Inlet.
The Litchfield area experienced erosion rates of
approximately 1.5 to 2.5 feet/year, in contrast, a reach of
shoreline in Huntington Beach State Park (Station #4565 to
4570) showed high erosion rate, about 10-12 ft/year.
Accretion on the south side of Murrells Inlet resulted in
shoreline changes as high as 42 ft/year. Long term erosion
rate along Garden City and Garden City Point ranged from 1
to 5 ft/year.

-120-
0~~~ -..

0-
0: \464

o 0

b3 -

b- I ! , , I I I i I
no850 1875 1900 1925 1950 1975 20
YEAR

FIGURE 6.4-4
SHORELINE MOVEMENT AT MONITORING
STATIONS ALONG GARDEN CITY

Table 6.4-1. Long-term shoreline accretion/erosion rate

Erosion Rate*
Station (ft/yr)

Debidue Beach

4305 -11.4
4310 -11.4
4315 -9.8
4320 -11.2
4325 -6.5
4330 -4.0
4335 -4.0
4340 -3.4
4345 -2.4
4350 0
4355 -1.3
4360 0
4365 2.4
4370 1.6

Pawlev's Island

4405 -2.0
4410 -0.6
4416 -2.0
4420 -0.6
4425 -1.8
4430 -1.3
4435 -0.7
4440 -1.4
4445 -0.6
4450 -3.4
4450 -5.4
4460 -2.9

*Negative value indicates erosion

Table 6.4-2. Long-term shoreline accretion/erosion rate

Erosion Rate*
Station (ft/yr)

Garden City

4605 11.3
4610 -0.8
4615 -3.5
.4620 -3.1
4625 1.0
4630 2.7
4635 -2.3
4640 -5.1
4645 -2.9
4650 -2.1
4655 -1.0
4660 -1.9

Maanolia Beach

4510 -0.3
4515 -2. 0
4520 -2.4
4525 -1.6
4530 -1.6
4535 -1.5
4540 -1.5
4545 1.5
4550 1.3
4555 -0.3
4560 0.1
4565 -11.8
4570 -10.0
4575 -2.7
4580 12.3
4585 35.0
4590 42.1

*Negative value indicates erosion

i..~~~~~~~~~~~~~~~

4510

MILLS~~~~~~ 44 5,0440SS)______

4~ ~~~I I I 4 2 5 II II
f~~~1 -1 - 6 4 -2 0 6 8 10 1

16 ~ ~ ~ ~ EOSO CRTO

4406(s)~~~~~~~~~~~~~~~(t/er

FIGURE 6.~4-5(s

LONG-TER3M EOINRAEAOG EIU

BEAC ANDPAWLY4S SLAN

y~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 42.1

6~~~~ACH 4515(S)~~~~~~~~455S

i I I I I II 4 6 5 I
-12 -10 -846 -45- 0 1
ERSIN6CCETO
4630~~~~~~~~(fler

F~~~~~~~~~~~~IGR 64-6
LONG-TERM EROSION RATE AONG LITCHEIELD BEACH AN
HUNTINGTON BEACH STATE PARK~~461

0 0 0 0 ~~~~~~~~~~~~~~~~600000

6.5 EFFECTS OF SEA LEVEL RISE
As presented in Section 3.1, one important result of sea
level rise is the readjustment of the beach profile to
maintain an equilibrium condition, which in turn results in
a net offshore sediment transport. To evaluate the
shoreline movement in response to sea-level rise using the
equilibrium beach-profile concept, one must assume the beach
profile is relatively stable for a given mean water level
and local wave conditions. The average shoreline recession
(horizontal) rate in response to sea-level rise depends on
sediment grain size, wave climate and location along the
coast. An estimate of horizontal recession using a
representative profile can be calculated using the Bruun
method from the following empirical formula:

R=S
(h* + B)

where: R = horizontal recession

S = vertical water rise in sea-level

W, = active width of the equilibrium profile

h, = limiting depth associated with active
prof-ile

B = berm or dune height

The limiting depth (h,) associated with the active profile
was determined using a composite of four profiles along the
Garden City and Litchfield Beach shorelines. Using offshore
beach profile data at Stations 4525 and 4540 and the local
rise in sea-level, the horizontal rate of shoreline
recession is computed as

0.4667 ft
opt- 49 years (1118.ft)
R = = 0.3 ft/year
(18.0 ft + 17.5 ft)

-126-

=I ~ -* ~ ACTIVE PROFILE, C .

HFRH

DUNES BEACH
. .SEA LEVEL AFTER RISE
,.. L~~~T
INITIAL SEA LEVEL

INITIAL PROFILE

EQUILIBRIUM PROFILE
AFTER SEA-LEVEL RISE

DEPTH OF CLOSURE, h*

FIGURE 6.5-1
EQUILIBRIUM PROFILE RESPONSE TO SEA-
LEVEL RISE (BRUUN METHOD)

The shoreline recession caused by sea level rise is small
when compared with short- and long-term erosion caused by
-the combined result of seasonal variation and storm impacts.

6.6 -THE IDEAL PRESENT PROFILE
In accordance with the prescribed methodology outlined in
the contract for this study, an Ideal Present Profile
analysis was performed for several reaches in the study
area. This procedure was developed by Research Planning
Institute, Inc. (RPI), as "the most objective way of
determining where today's shoreline would 'ideally' be
located in the absence of structures" and as "a means of
averaging the high and low areas along the beach and
evening-out the distribution of sand." The steps in
determining the "ideal" present shoreline are presented
below (Eiser et al., 1986).

1. Select existing "unaltered" profiles within the
study area that have a minimal dune (no structure),
intertidal beach, and a typical unit width volume of
sand. Profiles around tidal inlets, piers, or other
littoral obstructions are not included.
2. Develop a statistical composite profile (ideal
present profile) from the selected profiles.
3. Compute the reference unit width volume of sand
between the +10' and -5' MSL contour.
4. Superimpose the ideal present profile (IPP) on'each
surveyed profile so that the beach volume under each is
the same (apply minor corrections around piers or near
inlets).
5. Determine the ideal shoreline position as the point
at which the ideal dune crest falls on each
surveyed profile.

This methodology has been applied in the shorefront

management plans for Myrtle Beach, prepared by RPI (Kana et
al., 1984) and for North Myrtle Beach (Eiser et al., 1986)
prepared by Coastal Science and Engineering, Inc. (CSE). In
both of these applications, the study area consisted of one
continuous shoreline of approximately 9 miles in length,
uninterrupted by major inlets and, with the exception of
piers, devoid of any shore-perpendicular structures which
might be littoral barriers. In contrast, the present study
area consists of 31 miles of disjunct shoreline interrupted
by several major inlets, municipal boundaries and man-made
littoral barriers along certain sections of beachfront. As
a result, the IPP methodology was applied separately to
several reaches of the study area shoreline. The
methodology as employed in this study is presented in the
following paragraphs that essentially paraphrase the
methodology presented in the North Myrtle Beach Shorefront
Management Plan performed by CSE (Eiser et al., 1986).

IPP Generation
Prior to the establishment of an IPP for the shoreline
reaches along the Georgetown County study area, steps were
taken to insure that the IPP methodology and procedure was
properly understood and executed. This was done by first
applying the IPP methodology to-a section of shoreline in
Horry County that extends from Singleton Swash to Withers
Swash. As mentioned above, previous investigators had
performed IPP analyses over 9 miles of shoreline both to the
'L north and to the south of this section. The results from
these studies were used as a comparison and verification of
the results obtained in this application. As these
shoreline reaches are adjacent to each other, it was
iL expected that the IPP's should be similar, as should be the
computed reference unit width volumes of sand. The steps
taken to verify the IPP methodology are discussed in the
L_. following paragraphs.

-129-
/*

Eleven stations along the shoreline reach between Singleton
Swash and Withers Swash were examined for suitability in-the
determination of the IPP. Profiles affected by inlets,
shore-protection structures, littoral barriers or any form
-of-beach-maintenance were rejected as not meeting the
criteria of an "unaltered" profile. Remaining profiles were
then examined to insure that the criteria of a well-
developed upper-beach face and dune, as well as a typical
unit-width volume of sand were met. Six profiles met all
these criteria and were therefore determined suitable for
the generation of the IPP over this shoreline reach. These
profiles were taken at survey stations 5425, 5435, 5440,
5445, 5450, and 5455 in Horry County.

In accordance with the prescribed procedure, the first step
in determining the IPP is to align all the profiles about a
common reference point, thereby resulting in a composite or
representative profile. Selection of this reference point
is determined as that point which results in the least
variation about the mean profile. In their Myrtle Beach
study (Kana et al., 1984), RPI determined that the procedure
resulting in the least variation about the mean was to
overlay all profiles such that the location of the +10'
contour became a point in common for each profile. The +10'
contour was likewise used as the common reference point for
IPP generation in the subsequent North Myrtle Beach study.
Observations made when shifting profiles for this and other
shorelinereaches in the present study indicate that the
+10' contour does not always represent the point resulting
in the least variation about the mean. For this particular
shoreline reach, this point was determined to be the +2.5'
f contour, corresponding closely to the approximate mean high
water line. Figure 6.6-1 shows the superposition of the six
profiles shifted about a common reference point of +2.5'.

Having established this composite profile, the elevation of

-130-

MYRTLE BEACH NORTH AREA

Ideal Present Profile (IPP)
Profile Data

owN
-:] "-

Z 200 -100 100 200 300 400 500
0a00 - 0

OkV

-200 -100 0 100 200 300 400 500

DISTANCE (ft)

FIGURE 6.6-1
IDEAL PRESENT PROFILE FOR MYRTLE BEACH
NORTH AREA

each individual shifted profile was determined at 10 foot
increments by means of linear interpolation between actual
profile data points. The IPP was then calculated by
averaging the elevation of the six profiles at each 10 foot
distance increment. The resulting IPP is presented in
Figure 6.6-1 by a solid heavy line.

The reference unit volume of sand was computed as the volume
between the +10' and -2.5' contours. The -2.5' contour,
rather than the-$' contour as used in prior studies, was
the approximate seaward limit of beach-profile surveys in
this study and therefore the limit of available data. A
volume of 47.1 yd3/ft was calculated between the +10' and
2.5' contours for the IPP along this reach of shoreline.
The IPP has a dune crest elevation of +12', a dune width of
40' and a beach width of 312' between the +10' and -2.5'
contours (NGVD datum).

Figure 6.6-2 presents a comparison between the IPP derived
in this study for the section of Horry County Shoreline
extending from Singleton Swash to White Point Swash and the
IPP derived by CSE and RPI for the shoreline reaches to the
north and south. Table 6.6-1 presents the reference unit
volumes and other pertinent dimensions for each calculated
IPP. Comparisons of the data presented in this table, as
well as the profiles presented in Figure 6.6-2 indicate that
profile characteristics, unit volumes, and other pertinent
dimensions of the IPP generated in this study are quite
comparable to those of the IPP presented in the previous CSE
and RPI studies. The fact that the plotted IPP profile
falls between adjacent IPP profiles, as do most dimensions
magnitudes and volumetric quantities, corresponds
appropriately to the fact that the shoreline reach in this
study falls between the reaches associated with the two
previous studies. The results of this comparison provide an
adequate level of confidence as to the proper understanding

-132-

Myrtle Beach North IPP (OAI & ATM)
- -- Myrtle Beach IPP (CSE)
- . ..North Myrtle Beach IPP (CSE)

Z -m ',
(90....1".

�n-~~~~~~~~~~~~~~~~~~~~~~~~~~. ::=---
L''o .....

0-
I mm~~~mm~~mmm~~~mmmm~~~m~mmmm~~~m~~mm~~mmmmmI I I I IgaImmImIImI I I II I I IImI I
-200 -100 0 100 200 300 40 0 500 600
DISTANCE (ft)

FIGURE 6.6-2
COMPARISON OF THE IDEAL PRESENT PROFILE COMPUTED FOR MYRTLE
BEACH NORTH, MYRTLE BEACH AND NORTH MYRTLE BEACH SHORELINE
AREAS

-as r ... -j ' . '

Table 6.6-1. Comparison of Profile Characteristics for the IPP Generated in This Study and
Those Generated in Previous Studies

Study Area Unit Volume* Dune Crest Elevation Dune Width Beach Width**

North Myrtle Beach (CSE) 51.7 cy/ft 13.5 ft. 22 ft. 333 ft.
Singleton-White Point Swash 47.1 cy/ft 12.0 ft. 40 ft. 312 ft.
Myrtle Beach (CSE) 44.4 cy/ft 13.0 ft. 50 ft. 263 ft.

*Volume calculated between +10' and -2.5' contours
**Distance between +10' and -2.5' contours

and execution of the IPP methodology. Accordingly, the IPP
methodology was applied to the shoreline reaches along the
Georgetown County study area. A summary of procedures and
results for each reach is presented below.

Springmaid Beach to Garden City
The approximately 11.l-mile stretch of beach beginning at
Springmaid Beach and extending south to Murrells Inlet is
one continuous shoreline, uninterrupted by inlets, featuring
a more than sufficient number of adequate profiles along its
entirety for the generation of an IPP. Accordingly, an IPP
was developed for this entire reach of shoreline to be used
in the analysis and depiction of an IPP for each of the
municipalities along this reach.

A total of 36 profiles were originally examined for
suitability in the determination of an IPP. Of the 36, 10
were determined to meet all relevant criteria for selection.
These 10 profiles were taken at stations 5235, 5240, 5245,
5250 and 5255 in South Myrtle Beach, stations 5115 and 5140
at Surfside Beach, and stations 4630, 4635 and 4640 at
Garden City Beach. The +5 ft MSL contour was determined as
the common reference point resulting in the least variation
about the mean when superimposing all 10 survey profiles.
Figure 6.6-3 depicts depicts the superposition of the 10
profiles shifted about a common reference point of +5 ft
MSL. The solid line in Figure 6.6-3 presents the IPP
generated by averaging the elevations of each of these
profiles at 10 ft increments. A reference unit volume of
35.7 yd3/ft was calculated between the +10 ft MSL and -2.5
ft MSL contours for the IPP along this shoreline reach. The
IPP has a dune crest elevation of +11.5 ft, a dune width of
44 ft and a beach width of 242 ft between the +10 ft and -
2.5 ft MSL contours.

-135-

MYRTLE BEACH SOUTH AREA

Ideal Present Profile (IPP)'
o_ --- Profile Data

5- d=
I1- .5.

0 -

-200 -100 0 100 200 300 400 500
DISTANCE (ft)

FIGURE 6.6-3
IPP FOR MYRTLE BEACH NORTH AREA

Litchfield-Huntinaton Beach
A total of 18 profiles taken at stations along this 7.1 mile
reach of shoreline between Murrells Inlet and Midway Inlet
were examined for suitability in the'generation of an IPP.
Of the 18 profiles, 7 were determined as meeting all
relevant criteria for selection. These 7 profiles were
taken at stations 4510, 4515, 4525, 4530, 4535, 4540 and
4545. The +Sft contour was determine as the common
reference point resulting in the least variation about the
mean when superimposing all 7 profiles. Figure 6.6-4 shows
the superposition of the 7 profiles shifted about the common
+5 ft reference point as well as the IPP (heavy solid line)
generated by averaging the elevations of each of these
profiels at 10 ft distance increments. A reference unit
volume of 44.7 yd3/ft was calculated between the +10 ft and
-2.5 ft contours for the IPP along this shoreline reach.
The IPP has a dune crest elevation of +16 ft, a dune width
of 63 ft and a beach widts of 289 ft between the +10 ft and
-2.5 ft contours.

Pawlev's Island
Beach profile stations along the Pawley's Island shoreline
were determined to be unsuitable for the generation of an
IPP. The extensive groin field and intermittent seawalls
extending from the south end of the island to the Pawley's
Island fishing pier preclude any stations from
consideration. Stations to the north of the pier are
subject to sporadic shoreline fluctuations resulting
primarily from sand storage and bypassing processes at
Midway Inlet as well as the effects of the terminal
"training" groin there. Most recently, these fluctuations
have taken the form of shoreline accretion at these
stations. As a result, the IPP methodology was deemed
inapplicable for the Pawley's Island shoreline. Alternate
procedures were formulated to provide for the assessment of
present and future shoreline conditions and these are

-137-

HUNTINGTON/LITCHFIELD

Ideal Prese'nt'Profile (IPP)
Profile Data

I 1

FIGUR,6,6 -
IP O HNIGTNLTCRILDAE

presented in Section 8.1.

Debidue Island
The IPP methodology was also deemed inapplicable for the
Debidue Island shoreline, again due to a lack of profile
stations suitable for the generation of an IPP. Of the 14
survey stations established along this shoreline, 6 were
excluded from consideration due to their proximity to inlets
and 3 were deleted since they were located along the
seawalled shoreline near the center of the island. The
remaining 5 profiles exhibited highly variable shape and
slope characteristics, making it impossible to achieve a
composite profile with any acceptable degree of deviation
about the mean so that it could be considered as
representative of the natural, unarmored Debidue Island
shoreline. In addition, the rapid and highly variable
shoreline translations indicated by historical shoreline
change maps support the conclusion that the IPP methodology
was not appropriate. Alternate procedures were formulated
to provide for the assessment of present and future
shoreline conditions and these are presented in Section 8.1.

6.7 IPP COMPARISON WITH EACH STATION
In accordance with the prescribed procedure, the IPP
compiled for each shoreline reach was superimposed on the
April 1986 profile at each station along that reach. The
IPP was then shifted horizontally so that the volumes under
both profiles were equal. The volume of sand under each
profile was determined by means of an Interactive Survey
Reduction Program (ISRP), a computer software developed by
the USACE Coastal Engineering Research Center. Wherever,
possible, volumes were calculated between the +10' and -2.5'
contours, however, in a few instances the existence of
seawalls, lack of sufficient'dune heights, extensive survey
data or other profile anomalies necessitated the selection
of alternative contours for volumetric computations.

-139-

Accordingly, the IPP was superimposed over the actual
profile and horizontally shifted to equate the volumes
between these contours. Table 6.7-1 presents the unit
volumes under present profiles (April 1986), the variation
between this volume and the IPP unit volume and the position
of the IPP dune crest relative to the actual dune crest.
Once superimposed correctly, the actual and shifted IPP
profiles were plotted together. Figure 6.7-1 shows two
-example plots showing the superposition of the IPP on the
profiles at Stations 4555 and 4625, respectively.

Station 4555, located at the northernmost residence in North
Litchfield Beach, is an extreme example of IPP superposition
on a severely eroded shoreline. In this case the beach-dune
system has undergone severe erosion subsequent to the
construction of the jetties at Murrell's Inlet. The
elevation of the beachlforeshore has been lowered and the
dune severely scarped. Accordingly, the beach system in
front of the scarped dune has a lower unit volume than the
IPP. As a result, when superimposing the IPP on this
profile, it must be shifted well landward in order to equate
the beach volumes under both profiles. This results in the
IPP dune crest being located well landward of the existing
dune crest. This condition is characteristic of the
shoreline extending approximately 2,000' north and south
from this station, as well as other excessively eroded
sections of the Georgetown County shoreline.

Station 4625 is located along a residential section of
Garden City Beach. In this case, the unit volume of sand
for the actual profile is greater than that of the IPP. In
order to equate the volumes under the profiles, the IPP must
therefore be shifted seaward. This results in the IPP dune
crest being located seaward of the existing dune crest. In
presenting the IPP methodology, its originators infer that
"in cases where localized erosion of a natural dune has

-140-

Table 6.7-1. Unit Sand Volumes, Variation with IPP Unit
Volume and Position of IPP Dune Crest Relative
to Actual Dune Crest When Equating Volumes
Under the Profiles Along the Georgetown County
Shoreline.

IPP Dune
Variation Crest Position 0
Unit Volume with IPP Relative to
Station (cy/ft) Volume (cv/vr) Actual Dune Crest

Garden City

4660 36.40 0.70 Landward .
4655 34.43 -1.27 Landward
4645 30.49 -5.21 Landward
4640 34.86 -0.84 Landward
4635 43.67 7.97 Seaward
4630 46.37 10.67 Seaward
4625 48.57 12.87 Seaward 0
4620 33.63 -2.07 Landward
4615 45.87 10.17 Seaward
4610 48.53 12.83 Seaward
4605 45.27 9.57 Seaward

Huntinaton/Litchfield

4590 N/A .
4585 N/A .
4580 N/A -- --
4575 N/A . . .
4570* 49.57 4.87 Landward
4565 43.33 - -1.37 Landward
4560 50.15 5.45 Landward
4555 42.96 -1.74 Landward
4550 45.93 1.23 Landward
4545 42.90 -1.80 Landward
4540 41.77 -2.93 Landward
4535 47.84 3.14 -Landward
4530 45.70 1.00 Landward
4525 43.24 -1.46 Seaward
4520 42.85 -1.85 Seaward
4515 38.31 -6.39 Landward
4510 44.73 -0.37 Seaward
4505 N/A .

*Limit of applicability on Litchfield Beach
0

20 Profile Line 555

*~ I - - I , ----19 JUN 85 0
- 15 . , \

i0-

- I~~~~~~~~~~~~~~~~~~~~-
r

LLJ

-i50 -100 -50 0 50 100 150 200 250 300 350 400

Distance. FT

20 - Profile Line 625
W-jj~,lE~n8 1~220

--s1JUN86 0

0
" I t:~~~~~t

so too 150 200 250 300 350 400 450I 500 550 600

i I Oirtenel~~~~~~~Dstnc. FT

OL ~ FIGURE 6.7-1
COMPARISON BETWEEN IPP AND
A) PROFILE 4555 AND
B) PROFILE 4625
(i~~~~~

accelerated ... this methodology makes allowance for
artificial loss and places the ideal dune crest somewhat0
seaward of its present position" (CSE, 1986). While it is
not readily apparent how this allowance is made based upon
equating volumes (particularly in view of the preceding
example), it is obvious that localized erosion is not a
factor in this case. The location of the IPP dune crest
seaward of the-'actual dune crest is a result of excess sand
volume rather than a sand deficit. It is doubtful, in this
case, that the IPP dune crest represents the location of the
actual dune crest in the absence of structures along the
shoreline. In the application of the IPP in this study,, all
instances where the IPP dune crest fell seaward of the
actual dune crest were attributable to excess unit volumes
rather than sand deficits.

The IPP should not be considered to be applicable along the
area north of profile station 4570 and south of Murrells
Inlet. The latter is in a dynamic zone of littoral
processes due to the stabilization of the inlet. As with
other similar areas adjacent to tidal inlets, it has been
classified as an "Inlet Impact".

-143-

7.0 INLET ANALYSIS
Tidal inlets assume a major role in both the long and the
short-term fluctuations of shorelines within the study area.
For example, longshore sediment transport, also referred to-
as littoral drift, is continually directed toward an inlet-
channel or gorge. Tidal shoals are formed as the result of
the interruption of this longshore transport by strong tidal
currents near the inlets. Flood tidal currents transport
and deposit these sediments within the lagoon or embayment,
whereas ebb tidal currents transport the sediments to the
ocean shoals. A stable inlet has balanced the deposition of
littoral drift with the scouring effects of tidal currents.
Typically the ebb tidal shoal, seaward of the inlet, builds
and migrates in the predominating downdrift direction. This
is the basic mechanism by which the inlet naturally migrates
in the direction of the predominating longshore currents.
Correspondingly, the inlet may likewise migrate, in some
cases breakthrough at a new location on either the updrift
or downdrift shoreline as a result of low frequency storm
events.

Inlets, swashes, channels, etc. are examples of natural non-
structural barriers to littoral.processes, whereas groins
and jetties are man-made structural barriers. Significant
erosion problems can result when a barrier effectively
blocks a large portion of the longshore sediment transport
thereby resulting in sand starvation at some locations.
Significant sediment trapping potential exists at the
entrance of Murrells Inlet and North Inlet and, to a lesser
degree, Midway Inlet and Pawley's Inlet. Inlets are
continuously affected by reversals in longshore transport
and wave refraction around the ebb tidal shoals located
seaward of the entrance channel. It is those shorelines in
the immediate vacinity of inlets that typically experience
the greatest variation in erosion rates and fluctuations of
the beach and dune system. The area of influence along a

-144-

coast affected by a tidal inlet is directly related to the
inlet geometry and tidal prism which is an expression of the
quantity of water which moves through the inlet and which in
turn is responsible for sediment transport.

The stabilization of any natural inlet by dredging or jetty
construction would dramatically modify the hydraulic regime,
and therefore upsets the long-term dynamic equilibrium
previously in existence. The consequence is the initiation
of a new balance between hydraulic and sedimentary forces
which causes a reconfiguration of tidal shoal formations and
adjacent shorelines.

The shorelines adjacent to most natural inlets, formed of
unconsolidated sand, are dynamic landforms easily subjected
to the effects of storm surge flooding. During a hurricane,
the surge and wave set-up along the open coastline are the
primary driving mechanism of flow patterns into the bay
areas. Extraordinarily high tidal current, through inlets
during hurricane storm tides characteristically both erode
and flood adjacent channel banks as the increased flow
converges in the vicinity of the inlet.

These highly dynamic inlet areas require adequate coastal
planning and building criteria for protection of property
adjacent to inlets from the hazards of hurricane induced
flooding. Channel migration, often associated with
unstabilized inlets, may have severe effects on the
stability of adjacent inlet channel banks during these
severe storm events.

Murrells Inlet
An analysis of historical shoreline movements for Murrells
Inlet was based on aerial photographs and NOS-COE shoreline
movement maps (see Figure 7-1). For the period between 1872
and 1934 the long-term shoreline trends indicate that north

-145-

| ~~~~~~~~MURRELLS INLET

0 .5 ~~~~~~~LENGEND
(0:: : X ~~~~~~~~~~~~MILES -1983 (NOS AERIAL PHOTO)
L ~~~~~~~~SCALE FIKILOMETERS -1934 (FIELD SURVEY)
0 .5 1872 (FIELD SURVEY)
I_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~/'

I~~j l FIGURE 7-1
|- ~~HISTORICAL SHORELINE POSITIONS NEAR
MURRELLS INLET (18$72, 1934,', 1983)
r-~~~~~~~~~~~~~~rI

,...--~ ~ ~ , 1.j.,/.
.~~~' '!.
; ~~/
.1, /

i_~~ ~ ~~~~~~~ I~ t

I ~ ~ ~ ~

* ~~~~~~~~~~~~~~~MURRELLS INLET

.5 LENGEND
: - ~ ?. . ~~~~~~~~~MILES -1983 (NOS AERIAL PHOTO)
~~~~~~SAE.KILOETRS -'I 1934 (FIELD SURVEY)
0' .5 ....--1872 (FIELD SURVEY)

FIGURE 7-1
f-. ~ HISTORICAL SHORELINE POSITIONS NEAR
L ~~~MURRELLS INLET (1872, 1934, 1983)

spit migrated northwards approximately 6500 feet.
Subsequent long-term changes show this shoreline to have
consistently migrated south from 1934 to 1983. The same
shoreline moved south 2000 ft from 1934 to 1963 and 600 ft
from 1963 to 1970. During this same period the narrow spit
at the north end of Huntington Beach gradually receded until9
1970 (Figure 7-2).. A Federal navigation project to improve
Murrells Inlet'for navigation purposes was commissioned and
constructed between 1977 to 1979. Stabilization features
included two jetties, a navigation channel, a weir section
in the north jetty, a deposition basin and designated beach
nourishment areas on the adjacent shores. Because the
predominant direction of littoral drift was estimated to be
southerly, the COE designed the north jetty with a 1315 foot
section at a lower relative elevation (+2.2 ft MLW) to allow
southerly sediment transport into the deposition basin
(Figure 3.11-1).

Since 1979 sediment has accreted to the beginning of the
weir section and the remainder of the near shore area has
been relatively stable. Sand moving across the weir section
is depositing along the edge of the deposition basin and
onto a sand spit which has migrated into the navigation
channel. 'An extensive ebb tidal shoal is forming at the end
of the north jetty which appears to result from sediment
moving north around the south jetty, sand transported from
the depositional spit and sand transported by strong
offshore currents on the north side of the the north jetty.
Characteristically, the location, shape and size of an ebb
tidal shoal undergoes slow but substantial changes; the
modifications of waves by the ebb tidal shoal can cause
substantial localized effects on the adjacent shorelines
resulting in long-term erosion and accretion changes.

The south bank of Murrells Inlet, characterized by
substantial depositional dunes with healthy vegetation

-147-

0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/ sl~ ~ ~ ~ ~~~~~~~4
/~ /',

-> MURRELLS INLET

0 .5 LENGEND
' E MILES 1983 (NOS AERIAL PHOTO)
-- 1969-70(FIELD S URVEY)
SCALE KILOMETERS
0 .5 ---- 1962-63 (FIELD SURVEY)

FIGURE 7-2
HISTORICAL SHORELINE POSITIONS NEAR
MURRELLS INLET (1962,1969, 1983)

inland from the north jetty, should be relatively stable
with regard to future shoreline positions. Evidence of a
washover across the dunes immediately north of the weir
jetty was observed during a recent field investigation.
Significant winter storm tides often result in flooding of
shorelines adjacent to inlets. The shoreline areas in
relatively close proximity to this inlet should be regarded
as dynamic land forms and protected by judicious coastal
planning and management.

Beach profiles located 2.5 to 3.5 miles south from the
Murrells Inlet jetties have shown substantial erosion
whereas significant accretion has occurred for the length of
shoreline 1.5 miles south and adjacent to the south jetty.
In addition, an erosional "hot spot" can be detected
approximately 3 miles north of Murrells Inlet which could be
related to shoreline adjustment caused by inlet
stabilization. The relationship between the jetties
construction and the erosion of the adjacent shorelines at
Murrells Inlet is a typical example of the inlet jetty
effects, and have been experienced at numerous similar
locations such as the entrance to Charleston Harbor, SC and
St. Marys entrance, Florida.

As expected, the stabilization of Murrells Inlet is
resulting in the inlet being transformed into a littoral
trap. The predicted net result is the eventual collapse of
the pre-project ebb tidal shoal and the eventual creation of
a new shoal seaward of the approximately 3400 ft long
jetties. The modification of the bathymetry north and south
of the inlet will be expected to correlate to eventual
shoreline translations. The predicted short-term effects
will continue, especially near north and south of the inlet,
as detected by this study and the ongoing COE monitoring
program. Correspondingly, any long term net losses of
sediment to the reconfigured Murrells Inlet shoal system

-149-

will result in additiobal erosional pressures along the
adjacent barrier islands to the south. The effects of inlet
jetties will propagate to a greater distance than those
presently determined by surveys.

* ~~~Midway Inlet
Long-term trends indicate Midway inlet has migrated
southward for the last 57 years (Figure 7-3). From an
analysis of inlet movement, the north bank moved northward
600 feet between 1872 and 1926 (Figure 7-4). Subsequently
the north bank accreted from 1926 to the present, indicating
that the predominant direction of littoral drift is
southerly. Historical long-term shoreline changes for the
* ~~~southern spit of Litchfield Beach and the northern end of
Pawley's Island are summarized in Table 7-1.

Deposition of southerly littoral drift has resulted in the
formation of a substantial shoal migrating from the north
bank of Litchfield Beach. There is therefore a reasonable
expectation for further lengthening, as noted by the
previous shoreline growth (1963-1983), and correspondingly
substantial accretion along the northern channel bank.
Littoral drift material is being deposited at the mouth of
the channel during ebS tide, and the deposition is carried
into the inlet and re-deposited onto the flood tidal shoal
* ~~~during flood tide. This accretional flood tidal shoal,
exposed at low tide, constricts the flow as the main channel
separates and branches-along the northern and southern inlet
banks.

Midway Inlet channel has migrated south and is presently
located along the south bank adjacent to Pawley's Island.
The ebb tidal shoal extending southward from Litchfield
Beach has kept the main channel against the south bank of
the inlet causing moderate erosion. To stabilize this
shoreline, the southern bank was armored with a timber

-150-

MIDWAY INLET
,#/'~~~~~~~1

0 .5 LENGEND
, � MILES 1983 (NOS AERIAL PHOTO)
SCALE | I KILOMETERS __ 1962-63 (FIELD SURVEY)
0 .5 .--- 1934 (FIELD SURVEY)

FIGURE 7-3
HISTORICAL SHORELINE POSITIONS NEAR
MIDWAY INLET (1934, 1962, 1983)

/,|�2 ;' MIDWAY INLET
,f.~I
i'~~~~.,

00 .5 LENGEND
- MILES 1983 (NOS AERIAL PHOTO)
_~~~~' ., _

SCALE/I' - - ' 1926 (FIELD SURVEY)
SCALE~~~ KILOMETERS
0 .5 ....~~~---1872 (FIELD SURVEY)

FIGURE 7-4
HISTORICAL SHORELINE POSITIONS NEAR
MIDWAY INLET (1872, 1926, 1983)

Table 7.1 Historical Inlet Movement

Dates South Bank North Bank

Midwav Inlet

1872-1926 1100' N 600' N

1926-1934 2000' S 800' S

1934-1963 200' S 1000' S

1963-1983 400' S 1100' S

Pawlev's Inlet

1872-1926 3100' N 1450' N

1926-1934 -800' S 2800' S

1934-1963 2100' S 1100' S

1963-1983 1900' N 1900' N

North Inlet

1872-1926 5400' S 2100' S

1926-1934 340' N 1800' S

1934-1962. 650'-S 6700' S

1962-1983 1100' N 130' S

"training groin" extending seaward 685 feet, as well as a
combination of rubble and concrete sections extending inland
along the shoreline.

Although Midway Inlet has been stabilized along the southern
bank, continual deposition of sediment creates a
navigational hazard and unstable shorelines in the vicinity
of this inlet.' Periodic dredging, with spoil placed along
the northern tip of Pawley's Island would alleviate some of
the shoaling problems and stabilize the north channel bank.

Pawlev's Inlet
Pawley's Inlet is located between the southern tip of
Pawley's Island and the north end of Debidue Beach. This
historically dynamic inlet migrated north prior to 1926,
south between 1926 and 1963 and is presently migrating to
the north (Figure 7-5 and 7-6). Characterized by'a long
narrow spit (150-200 ft wide), the south and of Pawley's
Island is developed by single-family residences fronting the
open coast. This segment of beach is structurally armored
by a groin field. Comparative profile surveys along this
shoreline indicate accretion in the immediate vicinity of
the inlet which may have temporarily stabilized the
shoreline' in the short-term.'

From an analysis of long-term shoreline positions, the north
end of Debidue Island has accreted along a shoreline segment
extending approximately 3500 feet to the south. Longshore
sediment transport appears to be relatively balanced along
the beaches adjacent to Pawley's Inlet.

In recent years, an effort was made to stabilize the north
bank of the inlet using approximately 250 feet of rip-rap
placed along the southern tip of Pawley's Island.
Additionally, adjacent property owners on Pawley's Spit have
built two segments of seawall in an attempt to stabilize and

-154-

.' PA WLEY'S INLET
/,
* I~~~~~I

./.;
/:1~~~~~~~~~~I

*~~~~~~~~~~~~

0' .5 ---- 1872 (FIELD SURVEY)
{ :/~~~~

PAWLEY'S INLETE (1872, 1926, 1983)
*~~~~PWE' INE I17, 96 93

/a; ! PA WLEY'S INLET

ISa

o .5 LENGEND
MILES 1983 (NOS AERIAL PHOTO)
SCALE ,I KILOMETERS -- 1962-63 (FIELD SURVEY)
SAE-KOM EER ---- 1934 (FIELD SURVEY)

FIGURE 7-6
HISTORICAL SHORELINE POSITIONS NEAR
PAWLEY'S INLET (1934, 1962, 1983)

protect individual homes. During seasonal storm tides this
irregularity in seawall construction would be expected to
potentially destabilize the adjacent non-armored properties
along the terminal points of the seawall.

The future stabilization of Pawley's Inlet and protection of
buildings along the spit during moderate (50-year) or
extreme storm events (100-year) is doubtful. Inlet
stabilization for the developments along the adjacent low-
lying shorelines is not warranted at this time. Education
of homeowners to the hazards of inhabiting this area during
severe storms is well-advised. Continued periodic surveys
to document shoreline fluctuations at Midway Inlet and the
adjacent shoreline should provide the necessary short-term
data to assess local perturbations associated with the inlet
and temporal variations in the directions of littoral drift.

North Inlet
Documented shoreline movement at North Inlet was based on
field surveys and aerial photography from 1872 to 1983
(obtained from the NOS-CERC Shoreline Movement Maps). North
Inlet experienced a relatively high degree of variability
between 1872 and 1926 (Figure 7-7). Extreme shoreline
fluctuations associated with unstabilized inlets, such as
North Inlet, can occur through slow trends or rapidly during
a storm event. During the period of 1872 to 1926, a large
number of hurricanes crossed the South Carolina shoreline in
close proximity to North Inlet (Figure 3.3-2 and Figure 3.3-
3). Accordingly, the nearly 5400 ft southerly migration of
this inlet's south bank may have resulted from a break
through due to high storm surge, wave action and local
topography.

Long-term shoreline trends indicate the north bank of North
Inlet has consistently migrated southwards 6500 ft since
1872 (Figure 7-8). In contrast, the south bank receded

-157-

~ \,NORTHINLET

I 0 .5 ~ ~ LENGEND
*MILES 1983 (NOS AERIAL PHOTO)
SCALE I I KILOMETERS -- 1962*3 (FIELD SURVEY)
SCL K IOETR ---- 1934 (FIELD SURVEY)

FIGURE, 7-7
HISTORICAL SHORELINE POSITIONS NEAR
NORTH INLET (1934, 1962, 1983)

y A ,NORTH INLET

O~ ~ ~ ~~~ ~ .5 LENGEND

@ : ~~~~~~MILES 1983 (NO$ AERIAL PHOTO)
SCALE ; I KILOMETERS -- ~1926 (FIELD SURVEY)
0 .5 -- 1872 (FIELD SURVEY)

FIGURE 7-9
HISTORICAL SHORELINE POSITIONS NEAR
NORTH INLET (1872, 1926, 1983)
c,~ /'

* / ,--~~--.~S-~' NOR.H LNGETD

I~~~~~~~~~~~~~~~~~~~ 192 (FEDSUVY
~~~~~~~~SCL Il I KILMTR

NORTH INLET (1872, 1 52LENGEN3

approximately 5400 ft between 1872 and 1926, migrated north
from 1926 to 1934, receded between 1934 and 1962 and has
recently moved to the north about 1100 ft (1962 to 1983).
Since 1934, deposition of the southern littoral drift has
resulted in the formation of an extensive recurved sand spit
characterized by a series of beach ridges.

Tidal inlets along the South Carolina coastline can be
classified according to the magnitude of the tidal range and
inlet dynamic features as 1) microtidal and 2) mesotidal. A
spring tidal range from 0 to 2 meters defines a microtidal
coast where an increased tidal range (2 to 4 meters) is
characterized as mesotidal (Davies, 1964). The influence of
both spring tidal range (1.8 meters) and a relatively low
annual wave-energy environment at North Inlet has led to a
mesotidal classification (Nummedal and Humphries, 197). In
a 1975-76 USCOE-CERC study, North Inlet was selected to
evaluate the hydraulics and dynamics of a natural tidal
inlet. Over a two-year period, intensive field
investigations were undertaken to collect numerous physical
and morphological data, including continuous water surface
elevations, tidal channel hydrography, littoral processes,
and bathymetric profiles.

Based on vertical aerial photos, historical shoreline data
and field survey data, an intensive map of the intertidal
environment at North Inlet was developed. Analysis of
bathymetric changes since 1964 suggest the following: 1)
the main ebb channel has deepened and is oriented straight
toward the southeast; 2) three small shoals have developed
adjacent to the main ebb channel, one terminal shoal and one
on either side of the main ebb channel. The northern and
southern channel shoals are being controlled by the tidal
currents and wave swash. The overall planeform of the ebb
tidal delta may indicate a net southerly littoral drift.

-160-

Beach profile data were surveyed for 6 transects along
Debidue Island and 5 transects along North Island on a
quarterly basis from July 1974 to May 1976 (Figure 7-9).
Based on these profile data, the average trends in beach
erosion and deposition at Debidue Beach and North Island
were plotted for the period of July 1975 to May 1976 (Figure
7-10). These data indicate an annual change in beach-face
morphology along Debidue Spit, controlled by a seasonal
change in mean sea level (MSL) as opposed to the expected
dependence on storm cycles.

A longshore wave energy flux factor was computed based on
wave height and direction, and gross longshore sediment
transport was estimated at 800,000 cubic meters during both
years of observation. The net sediment transport for 1974
to 1975 and 1975 to 1976 was 87,000 and 390,000 cubic
meters, respectively. Finally, results of beach profile
data and intertidal shoal mapping data strongly suggests an
"out-of-phase" relationship between beach erosion and
channel scour (Figure 7-10) during mid-fall and the spring
of 1976. It is evident that there is a sediment exchange
and a direct relationship between variations of inlet
channel cross-section and the profile volume changes of the
adjacent beaches exists.

-161-

., b- .

North

\vC�~~ � km
00

FIGURE 7-9
BEACH AND OFFSHORE PROFILE LOCATIONS
(COE, 1978)

Summer Fall Winter Spring
BARRIER BEACHES

1000
, ooo-

Z '; o
500

TIDAL CREEKS
300-
U-* o 20

� I

-200

COMPARISON OF AVERAGE TRENDS IN BEACH
--200

JULY AUG. SEPT. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY
1975 1976

COMPARISON OF AVERAGE TRENDS IN BEACH
EROSION AND DEPOSITION AT DEBIDUE
BEACH AND NORTH ISLAND AND CHANNEL
CROSS-SECTIONS (COE, 1978) _

8.0 FUTUPE SHORELINE PREDICTION
8.1 IDEAL PRESENT SHORELINE
The ideal present profiles (IPP) of Garden City and
Huntington/ Litchfield Beach were developed in Section 6.6
Once the IPP for each shoreline reach was overlaid on each
of the April 1986 profiles such that the volumes under the
two were equal, the location of the ideal present dune crest
relative to each station was calculated. In accordance with
the prescribed methodology the ideal present dune crest was
determined as either the peak of the IPP dune or the
midpoint of the IPP dune crest, whichever was applicable
along each reach. The location of the ideal present dune
crest relative to each station was then plotted on the base
maps presented as Appendix D. The points representing
these locations were connected by a line on the base maps
that, in accordance with the prescribed methodology
represents the ideal present shoreline (IPS).

The ideal present shoreline is subject to some degree of
interpretation, primarily in areas where the ideal present
dune crest falls seaward of the existing dune crest. As
discussed in the application of the IPP methodology, this
situation occurred due to an excess of sand in the profile
unit volume rather than as an allowance for artificial loss
due to localized erosion. Accordingly, shifting the ideal
present dune crest seaward of the existing seawardmost dune
line in order to account for excess sand volume was
considered to be a miscomputation inherent in the IPP
methodology. In such instances, the point representing the
IPS defaulted landward to the existing dune crest.
Similarly, in other cases the line representing the IPS
tended to bulge seaward at stations in the immediate
vicinity of piers, reflecting their effect as partial
sediment traps. In accordance with the prescribed
methodology, the IPS was maintained as a straight line in
the vicinity of piers or similar structures.

-164-

0 ~~~Contrary to prior applications of the IPS, no concessions
were made in this study in the event that the IPS fell
"sharply" landward or on top of existing structures due to
sand deficits in the profile unit volumes. Prior
investigators have incorporated hypothetical assumptions
that such sand deficits may be made up by artificial means,
primarily beach'nourishment, thereby justifying a seaward
shift of the IPS. While beach nourishment projects are
considered as the preferred means of providing a
recreational beach and protecting existing upland
development, they are not designed to encourage or
accommodate seaward encroachment of building construction.
* ~~~Therefore, incorporation of such assumptions in the
establishment of any line that may be used to determine
building setbacks of other coastal development restrictions
is unjustified, potentially harmful to the beach-dune system
as well as. coastal development permitted under this premise
and inconsistent with accepted coastal management practice.
Accordingly artificial shoreline modifications such as beach
nourishment will not be considered as justification for
less-stringent building codes and/or setbacks within this
study.

As discussed in Section 6.6, the IPP methodology can not be
successfully applied for Pawley's Island and Debidue Beach
because of the predominate groin and seawall structures and
the inlet effects. Within these areas, the existing dune
crest is used as the reference point to derived future
shoreline positions. Where seawall or rip-rap exists at the
0 ~~~oceanfront, these shorefront structures are used as the

reference baseline.

Table 8.1-1 presents the location of IPS in relation to the
0 ~~~survey monuments at each monitoring station along
Huntington/Litchfield Beach and Garden City. Table 8.1-2

-165-

Table 8.1-1. Ideal Present Dune Crest Locationalong
Huntington/Litchfield Beach and Garden City

Station IPS Location (ft)*

Huntinaton/Litchfield

4505 -102
4510 -3
4515 -8
4520 -17
4525 4
4530 42
4535 7
4540 14
4545 9
4550 -29
4555 -4
4560 -24
4565 0
4570 **
4575 **
4580 **
4585 **
4590 **

Garden City

4605 300
4610 242
4615 195
4620 143
4625 156
4630 277
4635 263
4640 191
4645 138
4655 124
4660 97
t..
!f ~ *Negative value indicates landward of the monument.
L **Station is within inlet impact zone.

Table 8.1-2. Present Dune Line Location along Pawley's
Island and Debidue Beach

Station Dune Line Location (ft)*

Debidue Beach

4305., **
4310 **
4315 **
4320 26
4325 0
4330 0
4335 0
4340 0
4345 0
4350 17
4355 28
4360 11
4365 0
4370 0

Pawlev's Island

4405 104
4410 104
4416 136
4420 291
4425 194
4430 274
4435 650
4440 278
4445 270
4450 236
4455 247
4460 455

*Dune line location is measured seaward from the survey
monument.
**Station is within inlet impact zone.

shows the location of the present dune crest or seawall
structures. These ideal present dune lines are shown in
Appendix D.

8.2 PREDICTED 25 AND 50 YEAR SHORELINES
It has been established in this study and several previous
investigations that, with isolated exceptions, the shoreline
along the study'area is undergoing a long-term erosional
trend which spatially varies in magnitude. This erosion is
attributable to several factors including sea-level rise,.
localized littoral deficits, storms and, to a minor extent,
armoring of the shoreline. Whether expressed in volumetric
or linear terms, the net result of this long-term erosion is
a recession of the shoreline, a reduction of the dry beach
as both a recreational amenity and a valuable storm buffer,
and an ever increasing encroachment on upland development.
Predictions of long-term shoreline recession rates are
essential in the determination of setback lines, building
codes and erosion control permitting procedures; all of
which are elements of a prudent shorefront management plan.

Estimations of long-term shoreline recession rates are
projected based on extrapolation of observed historical
rates into the future.- Accordiingly, the accuracy of and
confidence level associated with these predictions is
directly related to the quality and quantity of information
comprising the historical database. The practice of
conducting beach profile surveys for the specific purpose of
V ~~quantifying shoreline change rates is relatively new along
the South Carolina coast. As a result, the existing
database is somewhat limited for the study area under
consideration. Shoreline change maps have been compiled
from other sources of shoreline information such as boat
sheets, navigation charts, aerial photographs and boundary
surveys. These maps while difficult to apply on a site-
specific basis, provide a large scale indication of the

-168-

rates of shoreline change over a longer period of time than
0 ~~~any existing profile data for the study area. Application - --.
of rates obtained from these maps preclude the large degree
of uncertainty that is often associated with the variation
in short-term erosion in rates observed at individual
profiles. As a result, the maps are quite appropriate in
determining an average long-term erosion rate over a
particular shoreline reach.

Once average long-term erosion rates were determined for
each individual shoreline reach along the study area, they
were then applied in the determination of future predicted
shorelines. Specifically, the rates were applied to either
0 ~~~the IPS or the existing dune line, whichever applicable,
over a period of 25 and 50 years thereby resulting in the
predicted 25 and 50-year shorelines. The setback distance
associated with these lines was consistent over each
shoreline reach with the exception of areas in the vicinity
of inlets. As previously discussed, shorelines in the
immediate vicinity of inlets are subject to significant
translation in the event of storms, as well as, long-term
natural inlet migration. Accordingly these areas are
designated as inlet Impact zones and are assigned an extra
buffer during the prediction'of-future shoreline locations.

* ~~~Predictions of potential short-term shoreline recession
along the open coast resulting from hurricanes and long-term
recession resulting from sea-level rise have also been
presented in this study. The former are intended to
indicate the immediate area of influence associated with
erosion resulting from severe storm events while the latter
is extracted as one component of the predicted overall long-
term recession rates. In determining predicted future
erosion rates for a specific shoreline reach, all available
data for that reach were compiled and subjectively evaluated
for accuracy and applicability. In order to maintain

-169-

continuity over each shoreline reach, an average rate was
obtained from individual profiles and applied to that reach.
Correspondingly, in the prediction of storm-related erosion,
the relevant distances were derived from average or
representative profiles and were directly applied to each
reach. A discussion of the available database and
methodology utilized in predicting future erosion rates and
distances over'each shoreline reach is presented in the
following paragraphs.

Garden City
Shoreline movement data for this reach of shoreline
consisted of: 1) beach profiles taken at various locations
in 1958, 1979, 1980, 1981, 1982, 1984 and 1986, and 2)
long-term linear MHWL changes obtained from the NOS-CERC
Shoreline Movement Maps for the period 1934-1983. In
addition, the IPP profile generated for this reach was used
in the calculation of erosion associated with the occurrence
of the 25 and 50 year storm.

Previous studies by Kana et. al. have applied linear erosion
rates, derived from long-term volumetric erosion rates
calculated at individual beach profiles. As discussed
previously the IPP methodology has been deemed inapplicable
along several sections of the study area. Furthermore, the
limited number of 1958 beach profiles and the extreme bias
in beach volumes at profiles influenced by inlet and swash
migration, as well as beach nourishment, make the
applicability of this profile data questionable in the
determination of long-term annual volumetric change rates.

Based on these two factors it was decided that a more
representative prediction of future shoreline positions
would result from the application of average linear erosion
rates, determined from the shoreline movement maps, to the
individual profiles along the shoreline reach. Accordingly,

-170-

erosion rates were determined at each station along the
reach and averaged to obtain a uniform average rate.
Stations that were armored or considered subject to inlet or
swash migration were not included in calculating the average-
rate. The resulting average long-term erosion rate was 1.5
ft/year which corresponds to a distance of 37.5 and 75 feet
respectively over-25 and 50 years. These distances were
then applied to the existing dune or structure line,
whichever was most seaward, along each profile in order to
represent the predicted 25 and 50 year shorelines.

Litchfield-Huntinaton Beach
Shoreline movement data for this reach of shoreline
extending from Murrells Inlet to Midway Inlet consisted of:
1) beach profiles taken at various locations in 1979, 1980,
1982 and 1986, and 2) long-term linear MHWL changes
obtained from the NOS-CERC Shoreline Movement Maps for thel
period 1962-1983. In addition, the IPP profile generated
for this reach was used in the calculation of erosion
associated with the occurrence of the 25 and 50 year storm.

The lack of beach profile data prior to 1979 precluded the
determination of an average linear erosion rate based on
long-term volumetric changes at individual profiles.
Accordingly, this precluded the application of a linear
erosion rate, derived from volumetric changes, to the IPS
for the prediction of future shoreline positions as
prescribed in the IPP methodology. In addition, the
majority of the beach profile data in this area since 1979
were collected for the purpose of monitoring shoreline
changes caused by the Murrells Inlet Navigation Project in
effect "disqualifies" much of it from being representative
of natural shoreline migration trends. As previously
discussed, the shoreline extending approximately 2.5 miles
south of Murrells Inlet has undergone accelerated rates of
erosion and accretion due to shoreline reorientation

-171-

subsequent to stabilization of the inlet. These planeform
changes, which may be expected to continue, result in an
unstable shoreline and introduces a significant bias if
included in the calculations of shoreline change rates.

As a result, the short-term shoreline movement data obtained
from beach profiles was not utilized in the determination of
an average long-term recession rate. Rather, the NOS-CERC
shoreline movement maps were utilized for this purpose.
Accordingly, erosion rates were determined at each station
along the reach and averaged to obtain a uniform average
rate. Stations that were armored or considered subject to
inlet effects were not included in calculating the average
rate. The resulting average long-term erosion rate was 1.3
ft/yr which corresponds to a distance of 32.5 and 65 feet
respectively over 25 and 50 years. These distances were
then applied to the existing dune line, defined as the crest
of the seawardmost dune, along each profile in order to
represent the predicted 25 and 50 year shoreline.

Pawlev's Island
Shoreline movement data for Pawley's Island consisted of:
1) beach profiles taken at 12 stations in 1981 and 1986,
and 2) long-term linear MHWL changes obtained from the NOS-
CERC Shoreline Movement Maps for the period 1934-1983 and
1962-1983. In addition, characteristic profiles obtained
from the 1986 beach surveys were utilized in the calculation
of erosion associated with the occurrence of the 25 and 50
year storm.

As discussed earlier, apparent discrepancies in datum
control and limited documentation were evident in the
establishment of the survey stations from which the 1981
beach profiles were conducted. This created an element of
uncertainty as to the accuracy level for several comparative
beach surveys in representing conditions at Pawley's Island.

-172-

Profile comparisons at three stations had to be discarded
due to obvious discrepancies in horizontal and vertical
control. Profile comparison at other stations failed to
reveal a discernible trend in shoreline movement patterns
from which an overall average rate could be assigned.
Whether this was due to inconsistencies in survey control or
merely short-term.(5 years) shoreline fluctuations,
comparisons of the 1981 and 1986 profiles were considered
inadequate for the determination of a shoreline recession
rate from which long-term future setback lines could be
established.

As a result, the NOS-CERC Shoreline Movement Maps were
referred to in the determination of future shorelines at
Pawley's Island. Erosion rates were calculated at each
station and were averaged to obtain a uniform rate.
Stations considered to be subjectto inlet effects were not
included in calculating this rate however, since the entire
remaining portion of the island is bulkheaded or influenced
by groins, armoring was not, in this case, a criteria for
eliminating a station from being included in the
calculations. The resulting average long-term erosion rate
was 1.3 ft/yr which corresponds to a distance of 32.5 and 65
feet respectively ove3 25 and 5D years. These distances
were then applied to the existing dune or structure line,
whichever was most seaward, along each profile in order to
represent the predicted 25 and 50 year shorelines. It is of
interest to note that the calculation of an average erosion
rate over both the periods 1934-1983 and 1962-1983 resulted
in a rate of 1.3 ft/yr thereby indicating a very consistent
trend in shoreline recession.

Debidue Island
Controlled beach profile survey stations had not been
established along Debidue Island prior to those set in April
1986 as part of this study. As a result, comparative beach

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profile data were not available for the assessment of
shoreline changes. However, long-term changes (1934-1983
and 1962-1983) are depicted on the NOS-CERC Shoreline
Movement Maps. As previously mentioned, the Debidue Island
shoreline exhibits the greatest magnitudes of, and
variations in, shoreline migration rates along the area.
This is reflected on the shoreline movement maps which
indicate high rates of erosion at the south end decreasing
northward and reversing to mild accretion at the extreme
north end. The maps also indicate a high degree of
shoreline instability at both ends of Debidue Island.

As a result of this variation in shoreline migration rates,
no uniform rate was determined as applicable across the
entire island. Accordingly, engineering judgement and
subjectivity were utilized in assessing variable rates along
the island, particularly at the north and south ends. The
south end of the island has undergone extreme shoreline
translation, resulting in erosion rates in excess of 10
ft/yr, directly related to the North Inlet shoal system.
Along the center of the island recession rates were fairly
consistent at 3.4 ft/yr. The north end of the island
exhibits a relatively stable to mildly accretional
shoreline.

Based on these rates the 25 and 50 year shorelines, when
interpreted literally, respectively fall in excess of 250
and 500 feet landward of the existing shoreline along the
southern peninsula of Debidue Island. These distances
decrease to approximately 150 and 300 feet, respectively at
the northern extent of this peninsula and to 85 and 170 feet
further north at a point 1700 feet south of the southern end
of the Debidue Tract seawall. These projected 25 and 50
year shoreline locations remain constant progressing
northward to a point approximately 4000 feet south of
Pawley's Inlet. At this point, despite an apparent mild

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accretional trend, the effects of inlet shoaling and
bypassing processes in concurrence with low-lying uplands
and historical inlet migration necessitate a more
conservative projection of future shoreline location.
Accordingly, this location progresses landward towards
Pawley's Inlet to a point corresponding to a 25 and 50 year
position of 225 and 450 feet, respectively from the existing
dune line.

8.3 STORM IMPACTS
As with any shoreline along the southeastern Atlantic coast,
the beaches included within the study area are subject to
substantial temporal erosion due to the effects of
northeasters, tropical storms and hurricanes. These events
are associated with short-term superelevations of the water
level (storm surge) and increases of onshore wave energy.
The setup of the water level allows wave-breaking and wave-
runup processes to occur at an increased elevation on the
beach foreshore, thereby subjecting the existing dune system
and/or upland development to direct wave attack and
consequential displacement and damage. The predictable
result is large-scale dune erosion or loss, dramatic rates
of shoreline recession and destruction of upland structures.

In most instances, however, eroded material is not totally
lost from the littoral system, but rather deposited in
nearshore bar formations. On a relatively stable shoreline,
seasonal variations in local wave climate will return much
of the eroded sediment to the beach foreshore and dunes over
a period of years, barring the occurrence of similar storms
during the rebuilding period. As a result, ,the extent of
erosion that takes place during such events is not always
accurately represented or accounted for when assessing long-
term erosion rates. When establishing a shorefront
management plan, short-term erosion events should be
considered to avoid potentially disastrous impacts

-175-

associated with major storm events.

The predicted storm-surge elevations for the study area are
discussed in Section 6.4 of this report. Although
substantial damage along the study area shoreline has been
documented as a result of land-falling hurricanes, erosion0
more frequently occurs from northeasters. It is interesting
to note that'the beach erosion caused by a long duration
northeaster and the associated high-water levels can often
exceed that of a hurricane passing offshore. More moderate
hurricane-induced erosional impacts are due to the
relatively shorter storm duration and the proximity of the
relatively fast-moving tropical storm to the local
shoreline. Nevertheless, erosion associated with the
occurrence of the predicted 25- or 50-year hurricane has
been considered as the worst-case condition when evaluating
setback criteria in this study.

A numerical model has been employed in this study in order
to predict the extent of potential future erosion that may
be expected along the various study area shoreline reaches
as a result of the occurrence of the predicted 25- and 50-
year hurricanes. The theoretical basis for the computer
model was developed by Dr. Robert G. Dean of the University
of Florida and is currently applied by the State of Florida
Department of Natural Resources - Division of Beaches and
Shores (DNR-DBS) Coastal Construction Control Line Program.
In essence, the model calculates the erosion of a
characteristic beach profile at each time interval
associated with a synthesized storm-surge hydrograph. The
model predicts linear erosion of the beach-dune system but
does not account for dune overtopping or breaching. The
hydrograph represents the rise and fall of the water level
over time that occurs during a tropical storm. The IPP or
other representative profiles along each reach were
simplified and input into the model as the pre-storm

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profile. Water levels associated with the 25- and 50-year-
hurricane along each reach were input as the peak of the
storm surge hydrograph for each stimulation. The hurricane
hydrograph was simulated using the characteristics of an
actual storm surge hydrograph. The components of the
hypothetical hydrograph correspond with the peak water
elevations of the 25- and 50-year hurricane for a 36-hour
total storm duration. The hydrograph was skewed with a long
rising limb (i.e., time to peak) and a slow falling limb.
The rising portion was approximately 20 hours; maximum or.
peak levels occurred for approximately 10 hours. The
falling or receding position was approximately 6 hours.
Specific input parameters and the results of these
stimulations are presented in the following paragraphs.

Garden City Beach
The previously determined IPP for this reach of shoreline
was utilized to represent the pre-storm profile condition.
Input requirements of the model necessitate simplifying the
profile as a series of straight-line slopes above the pre-
storm water level and an exponential equilibrium profile
below that water level. The maximum IPP dune height of
+11.5 ft was input into the model, as were the 25-and 50-
year maximum storm surge elevations of +9.5 ft and +11.5 ft
(NGVD), respectively. Landward dune erosion of 116 ft and
152 ft resulted from the model simulation of the 25- and 50-
year storm surge, respectively. Figure 8.3-1 presents the
IPP, the simplified IPP input as the pre-storm profile and
the eroded profiles resulting from the simulation of the 25-
and 50-year storm surges. Of particular note is the fact
that the primary IPP dune is breached during this
simulation. While the simulation of the IPP erosion
represents an average condition over the shoreline reach, it
is in this case a condition that would result in
considerable landward propagation of the flooding and wave
action associated with these storm events.

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SOUTH MYRTLE BEACH STORM EROSION
25

20-

15-

S 10-

W -5-

-10 , ,
-200 -o100 100 200 300 400 500 600
DISTANCE (ft)
ODUNE = 11.5' A 25-YR = 9.5' 050-YR = 11.5'

FIGURE 8.3-1
PREDICTED 25- AND 50-YEAR STORM EROSION
(GARDEN CITY)

0) 0 0 0 0 0 05 � � ]

Litchfield - Huntinaton Beach
The previously determined IPP for this reach of shoreline
was utilized to represent the pre-storm profile condition in
this simulation as well. Likewise, the profile was
simplified to meet input requirements of the model. The
maximum IPP dune height of 16 ft and maximum storm-surge
elevations of 10 ft and 12 ft were input into the model for
simulation of the 25- and 50-year storm events,
respectively. Landward dune erosion of 59 ft and 101 ft
resulted from model simulation of the 25- and 50-year storm
surge. Figure 8.3-2 presents the IPP, the simplified IPP
input as the pre-storm profile and the eroded profiles
resulting from the simulation of the 25- and 50-year storm
surges. Again, it should be noted that the primary IPP dune
is breached in both of these simulations. Likewise, while
erosion of the IPP represents an average condition along the
shoreline reach, it is in this case a condition that would
result in considerable landward propagation of both the
flood elevations and wave action associated with these storm
events.

Pawlev's Island
As we discussed in sedtion 6.2,-the IPP methodology is not
applicable for the Pawley's Island shoreline due to the
effects of both armoring and inlet proximity on beach
morphology there. This precluded the application of the
storm erosion model to a single profile representative of
average conditions along the entire island. As an
alternative approach, actual profiles determined to be
representative of individual reaches of the shoreline were
chosen for application in storm erosion modeling for that
reach. As discussed in section 3.10, Pawley's Island can be
divided into three distinct sections when addressing
characteristic beach morphology. Accordingly,
representative profiles were selected from the southern,

-179-

LInTHFIEL' BACIHI STORM EROSION
25

20 -

a 15-

I 10 -

- -

-200 -100 0 100 200 300 400 500 6b0
DISTANCE (ft)
0 DJDNE = A f 25-YR 10' 0 50-YR = 12'

FIGURE 8.3-2
PREDICTED 25- AND 50-YEAR STORM EROSION
(LITCHFIELD/HUNTINGTON BEACH)

S� S S S S S S)i

central and northern sections of the island for application
of the storm erosion model.

The southern spit section of Pawley's Island, while
exhibiting a distinctly characteristic profile, rarely
reaches elevations greater than the 25-year (+9.5) or 50-
year (+12 ft) storm surge. As a result, the majority of
this area would'be overtopped during either of these low-
frequency storm events. As the simulation of erosion
associated with overtopping is currently beyond state-of-.
the-art capabilities, such an erosion prediction for the
southern spit of Pawley's Island was deemed unfeasible.
Nevertheless, it can be safety assumed that the entire
southern spit area would be subject to extreme sediment
displacement, structural damage and potential breaching in
the event of storm surges of these magnitudes.

Dune elevations along the central and northern sections of
Pawley's Island are significantly greater than the surges
associated with the 25- and 50-year storms; accordingly,
profiles 4420 and 4450 were chosen to represent these
sections respectively. Table 8.3-1 presents the pertinent
input and output for the simulation of the 25-year and 50-
year storm erosion forf these profiles.

Table 8.3-1. Input Data and Results for Modeling
Erosion Associated With the 25- and 50-Year Storm Surge
Along Northern and Central Pawley's Island.

STORM SURGE LEVEL ISLAND REACH STATION DUNE EROSION
25 year 9.5' Center 4420 100'
25 year 9.5' North 4450 48'
50 year 12.0' Center 4420 135'
50 year 12.0' North 4450 90'

Figures 8.3-3 and 8.3-4 present the actual profile, the

PAWLEYS ISLAND STORM EROSION
25,

20 -

10 -
X-15
00

LID

-j0

100 2]00 300 40 50 So6 70 0 80
DISTANCE (ft.)
l DUNE HiT. = 14.5' A25-YR 9.5'. 050-YR = 12'

FIGURE 8.3-3
PREDICTED 25- AND 50-YEAR STORM EROSION
(NORTHERN PAWLEY'S ISLAND)

a B a 0 0 S 0 0 S~~~~~~~~~~~~~~~~~~~

PAWLEY5 !s'LAND 'STORM ERO0SION
25

I 10 -

5- I

(ETAPE IS
r~~ I
-J1

1200~ 200 30)0 400 500 60;0 j00 800 900
DISTANCE (ft.)
OD0UNE I-f.. 17.5' AP25-YR~ = 9.5' 050-YR 1- 2'

FIGURE 8.3-4
PREDICTED 25- AND 50-YEAR STORM EROSION
(CENTRAL PAWLEY'S ISLAND)

simplified profile input as the pre-storm profile and the
eroded profiles resulting from the simulation of the 25- and
50-year storm surges for both the northern and central
reaches of Pawley's Island. Analysis of these figures and
Table 8.3-1 indicate in the event of such storms the central
island shoreline may undergo a considerably greater amount
of dune recession-than the northern section. This is due
primarily to the greater volume of sand per ft. of dune and
the milder slopes characteristic of the northern shoreline
beach profile. It should be noted that the primary dune
would be breached at both profiles for both storm events.
Since these profiles were chosen as representatives of their
respective shoreline reaches, the degree of erosion
associated with each profile as a result of the 25- and 50-
year storm surge should be likewise considered
representative of each reach.

Debidue island
The IPP methodology was also deemed inapplicable for the
Debidue Island shoreline, and as a result, actual profiles
determined to be representative of individual shoreline
reaches were likewise chosen for application in storm
erosion modeling at that location. Similar to Pawley's
Island, Debidue Island can be~ divided into three distinct
sections when addressing characteristic beach morphology.
The southern spit on Debidue Island rarely reaches
elevations greater than the 25-year (9.5 ft) and 50-year (12
ft) storm surge. Accordingly, the majority of this area
would be subject to overtopping, thereby precluding accurate
modeling of erosion resulting from either of these low-
frequency storm events. It can be concluded, however, that
this southern spit section would be subject to considerable
sediment displacement and potential breaching in the event
of storm surges of these magnitudes.

Dune elevations along the central and northern sections of

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Debidue Island are significantly greater than: the surges
associated with the 25- and 50-year storms; accordingly,
profiles 4340 and 4360 were chosen to represent these
sections respectively. Table 8.3-2 presents the pertinent
input and output for the simulation of the 25- and 50-year
storm erosion for these profiles.

Table 8.3-2. Input Data and Results of Modeling
Erosion Associated with the 25- and 50-Year Storm Surge
Along Northern and Central Debidue Island.

STORM SURGE LEVEL ISLAND REACH STATION DUNE EROSION
25 year 9.5' Center 4340 129'
25 year 9.5' North 4360 110'
50 year 12.0' Center 4340 169'
50 year 12.0' North 4360 152'

Figures 8.3-5 and 8.3-6 present the actual profile, the
simplified profile input as the pre-storm profile and the
eroded profiles resulting from the simulation of the 25- and
50-year storm surges for both the northern and central
reaches of Debidue Island. It should be noted that along
the central reach, the extent of erosion is such that houses
located there may well be threatened by the occurrence of
these low-frequency storm events. Erosion along the
northern shoreline reach is substantial and, while this area
is currently undeveloped, the storm impacts should be taken
into account in the formulation of any future development
plans.

o" OEit9nE !SLANI STORM EROSION
25 . ._
2 I 0
20- I

10 -
I

-30 -200 -100 200 300 01

DISTANCE (f t.)
Cl UNE Hr. = 14.5' A25-YR = 9.5' O'- -YR = !S.0'

FIGURE 8.3-5
PREDICTED 25- AND 50-YEAR STORM EROSION
(NORTHERN DEBIDUE BEACH)

_ 0 5 5 5

DEBIDUE ISLANL STORM EROSION

20-

-~ 15 - i

z
10 -

-101 1
-300 -200 -100 ( 100 200 30 0 400
DISTANCE (ft.)
ODUNE HT. = 13' A25-YR = 9.5' 050-YR = 12.0'

FIGURE 8.3-6
PREDICTED 25- AND 50-YEAR STORM EROSION
(CENTRAL DEBIDUE BEACH)

9.0 SHOREFRONT MANAGEMENT RECOMMENDATIONS
9.1 HAZARD ZONES
In contrast to similar efforts by previous investigators,
the Shorefront Management Study under consideration has
identified multiple coastal hazard zones which are, at
present, not currently or effectively regulated by federal,
state and local governments along the shoreline of interest.
These hazard zones are associated with the:

Future location of the beach/dune system as a
result of erosion and shoreline recession,

Limit of upland erosion resulting from low
frequency storm events, and

Existing Flood Insurance Zones which in numerous,
locations under-predict the level of impact for a
1-in-100 year storm.

A conceptual depiction of these coastal hazard zones
relative to an existing beach/dune system is included as
Figure 9.1-1. It is important to note that the indicated
seawardmost two (2) zones are related to the expected long
and short-term dynamic fluctuation of both the beach and
dune, where existent. The flood insurance zones are the
result of the federal government's (i.e. FEMA) efforts to
map the impact zones of a 100-year storm for the purpose of
making available federally subsidized flood insurance. It
should be understood that the flood insurance zones,
depicted by FEMA for "A" and "V" zones respectively, are
indicative of the flooding limits without, and with waves
greater than three ft in height, resulting from a
probabilistically determined 100-year storm event. The FEMA
methodology does not however, include the prediction of
shoreline fluctuations and erosion during the 100-year
storm. For that reason, the predicted landward limits of V-

~ ZONE OF EROSION

FLOOD INSURANCE ZONES j~~ZONE OF RECESSION

- 50 Year Future Dune Crest

- ~~~~Existing.Beach/Dune System

1.~~OATAL HAZAR ZON:::ES
SHREROT ANGEEN PA

FIGURE~~ 9 .1-1....

SCHEMAT~~~ICDARMOTH COASTAL HAZARD ZONES

zones in coastal areas with dunes can be extremely
unreliable and inaccurate when the elevation of the existing9
dune crest exceeds the computed theoretical elevation of the
100-year storm surge. To a large degree, this condition
predominates throughout the study area. Hence it is
necessary for this shorefront. management study to address
existing flood insurance zones and the propriety of
considering additional building construction guidelines
within these extremely high-hazard areas.

9.2 EXISTING SHOREFRONT REGULATORY PROGRAMS
At present, the following three (3) types of developmental
regulation are in effect along the Georgetown County
shoreline of interest above the approximate MHflWL:

State of South Carolina Coastal Council permitting
requirements along the beach and within thie
adjacent primary oceanfront sand dune "critical
area" ( via Act 123 of 1977),

*Federal Flood Insurance requirements for
construction within "All or "VI' Zones ( 44 CPR,
Parts 59 and 60), and

*Where existent, any locally adopted zoning
ordinances and/or setbacks; developer's covenants
and restrictions; etc.

Coastal Council regulatory authority allows for the
protection of existing fragile beach/dune resources by
calling for their classification as "critical areas". The0
limit of Coastal Council jurisdiction in most instances is a
function of the location of the primary ocean front dunes
which by definition are "those dunes which constitute the
front row of dunes adjacent to the Atlantic Ocean".
Accordingly, the "critical area boundary" is further defined

-190-

in the governing Rules and Regulations for Permitting as
* ~~~follows:
if the crest of a primary front row sand dune is not
reached within 200 feet landward from mean high water,
that sand dune is not considered adjacent to the
* ~~~~Atlantic Ocean. Council permitting authority shall
extend: (I)-to the landward trough of the primary
front row'sand dune if the crest of this dune is
reached within 200 feet landward from mean high water;.,.
(2) to the seaward side of any maritime forest or
upland vegetation if reached before the primary front
row sand dune; and (3) to the seaward side of any
permanent man-made structure which was functional in
its present form on Septemiber 28, 1977.

At present, the Coastal Council's regulatory authority is
limited strictly to existing conditions. No allowances are
* ~~made for where the dune crest and/or beach face will be in
the future as a result of shoreline recession in areas with
historically known rates of erosion. Furthermore, the
Council cannot cons'ider the adverse effects of low frequency
* ~~~storm events which can both literally destroy the primary
dune in a matter of hours and correspondingly adversely
impact life, limb and-property.-

In accordance with the published regulations for the
National Flood Insurance Program, FEMA defines "coastal high
hazard areas" as "areas subject to high velocity waters,
including, but not limited to hurricane wave wash". These
areas are designated by means of maps as V-zones.
Construction of habitable structures within such areas must
comply with elevation and limited building standard
criteria. Areas of "special flood hazard" (i.e. 100-year
storm flooding) are likewise designated by mapping for
insurance purposes as A-zones. Both A and V zone phenomena
are considered to have a one percent or greater chance of

occurrence in any given year (i.e. probability of .01). As
previously discussed, the methodology for the prediction of
100-year flooding and simultaneous wave action utilized by
FEMA does not account for erosion of the beach/dune system.
Accordingly, the landward limits of the V-zone for much of
the Georgetown County shoreline is grossly inaccurate and
therefore unconservative. The result of this shortcoming in
the methodology'is.that both existing and future new
construction and/or substantial reconstruction is occurring
in certain high hazard areas without having to consider
appropriate design criteria. Without state or local
intervention, this shortcoming is not expected to change in
the foreseeable future.

The third general area of potential existing regulation of
construction within coastal high hazard areas is "local
government", or developer initiated control. For the
project area under consideration, no local beach and dune
type setback restrictions are in existence. A recent
(August 1985) shoreline assessment contracted by the
developers of Arcadia I & II and Debidue tracts at Debidue
Island, resulted in the recommendation of the adoption of
setbacks "ranging from 150 ft. to 250 ft. from the seaward
toe of the seawardmost dune or seawall, where existent"
(Kana, et al. 1985). The estimated level of storm
protection predicted by the consultant for the recommended
setbacks varied between the 25 and 50 year storm, dependent
on location on the island. To date, the developer for the
Debidue properties under discussion is continuing to assess
the propriety of the recommended setbacks, (written
correspondence).

9.3 EXISTING FLOOD INSURANCE ZONES AND STANDARDS
Both a review of the existing Flood Insurance Rate Maps
(FIRMs) for the study area in Georgetown County, as well as
the preliminary results of the storm impact analyses,

-192-

indicate that the V-zone conditions depicted by the FIRMs
are extremely unconservative. Along the Georgetown County
coast, the V-zones terminate at/or about the seaward face of
any dune or similar features which have an elevation
exceeding the predicted base flood elevation (BFE) for a
100-year storm. Due to the adoption of nationwide uniform
standards for the performance of Flood Insurance Studies by
subcontractors, FEMA does not consider erosion of existing
beach/dune systems, or other features in the prediction of-
V-zones.

In Georgetown County, as well as adjacent counties, this
shortcoming results in a gross underestimation of the shore
normal extent of the impact zone with waves greater than
three feet in height expected to occur coincident with a
100-year storm event. Of immediate concern is not only the
specified elevation for future construction within V zones,
but more importantly the tvypes of construction allowed
immediately landward of the beach-dune system. For example,
A-zone standards do not require pile foundation, nor the
consideration of wave forces. Areas which are mapped as A-
zones, but in reality will be subject to severe wave effects
during a 100-year storm, therefore are not necessarily
subject to prudent building requirements for not only single
family residence construction, but also multi-family and
commercial buildings. The potential future consequences of
this situation are intuitively obvious.

As a specific example, Figure 9.3-1 is an excerpt from FIRM
No. 450085 0205 C for an area located within Magnolia Beach,
north of Midway Inlet in unincorporated Georgetown County.
As noted, the landwardmost V-zone which terminates at the
dune line is at elevation +19 ft. Landward of that point is
an A-zone at elevation +14 ft. Also noted on Figure 9.3-1
is the location of survey profile No. 5525 which was
established as part of this study. The depiction of the

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ZONE A16 I
(EL 15)

MAGNOLIA BEACH ZOE A16
(EL 14)nf

I PROFILE 4525

ZONE V21
(EL 19)

ATLANTIC OCEAN

REFERENCE:

COMMUNITY PANEL NO. 450085 0205 C
Mar. 1,1984
GEORGETOWN COUNTY,S.C.

FIGURE 9.3-1
FLOOD INSURANCE MAP NEAR
LITCHFIELD BY THE SEA

FEMA flood zones as they relate to the cross section of the
beach at profile No. 5525 is shown in Figure 9.3-2.

Previously referenced erosion analyses of the IPP within the
Litchfield Beach area for both 25 and 50 year storm events
have indicated the dune at this location can reliably be
considered to be eroded away as a result of erosion during a
100 year storm. For that reason, the actual physical
phenomena expected with such an event will not be as
depicted on FIRM No. 450085 0205 C and as interpreted by
Figure 9.3-2. Instead, the expected nearshore impact zones
will be as shown in Figure 9.3-3 which demonstrates the
recalculated elevation and location of the V-zone concurrent
with the 100 year storm, including erosion. As shown in
this Figure, any structure built immediately landward of the
dune should be constructed in accordance with V-zone
criteria at elevation +18, and not A-zone criteria at
elevation +14. The situation highlighted by this example is
typical of existing conditions throughout the majority of
the Georgetown County shoreline considered by this study.

Correspondingly, a major recommendation of this study is the
implementation of a building construction zone(s) landward
of the dune line which will result in the consideration of
design criteria sufficient to accommodate the expected
impacts of a 100-year storm.

9.4 RECOMMENDED SETBACKS
It is intuitively obvious that in order to adequately
protect existing and future beach/dune resources, both the
predicted short-term and long-term shoreline impact zones
must be accounted for in an enforceable shorefront
management plan. For example, the premise of a minimum
setback from the 50-year future shoreline is simplistically
an effort to prevent construction landward of the location
where the active beach is expected to be 50 years hence,

-195-

el. 22

20 -
20- pREDICTED v-ZONE

1elev.14.3' 100 YR. BFE
IPP id ( NO WAVES)

to-/ _;V-'\ EXISTING DUNE

/ ACTUAL \
PROFILE

PREDICTED
ERODED PROFILE < X

-5-

Monument 4525 NOTE DISTORTED SCALE

-150. -100 -50 0 50 100 150 200 250
DISTANCE (FT)

FIGURE 9.3-2
DEFINITION OF V-ZONE WITHOUT
CONSIDERATION OF STORM IMPACTS

A-ZONE V-ZONE
(e1.14) (el.19)

20- A \1 elev.19 100 YR. BFE
(w/WAVES)

15- / \ elev.14.3' e 100 YR. BFE
(NO WAVES)

EXISTING DUNE

I --
U.

-5-

Monument 4525 NOTE DISTORTED SCALE

. I I , I , I , I . I . I . I . I
-150 -100 -50 0 50 100 150 200 250
DISTANCE (FTJ

FIGURE 9.3-3
PREDICTED V-ZONE CONSIDERING THE STORM
IMPACTS NEAR LITCHFIELD BY THE SEA
S.

conservatively assuming relatively modest but continuous
annual rates of beach erosion.0

on the other hand, additional magnitudes of setback
associated with storm impacts serve two functions:

1. To protect upland development from being constructed
in an area subject to significant fluctuation due to
storm induced erosion, and

2. To allow for sufficient rebuilding of a comparable
dune system by natural processes subsequent to
severe storms. Without such, the expected result
will be a proliferation of shoreline stabilization
necessitated by buildings in eminent danger of
structural damage and/or loss. The latter would
literally preclude natural dune reconstruction and
would result in the expected ultimate loss of the
dry recreational beach and the requirement for large
scale beach renourisbhnent at significant expense.

The following paragraphs present the recommended setbacks
for the individual shoreline reaches along the Georgetown
County'study area. Th'ese setbacks are represented as lines
on the maps presented in Appendix D. It should be noted
that in establishing these lines, anomalous conditions
associated with grains, inlets, etc. which theoretically
result in the prediction of a future seaward progradation of
the shoreline due to small-scale temporal sand storage, have
been "average out" in this analysis. The purpose of this
action is to preclude physical discontinuities which be
detrimental to area wide recommendations for future
shoreline management practices. Furthermore," additional
setbacks were employed in the immediate vicinity of inlets
in an attempt to provide a buffer zone which would account
for the severe sudden shoreline translations and erosional

losses that are likely to occur in the event of storms or
over the normal course of expected inlet migration.

Garden City
Analysis of shoreline processes along the approximately 3.3
0 ~~mile stretch of Garden City Beach shoreline indicates a
prognosis of long-term erosion and associated recession. At
present, existing shorefront development within the
Georgetown County portions of Garden City Beach is
0 ~~predominantly single family residence. In contrast, along
the Horry County portion of Garden City Beach where new and
reconstructed development is occurring, the trend is
predominately high density multi-family usage. With the
* ~~~evolving reorientation of the general shoreline from Garden
City southward attributable to the stabilization of Murrells
Inlet, this segment of Garden City Beach can be expected to
potentially undergo highly variable rates of shoreline
* ~~~migration including accelerated rates of erosion and
recession. In areas where the shoreline location has been
fixed by means of seawalls, groins, etc., landward recession
v ~~may be terminated but vertical erosion of the wet or dry
* ~~~beachface is expected to continue to occur.

On the average, the 50-year future shoreline recession for
Garden City Beach, resulting from analysis of shoreline
* ~~movement rates, is expected to be approximately 75 feet
landward of the existing dune line. As previously
discussed, this landward recession is hypothesized solely on
historical long-term shoreline recession rates and does not
account for short-term effects. Figure 8.3-1 is a depiction
of the results of computer modeling of the IPP for this
shoreline reach for both the 25-year and 50-year storm
event. As noted, this analysis indicates that the impact
zone of the 50-year storm is expected to be twice that of
the existing dune line. Similarly, the impact zone of the
25-year storm is computed to be about 116 ft landward of the

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IPP or approximately one and one-half times the 50-year
long-term linear rate.

In consideration of these findings and their relevant
application to the shoreline in its present developed state,
the minimum recommended setback from the existing dune line
along the Georgetown County portion of Garden City Beach
should be that, distance dictated by the 50-year future
shoreline location as predicted from historical long-term
recession rates. This corresponds to a distance of 75 feet
landward of the existing dune line which is more
specifically defined in this application as the crest of. the
seawardmost dune. In locations where the shoreline has been
seawalled, the setback line would default to a point 75 feet
landward of the top of the seawall.

Allowances for construction of major habitable structures
seaward of the setback line should only be made if a
building cannot be constructed or reconstructed landward of
that location, and if the setback would result in denial of
"reasonable use" of property. It is recommended that the
latter should be considered to be no more than single family
residence usage. Non-habitable structures should not be
allowed seaward of this point except for dune overwalks,
sand fencing, and erosion control measures, where warranted.
In no event should these recommendations take precedence
over existing or future setbacks or regulatory programs
which are considered to be more stringent.

Litchfield-Huntinerton Beach
Analysis of shoreline processes along this reach extending
from Murrells Inlet to Midway Inlet continue to indicate a
relatively uniform long-term erosion rate and associated
shoreline recession along its majority. An exception to
this is the shoreline immediately south of Murrells Inlet
where considerable accretion has occurred as a result of the

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construction of the navigation project there. It should be
noted, however, that accelerated erosion has occurred at the
south end of Huntington Beach State Park and along the
adjacent residential section that is North Litchfield Beach
as a result of the Murrells Inlet Navigation Project. The
potential acceleration of these rates of erosion and
accretion due to reorientation of the shoreline and the
effects of the jetties in blocking littoral drift has been
presented previously in this report.

The Huntington Beach State Park shoreline is currently
undeveloped and is very likely to remain that way. Single
family residences line the central portion of the shoreline
reach comprising Litchfield and North Litchfield Beach.
South of this, several low-density multi-family resort
complexes have been constructed. The southernmost tip of
this reach is currently undeveloped. With the exception of
the concrete block wall fronting the Litchfield Inn, this
entire shoreline reach is unarmored. These development
trends and the aforementioned shoreline processes are
important factors in the determination of a setback line
along the Litchfield-Huntington Beach shoreline.

The quantification of shoreline erosion trends for this
section of the study area, based upon analysis of historical
shoreline movement rates, indicates shoreline recession
rates which, when extrapolated into the future, result in a
predicted 50-year shoreline location approximately 65 feet
landward of the existing dune line. Figure 8.3-2 presents a
depiction of the results of computer modeling of the IPP for
this shoreline reach for both the 25-year and 50-year storm
event. As noted, this analysis indicates that the impact
zone of the 50-year storm is expected to be about 100 ft
landward of the existing dune line or one and one-half times
the predicted 50-year shoreline recession. The impact zone
associated with the 25-year storm, at 59 ft from the

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existing dune line, is actually expected to be less than the
predicted 50-year shoreline recession. The relatively
narrow storm impact zones, as compared to the 50-year
predicted shoreline recession, is attributable primarily to
the relationship between the beach profile and the volume of
sand associated with the profiles on this shoreline reach.
The latter result-is less predicted erosion during storm
events.

Again, allowance for construction of major habitable
structures seaward of an adopted setback should only be made
L ~~if a building cannot be constructed or reconstructed
landward of that location, and if the setback would result0
in denial of "reasonable use" of property. The latter
should be considered to be no more than single family
residences. In no event should these recommendations take
precedence over more stringent future or existing setbacks.
Non-habitable structures seaward of the propose~d setback
should be limited to dune overwalks, sand fencing and
erosion control measures, where warranted and fully
permitted.

Pawlev's Island
Along the approximate 3.8 mile stretch of Pawley's Island
shoreline, analyses of shoreline processes continue to
indicate a prognosis of long-term erosion and associated
shoreline recession. The only potential exception to this

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is at the immediate north end of the island where ebb tidal
shoal migration has resulted in accretion there over the
past few years. A groin field extends south of the Pawley's
Island Fishing Pier over the majority of the island and is
believed to have some beneficial effect in reducing the
rates of shoreline recession there. Much of the southern
half of the shoreline is also bulkheaded which, while
"fixing" the shoreline location and attenuating normal
upland recession, contributes to vertical erosion of the
beachface.

On the average, the 50-year future shoreline recession for
Pawley's Island, as determined from historical shoreline
migration trends, is expected to be about 65 feet landward
of the existing dune line. In locations where the shoreline
has been seawalled or bulkheaded, the recession is
determined to be 65 feet from the structure. As previously
noted, this landward recession is hypothesized solely on
historical long-term linear recession rates and does not
account for short-term effects. Figures 8.3-3 and 8.3-4
depict the results of computer modeling of representative
profiles of the Pawley's Island shoreline for both the 25
and 50-year storm event. As noted, this analysis indicates
that the impact zone of the 25 and 50-year storms are 100
feet and 135 feet respectively or about 1.5 and 2 times the
long-term recession rate.

Based on these findings, an inconsideration of the type of
development as well as the shorefront armoring in existence
along Pawley's Island, the minimum recommended setback from
the existing dune line or shorefront structure along the
island shoreline should be that distance dictated by the
future location of the 50-year shoreline. As predicted by
analysis of linear shoreline migration trends, this distance
correponds to 65 feet landward of the existing dune line as
shorefront structure.

-203-

As is the case in the establishment of all setback lines,
allowance for construction of major habitable structures
seaward of an adopted setback should -only be made if a
building cannot be constructed or reconstructed landward of
that location, and if the setback would result in denial of
"reasonable use" of property. The latter should be
considered to be no more than single family residences. In
no event should these recommendations take precedence over
more stringent future or existing setbacks. Non-habitable
structures seaward of the proposed setback should be limited
to dune overwalks, sand fencing and erosion control
measures, where warranted and fully permitted.

Debidue Island
The Debidue island shoreline exhibits both the largest
magnitude and variation in shoreline migration rates over
the entire study area. The southern end of the island is0
experiencing extremely high erosion rates while the northern
end has of late been undergoing mild accretion. The central
portion of the shoreline exhibits a mild erosional trend.
The majority of the island is undeveloped with the exception0
of the Debidue Tract along the center of the island where
the shorefront is hardened by a seawall. Predictably, the
beach in front of the seawall has undergone vertical erosion
such that virtually no dry beach exists at high tide. The
south end of the island is part of the Belle W. Baruch
nature preserve and is unlikely to be developed in the
future while the north end of the island is slated for
future development.

The quantification of shoreline erosion trends along the
Debidue Island shoreline, as based on linear'shoreline
migration, resulted in varying locations of the 50-year
shoreline. This was a result of the spatial variation in
shoreline erosion rates over the length of the island

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shoreline. The southernmost extent of the island was
designated as an inlet Impact Zone and, accordingly, the
entire peninsula making up this section should he subject to
the restrictions of the prescribed setback program. As
mentioned previously, this area is designated as a nature
preserve which should preclude any future development there.
North of this point a setback of 315 feet corresponding to
the predicted 50-year future shoreline is recommended to a
point 1700 feet south of the Debidue Tract seawall,
whereupon the setback reduces to 170 feet, reflecting the
milder recession rates observed there. These setbacks are
relative to the existing dune line or seawall, whichever.
applicable. The 170 feet setback continues north to a point
approximately 4000 feet south of Pawley's Inlet where
historical inlet migration trends, low-lying uplands and
inlet effects necessitate a setback gradually increasing to
450 feet near the inlet and the designation of this area as
0 ~~~an Inlet impact Zone.

Once again, allowance for construction of major habitable
;L ~~ structures seaward of an adopted setback should only be made
0 ~~~if a building cannot be constructed or reconstructed
landward of that location, and if the setback would result
in denial of "reasonable use" of property. The latter
should be considered to be no more than single family
* ~~~residences. in no event should these recommendations take
r ~~ precedence over more stringent future or existing setbacks.
Non-habitable structures seaward of the proposed setback
should be limited to dune overwalks, sand fencing and
* ~~~erosion control measures, where warranted and fully
permitted. It is recommended that no future major habitable
structure be constructed in designated Inlet Impact Zones.

* ~~~9.5 COASTAL CONSTRUCTION ZONE
The implementation of minimum coastal construction standards
landward of the MHWL are recommended as a result of the

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analyses performed in conjunction with this study. These
standards should be in addition to all existing building
codes and should not supercede local, state or federal
standards which can be considered to be more stringent.

The most obvious technique for the local implementation of
such standards is through the adoption of a zone specifying
an area of interest extending landward from the MHWL a
specified distance. Within this "coastal construction
zone", the following minimum criteria should be addressed:

Design wind speed should be computed in accordance
with the 1986 revisions to the 1985 Standard
Building Code.

Effects of waves where appropriate. All wave,
hydrostatic land hydrodynamic loads should be
considered during design as acting concurrent with
the design wind speed.

Elevation criteria of the lowest supporting
structural member in the shore parallel direction
which would include the effects of waves.

Erosion during a 100 year storm event which would
affect foundation design.

- Others.

For ease of implementation at the local level, all new or
substantially improved structures built within such a zone
should be certified by an appropriate design professional as
to compliance with the adopted standards.

9.6 EROSION CONTROL PERMITTING PROCEDURES
The analyses and results contained herein indicate that long

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* ~~term erosion trends are expected to continue unabated
throughout the majority of the study area. Short term
variations in this prediction include lower rates of erosion
and varying accretion in depositional areas adjacent to
tidal inlets or within designated spoil areas north and
South of Murrells Inlet.

In the long run, however, continuing shoreline recession and
the effects of development pressures, both old and new, will'
result in the requirement for permit requests for erosion,
control structures. Additionally, it is easily shown that
average annual long term recession rates will be exceeded by
the impacts of low frequency storms, which statistically can
be expected to occur. Due to the demonstrated proximity of
existing lines of construction to tot only the 50 year
future shoreline position, but also the zone of impact of
even a 25 year storm, a comprehensive and consistent policy
should be developed and enforced regarding future erosion
control measures.

Erosion along South Carolina's shoreline has progressed to a
5 ~~degree that a substantial number of habitable structures can
be jeopardized by future major storms. It is in the State's
general interest to allow protection of upland property, but
not in a manner that will damage or degrade the beach--dune
system. Beach restoration is unequivocally the protective
measure considered as most beneficial to the. beach-dune
system. However, in some locations, economics may not favor
beach restoration; and even if restoration is expected, the
0 ~~time scales for implementation of such projects may be so
long that interim protection for upland structures in
immediate jeopardy may be justified. Coastal armoring,
e.g., sloping stone revetments, is a possible means of
providing such interim protection. However, it is known
that armoring can notentiallv adversely impact the adjacent
beach-dune system.

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In brief, seawalls and shoreline azmoring can be expected to
adversely affect the beach/dune system in the following
ways:

1) They can interfere with alongshore sediment
transport processes,

2) They prevent sand from being added to the littoral
system during storms, and

3) They can cause additional erosional stress on
adjacent non-armored properties during storms.

Regardless, armoring or hardening of natural shorefront
areas is detrimental to the beach/dune system and should be
avoided if at all possible. Since it is logical, however,
to assume that future structures will be required, it is
likewise logical to require applicants for permits required
to construct such erosion control measures to mitigate their
known quantifiable impacts.-

Prior to the issuance, or local approval of any shoreline
armoring permit, the following minimum type of assessment
should be made:

1) Alternative to Armorina - Possible alternatives to
armoring include: (a) relocating the endangered
structure landward, (b) elevating the structure on

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piling, or (c) both.

2) Leaalitv of Structure - If the structure to be
protected was constructed legally, this would tend
to favor armoring.

3) Dearee of Jeopardv of Structure - This factor
addresses the possibility that a moderate storm
could jeopardize the integrity of the structure.
If the foundation type and degree of erosion are
such that a storm of moderate intensity (return
period of 10 to 20 years) would jeopardize the.
stability of the structure, this would tend to
favor the issuance of a permit to armor.

4) Conformina or Non-Conformina Structure - If a
structure has a conforming (i.e. pile-supported)
foundation, then the structure is not as
vulnerable to erosion damage as if the structure
were on shallow footings or a slab foundation. A
conforming foundation can lose all fill beneath
the structure as a result of a severe storm and
retain the structural integrity. Hence the
recommendations for coastal construction zones.

5) Presence of Other Armorina in the Area - If there
exists armoring along the same alignment as
proposed, this would tend to favor armoring.
Filling in small gaps along heavily armored
shoreline is in some instances desirable.

6) General Potential for Adverse Impact on Beach/Dune
System - Consideration should be given to the
magnitude of the effect that armoring would have
on the supply of sediment to the beaches and the
potential for interference with the longshore

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sediment transport.

Similarly, a quantitative assessment should be made to
establish a required annual volume of mitigative sand
placement in order to ensure no adverse impact to the beach-
dune system would result from the issuance of the requested
permit. This mitigation approach would take the form of
quantifying the volume of sediment that would be lost to the
beach system due to gradual erosion in addition to possibly
adverse alongshore effects.

The result of quantifying "sediment impacts" would be to.
allow for the addition of appropriate permit stipulations
requiring mitigation through sand placement on an average0
annual basis concurrent with all future permit applications
for shoreline armoring or hardening.

9.7 SHORELINE RESTORATION0
As previously mentioned, large scale beach restoration or
"nourishment" is the preferred erosion control alternative
for a section of shoreline for the following major reasons:

It can result in substantial protection of upland
property,

*It results in the creation and/or maintenance of a
beach suitable for active and passive recreational
activities, and

*It compensates for the long term effects of
erosional forces by offsetting deficits in the
littoral budget.

Since the success of beach nourishment projects constructed
to date has generally been demonstrated to be directly
related to the length of shoreline restored, the solution

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* ~~~does not necessarily lend itself to small scale applications
in either a practical or cost-effective manner. The
determination of applicability is best performed on a case--
by-case basis. There is no question, however, that the
beach nourishment experience has been proven to be a -
technically viable approach to mitigating beach erosion.

In cases where-'large scale beach restoration is not
feasible, the combination of smaller sand fills in
combination with stabilizing structures should be
considered. Typically, the latter take the form of terminal
groins at the ends of barrier islands and/or groin fields.
The utilization of stabilizing structures is generally most
0 ~~~viable when the adverse effects of inlets must be accounted
for such as in lower Georgetown County. For example, on
Pawley's Island, which can be considered to be a high
probability "candidate" for future beach restoration, the
upgrading of the existing groin field could serve to greatly
increase the longevity of a nourishment project constructed
at that location.

Short-term, smaller scale erosion control measures which can
address either limited or emergency type erosional
conditions without resorting to armoring would include:

*Beach scraping from the intertidal beach,

U et-pumping of sediment from the outer reaches of
the alongshore bar or littoral zone, and

*Trucking of beach quality fill from an acceptable
upland source or inlet shoals.

0 ~~~Except for the placement of compatible fill from a remote
source, both scraping and jet-pumping should not be carried
out on a frequent basis without the requirement for

monitoring to determine the response of the local shoreline
to the removal of sediment from the intertidal beach, since
the latter could potentially adversely affect adjacent
properties and the beach/dune system.

9.8 LONGTERM MONITORING OF SHORELINE PROCESSES
The South Carolina Coastal Council has recently embarked on
a longterm program to monitor statewide beach conditions by
means of beach surveys performed several times per year.
The purpose of the effort is to generate a data base of
historical shoreline trends and to begin to develop a
capability to predict future trends. Portions of the survey
baseline used to acquire this data will result from the
utilization of the monumented baseline established for this0
study and by those of similar studies performed along the
Grand Strand and other areas of the State.

Recommendations for future expansions of this data
acquisition program based upon similar efforts in other
coastal states would include the following at a minimum:

a. The acquisition of offshore data for eventual
comparative p.urposes on an annual basis. Ideally,
of fshore profiles should be taken at no less than
one per mile and should extend to the limit of
active sediment transport which is typically -15 to
-20 ft.

b. Aerial photography of the state's coastline on a
yearly basis. Any contract for such work should
allow for re-flights of specific areas within seven
C7) days of a major storm event affecting the South
Carolina coast.

c. The eventual rigorous monumenting of a statewide
survey baseline to include both vertical and

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horizontal control (i.e., South Carolina State
Plane Coordinate System) and appropriate legal
descriptions of the resultant baseline.

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REFERENCES

Baca, B.J., Siah, S.J., and Kana, T.W. 1986. A Wetlands
Enhancement Plan for Debordieu Development. Coastal Science
and Engineering, Inc., Columbia, South Carolina.

Clemson University, Clemson. Department of Forestry. 1976.
Debidue Beach and North Inlet Land Form History Since 1733.
Technical Paper No. 4.

County of Georgetown. 1981. Pawley's Island, South
Carolina, Beach Erosion Management Strategy. Georgetown,
South Carolina. Cubit Engineering, Limited. Clemson, South
Carolina.

Douglass, S.L. 1985. Coastal Response to Navigation
Structures at Murrells Inlet, South Carolina. U.S. Army
Coastal Engineering Research Center Technical Report CERC-
85-8. Vicksburg, Mississippi.

Eiser, W.C., Kana, T.W., and Williams, M.L. 1986. Analysis
of Historical Erosion Rates and Prediction of Future
Shoreline Positions. Summary Report for the City of North
Myrtle Beach, South Carolina. Coastal Science and
Engineering, Inc., Columbia, South Carolina.

Federal Emergency Management Agency. 1983a. Flood
Insurance Study, County of Horry, South Carolina.

Federal Emergency Management Agency. 1983b. Flood
Insurance Study, Georgetown County, South Carolina.

Jordan, L.W., Dukes, R., and Rosengarten, T. 1986. A
History of Storms on the South Carolina Coast. South
Carolina Sea Grant Consortium, Charleston, South Carolina.

Kana, T.W., Siah, S.J., Williams, M.L., and Sexton, W.J.
1984. Analysis of Historical Erosion Rates and Prediction
of Future Shoreline Positions. Summary Report for the City
of Myrtle Beach, South Carolina. Coastal Science and
Engineering, Inc., Columbia, South Carolina.

Myers, V.A. 1975. Storm Tide Frequencies on the South
Carolina Coast. NOAA Technical Report NWS-16. Silver
Springs, MD.

North Inlet Corporation and Prince George Corporation.
1985. Shoreline and Environmental Assessment of the
Debidue, Arcadia I, and Arcadia II Tracts, Debidue Island,
South Carolina. Prepared by RPI Coastal Science and
Engineering, Inc., Columbia, S.C.

-214-

North Inlet Corporation. 1985. Debordieu, South Carolina,
A Planned Unit Development: Development Standards.
Georgetown, South Carolina.

Nummedal, D. and Humphies, S.M. 1978. Hydraulics and
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for U.S. Army Coastal Engineering Research Center, GITI
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South Carolina Coastal Council. 1981. A Study of Shore
Erosion Management Issues and Options in South Carolina.
Columbia, South Carolina. Prepared by the South Carolina
Sea Grant Consortium, Charleston, South Carolina.

South Carolina Coastal Council. '1979. Guidelines and
Policies of the South Carolina Coastal Management Program.
Columbia, South Carolina.

South Carolina Sea Grant Consortium. 1984. Beach Erosion
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Report. Charleston, South Carolina. Prepared by the
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South Carolina.

South Carolina Sea Grant Consortium. 1977. Beach Erosion
Inventory of Horry, Georgetown, and Beaufort Counties, South
Carolina. Prepared by University of South Carolina, Coastal
Research Division, Geology Department, Columbia, South
Carolina.

Town of Surfside Beach. 1985. Land Use Plan for Surfside
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U.S. Army Corps of Engineers.. Charleston District. 1983.
Myrtle Beach, Horry, and Georgetown Counties, South
Carolina: Reconnaissance Report on Beach Erosion Control
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U.S. Army Corps of Engineers. Charleston District. 1977.
Specifications for Construction of Channel and Jetty System:
Murrells Inlet Navigation Project. Charleston, South
Carolina.

U.S. Army Corps of Engineers. Charleston District. 1976.
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Murrells Inlet Navigation Project. Charleston, South
Carolina.

U.S. Army Corps of Engineers. 1962. Interim Hurricane
Survey of Myrtle Beach, South Carolina. Charleston, South
Carolina.

Waccamaw Regional Planning and Development Council. 1983.
Horry County Land Use Plan, 1980. Conway, South Carolina.

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Wilson, H.S., ed. 1983. South Carolina's Migrating
Beaches. Proceedings of a Conference Sponsored by the South
Carolina Sea Grant Consortium. The South Carolina Sea Grant
Consortium, Charleston, South Carolina.

Zarillo, G.A., Ward, L.G., and Hayes, M.O. 1985. An
Illustrated History of Tidal Inlet Changes in South
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3 6366 00001 4094

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