Horry County shorefront management plan from Briarcliffe Acres to Singleton Swash and from Springmaid Beach to Garden City

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

"HORRY COUNTY

'SHOREFRONT MANAGEMENT PLAN

From Briarcliffe Acres to Singleton Swash, and from
Springmaid Beach to Garden City

Prepared for:
SOUTH CAROLINA COASTAL COUNCIL

Prepared by-
APPLIED TECHNOLOGY AND MANAGEMENT, INC.
* ~and
OLSEN ASSOCIATES, INC.

July 1986

GB
451
.H167-
1 986

0 -~~~~~~~~~~~~~~~~~~~~~~~~~~~-

HORRY COUNTY SHOREFRONT MANAGEMENT PLAN

FROM BRIARCLIFFE ACRES TO SINGLETON SWASH

AND FROM SPRINGMAID BEACH TO GARDEN CITY

Prepared for:

South Carolina Coastal Council
Charleston, South Carolina

By:

Applied Technology and Management, Inc.
Myrtle Beach, South Carolina

Olsen Associates, Inc.
Jacksonville, Florida

July 1986

U.S. DEPARTMEN1 OF COMMERCE NOAA
COASJAL SERVICES CENTER
2234 SOUTH HOBSON AVENUE
CHARLESTON, SC 29405-2413 TABLE OF CONTENTS

PaEe

Executive Summary....................................

Acknowledgement ......................................

List of Tables .......................................
List of Figures ......................................

1.0 Introduction ......................................... 1
1.1 Purpose ....................... 1
12study Area::....:............................::: 3
1.3 Previous Study ................................. 6
1.4 Present Study .................................. 8

2.0 Land Use Plan ........................................ 11
2.1 Existing Land Use ............. .... . ............. 11
2.2 Future Land Use ..................... .13

3.0 Background Information and Data Collection ...........16
3.1 Tides ................................16
3.2 Wind Data ........................1
3.3 Storm Data ..................... .................22
3.4 Waves .....!.... ............ ...............32
3 .5 Littoral Drift. ...................... 34
3 * 6 Historical Photograph .......36
3.7 Shoreline Data ..... ........ ......... ..........38
3.8 Beach Profile Data .............................39
3.9 Sediment Data .................................. 45
3.10 Beach Morphology ................................ 50
3.11 Coastal Structure Inventory .................... 58

4.0 Development Pattern ................................... 63

5.0 Sediment Analysis .....................................70

6.0 Beach Profile and Erosion Analysis ...................77
6.1 Comparative Beach Profiles .....................77
6.2 Volumetric Analysis ............................. 79
6.3 Short Term Shoreline Erosion Rate ..............89
6.4 Long Term Shoreline Erosion Rate ..... ..........98
6.5 Effects of Sea Level Rise ......................99
6.6 Ideal Present Profile .........................107
6.7 IPP Comparison with Individual Profile ........116
7.0 Inlet Analysis ................122

8.0 Future Shoreline Prediction .............128
-- 8.1 Ideal Present Shoreline... 128
8.2 Predicted 25 and 50 Year Shorelines ........... 129

r--

a=d~= 0~9 2o er:Xoo=
8.3 Storm Impacts ............... ....................135

9.0 Shorefront Management Recommendation ................141
9.1 Hazard Zones .................................. 141
9.2 Existing Shorefront Regulatory Programs .......143
9.3 Existing Flood Insurance Zones And Standards..146
9.4 Recommended Setbacks............. ............. 151
9.5 Coastal Construction Zones ....................156
9.6 Erosion Control Permitting Procedures ......... 157
9.7 Shoreline Restoration ......................... 160
9.8 Long Term Monitoring of Shoreline Processes...162

References ..............................................164

Appendix A Survey Monuments Descriptions
Appendix B Beach Profile Data
Appendix C Sediment Data Analysis
Appendix D Maps
Appendix E Garden City Development Pattern

LIST OF TABLES

Tables Paqe

2.1-1 Myrtle Beach Census Division Resident
� Population Trends (1960-1980) .......... ...... 12

2.1-2 Grand Strand Tourists 1972-1978 .............. . 12

2.1-3 Population Projections for 1985, 1990, 1995,
and 2000 ..................................... 14

2.1-4 Tourist and Peak Day Population Projections for
Grand Strand, Horry County .................... 14

2.1-5 Existing Land Use Myrtle Beach Division, 1981. 15

2.2-1 Year 2000 Land Use Projection for Myrtle Beach
Division ...................................... 15

3.1-1 Tidal Elevation Along Horry and Georgetown
County Coast ................................. 19

3.2-1 Seasonal Mean Local Wind Speed Versus Wind
Direction Given in Miles Per Hour (Measured
at the Myrtle Beach Air Force Base) .......... 21

3.3-1 Probability of Storm Occurrence Near Study
Area .......................................... 28

3.4-1 Average Occurring Wave Heights (ft) by
Direction and Season for the Myrtle Beach
Area (Siah et al, 1984) ....... 00 ............... 35

3.5-1 Previous Estimates of Net Littoral Drift
Rates in the Myrtle Beach Vicinity ........... 37

3.8-1 Survey Stations Cross-Reference Table ......... 46

3.9-1 Summary of Sediment Characteristics ........... 49

5-1 Summary Sediment Statistical Parameters Along
Horry County Shoreline ....................... 75

6.1-1 Inventory of Comparative Survey Data .......... 78

6.2-1 Average, Net, and Unit-Width Volume Changes
Between +10.0 ft and -3.0 ft MSL (Myrtle
Beach North and Myrtle Beach South) .......... 83

6.2-2 Average, Net and Unit-Width Changes Between
+10.0 ft and -3.0 ft MSL (Surfside and
Garden City) ................................. 84

6.2-3 Average and Net Volume Changes Between
Comparative Profile Surveys (Myrtle Beach
North and South) ............................. 85

6.2-4 Average and Net Volume Changes Between
Comparative Profile Surveys (Garden City
and Surfside) ................................ 86

6.3-1 Mean High Water Contour Position (Myrtle
Beach North Area) ............................ 93

6.3-2 Mean High Water Contour Position (Myrtl3e
Beach South Area) ... . ......................... 94

6.3-3 Mean High Water Contour Position (Garden City
and Surfside Beach) .......................... 95

6.3-4 Mean High Water Contour Movement (Garden City
and Surfside Beach) .......................... 96

6.3-5 Summary of Short-Term Shoreline Recession
Rate in Horry County ......................... 97

6.4-1 Long-Term Shoreline Accretion/Erosion Rate
(Garden City and Surfside Beach) ............. 103

6.4-2 Long-Term Shoreline Accretion/Erosion Rate
(Myrtle Beach and Myrtle Beach South Area) ... 104

6.6-1 Comparison of Profile Characteristics for the
the IPP Generated in this Study and Those
Generated in Previous Studies ................ 115

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 Horry
County Shoreline ......... .................... 118

8.1-1 Ideal Present Dune Crest Locations............ 130

~~~~~~01~ ~ ~ ~ ~ ~ ~ ~

LIST OF FIGURES

Figure Paqe

1.2-1 Study Area Location Map .......................... 4

3.1-1 Sea-Level Rise over the Last Century and
Projections .................. . .................. 17

3.2-1 Wind Rose at Myrtle Beach ........................20

3.3-1 Hurricane Tracks for Storms Impacting
South Carolina Coast, 1952-1979 .................23

3.3-2 Hurricane Tracks for Storms Impacting
South Carolina Coast, 1883-1906 ..........25

3.3-3 Hurricane Tracks for Storms Impacting
South Carolina Coast, 1887-1920 .................26

3.3-4 Crossing Axis and Circle for Storm
Statistical Analysis, Horry and
Georgetown Counties ............................. 27

3.3-5 Predicted Peak Total Combined Storm
Tides for Varying Return Intervals ..............29

3.3-6 Predicted Peak'Combined Total Storm
Tides Along Horry and Georgetown County
Shoreline ....................................... 30

3.3-7 Splash Simulation of Hurricane Hazel's
Total Combined Storm Tides Along the
South Carolina Coast ............................ 31

3.4-1 Wave Rose Offshore of Myrtle Beach ...............33

3.8-1 Survey Profile Location Map for Murrells
Inlet Monitoring Program ....................... .42

3.8-2 Beach Profile Survey and Sediment Sampling
Stations in Myrtle Beach North Study Area .......43

3.8-3 Beach Profile Survey and Sediment Sampling
Stations Between Myrtle Beach and Georgetown
County .......................................... 44

3.10-1 Typical Beach Profile of
A) Myrtle Beach North Area Near White
Point Swash
B) Lake Arrowhead ........ ......................52

3.10-2 Typical Beach Profile of
A) Springmaid Beach
B) Ocean Lake Campground ................... 54

3.10-3 Typical Beach Profile of Surfside Beach ..........57

3:10-4 Typical Beach Profile of
A) Northern End of Garden City
B) NearGarden City Pier .......................57a

5-1 Grain Size Scales and Wentworth Size Class
Descriptions .................................... 71

5-2 Example of Sediment Statistical Parameters
for Samples Collected at Station #5430
Near Arcadian Shores... ..... ... ................. 73

6.2-1 Definition Sketch for Computing Average Volume
Changes Using the Control Volume Method at
Profile #4555 ................................... 81

6.2-2 Definition Sketch for Computing Average Volume
Changes Using the Comparative Profile Segment
Method at Profile #4555 .........................82

6.2-3 Idealized Seasonal Profile Variation and the
Associated Volume Changes .......................88

6.4-1 Shoreline Movement Along Myrtle Beach North
Area ................ .................... .100

6.4-2 Shoreline Movement Along Myrtle Beach South
Area ........... ......... ......................101

6.4-3 Shoreline Movement Along Surfside Beach and
Garden City.. a........ ece........... .102

6.4-4 Long-Term Erosion Rate in Myrtle Beach North
Area . . ........... .. .. ............... . ........105

6.4-5 Long-Term Erosion Rate Between Myrtle Beach and
Georgetown County .... .. . ....................... 106

6.5-1 Equilibrium Profile Response to Sea-Level Rise..108

6.6-1 Ideal Present Profile for Myrtle Beach North
Area .... ..... . . . . . ............................. 112

6.6-2 Comparison of the Ideal Present Profile Computed
for Myrtle Beach North, Myrtle Beach and North
Myrtle Beach Shoreline Areas ... ........... .114

6.6-3 IPP for Myrtle Beach North Area ................ .117

6.7-1 Comparison Between IPP and
A) Station 5020
B) Station 4625 ...............................120

7-1 Historical Shoreline Positions Near
White Point Swash... ......... ........ 125

7-2 Historical Shoreline Positions Near
Singleton Swash ...... ................ .126

8.3-1 Predicted 25- and 50-year Storm Erosion
(Between North Myrtle Beach and Myrtle Beach)..138

8.3-2 Predicted 25- and 50-year Storm Erosion
(Between Myrtle Beach and Surfside Beach) ...... 139

9.1-1 Schematic Diagram of the Coastal Hazard
Zones .......................................... 142

9.3-1 Flood Insurance Map Near Long Bay Estate ........148

9.3-2 Definition of V-Zone Without Consideration
of Storm Impacts ...............................149

9.3-3 Predicted V-Zone Considering the Storm
Impacts Near Long Bay Estate ................... 150

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. Thke 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
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

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 likewise 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 those sections of Horry County, as well as that
portion of the Garden City section of coastline within
Georgetown County, the methodologies utilized by this study
to recommend building setbacks were similar to'the formats
developed for similar studies proposed by previous
investigators for both Myrtle Beach and North Myrtle Beach.
Simplistically, 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. It does not include short-term, and
potentially more severe erosional effects associated with
low frequency storm events (i.e., severe nor'easters,
tropical storms and hurricanes). For that reason, a
separate computer analysis has been included which models
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

-2-

and .02 respectively. A 25-year storm, for example, is an
event which would be expected to be experienced or exceeded
on the averaae, once in 25 years.

1.2 STUDY AREA
Located within the'Grand Strand, the Horry County coastline
in its entirety extends from Little River Inlet to a
location 3.4 miles north of Murrells Inlet, a shoreline
length of approximately 22 miles. From north to south, the
areas investigated include the 3.5 miles of unincorporated
shoreline beginning south of Briarcliffe Acres and extending
to Singleton Swash, Springmaid Beach, Myrtle Beach State
Park, Surfside Beach and the northern portion of Garden
City. The study area is interrupted by a shoreline segment
of approximately 10 miles, extending from Singleton Swash to
Springmaid Beach which defines the incorporated area of
Myrtle Beach, is not included in this study. This study
report referred to the area between North Myrtle Beach and
Myrtle Beach as "Myrtle Beach North" and the area between
Myrtle Beach and Georgetown County as "Myrtle Beach South".
Figure 1.2-1 shows the general location of the study area.

Extreme variability in development pressures, including both
development patterns and density, exists between Briarcliffe
Acres and Garden City. As the population along the
coastline has grown, the contribution of South Carolina's
northern beaches to the local and state economy has become
considerable. The economic value of the Grand Strand should
continue to increase as long as adequate sandy beaches
suitable for recreation are properly preserved and
maintained.

From Little River Inlet, the Grand Strand coastline follows
a general arc to North Inlet at the southernmost point.
Overall, specific stretches of Horry County's shoreline
appear to be migrating as the result of long- and short-term

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LittleR.7~

Myrtle Be'sh
-STUDY AREA

North~~~~~~~~~~~~~~~

owees~~~~~~~~~~~~~~~~~~~

30 KM

FIGURE 1.2-1
STUDY AREA LOCATION MAP

local differences in sand supply, shoreline orientation and
the proximity to inlets, and coastal structures. The effect
of sea-level rise on shoreline recession is relatively
unifoTm along the coastline and results in a persistant net
offshore sediment transport.

Coastal structures, including shoreline armoring and inlet
improvements, were employed to protect and improve the
coastal resources. In some cases, however, shoreline
hardening has resulted in shoreline instability when the
littoral processes were disturbed by man-made structures.
Problems associated 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, for
example, has altered sediment transport in the nearshore
littoral zone along the adjacent beaches.

Beach and offshore erosion is a condition that exists along
the majority of Horry County's coastal areas. Erosional
impacts from shoreline development are most directly related
to the demand for shoreline armoring or hardening. In
general, this area has had significant 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 beach
renourishment.

Groins, piers and jetties are man-made structural barriers,
each of which interrupts the natural sand transport across
the nearshore littoral zone. Net sediment transpor along
the county coastline is generally southward, with periods of
large reversals toward the north caused by lonigshore
currents. The magnitude and direction of the longshore
currents, created by waves breaking at an angle to the
coast, determine sand transport along the coastline.

and .02 respectively. A 25-year storm, for example, is an
event which would be expected to be experienced or exceeded
on the averaae, once in 25 years.

1.3 STUDY AREA
Located within the Grand Strand, the Horry County coastline
in its entirety extends from Little River Inlet to a
location 3.4 miles north of Murrells Inlet, a shoreline
length of approximately 22 miles. From north to south, the
areas investigated include the 3.5 miles of unincorporated
shoreline beginning south of Briarcliffe Acres and extending
to Singleton Swash, Springmaid Beach, Myrtle Beach State
Park, Surfside Beach and the northern portion of Garden
City. The study area is interrupted by a shoreline segment
of approximately 10 miles, extending from Singleton Swash to
Springmaid Beach which defines the incorporated area of
Myrtle Beach, is not included in this study. This study
report referred to the area between North Myrtle Beach and
Myrtle Beach as,"Myrtle Beach North" and the area between
Myrtle Beach and Georgetown County as "Myrtle Beach South".
Figure 1.2-1 shows the general location of the study area.

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 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. The scope was reduced at that time to include
field surveys (Phase II) to monitor 18 transects semi-
annually through October 1987.

The Murrells Inlet Monitoring Study provides valuable data
to assess the effects of inlet stabilization on long- and
short-term shoreline fluctuations for the Surfside and
Garden City 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 Horry County study
area.

The COE published a 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:

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.

-7-

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
jetties, while the sheltering effects of the jetties allow
minimal southerly transport within an area 2.5 miles south
from the jetties.

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 U.S. Army 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. I

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
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,

-8-

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 thirty-eight survey stations along the
Horry 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 11 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.

-9-

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.

2.0 LAND USE
2.1 EXISTING LAND USE
Horry County's establishment is said to have begun in 1731,
when Governor Robert Johnson began to lay out 11 townships
in South Carolina, among which the Kingston Township
comprised most of the land now in Horry County. Horry
County has had its name since the 1868 Constitution
(Waccamaw Regional Planning and Development Council, 1983).
Prior to the 1800's, the chief source of income was naval
stores industry, farming, and trapping. From that time
until the turn of the century, cotton was the major economic
sector in the area. By the early 1900's, however, tobacco
had replaced cotton as the major crop. Diversification of
the economy began to take place in the 1920's, when new
roads opened up many areas of the County to other markets in
the region. During the post World War II period, the
development of the coastal area as a tourist attraction
became a dominant trend.

There are eight County Census Divisions (CCD) in Horry
County.. Most of the present shorefront management study
area, except Briarcliffe Acres, is located in the Myrtle.
Beach Division, the most populated CCD. The following
presentation of land use data was extracted from the land
use plan prepared by the Waccamaw Regional Planning and
Development Council (1983).

The resident population trend in the Myrtle Beach Division
from 1960 to 1980 is shown in Table 2.1-1. It shows a sharp
increase in population from 1970 to 1980 which is more than
the total increase in the three previous decades. The net
migration into the County resulted in more than twice the
natural increase in population. Because of the predominant
tourism industry, the tourist population has a major
seasonal impact on the Grand Strand area. The tourist
population from 1972 to 1978 is shown in Table 2.1-2, which

Table 2.1-1. Myrtle Beach Census Division Resident
Population Trends (1960-1980)

% change
1960 1970 1980 1960- 1980

Myrtle Beach Division 17,619 21,211 34,827 97.7 %

Myrtle Beach 7,834 9,035 18,758 139.2 %
Surfside Beach N/A 1,329 2,522 N/A

HORRY COUNTY TOTALS 68,247 69,992 101,419 48.6 %

Source: U. S. Department of Commerce, Bureau of the Census,
Census of Population 1960. 1970. and 1980.

Table 2.1-2. Grand Strand Tourists 1972-1978

Year Tourists. % of State

1972 2,900,000 36.1 %
1973 3,400,000 36.5 %
1974 3,600,000 35.5 %
1975 3,900,000 33.7 %
1976 4,200,000 33.5 %
1977 4,800,000 33.2 %
1978 6,500,000 38.0 %

Source: South Carolina Department of Parks, Recreation
and Tourism, Travel and Tourism Data 1972-1978.

indicates an 124% increase in tourists in a six year period.
The resident population projections are shown in Table
2.1-3. The projected tourist populations are shown in Table
J'7 ~2.1-4. Because of rapid increase of permanent resident
population and the large influx of tourists, the future land
use and coastal management plan should be compatible with
the commercial and recreational needs as well as the public
safety and conservation of the coastal resources.

The land use in the study area is dominated by residential
development. The existing land use of the Myrtle Beach
Division is shown in Table 2.1-5. The land use study
* -- ~indicated that the residential development in the Grand
Strand is accelerated in a fast pace. Seasonal use accounts
for much of this growth., but permanent residential use is
also expanding. The area between North Myrtle Beach and
Myrtle Beach has developed into an area for condominiums,
apartments, and planned unit development. This same
V ~~development pattern continues toward south of Myrtle Beach.
The high cost of land, and lack of suitable land due to
marsh and flood areas and soil conditions, is making it
increasingly difficult to satisfy single-family residential
needs. Future development is expected. to continue in this
same manner for the next 20 years.

2.2 FUTURE LAND USE
As the population of the Horry County grows, there will be
additional land needed for each land use category. By
considering the existing patterns of development, future
goal and policies, and the population projection, the future
land use for the Myrtle Beach Division was projected by the
Waccamaw Regional Planning and Development Council (1983).
The projections for year 2000 are shown in Table 2.1-1.

Table 2.1-3. Population Projections for 1985, 1990, 1995, and.
2000

Census County Division 1985 1990 1995 2000

Myrtle Beach Division 42,853 50,447 60,151 69,421

Myrtle Beach 20,885 22,824 25,649 28,286
Surfside 3,122 3,709 4,312 4,903

HORRY COUNTY TOTALS 120,910 139,677 161,073 181,481

Source: South Carolina State Budget and Control Board,
Research and Statistical Services Division; and
Waccamaw Regional Planning and Development council,
1982.

Table 2.1-4. Tourist and Peak Day Population Projections for
Grand Strand, Horry County
I
i , ~ ~Il

1982 1987 1992 1997

Overnight transits 264,270 312,166 330,498 335,243
Day Visitors 38,600 44,726 51,825 60,000
Residents 52.000 70.000 89.000 103.075

Peak Day 354,870 426,892 471,323 498,418

Source: Grand Strand Environmental Impact Statement (EIS)
1977.

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Table 2.1-5. Existing Land Use Myrtle Beach Division, 1981.

% of % of
Developed Total
�.~ ~ Acres Land Land

Residential 2,470 41.6 % 4.3 %
Commerical- 537 9.0 % 0.9%
Industrial 81 1.4% 0.1%
Public & Semi-Public 1,286 21.7 % 2.2 %
Roadways and Railroads 1,563 26.3 % 2.7 %

Total Developed Land 5,937 100.0 % 10.4 %

Myrtle Beach (City) 5,916 10.4 %
Surfside Beach (Town) 1,204 2.1 %
Agricultural or Undeveloped 43,903 77.1 %

CCD Total 56,903 100.0 %

Source: Waccamaw Regional Planning and Development Council,
1981.

1~~~~~~~~~~~~

Table 2.2-1. Year 2000 Land Use Projections for Myrtle Beach
Division.

1981 2000

Population 36,232

Residential (acres) 2,470 5,765

Commercial (acres) 537 1,333

Industrial (acres) 81 199

Public & Semi-Public (acres) 1,286 3,188

Roadway (acres) 1,563 3,876

TOTAL DEVELOPED LAND (acres) 5,937 14,361

Source: Waccamaw Regional Planning and Development Council, 1982

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 im 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 the 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.

-16-

X- 3--
0

;> �/ Results from
2- I O�7!!:42 ~~~~EPA Study
< (1984)

Post | /;
[Century | /.1 . ' Projection of
/ I'/..~'_ Present Trend

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
4 ~~~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 o~er
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 sunmer 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

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

c._~~~~~~~~~~~~~~~

AVERAGE WIND ROSE FOR 1942-19'47
&1949-1972 AT MYRTLE BEACH, SOUTH CAROLINA

FIGURE 3.2-1
WIND ROSE AT MYRTLE BEACH, SOUTH
CAROLINA
WIN RSE T MY`WSW ESE SUT
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... -

!-�~~~~~~~~~~~~~~~

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
resultingin 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.

-22-

, KEY:
TROPICAL STORM STAGE
j HURRICANE STAGE

0,9
/~~~~~~~~~~

FRMz92 TO 97
~~~~~~~~'~~~~~, N.

'"../

�~~~~~~ So,
!~ ' /~~~~

C.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
� � �~~~~~~~~~~

�~~~~~~~~~~~~
FIGURE 3.3-1~~

j ~~~~~~~.

Historically significant hurricanes that have tracked in
relatively close proximity to the northern portion of the
South Carolina coast have been analyzed by FEMA'to determine
site-specific hurricane characteristics.. These historical
storm parameters were applied in 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 (1983)
study estimates that 136 landfalling, exiting and alongshore
storms can be expected to track within 150 nm of a point
along the Horry and 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.

-24-

KEY-~~~~~~~~~~

TROPICAL STORM STAGE
HURRICANE STAGE

00001,0

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

KEY:
*-uTROPICAL STORM STAGE
HURRICANE STAGE

~~~190

4--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0

- - SC~~~~~~~~~~~~ALE IN MAUTIt AL. MILES

FIGURE 3.3-4
CROSSING AXIS AND CIRCLE FOR STORM
STATISTICAL ANALYSIS - HORRY AND
- ~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 (1975) predicted Hurricane Hazel's
storm tide variation along the coast from Georgia to the
South Carolina/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.

FREQUENCY
0.10 0.05 0.04 0.02 0.01
22

21
TIDE FREQUENCIES
20

17
GEORGETOWN COUNTY
u 16
_5. //

I3: //.. 1-HoRRY COUNTY
I ii
14 J

I 13 /
LU
...I

6
10 25 50 100 500
RETURN PERIOD (years)

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

I<- GEORGETOWN COUNTY HORRY COUNTY
20
500-YEAR RETURN PERIOD
17.8 17.8 17.8 17.8 17.9 17.9 17.9
- - 17. 9 - ; 17.4 17.4 17.4
17.9

100-YEAR RETURN PERIOD
15 - 14.3 14.3 143 14.3 14.3 14.3 14.3
E 14.3
1 .0 13.0 13.0

50-YEAR RETURN PERIOD 11.3 1 5 112 1s10

IL -I ,.

'1- 10-YEAR RETURN PERIOD 11.5
7.1 7.1 _ 7_13 7-713 6611,2

F- -5 - .11.0

0o i I7 I I I I I I I I I I I I7.

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 .. v CHARELSTONj GEORGETOWNq. HORRY
H-COUNTY - I- COUNTY COUNTY~ COUNTY
GA SO ~COLLETON sN
COUNTY

20 -

~~~~~~~~~EIO

100-YEAR RETURN PERIOD/
10-

5 ~~~~~~~HURRICANE HAZEL

0 20 40 60 80 100 120 140 160 180

DISTANCE FROM GAISO BORDER (m

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

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 33.640 north and
longitude 78.130 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

-32-

STRTION 47
JAl. - DEC.
51440 CASES

OVER 2.99 m

2.60-2 .99
2.00-2.49 H2cozo Kcloi~o

1.00-1.49 N

0.60-0.99 N

0.00-0.49 H

FIGURE 3.4-1
WAVE ROSE OFFSHORE OF MYRTLE BEACH

()~~~ 0 0

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 II 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 ESTIMATES
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.

-34-

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

I :

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 volumes. 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.

-36-

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.

S~( 5 0 0) S

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 25h, 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 a valuable indicator to
measure erosion trends and assess littoral processes.

-38-

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

To qualitatively depict shoreline changes, the National0
ocean services (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,0
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
V ~~high water line relative to 1929 NGVD. Shoreline movement
maps covering the study area were compiled 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 horizontal'ly 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 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), these data will
be useful in predicting local long-term erosion rates. in
addition, the shoreline recession associated with sea-level
rise and storm effects can be more accurately quantified.

-39-

During a 1955-58 COE post-hurricane reconnaissance study for
O*-- Horry and Georgetown Counties (COE,1983), surveys were
conducted within Horry County along Surfside Beach and
Garden City shoreline areas. In April 1958, 12 stations
were established and profiles surveyed, of which 4 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. In addition, 11 new stations were established along
the shoreline between White Point Swash and Singleton Swash.
Along the shoreline fronting Myrtle Beach State Park and
Surfside Beach the COE established control points and
surveyed 7 new stations. All beach profiles were surveyed
by the Charleston District COE and referenced to MSL.
Documentation of several profile surveys, provided by the
COE, required considerable investigation to vertically and
horizontally adjust these data into the 1986 replicated
station data. Station control points (Bench Marks) were
located and surveyed by Sur Tech (registered land surveyers)
to assure vertical control for the analysis of comparative
beach profiles in the present study.

Comprehensive monitoring to evaluate both the effects of the
Murrell's 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 and extending 7 miles south to Midway Inlet.
Monitoring stations, extending both north and south, were
located at greater spacing intervals with increasing
distance from the inlet. A total of 43 offshore profiles
were surveyed quarterly by the Charleston District COE over
a 5-year period, after which 18 profiles are to be surveyed

-40-

on a semi-annual basis through 1987. Profiles were surveyed
offshore to the -18.0 ft contour for all profiles, using a
fathometer at high tide to overlap points surveyed from land
using a rod and level.

Profiles along the Horry County study area were located
along the Surfside and Garden City shoreline extending from
2500 ft north of Surfside Fishing Pier south 2.8 miles to a
point approximately 500 ft north of Kingfishers Pier. These
profile transects were spaced at 5000 ft intervals
perpendicular to the 1977 shoreline as shown in Figure 3.8-
1.

Comparative beach surveys were analyzed using the CERC-
developed program Interactive Survey Reduction Program
(ISRP). Capabilities of ISRP include data reduction,
editing, plotting and volumetric changes between successive
surveys along the length of the profile.
L -~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I
A beach profile survey program was conducted by the project
team in April 1986. After reviewing the historical beach
profile data collected by U.S. COE and other investigators
between 1958 and 1984, 38 survey stations were established
in the Horry County study area. The spacing between the
stations was generally 1/3 mile. Of these stations, 22
stations coincided with the historical survey stations which
were either recovered or replicated according to the
historical survey notes. The remaining 16 stations were new
stations established during the present study. There were
13 stations located in the Myrtle Beach North area, 11 in
the Myrtle Beach South area, 9 in Surfside Beach, and 5 in
Garden City within Horry County. Figures 3.8-2 and 3.8-3
show the locations of each survey station.

Each survey station consisted of a survey monument and
corresponding benchmark (BM). The survey monument provides

-41-

0,,

SURVSIDE BEACH

14
GLRTEN CIET BEACH

MURRELLS INLET MG

�`.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~6

MURRELLS~~~~~~~~~4 MURRILL INLIIG ROR

X THH~~~~~~~~~~~~~~~~ OUJNES

... .~ ......

MAP SHOWIN6 LOCATION OF
HORNY COUNTY IN"SOUTH CAROLINA

SCALE
I 01 2 4 MILES

1 0 1 2 3 4 ~ ~~~5 6 XILOMETERS

LEGEND

MYATLE BEACH 5225 NEW STATIONS
Pd j446 ~~~~5210 EXISTING STATIONS
(S) SEDIMENT SAMPLES

'1~RTI riff~l Ii MAC~l 5255

-ilk- lit 6502

SAMP~~~~~~~~~~~~~~~LING 1A STATEOSINMRLBEC

NORTH~~~~~~~~~UFD STDYAEAC-52
512~~~~~0

-x GROVEG~~~~~~~~~ EGEN
shift. ~ ~ ~ ~ ~ ~ ~ 25 E TAIN
* 5210 EXISTING STATIONS~~~~~~~~~~~~~~~~~~~~~~~1

C~~~~~~eS~~~ ~CALEE

FIGURE~~~~~~~~~~M 3.3-

BEACH PROFI~~~~~~~~~~LEGSREY ND SDMN

~~~~~~~~~~~~~~~~~~~21EXSAMTING STATIONS BTENMRL
BEACH AND GEORGETOWN COUNTY42

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
survey notes which include general location descriptions,
monument descriptions and tie-in distances to nearby
landmarks, profile azimuths and relative offsets. The
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,X. 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
11 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 Figures 3.8-2 and 3.8-3 and Table 3.8-1

3.9 SEDIMENT DATA
Previous studies to evaluate the native beach sand on Horry
County's shoreline for grain size characteristics and
statistics were collected and documented for this 1983 COE

-45-

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

CERC # COE # Sediment
Area SCCC # (1979-82) (1958-84) Bearing Sample

Myrtle Beach
North 5465 -- -- S38E
5460 -- 78+08 S32E x
5455 -- 98+08 S32E
5450 -- 118+08 S32E
5445 -- 138+08 S32E x
5440 -- 158+08 S32E
5435 -- 178+08 S32E
5430 -- 198+08 S32E x
5425 -- 218+08 S32E
5420 -- 238+08 S34E
5415 -- 258+08 S36E
5410 -- 278+08 S38E x
5405 -- -- S38E

Myrtle Beach
South 5255 -- -- S44E
5250 -- -- S44E
5245 -- 500+00 S42E x
5240 -- 540+00 S50E
5235 -- 540+00 S50E
5230 -- -- S48E
52251 -- 565+00 S54E x
5220 -- -- S54E
5215 -- 594+55 S48E
5210 -- 610+00 S50E
5205 -- 630+00' S50E x

Surfside
Beach 5145 -- 650+00 S44E
5140 -- -- S46E
5135 341+50 -- S52E x
5130 -- -- S44E
5125 -- -- S44E
5120 -- 71+08 S44E
5115 291+50 -- S54E x
5110 -- 93+33 S44E
5105 -- -- S44E

Garden
City 5025 241+50 -- S53E x
5020 -- 151+08 S48E
5015 191+50 -- S55E x
5010 -- 182+70 S53E
5005 175+00 -- S54E

Sources: Applied Technology and Management, Inc. and
Olsen Associates, Inc. 1986

Table 8.1-1. Ideal Present Dune Crest Locations

Station IPS Location (ft)*

Garden City

5005 89
5010
5115 114
5020 174
5025 175

Surfside Beach

5105 159
5110 194
5115 210
5120 233
5125 296
5130 281
5135 219
5140 193
5145 -16

Mvrtle Beach South

5205 -13!
5210 -14
5215 -19
Lj. ~ 5220 80
5225 -6
5230 16
5235 -12
5240 -2
5245 8
5250 -6
5255 -17

Myrtle Beach North

5404 -12
5410 -6
5415 -49
5420 -16
5425 -23
5430 -30
5435 -37
5440 -23
5445 -21
5450 -21
5455 -17
5460 7

*IPS location is measured seaward from the survey monument.

Reconnaissance Report, North Myrtle Beach Study (1986) and
Myrtle Beach Study.. References to beach and dune sediments
are described qualitatively in the geomorphology sections of
recent shoreline studies (CSE; 1985 and Cubit, 1981)
apparently sediment sampling was not included as a data
collection task.

To provide basic sediment grain size statistics such as mean
phi, median phi, and the relative grain size
distributions(phi-84 and phi-16) along the Myrtle Beach
shoreline, a summary of data collected in a 1955 COE study
is presented. Surface sand samples were taken at Myrtle
Beach during September and October field reconnaissane
survey and analysed 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'analysed 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 "at water's edge".

Beach sediment samples along North Myrtle Beach (Kana, et.
al.) were colleted 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. They descibed these samples 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

-48-

Table 3.9-1. Summary of Sediment Characteristics

NATIVE BEACH SAND AT THE MID-TIDE LEVEL

AVERAGE Phi84 _/ Phil6 _ Phi Mean Phi sorting/ Median Dia (mm)/

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 (0.33mm) 0.43 0.27

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

/ 84% of the sand has a diameter greater than that shown.
2/ 16% of the sand has a diameter greater than that shown.
1/ Average of Phi and Phil6.
A/ One-half the difference between Phi8A and Phii.
/ Half the sand is larger and half smaller than Ehe 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

0~~ 0 0) 0 0 0

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, MEW and MLW. The sampling
stations are shown in Figures 3.8-2 and 3.8-3 and Table 3.8-
1. The results of the sediment analysis are presented in
Section 5.

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
supply.

In general, the intertidal portion of the beaches in the
study area may be classified as mildly sloping beach of low
elevation. This combination results in a relatively wide,
low-tide beach, and also results in minimal or nonexistent
high tide beaches at many locations. This characteristic is
a result of the considerable 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 beach face is interrupted by an upper
beach berm above the mean high water line (MHWL). It leads
up to the dunes or to the immediate upland where the dunes

-50-

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 expevted
during the month of the survey, i.e. April. The shorelines
adjacent to tidal swashes along barrier islands within the
study area exhibit southerly migration trends in the form of
migrating spits.

White Point Swash to Sinaleton Swash
The northern 1.7 miles of this reach are characterized by a
well-developed, well-vegetated dune system consisting of 2
and 3 distinct dune ridges averaging +15 to +18 feet in
elevation (NGVD). During the survey, the seawardmost dunes
along the entire northern reach showed some evidence of
scarping resulting from high water levels and run-up
associated with storms and/or abnormally high tides.
Scarping is potentially indicative of a receding shoreline.
At the toe of these dunes begins the beach face at an
average elevation of +6 ft. Due to the absence of a beach
berm, the beach profile slopes continuously towards the
ocean. A somewhat wider and flatter beach exists along the
northernmost 1,000 ft of this reach as a direct result of
the small shoal system in the vicinity of White Point Swash.
Figure 3.10-la presents a profile typical of this stretch of
shoreline.

The remaining 2.2 miles of this reach, extending south to
Singleton Swash, have been significantly affected and
altered by coastal development. As a result, the high dune
ridges that characterized the northern reach are virtually
non-existent along the southern reach. Likewise, vegetation
has been severely depleted here. The upper or back beach
profile is typically defined by either shoreline armoring or
the low (+10 ft or less) sand mounds which is typical of the
campgrounds in the study area. Virtually the entire beach

Profile Line 445
- 16 APR 86 1330
.

15 -

-5-

-il

S r
-15: -100 -50 0 50 100 150 200 2�0 300 350 400
0Dstancr. FT

TYIA ProfAle Line 415
-W6 PPO6N S540

I A
I

- -.............

-to

-SO -.00 -50 a SO too :50 200 250 300 ag50 )O
it arnel. FT

FIGURE 3.10-1
TYPICAL BEACH PROFILE OF
A) MYRTLE BEACH NORTH AREA NEAR
WHITE POINT SWASH
B) LAKE ARROWHEAD

face is below +5 ft in elevation resulting in a very narrow
to sometimes non-existent high-tide beach. The beach face
is also steeper at the southern end and therefore narrower
at all phases of the tide. A small drainage.swash is
located at the northern end of this reach -as iwell as
culverts at varying intervals as one progresses southward.
Typically, these small swashes and culverts result is a
lowering of the beach face in their immediate vicinity,
however, the significance of their effects on littoral
transport was not determined. Figure 3.10-lb typifies the
beach profile of this section of shoreline.

Sprincmaid Beach to Ocean Lake Camparound
A distinct variation in beach morphology exists between the
northern and southern reaches of this segment of shoreline.
The northernmost 1.5-mile reach, extending along Springmaid
Beach and Myrtle Beach State Park, exhibits a well-vegetated
back beach profile and a single, apparently unaltered dune
ridge with elevations ranging from +12.5 to +15 feet. The
seaward toe of this ridge meets a narrow berm at an average
elevation of about +9 ft. The transition from berm to beach
face occurs at approximately +7 ft elevation, whereupon the
beach presently slopes rather steeply seaward. Exposed peat
deposits were present near the mean water line, which is a
phenomenon usually indicative of long-term ocean
encroachment. A small drainage swash empties onto the beach
just south of the State Park Pier which has effectively
lowered the beach face in its immediate vicinity. Figure
3.10-2a presents a profile typical of the shoreline along
this reach during the April, 1986 survey.

The southern 2.4 miles of shoreline extending south to
Surfside Beach are characterized by low dunes and a
relatively steep beach face. These dunes can be described
as a series of sand mounds rarely exceeding +10 ft in
elevation. This condition is probably due to the high

-53-

25 F Profile Line 250
8 APR56 3.40

�.~~~~~~P

~~~~~~~~Dstac.F

,, C ~ ~~~~~~~~~~~Profile Line 2to

8 APR 86 035
20 i-

S-

-10

-ISO -100 -50 0 50 to o ISO 200 W;O qoo 350 400

Distance. FT

FIGURE 3.10-2
TYPICAL BEACH PROFILE OF
A) SPRINGMAID BEACH
B) OCEAN LAKE CAMPGROUND)

volume of pedestrian foot traffic crossing the dunes when
accessing the beach from the campgrounds and trailer parks.
Fronting this segment of shoreline are a significant number
of high-density trailer parks and campground developments.
Specific attention should be given to the region near
profile 5220, the northern extent of Lakewood Campground,
where beach elevations barely reach +8 ft. Natural
vegetation has been maintained to some degree along the
northern half of this reach but this quickly diminishes
progressively southward. Generally, a narrow plateau or
berm meets the seaward toe of the dunes at approximately +7
ft in elevation and descends to the +5 ft contour at which
point the beach face slopes rather steeply into the ocean.
This steep beach face results in a relatively narrower beach
at all phases of the tide. Recent evidence of scarping of
the seaward berm face near the +5 ft contour elevation was
observed during the field study. Small drainage swashes
exist at the immediate northern, central and southern
portions of this reach which, causes a local lowering of the
beach face. A typical profile along this shoreline reach is
presented in Figure 3.10-2b.

Surfside Beach
Surfside Beach is characterized by a well-vegetated back
beach system with dune crest elevations rarely below +10 ft
along this approximately 2.2-mile stretch of shoreline. In
its natural state, a single dune ridge with an average crest
L. elevation of +12 ft exists at the seaward edge of this back
beach. Along much of the Surfside Beach shoreline, an
artificial dune has been constructed to elevations exceeding
+15 ft. This artificial dune is unvegetated and consists of
coarser grain sizes than normally found in natural dunes,
indicating that the dune was created from sand scraped from
the lower intertidal beach. Along unaltered, natural
reaches of shoreline, berm widths range from 20 ft to 30 ft
at elevations between +8 ft and +9 ft. The beach face slope

-55-

steepens progressively southward at Surfside Beach. Figure
3.10-3 presents the typical Surfside Beach profile.

An exception to this general morphological characterization
of the study area is the'beach in front of the Holiday Inn
at the north end of Surfside Beach. At this location the
construction of a seawall, +13 ft in elevation, defines the
back beach. The sandy beach at this location consists of a
25 ft-wide berm at 8 ft elevation, dropping steeply to the
ocean at high tide. The beach in the immediate vicinity of
the Surfside Pier is also structurally armored with a
seawall. The pier appears to act as a partial sediment trap
(i.e. groin) thereby resulting in a generally wider beach at
that location. Several culverts at intermittent locations,
as well as drainage swashes 1,100 ft south and 1,950 ft
north of the Surfside Pier, act to lower the beach face in
their immediate vicinity.

Garden City Beach
The northern 1.5 miles of Garden City Beach lie within Horry
County. The back beach along the entire stretch of this
shoreline has been altered by shorefront development. The
'transition from back beach to beach face is defined by an
unvegetated artificial dune at the extreme north end and
seawalls along the central and southern portions. Natural
salt-tolerant vegetation has been severely depleted. The
crest of the artificial dune at the north end of this reach
averages +13 ft in height and 20 ft in width and consists of
coarser-than-average sediment sizes. A characteristic +25
ft-wide berm meets the toe of the dune at the +8.5 ft
contour and the beach face at the approximate +7.5 ft
contour. The beach face slopes rather steeply to the high
water line whereupon it flattens out considerably towards
the ocean. Figure 3.10-4a illustrates this artificial dune
on a typical profile along the north end of Garden City
Beach.

-56-

a r Profile Line 1tS
,~;~~~~~ --~~ 9g ~ AR a6 14W6

15 r

lo
LI

------------ i----------

a0 so 00 150 200 250 300 350 400 450 500 550
Oistanc. FT

FIGURE 3.10-3
TYPICAL BEACH PROFILE OF SURFSIDE
BEACH

Profile Line 25
-0 A cc86- 920
A

- .

s0 �00 150 200 250 �00 350 400 45C o0. 5. eg
ODisaanca. FT

B 20

-10

OLstanc. FT

FIGURE 3.10-4
TYPICAL BEACH PROFILE OF
A) NORTHERN END OF GARDEN CITY
B) NEAR GARDEN CITY PIER

The shoreline along the central and southern portion of this
reach exhibit a back beach system that is often paved or
landscaped to an elevation of less t~ian +10 ft and located
immediately landward of the beach face. Progressing
landward, elevations along this shoreline reach are
characteristically between +5 ft and +8 ft, resulting in a
low-lying upland region immediately adjacent to the back
beach system. Seaward of the back beach system, the sandy
beach face intersects seawalls or adjacent beach accesses at
an elevation of +5 ft to +6 ft and steeply recedes to the
high-water line. A minimal high-tide beach exists at this
location. At survey station 5010, located near the Garden
City Pier, the beach face is very low as it intersects the
base of the seawall at elevation +3.6 ft. As a result, the
beach is nonexistent at this location at high tide. Figure
3.10-4b depicts a typical seawalled profile along this
shoreline segment.

3.11 COASTAL ST~RUCTURE INVENTORY
A wide variety of coastal structures exist throughout the
study area. These structures vary greatly as to their type,
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 which are often referred to as
a "soft structure". Structure functions include 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

-58-

varies among concrete, timber, rock, gravel, filter cloth
and beach sand. Frequency of occurrence ranges from the
heavily armored shoreline reaches of North Myrtle Beach to
the virtually structure-free beach along t-he Myrtle Beach
State Park shoreline.

The inventory maps, included as Appendix D, provide a
detailed depiction of the type, composition and frequency of
structures presently in existence along the Horry County
study area. The following paragraphs include 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.

Garden City Beach
Approximately 75% of the shoreline along that portion of
Garden City Beach that falls within Horry County is armored.
The remaining portion consists either of public right-of-
ways, undeveloped shoreline or sections where artificial
dunes have been constructed. The majority of shoreline
armoring takes the form of timber seawalls of varying
elevation and overall state of repair. These timber
seawalls serve dual purposes: to withstand forces
associated with water levels and wave run-up resulting from
a moderate storm, and to serve as retaining walls to hold
backfill ~or swimming pools, patios and other upland
development facilities.

Concrete seawalls of significantly greater structural
integrity are present at the Garden City Pier and in front
of several larger, newer condominiums. Stone rip-rap that
serves to attenuate scour and absorb wave energy at the base
of the seawalls is present at several locations along this
shoreline reach. Numerous discontinuities in lateral and

-59-

seaward extent of shoreline armoring is the result of
individual property owners building to different
specifications along their property lines. As a result,
back beach erosion is often intensified along these sections
as they undergo the effects of flanking iniduced by adjacent
seawalls.

The majority of unarmored shoreline is associated with the
northernmost 1,000 ft of Garden City Beach. The seawardmost
dune line along this stretch of beach has been enhanced by
fill material scraped from the inter-tidal zone. Generally
this sand is placed on top of and adjacent to the seaward
face of the existing dune and sculpted to a designated
elevation. Enhancement of the dune system makes it a more
effective barrier to landward encroachment of the ocean
during storms and it provides the dune system with an
�ncreased reservoir of sand prior to erosion of upland
property.

The pier at Garden City is owned and operated by the
adjacent Kingfisher Inn and is officially named the
Kingfisher Pier. Built in the 1940's, it was destroyed by
Hurricane Hazel in 1954 and rebuilt immediately thereafter.
It has been repaired several times and in 1979 was expanded
to its current 720 ft length and 20 ft width. The owners
constructed a concrete block wall perpendicular to the
shoreline at the base of the pier to function as a groin to
retain sand. A slight buildup of sand was noted on the
updrift side of the wall during the field survey. This
concrete seawall does not function to pose significantly
block littoral transport as it does not extend seaward to
the mean high water line. The pier appears to be
structurally sound to endure moderate storm conditions.

Surfside Beach
With the exception of an approximately 300 ft concrete

-60-

seawall at the Surfside Pier and the 310 ft concrete seawall
fronting the Holiday Inn to the north, the Surfside Beach
shoreline is unarmored. Both of these seawalls serve to
protect and retain the upland amenities that are part of the
pierfront and hotel complex. Approximately 1.5 miles of
~* Surfside Beach shoreline, divided over several sections, has
continual dune restoration as the result of additional sand
fill material scraped from the inter-tidal beach. The
purpose and procedure of this sand scraping operation is
*' similar to that described previously for Garden City Beach.
These beach-scraping projects have been employed since the
late 1970's (SCCC Permit Review) as a means to provide
upland protection during storms along otherwise low-lying
:* reaches of shoreline.

Myrtle Beach South
Of the approximately 4 miles of shoreline extending north
from Surfside Beach through Springmaid Beach, only 1,200 ft
fronting Lakewood Campground is armored with
shore-protection structures. The structures along this
stretch consist of stone rip-rap placed at a maximum
* elevation of +12.5 ft against a concrete block wall. The
rip-rap serves to protect this wall and adjacent uplands
from erosion and structural damage that may be caused by
higher-than-normal water levels and wave heights.

Stone rip-rap extends approximately perpendicular to the
shoreline along the swash that separates Lakewood and
Pirateland Campgrounds. The rip-rap serves to prevent any
further southerly migration of the swash and extends only as
far seaward as the mean high water line. Therefore it
probably does not have significant impacts on littoral
processes.

Oi.
Two piers are present along this stretch of shoreline. The
pier at Myrtle Beach State Park was originally built in the

-61-

1940's about one-half mile north of its present location.
In 1954, Hurricane Hazel destroyed most the of pier except
for the pilings. The pier was subsequently rebuilt on top
of these pilings at its present location in accordance with
a request from the Myrtle Beach Air Force Base. Owned and
operated by the State of South Carolina, the pier is 720 ft
long (personal communication, Merl Roads).

Springmaid Pier was built in 1973 in conjunction with the
Springmaid Beach development and is currently owned and
operated by Spring Textile. It is approximately 1,050 ft in
length and has a deck elevation of +25 ft. The pier serves
as an official weather station for the U.S. Department of
Commerce. Both this pier and the State Park Pier appear to
be structurally sound.

Sinaleton Swash to White Point Swash
The southern end of that portion of Myrtle Beach shoreline
that extends from Singleton Swash north to White Point Swash
is lined with an assortment of seawalls, bulkheads, and rip-
rap. Shoreline armoring differs considerably in height,
eastern extent and design to exhibit significant shoreline
irregularity. The shoreline along this southern reach is
characterized by seawalls of varying elevations and
horizontal offsets. At several locations, the exposed toe
of the seawalls is generally no higher than about the high
water line. The offset between two adjacent seawalls often
results in localized accretion and erosion at various
location along this shoreline reach. The majority of the
seawalls along this reach appear to be structurally sound,
with the exception of the timber bulkhead in front of the
Hilton Hotel that appear to retain landscaped fill only.
Commencing 1.75 miles north of Singleton Swash and extending
to White Point Swash, the shoreline is entirely unarmored.

-62-

4.0 SHOREFRONT DEVELOPMENT PATTERNS
Shorefront development along the section of Horry County
shoreline encompassed in this study may be generally
classified as commercial and high-density multi-family.
With the exception of sections of Surfside Beach and the
single-family residential area just south of Myrtle Beach
State Park, virtually the entire study area shoreline is
lined with high-rise hotels and condominiums, low-rise
motels, campgrounds and mobile home parks. This is in
contrast to the Georgetown County shoreline, where virtually
all buildings are either single-family residences,
relatively low-density multi-family condominiums or resort
complexes. Also in contrast to Georgetown County is the
fact that only about 20% of the Horry County study area
shoreline remains undeveloped while approximately 48% of the
Georgetown County study area is still undeveloped. The
following paragraphs present a more detailed breakdown of
the shoreline development patterns along the Horry County
study area.

Garden City Beach
With the the exception of a few vacant oceanfront lots, the
entire 1.8-mile Horry County portion of Garden City Beach
shoreline has been intensely developed. The 0.35-mile reach
south of Garden City Pier consists primarily of single-
family residences. Extending north from the pier, shoreline
development becomes increasingly high-density multi-family
and/or commercial. In all, development along the Garden
City Beach (Horry County) shoreline is approximately 62%
multi-family/commercial and 38% single-family residence.
Most of the multi-family/commercial development has been
constructed in the last 10 years while the majority of
single-family residences are considerably older. Appendix E
provides a chronological history of development trends along
the Garden City shoreline. Figure 4.0-1 and 4.0-2 show
examples of these exhibits. A discussion of these trends

-63-

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follows.

Garden City Beach DeveloPment History
Of specific interest to the South Carolina Coa.tal 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
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 1"
= 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 buildings that were
razed to make room for newer structures, however, the
majority of those buildings erected along the coastline
after 1982 have been included.

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

-66-

that time. Pat example, post-storm photography indicates
* ~~~that approximately 75 homes within a one-mile radius of the
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 their
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
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

-67-

trends have consisted typically of single-family residences
in the Garden City Point region and multi-family
condominiums and high-rises in northern Garden City.

Surfside Beach
The 2.1 miles of shoreline within the incorporated
boundaries of Surfside Beach represents the highest
percentage of single-family residence of any reach along the
study area. Commercial development is generally limited to
the immediate vicinity of the Surfside Beach Pier and the.
Holiday Inn.to the north. Within the last 5 to 10 years,
several condominium complexes have been constructed at
intermittent locations along the shoreline. These complexes
are generally low in density, ranging from 8 to 20 units.
Most of the single-family residences are considerably older
and in several cases, homes have been demolished to make way
for new condominium development. In all, development along
the Surfside Beach shoreline is approximately 68% single-
family residences, 16% multi-family/commercial and 16%
undeveloped.

Mvrtle Beach South
Development trends exhibit distinct variations along this
section of shoreline extending 3.9 miles north of Surfside
Beach to the incorporated city limits of Myrtle Beach. The
southern 2.4 mile reach is entirely multi-family/commercial
consisting primarily of campgrounds and mobile home parks.
Several new high-rise condominiums were built recently just
south of the Lakewood campgrounds. Commencing north of the
Pirateland campground/mobile home complex, single-family
residences extend for some 2,000' to Myrtle Beach State
Park. The Park shoreline is approximately 1.1 miles in
length and is entirely undeveloped. Springmaid Beach,
extending 0.4 miles north of the Park, includes a campground
and adjacent resort complex and may be classified as multi-
family/commercial. Overall, this 3.9 mile stretch of

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shoreline is approximately 62% multi-family/commercial, 10%
single-family residence and 28% undeveloped.

Myrtle Beach North
Development trends along the shoreline extending from
Singleton Swash north to White Point Swash exhibit a
distinct variation between its north and south extremities.
With the exception of the undeveloped portions along the
southernmost 500' and a 700' gap near its midpoint, the
southern reach of this shoreline is almost entirely multi-
family/commercial. Hotels and condominiums line the
southernmost 0.65 miles of this reach while campgrounds and
mobile home parks are found over the remaining northern
portion. The northern half of this shoreline is entirely
undeveloped. The residential communities of Lake Arrowhead
Dunes and Briarcliffe Acres, while maintaining access to the
beach, have built well landward of the shoreline, leaving it
in its natural state. Overall, this shoreline may be
classified as 40% undeveloped, primarily along the northern
half, and;51% multi-family/commercial entirely along the
southern half.

-69-

5.0 SEDIMENT ANALYSIS
Beach sediment data were collected at 11 stations within the
Horry County study area. With the exception of Garden City
(1955), sediment data collection-has not been included in
previous investigations along the local shoreline of
concern. Selection of the sample locations was done in
consideration of the proximity to inlets, piers and
shorefront structures to accurately represent the local
shoreline sand characteristics along specific reaches.

Sediment samples were taken at approximately every third
station and at stations adjacent to inlets to provide
information on sediment statistics and grainsize
distribution. 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. 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) inits which are related to grain
diameter by the expression: 0 = -log2 (mm). Figure 5.0-
1 presents grain size scales with conversion 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 portion (<1%) of the sample grains are 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 with a brief description of
the visual characteristics of the remaining pan fraction
noted. Although the majority of the samples were comprised

-70-

Millimeters Microns Phi (W)' 'entworth Size Class
(I Kilometer)
-20
4096 -12
1024 -10 Boulder (-8 to -12$)
-256 -8
64 -6 Cobble (-6 to -84) u
16 ' -4 Pebble (-2 to -6) >
4 -2 .
3.36 -1.75
2.83 -1.5 Granule
2.38 -1.25
2.00 -1.0
1.68 -0.75
1.41 -0.5 Very coarse sand
1.19 -0.25
1.00 0.0
0.84 0.25
0.71 0.5 Coarse sand
0.59 . 0.75
0.50- 500 .0
0.42 420 1.25
0.35 350 1.5 Medium sand
0.30 300 1.75
0.25 250 2.0 '.
0.210 210 2.25 v/
0.177 177 2.5 Fine sand
0.149 149 2.75
0.125 - 125 5 3.0
0.105 105 3.25
0.088 88 3.5 Very fine sand
0.074 74 3.75
-0.0625-- 62.5 4.0
0.053 53 4.25
0.044 44 4.5 Coarse silt
0.037 37 4.75
-0.031 31 5.0
0.0156 15.6 6.0 Medium silt
0.0078 7.8 7.0 Fine silt
0.0039 3.9 8.0 Very fine silt
0.0020 2.0 9.0
0.00098 0.98 10.0 Clay
0.00049 0.49 11.0 (Some use 2$ 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)

S~~~~~~~~~~~~~~~~~~~~

of grains smaller than 0.75 phi, a few samples contained an
unusually large fraction of very coarse sand sizes with0
shell fragments.

Grain size data were entered into a computer data base and
statistically analysed 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 of sediment sizes as opposed to
alternative methods (Inman, 1952) which include only the
distribution of sizes within the first standard deviation.
The methods of Folk and Ward adequately analyze data which
are skewed or demonstrate a bi-modal distribution.

Mean grain size, median grain size, standard deviation,
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, weighti retained, cumulative weight, weight
percent and cumulative percent are presented for each sample
in Appendix B. Typi~cal statistical parameters for sediment
samples collected at the toe of seawall and mean high water
line for Station #5430 are presented in Figure 5.0-2. Most
commonly, to characterize a sample, the average grain size
(mean) and the standard deviation (a ~) or degree of
sorting are discussed. The greater the standard deviation,
the less the sorting and greater variability of sediment
sizes.

For more specific analysis,, skewness ()as a measure of
the degree of departure from a normal distribution of grain
sizes is computed. A positive value is skewed (contains a
greater range of sediment sizes) to the right and a negative
value (excess coarse grains) is skewed to the left.
Kurtosis ( j3) is a measure of the peakedness of the
distribution of sediment sizes, where j3=1.0 is associated

-72-

CUMULATIVE FREQUENCY CURVE OF SAMPLE- 5430 TOSW CUMULATIVE FREQUENCY CURVE OF SAMPLE: 5430 MHW

0 ' 60 2.0 0 -o D o 2.0 3.04 10

~~~~~~~In I In. I i
1-3~~~~GAI IEIil G A N S Z M

-5 1 0In (a0a

(20 t o 5 9 1

0~~~~~~~~~~~~~~~~~~~~~~~~~~~~37 2165 -. 1O. .1
PAN ~ ~ ~ ~ ~ 20 la.0 4.00A
ST~GATINSICE (H)GAIN SIZE (TEI)
,.,ED ~ ~ IAN 4 STT IAL PREEti
6RAP ~ ~ GRI SIZE Uf)GAN SIZ ED(IAN-
INLSIVPE U43Rs1 OPH E, S90.3 TAIIND43 ARPLE D401M ~EV IS 4SATION. 134 GRPHI
INCLSIVE6RA PROJSECT. SCCC SAMPL WINCLUSIV 22. GRASPHIJC tTAN,l DEITCCC ~ SAPEHIGT.5 .5 RM

PHIC WEIGHSIS C.IUNTE IHTCUMLAUSIVE 6RPHIWIHI CUUAiVEW WEIGHT CUMUATI
RET. 1131 HEI~~~~~~~~~~~~~~~~~~~~~~~~GHTHI 10VECN ECH E.(rG)WIGHT 0.1ERET -ALN

FIGURE ~~~0.5-00 ~ ~ 13 020 .0 011 .0 00 Gl
EXAMPLE~~~.2 OF3 SEDME N 0. .S T A T I S T I C A L 5 00 .0
PARAMETERS~2.0 FOR2 SAMPLE COLLC TE AT2 .5 .0 730 ~ 5 2
STATION~~~.2 9.1 1533.0 NEAR AR.7CA00D~ IAN SHORES2.4 22

with a normal distribution.

Table 5-1 presents a summary of sediment statistical
parameters for sample data collected between White Point
Swash south to Singleton Swash and from a point 100 ft south
of Myrtle Beach State Park Pier (#5245) to Garden City
Beach. These samples, listed from north to south, indicate
increasing grain sizes with some size variation across the
profile (between the toe of the dune and mean low water).
For the shoreline between North Myrtle Beach and Myrtle
Beach grain sizes ranged from 2.1 to 2.5, or 0.23 mm to 0.18
mm. Generally, across the profile, sediments were well-
sorted with slightly greater variation found between the
dunes and MLW (c(r) = 0.4 versus U( ) = 0.6).

South along Myrtle Beach State Park, Surfside Beach and
Garden City the distributions of grain sizes were
characterized by moderate sorting where average standard
deviations ranged from a(I) = 0.7 to U( ) = 0.9 across the
profile. One explanation for the nonuniform sediment
distributions is recent placement of artificial fill along
this shoreline in combination with the renourishment project
at Myrtle Beach may have significantly biased this data set.
Analysis of samples with large fractions of very coarse
grains was not found to provide valuable information to
characterizing the natural equilibrium beach conditions.
These samples are depicted by an asterik in the table of
sediment characteristics for cases where grain size
frequency analysis was insufficient to compute accurate
values of standard deviation, skewness and kurtosis.

Assuming a possible bias associated with the overall
distorted distribution of grain sizes, specific conclusions
drawn from these sample data, regarding the beach-dune
sediment characteristics, would be expected to change as the
natural shoreline processes (waves conditions, nearshore

-74-

Table 5-1 Summary Sediment Statistical Parameters Along Horry County Shoreline

TOD -- MHW MLW
Station 'P50 mm a a 950 mm a a a50 mm O a

White Point
Swash -

5460 2.5 0.18 0.3 -0.3 2.3 0.20 0.4 -0.3 2.3 0.20 0.5 -0.4

5445 2.4 0.19 0.4 -0.4 2.4 0.19 0.4 -0.4 2.2 0.22 0.7 -0.1

5430 2.4 0.19 0.4 -0.3 2.1 0.23 0.5 -0.3 2.1 0.23 0.6 -0.4

5410 2.1 0.23 0.5 -0.2 2.1 0.23 0.6 -0.3 2.4 0.19 0.5 -0.6

Singleton
Swash
Avg - 2.4 0.19 Avg - 2.2 0.22 Avg - 2.3 0.20

5245 2.4 0.19 0.4 -0.2 1.6 0.33 0.7 0.1 1.3* 0.41

5225 1.6* 0.33 1.9 0.27 0.6 0.0 1.9 0.27 0.8 -0.5

5205 1.7 0.31 0.8 0.0 1.2 0.44 0.5 0.6 1.4* 0.38

5135 1.5* 0.35 1.8 0.29 0.6 0.0 1.3* 0.41

5115 1.8 0.29 0.8 -0.3 2.1 0.23 0.4 -0.2 2.1 0.23 1.0 -0.4

5025 1.8 0.29 0.8 -0.2 2.0 0.25 0.5 -0.1 2.0 0.25 0.9 -0.5

5015 1.5 0.35 0.6 0.0 1.2 0.44 1.8 0.29 0.9 -0.1

Avg - 1.8 0.29 Avg - 1.7 0.31 Avg - 1.7 0.31

*Large fraction of coarse-grained sediment

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

Source: Applied Technology and Management, Inc. and Olsen Associates, Inc. 1986

slope, shoreline orientation and normal sediment population)
sort and distribute the artificially placed sediments. 0

. 0

0
L-.

V.-

4.
4-,
S

-76-
4-- 0

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
collected from 4 profile surveys conducted in 1958 and 17
new profiles established in 1983-84 by the USCOE, Charleston
District. Shoreline response associated with the
construction of the Murrell's Inlet jetties necessitated
monitoring of adjacent beaches that provided yearly data
from 1979 to 1982 for 4 new stations along Surfside and
Garden City.

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:0f comparative
surveys could not be established, after judicious
investigation, 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 Surfside and
Garden City, collected between 1979 and 1986, were surveyed
to monitor the spatial effects of the Murrell's Inlet
jetties and represented short-term profile data. Short-term
seasonal shoreline variation are represented when comparing
survey data between November 1983 and April 1986. These
were collected along the shoreline from Briarcliff Acres
South to Singleton Swash.

Analysis of volumetric changes and shoreline movement using
these comparative profile data were encumbered by the

-77-

Table 6.1-1. Inventory of Comparative survey data

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

NORTH MYRTLE 5405 1986 1
5410 1983, 1986 2
5415 1983, 1986 2
5420 1983, 1986 2
5425 1983, 1986 2
5430 1983, 1986 2
5435 1983, 1986 2
5440 1983, 1986 2
5445 1983, 1986 2
5450 1983, 1986 2
5460 1983, 1986 2
5465 1983, 1986 2

SOUTH MYRTLE 5205 1984, 1986 2
5210 1984, 1986 2
5215 1984, 1986 2
5220 1986 1
5225 1984, 1986 2
5230 1986 1
5235 1984, 1986 2
5240 1986 1
5245 1984, 1986 2
5250 1986 1
5255 1986 1

SURFSIDE BEACH 5105 1986 1
5110 1958, 1984, 1986 3
5115 1979, 1980, 1981, 1982, 1986 5
5120 1958, 1984, 1986 3
5125 1986 1
5130 1986 1
5135 1979, 1980, 1981, 1982, 1986 5
5140 1986 1
5145 1984, 1986 2

GARDEN CITY 5005 Established 1986 1
5010 1958, 1984, 1986 3
5015 1979, 1980, 1981, 1982, 1986 5
5020 1958, 1984, 1986 3
5025 1979, 1980, 1981, 1982, 1986 5

limited data base. Accordingly, long-term erosion/accretion
rates were limited to 4 stations within the entire Horry
County study area. To supplement this limited data set, 12
new profiles were established at approximately 2,000-ft
intervals. The survey profile locations were shown as
Figure 3.8-2.

6.2 VOLUMETRIC ANALYSIS
Comparative beach-dune profiles were analyzed along Horry
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, termed
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), sand will be transported shoreward ahd 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.

Two methods were used to compute volume changes, the first
method follows a prescribed control-volume approach and the

-79-

second method computes volume changes across the profile for
the limits of the region in common comparison. Figure 6.2-1
and 6.2-2 defines the width of the profile over which volume
changes are computed usingthe 1)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
and 6.2-2 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 Xmax 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.

A second approach to evaluate volumetric changes examines
volume changes over a greater portion of the active profile.
This method will attempt to qualify and substantiate the
control volume methodology that may inadequately represent
the magnitude of erosion/accretion along a profile. Tables
6.2-3 and 6.2-4 present the average annual volume changes
and the net volume changes including notes depicting
locations of man-induced profile modifications using the
comparative profile segment approach. For all comparative

CONTROL VOLUME METHOD

25
Profile Line 555
o20 APR 79 0
20 -

IS -\

CONTROL ,
I- is-_ VOLUME #1 (CV1) . N
DEFINES ACTIVE ~ N
PROFILE SEGMENT

w -S- i CONTROL ._
IT VOLUME 1
Xmin Xmax

-is -

-200 -100 0 100 200 300 400 500 600

Distance. FT

25
Pratile Line 555
VOUM -2 APR 86 i500

10-

. 5 - CONTROL
VOLUME #2 (CV2)

------- -----___ --

-0 -

-15 -

CV1 - CV2
-20- AVERAGE VOLUME CHANGE (1979-1986) =NUMBER OF YEARS

-200 -100 0 oo00 200 300 400 500 600

Distance. FT

FIGURE 6.2-1
DEFINITION SKETCH FOR COMPUTING
AVERAGE VOLUME CHANGES USING THE
CONTROL VOLUME METHOD AT PROFILE
#4555

COMPARATIVE PROFILE SEGMENT METHOD

25
Profile Line 555
20 2 APR 86 1500
20 - ___ 0 APR 79 0

15 -

i _ ERRO ODED VOLUME

c * ,DEPOSITED VOLUME
�--- --- ----- -------------0-- -�__

X _5 _ I, COMPARATIVE _
UA PROFILE SEGMENT

-10o i i

-15 -
DEPOSITED VOLUME - ERODED VOLUME
-20 _ AVERAGE VOLUME CHANGE (1979-1986) = NUMBER OF YEARS

-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 04555

Table 6.2-1. Average, Net, and Unit-width Volume Changes between +10.0 ft
and -3.0 ft MSL

Average Volumetric Gross Volumetric Unit-WidTh Volume
Change (yd /ft/yr) Changes (yd /ft) (yd /ft)

Station 1983-86 1983-86 Nov April
(2.4 fyrs) (2.4 yrs) 1983 1986

Mvrtle Beach North

5460 6.4 15.7 68.4 84.0

5455 16.0 38.4 68.7 107.1

5450 3.0 7.2 86.7 93.7

5445 2.0 4.9 28.9 33.8

5440 1.1 2.7 52.5 55.2

5435 -6.8 -16.3 91.0 74.7

5430 3.0 7.3 50.9 58.2

5425 -2.3 -5.4 67.8 62.4

5420 . 1.1 2.7 54.9 57.6

5415 -2.8 -6.7 45.1 38.5

5410 -6.3 -15.2 71.7 56.5

Average Volumetric Gross Volumitric Unit-WidTh Volume
Change (yd /ft/yr) Changes (yd /ft) (yd /ft)

Station 1984-86 1984-86 Nov April
(2.1 yrs) (2.1 yrs) 1983 1986

Mvrtle Beach South

5205 4.1 2.0 32.9 36.9

5210 0.5 0.3 37.1 37.6

5215 0 0 36.2 36.2

5225 -1.3 -0.6 50.3 49.0

5235 6.5 3.2 35.5 41.9

S-

Table 5.2-2. Average, Not and Unit-Width Changes Between +10.0 ft and -3.0 ft MSL

Average V.~umstria Net Volumetiic.
Change (yd /ft/yr) Changes (yd /ft)

Station 1958-94 1979-90 1980-81 1981-82 1982-95 1984-86 1979-86 1959896 1984-96
(26 yra) (I yr) (I yr) (I yr) (4 yrs) (2 yr.) (7 yrs) (28 yra) (2 yrs)

5110 0.1 -1.3 -0.6

5115 -1.2 -5.8 -5.4 -0.1 -12.9

5120 -0.1 2.8 2.4

5135 2.8 4.1 -5.7 0 .

5145 1.1 2.1

5010 0.1 -3.7 -4.8

5015 5.8 -1.0 -3.4 0.9 4.8

5025 13.1 0.3 -6.0 -2.2 -1.3

Unit-W'dth Volume
(Yd'/ft)

Station January Sept Sept Sept Sept March April
1958 1979 1980 1981 1982 1984 3.986

Surf~naid

5110 63.8 65.8 63.2

5115 54.4 53.3 47.5 42.0 41.6

5120 148.9 145.7 15.1.2

5135 34.1 37.0 41.1 35.4 35.3

5145 40.9 43.0

5010 44.6 47.2 39.9

5015 29.0 34.8 33.9 30.5 33.9

5020 39.8 31.3 27.9

5025 46.7 59.7 :35.9 54.1 45.5

Table 6.2-3. Average and Net Volume Changes Between Comparative
Profile Surveys (Myrtle Beach North and South)

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

Station 1983-86 1983-86
(2.4,yrs) (2.4 yrs)

Mvrtle-North

5460 4.8 11.6

5450 0.3 0.8

5445 1.0 2.5

5440 0.5 1.3

5435 -9.2 -22.1

5430 3.2 7.6

5425 -1.0 -2.4

i5420 1.3 3.2

5415 -2.3 -5.6

5410 -4.8 -13.7
- -----------------------------------m----------------------
* Station 1984-86 1983-86 Shoreline
(2 yrs) (2.4 yrs) Structures
Nourishment,
etc.

Myrtle-South

5205 1.2 2.3

5210 0.1 0.2

5215

5225 -1.5 -3.0

5235 3.1 6.1

Table 6.2-4. Average and Net Volume Changes Between. Comparative Profile
Surveys (Garden City and Surfside)

Average Vo umetric Net Volumet ic Notes
Change (ydi/ft/yr) Changes (yd /ft)

Station 1958-86 1979-86 1984-86 1979-86 1958-86 1984-86 0
(28 yrs) (7 yrs) (7 yrs) (28 yrs) (2 yrs)

Garden City

5010 -0.2 -5.7

5015 1.4 9.5

5020 -0.3 -9.3

5025 -2.0 -14.2

Surfside

5110 -0.2 -6.5

5115 -1.9 13.0

5120 4.1 2.8

5135 0.2 1.1 Artif.
Fill
5145 0.8 1.6

surveys analyzed, the nature of the variability, either
erosion of accretion, was consistent between the control
volume and the comparative profile segment approach.

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 summer profile.
Figure 6.2-3 represents the seasonal profile variations of a
hypothetical survey depicting volume changes which result
from winter and summer wave conditions.

Sinaleton Swash to White Point Swash
In general, volume changes along the shoreline reach
extending south from Singleton Swash some 8000 ft depict
depositional trends. It is important to note that the
profile data collected along the shoreline north of Myrtle
Beach were measured in late fall and the 1986 profiles were
surveyed in early spring. Accordingly, the short-term
volume changes presented in Table 6.2-1 along the Myrtle
Beach north shoreline represent seasonal shoreline
variation, i.e. summer/winter profiles and must be regarded
as representing a seasonal short-term shoreline change.
Erosional trends were measured for the station fronting
Trav-1 Campground (#5435) and the station fronting Lake
Arrowhead Campground (#5425). Volume changes for the
shoreline immediately north and south from White Point Swash
ranged -2.8 to -6.3 yd3/ft/yr between November 1983 and
April 1986.

Sprincmaid Beach to Myrtle Beach State Park
Short-term beach profile volume changes along this shoreline
reach should not reflect seasonal variation as successive
surveys were during March 1983 and April 1986.

-87-

SUMMER PROFILE

MEAN SEA LEVEL

WINTER OR STORM PROFILE

STORM WATER LEVEL
MEAN SEA LEVEL

AN TE SOCATDVOLUME CHANGESFOSTRPOIL

Profile variability, based on average annual volume changes
along the shoreline segment south from Myrtle Beach State
Park to Surfside (denoted Myrtle Beach South), was greatest
at stations 5205 and 5235. Net accretion occurred at these
two profiles, one located adjacent to Ocean Lake Campground
and another profile fronting Long Bay Estates. Short-term
volume changes computed using the comparative profile
segment method were generally lower and ranged between +3.1
to -1.5 yd3/ft/yr. Erosional trends were observed at
profile 5225, located adjacent to Pirateland Campground.

Surfside Beach to Garden Citv
Long-term volumetric changes were computed at 4 stations
along the Surfside and Garden City shoreline. These beach
profiles exhibited average long-term erosional trends
ranging from +0.1 to -0.3 yd3/ft/yr during the 28-year
period. The accretion shown for station 5120 appears to be
the result of beach scraping along the shoreline fronting
this station. Short-term volume changes ranged from +1.4 to
-2.0 yd3/ft/yr for the Surfside and Garden City shoreline
between the 1979 and 1986 surveys.

Profile 5025 presents a fair example of the differences in
the two methods, the control volume fails to account for
erosion landward or seaward of the original control points
(Xmin and Xmax) established using the dune profile of the
earliest survey. Thereby, areas with large volumetric
fluctuations or surveys that represent a steeper
winter/storm profile may not be adequately assessed. Also,
the dynamic portion of the profile out to the depth of
closure, or the limiting depth associated with an active
profile, is not represented in these results.

6.3 SHORT-TERM SHORELINE EROSION RATE
Shoreline changes or beach erosion can be characterized

-89-

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, imumediately following storm erosion, beach0
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 experienced 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
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

-90-

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 an
comparative beach profile data.

Beach survey data were available between 1979 and 1986. A
* ~~~few stations also have the 1958 data. At individual
stations, the num~ber of surveys is no greater than 5 sets of
data. The time period between consecutive surveys was from
7 months to 4 years, excluding the 1958 data. The
* ~~~comparisons between consecutive profiles are presented in
Appendix B.

Two methods were used to assess the short-term erosion rate
* ~~~and both were based on the comparative profile data: a)
contour 'movement rate, and b) 'volumuetric erosion rate.

The shoreline changes, or the contour movement of the beach
* ~~~topography, can be interpreted as the shoreline recession
rate. However, an appropriate elevation should be selected
for the contour in order to get meaningful results. The
beach face near MSL usually has a mild slope (about 2%),
* ~~~consequently, the MSL contour position is very sensitive to
profile changes. For example, when the dune was eroded, the
material may be deposited to the foreshore area. Therefore,
the XSL contour is moved offshore. The MSL contour appeared
* ~~~to be the result of beach accretion, but in reality it would
be the result of dune erosion. Therefore, the movement of a
contour in a dynamic zone below MSL could yield misleading
results. The mean high water line (about 2.981 NGVD) was
* ~~~located on a steeper beach slope (about 5%) and consequently
was less influenced by the special redistribution of the
beach material and would reflect erosion.

Tables 6.3-1 and 6.3-2 show the MHW contour locations and
recession rate in the Myrtle Beach North and Myrtle Beach
South area respectively between 2 consecutive dates. Tables
6.3-3 and 6.3-4 show the MHW contour movement in the Garden
City/Surfside Beach area.

The short-term shoreline recession rate calculated from the
available beach-profile data base showed a wide range of
values, from 108 ft/yr accretion to 135 ft/yr erosion. Most
of the large erosion/accretion rates were derived from data
between short term period (about 1 year) and reflected the
effects of seasonal changes and storm events.

Although the seasonal and yearly shoreline changes were
large, the average recession rates over 2 to 7 years were
much smaller (from 24 ft/yr accretion to 43 ft/yr erosion).
Table 6.3-5 summarizes the short-term shoreline recession
rates for each area. The results showed the variability of
the data. Since the temporal data base 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 1980-81 data showed mostly accretion in the same area.

Mvrtle Beach North
The only available comparative beach profile data in Myrtle
Beach North area were from November 1983 and April 1986.
Table 6.3-1 shows large spatial variation of the erosion
rate ranging from 23 ft/year accretion to 33.5 ft/year
erosion. The spatial average of the MHWL changes between
these dates was about 1.5 ft/year accretion. It should be
emphasized that Table 6.3-1 only depicts the MHWL changes
between two specific dates, and it can not be soley used as
a basis to make any future predictions.

-92-

Table 6.3-1. Mean High Water Contour Position
(Myrtle Beach North Area)

MHW Position (ft)

Rate of change*
Station 11/83 4/1986 (ft/year)

5410 147 128 -7.9

5415 71 73 0.8

5420 91 107 6.6

5425 95 117 9.1

5430 78 135 23.6

5435 168 87 -33.5

5440 85 99 5.8

5445 119 103 -6.6

5455 91 100 3.7

5460 105 138 13.7

Negative value indicates erosion.

Table 6.3-2. Mean High Water Contour Position
(Myrtle Beach South Area)

MHW Position (ft).

Rate of change
Station 3/1984 4/1986 (ft/year)

5205 71 82 5.3

5215 82 78 -1.9

5225 111 82 -13.9

5235 60 83 11.1

5245 189 100 -42.8

* Negative number indicates erosion.

I'I

Table 6.3-3. Mean High Water Contour Position (Garden City and Surfside Beach)

Mean High Water Contour Position (feet from baseline)

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

5015 202 212 235 217 211

5020 341 312 266

5025 291 300 307 266 265

5110 295 281

5115 343 349 354 332 292

5120 327 318

5135 319 339 402 323 315

5145 81 81

Sources: Applied Technology and Management, Inc. and
Olsen Associates, Inc., 1986

Table 6.3-4. Mean High Water Contour Movement (Garden City and Surfside Beach)

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

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

5015 10.0 16.2 -30.9 -1.5 2.5 1.3 -0.2

5020 -1.1 -22.1

5025 9.0 4.9 -70.3 --0.3 -17.0 -3.7 -5.8

5110 -6.7

5115 5.0 3.5 -37.7 -10.0 -8.5 7.3 -9.5

5120 -4.3

5135 20.0 44.5 -135.4 -2.0 -8.0 -0.6 -4.0 0.0

5145

97 9 0

Table 6.3-5 Summary of Short-Term Shoreline Recession Rate
in Horry County

Myrtle Beach Myrtle Beach Garden City/
North South Surfside Beach

2 year maximum 23.6 11.1 -4.3
2 year minimum -33.5 -42.8 -22.1
2 year average 1.5 -8.4 -11.0

4 year maximum -0.3
4 year minimum -10.0
4 year average -3.5

6 year maximum -0.2
6 year minimum -9.5
6 year average -4.9

7 year maximum 1.3
7 year minimum -7.3
7 year average -2.6

*Negative value indicates erosion

Source: Applied Technology and Management, Inc. and
Olsen Associates, Inc., 1986,

0I)

Mvrtle Beach South
The only available comparative beach profile data in Myrtle
Beach South area were from March 1984 to April 1986. The
MHWL movement rate ranged from 11 ft/year accretion to 43
ft/year erosion. The spatial average is about 0.7 ft/year
erosion.

Garden City and Surfside Beach
There were a total of 7 sets of survey data available for
Garden City and Surfside Beach, however, only 5 or less were
available at an individual survey station. Table 6.3-4
indicates that this area has experienced moderate short-term
erosion. The spatial average of 1980-1982 MHWL changes in
this area was 7.8 ft/year erosion, and the spatial average
of 1984-1986, 1982-1986, and 1979-1986 (all in April) were
11.0, 3.5, and 2.6 ft/year erosion respectively.

The changes between April 1980 and September 1981 showed an
average accretion of 17.3 ft/year which indicated the
changes from winter profile to summer profile. Similarly
the spatial average of September 1981 to April 1982 was
-68.5 ft/year (erosion) which reflected the effects of
winter waves.

6.4 LONG-TERM SHORELINE EROSION RATE
The 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
the 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

-98-

were shown in Figures 6.4-1 to 6.4-3 for different section
of the study area. The data indicates that the Horry County
coastline was relatively stable in long-term. The shoreline
fluctuated but on a smaller scale than other part of the
South Carolina coasts. To obtain a long-term trend, linear
regression analysis was used to predict the future erosion
rate using the last 50 years data. The results were shown
in Tables 6.4-1 and 6.4-2 and Figures 6.4-4 and 6.4-5.

In general, the Myrtle Beach North area was quite stable and
the long-term erosion rate had a spatial trend of a higher
rate toward the southern portion of Surfside Beach. The
maximum recession rate occurred at station 5110 where the
erosion rate was 4.8 ft/year.

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 along
the study area, shoreline to maintain an equilibrium
condition, which 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)

-99-

o6 0
0- 0-

o - - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~5420
o -

in-
-435

q ~~~~~~~~~~~~~~~~~~~a)
a): 41 5~0:~
I.- - '- 0-
-- -
W
643

.4eJ - t6 a: 5405
U) : ()10

a. a
a) -- -- a):

L~~~~~~~~~~~~~~~~~ 0

FIUR 6.4-1O
-t -~~~~~~~~~~~~~~~~~~C o:

0-
CO1 1550 1555 115 us.i.s (5,.uu 5IS suuuuuu 11111555sssgu .
~l85 185 100 125 950 1975 200 1150 875 1900 1925 1950 1975 2000
YEAR YEAR

FIGURE 6.4-1
SHORELINE MOVEMENT ALONG MYRTLE
BEACH NORTH AREA

0 0 0 0

Salo
U)- N--

6250
0-
_r - _\ -

- a

~~~~~~~~~~~~~~~~~~~~~U)co

0A-

FIUR 6.4-2O
L. - L.t�s

co - \\\~d(~\'1"

SHORELINE MOVEMENT ALONG MYRTLE
BEACH SOUTH AREA

5025
~~~~~SolC

oI -c a -

~~~~500)
Id) 4- 5

- mI - 56115

0- cn 6126

c :

c- C55:

I-~~~

WIasou 1875 1900 1925 1950 1975 2000 1'850 .1.8.7. 19100 . . . . 1912; '19V 150 975 . . .. 2006

YEAR YEAR

FIGURE 6.4-3
SHORELINE MOVEMENT ALONG SURFSIDE
BEACH AND GARDEN CITY

Table 6.4-1. Long-term shoreline accretion/erosion rate
(Garden City and Surfside Beach)

Erosion Rate*
Station (ft/yr)

Surfside Beach

5105 -4.5
5110 -4.8
5115 -2.8
5120 -1.8
5125 -1.4
5130 -0.5
5135 -2.1
5140 -1.5
5145 -2.3

Garden City

5005 -1.9
5010 -0.1
5015 -0.2
5020 0.0
5025 -3.6

Negative value indicates erosion.

Source: Applied Technology and Management, Inc. 1986

0)�-

Table 6.4-2. Long-term shoreline accretion/erosion rate
(Myrtle Beach and Myrtle Beach South area)

Erosion Rate*
Station (ft/yr)

Myrtle Beach North Area

5405 -2.3
5410 -1.5
5415 -0.7
5420 -3.2
5425 -3.2
5430 -1.6
5435 -1.4
5440 -1.6
5445 -0.3
5450 4.0
5455 -0.6
5460 -1.1
5465 � -1.5

Myvrtle Beach South Area

5205 -1.0
5210 -1.5
5215 -1.6
5220 -0.2
5225 -1.1
5230 -2.1
5235 -1.5
5240 -1.7
5245 -1.1
5250 -0.3
5255 -1.8

* Negative value indicates erosion.

NORTH MYRTLE BEACH

C AN DRIVE 13EACH

POP. 339 5460(S)

x~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~- -5 -45- 2 1 0 1 2 3 4 5 6
_L_~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~RSO (ftyer)ACREIO

FIGURE 6.~~~~~~~~~4-4
LONG-TERM EROSION RATE IN MYRTL
BEACH NORTH AREA~~~~~543(S

vmv~~~s~* " Io.
k Fl., ~~~~a "i

m SUAFJOE BECH- 525

N7a5235__
-B - 4 -3 - 1 0 1

522M)~ERSONACRTO
5220~~~~~~~~~~~~~~~(fler

FIGURE 6.4-5~~~~~~~~~21

LONG-TERM ERO~~~~~SIONRAE BEACHEEN2
MYRTLE REACH AND GEORGETOWN COUNTY

I p I I b~~~~~~~$153

where: R = horizontal recession

S = vertical water rise in sea-level

W, = active width of the equilibrium profile

h, = limiting depth associated with active
profile

B = berm or dune height

The limiting depth: (h,) associated with the active portion
of the beach profile was determined using a composite of 4
profiles representing 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 along Garden City is
computed as

0.4667 ft
49 years, (lll8.ft)
R = = 0.3 ft/year
(18.0 ft + 17.5 ft)

The shoreline recession caused by sea level rise is small
when compared with short- and long-term erosion that is 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 as
follows (Eiser et al., 1986).

-107-

!=-~ ~ ACTIVE PROFILE, Ot* -I

DUNES BEACH
/SEA LEVEL AFTER RISE

INITIAL SEA LEVEL LB
s

INITIAL PROFILE

EQUILIBRIUM PROFILE
AFTER SEA-LEVEL RISE No"==-.

DEPTH OF CLOSURE, h*

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

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 ideallldune crest falls on each
surveyed profile, measured from the survey
monument.

This methodology has been applied in the shorefront
management plans for Myrtle Beach, prepared by RPI (Kana et
al., 1984) and 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
(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. As a result, the
IPP methodology was applied separately to several reaches of
the study area shoreline. The methodology as employed in

-109-

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
In order to insure that the IPP methodology and procedure
was properly understood and executed, it was first applied
to the section of North Myrtle Beach (Horry County)
shoreline between Singleton Swash and Withers Swash. As
mentioned above, previous investigators had performed IPP
analyses over 9 miles of shoreline both to the north and to
the south of this reach. The results from these studies
were used as a comparison and check of the results obtained
in this application. As these shoreline reaches are
adjusted to each other, it was expected that the IPP's
should be similar, as should the computed reference unit
width volumes of sand.

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 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

mean 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
shoreline reaches in the present study indicate that the
+10' contour does not always represent the point resulting
in the least variations about the mean. For this particular
shoreline reach, this point was determined to be the +2.5'
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
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'
distance increment. The resulting "Ideal" Present Profile
(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 -5' 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).

MYRTLE BEACH NORTH AREA

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

RDl-
m

=--

Ld I-I
'~-'/o- /~~~ / v/

0-
II I

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

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

0 0 0 6 0 0 0 0 0

Figure 6.6-2 presents a comparison between the IPP derived
in this study for the section of Horry County 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 6.2-1 presents the reference unit volumps 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 plotted IPP profile falls between
adjacent IPP profiles (as do most dimensions magnitudes and
volumetric quantities) and corresponds appropriately 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 and execution of
the IPP methodology. Accordingly, the IPP methodology was
applied to the shoreline reach extending from Springmaid
Beach to Garden City Beach. A summary of procedure and
results for this application is presented below.

Surinamaid Beach-Surfside-Garden City Beach
The approximately 11.1-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 Ideal Present Shoreline
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.

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

I to-

,+~~~~~~~~~~~~~~~~~~~~~~~~~~- - -
An-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ..
Z - .

2- -,

-200 -100 0 100 200 300 400 500 600
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

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

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'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 the superimposition of the 10 profiles
shifted about a common reference point of +5' MSL. The
solid heavy line on Figure 6.6-3 presents the IPP generated
by averaging the elevations of each of these profiles at 10'
increments. A reference unit volume of 35.7 yd3/ft was
calculated between the +10' MSL and -2.5' MSL contours for
the IPP along this shoreline reach. The IPP has a dune
crest elevation of +11.5', a dune width of 44' and a beach
width of 242' between the +10' and -2.5' MSL contours (NGVD
Datum).

6.7 IPP COMPARISON
In accordance with the prescribed procedure, the IPP
computed for each shoreline reach was superimposed on the
April 1986 profile at each station along that reach. The
IPP was then shifted horizontally in a manner such that the
volumes under both profiles were equal. 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. Accordingly, the IPP
was superimposed over the actual profile and shifted over
the distance necessary to equate the volumes between these
contours. Table 6.7-1 presents the unit volumes under each
profile (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 the volumes have been
equated. Once superimposed correctly, the actual and

MYRTLE BEACH SOUTH AREA

Ideal Present Profile (IPP)
Profile Data

Cd0- N

-I I _

0:_

In-

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

FIGURE 6.6-3
IPP FOR MYRTLE BEACH NORTH AREA

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 Horry County Shoreline.

Variation
Unit Volume With IPP � IPP Dune Crest Relative
Station (cy/ft) Volume (cy) to Actual Dune Crest

5405 46.95 -0.15 Landward
5410 51.80 4.70 Landward
5415 38.85 -8.25 Landward
5420 53.85 6.75 Landward
5425 54.40 7..30 Seaward
5430 46.94 -0.16 Landward
5435 47.09 -0.01 Landward
5440 45.27 -1.83 Landward
5450 26.82 -20.28 Landward
5455 49.92 -2.82 Landward
5460 41.54 -5.56 Seaward
5465 60.82 13.72 Landward

5255 33.71 -1.99 Landward
5250 38.00 2.30 Landward
5245 47.46 11.76 Landward
5240 37.56 1.86 Landward
5235 37.42 1.72 Landward
5230 33.18 -2.52 Landward
5225 36.51 0.81 Landward
5220 51.15 15.45 Landward
5215 29.01 -6.69 Landward
5210 35.69 -0.01 Landward
5205 37.94 2.24 Landward

5145 39.53 3.83 Landward
5140 32.83 -2.87 Landward
5135 54.48 18.78 Landward
5130 34.08 -1.62 Landward
5125 ' 34.42 -1.28 Landward
5120 41.11 -5.41 Landward
5115 39.75 4.05 Landward
5110 36.32 0.62 Landward
5105 34.16 -1.54 Landward

5025 36.28 0.58 Landward
5020 15.81 -19.89 Landward
5015 30.72 -4.98 Landward
5011 25.09 -10.61 Landward
5010 23.09 -12.61 Landward
5005 40.34 -4.64 Landward

shifted IPP profiles were plotted together. Figures 6.7-la
and 6.7-lb are two example plots showing the superposition
of the IPP on the profiles at Stations 5020 and 4625
respectively.

Station 5020, located at the Atalaya Towers in Garden city
Beach, is an extreme example of IPP superposition on an
armored shoreline. In this case a seawall was built and
backfilled at or near the seaward extent of the upland
property line. Accordingly, the beach system in front of
the seawall, either due to erosion or the initial seaward
placement of the wall, does not include a dune, is of
relatively low elevation, and therefore, 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 seawall. This condition is characteristic of the
shoreline extending north from Singleton Swash, as well as
other armored sections of the Horry County shoreline.

Station 4625 is located along a residential section of
Garden City Beach in Georgetown County. It is presented in
Figure 6.7-1b in order to provide a clear example of the
shifted IPP dune crest falling seaward of the actual profile
dune crest. 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
accelerated...this methodology makes allowance for
artificial loss and places the ideal dune crest somewhat
seaward of its present position" (CSE-1986). While it is
not readily apparent how this allowance is made based upon

20
Profile Line 20
.ProtieAAInae6 iO"
I--16 JUN 86 0
A

101

0 5 -

uj
- - -- - . ______

! . . . . . . . . . . . i . . . . . . . . i t

50 t00 150 200 250 300 350 400 450 500 550 600

Distancs. FT

20 - Profile Line 625

_ --15 JUN 88 0
B 5- 5i

la
u t

0 - - --------------------------- -- .

L.. . '~.

I . * . * I I I I . .

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

Distance. FT

FIGURE 6.7-1
COMPARISION BETWEEN IPP AND
A) STATION 5020
B) STATION 4625

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 landward of the
actual dune crest were attributable to excess unit volumes
rather than sand deficits.

7.0 INLET ANALYSIS
Tidal swashes assume an important role in both the long and
the short-term fluctuations of adjacent shorelines within
the study area. For example, longshore sediment transport,
also referred to as littoral drift, is continually directed
toward a swash or gorge. Flood tidal currents transport and
deposit these sediments within the lagoon or embayment,
whereas ebb tidal currents return the sediments to the
ocean. Typically the updrift beach builds and migrates in
the predominating downdrift direction. This is the basic
mechanism by which the swash naturally migrates in the
direction of the predominating longshore currents.
Correspondingly, the swash channel may likewise migrate, in
some cases break through 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,
piers 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. Sediment trapping potential exists at both
Singleton and White Point Swash. Since tidal channels are
continuously affected by reversals in longshore transport,
it is those shorelines closest to tidal inlets which
typically experience the greatest variation in erosion rates
and fluctuations of the beach and dune system. The area of
influence along a coast affected by a tidal swash is related
to the tidal prism which is an expression of the quantity of
water that moves through the inlet.

The stabilization of any naturally functioning tidal swash
by dredging and/or the construction of groins and rip-rap
placement may modify the hydraulics of the prior regime, and

-122-

therefore upset 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 the adjacent shorelines.

The adjacent shorelines of most natural swashes, since
formed of unconsolidated, sand, are obviously 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 embayments. Extraordinarily high
discharges through swashes during hurricane storm tides
characteristically both erode and flood the adjacent channel
margins as the increased flow converges in the vicinity of
the entrance channel.

These dynamic areas require adequate coastal planning and
building criteria for protection of property in close
proximity to tidal swashes from the hazards of hurricane
induced flooding. Channel migration, often associatedI with
unstabilized inlets, may have severe impacts on the
stability of adjacent swash channel banks during these
severe storm events.

White Point Swash
White Point Swash is located 1700 ft south of Kitts Pier
along the shoreline fronting Briarcliffe Acres. Kitts Pier
extends 750 ft seaward of the local shoreline and appears to
shelter the shoreline reach immediately north of White Point
Swash. In recent years, short-term (2.4 years) volume
changes indicate the beach transects both north and south
(#5460 south to #5440) from White Point Swash have
experienced depositional trends. Well-vegetated sand dunes
and a depositional spit characterize the adjacent shoreline
of the north bank.

-123-

The long-term shoreline trends indicate the north bank of
White Point Swash migrated approximately south 3800 ft
between 1873 and 1925, as presented in Figure 7-1. This
shoreline consistently migrated north from 1925 to 1962 and
has subsequently remained relatively unchanged. The White
Point Swash entrance channel is presently oriented along a
line approximately 500 west of the adjacent open ocean
coastline. In recent years, rip-rap was placed over nearly
200 ft of the south bank along White Point Swash in an
apparent effort to prevent southerly migration of the swash
channel. The size and placement of this rock (0.8-1.5 ft
diameter) should offer protection during normal wave
conditions. The tidal prism associated with White Point
Swash has been sufficient for this swash to remain open for
the past 100 years. The flow appears to be tidally dominant
while providing a route for stormwater drainage from upland
areas.

Sinaileton Swash
Singleton Swash north bank is located along the shoreline
fronting Lake Arrowhead and fronting The Dunes. In recent
years short-term (2.4 years) beach profile changes indicate
the shoreline segment extending 2000 ft north of this swash
has experienced an erosional trend. The adjacent shoreline
north from Singleton Swash suffers erosion along the
foreshore area, in part due to discontinuous seawalls in
close proximity to the shoreline which has resulted in
significant shoreline irregularity.

In recent years, Singleton Swash has been relatively stable,
as shown in Figure 7-2. Singleton Swash moved north prior
to 1962 and has remained stable, A two foot vertical scarp
was observed along the south channel bank during the April
1986 field investigation. Breaches of the dunes along the
south channel margin were apparent although dunes were
generally higher and well vegetated.

-124-

WHITE POINT SWASH
lI

I~~~~~~~~~~~ I

1873 1925-26 1934

I I I

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~II
1962-63 1969-70 1983
,, FT
-1983 (NOS AERIAL PHOTO)
--- FIELD SURVEY YEAR

FIGURE 7-1
HISTORICAL SHORELINE POSITIONS
NEAR WHITE POINT SWASH

SINGLETON SWASH

1873 1926 1934

1962 1969-70 1983 0 5w
I -a. I - I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I'!F
a-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~E

-9-,3 (NOS AERIAL PHOTO)I
--I |~~~~~~~~~~~~ ~ --- FIELD SURVEY YEAR

FIGURE 7-2
HISTORICAL SHORELINE POSITIONS NEAR
SINGLETON SWASH

Peat deposits are exposed along the north channel bank.
This adjacent shoreline has 12 ft. dune heights which follow
a recurved spit along the channel margin.

Evidence of a recent washover were observed during the April
1986 field survey along the southern property boundary of
the condominium immediately north of Singleton Swash.
Initially this washover channel (30-40 ft wide) probably
scoured in part due to wave action along the terminal point
of this condominium's seawall. During high tides, water
appears to flow into a marsh area formed by the recurved
spit. In addition, stormwater runoff from the condominium
parking area is directed into this washover channel.

-127-

8.0 FUTURE SHORELINE PREDICTION
8.1 IDEAL PRESENT SHORELINE
The ideal present profiles (IPP) of Myrtle Beach North and
Myrtle Beach South were established as presented in Section
6.6. Once the IPP for each shoreline reach was overlaid on
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 the0
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 representing0
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, this0
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 dune0
line in order to account for excess sand volume was
considered to be a miscomputation inherent in the
methodology if interpreted literally. 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 immuediate 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.

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.
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. Therefore incorporation of such assumptions in
the establishment of any line that may be used to determine
building setbacks ofl 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.
Table 8.1-1 presents the locations of IPS in relation to the
survey monuments at each monitoring station in the study
area.

8.2 PREDICTED 25 AND 50 YEAR SHORELINES
It has been established in this study and several previous
ones, that with isolated exceptions, the shoreline along the
study area is undergoing a long-term erosional trend which
varies spatially 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

-129-

Table 8.1-1. Ideal Present Dune Crest Locations

Station IPS Location (ft)*

Garden.Citv.

5005 89
5010
5115 114
5020 174
5025 175

Surfside Beach

5105 159
5110 194
5115 210
5120 233
5125 296
5130 281
5135 219
5140 193
5145 -16

Mvrtle Beach South

5205 -13'
5210 -14
5215 -19
5220 80
5225 -6
5230 16
5235 -12
5240 -2
5245 8
5250 -6
5255 -17

Mvrtle Beach North

5404 -12'
5410 -6
5415 -49
5420 -16
5425 -23
5430 -30
5435 -37
5440 -23
5445 -21
5450 -21
5455 -17
5460 7

*IPS location is measured seaward from the survey monument.

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
usually made based on extrapolation of observed historical
* ~~~rates into the future. Accordingly, the accuracy of and
confidence level associated with these predictions is
directly related to the quality and quantity of information
comprising the historical database. Tl~e practice of
* I ~~conducting beach profile surveys for the specific purpose of
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
shoreline change rates over a longer period of time than 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
the IPS or the existing dune line, whichever applicable,

-131-

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 vidinity
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 receslsion 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
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.

Sinaleton Swash to White Point Swash
Shoreline movement data for this reach of shoreline
consisted of: 1) beach profiles taken in November, 1983 and
April, 1986, 2) long term linear MHWL changes obtained from

-132-

the NOS-CERC shoreline movement maps for the period 1934-
1983, and 3) volumetric and linear rates determined by Kana
et. al. for the shoreline immediately adjacent to the north
and south'of this reach. In addition, the IPP profile was
used in the calculation of erosion associated with'the
occurrence of the 25 and 50 year storm.

In accordance with the IPP methodology, predicting the
future position of the IPS is done by first calculating a
historical annual volumetric change rate and then
calculating the distance over which the IPS must be shifted
to account for the total volume obtained when applying that
volumetric rate over the number of years in question. The
determination of an accurate annual volumetric change rate
was not possible, however, with the limited amount of-
profile data available for this reach. The difference in
profile volume associated with the short term, seasonal
differences between the November, 1983 and April, 1986 beach
profiles would severely bias any attempt to assign a long
term, annual volumetric change rate using only these two
sets of survey data. In order to remain consistent with
methodology used in previous studies to predict the future
IPS position along adjacent shorelines to the north and
south of this reach, volumetric change rates determined in
these studies were employed here.

In the RPI study (Kana et. al. 1984) a long term linear
recession rate of 0.68 ft/yr was determined from volumetric
erosion rates for the Myrtle Beach shoreline south of the
reach under consideration. Likewise, in the CSE study
(Eiser et. al. 1986) a long term linear recession rate of
0.40 ft/yr was determined from volumetric erosion rates for
the North Myrtle Beach shoreline north of this reach.
Analysis of the data and procedures employed in each of
these studies, along with the previous determination that
beach profiles over this reach and the shorelines to the

-133-

north and south are quite similar, resulted in the
application of a long term linear recession rate of 0.60
ft/yr which corresponds to a distance of 15 and 30 feet
respectively over 25 and 50 years. These distances were
applied to the previously determined IPS for this reach in
order to represent the predicted 25 and 50 year shorelines.

Sprintmaid Beach to Garden City
Shoreline movement data for this reach of shoreline
consisted of: 1.) beach profiles at various locations taken
in 1958, 1979, 1980, 1981, 1982, 1984, and 1986 and 2) long
term linear MHWL changes obtained from 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.

Based on the limited number of 1958 profiles as well as the
potential for extreme bias in beach volumes due to recent
nourishment, as well as inlet effects, it was concluded that
the available profile data were inadequate for the.
prediction of long term annual volumetric change rates.
Accordingly, the shoreline movement maps were referred to in
the determination of an average erosion rate for this reach
of shoreline. Approximate erosion rates were calculated at
each station along the reach and averaged to obtain a
uniform rate. Stations that were armored or considered
subject to inlet or swash migration were not considered 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 applied to the previously
determined IPS for this reach in order to represent the
predicted 25 and 50 year shorelines.

-134-

8.3 STORK 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 increased 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 a large
scale dune erosion or loss, dramatic rates of shoreline
recession and destruction of upland structures.

In most instances, however, eroded material in 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
associated with major storm events.

The predicted storm surge elevations for the study area are
discussed in Section 3.3 of this report. Although
substantial damage along the study area shoreline has been
documented as a result of land-falling hurricanes, much more
frequent erosion occurs from northeasters. It is
interesting to note that the beach erosion caused by a long
duration northeasters and 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 lack of immediate
'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 type 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.
Simplistically, 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
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 simulation. 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.

-136-

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
simulations are presented in the following paragraphs.

White Point Swash to Sinaleton Swash
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
prestorm water level and an exponential equilibrium profile
below that water level. The maximum IPP dune height of 12
ft was input in to the model as were 25 and 50-year maximum
storm surge elevations of +9 ft and +11 ft (NGVD),
respectively. Landward IPS erosion of 95 ft and 130 ft
resulted from the model simulation for 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 simulated 25 and 50-year
storm surge. Of particular note is the fact that the IPP
dune is breached as a result of both these simulations.
While the simulations of the IPP erosion represents an
average condition, 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.

Springmaid Beach to Garden City
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 11.5 ft and maximum storm surge
elevations of 9.5 ft and 11.5 ft were input into the model
for simulation of the 25 and 50-year storm events,
respectively. Landward dune erosion of 116 ft and 152 ft

-137-

NORTH MYRTLE BEACH STORM ERO0ION
25

-~~~ I

-.a

-j-

-10 1

-200 -100 0 100 200 300 400 500
DISTANCE (ft)
OSURGE = 11 It ffA)UNE = 12 ft

FIGURE 8.3-1
PREDICTED 25- AND 50-YEAR STORM EROSION
(BETWEEN NORTH MYRTLE BEACH AND
MYRTLE REACH)

0� 0 0 0 0 0

NORTH MYRTLE 8EA!.-H STORM EROSION
25

"- 15

Li
10

-5-

-200 -100 0 100o 200 300 400 500 600
DISTANCE (ft)
SURGE = 11 ft DOUNE = 12 ft

FIGURE 8.3-2
PREDICTED 25- AND 50-YEAR STORM EROSION
(BETWEEN MYRTLE BEACH AND SURFSIDE
BEACH)

resulting from the model simulation of the 25 and 50-year
storm surges is shown in Figure 8.3-2. 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 the flooding and wave action
associated with these storm events.

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9.0 SHOREFRONT MANAGEMENT RECOMMENDATIONS
9.1 HAZARD ZONES
In contrast to similar efforts by previousinvestigators,
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 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 "VI' 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-zones in
-141-

I --ZONE OF EROSION

(jFLOOD INSURANCE ZONES II'ZONE OF RECESSION

I ~50 Year Future Dune Crest

- ~~~~Existing Beach/Dune System

*Locaion arie.s with..:. prbblt of s torm evn

..~CATA HZRDZOE

* ~ .*........~..*.:OREFRONT MANAGEMENT PLA0N~

FIGURE~~~~~~*~..* 9-.
SCHEMA~**TIC9~ -IGA OFTECATLHZR OE

coastal areas with dunes can be extremely unreliable and
inaccurate when the elevation of the existing 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 the necessity 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
regulations are in effect along the Horry County shoreline
of interest above the approximate MHWL:

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

Federal Flood Insurance requirements for
construction within "A" or "V" Zones ( 44 CFR,
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". The
limit of Coastal Council jurisdiction in most instances is a
function of the location of the primary oceanfront 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

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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: (1) 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 September 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
ihe future as a result of shoreline recession in areas with
historically known rates of erosion. Furthermore, the
Council cannot consider 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

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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 behch/dune system.
Accordingly, the landward limits of the V-zone for much of
the Horry 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 potentially existing regulation of
construction within coastal high hazard areas is either
"local government", or developer initiated control. For the
project area under consideration, the only local beach and
dune type setback restrictions in existence are enforced
within the Town of Surfside Beach. Simplistically, zoning
ordinances at that location required the establishment of a
"Shore Protection Line (SPL) on all lots lying contiguous to
the Atlantic Ocean. In such areas, the SPL is determined to
be a line twenty (20) linear feet landward of the property
line nearest the Atlantic Ocean (i.e., rear property line),
or the line twenty (20) linear feet landward of the landward
trough of the primary ocean front sand dune, as determined
by the SCCC, whichever line is more landward. In areas
where the primary dune is non-existent, a new dune must be
constructed prior to construction. In such cases the
setback must be fifteen (15) feet. No construction is
allowed seaward of the SPL except for dunes, vegetation,
minor non-habitable structures, and emergency erosion
control measures. Structures seaward of the SPL which in
the future that suffer 51% or more damage will be considered

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to be non-conforming and subject to removal at the owner's
expense.

-Although not necessarily physically-based, such resource
oriented setbacks as adopted by the Town of Surfside Beach
are a reasonable first approach to the preservation of the
beach/dune system.

9.3 EXISTING FLOOD INSURANCE ZONES AND STANDARDS
Both a review of the existing Flood Insurance Rate Maps
(FIRMs) for the study area in Horry County, as well as the
preliminary results of the storm impact analyses, indicate
that the V-zone conditions depicted by the FIRMs are
extremely unconservative. Along the Horry County coast, the
V-zones terminate at/or about the seaward face of any dune
or similar feature that has 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 Horry County, as well as in 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 types 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
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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. 450104 0309 C for an area located immediately south of
Myrtle Beach State Park in unincorporated Horry County. As
noted, the landwardmost V-zone which terminates at the dune
line is at elevation +17 ft. Landward of that point is an
A-zone at elevation +16 ft. Also noted on Figure 9.3-1 is
the location of survey profile No. 5235 that was established
as part of this study. The depiction of the FEMA flood
zones as they relate to the cross section of the beach at
profile station 5235 is shown in Figure 9.3-2.

Previously referenced erosion analysis of the IPP typical of
this 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 reasoD, the actual physical
phenomena expected with such an event will not be as-
depicted on FIRM 450104 0309 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 +16 ft.
The situation highlighted by this example is typical of
existing condition throughout the majority of the Horry
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 MHWL which will result in the consideration of design

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N~~~~~

~~~~ZONE V2111
(EL 17)

PROFILE 5 235

ATLANTIC OCEAN

REFERENCE:

COMMUNITY PANEL NO. 4-5104 0309 C
Feb. 15,1984
HORRY COUNTY,S.C.

FIGURE 9.3-1
FLOOD INSURANCE MAP NEAR LONG BAY
ESTATE

A-ZONE V-ZONE g el. 21'
elev. 16'

el. 17'2-

15 - elev. 14.0' 100 YR. BFE
(NO WAVES)

LIE
Z
� \ EXISTING DUNE

"L' o
wo - - -- -- -

-5-

Monument 5235 NOTE DISTORTED SCALE
. , . , , , . I , I . . * . I * .
-50 O 50 100 150 200 250 300 350
DISTANCE FT.

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

.0t~~~~~~~s ~

20-toVE

V-ZONE
15 - 14' elev. 100 YR. BFE
(NO WAVES)

10-

o ~~~~~PREDICTED ERODED PROFILE

Monument5235 NOE DISTORED SCAL
w~~-0 0 s 0 5 0 5 0 5

PRoumn 23OE DISTOTED VZNCOSCALERNTH
STORM~~ IMAT NE A LO N BA E S T A T E * I * * I

20-- A-ZONE V-ZONEe.21
* 20- ~~~elev. 160

15- elev. 14.0' 10D YR. BFE
(NO0 WAV ES)

10-

Monument 5235 NOTE DISTORTED SCALE

-50 0 50 100 150 200 250 300 350
* ~~~~~~~DISTANCE FT.

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

20--

V-ZONE
15- 14' elev. 100 YR. BFE
(NO WAVES)

10-
EXISTING DUNE

w0 ..---i----- --
'= N .d PREDICTED ERODED PROFILE

Monument 5235 NOTE DISTORTED SCALE
. I , . I i I , I . I . I , I . I
-50 0 50 100 150 200 250 300 350
DISTANCE FT.

FIGURE 9.3-3
PREDICTED V-ZONE CONSIDERING THE
STORM IMPACTS NEAR LONG BAY ESTATE

criteria sufficient to accommodate the expected impacts of a
100-year storm.

9.4 RECOMMENDED SETBACKS
Unincorporated Area Between Briarcliffe Acres and Sinaleton
Swash
Similar studies performed by Kana, et. al. for both Myrtle
Beach and North Myrtle Beach have indicated a continuing
trend of erosion and shoreline recession for this general
section of the Grand Strand in northern Horry County. These
rates have been likewise corroborated by this analysis.
Correspondingly, the predicted 50-year future shoreline has
been computed to be landward of its existing location
throughout that section of the area of interest in Horry
County.

It should be noted, however, that anomalous conditions
associated with piers, 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 "averaged out" in this analysis. The purpose of this
action is to preclude physical discontinuities which could
be detrimental to area wide recommendations for future
shoreline management practices.

On the average, the 50-year future shoreline recession for
this section of incorporated Horry County resulting from a
volumetric analysis is expected to be about 30 feet landward
of the predicted ideal present shoreline (IPS). As
previously discussed, this landward recession is
hypothesized solely on historical long term volumetric
erosion 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 the study shoreline 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

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expected to be as much as 5 times greater than the long-term
recession rate, or about 130 ft. landward of the crest of
the IPP. Similarly, the 25-year storm recession is computed
to be about 95 ft. landward of the IPP or between 3 and 4
times the predicted long-term rate.

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 keep construction landward of the location
where the active beach is expected to be 50 years hence,
conservatively assuming relatively modest but continuous
annual rates of beach erosion.

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

1. To protect upland development from being
constructed inan area subj ect to significant
fluctuation due to storm induced erosion, and0

2. To allow for sufficient rebuilding of a comparable
dune system by natural processes subsequent to
severe storms. Without such, the expected result0
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
C ~~~~large scale beach restoration at significant

expense.

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For the unincorporated area under consideration in northern
Horry County, the minimum recommended setback from the
beach/dune system should be that distance dictated by the 50
year future shoreline location as predicted by a volumetric
analysis. Allowances for construction of major habitable
structures seaward of that 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 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.

Unincoroorated Area'Between Mvrtle Beach and Surfside;Beach
Although existing land use practices within this section of
the study shoreline are dramatically different than that of
adjacent Myrtle Beach to the north, intense developmental
pressures in the future can reasonably be expected to occur,
except within the limits of Myrtle Beach State Park. For
that reason, the adoption of appropriate setbacks is
similarly recommended for this area. All recommendations,
however, should be considered to apply equally to both
privately and publicly owned lands.

Analyses of shoreline erosional trends indicate long-term
shoreline recession rates based upon a linear shoreline
erosion analysis result in a 25-year future shoreline
location approximately 37.5 feet landward of the predicted
ideal present shoreline (IPS). It should be noted that the
25 year linear shoreline recession analysis used in this
section of Horry County can be considered to be
approximately equivalent to the 50-year volumetric analysis

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employed along the shoreline between Singleton and White
Point Swash. As expected, the storm related short term
recession predictions for the same area are significantly
greater. The computer calculations for the IPP typical of
this area predict that the shoreline recession resulting in
a 25-year storm will be about 3 times greater than the long
term recession rates, or about 116 feet landward of the
crest of the IPP. Figure 8.3-2 is a depiction of the
computer modeling of storm erosion of the IPP'typical of the
shoreline south of Myrtle Beach for both a 25 and 50-year
storm event.

For the unincorporated area under consideration south of
Myrtle. Beach, the minimum recommended setback from the
beach/dune system should be that distance dictated by thie
future location of the 25-year shoreline as predicted by a
linear recession analysis. Allowantces for construction of
major habitable structures seaward of that 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
or regulations. 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.

Surfside Beach and Unincorporated Garden City Beach
Along the approximate 4 mile stretch of shoreline
encompassed almost equally by Surfside Beach and the section
of unincorporated Garden City Beach within Horry County
analyses of shoreline processes continue to indicate a
prognosis of long term erosion and associated recession. At
present, existing shorefront development within the limits

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of Surfside Beach is predominantly single family residences.
In contrast, in the northern portion of Garden City where
new and reconstructed development is occurring, the trend is
predominantly high density multi-family usage.

With the evolving reorientation of the general shoreline
from Garden City southward attributable to the stabilization
of Murrells Inlet, the segment of Garden City Beach within
Horry County can be expected to potentially suffer
accelerated rates of erosion and recession. In areas where
the shoreline location has been fixed by means of seawalls,
groins, etc., recession may be terminated, but vertical
erosion of the wet or dry beachface is expected to occur.

The quantification of shoreline erosion trends for this
section of the study area based upon a linear analysis
indicates shoreline recession rates resulting in a 25-year
future shoreline location approximately 37.5 feet upland of
the predicted IPS. In accordance with similar
recommendations made for the remainder of the County, the
minimum recommended setback from the beach/dune system
should be the future location of the 25-year shoreline.

Again, 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 setba'ck
should be limited to dune overwalks, sand fencing and
erosion control measures, where warranted and fully
permitted.

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9.5 Coastal Construction Zones
The implementation of minimum coastal construction standardsS
landward of the MHWL are recommended as a result of the
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 federal0
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 and 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.

0 ~~9.6 Erosion Control Permittina Procedures
The analyses and results contained herein indicate that long
term erosion trends are expected to continue unabated
throughout the majority of the study area. Short term
0 ~~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
0 ~~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. bus to the demonstrated proximity of
existing lines of construction to not 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 arid enforced regarding future erosion
* ~~~control measures.

Erosion along South Carolina's shoreline has progressed to a
degree that a substantial number of habitable structures are
* ~~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
0~~~ 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
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, for
example, sloping stone revetments, is a possible moans of

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providing such interim protection. However, it is known
that armoring can notentiallv adversely impact the adjacent
beach-dune system.

i Simplistically, seawalls dnd shoreline armoring can be
expected to adversely affect the beach/dune system in the
following ways:

Fr 1) They can interfere with alongshore sediment
transport processes, 0
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
C' 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 Armoring - Possible alternatives to
F, .armoring include: (a) relocating the endangered

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structure landward, (b) elevating the structure on
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
shorelines 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
sediment transport.

Similarly, a quantitative assessment should be made to
establish a required annual volume of mitigative sand

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placement in order to ensure no adverse impact to the beach-
dune system would result from the issuance of the requested0
permit. Although the methodology for establishing such
mitigation is beyond the scope of this study, such an
approach would take the form of quantifying the volume of
sediment that would be lost to the beach system due to0
gradual erosion in addition to possibly adverse alongshore
effects.

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

9.7 Shoreline Restoration
As previously mentioned, large scale beach restoration or
"nourishment" is the perederosion 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.0

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 solution0
does not necessarily land itself to small scale applications
in either a practical or cost-effective manner. The

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determination of applicability is best performed on a case-
0 ~~by-case basis. There is no question, however, that the
beach nourishmnent experience has been proven to be a
technically viable approach to mitigating beach erosion.

0 ~~~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
viable when the adverse effects of inlets must be accounted
for such as in lower Horry County. For example, on Pawley's
0 ~~~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
0' ~~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,

* ~~~~~Jet-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.

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

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the latter could potentially adversely affect adjacent
properties and the beach/dune system.

9.8 Lona-Term Monitorina 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 this
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 purposes on an annual basis. Ideally,
offshore 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
(7) days of a major storm event affecting the South
Carolina coast.

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The eventual rigorous monumenting of a statewide
survey baseline to include both vertical and
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 Corp6ration.
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.

-164-

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

Ninmnedal, D. and Humphies, S.M. 1978. Hydraulics and
Dynamics of North Inlet, South Carolina, 1975-76. Prepared
for U.S. Army Coastal Engineering Research Center, GITI
Report 16. Vicksburg, Mississippi.

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
Inventory of Charleston, South Carolina: A Preliminary
Report. Charleston, South Carolina. Prepared by the
University of South Carolina, Geology Department, Columbia,
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
Beach, South Carolina. Surfside Beach, South Carolina.

U.S.- Army Corps of Engineers. Charleston District. 1983.
Myrtle Beach, Horry, and Georgetown Counties, South
Carolina: Reconnaissance Report on Beach Erosion Control
and Hurricane Protection. Charleston, South Carolina.

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.
Revision of Weir System and Jetty and Channel Alignments:
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.

-165-

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
Carolina. South Carolina Sea Grant Consortium, Charleston,
South Carolina.

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