    [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

                                 -3-

                                                                             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.

    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

    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.

                                      -14-

    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-

         5-

         4-

      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

                             NN

     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

               19

               17
                               GEORGETOWN COUNTY
             u  16
             _5.                        //

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

             I 13                   /
             LU
             ...I

               11

               10

                          /

                8

                7

                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

                                                                                          U,

                         �`.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~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-

                   20

                      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-

                                                                                        II

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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

                                -68-

    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

                                                                                      0

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

    4-

                                                                 .                   0

    4-

                                                                                      S

                                                                                      0

                                                                                      0
    L-.

                                                                                      0

                                                                                      0

    V.-

    4.
    4-,
                                                                                      S

                                                                                      0

                                             -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

                                                                                                S

    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:

                 W,

        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--

       C:

                                                                    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)

       9-

      I to-

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

    2-                                    -,

      0-

        -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

              1-

              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

              20

            -~~~ 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

                20

             "-  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.

                               -140-

    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

                                -143-

    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

                                -144-

    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

                                -145-

     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
                                 -146-

    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

                              -147-

                                                   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-

       Z

              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

                               -151-

          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.

                                      -152-

    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

                                -153-

    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

                                -154-

    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.

                               -155-

    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

                                           -157-

                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

                                             -158-

              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

                                 -159-

    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

                               -160-

              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

                                           -161-

    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.

                               -162-

    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.

                       -163-

                            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.
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    Sea Grant Consortium, Charleston, South Carolina.

    South Carolina Coastal Council.  1979.  Guidelines and
    Policies of the South Carolina Coastal Management Program.
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    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
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    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
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    Zarillo, G.A., Ward, L.G., and Hayes, M.O. 1985. An
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