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TECHNICAL REPORT CERC-83-1 

SHORELINE MOVEMENTS 

Report 2 

TYBEE ISLAND, GEORGIA, TO CAPE FEAR, 
NORTH CAROLINA, 1851-1983 

by 

Fred J. Anders, David W. Reed, Edward P. Meisburger 

Coastal Engineering Research Center 

DEPARTMENT OF THE ARMY 

Waterways Experiment Station, Corps of Engineers 

3909 Halls Ferry Road, Vicksburg, Mississippi 39180-6199 




May 1990 
Report 2 of a Series 

Approved For Public Release; Distribution Unlimited 



Prepared for DEPARTMENT OF THE ARMY 
US Army Corps of Engineers 
Washington, DC 20314-1000 

National Oceanic and Atmospheric Administration 
Rockville, Maryland 20852 

and 

State of South Carolina 

Division of Research and Statistical Services 

Columbia, South Carolina 29201 



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The findings in this report are not to be construed as an 

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Technical Report CERC-83-1 



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1 1 . TITLE (Include Security Classification) 

Shoreline Movements; Report 2, Tybee Island, Georgia, to Cape Fear, North Carolina, 1851- 

1983 



12. PERSONAL AUTHOR(S) 

Anders, Fred J.; Reed, David W. ; Meisburger, Edward P. 



13a. TYPE OF REPORT 13b. TIME COVERED 
Report 2 of a series FROM to. 



14. DATE OF REPORT (Year, Month, Day) IS. PAGE COUNT 
May 1990 164 



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Available from National Technical Information Service, 5285 Port Royal Road, Springfield, 

VA 22161 



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18 SUBJECT TERMS (Continue on reverse if necessary and identify by block number) 
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19. ABSTRACT (Continue on reverse if necessary and identify by block number) 

The history of shoreline change along the coast of South Carolina is examined. Maps 
depicting the entire shoreline at various points in time were prepared by the National 
Oceanic and Atmospheric Administration, National Ocean Service, and the South Carolina 
Division of Research and Statistical Services. These maps were used by Staff of the 
US Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, to 
analyze changes in shoreline position over the past 150 years. 

The shoreline maps were digitized at an along-the-coast interval of 50 m. Cross- 
shore transects were established at each location to facilitate examination of shoreline 
position changes. Shoreline position was compared both spatially and temporally to deter- 
mine net and average rate of change. Data are summarized in this report for each tran- 
sect, defined segments of shoreline, each barrier island or mainland beach, and defined 

(Continued) 



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8a. NAME OF FUNDING/ SPONSORING ORGANIZATION (Continued). 

US Army Corps of Engineers 

National Oceanic and Atmospheric Administration; 

Division of Research and Statistical Services, State of South Carolina 

8c. ADDRESS OF FUNDING/SPONSORING ORGANIZATION (Continued). 

Washington, DC 20314-1000; 
Rockville, MD 20852; 
Columbia, SC 29201 

19. ABSTRACT (Continued). 

geomorphic regions. The technique allows quantification of shoreline change in an onshore- 
offshore direction. Pronounced alongshore changes, such as often occurs at inlets or capes 
were examined using manual techniques to measure areal changes. Results are presented for 
the entire Atlantic coast from Tybee Island, Georgia to Cape Fear, North Carolina, in both 
graphic and tabular format. Erosion and accretion were variable spatially and temporally 
throughout the period of record. Results show that long-term erosion (>1 m/year) predomi- 
nated throughout the region of coast fronted by barrier islands. Mainland beaches, such as 
those along the "Grand Strand" were relatively stable. In both regions, erosion rates were 
most variable and greatest in the vicinity of inlets. 

A variety of factors were compared with the shoreline change data to determine the 
cause for measured patterns of erosion and accretion. Proximity to inlets was a major cause 
for variable erosion present along the barrier island coastline. Lack of inlets could also 
be a major reason for stability of "Grand Strand" beaches, along with the shallow depth to 
less erodible pre-Holocene sediments. Human impacts in the coastal zone had localized mea- 
surable effects on erosion/accretion patterns. Maximum wave height also correlated well 
with erosion, suggesting that susceptibility to storms was an important factor in determin- 
ing shoreline stability. Other factors, such as nearshore bathymetry and shoreline orienta- 
tion showed little effect on shoreline changes. 



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PREFACE 

This report is the result of a cooperative effort of the National Ocean 
Service (NOS) , National Oceanic and Atmospheric Administration (NOAA) , 
US Department of Commerce; the Division of Research and Statistical Services 
(DRSS) of the State of South Carolina; and the Coastal Engineering Research 
Center (CERC) of the US Army Engineer Waterways Experiment Station (WES) . 
The study, based on a comparison of historic survey data contained in the NOS 
archives, was funded jointly by Headquarters, US Army Corps of Engineers 
(HQUSACE) , NOAA, and the State of South Carolina. All survey data reduction, 
quality control, and publication of the shoreline maps were performed by NOS 
with support from DRSS ; data analyses and report preparation were completed by 
CERC under the Barrier Island Sedimentation Studies work unit of the Coastal 
Program. Dr. C. Linwood Vincent was the Coastal Program Manager, and 
Messrs. John H. Lockhart, Jr., and John G. Housley were HQUSACE Technical 
Monitors . 

The report was prepared by Messrs. Fred J. Anders, David W. Reed, and 
Edward P. Meisburger, CERC. Work was carried out under the general supervi- 
sion of Dr. Steven A. Hughes, Chief, Coastal Processes Branch, Research 
Division (RD) , CERC; Ms. Joan Pope, Chief, Coastal Structures and Evaluation 
Branch, Engineering Development Division (EDD) ; Mr. H. Lee Butler, Chief, RD; 
Mr. Thomas W. Richardson, Chief, EDD; Dr. James R. Houston, Chief, CERC, and 
Mr. Charles C. Calhoun, Jr., Assistant Chief, CERC. Original programs to 
analyze shoreline change data were developed by Mr. Steven Knowles , formerly 
of CERC. The section describing map production procedures was modified from a 
report by Everts et al . (1983) (see References at the end of the main text). 
Numerous contributions by all members of the Coastal Geology Unit, CERC, 
including review of the manuscript, are gratefully acknowledged. This report 
was edited by Ms. Lee T. Byrne of the Information Technology Laboratory, WES. 

Shoreline change maps for Tybee Island, Georgia, to Cape Fear, North 
Carolina, are included as a separate enclosure to this report. 

Commander and Director of WES during publication of this report was 
COL Larry B. Fulton, EN. Technical Director was Dr. Robert W. Whalin. 



CONTENTS 

Page 

PREFACE 1 

LIST OF TABLES 3 

LIST OF FIGURES 3 

CONVERSION FACTORS, NON-SI TO SI (METRIC) 

UNITS OF MEASUREMENT 7 

PART I : INTRODUCTION 8 

PART II : STUDY AREA 11 

Geographical Setting 11 

Coastal Environment 12 

Geology 24 

Present Geomorphology 30 

PART III : METHODOLOGY 38 

Data Sources 38 

Map Production 42 

Data Analysis 46 

PART IV : SHORELINE DATA ANALYSIS 54 

Changes in Shoreline Position 57 

Inlet Changes 102 

PART V: PRESENT AND FUTURE SHORELINE CHANGES 123 

Analysis of Present Shoreline Positions 123 

Waves 124 

Future Shoreline Changes 142 

PART VI : SUMMARY AND CONCLUSIONS 145 

REFERENCES 148 

APPENDIX A: SUMMARY OF SHORELINE CHANGE DATA PER SEGMENT Al 



LIST OF TABLES 
No. Page 

1 Known Storms Affecting the South Carolina Coast 20 

2 Dates of Historical T Sheets Used in Shoreline Change Map 

Production 40 

3 Geographical Positions of Base Maps 47 

4 Average Shoreline Movement, Tybee Island, Geergia, to 

St. Helena Sound, South Carolina 60 

5 Average Shoreline Movement, St. Helena Sound to Charleston 

Harbor , South Carolina 69 

6 Average Shoreline Movement, Charleston Harbor to Bull 

Island, South Carolina 75 

7 Average Shoreline Movement, Bull Bay, South Carolina 81 

8 Average Shoreline Movement, Sandy Point to North Inlet, 

South Carolina 86 

9 Average Shoreline Movement, North Inlet to South Carolina/ 

North Carolina State Line 92 

10 Average Shoreline Movement, South Carolina/North Carolina 

State Line to Cape Fear, North Carolina 98 

11 Summary of Inlet Changes 104 

12 Area Changes South of the Winyah Bay Jetties 117 

13 Subaerial Surface Area Changes at Cape Fear 121 

14 Cumulative Percentage of Total Shoreline Distance with Nearshore 

Slopes to -1.8, -5.5, and -9.1 m, MLW Steeper than Designated 

Values 134 



LIST OF FIGURES 

No. Page 

1 Map of the study area: the coastline from Tybee Island, 

Georgia, to Cape Fear, North Carolina 9 

2 Summarized wind and offshore wave conditions near Charleston, 

SC 13 

3 Seasonal directionality of offshore wave conditions near 

Charleston , SC 14 

4 Alongshore variation of wave height within the study area 15 

5 Alongshore variation of wave period and wave power flux within 

the study area — 16 

6 Alongshore variation in tide conditions and average annual tidal 

variation at Charleston 18 

7 Tracks of known hurricanes affecting the area between 1890 

and 1970 21 

8 Tide frequencies at selected points on the South Carolina coast, 

based on hurricane specifications 22 

9 Alongshore variation in total tidal height at various return 

intervals 23 

10 Regional sea level versus time curve developed from South 

Carolina data 24 

11 Relative sea level changes from tide gage data at Charleston, 

SC, and summary data for the southern east coast.... 25 

12 General stratigraphy of the east coast 26 



LIST OF FIGURES 
No. Page 

13 Lower Coastal Plain marine terraces 28 

14 Sea level curve for the last 35 , 000 years 29 

15 Environmental parameter changes along the coast as a function 

of distance and tidal ranges 32 

16 Wave refraction diagram showing drift reversal 'as a result of 

ebb delta bathymetry 36 

17 Three types of shoreline change resulting from inlet processes.... 37 

18 Map of the study area showing location of quadrangles selected 

as base maps 39 

19 Digitization procedure for correcting shoreline position 

locations when original shoreline movement map distortions 

exist 45 

20 Idealized segment for digitizing shoreline change information 49 

21 Map of the study area showing division into zones and 

subdivisions into seven reaches 52 

22 Map of the study area showing division of the shoreline into 

short segments for digitizing and subsequent analysis 55 

23 Average net shoreline movement and standard deviation of 

movement for coastal reach 1, 1852-1983 58 

24 Maximum net shoreline movement, number of surveys used, and 

time interval of surveys for coastal reach 1 59 

25 Temporal division of average net shoreline movement data for 

coastal reach 1 62 

26 Summary of shoreline movement for coastal reach 1, 1852-1983 64 

27 Average net shoreline movement and standard deviation of 

movement for coastal reach 2, 1851-1983 65 

28 Maximum net shoreline movement, number of surveys used, and 

time interval of surveys for coastal reach 2 66 

29 Temporal division of average net shoreline movement data for 

coastal reach 2 67 

30 Summary of shoreline movement for coastal reach 2, 1851-1983 71 

31 Average net shoreline movement and standard deviation of 

movement for coastal reach 3, 1857-1983 72 

32 Maximum net shoreline movement, number of surveys used, and 

time interval of the surveys, for coastal reach 3 73 

33 Temporal division of average net shoreline movement data for 

coastal reach 3 74 

34 Summary of shoreline movement for coastal reach 3, 1857-1983 76 

35 Average net shoreline movement and standard deviation of 

movement for coastal reach 4, 1874-1983 77 

36 Maximum net shoreline movement, number of surveys used, and 

time interval of surveys, for coastal reach 4 78 

37 Temporal division of average net shoreline movement data for 

coastal reach 4 80 

38 Summary of shoreline movement for coastal reach 4, 1874-1983 82 

39 Average net shoreline movement and standard deviation of 

movement for coastal reach 5, 1857-1983 83 

40 Maximum net shoreline movement, number of surveys used, and 

time interval of surveys , for coastal reach 5 84 



LIST OF FIGURES 
No. Page 

41 Temporal division of average net shoreline movement data for 

coastal reach 5 85 

42 Summary of shoreline movements for coastal reach 5, 

1857-1983 88 

43 Average net shoreline movement and standard deviation of 

movement for coastal reach 6, 1872-1983 89 

44 Maximum net shoreline movement, number of surveys used, and 

time interval of surveys, for coastal reach 6 90 

45 Temporal division of average net shoreline movement data for 

coastal reach 6 91 

46 Summary of shoreline movements for coastal reach 6, 

1872-1983 93 

47 Average net shoreline movement and standard deviation of 

movement for coastal reach 7, 1857-1983 94 

48 Maximum net shoreline movement, number of surveys used, and 

time interval of surveys , for coastal reach 7 96 

49 Temporal division of average net shoreline movement data for 

coastal reach 7 97 

50 Summary of shoreline movement for coastal reach 7, 1857-1983 99 

51 Summary of shoreline movements for coastal reach 7 west of 

the Cape Fear River and from the Cape Fear River to New Inlet. . . 100 

52 Summary of shoreline movement in the barrier island and arcuate 

strand geomorphic zones 102 

53 Summary of shoreline movement for the entire study area, 

1851-1983 103 

54 Average net shoreline change versus occurrence of significant 

wave heights greater than 2 m 125 

55 Maximum net shoreline change versus average significant wave 

height 125 

56 Maximum net shoreline change versus maximum significant wave 

height 127 

57 Typical example of data scatter for average shoreline change 

versus wave period 127 

58 Maximum net shoreline movement versus occurrence of waves with a 

period greater than 11 sec 128 

59 Division of shoreline segments into specified orientation 

categories 130 

60 Shoreline orientation versus average and maximum net shoreline 

movement 131 

61 Shoreline orientation versus average and maximum net shoreline 

movement in reach 2 132 

62 Average and maximum net shoreline change versus nearshore slope 

out to -5.5 m Mean Low Water (MLW) 133 

63 Maximum net shoreline change versus nearshore slope out to 

-5.5m MLW for reach 6 134 

64 Cumulative percentage of total shoreline distance versus 

maximum shoreline change greater than specified values 135 

65 Cumulative percentage of total shoreline distance versus average 

net shoreline changes greater than specified values 135 



LIST OF FIGURES 
No. Page 

66 Cumulative percentage of shoreline distance of segments having 

slopes steeper than 1:300 to -1.8 m MLW versus average and 

maximum net shoreline changes greater than specified values 136 

67 Cumulative percentage of shoreline distance of segments having 

slopes steeper than 1:900 to -5.5 and -9 m MLW versus average 

and maximum net shoreline changes greater than specified 

values 137 

68 Average net shoreline change versus nearshore slope to -5.5 m 

MLW for reaches 1 through 5 and 6 and 7 139 

69 Maximum net shoreline change versus nearshore slope to -5.5 m 

MLW for reaches 1 through 5 and 6 and 7 140 

70 Map showing locations of inner continental shelf cores 

containing pre-Holocene sediment. Numbers indicate downhole 

depth in metres to the pre-Holocene 141 



CONVERSION FACTORS, NON-SI TO SI (METRIC) 
UNITS OF MEASUREMENT 



Non SI units of measurement used in this report can be converted to SI 
(metric) units as follows: 



Multiply 



feet 

foot-pounds (force) 

knots (international) 



Jv_ 



0.3048 

1.355818 

0.5144444 



To Obtain 



metres 

metre -newtons or joules 

metres per second 



SHORELINE MOVEMENTS 
TYBEE ISLAND, GEORGIA, TO CAPE FEAR, NORTH CAROLINA, 1851-1983 

PART I: INTRODUCTION 

1. This is the third and final report in a series of shoreline change 
studies undertaken cooperatively between the National Oceanic and Atmospheric 
Administration (NOAA) ; National Ocean Service (NOS) ; and the Coastal Engineer- 
ing Research Center (CERC) , US Army Engineer Waterways Experiment Sta- 
tion (WES) . Maps accompanying this report received additional support from 
the Division of Research and Statistical Services of the State of South 
Carolina. The study area comprises the ocean coast of northern Tybee Island, 
Georgia, the entire ocean coastline of South Carolina; and the contiguous 
coastline of North Carolina to Cape Fear (Figure 1) . Unlike previous series 
reports, map data were insufficient to include bay side shorelines of barrier 
islands. Changes in ocean shoreline position from 1852 to 1983 were available 
using survey data from NOS and its predecessor, the US Coast and Geodetic 
Survey (USC&GS) . Shoreline change maps for Tybee Island, Georgia, to Cape 
Fear, North Carolina, are included as a separate enclosure to this report. 

2. Evolution of the shoreline has become a point of increasing concern 
within the coastal community during the last two decades. Evidence is based 
on the increasing number of reports in the scientific literature which use 
shoreline change information. Coastal managers, engineers, and scientists 
have recognized the value of these data sets for management and engineering 
decisions in the coastal zone. Historic shoreline change data are easy to 
acquire, exhibit, and update as new data become available. Also, with some 
reservations, shoreline change data can be carefully extrapolated to predict 
future shoreline changes resulting from natural and man-made causes. 

3. Use of maps and aerial photos to examine spatial and temporal 
changes in the shoreline has a long history; however, quantitative assessment 
of shoreline change from photos and maps was not well documented until 1970 
(Langfelder, Stafford, and Amein 1970; Stafford 1971;, Stafford and Langfelder 
1971) . Since then, coastal scientists have used a variety of techniques to 
measure shoreline change (Fisher 1977; Dolan, Hayden, and Heywood 1978; Leath- 
erman 1983). Aerial photographs can be used to provide detail and short-time 



WLMNGTON. N.CX 

CAPE FEAR RIVER, 

I J NEW INLET 
^ SMITH ISLAND 
^^ CAPE FEAR 
IJ^-^LOCKWOOO FOLLY INLET 
SHALLOTTE INLET 
_ LITTLE RIVER tILET 




PORT ROYAL SOUND 
/ HILTON HEAD ISLAND 
JDAIFUSKE ISLAND 
GA^7 ^BEE BLAND 

Figure 1. Map of the study area: the coastline from Tybee 
Island, Georgia, to Cape Fear, North Carolina 

interval data required for evaluating processes shaping the coastline. How- 
ever, until the many episodic events that form the coastline are integrated, a 
detailed understanding and interpretation of long-term processes and morpho- 
logical response are precluded. Use of historical maps expands the temporal 
view of the coastline, smoothing peaks and valleys of short-term changes, 
allowing managers, engineers, and scientists to view long-term coastal trends. 
4. This investigation of shoreline change used up to a 132 -year span of 
NOS/USC&GS map data derived from original field and air photo surveys . Maps 
depicting shoreline position are available prior to the first USC&GS map used 
here (1851); however, accuracy of earlier maps cannot be determined. 



Likewise, additional maps are available between dates of those used in this 
investigation, but their level of accuracy and/or scale were not suitable. 
Accuracy in original data sets and in their interpretation is an essential 
ingredient in producing believable shoreline change information. 

5. This study is intended to enhance and explain the accompanying 
shoreline change maps. The maps were used to establish transects perpendicu- 
lar to shoreline trend at a 50-m alongshore interval. Shoreline position at 
each survey date was digitized on the transect allowing linear comparisons of 
shoreline position to calculate shoreline change. Average and maximum net 
rate of change and standard deviation of shoreline change are among data pre- 
sented for each transect. Shoreline change transect data are presented in 
summary form (a) in short, defined alongshore coastal segments; (b) by Barrier 
Island/Mainland beach; (c) by defined coastal reach; (d) by geomorphic zones; 
and (e) for the entire study area. Extremely dynamic changes around inlets 
and capes were not measurable using this technique and had to be specially 
treated. Where possible, temporal and alongshore spatial variations in shore- 
line change rates were compared with physical characteristics of the coast and 
process information to explain observed variability. 

6. Several important differences exist between this report and the pre- 
vious two. First, very limited bay side shoreline information was available 
on the NOS maps, and where it was present, shoreline change was so small as to 
fall outside accuracy limits of this technique. Consequently, no bay shore- 
line data are presented, only data from coastlines facing the open ocean. 
This factor allowed the use of linear measurement of shoreline change, as in 
Report 3 (Knowles and Byrnes, in preparation), not aerial changes as in 
Report 1 (Everts, Battley, and Gibson 1983). A second difference is the 
length of shoreline examined in this report. Report 1 covered 210 km of gen- 
erally linear barrier island coastline. Report 3 covered 208 km of mixed lin- 
ear, elongated barriers and short barriers with frequent inlets. This report 
covers over 336 km of shoreline composed of short barriers with frequent in- 
lets and a wide range of coastal orientations, shallow open-water bays, and 
long, arcuate coastal headlands. The length of shoreline required subdivision 
of the coastline into smaller reaches to allow presentation of data. For this 
study, the shoreline change maps were produced by NOS in a south- to -north 
direction, opposite of previous reports. This necessitated some changes in 
procedures used to obtain quantitative information. 

10 



PART II: STUDY AREA 
Geographical Setting 

7. The study area encompasses approximately 336 km of open Atlantic 
coastline from the northern end of Tybee Island, Georgia, north along the 
South Carolina coast to Cape Fear, North Carolina (Figure 1). The southern 
portion of this reach is composed of numerous barrier islands averaging 7 km 
in length, separated by frequent tidal inlets. Many of these inlets are 
large, representing the point of debouchere for major coastal plain rivers. 
From south to north, these include Tybee Roads/Calibogue Sound, Port Royal 
Sound, St. Helena Sound, Charleston Harbor, Bull Bay, and Winyah Bay. Tybee, 
Hilton Head, Pritchards , Hunting, Edisto, Seabrook, Kiawah, Folly, Morris, 
Sullivans, Isle of Palms, Dewees, Capers, Bull, and Cape Island are the major 
barrier islands within this section from south to north. This segment of the 
coastal plain, often referred to as the "Carolina low country" because of its 
low relief, is also characterized by wide salt marshes, dissected by 
meandering tidal creeks, between the barrier islands and mainland. Fresh- 
water swamps are abundant throughout the region. The general orientation of 
the coastline in the southern section is northeast to southwest. 

8. Cape Island, which includes the prominent Cape Romain, lies roughly 
in the middle of the study area (Figure 1) . At Cape Romain, the shoreline 
reorients to north-northeast. North of Cape Island, the shoreline changes 
under influence of the Santee, Waccamaw, Pee Dee, Sampit, and Black Rivers. 
The Santee had the fourth largest discharge of any river on the east coast 
(Kjerfve 1976). Small barrier islands, backed by wide expanses of salt marsh, 
dominate this deltaic coastline. 

9. North of this region, bordering Long Bay, begins a coastal reach 
characterized by relatively few and small inlets, little coastal marsh, main- 
land beaches, and limited barrier islands, referred to as the "arcuate 
strand" (Brown 1977) . This arcuate segment of coastline extending from Winyah 
Bay to Cape Fear, North Carolina, is generally less than 8 m above mean sea 
level (MSL) and has an orientation of north-northeast to south- southwest in 
the south, reorienting to approximately east-west at Cape Fear. North, 
Murrells , and Little River are the major South Carolina inlets within this 
reach. Debidue, Pawleys Island, Litchfield, Huntington, Garden City, 

11 



Surf side, Myrtle, and North Myrtle are beaches from south to north that are 
located in South Carolina. These beaches have been important in the recre- 
ation industry of the state. The North Carolina segment is composed of main- 
land beach and six barrier islands separated by small inlets. From east to 
west, these include Smith, Oak, Ocean Beach, Ocean Isle Beach, Sunset Beach, 
and Bird islands. They are separated from the mainland by marsh, tidal 
creeks, and the Atlantic Intercoastal Waterway. Most are less than 5 m above 
MSL. Inlets from east to west include New Inlet, which is north of Cape Fear; 
Cape Fear River; Lockwood Folly; Shallotte Sound; Tubbs ; and Mad Inlet. 

Coastal Environment 

Winds and waves 

10. Along this reach of coast, south and southwest winds prevail, espe- 
cially during spring and summer months (Figure 2*). During fall and winter, 
north, northeast, and easterly winds prevail. Northeast quadrant winds are 
generally strongest and thus dominate in effect on the coastline. Initiation 
of sediment motion by wind requires a minimum velocity of 16 km/hr, and at 
least 25 km/hr are required to sustain transport (Bagnold 1941) . Winds of 
this velocity are most likely to occur from the northeast quadrant. 

11. Wind direction is influential in controlling wave approach along 
this coastline. Sea and swell data for the block of 30- to 35-deg north lati- 
tude and 75- to 80-deg west longitude (US Army Corps of Engineers (USACE) 
1974, taken from the US Naval Oceanographic Office, Oceanographic Atlas) indi- 
cate the effect of wind in controlling wave direction (Figure 2) . Predominant 
seas are from the northeast and southeast, and swell most frequently occurs 
from the northeast and east followed by the southeast. Seasonal directional- 
ity of offshore waves are indicated in Figure 3. Bloomer (1973) concluded 
that water circulation patterns on the south Atlantic inner shelf are con- 
trolled primarily by wind direction and secondarily by tides. Wave direction 
is the driving force behind movement of littoral drift, which is predominantly 
to the southwest along this entire stretch of coast (Brown 1977) . Local 
reversals because of nearshore bathymetry and coastal orientation do occur. 

* A table of factors for converting non-SI units of measurement to SI 
(metric) units is presented on page 7. 



12 




BAT* SHOWN 

XTRACTED FROM THE 1963 
OCEANOORAPHIC ATLAS NORTH 
ATLANTIC OCEAN. PUBLISHED BY 
THE US NA\«L OCEANOGRAPHIC 
OFFICE. WASHINGTON. C FOR THE 



OFFSHORE 

SWELL DIAGRAM 





I 



SURFACE WINDS (ONSHORE STATION) 

NOTF CI 

, wEaThei 



COMPUTED FROM DATA 9TUS 
R BUREAU CHARLESTON.SC 
FROM JAN I. I9H-0EC U65 



OFFSHORE 

SEA DIAGRAM 




SLIGHT « 31 
MODERATE 13-5) 
ROUGH (»-»') 
VERT ROUOH 18-12) 
HIGH (>I2'1 



Figure 2. Summarized wind and offshore wave conditions near Charleston, 

SC (USACE 1974) 



13 




Figure 3. Seasonal directionality of offshore wave 
conditions near Charleston, SC (USACE 1974) 

Net rate of littoral drift was estimated to be 128,000 cu m/year at Murrells 
Inlet (Kana 1977); 290,000 cu m/year at Bull Island (Knoth and Nummedal 1977); 
130,000 cu m/year at Capers Island (Kana 1977); and 200,000 cu m/year at 
Charleston (FitzGerald, Fico, and Hayes 1979). 

12. Hubbard, Barwis , and Nummedal (1977) and Nummedal et al. (1977) 
noted wave energy flux for South Carolina and the South Atlantic coast of the 
United States decreased from north to south. Wave energy flux, the amount of 
energy expended by a wave per unit distance per unit time, is related to wave 
period and the square of wave height. Height and period data for the study 
area were obtained from the Phase III, USACE, Wave Information Study (WIS) 
(Jensen 1983) , which contains inner shelf wave statistics hindcast from a 
20-year period of meteorological data (1956-1975) at an along-the-coast inter- 
val of 16 km. Average significant wave height, maximum significant wave 
height, and average period were plotted from WIS data and show alongshore 
variation within the study area (Figures 4 and 5) . Wave height and period 



14 



ALONGSHORE VARIATION OF MAX. Hs 

PER WB SEGMENT. SOUTH TO NORTH 




80 120 ISO 200 

ALONGSHORE DISTANCE S N (km) 



ALONGSHORE VARIATION OF AVG. Hs 

PER WIS SEGMENT. SOUTH TO NORTH 




SO 120 160 200 240 280 320 

ALONGSHORE DISTANCE S — N (km) 

Figure 4. Alongshore variation of wave height within the 
study area 



15 



ALONGSHORE VARIATION OF WAVE PERIOD 



PER WB SEGMENT. SOUTH TO NORTH 




1 1 — 

280 



160 200 

MJDNSSHORE DISTANCE S — N (km) 



ALONGSHORE VARIATION OF WAVE POWER FLUX 



PER WB SEGMENT. SOUTH TO NORTH 




ALONGSHORE DISTANCE S — N (km) 

Figure 5 . Alongshore variation of wave period and wave power 
flux within the study area 



16 



were generally lowest in northern sections of the study area, increasing rap- 
idly southward towards Cape Romain and Charleston, and then decreasing towards 
Savannah, GA. Wave power flux calculated from WIS data (Figure 5) mimics the 
general trends of average wave height and period. A net increase in wave 
energy flux of approximately 80 percent is evident from the northern end of 
the study area to the southern end. This does not agree with Hubbard, Barwis, 
and Nummedal (1977) and Nummedal et al . (1977), who based their conclusions on 
1970 Naval Weather Service Command data Summary of Synoptic Meteorological 
Observations (SSMO) . The WES investigators feel that the differences are a 
result of the longer period of record and more frequent along-the-coast inter- 
val of WIS data. 
Tides 

13. The coast of South Carolina has been classified as mesotidal (2- to 
4-m tidal range) by Hayes (1975) based on a classification system by Davies 
(1964). Brown (1977) and Hubbard, Hayes, and Brown (1977) indicate mean tidal 
range and spring tidal range increase towards the south along this coast (Fig- 
ure 6) . Calculations based on predicted tide tables (US Department of 
Commerce 1986) show an increase of 1 . 7 to 2 .4 m in maximum tidal range from 
Wilmington, NC, to Charleston, SC, and an increase of 2.4 to 3.2 m from 
Charleston to Savannah, GA. Overall, there is an 88 -percent increase in 
maximum tidal range from north to south in the study area, while wave power 
flux increased 80 percent from north to south. Finley (1978) describes the 
tide at North Inlet as being semidiurnal, with a diurnal inequality averaging 
0.37 m. Annual variations in tide level are also present (Figure 6). Annual 
variation is due to a variety of factors including effects of storms. 

Storms 

14. Short-term increases in tidal height within the study area occur 
with passage of storms. Coastal flooding is one of the most significant storm 
damages in this area because adjacent land elevations are so low. The study 
area is subject to late summer and fall tropical cyclones (minimum wind speed 
of 64 km/hr) and hurricanes (minimum wind speed of 118 km/hr) , and extratropi- 
cal northeast storms during winter. The scientific literature includes dis- 
cussions of relative damages produced by northeast storms and tropical storms 
along the east coast of the United States; however, most researchers (e.g., 
Machemehl 1974; Myers 1975) contend that extratropical storms play a subordi- 
nate role within this study area. Simpson and Miles (1971) report a 

17 



SPMNO TIDE RANOE • • TttAL HEWHT ■ ■ 

TIDAL RAN0E H I" •««• TIOE HEIOHT is A 





Figure 6. Alongshore variation in the tide conditions 
(modified from Brown 1977) and average annual tidal 
variation at Charleston (Myers 1975) 



18 



16 -percent probability of some type of tropical storm striking the South 
Carolina-Georgia border area in any one year and a 7-percent chance that it 
will be a hurricane. The probability decreases northward to 8 percent for a 
tropical storm, with a 5- to 8 -percent chance of a hurricane. The region 
around the North Carolina- South Carolina border increases again to 13 -percent 
probability for a tropical storm in any one year and a 6 -percent chance of it 
being a hurricane. Table 1 is a listing of known major storms affecting the 
coast of South Carolina. Figure 7 shows tracks of late 19th-century and 
20th-century hurricanes affecting the study area. 

15. Increased tidal elevation along the coast during both tropical and 
extratropical storms results from surge that accompanies the storm. Storm 
surge is due to a combination of low pressure over water allowing the water to 
bulge upward under the storm and rapid wave advance inshore resulting in wave 
buildup at the shoreline and limited return flow offshore. Increased water 
levels of 0.3 to 1 m above MSL can be expected along this coast, and records 
up to 5.8 m above MSL have been reported for major hurricanes (USACE 1974). 
Myers (1975) used data from South Carolina hurricanes to determine return 
intervals of total tidal height (astronomical tide height plus storm surge) at 
selected locations along the South Carolina coast (Figure 8) . Along coast 
variation in total tidal height from hurricanes of various return intervals is 
plotted in Figure 9. These data indicate that a tropical storm with a 10-year 
return interval could be expected to produce a tide 2.1m above MSL at 
Charleston and a storm with a 500-year return interval (probability of occur- 
rence is once in 500 years) would produce a tide 5.3m above MSL at 
Charleston. 

16. Alongshore variation in tidal height for any given return period 
(Figure 9) was explained by Myers (1975) as being due in part to a shoaling 
factor, which is a function of inner continental shelf bathymetry. In gen- 
eral, shallower water produces higher surge. Other factors that influence 
maximum surge height are strength of the storm, forward speed, radius of the 
maximum winds, and track of the storm with its distance from the coast. Surge 
dynamics vary from alongshore moving storms to inshore moving storms. 
Long-term sea- level variations 

17. Daily and seasonal water-level fluctuations play an important role 
in South Carolina coastal geomorphology, but in their examination of long-term 
trends in shoreline change, the WES researchers must also consider long-term 

19 



Table 1 
Known Storms Affecting the South Carolina Coast 



















Year 


Date 


Year 
1904 


Date 




Name 


1686 


Sep 


4-5 


Sep 


15 






1700 


Sep 


16 


1906 


Sep 


17 






1713 


Sep 


16-17 


1906 


Oct 


20 






1728 


Aug 


13 


1907 


Sep 


27- 


29 




1752 


Sep 


30 


1911 


Aug 


27- 


28 




1781 


Aug 


10 


1916 


Jul 


13- 


14 




1783 


Oct 


7-8 


1920 


Sep 


20 






1787 


Sep 


19 


1924 


Sep 


16- 


17 




1797 


Oct 


19-20 


1927 


Oct 


1-2 


1 




1804 


Sep 


3-9 


1928 


Aug 


10- 


11 




1811 


Sep 


10 


1928 


Aug 


14- 


15 




1813 


Aug 


27 


1928 


Sep 


17- 


19 




1814 


Jul 


1 


1929 


Oct 


1-2 


i 




1815 


Sep 


28 


1934 


Jul 


21- 


25 




1822 


Sep 


27 


1940 


Aug 


11 






1830 


Aug 


12-17 


1944 


Oct 


19 






1837 


Sep 


1 


1945 


Sep 


17 






1837 


Oct 


8-9 


1947 


Oct 


15 






1841 


Sep 


16 


1949 


Aug 


28 






1844 


Sep 


14 


1952 


Aug 


31 






1846 


Aug 


16 


1954 


Oct 


15 




HAZEL 


1850 


Aug 


24 


1955 


Aug 


12 




CONNIE 


1851 


Aug 


24 


1955 


Aug 


17 




DIANNE 


1852 


Aug 


27 


1955 


Sep 


19 




IONE 


1854 


Sep 


7-8 


1957 


Sep 


27 




HELENE 


1871 


Aug 


16-18 


1959 


Sep 


29 




GRACIE 


1874 


Sep 


28 


1962 


Oct 


18 




ELLA 


1878 


Sep 


11-12 


1963 


Oct 


25 




GINNY 


1881 


Aug 


21-27 


1964 


Sep 


12- 


13 


DORA 


1882 


Oct 


11 


1964 


Oct 


30 




CLEO 


1885 


Aug 


24-25 


1966 


Jun 


10 




ALMA 


1888 


Oct 


11 


1968 


Jun 


7 




ABBY 


1889 


Sep 


23 


1968 


Oct 


19 




GLADYS 


1893 


Aug 


22-30 


1972 


Jun 


20- 


21 


AGNES 


1894 


Sep 


26-17 


1979 


Sep 


5 




DAVID 



20 




21 









,, 














::■-:;:: 












::: 










:# 




r.:: 


1 


..::■ 


..._ 




.... i 


• 


■ 


.... 











,__„ 




: 


::• 


::: 






zz~ 




-l-J-J-i-j-r 






■-" 


:•* 


'■'■: 


























;eT;;: 




:: ; 


tni 




::. 


_... 


.. 1 ■ ' 




::: 


iR 




i . . 


_..:;: 


:::: 


:::: 




4 


.... 




..." 


"•■ 
















:::■•• 


- 


. .. 


::.:...:: 


'3 


.:: 


r 




1! L" [jjj 


,::. ': 






■ 


<:■ 




::.. 


i- - 


























- 






~~. 


."-. 




; ■ 






: : - 


W 




f 












&/; 


;~~ 




-_-LUi 








J 






-±r.': 


-:: 












it 


f 


fr 




:::.:: 




__ . : 









■ - •• 


















ETF 


-" 






i 








ft 


f 




11 








z 

<3 


;::L: 




.. :: : 


I M 






;±i~ 








r • 

i 


y 
















a 








- 


."..'.". 


\\W 


o 
















i * 


ji 








... 




-::: 






|- 












^ 


A 


1 I::. 

ii ' 









•■)■-••- 




-- — 

















1 












2 


1 i 








-;: 


:;d 




::.:. 




/ 






I 


■ 


.. 






4 


- 




/■// 


^ 


! . 


i 


J !" 












; ;~ _} [ r 








. ::- 






r 
i 


!.! 




• 






-" 


„ 




: ' : jfT 








//t 


v' 


... 


-l 


1 ■ 
1 




.-:_:- 






~ 


:::■ 


i-izi 














-- -- 








f.y 

~?LZZ~ 








i 
i 


t-: 

i 


i 










: : z~ 




. :■■.: 


:. ■ 



RETURN PERIOD lyrl 

Figure 8. Tide frequencies at selected points on 
the South Carolina coast, based on hurricane 
specifications (Myers 1975) 

changes in sea level. Sea level changes can be examined from two points of 
view, eustatic rise and relative rise. Eustatic rise deals with worldwide 
changes in sea level resulting from continental and alpine glacier advance and 
retreat, thermal expansion and contraction of ocean waters, and global scale 
changes in ocean basin dimensions. Relative rise also incorporates local 
shoreline movements due to tectonics or subsidence, which influence the per- 
ception of water levels along the coastline. 

18. Several geological investigations have shown a steady rise in sea 
level for the last 15,000 years (e.g., Millman and Emery 1968). This corre- 
lates with continued climatic warming since maximum glacial ice advance during 



22 





10 yr 



200 



ALONGSHORE DISTANCE S — N (km) 
+ 50 yr O 100 yr 



300 



400 



500 yr 



Figure 9. Alongshore variation in total tidal height at various return 
intervals (modified from Myers 1975 and Ho and Tracey 1975) 

the Wisconsin age. Sea level rise curves show a definite break in slope to a 
much slower rate of rise about 4,000 years BP. Along the South Carolina coast 
Colquhoun and Brooks (1986) postulate a curve (Figure 10), which shows an epi- 
sodic rise and fall of sea level since 4,000 years BP. This curve, based on a 
combination of archeological and geological (C14) dating, shows a slow overall 
rise in sea level to present day. 

19. Examination of tide gage data in the vicinity of the study area 
shows a highly variable but steady overall rise in relative sea level during 
the recent past (Figure 11). Since the late 1920' s, relative sea level at 
Charleston Harbor, South Carolina, has risen approximately 15 cm. General 
trends in long-term eustatic (15,000 years BP) rise and present relative rise 
along the study area coincide, suggesting continued sea level rise for the 



23 



THOUSANDS OF RADIOCARBON i'EARS BEFORE PRESENT 



3 


r 


5 5 




3 2 













(^ 


- r, ' 


/ 


\ / 
\ / 

\ / 








/I 

/I 1 


\ 

1 ' / 
1 l / 


i;/ 












II 1 
II 1 
1 1 1 


1 ' 1 

1 ' / 
1 1 I 

1 \ 1 


i; 








/ 

/ 
/ 




1 1 / 

1 \ / 

1 w 

/ 


1 1 

( ' ',1 


\' 








1 
1 

1 
1 




/ 

J 












1 
/ 
/ 














/ 


/ 














/ 
/ 
/ 

/ 

















Figure 10. Regional sea level versus time curve developed from South Carolina 
data (after Colquhoun and Brooks 1986) 

near future. Rate of rise in the future is presently the subject of much 
debate . 

Geology 

Pre-Holocene 

20. Approximately 40 percent of the State of South Carolina is coastal 
plain (Hubbard, Hayes, and Brown 1977) of pre-Holocene age (more than 
10,000 years BP) . The Atlantic Coastal Plain, which extends along the entire 
east coast of the United States, is composed of sands, silts, and clays of 
Cretaceous, Tertiary, and Quaternary age. It overlies and is bounded on the 
west by older rocks of the Piedmont Province. The Piedmont in turn is bounded 



24 



YERRLY MEAN SER LEVEL 

STRTION NO. 866-5530 

CHARLESTON, SC 




1950 

YEAR 



SOUTHERN ERST CORST 




Figure 11. Relative sea level changes 

from tide gage data at Charleston, SC , 

and summary data for the southern east 

coast* 

to the west by the Blue Ridge Province and/or the Valley and Ridge Province 
(Figure 12) . 

21. The coastal plain of South Carolina is divisible into Upper, Mid- 
dle, and Lower sections (Cooke 1936; Richards 1945, 1967). The Upper section 
is composed of unconsolidated sediments ranging in age from Cretaceous to 
Early/Middle Miocene. Cretaceous sediments outcrop along the western edge of 
the coastal plain, adjacent to the fall line that separates them from 

* Personal Communication, 1985, Stacey Hicks, NOS , Rockville, MD. 



25 



Figure 12. General stratigraphy of 
the east coast (Richards 1967, 
reprinted by permission) 

Pre-Cambrian and Paleozoic rocks of the Piedmont. Cretaceous sediments dip 
seaward beneath younger Tertiary age sediments and apparently underlie the 
entire coastal plain. Beneath the coastal plain in this study area are deeply 
buried crystalline rocks of the Piedmont. Major structural features are evi- 
dent in these basement rocks underlying the Coastal Plain (Richards 1967). 
Cape Fear Arch is responsible for bringing basement rocks to within 365 m of 
the surface near Wilmington, NC. South of the Arch, basement rock dips down 
to the Beaufort Basin. These structural features influence thickness and 
depth of younger sediments. Cretaceous sediments have appeared in shallow 
vibracores on the nearshore shelf in the vicinity of Cape Fear (Meisburger 
1979) . Evidence is presented from a variety of sources (Richards 1967) to 
suggest that parts of the Carolina coastal plain are underlain by Triassic 
Basin rocks. 

22. Topography of the Middle and Lower Coastal Plain is dominated by 
marine "terraces," as they were first named by Cooke (1936). These terraces 
were named chiefly on the basis of topography. Their origin is related to 

26 



eustatic fluctuations in sea level that resulted in alternating submergence 
and emergence of the landscape. The sequence of events forming each terrace 
was similar. Sea level rose to some maximum altitude during a period of 
submergence (transgression) . Submergence resulted in formation of a barrier 
island chain with associated lagoonal/marsh sediments on the landward side, 
similar to the present coastline. Inlet deposits, estuarine and channel sedi- 
ments, and a seaward thinning wedge of offshore sediments were also deposited 
much as present day. This cycle was terminated by climatic changes that 
resulted in shoreline emergence (regression) . When climate once again 
shifted, a new cycle of submergence began, with sea level stabilizing at an 
altitude slightly lower than a previous cycle. The new barrier complex (ter- 
race) formed seaward and lower than the first one. Geological evidence indi- 
cates that from North Carolina south into Georgia, these cycles of submergence 
followed by emergence occurred at least three times over the Middle Coastal 
Plain and six times over the Lower Coastal Plain. Present barrier/marsh/ 
lagoon sequences constitute a seventh cycle. Advance of the sea landward in 
each instance was less than prior cases, thus preserving the old shoreline. 
Likewise, withdrawals of the sea were probably not of similar magnitude. Some 
may have been relatively minor. Field recognition of terraces in the Middle 
Coastal Plain is made difficult by long exposure to erosive forces. 

23. The Middle Coastal Plain is separated from the Upper Coastal Plain 
by the Orangeburg Scarp (Colquhoun 1965) , which is the landward margin of the 
Duplin Formation. The Duplin Formation was deposited during a marine trans- 
gression; the Duplin shoreline has a maximum altitude of 65 m above MSL. 
According to Colquhoun (1974) , subsequent overall slow recession with episodic 
transgressions or still stands resulted in formation of the Coharie (65 m 
above MSL), Sunderland (52 m) , and Okefenokee (41 m) terraces. Colquhoun 
assigns the transgressive Duplin and terrace deposits to late Miocene age. 
The Miocene sea level rise was followed by a slow emergence during Pliocene. 

24. Tertiary sediments of the Middle Coastal Plain are separated from 
Quaternary sediments of the Lower Coastal Plain by the Surry Scarp. Terraces 
formed during early Pleistocene include the Wicomico (33 m) and the Penholoway 
(21 m) of Colquhoun (1974). The Talbot (12 m) , Pamlico (8 m) , and Princess 
Anne (5m) appear to have formed during the Sangamon inter -glacial period of 
late Pleistocene. The youngest Pleistocene terrace is the Silver Bluff (3 m) , 
which is assigned to Sangamon age by Colquhoun (1974) and to mid-Wisconsin by 

27 



Hoyt and Hails (1974) . Figure 13 is a cross section through the Lower Coastal 
Plain of Georgia showing relationships between the terraces. The cross sec- 
tion is similar to that presented by Colquhoun (19-74) for central South Caro- 
lina. In the vicinity of the North Carolina -South Carolina border, a similar 
number of terraces in the Lower Coastal Plain, with similar elevations, have 
been recognized by DuBar (1971). Terrace names in this locality differ from 
those recognized by authors previously discussed; however, their mode and tim- 
ing of formation are the same. The most seaward Pleistocene terrace is termed 
Myrtle Beach. 

25. Elevation of terraces above present sea level suggests a progres- 
sive, although episodic, drop in sea level since Miocene time. An alternative 
explanation for elevation of the terraces above the modern coast is offered by 
Cronin (1981) . According to Cronin, sediment loading in a Mesozoic/Cenozoic 
trough 200 km seaward of the South Carolina coast could be resulting in corre- 
sponding uplift of the Coastal Plain lithosphere in excess of 1 to 3 cm/ 
1,000 years. This could have resulted in a 60-m uplift of the Orangeburg 
Scarp since Miocene time and corresponding uplift of each of the terraces. If 
some part of the elevation of terrace sediments is due to upward flexure of 
the lithosphere, it would imply that the magnitude of eustatic changes in sea 
level since Miocene would be less than presently supposed. 

Holocene 

26. Superimposed on the long-term (approximately 20 million years) 
trend of falling sea level since Miocene time are Holocene sea level curves. 
These curves generally show a worldwide rise in sea level during the last 
15,000 years (Figure 14), with a decrease in rate of rise from 4,000 years BP 
to present. Data collected by Colquhoun and Brooks (1986) show rise in sea 



A WEST 

WICOMICO 

[FORMATION 



£»ST A' 




Figure 13. Lower Coastal Plain marine terraces (Hoyt and Hails 1974, 
reprinted by permission) 



28 



Figure 14. Sea level curve for the last 35,000 years (after 
Millman and Emery 1968) 

level over the last 4,000 years has been very episodic (Figure 10). The same 
rising sea level trend is visible on modern tide gage data (Figure 11) . 

27. Evolution of the modern coastline of South Carolina is intimately 
linked with the present episode of sea level rise, sediment supply, bathyme- 
try, ancient topography, and various environmental factors such as tide and 
wave conditions. All of these factors, except for sediment supply and bathym- 
etry, have been discussed previously for the modern coast of South Carolina. 
Erosion, accretion, or stability measured in this report is a function of all 
these factors. This report has briefly examined the magnitude of each factor 
in contributing to measured erosion and accretion. 

28. Sediment supply. Present day erosion/accretion patterns of barrier 
islands and beaches within the study area depend on sediment supply along the 
coast. Two potential origins for sediment are fluvial input and sources on 
the continental shelf. Meade (1982) concluded that in recent time, a decrease 
in cropland area and improved management practices have resulted in decreased 
soil erosion. Additionally, all of South Carolina's rivers, except for the 
Santee (which has been dammed and diverted since 1942) , are headwatered in the 
Coastal Plain and therefore do not have large discharges. Meade's conclusion 
is that little sand size sediment is reaching the coast from fluvial sources. 
Further, he estimates only 5 percent of that sand reaches the inner continen- 
tal shelf; most sand is being trapped in estuaries and bays. This may have 
been different in the not-too-distant past. Carver (1971) traced the origin 
of heavy minerals along the Georgia coast to the Santee River, suggesting it 



29 



may have previously contributed a large amount of sediment to the coastal 
zone. 

29. Consistent with this discussion, Pilkey et al. (1969) noted that 
sedimentation on the outer shelf is presently very slow. Pilkey and Field 
(1972) conclude that much of the modern beach sand along South Carolina 
originates from onshore transport across the inner continental shelf. Carver 
(1971) postulated that most modern beach sediment along the Georgia coast was 
from reworked Pleistocene Silver Bluff sediments. These reworked sands inter- 
mixed with fluvial input from the Santee River. Swift et al . (1972) suggest 
deposition of ebb-tidal delta complexes on the inner shelf during Pleistocene 
low sea level stands, and likewise deposition in estuaries which would have 
been seaward of the present shoreline, provide the principal sediment source 
for modern beaches. Pleistocene estuary, inlet, and barrier deposits form a 
20- to 40-km-wide lens of sand (up to 30 m thick) along the inner continental 
shelf of the South Atlantic coast. According to Swift et al. (1972), ero- 
sional shoreface retreat during Holocene transgression has moved these sedi- 
ments in a landward direction, assisting in construction of the modern 
shoreline. 

30. Shelf topography. In addition to sediment supply, topography of 
the inner continental shelf affects shoreline erosion and accretion. Wave 
refraction over shelf topography creates zones of potential erosion and depo- 
sition along the coastline. Wave refraction also influences direction of wave 
approach to the shoreline and therefore can influence littoral drift. Wave 
convergence or divergence because of refraction may be influential in shaping 
a large portion of South Carolina's coastal morphology. For example, Fico 
(1978) conducted a wave refraction analysis along selected portions of coast- 
line within the study area. She concluded that long-term erosion on Bull and 
Capers islands was due in part to concentration of wave energy along these 
shorelines by refraction across the shelf. 

Present Geomorphology 

31. In describing the modern coastline geomorphology, many authors 
(e.g., Brown 1977; Nummedal et al. 1977; Hubbard, Hayes, and Brown 1977) have 
considered the study area as being transitional between the microtidal (less 
than 1.5-m tidal range) coastline of North Carolina and the mesotidal coast of 

30 



Georgia. North Carolina, with a small tidal range and dominance of wave 
energy, has long, narrow barrier islands with few inlets, backed by large, 
open lagoons. Georgia has short, stubby barrier islands, numerous and large 
inlets, large ebb deltas and no flood deltas, and marsh- filled lagoons, 
resulting from a dominance of tidal effects over wave influence. Nummedal 
et al. (1977) note that North Carolina lagoons have 30-percent or more open 
water, but southern South Carolina lagoons have a maximum of 20 -percent open 
water. The coast within the study area ranges from high microtidal/low meso- 
tidal in the north to mesotidal in the south. Nummedal et al . (1977) illus- 
trate a variety of factors, including tidal range, which vary along the South 
Atlantic coast (Figure 15) . Variation in these factors influences the nature 
of the shoreline transition from north to south. 
Arcuate strand 

32. Brown (1977) recognized three distinct geomorphic zones along South 
Carolina's coast. Northernmost is the arcuate strand, extending from Winyah 
Bay north to the state border. This is the most stable area of the coast, 
being immediately backed by the Myrtle Beach (DuBar 1971) Pleistocene beach 
ridge terrace. Dunes are well developed along this coast. Hubbard et al . 
(1977) measured erosion rates along the arcuate strand of 1 m/year or less. 
Erosion rates for the North Carolina extension of the arcuate strand were also 
less than 1 m/year in an investigation by Wahls (1973). Nearshore cores col- 
lected by Meisburger (1979) and cores recently collected for the US Army Engi- 
neer District, Charleston,* show Pleistocene, Tertiary, and/or Cretaceous 
sediments within a few metres of the surface in this area. Partially consoli- 
dated pre-Holocene sediments are probably more stable against erosion. 

33. Hubbard et al . (1977) noted that an exception to stability of the 
arcuate strand coastline was in the vicinity of inlets. They measured changes 
up to 15 m/year at Murrells Inlet. Miller (1983), in investigating beach pro- 
file changes at Holden Beach, North Carolina, noted that largest variations 
occurred near inlets. The arcuate strand has relatively few inlets, and they 
are small in comparison to those farther south. FitzGerald, Hubbard, and 
Nummedal (1978) note that only 2 percent of northern South Carolina coast is 
occupied by inlets, compared with 20 to 25 percent in southern South Carolina. 



* Personal Communication, 1987, T. W. Kana, Coastal Science & Engineering 
Inc., Columbia, SC. 



31 





>• 
O 

m 

Z 

> 
< 


TIDAL RANGE 
INNER SHELF SLOPE 
LAGOON SIZE 


< 
< 

HI 

< 

Z 
*. 

o 

> 
< 


< 
< 
< 

< 


< 

ac 
< 

< 

o 

X 

z 

z 


S 
< 


NORTH 
CAROLINA 


I 




V 


i 




1 


f 


SOUTH 
CAROLINA 










11 




GEORGIA 


| 




i 


FLORIDA 




1 






1 



s 



RIVER 
DELTAS 


BARRIER 
ISLANDS 


TIDAL 
DELTAS 


LINEAR 

SAND 1 INLETS 

RIDGES ! 


TIDAL I SALT 
FLATS | MARSHES 




i 


i 


A 


T 


1 


1 


! 


I 


h 


\ 


i 




■ 


! 







Figure 15. Environmental parameter changes 
along the coast as a function of distance 
(Nummedal et al. 1977, reprinted by per- 
mission) and tidal range (Hayes 1975, 
Copyright 1975 by Academic Press, reprinted 
by permission) 



32 



Arcuate strand inlets have both flood and ebb -tidal deltas (Nummedal et al. 
1977). In discussing North Inlet, Finley (1976) indicates that although the 
inlet is in a microtidal range, its morphology is more closely aligned to 
mesotidal inlets. 

34. Origin of sediments on arcuate strand beaches appears to be pre- 
Holocene sediments immediately behind and under it. Few rivers drain into 
this area. Examination of sediment grain size by Brown (1977) reveals a wide 
range of size and sorting values, with no consistent alongshore trends. Mean 
grain size is approximately 0.175 mm. Nearshore bathymetry is fairly steep. 
Brown measured an average slope of 7.4 m/km for the first 0.8 km offshore. 
Beyond this is a fairly level, uniform, slope out to -15 km. 

Cuspate delta 

35. The cuspate delta area, extending from Winyah Bay south to Bull 
Bay, was the second geomorphic zone defined by Brown (1977) . Most sediment 
composing the delta originated from the Santee River. The Santee headwaters 
in the Blue Ridge and Piedmont Provinces. Before 1942, the Santee had the 
fourth largest discharge of any east coast river (Kjerfve 1976). Brown notes 
the delta was constructional until the early 1940's, when damming and diver- 
sion of the Santee into the Cooper River occurred. Kjerfve indicates an 

88 -percent loss in discharge reaching the Santee delta. It is the largest 
delta complex on the east coast, but since diversion, it has been eroding, as 
evidenced by washover terraces and truncated beach ridges. Hubbard et al. 
(1977) indicate an erosion rate similar to the arcuate strand, but with much 
more variability at any point alongshore. 

36. Proximity of cuspate delta beaches to sediment source results in a 
coarse, but variable, beach sediment size (average = 0.248 mm). These gener- 
ally immature sediments accompany steep, narrow beaches, with a gently sloping 
but irregular shelf. Average nearshore slope is about 2.0 m/km (Brown 1977). 

37. One of the prominent features of the cuspate delta region is Cape 
Romain. Together with Cape Fear at the northern end of the study area, it is 
part of the Carolina Capes extending south from Cape Hatteras , North Carolina. 
Brown (1977) attributes the origin of Cape Romain to convergence of waves and 
littoral drift over a yearly cycle. Hoyt and Henry (1971), in a review of 
theories on origins of the Carolina Capes, note most authors attribute cape 
origin to wave and current actions. They observe, however, the association of 
capes with major rivers and their similarity to ancestral capes of the region. 

33 



White (1966) believes capes are merely the present stage of a long temporal 
sequence of capes . He feels the capes are self maintaining because of 
continuous emergence of off-cape shoals during emergence of the Coastal Plain. 
During rising sea level, relict capes formed by major rivers localized younger 
capes. Present capes, while modified by local conditions, are the present 
stage in sequences of capes that endured through long periods of sea level 
change and shoreline migration. 
Barrier islands and tidal inlets 

38. The third geomorphic zone of Brown (1977) is a 160-km-long stretch 
of barrier islands and tidal inlets extending from Bull Bay south to the South 
Carolina-Georgia border. This zone is characterized by barriers averaging 

7 km in length, separated from the mainland by a zone of salt marsh that 
increases in width southward. Beach face slopes are gentle (1.5 to 2.5 deg) , 
and sediment is finer (average = 0.143 mm) and better sorted than beaches to 
the north (Brown 1977) . Greater textural maturity of these sediment indicates 
their reworking and implies limited new sources of sediment. Offshore slopes 
are gentle, but irregular spatially depending on their mode of origin; mid- 
barrier offshore profiles differ considerably from inlet offshore profiles. 

39. Brown recognized two predominant types of barriers occurring within 
this zone. Transgress ive barriers, generally less than 6 km long, are charac- 
terized by having a thin pocket of sand overlying back barrier sediments. 
These rapidly retreating barriers have wide washover terraces, no dunes, nar- 
row beaches, and straight shorelines. Morris Island, Edingsville Beach, and 
Bay Point are examples of transgressive barriers. The transgressive nature of 
these barriers is due in large part to reduction in sediment supply. Wagener 
(1970) measured over 275 m of retreat for Morris Island between 1949 and 1964 
as a result of sediment starvation downdrift of the Charleston jetties. 

40. Regressive barriers, also called beach-ridge barriers, are the most 
common in South Carolina (Brown 1977) . They are characterized by a bulbous 
updrift (northern) end, a straight to crescentic central portion, and down- 
drift recurved spits. These barriers are generally unstable at the north 
ends, prograding at the downdrift end, and stable or slightly accretional in 
their central portions (Hubbard et al . 1977). They generally exceed 6 km in 
length and have numerous vegetated beach ridges. 

41. Kiawah Island is an example of a beach- ridge barrier that has been 
extensively studied. Hayes et al. (1975) recognized the prograding nature of 

34 



this island through recent time. Moslow and Colquhoun (1981) examined multi- 
ple beach ridges and attempted to correlate them with recent sea level rise. 
They suggest Kiawah originally formed between 6,000 to 8,000 years BP and 
transgressed landward under rapidly rising sea level until about 4,000 years 
BP. Since then Kiawah has been episodically prograding seaward because of an 
excess in sediment supply over sea level rise. 

42. The erosional/accretional nature of South Carolina's barrier 
islands is intimately connected with tidal inlets and associated ebb- tidal 
deltas. Nummedal et al . (1977) point out increasing tidal range toward the 
south because of widening of the continental shelf towards Georgia. The 
result is a tide -dominated coastline where inlet size is relatively large and 
inlets are strongly ebb dominant. This in turn leads to seaward- directed sed- 
iment transport and large ebb -tidal deltas extending far out onto the shelf. 
These inlets exert a strong influence over erosion and accretion of the bar- 
riers. As Hubbard et al . (1977) note, only where there is 10 to 15 km between 
inlets does one get away from their influence. 

43. The large ebb deltas in the vicinity of Kiawah and other barriers 
have resulted in its bulbous updrift end (Hayes et al. 1975). This is a 
result of wave refraction over ebb shoals and protection of updrift ends of 
islands from storm waves (Figure 16) . Wave refraction results in localized 
alongshore drift reversals toward the north. Large storm waves are attenuated 
as they break across shoals, thus protecting landward shorelines from storm 
damage. As a result, sediment accumulates on updrift ends of the barriers. 
Finley (1976) examined North Inlet, near Winyah Bay, and found that following 
inlet stabilization, ebb shoals are efficient sediment traps for littoral 
drift. FitzGerald and Hayes (1980) suggest ebb-tidal delta development could 
result in sand starvation of downdrift beaches. Measurements of ebb delta 
volume by Hayes (1977) showed that volume of sand in ebb deltas adjacent to 
Kiawah Island are 78 percent of the volume of the barrier itself. 

44. Three primary types of shoreline changes were recognized by 
FitzGerald, Hubbard, and Nummedal (1978) and were associated with three types 
of inlets found along the South Carolina coast (Figure 17). Stable inlets, in 
which the ebb channel appears to be anchored in pre-Holocene cohesive sedi- 
ments, influence shorelines depending on ebb delta size and position. As dis- 
cussed previously, wave refraction around an ebb shoal causes local drift 
reversals. Wave shoaling over the delta shelters the barrier from storm waves 

35 



DEWEES ISLAND 



CAPERS INLET 

CAPERS ISLAND 
Longshore drift direction 




ATLANTIC OCEAN 



WAVE PEBOO 4.0 SEC 
DEEPWATER ANGLE 90.0 DEGREES 
DATE PLOTTED 08/14/78 
DEEPWATER WAVE HEIGHT ■ 1.0 FT 



CONTOUR AT MLW 

RELATIVE WATER LEVEL-; qoo FT 

MAP DATE. 1921 



Figure 16. Wave refraction diagram showing drift reversal as a result 
of ebb delta bathymetry (Fico 1978, reprinted by permission) 

and forces landward migration of swash bar complexes that periodically nourish 
the shoreline. Migrating inlets, which are shallow and not anchored in 
pre-Holocene material, move under the influence of littoral drift. Typically, 
southward migration is accompanied by spit elongation on the north side of an 
inlet. Eventually, the elongated inlet channel becomes inefficient, and a new 
channel breaches the spit to the north, renewing the cycle. The severed spit 
generally welds to the downdrift beach. A third type of inlet is one in which 
the ebb channel, under influence of the littoral drift, is pushed south across 
the delta until it becomes inefficient. It then cuts a new channel to the 
north side of the ebb delta, where it again begins its southward migration. 
Sand along the old southern channel migrates landward and welds to the beach, 



36 



Inlet Migration 

/J 



M.*i EMl Gunnel 



Dominent Longshori 
Transport Dkection 




Spit Accfelion and HeJ Migration 



Time 3 



Ebb-Tidal Delta Breaching 




u..lw,wd Bar Migration 



_ *y^^* \ t//S Dieclfon 
O .. . • ' Marginal Flood Channels 



I54-" 




Stable Inlet 



— ' '■ 

77* & 



i 



-Main Ebb Channel 



Domhent 
Longshore 

D»ecbon 



M-M'^? 



^^ 



Figure 17. Three types of shoreline change resulting from inlet processes 
(FitzGerald, Hubbard, and Nummedal 1978, reprinted by permission) 

causing rapid accretion. Hubbard et al . (1977) measured short-term shoreline 
changes along central portions of South Carolina's barriers, but found regions 
around inlets too variable for accurate measurement. 



37 



PART III: METHODOLOGY 

45. Procedures used for selection of data sources, shoreline defini- 
tion, and map production were established by the NOS and were common to all 
three shoreline reports in this series. The first report (Everts, Battley, 
and Gibson 1983) clearly outlines methodology used to construct the shoreline 
change maps. Text in this part of the report covering map-making procedures 
borrows heavily from Everts, Battley, and Gibson (1983); however, procedures 
for map analysis are substantially different. 

Data Sources 

46. Thirty-two 1: 24,000-scale US Geological Survey (USGS) quadrangles 
were selected as base maps for this project (Figure 18). They were revised by 
the Cartographic Revision Section of the Photogrammetry Division of NOS with 
l:24,000-scale color photography taken in 1982-83 at near high water, covering 
all of the ocean coast within the project area. Historical shoreline data, 
obtained from NOS and USC&GS topographic surveys (T sheets) compiled since the 
early 1800's, were added to the base maps. Table 2 lists dates of historical 
T sheet surveys available for each base map. A particular sheet may often be 
listed on more than one base map; each base map usually comprises sheets of 
varying scales and area limits. 

47. Copies of all historical maps used as source data in this study 
were obtained from the NOS vault in Riverdale, MD, through the NOS Reproduc- 
tion Division. Copies were initially bromide prints (a photographic process 
that provides a long shelf- life copy) and were later made into more stable 
matte- finish film positives. 

48. Topographic surveys are the basis for delineation of shorelines on 
nautical charts published by NOS. Present and historical surveys map the mean 
high-water line (MHWL) as the shoreline. According to Shalowitz (1964), the 
authority on historical significance of early topographic surveys of NOS, "The 
most important feature on a topographic survey is the high-water line." Accu- 
racy of the early surveys was addressed before any of the historical dates 
were used in this study. 

49. About 1840, Ferdinand Hassler, the first Superintendent of the 
Survey, issued the earliest instructions for topographic work. Those 

38 



LOCALITY 



1 


Tybee Island North 


2 


Blullton 


3 


Hilton Head 


4 


Parns Island 


5 


St Phillips Island 


6 


Fnpp Inlet 


7 


St Helena Sound 


8 


Edisto Beach 


9 


Rockville 


10 


Kiawah Island 


11 


James Island 


12 


Charleston 


13 


Fort Moultrie 


14 


Capers Inlet 




wgv* 



MAP NO 



LOCALITY 



15 


Bull Island 


16 


Awendaw 


17 


McClellanville 


18 


Cape Romam 


19 


Minim Island 


20 


Santee Point 


21 


North Island 


22 


Magnolia Beach 


23 


Brookgreen 


24 


Myrtle Beach NW 


25 


Myrtle Beach N E 


26 


Wampee 


27 


Little River 


28 


Shallolte 


29 


Holden Beach 


30 


Lockwoods Folly 


31 


Southport 


32 


Cape Fear 



Figure 18. Map of the study area showing location of quadrangles selected as 

base maps 



39 



Table 2 

Dates of Historical T Sheets Used in 

Shoreline Change Map Production 



Map No . 


Map Name 


1 


Tybee Island North 


2 


Bluffton 


3 


Hilton Head 


4 


Parris Island 


5 


St. Phillips Island 


6 


Fripp Inlet 


7 


St. Helena Sound 



Dates of Historical T Sheets 



8 Edisto Beach 

9 Rockville 

10 Kiawah Island 

11 James Island 

12 Charleston 

13 Fort Moultrie 

14 Capers Inlet 

15 Bull Island 

16 Awendaw 

17 McClellanville 

18 Cape Romain 

19 Minim Island 

20 Santee Point 

21 North Island 

22 Magnolia Beach 

23 Brookgreen 

24 Myrtle Beach, NW 

25 Myrtle Beach, NE 

26 Wampee 

27 Little River 



1852, 1859/63, 1870/74, 1900, 1964, 1970/71 

1859/60, 1870/71, 1920, 1964, 1970/71 

1859/60, 1920, 1955, 1963, 1970/71 

1859/60, 1864/65, 1870/71, 1921, 1955, 1964, 
1971/74 

1859/60, 1865, 1920/21, 1955, 1964, 1971/74 

1856/59, 1920, 1955, 1964, 1971 

1856/59, 1920, 1952/55, 1964, 1971 

1852, 1856/59, 1920, 1933, 1952/55, 1964, 
1970/74 

1851/54, 1920/21, 1933, 1964, 1970/74 

1854, 1921, 1933, 1955, 1964, 1970/71 

1854/58, 1862/64, 1900, 1921, 1933, 1955, 
1962/64, 1970/71 

1857/58, 1916, 1933, 1962/63 

1857/58, 1862/64, 1875, 1900, 1921, 1933/34, 
1955, 1962/64 

1856/57, 1875, 1921, 1934, 1962/63 

1875, 1921, 1934, 1962 

1874/75, 1921, 1934, 1962/63 

1874, 1925, 1934, 1962/63 

1873/74, 1925, 1934, 1962/63 

1873, 1925, 1934, 1962/63 

1857/58, 1872/73, 1925, 1934, 1962/63 

1857/58, 1872, 1925/26, 1934, 1962 

1872, 1926, 1934, 1962/63 

1872, 1926, 1934, 1963, 1969/70 
1872/73, 1926, 1934, 1962, 1969/70 

1873, 1926, 1934, 1962, 1969/70 
1873, 1925/26, 1934, 1962/63, 1969/70 
1873, 1924/26, 1933/34, 1962/63, 1969/70 



(Continued) 



40 



Table 2 (Concluded) 



Map No . 


Map Name 


28 


Shallotte 


29 


Holden Beach 


30 


Lockwoods Folly 


31 


Southport 


32 


Cape Fear 



Dates of Historical T Sheets 



1857/59, 1924, 1933, 1962/63, 1969/70 
1857/59, 1924, 1933, 1962/63, 1969/70 
1856/57, 1924, 1933/34, 1962, 1969/70 
1878, 1914, 1923/24, 1933/34, 1962, 1969/70 
1878, 1914, 1923, 1933/34, 1972/73/75 



instructions (Everts, Battley, and Gibson (1983), taken from Volume 17, Coast 
Survey, Scientific, 1844-1846, handwritten) included the following: 

On the sea shore and the rivers subject to the 
tides, the high and low-water lines are to be surveyed 
accurately; and the kind of ground contained between 
them, whether sand, rock, shingle or mud marked 
accordingly. The low-water line is taken by offsets 
while running the high water, and when not too far 
apart from each other, but when their distance is 
great, they must be surveyed separately: a couple of 
hours before the end of the ebb, and the same time 
during the commencement of the flood tides will be the 
proper time for taking the low-water line, and your 
operations must be so timed, as to be on the shore on 
those periods. 

50. The first specific instructions regarding the nature of the line to 
be surveyed is contained in the "Plane Table Manual" (Wainswright 1889) , which 
states: "In tracing the shoreline on an exposed sandy coast, care should be 
taken to discriminate [sic] between the average high-water line and the storm 
water line." Still later, Shalowitz (1964) elaborated by stating: 

The mean high-water line along a coast is the 
intersection of the plane of mean high water with the 
shore. This line, particularly along gently sloping 
beaches, can only be determined with precision by run- 
ning spirit levels along the coast. Obviously, for 
charting purposes, such precise methods would not be 
justified, hence, the line is determined more from the 
physical appearance of the beach. What the topog- 
rapher actually delineates are the markings left on 
the beach by the last preceding high water, barring 
the drift cast up by storm tides. On the Atlantic 
coast, only one line of drift would be in evidence 



41 



. . . . If only one line of drift exists, as when a 
higher tide follows a lower one, the markings left by 
the lower tide would be obliterated by the higher tide 
and the tendency would be to delineate the line left 
by the latter, or possibly a line slightly seaward of 
such drift line. 

In addition to the above, the topographer, who 
is an expert in his field, familiarizes himself with 
the tide in the area, and notes the characteristics of 
the beach as to the relative compactness of the sand 
(the sand back of the high-water line is usually less 
compact and coarser) , the difference in character and 
color of the sun cracks on mud flats, the discolor- 
ation of the grass on marshy areas, and the tufts of 
grass or other vegetation likely along the high-water 
line . 

51. Historical references are included to emphasize that it was the 
intention of all the agency's topographic surveys to determine the line of 
mean high water (MHW) for delineation on maps. With the exception of tidal 
marsh areas, where in most cases the outer limit of vegetation is mapped, MHW 
delineated on the surveys by the experienced topographer or photogrammetrist 
was that line at the time of survev or date of photography. 

Map Production 

52. The following procedures for producing shoreline change maps are 
identical to those used by Everts, Battley, and Gibson (1983). To make this 
study as current as possible, USGS quadrangle maps were revised to show a 
1982/83 MHWL. Revision was made using 1982/83 color aerial photographs flown 
for this study. Date and time of photography were correlated with stage of 
the tide, and a detailed stereoscopic examination of the photographs was made 
to determine the MHW line. This process was completed by the Cartographic 
Revision Section of the Photogrammetry Division of NOS . Their method was by 
direct transfer of photo -interpreted lines (see paragraph 60) from 1:24,000- 
ratioed film positives to USGS base maps. Using the ratioed photography, base 
maps (manuscripts) were held planimetrically to local physical features. In 
the absence of triangulation stations to position manuscripts accurately 
against photographs, it is possible to use "hard" planimetric features, such 
as road intersections or other permanent physical structures without great 
relief, to assure good photographic positioning. In areas where there were 

42 



not enough features to assure proper positioning, stereo models were set on 
the National Ocean Survey Analytical Plotter (NOSAP) . The NOSAP is a high- 
precision stereoscopic plotter that allows the operator to bridge over areas 
of sparse control and accurately determine correct relationships between pho- 
tographic models and base maps. Because of time restraints, no field check of 
the office-determined MHWL was made. All shorelines compiled by this method 
were reviewed to assure a uniformity of photo- interpreted shoreline, accuracy 
of compilation, and proper symbolization. These maps were then checked and 
reviewed in the manner identical to that used for all historical source maps. 

53. Digitizing of the shoreline on each historical map, and contempo- 
rary shoreline base maps, was then completed by the Data Translation Branch, 
Environmental Data and Information Service, Asheville , NC. Digitizing was 
completed on a Calma-Graphics III system, with a repeatability factor of 
±0.025 mm and a maximum absolute error of ±0.076 mm. Digitized data tapes 
were processed using a program developed by the NOS Marine Data Systems Proj - 
ect for use with the NOAA UNIVAC computer (GP0LYT2) ; this program allows for 
conversion of digitized data to geographic positions (GP's). Since many of 
the historic sheets used in the study were completed before the North American 
Horizontal Datum of 1927 (NA1927) was established, GP's for these sheets were 
converted to that datum so that accurate comparisons between pre-NA and 
post-NA 1927 surveys could be made. Conversion was completed mathematically, 
based on conversion factors for triangulation stations in the area, with a 
program written by the NOS Marine Data Systems Project. 

54. After processing of data was completed, plot tapes were generated 
using the NOS McGraphics program. Plot tapes were used with a Calcomp 748 
plotter and Calcomp 925 Controller to plot the shoreline movement maps. This 
task was completed with the assistance of the NOS Automated Cartography Group. 

55. All sections of shoreline from the source maps were digitized so 
that all shoreline points could be converted into GP's and replotted at any 
desired scale (before the final portrayal scale of 1:24,000 for the shoreline 
movement maps was chosen, other scales were tested to determine which map 
scale would portray the data in the most readable form) . Digitizing also 
removed inherent media distortion caused by the age of the original manu- 
scripts. Mechanics and mathematics of the digitizing system required that all 
projection (latitude and longitude) intersections completely enclose the data 
to be digitized. By assigning known and true values for each projection 

43 



intersection, the GP0LYT2 program adjusted each of the shoreline points 
enclosed within a projection cell based on true values of intersections versus 
digitized and computed values for those same intersections. Values for each 
shoreline point are thus correct in their position relative to known (true) 
projection intersections and to known triangulation data (Figure 19). 

56. Following the digitizing process, each sheet was reviewed visually 
with use of a raw data plot in which shoreline positions were shown at the 
same scale as the original map. Plotted shorelines were superimposed on orig- 
inal maps and checked for completeness and accuracy of tracking during 
digitization. This review helped to minimize a potential source of human 
error that could occur during the digitizing process. 

57. Other sources of potential error also were considered. The most 
difficult of these to determine precisely was location accuracy of the MHWL on 
source surveys and maps, on either (a) early surveys prior to approximately 
1930 and (b) maps based on photogrammetric surveys. In discussing early sur- 
veys, Shalowitz (1964) has stated: 

The accuracy of the surveyed line here consid- 
ered is that resulting from the methods used in locat- 
ing the line at the time of survey. It is difficult 
to make any absolute estimates as to the accuracy of 
the early topographic surveys of the Bureau. In gen- 
eral, the officers who executed these surveys used 
extreme care in their work. The accuracy was of 
course limited by the amount of control that was 
available in the area. 

With the methods used, and assuming the normal 
control, it was possible to measure distances with an 
accuracy of 1 meter (Annual Report, US Coast and Geo- 
detic Survey 192 (1880)) while the position of the 
planetable could be determined within 2 or 3 meters of 
its true position. To this must be added the error 
due to the identification of the actual mean high 
water line on the ground, which may approximate 3 to 
4 meters. It may, therefore, be assumed that the 
accuracy of location of the high-water line on the 
early surveys is within a maximum error of 10 meters 
and may possibly be much more accurate than this. This 
is the accuracy of the actual rodded points along the 
shore and does not include errors resulting from 
sketching between points. The latter may, in some 
cases, amount to as much as 10 meters, particularly 
where small indentations are not visible to the topog- 
rapher at the planetable. 



44 



-k- 



-H- 




-\- DIGITIZED VALUES 



-1-- CORRECTED VALUES 
' ADJUSTED TO TRUE 
VALUES FOR 
INTERSECTIONS 



Figure 19. Digitization procedure for correcting 
shoreline position locations when original shore- 
line movement map distortions exist (Everts, 
Battley, and Gibson 1983) 

58. Accuracy of the high-water line on early topographic surveys of the 
Bureau was thus dependent upon a combination of factors , in addition to the 
personal equation of individual topographers, but no large errors were allowed 
to accumulate. By means of triangulation control, a constant check was kept 
on the overall accuracy of the work. 

59. On aerial photographs, the MHW line is located to within 0.5 mm at 
map scale (USC&GS 1944) . This translates to less than 5 m on the ground for a 
map scale of 1:10,000 or 9.99 m on the ground for a map scale of 1:20,000. 
Since the great majority of source maps were of a larger scale than the 
1:24,000 base maps, the 0.5 -mm accuracy of source maps made using aerial pho- 
tography was at least maintained by reducing most source maps to the common 
base scale of 1:24,000. Present NOS survey maps are even more accurate. In a 
recent shoreline mapping project in the State of Florida using NOS charts, 

36 random features such as road intersections and shoreline features, includ- 
ing points of marsh, were scaled from maps compiled from aerial photography. 
These features were located by field traverse, and geodetic coordinate values 
compared. The check revealed a maximum error of ±3.0 m. This accuracy is not 
claimed for all surveys, but it does serve as an indicator of accuracy of sur- 
veys conducted by NOS . 

60. The last source of potential error in map production is conversion 
of digitized values to GP's. Digitizing equipment automatically recorded 
1,000 coordinate values for every inch of shoreline traced, which were 



45 



corrected to true latitude and longitude positions as previously discussed. 
The GP0LYT2 program printout provided a final error column each for "Latitude 
Y" and "Longitude X," which were examined on each printout. In the event any 
errors exceeded 0.5 mm (at map scale), the digitizing effort was rejected, and 
the original sheet was redigitized. Maximum allowable error from this source 
was 4.99 m on the ground for a 1: 10,000-scale map and 9.99 m on the ground for 
a 1: 20, 000 -scale map. However, rarely were error column values as high as 
0.5 mm; in most cases, they were 0.2 mm or smaller. Possible errors from this 
source were more likely to be on the order of 1.99 m on the ground for a 
1: 10,000-scale map and 3.99 m on the ground for a 1 : 20,000-scale map. Since 
most data were finally portrayed at a scale smaller than maps being digitized, 
the shoreline movement maps produced are well within map accuracy standards. 
Table 3 is a listing of the GP's of each base map used in this study. 

Data Analysis 

61. Data for this shoreline analysis report were obtained by digitizing 
shoreline positions on 30 of the 32 base maps produced by NOS (Figure 18) . 
Maps 12 and 19 did not contain any information on oceanic shoreline changes. 
Shorelines were digitized from individual mylar copies of each survey since 
composite mylars were unavailable and paper is an unsuitable medium for accu- 
rate results because of shrinkage and expansion. Digitizing is the process by 
which map data are transformed into a digital format. In the case of shore- 
line analysis, coordinate pairs are assigned to shoreline locations relative 
to some arbitrary axis system. Data pairs were compared by employing various 
numerical techniques to produce estimates of mean shoreline movements, vari- 
ations in the rate and direction of movements, and maximum net movements. 

62. The entire coastline for this report was divided into segments 
based on general orientation and natural breaks in shoreline continuity, i.e. 
inlets (Figure 20) . Baselines were chosen for each segment to lie as parallel 
as possible with the natural trends of the shoreline. Start and end points 
were located on the composite paper copies midway between the most landward 
and seaward shorelines. Baseline end points were superimposed onto the indi- 
vidual mylar copies to define the baseline for each segment for each map. A 
standard Cartesian coordinate system was then assigned to each segment with 
the positive x-axis directed generally north to south and the positive y-axis 

46 



Table 3 
Geographical Positions of Base Maps 





























Map 




Central 


NW 




NE 






SE 






SW 


No. 


Name 


Long. 
8051 


C. 
32 


jrner 
07 30 


Corner 
32 07 30 


C« 
32 


Drner 
00 00 


C. 
32 


Drner 


1 


Tybee Island North 


00 00 








80 


55 30 


80 


46 


30 


80 


46 


30 


80 


55 30 


2 


Bluffton 


8050 


32 


15 00 


32 


15 


00 


32 


07 


30 


32 


07 30 








80 


54 00 


80 


46 


30 


80 


46 


30 


80 


54 00 


3 


Hilton Head 


8043 


32 


15 00 


32 


15 


00 


32 


07 


30 


32 


07 30 








80 


46 30 


80 


39 


30 


80 


39 


00 


80 


46 30 


4 


Parris Island 


8043 


32 


22 30 


32 


22 


30 


32 


15 


00 


32 


15 00 








80 


47 00 


80 


39 


30 


80 


39 


30 


80 


47 00 


5 


St. Phillips 


8036 


32 


22 30 


32 


22 


30 


32 


15 


00 


32 


15 00 




Island 




80 


39 30 


80 


32 


00 


80 


32 


00 


80 


39 30 


6 


Fripp Inlet 


8028 


32 


24 45 


32 


24 


45 


32 


17 


15 


32 


17 15 








80 


32 00 


80 


24 


30 


80 


24 


30 


80 


32 00 


7 


St. Helena Sound 


8029 


32 


32 15 


32 


32 


15 


32 


24 


45 


32 


24 45 








80 


32 30 


80 


24 


30 


80 


24 


30 


80 


32 30 


8 


Edisto Beach 


8021 


32 


34 30 


32 


34 


30 


32 


27 


00 


32 


27 00 








80 


24 30 


80 


17 


00 


80 


17 


00 


80 


24 30 


9 


Rockville 


8013 


32 


37 30 


32 


37 


30 


32 


30 


00 


32 


30 00 








80 


17 00 


80 


09 


30 


80 


09 


30 


80 


17 00 


10 


Kiawah Island 


8006 


32 


39 45 


32 


39 


45 


32 


32 


15 


32 


32 15 








80 


09 30 


80 


02 


00 


80 


02 


00 


80 


09 30 


11 


James Island 


7958 


32 


43 30 


32 


43 


30 


32 


36 


00 


32 


36 00 








80 


02 00 


79 


54 


00 


79 


54 


00 


80 


02 00 


12 


Charleston 


7958 


32 


51 00 


32 


51 


00 


32 


43 


30 


32 


43 30 








80 


01 30 


79 


54 


00 


79 


54 


00 


80 


01 30 


13 


Fort Moultrie 


7950 


32 


47 42 


32 


47 


42 


32 


40 


12 


30 


42 12 








79 


54 00 


79 


46 


30 


79 


46 


30 


79 


54 00 


14 


Capers Inlet 


7943 


32 


54 00 


32 


54 


00 


32 


46 


30 


32 


46 30 








79 


46 30 


79 


39 


00 


79 


39 


00 


79 


46 30 


15 


Bull Island 


7935 


32 


59 00 


32 


59 


00 


32 


51 


30 


32 


51 30 








79 


39 00 


79 


31 


30 


79 


31 


30 


79 


39 00 


16 


Awendaw 


7933 


33 


06 30 


33 


06 


30 


32 


59 


00 


32 


59 00 








79 


36 45 


79 


29 


15 


79 


29 


15 


79 


36 45 


17 


McClellanville 


7926 


33 


06 30 


33 


06 


30 


32 


59 


00 


32 


59 00 








79 


29 15 


79 


21 


45 


79 


21 


45 


79 


29 15 


18 


Cape Romain 


7918 


33 


07 30 


33 


07 


30 


33 


00 


00 


33 


00 00 








79 


21 45 


79 


15 


00 


79 


15 


00 


79 


21 45 








(Continued) 



















47 



Table 3 (Concluded) 



Map 




Central 




NW 






NE 






SE 






SW 


No. 


Name 


Long. 
7918 


Corner 
33 15 00 


Corner 
33 15 00 


Corner 
33 07 30 


C< 
33 


>rner 


19 


Minium Island 


07 30 








79 


21 


45 


79 


15 


00 


79 


15 


00 


79 


21 45 


20 


Santee Point 


7911 


33 


15 


00 


33 


15 


00 


33 


07 


30 


33 


07 30 








79 


15 


00 


79 


07 


30 


79 


07 


30 


79 


15 00 


21 


North Island 


7911 


33 


22 


30 


33 


22 


30 


33 


15 


00 


33 


15 00 








79 


15 


00 


79 


07 


30 


79 


07 


30 


79 


15 00 


22 


Magnolia Beach 


7907 


33 


30 


00 


33 


30 


00 


33 


22 


30 


33 


22 30 








79 


10 


45 


79 


03 


15 


79 


03 


15 


79 


10 45 


23 


Brookgreen 


7901 


33 


37 


30 


33 


37 


30 


33 


30 


00 


33 


30 00 








79 


04 


30 


78 


57 


00 


78 


57 


00 


79 


04 30 


24 


Myrtle Beach NW 


7856 


33 


45 


00 


33 


45 


00 


33 


37 


30 


33 


37 30 








79 


00 


00 


78 


52 


30 


78 


52 


30 


79 


00 00 


25 


Myrtle Beach NE 


7849 


33 


48 


45 


33 


48 


45 


33 


41 


15 


33 


41 15 








78 


52 


30 


78 


45 


00 


78 


45 


00 


78 


52 30 


26 


Wampee 


7841 


33 


52 


30 


33 


52 


30 


33 


45 


00 


33 


45 00 








78 


45 


00 


78 


37 


30 


78 


37 


30 


78 


45 00 


27 


Little River 


7834 


33 


57 


00 


33 


57 


00 


33 


49 


30 


33 


49 30 








78 


37 


30 


78 


30 


00 


78 


30 


00 


78 


37 30 


28 


Shallotte 


7826 


33 


57 


00 


33 


57 


00 


33 


49 


30 


33 


49 30 








78 


30 


00 


78 


22 


30 


78 


22 


30 


78 


30 00 


29 


Holden Beach 


7819 


33 


57 


00 


33 


57 


00 


33 


49 


30 


33 


49 30 








78 


22 


30 


78 


15 


00 


78 


15 


00 


78 


22 30 


30 


Lockwoods Folly 


7811 


33 


57 


00 


33 


57 


00 


33 


49 


30 


33 


49 30 








78 


15 


00 


78 


07 


30 


78 


07 


30 


78 


15 00 


31 


Southport 


7804 


33 


57 


00 


33 


57 


00 


33 


49 


30 


33 


49 30 








78 


07 


30 


78 


00 


00 


78 


00 


00 


78 


07 30 


32 


Cape Fear 


7757 


33 


57 


00 


33 


57 


00 


33 


49 


30 


33 


49 30 








78 


00 


00 


77 


53 


00 


77 


53 


00 


78 


00 00 



48 



Shoreline t-1 ■ i Shoreline t-2 



South Carolina 



Atlantic Ocean 




Starting Point 
<r-Y-axis 



Transects (50m spacing) 



Baseline (x-axjs) 



Figure 20. Idealized segment for 
digitizing shoreline change 
information 

orthogonally seaward. Thus, in the resulting paired data sets, the x value 
was the distance from the origin along the baseline, and the y value was the 
corresponding perpendicular transect distance of the shoreline from the base- 
line. From 1 to over 25 segments were defined for each base map depending on 
the length and irregularity of the depicted shoreline. Within any segment, 
the same number of x-y pairs were digitized for each shoreline. The number of 
x-y pairs, or transects, depended on segment length. 

63. Start and end points of each segment were punched into the mylar GP 
grid accompanying each base map to allow easy identification when placed on a 
light table. The individual survey mylars were overlaid onto this grid sys- 
tem. Each segment was then digitized with a NUMONICS Model 1224 Digitizer. 
As the cursor was traced across the shoreline, coordinate pairs were produced 
and recorded at equal intervals (50 m) along the x-axis from north to south. 
Each segment was digitized until the entire survey had been completed. The 
overlying mylar was replaced by the next survey and digitized in the same 



49 



manner. This process continued until all available surveys for the map were 
digitized. "Flags" were inserted where necessary to signal missing data. 
When one map was completed, the entire data set was sorted by combining the 
surveys of each particular segment for further analysis. 

64. This procedure is suitable for coastlines where temporal reorienta- 
tion and erosion/accretion is directed predominantly onshore - offshore . How- 
ever, these conditions are usually not met in the vicinity of inlets and 
capes. Large aerial changes, abrupt reorientation of the shoreline, and pro- 
nounced alongshore changes required special analysis for most inlets and capes 
along this study area. Linear measurement of temporal alongshore changes and 
digitization of aerial differences were made from paper composite maps. Use 
of paper maps reduces precision of the measurements, and data presented here 
have been rounded off accordingly. However, because the magnitude of changes 
are large in these special areas relative to precision lost, the overall 
trends suggested by the data are valid. 

65. FORTRAN programs to perform numerical analysis of digitized data 
were written on a Digital Equipment Corporation VAX 11/750 computer. Shore- 
line positions for each survey for each segment were compared at each 50-m 
transect. Mean change in shoreline position between the earliest and latest 
survey dates and interval changes in shoreline position between each survey 
date were calculated as follows: 



_ S 1 - S n 

s = z (1) 



where 



S = average change in shoreline position 
S 1 - S n = net shoreline change between earliest and last dates 
N t = total number of years between earliest and last dates 



Y, - Y 1+1 
S, = „ (2) 



where 



S, = interval change 



50 



Y ( - Y, +1 = difference in distance from the baseline between two 
consecutive surveys 

N s = number of years between consecutive surveys 
Standard deviations were calculated and are an indication of relative variance 
among shoreline positions at each transect. Maximum shoreline change repre- 
sents the difference between the most landward and seaward shoreline position, 
regardless of date. It thus defines the envelope of change for the shoreline 
over the range of data. Shoreline change statistics produced by this analysis 
are based on specific shoreline positions at distinct points in time. It is 
important to note that no attempt is made to identify or represent changes 
that may have occurred during the interval between successive surveys. The 
analysis simply distributes these changes uniformly over the entire period. 

66. The length of coastal region investigated in this study (336 km) 
required that data presentation be subdivided into discrete reaches that could 
be plotted on report size paper at a reasonable scale. A total of seven 
reaches were defined based on a combination of natural morphology and politi- 
cal boundaries (Figure 21) . Continuous plots of mean change in shoreline 
position, standard deviation, and maximum shoreline change are included here 
for each reach of coastline. Continuous plots of temporal divisions of aver- 
age shoreline change are also presented for each reach. These plots were pro- 
duced by FORTRAN computer programs generated with the aid of Display 
Integrated Software System and Plotting Package (DISSPLA) , a proprietary prod- 
uct of Integrated Software Systems Corporation. Calculated quantities are 
graphed versus actual alongshore distance. Some alongshore distortion is 
introduced when individual segments of varying orientations are projected onto 
the nonparallel axis of the graph. 

67. Summary tables list average shoreline movements for each possible 
time interval, for various geographic locations. The numbers displayed are 
averages obtained by summing interval shoreline position changes for each 
transect within boundaries of the geographic location and dividing by the 
total number of transects. The numbers in parentheses indicate the percentage 
of shoreline for which data were available during the particular period. 

68. Information derived for each segment of each base map was compared 
with environmental data obtained for each segment to investigate the possible 
causes of measured shoreline changes. Data were compared for each of the 
seven coastal reaches and the entire shoreline with the use of LOTUS 1-2-3 



51 



WlAWNGTON, N.C. 
CAPE FEARWVERiA 

"7 _v# NEW INLET 



MYRTLE BEACH 



GEORGETOWN 





NORTfflSUNO 
T» WINYAH BAY- ^ / 

-= ^fSOUTH ISLAND ^/ 

MURPHY ISLAND 4/* 

CAPE ISLAND \ -. 

CAPE ROMAN .V 1 t X" 

U. ISLAND" -. ft O 

CAPERS SUUtf) ~- O* 



CHARLESTON . *■ ^ DEWEES ISLAND 

--V| ISLE OF PALMS 

ig^SULLIVANS ISLAND 
C^MORRtS INLAND Q 
O J^fOLLY ISLAND"" -« 





> yP KIAWAH ISLAND A^ 
<2=^f/SEABROOK ISLAND ,?» 




- -^ £j/ EDISTO ISUND 


*V 




-^c2cr- .ST. HELENA SOUND 
. "^/JHUNTIITO ISLAND 


/ 


1 


N\ V «p>FRIPP ISLAND^ ^ 
^^7/PRITCHARDS ISLAND 

^jT^^ 0RT royal sound 








■^TJ /hiLTON HEAD ISLAND 


SAVANNAH, GA.^ 


gCJjDAUrUSKIE ISLAND 
~^AV7 TYBEE ISLAND / 



Figure 21. Map of study area showing division into geomorphic 
zones and subdivision into seven reaches 

software, a product of Lotus Development Corporation, on a personal computer. 

69. Several sources of error are possible in analysis of map data 
beyond those previously mentioned in producing base maps. The most basic is 
inherent in the digitizing equipment. The resolution of the NUMONICS Model 
1224 digitizer is published to be 0.127 mm with an absolute accuracy of 
0.508 mm. At a scale of 1:24,000, these specifications translate into a maxi- 
mum resolution of ±3 m. This error potential was minimized by digitizing each 

52 



survey in short segments, causing the coordinate axes to be reset often. 

70. Laboratory testing also discovered inaccuracies in the digitizer's 
axis rotation algorithms. Axis rotations of greater than 2 to 3 deg resulted 
in unacceptable measurements over extended distances. To compensate, the 
mylar grids remained fixed relative to the digitizer until all surveys for a 
particular map were completed, thereby keeping the angle of axis rotation to a 
minimum. 

71. Actual tracing of the survey line with the digitizer cursor is a 
third potential source of error. At the 1:24,000 scale, errors resulting from 
tracing and actual line width are approximately 3 to 4 m. However, assuming 
such tracking errors to be random, they are dampened when averaged over finite 
distances of shoreline. 



53 



PART IV: SHORELINE DATA ANALYSIS 

72. This part of the report presents the first level of analysis of data 
obtained from digitizing shoreline positions on the accompanying NOS map set. 
Length of coastline investigated in this study (336 km) prevented adequate 
display of shoreline change data at a scale suitable to page size format. 
Therefore, for display purposes, the coastline was subdivided into seven 
reaches (Figure 21). Reaches one (Tybee Island to St. Helena Sound), two 

(St. Helena Sound to Charleston), and three (Charleston to Bull Bay) corre- 
spond to Brown's (1977) barrier island geomorphic unit. Reach four is Bull 
Bay. Reach five (Bull Bay to North Inlet) and six (North Inlet to the North 
Carolina/South Carolina border) correspond to Brown's cuspate delta and arcu- 
ate strand geomorphic units respectively. Reach seven covers the remainder of 
the study area, which lies within the State of North Carolina (North Carolina- 
South Carolina border to New Inlet) . 

73. Within Part IV of the report, data for each reach are presented in 
both graphic and tabular format. Average shoreline change and standard devia- 
tion for the maximum range of years (e.g., 1856 to 1983) and several interven- 
ing shorter periods (e.g., 1850 to 1929, 1920 to 1965, 1960 to 1983) were 
calculated and displayed to show spatial and temporal changes in shoreline 
positions. Header dates presented on temporal graphs in this part of the 
report are not exact. Exact dates used in the comparison can be found by con- 
sulting Table 2. Maximum shoreline change during the period of study (the 
envelope of shoreline change) and the number of surveys and length of survey 
period used in data analysis are given for each coastal reach. Graphical 
scales are the same for comparison between reaches. Average shoreline move- 
ment for every temporal interval of data is presented for each barrier island 
or mainland beach within each coastal reach. For digitization, the shoreline 
of each map was divided into straight line segments (Figures 22a and b) . 
Average maximum movement, average shoreline change, maximum movement, and max- 
imum deviation are presented for each of these segments in Appendix A. Summa- 
ries of erosion and accretion are present for each reach, each geomorphic 
zone, and the entire study area. 

74. Changes at inlets are presented as a separate section. Inlet 
changes are frequently quite radical and often occur in an alongshore direc- 
tion rather than onshore or offshore. Methods used here to measure shoreline 

54 



MAP NO. 


LOCALITY NO. 


SECTIONS 


1 


TYBEE ISLAND NORTH 


19 


2 


BLUFFTON 


1 


3 


HILTON HEAD 


14 


4 


PARRIS ISLAND 


2 


5 


ST. PHILLIPS ISLAND 


11 


6 


FRIPP INLET 


11 


7 


ST. HELENA SOUND 


5 


8 


ED IS TO BEACH 


16 



79° 29' 15" 

33°06'30" 




80°17'00" 



32°30'00" 



LOCALITY 

ROCKVILLE 
KIAWAH ISLAND 
JAMES ISLAND 
CHARLESTON 
FORT MOULTRIE 
CAPERS INLET 
BULL ISLAND 
AWENDAW 



NO. SECTIONS 

9 
6 

7 



16 
11 
23 
27 



a. Shoreline from Tybee Island, Georgia, to Bull Bay, South Carolina 

Figure 22. Map of the study area showing division of the shoreline into 
short segments for digitizing and subsequent analysis (Continued) 



55 




33°30'00" 



LOCALITY NO. SECTIONS 


MCCLELLANVILLE 


2 


CAPE ROMAIN 


10 


MINIM ISLAND 





SANTEE POINT 


6 


NORTH ISLAND 


5 


MAGNOLIA BEACH 


7 


BROOKGREEN 


10 


MYRTLE BEACH N.W. 


7 




^^r^^^^-^SfM 7 




77°53'00- 

33°57'OCT 



pe Fear 



MAP NO. 


LOCALITY NO. 


SECTIONS 


25 


MYRTLE BEACH N.E. 


6 


26 


WAMPEE 


7 


27 


LITTLE RIVER 


6 


28 


SHALLOTTE 


7 


29 


HOLDEN BEACH 


8 


30 


LOCKWOODS FOLLY 


7 


31 


SOUTHPORT 


11 


32 


CAPE FEAR 


7 



b. Shoreline from Bull Bay, South Carolina to Cape Fear, 
North Carolina 

Figure 22. (Concluded) 



56 



change cannot adequately handle this type of data; therefore, measurements 
were made separately at each inlet to show associated alongshore and aerial 
changes . 

Changes in Shoreline Position 
Coastal reach 1 

75. Average shoreline movement within coastal reach 1 (Tybee Island to 
St. Helena Sound), between 1852/59 and 1982/83, was quite variable, ranging 
from just over 10 m of accretion/year to 8 m/year of erosion (Figure 23) . 
Overall, erosion dominated accretion in spatial distribution along this shore- 
line. Substantial accretion (defined here as greater than 1 m/year) occurred 
along a small segment of Tybee Island, the south end of Hilton Head Island, 
Bay Point Island, the southern and northern ends of Fripp Island, and the 
extreme northern terminus of Hunting Island. A small percentage of shoreline 
showed little net change (less than ±1 m/year) over the time span. The 
remainder of shoreline was strongly erosional. 

76. Rate of shoreline change is quite variable spatially along the 
entire reach (Figure 23) . Standard deviation is an indicator of variability 
of shoreline position changes. It is evident from this graph that magnitude 
of variability increases dramatically in the vicinity of inlets. It can be 
observed in the plot of standard deviation along the coast that every occur- 
rence of a standard deviation in excess of 5 m/year is adjacent to an inlet. 
This agrees with conclusions reached by authors previously discussed, that 
shoreline position is most dynamic in the vicinity of inlets. 

77. Maximum shoreline movement, the difference between the two most 
divergent shoreline positions regardless of temporal position, is quite large 
in this coastal reach (Figure 24) . Range of shoreline movement is from 
approximately 50 m at Hilton Head to almost 1,400 m at Hunting Island over the 
period of record. In all cases where maximum shoreline movement has exceeded 
500 m, it has been in the vicinity of inlets. Average shoreline movements 
summarized by barrier island for each interval of survey data are presented in 
Table 4. 

78. Changes in average rate of shoreline movement are presented in Fig- 
ure 25. Average shoreline movements are presented in three distinct time 
groups to observe temporal changes. Prior to the 1920's, the shoreline was 
strongly erosional. This same trend is visible right up to the last survey 

57 



3D.0-T 
25.1 

2D.I 



> 
hi 
q 15.0' 

a 

I 
z 
< 



j LLi u...kt^ 




Figure 23. Average net shoreline movement and standard deviation of movement 
for coastal reach 1, 1852-1983 



58 



o w 

DC hi 

CD cr 

2 D 

3 W 

Z 




10.0 
B.0 
5.0 

u- 

2.0- 



■llIB IHHH1I 



z 

HI 

111 

> 
o 

h- 
ui 
z 

I 

X 

< 
2 



1SD0J 
M0D.Q 
13DD.0 
1X0.0 
1100.0 
1000.8 
900.0 
800.0 
HO.0 
600.0 
500.0 
CO.0 
XO.0 
200.0 
100.0 





■ 
















• 




■ 






■ 


Jl 




■ 


L 1 




■ 


1 1 




• 


1 II .■ i 




■ 


1 -T\m '1 IT Tl 

1 ' 1 VI' 1 1 ' 

III 

i nil 


^ Ixl 




A 1 i 1 


: 1 


■mr tv i i 




■r ■ 


r i 




Figure 24. Maximum net shoreline movement, number of surveys used, and time 
interval of the surveys for coastal reach 1 



59 



0"» o 

oo cm 



a O - C-J 
u-i ol O CO 
CO CM ^ 



T3 -— ^-t 1 



..in ^c fuco wi-H Ch Cm m oo h n) r- ,C *h 

^ V)^ _(-^ 3-^, o^o—. *-* p« —- u —• o -~ 



El 



U \£> 



C PC 
o * 



60 






<N -CO 






O f*. N i 



O --» lO . 



«H CU>n 



— 



I — - o **. 



61 



IS.D-i 




Figure 25. Temporal division of average net shoreline 
movement data for coastal reach 1 



62 



date (1982/83). Large spatial variability is evident during all three peri- 
ods. The magnitude of erosion and accretion appears lowest along Hilton Head 
Island. In all three periods, large average shoreline movement rates appear 
to occur most often in the vicinity of inlets. 

79. It is important to note that some localities, such as Pritchards 
Island, alternate between erosion, accretion, and erosion during the three 
time intervals represented. This points out that often erosion/accretion pro- 
cesses are not steady, but rather fluctuate with changes in environmental 
parameters. Magnitude of erosion and accretion appears to increase from the 
earliest to last period; however, this is probably due to a decrease in number 
of years over which data were averaged. Over shorter periods, extreme events 
have a greater influence on average shoreline movement rates. Aerial distri- 
bution of accretion also seems to increase slightly toward the most recent 
period, which may also be an artifact of decreasing length of time between 
survey dates. These data illustrate increased variability in the shoreline 
change rates over increasingly smaller intervals of time and underline the 
need for temporally large data sets when using historical shorelines to 
predict future shorelines. 

80. Shoreline changes over the entire temporal range of data from each 
digitized transect were categorized into one of three modes: erosional (erod- 
ing more than 1 m/year) , stable (less than or equal to 1 m/year of change) , 
and accretional (accreting more than 1 m/year) . Results were summed for each 
coastal reach and presented as pie graphs. The summary for coastal reach 1 
(Figure 26) shows the majority of shoreline is erosional (54.9 percent) or 
stable (30.5 percent). Only a very small proportion (14.6 percent) of tran- 
sects measured showed long-term accretion rates in excess of 1 m/year. 
Coastal reach 2 

81. Average shoreline movement within coastal reach 2 (St. Helena Sound 
to Charleston Harbor) is similar in character to reach 1. The range is from 

7 m/year accretion to 12 m/year of erosion over the period of record (Fig- 
ure 27). The northern end of this reach, which lies immediately downdrift of 
the Charleston Harbor jetties, is strongly erosional. This zone of strong 
erosion includes all of Morris Island and most of Folly Island. The north end 
of Kiawah Island is strongly accretional, changing to erosional toward its 
south end and back to strongly accretional on Seabrook Island. Almost the 
entire length of Edisto Island is strongly erosional, except for some 

63 



ACCRETING (14.6%) 



STABLE (30.5%) 




ERODING (54.975) 



Figure 26. Summary of shoreline movement for coastal 
reach 1, 1852-1983 

accretion on the south. This accretion may be attributed to groins built in 
this area to retard erosion. Otter Islands, which are partially sheltered in 
St. Helena Sound, are variable but mainly accretional. Spatially, erosion 
predominates over this reach during the total study time interval. 

82. A pattern of highest variability in the vicinity of inlets is evi- 
dent in reach 2. Each place where standard deviation of shoreline movement 
exceeds 5 m/year is in the immediate vicinity of inlets (Figure 27) . Central 
portions of barrier islands, while still variable in long-term rate of ero- 
sion, are steady in shoreline change compared with areas adjacent to inlets. 
Variability of shoreline change is echoed in the maximum shoreline movement 
(Figure 28), which shows several changes in excess of 1,000 m over duration of 
the study. Only in the vicinity of inlets are shoreline changes found in 
excess of 500 m. Along central portions of barriers, maximum change over 

130 years of record drops below 100 m in several areas. 

83. Temporal examination of average rates of shoreline change (Fig- 
ure 29) demonstrates the effect of jetty construction at Charleston Harbor. 
The jetties were completed around the turn of the century. The first period 



64 




Figure 27. Average net shoreline movement and standard deviation of movement 

for coastal reach 2, 1851-1983 



65 




Figure 28 



Maximum net shoreline movement, number of surveys used, 
interval of the surveys for coastal reach 20 



and time 



66 



z 
g 

z 
g 

o 



> ? 
O 

5 ' 




Figure 29. Temporal division of average net shoreline 
movement data for coastal reach 2 



67 



shown in this figure includes data mainly from preconstruction of the jetties. 
The result is an average erosion rate exceeding 5 m/year. The second period, 
from early 1920 's to early 1960's, shows a postconstruction phase of erosion 
that has shoreline erosion rates exceeding 20 m/year. Morris Island is 
clearly sediment starved as a result of the jetties. The early 1960 's to 1983 
graph shows continued erosion of Morris Island; however, despite the shorter 
time interval represented, magnitude of the erosion has decreased. Erosion 
rates over this 20-year interval barely exceed 10 m/year. Folly Island is 
generally eroding during all three time intervals. Accretion along the length 
of Folly Island appears to be at a minimum during the 1960 to 1983 period. 
Along Kiawah Island, erosion and accretion seem to reverse with changing time 
intervals. The most recent period shows Kiawah to be largely accretional. 
Edisto Island has been erosional through time, except at the very southern 
end. Pine and Otter Islands were accretional during the 1850 to 1929 time 
period, but have been largely erosional since then. A summary of average 
shoreline change rates per island for every available time interval is pre- 
sented in Table 5 . 

84. The summary of data within reach 2 (Figure 30) shows erosion to be 
dominant (40.0 percent). However, despite the effects of Charleston Harbor 
jetties, the percent occurrence of accretion is greater (28.5 percent) than in 
reach 1 (14.6 percent). Approximately 31.5 percent of the transects measured 
in reach 2 showed +1 m/year or less change between 1851 and 1983. 

Coastal reach 3 

85. Coastal Reach 3 (Charleston Harbor to Bull Bay) also falls within 
Brown's (1977) barrier island geomorphic zone and is similar in character to 
reaches 1 and 2 discussed previously (Figure 31). Average net accretion 
varies up to a maximum of approximately 6 m/year, and average net erosion 
exceeds 8 m/year. Sullivans Island and Isle of Palms, both immediately north 
of the Charleston Harbor jetties, predominantly show accretion. Rate of 
accretion increases toward the jetties, suggesting trapping of littoral drift 
as the reason for sediment accumulation. Dewees and Capers Islands, north of 
Isle of Palms, are predominantly erosional, although both show a small area of 
accretion near their northern ends. Bull Island, the northernmost barrier 
island in this reach and within Brown's barrier island geomorphic zone, starts 
out strongly accretional in the south and ends up strongly erosional at its 
northern terminus . 

68 



O ^s O x-n 

■ <r ■ \o 

N PI O 00 



iO N MA H 



CO 00 I ^ 



eg h in 



■ — C — -^ ■-' 



00 13 

C 

0) <u 



£3 

3 — 



U C 



69 



m oo c oo 



c — -h — • -^ *— 






70 



ACCRETING (28.5%) 




ERODING (40.0%) 



STABLE (31 .5%) 



Figure 30. Summary of shoreline movement for coastal 
reach 2, 1851-1983 

86. Standard deviations in excess of 5 m/year occur only in the vicinity 
of inlets (Figure 31) . Central portions of islands appear more stable through 
time. Maximum shoreline movements (Figure 32) are not as large in magnitude 
as in previous reaches , but they do approach 1 , 000 m and are at a maximum in 
the vicinity of inlets. 

87. Sullivans Island and Isle of Palms have generally been accretional 
throughout the period of data examined (Figure 33). From 1960 to 1983, the 
largest spatial distribution of accretion occurred along these two islands. 
Dewees Island has been consistently erosional through the period except near 
Capers Inlet. The most recent period shows erosion even in this area. Like- 
wise, Capers Island has been dominated temporally by erosion. The most recent 
period shows some accretion in the vicinity of Price Inlet on Capers Island. 
Price Inlet has affected Bull Island to the north also. Erosion and accretion 
rates alternate and vary in magnitude along the southern portion of Bull 
Island, while the north end has been consistently eroding through time. A 
summary of average shoreline change rates per island for each possible data 
interval are presented in Table 6. 



71 




Figure 31. 



Average net shoreline movement and standard deviation of 
movement for coastal reach 3, 1857-1983 



72 




1500. 
1400. 
1300. 
1200. 
HOD. 
1000. 
900. 
800. 
700. 
600. 
500, 

m 

300 

200 
100 



II 1 


II 


!■ 


II 


" . ~ ■:■: M 




II H ■■■■ 




















Figure 32. Maximum net shoreline movement, number of surveys used, and time 
interval of the surveys , for coastal reach 3 



73 




Figure 33. Temporal division of average net shoreline 
movement data for coastal reach 3 



74 



Table 6 
Average Shoreline Movement (metres/year) . Charleston 





Harbor 


to Bull 


Island, 


South Carolina 














Survey Date 








1875- 


1921- 


1921- 


1933- 1934- 


1962- 


1964 


Location 


1921 
1.5 


1933 
0.5 


1964 


1964 1962 
1.9 


1983 


1983 


Sullivans Island 


2.6 


[13/7 - 13/13] 


(15) 


(94) 




(94) 




(94) 


Isle of Palms 


2.1 


-0.2 


2.3 


1.8 0.0 


-0.5 


2.1 


[13/14 - 14/8] 


(91) 


(92) 


(8) 


(28) (63) 


(63) 


(36) 


Dewees Island 


-4.2 


6.2 




-4.7 




-4.1 


[14/9] 


(96) 


(96) 




(100) 




(100) 


Capers Island 


-7.3 


-1.1 




-5.3 




-1.5 


[14/10 - 14/11] 


(100) 


(99) 




(99) 




(100) 


Bull Island 


0.7 


-1.9 




-3.0 




-1.5 


[15/1 - 15/6] 


(99) 


(99) 




(98) 




(98) 



Note: Numbers in parentheses indicate percent shoreline surveyed during the 
given time interval. Numbers in brackets indicate the maps and segments con- 
tained in the data block; e.g., Bull Island [15/1 - 15/6] extends from map 15 
segment 1 to map 15 segment 6 . 

88. The summary of transect data for all of coastal reach 3 (Figure 34) 
is quite different from reaches 1 and 2. Accretion predominates (44.4 per- 
cent) in this reach over the 1857-1983 time interval. Undoubtedly, the trap- 
ping of littoral drift north of the Charleston Harbor jetties have played a 
strong role in this reach. Erosion (30.1 percent) is reduced from reaches 1 
and 2 (54.9 percent and 40.0 percent, respectively). Only 25.4 percent of 
reach 3 can be considered stable over the long term. 

Coastal reach 4 

89. The marsh-bordered shoreline of Bull Bay comprises coastal reach 4. 
The sheltered nature of this bay is reflected in the long-term average shore- 
line change rates, which reach a maximum of approximately 3 m/year average 
erosion and 2 m/year average accretion (Figure 35) . Average erosion and 
accretion in the bay is considerably less than along barrier islands to the 
south. Maximum rates of accretion occur on the northeast side of the bay, 
which is most sheltered from dominant northeast quadrant winds and waves. 



75 



ACCRETING (44.4%) 




ERODING (30.1 X) 



STABLE (25.4%) 



Figure 34. Summary of shoreline movement for 
coastal reach 3, 1857-1983 

Much of the central section of the bay is slightly erosional or stable. The 
southwest portion, in the vicinity of Venning, Anderson, and Bull Creeks, has 
the most rapid erosion. Orientation of this segment of the bay makes it most 
susceptible to waves from the northeast. Overall, this shoreline appears sta- 
ble to slightly eroding. 

90. Standard deviation, a measure of variation in shoreline change 
rates, is small in comparison with reaches 1, 2, and 3 (Figure 35). Maximum 
standard deviations reach ±3 m/year, although most of the shoreline does not 
exceed ±2 m/year. The trend in reaches 1, 2, and 3 of greatest variability in 
shoreline position in the vicinity of inlets is not evident in this reach. 

The small tidal creeks entering Bull Bay have limited discharge and, there- 
fore, limited ability to erode/deposit sediment. 

91. Maximum net movement (Figure 36) reaches a peak in the northeast 
and southwest corners of the bay, where average accretion and erosion, respec- 
tively, were at their maximums. Maximum net movement up to 300 m is evident, 
but most of the shoreline has had a net change of less than 100 m over the 
span of record. 



76 



3D.0 
25.0- 
2D.0- 
15.0- 
1D.0- 



JililyUjLLliwJ 




Figure 35. Average net shoreline movement and standard deviation of movement 
for coastal reach 4, 1874-1983 



77 



CO 



u. 
O co 

>■ 

UJ 



a. 



UJ 

13 



1950- 
1900- 



10.0- 

B.0- 
6.0- 
4.0- 
2.0- 



19DO.0- 
HOO.0- 
1300.0- 

ian.o- 

1100.0- 
1000.0- 
900.0- 
800.0- 
700.0 : 
800.0- 
5DO.0 : 
«O.0 : 
300.0- 
2OO.0 : 
1O0.0- 



Figure 36. 



■■■■1MB 

llll II 

HMMllBM 




it TTttT 



'IfirT-ryi^i ■ i pr 



I 




Maximum net shoreline movement, number of surveys used, and time 
interval of the surveys, for coastal reach 4 



92. Separation of average net shoreline change rates into three periods 
reveals some changes in erosional character of the bay over the period of 
study (Figure 37). From 1850 to early 1920's, most of the bay was slightly 
accretional. The exception to this was the southwest corner, which is ero- 
sional during all periods, although magnitude of the erosion appears to be 
decreasing with time. The period from 1920 to early 1960 shows a mix spa- 
tially of erosion and accretion. The most recent period, from 1960 to 1983, 
is primarily erosional, with the center of the bay showing a strong erosional 
signature. Spatial distribution of accretion is at its lowest during the most 
recent period. Average net shoreline change rates for discrete sections of 
the bay for each possible survey interval are presented in Table 7. 

93. Unlike the barrier coastline to the south, shoreline changes in 
Bull Bay are slow and reasonably predictable. Wind, wave, and storm effects 
are markedly reduced because of sheltering by Bull Island and Sandy Point and 
shallow bathymetry. With reduction of these parameters as shoreline change 
agents, the role of relative sea level rise increases. Wave refraction, long- 
term sea level rise, and short-term storm surge are probably key factors in 
spatial and temporal erosion/deposition of bay shoreline. Figure 38 demon- 
strates the stability of this reach. Over 82 percent of Bull Bay coastline 
has had less than ±1 m/year of shoreline change between 1874 and 1983. The 
remainder of Bull Bay is eroding (13.9 percent) or accreting (3.9 percent) 
depending on orientation to waves that can directly enter the bay. 

Coastal reach 5 

94. Coastal reach 5 (Bull Bay to North Inlet), which corresponds to 
Brown's (1977) cuspate delta geomorphic zone, is characterized by erosion/ 
accretion trends similar to the barrier island zone (Figure 34) . From Sandy 
Point north to Cape Romain Harbor entrance, including all of Cape Romain, 
erosion dominates. Maximum erosion rates of approximately 12 m/year occur in 
the vicinity of the cape. Murphy Island, just north of Cape Romain harbor, is 
strongly accretional at its southern end and erosional along most of its 
northern end. Cedar Island, between branches of Santee River, is entirely 
erosional. South Island, downdrift of the jetties at Winyah Bay, has gener- 
ally been accreting over the duration of this data set. Maximum accretion for 
the entire reach, approximately 9 m/year, is at the southern end of this 
island. North of Winyah Bay, the area adjacent to the jetties is mildly 
accretional switching to erosional as North Inlet is approached. Overall, 

79 



15.0- 
1D.0-I 



-5.0- 



-10.0- 



-15.8- 
15.0 



3 




10.0 


H 
Z 

HI 

2 

111 
> 


CO 

CO 


5.0 


2 
H 

LU 

z 

LU 

O 
< 

cr 

UJ 

> 
< 


1 
o 

05 


D.0 
-5.0 
-10.0 

-15.0 

15.0 

1D.0 




CD 


5.0 



^Yfirf 



t r f " 4 * w «i 




Figure 37. Temporal division of average net shoreline 
movement data for coastal reach 4 



80 



Table 7 
Average Shoreline Movement (metres/year) 
Bull Bay. South Carolina 



Location 



Bull Harbor 
[15/7 - 15/15 

Anderson Creek - Venning Creek 
[15/16 - 15/19] 

Venning Creek - Graham Creek 
[15/20 - 16/2] 

Graham Creek - Harbor River 
[16/3 - 16/15] 

Harbor River - Bull River 
[16/16 - 16/20] 

Bull River - Five Fathom Creek 
[16/21 - 16/26] 







Survey Dates 






1874- 


1875- 


1921- 


1934- 


1962- 


1934 


1921 


1934 


1962 


1983 




-0.1 


-0.8 


-0.5 


-0.5 




(100) 


(100) 


(100) 


(100) 




-2.2 


-2.3 


-1.9 


-0.4 




(83) 


(95) 


(98) 


(100) 




-0.5 


-0.5 


-0.4 


0.1 




(99) 


(99) 


(99) 


(95) 




0.4 


-0.6 


0.1 


-1.4 




(98) 


(98) 


(99) 


(98) 


-0.2 


0.2 


-0.8 


0.1 


-0.9 


(5) 


(95) 


(95) 


(100) 


(73) 




1.3 


1.3 


-0.2 


-0.1 




(97) 


(100) 


(98) 


(98) 



Note: Numbers in parentheses indicate percent shoreline surveyed during the 
given time interval . Numbers in brackets indicate the maps and segments con- 
tained in the data block; e.g., Bull River-Five Fathom Creek [16/21 - 16/26] 
extends from map 16 segment 21 to map 16 segment 26 . 

between 1874 and 1983, erosion dominated over accretion. Undoubtedly, the 
previously discussed diversion of the Santee River had a role in this. 

95. Standard deviation along this reach varies from less than ±2 m/year 
up to ±30 m/year (Figure 39) . South Island, which lies downdrift of Winyah 
Bay, shows extreme variability in shoreline position. A second peak of large 
standard deviations occurs in association with accretion along the central 
part of Murphy Island. Within reach 5, the pattern of highest variability in 
shoreline positions adjacent to inlets is not as apparent. The trend is not 
evident at all on Murphy Island, where the central section of the island is 
most variable. North and South Islands and Sand Point Beach do exhibit a more 
stable central portion with greater deviations toward inlets. The remainder 
of reach 5 has a vaguely linear trend between inlets. 



81 



REACH 4 



ACCRETING (3.9J5) 



ERODING (13.9%) 




STABLE (82.2%) 



Figure 38. Summary of shoreline 
movement for coastal reach 4, 
1874-1983 

96. Maximum movement is quite high along this entire shoreline (Fig- 
ure 40). Over the 1857 to 1983 time range, the only location that has less 
than a 100-m net change is central North Island. Movements over 1,300 m 
occurred near Cape Romain, and throughout the reach, movement in excess of 
500 m is common. 

97. Temporal separation of average shoreline movement data into three 
periods reveals steady erosion south of Cape Romain Harbor (Figure 41) . Mur- 
phys Island was predominantly accretional prior to the early 1920's, except 
for the north end. From the early 1920 's to early 1960, it was mainly ero- 
sional, except for the extreme southern end. During the most recent time 
interval, it has become strongly accretional again, but with erosion dominat- 
ing adjacent to inlets. Cedar Island has changed from modestly accretional to 
erosional through time. South Island, south of the Winyah Bay jetties, was 
mixed spatially between erosion and accretion prior to the 1920's. Between 
1920 and 1965, it was very strongly accretional, reaching a maximum of 

48 m/year between 1926 and 1934. During the 1960 to 1983 time span, it was 
erosional to the south and accretional along the north end. North Island has 



82 




Figure 39. Average net shoreline movement and standard deviation of 
movement for coastal reach 5, 1857-1983 



83 



2D00- 

ui> 19S0- 

DC in 

2* 1900- 



1 II HI Ml 
] I HIM g 




Figure 40. Maximum net shoreline movement, number of surveys used, and time 
interval of the surveys, for coastal reach 5 



84 




Figure 41. Temporal division of average net shoreline 
movement data for coastal reach 5 



85 



shown the same general pattern of strong shoreline erosion along its northern 
half and slight erosion to accretion along its southern half. The magnitudes 
of erosion and accretion were at their maximums in the 1920 to 1965 period. 

98. Average net shoreline change rates for each barrier island or 
beach, for every possible survey interval, are presented in Table 8. It is 
interesting to note that accretion occurred on both sides of the Winyah Bay 
jetties during the 1920 to 1965 period. Jetty construction was completed 
about 1900. Typically, accretion occurs only on the updrift side, and erosion 
occurs downdrift. Morris Island, downdrift of Charleston Harbor jetties, is 
an ideal example of shoreline erosion caused by sediment starvation by jet- 
ties. However, South Island showed an amazing rate of accretion even though 
it is downdrift of the Winyah Bay jetties. A second interesting fact to con- 
sider is that damming and diversion of the Santee River were completed by 

Table 8 

Average Shoreline Movement (metres/year) . Sandy 

Point to North Inlet. South Carolina 



Survey Dates 



Location 



Bull Harbor 
[15/7 - 15/15] 

Anderson Creek - Venning Creek 
[15/16 - 15/19] 

Venning Creek - Graham Creek 
[15/20 - 16/2] 

Graham Creek - Harbor River 
[16/16 - 16/20] 

Harbor river - Bull River 
[16/16 - 16/20] 

Bull River - Five Fathom Creek 
[16/21 - 16/26] 



1874- 


1875- 


1921- 


1934- 


1962- 


1934 


1921 


1934 


1962 


1983 




-0.1 


-0.8 


-0.5 


-0.5 




(100) 


(100) 


(100) 


(100) 




-2.2 


-2.3 


-1.9 


-0.4 




(83) 


(95) 


(98) 


(100) 




-0.5 


-0.5 


-0.4 


0.1 




(99) 


(99) 


(99) 


(95) 




0.4 


-0.6 


0.1 


-1.4 




(98) 


(98) 


(99) 


(98) 


-0.2 


0.2 


-0.8 


0.1 


-0.9 


(5) 


(95) 


(95) 


(100) 


(73) 




1.3 


1.3 


-0.2 


-0/1 




(97) 


(100) 


(98) 


(98) 



Note: Numbers in parentheses indicate percent shoreline surveyed during the 
given time interval. Numbers in brackets indicate the maps and segments con- 
tained in the data block; e.g., Bull River-Five Fathom Creek [16/21 - 16/26] 
extends from map 16 segment 21 to map 16 to segment 26. 



86 



1942. This should have led to erosion of the adjacent coastline since dis- 
charge and sediment supply were reduced at the river mouth by 90 percent. 
Instead, downdrift of the river mouth, South Island shows accretion. One pos- 
sible explanation for these two anomalies is that with damming and diversion, 
reduced discharge at the mouth of the Santee may have allowed ebb -tidal sedi- 
ments to migrate onshore to nourish downdrift beaches. The Santee was the 
fourth largest river on the east coast prior to 1942. Its large discharge 
probably moved large amounts of sediment onto the inner continental shelf. 
With a severe reduction in the freshwater input to the ebb flow, nearshore 
portions of the ebb delta may have migrated onshore under the influence of 
flood currents and/or waves . 

99. Despite accretion immediately adjacent to Winyah Bay jetties, the 
majority of reach 5 can be classified as eroding over the long term (Fig- 
ure 42). Approximately 54.5 percent of reach 5 showed erosion in excess of 

1 m/year, undoubtedly related to reduction in sediment supply from the Santee 
River. This is surpassed only by erosion in reach 1. Accreting (24.1 per- 
cent) and stable (21.4 percent) transects are approximately equal along this 
shoreline . 
Coastal reach 6 

100. The arcuate strand geomorphic zone (Brown 1977), defined here as 
reach 6, has been primarily a stable shoreline (Figure 43). Unlike reaches 1, 
2, 3, and 5, most of this shoreline has shown less than ±1 m/year of shoreline 
change over the period of record. Only downdrift of Murrells Inlet does an 
area exceed 2.5 m/year. 

101. Standard deviations of average net rate of change are small 
throughout most of this reach, suggesting that shoreline change rates have not 
varied considerably (Figure 43) . Maximum variability (±14 m/year) occurs 
immediately downdrift of Murrells Inlet. Most of the coastline has less than 
±2.5 m/year of variability over 130 years of data. This variability tends to 
increase in the vicinity of those few inlets that punctuate this shoreline. 
Only at inlets does the standard deviation exceed ±5 m/year. 

102. Maximum net movement is greatest in the vicinity of Murrells Inlet 
(over 500 m) and other inlets (Figure 44) . Most of reach 6 has experienced 
less than 100 m of net change over the span of data. The magnitude of maximum 
net changes is small compared with changes occurring in the barrier island 
geomorphic zone , reaches 1 , 2 , and 3 . 

87 



REACH 5 



ACCRETING (24 




ERODING (54.5%) 



STABLE (21 



Figure 42. Summary of shoreline movements for coastal 
reach 5, 1857-1983 

103. Temporal examination of average shoreline movement rates shows 
alternating erosion and accretion along the shoreline through time (Fig- 
ure 45). Prior to 1929, most of the shoreline was mildly erosional, except 
near inlets where strong erosion and accretion were evident. From 1920 to 
1965, most of the shoreline was accretional. Areas that were accretional dur- 
ing the previous period are now erosional. The most recent period, 1960 to 
1983, alternates again, with erosion now predominant. Areas of erosion 
between 1920 and 1965 are now areas of accretion. These data suggest large 
changes in shoreline position occur, but net change over a long time interval 
is quite small, as indicated in Figure 43. This is further substantiated by 
the interval shoreline change data presented for each beach in Table 9. 

104. The long-term stable nature of this coastline is demonstrated in 
Figure 46. Of the transects digitized in reach 6, 92.3 percent were stable 
over the 1872-1983 span. The remainder of shoreline was equally divided 
between accretion (4.4 percent) and erosion (3.3 percent). Temporal data sug- 
gest alternating erosion and accretion along the arcuate strand, but clearly, 
net changes for most of this reach are relatively minor. 



88 




5.0 



-ID. 



-15.0 



- 








2 




















o 




















i- 




















o 




















o 




















< 


























.L 


— 1 ,Jk ■ 


JA 




jV'T" 












^ ^ 










z 




















o 




















CO 

o 




























1 










ct 










1 










u 










1 
1 














u 




1" 














^ 




15 














e! 




I" 


-lie i- ! 












r 






i-iiuvj 1 












i w 






i/SLZki 












Jh 




/ '? 


X3*ii\ 














/o \ 


' Jfe 




^>nI \ 




X 






X 


/ l£ 


/ LU 





Figure 43. Average net shoreline movement and standard deviation of movement 
for coastal reach 6, 1872-1983 



89 



>■ < 

CC iii 




Figure 44. Maximum net shoreline movement, number of surveys used, and time 
interval of the surveys, for coastal reach 6 



90 




Figure 45. Temporal division of average net shoreline 
movement data for coastal reach 6 



91 



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ACCRETING (4.455) 



ERODING (3.3%) 




STABLE (92.3J5) 

Figure 46. Summary of shore- 
line movements for reach 6, 
1872-1983 

Coastal reach 7 

105. Northernmost, reach 7 lies within the State of North Carolina. 
Geomorphologically , it appears to be an extension of Brown's (1977) arcuate 
strand zone. However, it differs in that it has more frequent inlets and some 
true barrier islands, and it includes Cape Fear. The data set extends around 
Cape Fear to New Inlet on the north side of the Cape. 

106. A visible change occurs in average movement of the shoreline in 
the vicinity of Cape Fear (Figure 47). West of 'Cape Fear River, shoreline 
movement is similar to reach 6, the arcuate strand. Erosion or accretion 
never exceeds 2.5 m/year except near Cape Fear River Inlet. Spatial distribu- 
tion of standard deviation west of Cape Fear River is not as consistent as the 
arcuate strand or barrier island reaches; peaks occur along central portions 
of islands /beaches as well as in the vicinity of inlets. Two peaks of 
accretion in average movement and higher standard deviation between Shallotte 
Sound and Lockwoods Folly Inlet coincide with positions of two ephemeral 
inlets that opened sometime before 1924 and closed between 1933 and 1962. In 



93 




Figure 47. Average net shoreline movement and standard deviation of movement 
for coastal reach 7, 1857-1983 



94 



general, west of Cape Fear River, standard deviations are less than 2.5 m/year 
and exceed 5 -m/year only in the vicinity of inlets. At Tubbs Inlet, standard 
deviation reaches a maximum of 22 m/year. 

107. East of Cape Fear River and north of Ca>pe Fear (Map 32), patterns 
of average movement and standard deviation change. Average movement increases 
in magnitude, ranging from 5-m/year accretion to 6-m/year erosion. Bald Head 
Island is strongly accretional on its western end, but becomes erosional as 
Cape Fear is approached. North of Cape Fear, erosion predominates to New 
Inlet. The updrift side of New Inlet is accretional. Standard deviation 
around and north of Cape Fear is similar to the barrier island zone, 

reaches 1, 2, and 3. Maximum deviations (greater than ±5 m/year) occur near 
inlets, and central portions of islands tend to be more stable. This trend is 
not clear at New Inlet, which has migrated since 1852. For the entire reach, 
erosion clearly predominates over accretion during the 1852 to 1982 span. 

108. Maximum net movement is highest north of Cape Fear, exceeding 
600 m in the 1852 to 1982 span (Figure 48). West of Cape Fear River, maximum 
movements do not exceed 200 m except in the vicinity of inlets. Magnitude of 
maximum movement is greater than the arcuate strand zone, but less than the 
barrier island zone. Peaks of maximum movement correlate with inlets. 

109. West of Cape Fear River, division of the average net movement data 
into three periods reveals a behavior similar to reach 6 (Figure 49). Erosion 
and accretion appear to alternate from one period to the next. East of Cape 
Fear River, erosion seems to predominate during all three time intervals. The 
magnitude of erosion appears greatest prior to 1965. Accretion is generally 
limited to the immediate vicinity of inlets. Average net shoreline change for 
each survey interval for every beach and island in reach 7 is presented in 
Table 10. 

110. Summarizing shoreline movement over reach 7 demonstrates just how 
similar it is to reach 6 (Figure 50) . If the transects around and north of 
Cape Fear (Map 32) are separated out of the summary, the remainder of the 
shoreline is even more similar to reach 6 (Figure 51) . Most of the shoreline 
west of Cape Fear is stable (78.5 percent) with only small percentages showing 
long-term accretion (11.9) or erosion (9.6 percent). The shoreline east of 



95 



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Maximum net shoreline movement, number of surveys used, and time 
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96 




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REACH 7 



ACCRETING (15. 




ERODING (22.7%) 



STABLE (61. 6%) 



Figure 50. Summary of shoreline movement 
for coastal reach 7, 1857-1983 

the Cape Fear River and north of Cape Fear to New Inlet is strongly erosional 
(61.0 percent). This small segment of coastline equals reaches 1 and 5 in 
spatial distribution of erosion. Very little of the coast around Cape Fear 
can be considered stable (12.3 percent) or accretional (26.7 percent) over the 
long term. 

111. In general, the segment of North Carolina coast west of Cape Fear 
is very similar to the arcuate strand geomorphic zone in terms of its shore- 
line change. More numerous inlets in comparison to the arcuate strand intro- 
duce greater variability in spatial distribution of peaks in average movement, 
maximum net movement, and standard deviation. Likewise, greater temporal 
variation is evident by larger magnitude changes, especially at inlets. The 
segment east and north of the Cape Fear River (Map 32) is highly erosive spa- 
tially, similar to reaches 1 and 5. 

Entire study area 

112. The barrier island geomorphic zone is composed of reaches 1, 2, 
and 3. Within this zone, spatial distribution of erosion appears to increase 
southward (reach 3 = 30.1-percent erosion, reach 1 = 54.9-percent erosion) 



99 



ACCRETWO (19.7*) 




OWOWO C22.7S) 



STABLE (aiJOJ) 



"WCH 7 EXCEPT CAPE FEAR 



AOCRETMC (11.M) 



ercono (tax) 




STABLE (TUX) 

Figure 51. Summary of shore- 
line movements for coastal 
reach 7 west of the Cape Fear 
River and from the Cape Fear 
River to New Inlet 



100 



while accretion increases to the north (reach 1 = 14. 6 -percent accretion, 
reach 3 = 44.4-percent accretion). Overall, the barrier island geomorphic 
zone is spatially dominated by erosion (44.5 percent) over the long term (Fig- 
ure 52). Approximately 25.7 percent of the barrier island coastline is 
accreting, and 29.8 percent can be considered stable. Magnitude of average 
and maximum shoreline changes and variability in shoreline changes are large 
in this geomorphic zone. 

113. The cuspate delta geomorphic zone is composed entirely of reach 5. 
Within this zone, erosion predominated (54.5 percent) at most locations (Fig- 
ure 42) . Approximately one quarter of the shoreline in reach 5 was stable 
(21.4 percent) and one quarter was accreting (24.1 percent). This zone is 
very similar in overall behavior to the barrier island zone. 

114. Reaches 6 and 7 west of Cape Fear River compose the arcuate 
strand geomorphic zone, which is very different from the barrier island or 
cuspate delta zones (Figure 52) . Long-term analysis of shoreline changes 
reveals most of the arcuate strand is stable (86.9 percent of shoreline has 
less than ±1 m/yr change). Accretion (7.3 percent) slightly outweighs erosion 
(5.8 percent) in the remainder of shoreline. Clearly, the factors controlling 
long-term shoreline changes are different between the arcuate strand and geo- 
morphic zones to the south. The arcuate strand is most similar in shoreline 
response to reach 4; Bull Bay, which had 82.2 percent of its shoreline in the 
stable classification (Figure 38). 

115. Summarizing transect data over the entire study area for the 
entire range of surveys available, approximately half the coastline is stable, 
31.3 percent is eroding in excess of 1 m/yr, while 18 percent is accreting 
seaward (Figure 53) . Variability in erosion and accretion is greatest at 
inlets. Most shoreline has changed less than 400 m over the 130-year span of 
data. Changes in excess of 1,000 m are relatively unusual. 

116. In summary, this analysis indicates two primary types of histori- 
cal shoreline changes: those associated with barrier islands and tidal inlets 
and those associated with continuous mainland beach. The former is dynamic 
and closely dependent on local changes at inlets. The latter, being freed 
from inlet disturbances, is mildly dynamic, but with little long-term net 
change . 



101 



BARRIER ISLAND CEOMORPHIC ZONE 



ACCRETING (25.7%) 




ERODING (44.5X) 



ARCUATE STRAND CEOMORPHIC ZONE 



ACCRETING (7.3X) ERODING (5.BX) 




Figure 52. Summary of shoreline 
movement in the barrier island 
and arcuate strand geomorphic 
zones 



Inlet Changes 



117. From previous discussions in Parts II and IV, it should be appar- 
ent that inlets are extremely important in affecting changes along adjacent 
shorelines. However, many changes produced by inlets are not in an onshore/ 
offshore direction. Alongshore changes have been quite radical at many 
inlets; yet at others, alongshore changes are small. To examine alongshore 



102 



ALL REACHES COMBINED 



ACCRETING (18.0%) 




ERODING (31. 3%) 



STABLE (50.8%) 



Figure 53. Summary of shoreline movement for 
the entire study area, 1851-1983 

changes, the authors made simple measurements of updrift and downdrift spit 
lengths at each time interval on each map. It was assumed that littoral drift 
along this coast is from north to south. Inlet throat width was also mea- 
sured. This information is presented in summary form in Table 11. In some 
instances, subaerial area measurements were made to observe changes in island 
or spit growth/erosion through time. Aerial change data are presented along 
with a brief descriptive narrative of each inlet. No attempt was made to 
estimate volume changes. Inlets that showed little alongshore change have 
been omitted, their across -shore changes having been reported in the previous 
discussion. The reader is reminded that the following discussion is based on 
inlet position as mapped at distinct points in time and should not be used to 
assume other than equally distributed changes during intervening periods. 
Examination of shoreline changes around inlets on the accompanying shoreline 
change maps is essential to understanding the descriptive narratives. Discus- 
sion proceeds from south (Map 1) to north (Map 32) . 

118. Savannah River, New River, Calibogue Sound, and Port Royal Sound 
are inlets located on maps 1 through 4 that have primarily onshore/offshore 
changes and are adequately characterized by the shoreline change technique. 

103 



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105 



The reader is referred to previous shoreline change sections for information 
on shorelines adjacent to these inlets. 
Trenchards Inlet (Map 5) 

119. From 1859/60 to 1920/21, the updrift side of Trenchards Inlet grew 
southwest about 730 m, at an average rate of 13 m/year. The downdrift side 
eroded in response as the inlet throat decreased in width only slightly 

(60 m) . By 1955, the updrift shoreline had receded northeast over 1,030 m, 
putting it landward of the 1859/60 position. Throat width remained constant, 
and only minor changes occurred on the downdrift side. Shoreline recession 
was evident along Capers Island throughout the time span. Erosion of the 
updrift spit continued until the 1982/83 survey, having moved northeast an 
additional 7 m/year since 1955. Surface area of the updrift spit on Capers 
Island had increased 3 . 3 x 10 6 m 2 between 1859/60 and 1920/21 (54,000 m 2 / 
year), but lost 7 . x 10 6 m 2 by 1982/83 (111,000 m 2 /year) . 
Pritchards Inlet (Map 5) 

120. Two tidal creeks intersected at the shoreline in 1859/60 forming a 
"V" shape with the point of the "V" seaward. The single inlet formed from 
these two creeks is Pritchards Inlet. Constant landward erosion until 1955 
resulted in removal of the base of the "V" and intersection of two separate 
inlets within the shoreline. In 1859, distance between opposite sides of the 
inlet was about 425 m. By 1955, it had grown to 1,000 m. In 1859, distance 
from the land inside the "V" to the shoreline trend was about 240 m. With the 
pattern of erosion described, this center section was cut back approximately 
180 m so that by 1983, the gap between inlets had a receded shoreline of only 
60 m. The largest change came between 1859/60 and 1920/21, when the updrift 
side of the inlet retreated northeast about 270 m and the downdrift side 
retreated westward 120 m. Since 1920, updrift and downdrift spits have been 
small, both showing a maximum alongshore extension in 1971. 

Skull Inlet (Map 6) 

121. In 1859/60, Skull Inlet had a east-west orientation at its point 
of juncture with the shoreline. Updrift accretion and erosion downdrift have 
resulted in a nearly north-south orientation on the 1982/83 survey. Much ero- 
sion and accretion was accomplished between 1856/59 and 1920. The downdrift 
side was eroded approximately 185 m alongshore during this interval while the 
updrift side accreted approximately 890 m. The inlet throat narrowed consid- 
erably, from 1,030 m wide to about 245 m. Since 1920, throat width decreased 

106 



s-lightly to 180 m in 1982/83. Updrift and downdrift sides of the inlet have 
been relatively stable since 1920 with only minor erosion updrift between 1920 
and 1955 and accretion (60 m) of a small spit on the downdrift side between 
1971 and 1982/83. 
Fripp Inlet (Map 6) 

122. Fripp Inlet has become progressively offset seaward downdrift 
through shoreward erosion on the updrift side and accretion downdrift. Down- 
drift accretion reached its maximum in 1955, having accreted approximately 

1.8 x 10 6 m 2 since 1856/59 (18,000 m 2 /year) . This accretion reversed between 
1955 and 1962. Little change occurred since 1962 on the downdrift side. Net 
change between 1955 and 1983 is erosion of 1.4 x 10 6 m 2 (50,000 m 2 /year) . Most 
change in area is due to onshore/offshore changes; however, there was a net 
60-m alongshore erosion on the southwest side of the inlet. Alongshore 
changes updrift had a comparable 60-m accretion. However, between 1856/59 and 
1955, shoreline erosion resulted in a 2.3 x 10 6 m 2 loss, followed by slight 
accretion (0.2 x 10 6 m 2 ) by 1982/83. Most of this was due to onshore/offshore 
sedimentation. Inlet throat width varied only slightly during this period, 
from 610 m wide in 1856/59 to 790 m in 1964 to 670 m wide in 1982/83. 

St. Helena Sound (Map 6) 

123. In 1856/59, a large spit extended northeast from Hunting Island 
into St. Helena Sound. Landward shoreline erosion and alongshore erosion on 
the order of 2,000 m by 1920 resulted in a 6.0 x 10 6 m 2 (99,000 m 2 /year) loss 
to the spit. Spit erosion continued to 1964 (1.1 x 10 6 m 2 lost, 26,000 m 2 / 
year) , but alongshore accretion to the northeast dominated between 1964 and 
1983 (12,000 m 2 , 640 m 2 /year) . With spit losses, the north end of Harbor 
Island, which lies north of Hunting Island, began accreting. From 1856/59 to 
1955, it grew about 850 m north into St. Helena Sound. This 0.6 x 10 6 m 2 
increase in area (10,000 m 2 /year) was followed by an increase between 1920 and 
1964 (50,000 m 2 ) and a small amount of erosion (200,000 m 2 ) between 1964 and 
1982/83. Net change to the spit was 7.2 x 10 6 m 2 erosion, with a coincident 

2.9 x 10 6 m 2 growth of Harbor Island. The absence of data between the dates 
presented here makes it impossible to investigate causal relationships of spit 
loss and growth of Harbor Island, but it is reasonable to speculate that sedi- 
ment composing the 1859 spit may have migrated landward to build out Harbor 
Island. 



107 



124. Changes on the northeast side of St. Helena Sound, Fish Creek 
Inlet, and South Edisto River Inlet have been adequately represented by the 
shoreline change mapping. Likewise, shoreline changes surrounding a small, 
unnamed inlet just south of Frampton Inlet on map 9 are also represented by 
the shoreline change mapping technique; however, it had some small alongshore 
changes as well. From 1851/54 to 1920/21, it moved slightly northeast; and 
from 1920/21 to 1933, it moved southwest. Since 1933, it has remained sta- 
tionary in its alongshore position. 

Frampton Inlet (Map 9) 

125. At Frampton Inlet, from 1851/54 to 1933, there were two tidal 
creeks that merged to form one inlet, similar to previously discussed 
Pritchards Inlet. Inlet throat width was approximately 180 m in 1851/54 and 
120 m in 1933. During this interval, the throat migrated northeast. Between 
1933 and 1964, throat width increased to 420 m, by alongshore retreat (610 m) 
on the southwest side of the inlet relative to 300 m of elongation on the 
northeast side. By 1970/74, additional alongshore losses on the southwest 
side (120 m) had combined with movement of the northeast side of the inlet 
610 m to the northeast and separation into two inlets. On the 1983 survey, 
two distinct inlets, each about 300 m wide, are separated by approximately 
900 m of shoreline. The southwest spit moved southwest an additional 120 m, 
and the northeast spit retreated 240 m as the inlets migrated apart. 

North Edisto River Inlet (Map 9) 

126. Over the time range of data used in this study, there has been 
little alongshore migration of North Edisto River Inlet. Most change has been 
in the onshore/offshore direction. The southwest side of the inlet has 
retreated landward steadily since 1851/54. The northeast side advanced sea- 
ward from 1851/54 to 1933, was stable to 1964, and advanced slightly from 1964 
to 1970/74. From 1970/74 to 1983, it eroded back to about the 1964 position. 
Onshore/offshore changes resulted in widening of the inlet throat southwest- 
ward from approximately 975 m in 1851/54 to 1,830 m in 1964, to approximately 
1,890 m in 1983. The magnitude of the onshore/offshore changes are given in 
Appendix A, Map 9, sections 4 through 9. 

127. Deveaux Bank, which sits at the inlet mouth has undergone dramatic 
changes since it was first mapped in 1920/21. At that time, it was approxi- 
mately 150 m long, extending in a north-northwest, south- southeast direction, 
and had approximately 24,000 m 2 of subaerial surface area. By 1933, it 

108 



migrated approximately 670 m northwest and was composed of two small islands 
totaling about 61,000 m 2 in surface area. No evidence of the island appears 
on the 1964 survey, but in 1970/74, it was at its maximum mapped extent. It 
trended northwest -southeast, starting at the same point as the island in the 
1920's. Its long axis was about 2,070 m, and it was about 2.2 x 10 6 m 2 in 
area. By 1983, it was back to two small, thin, islands, the longest being 
approximately 600 m with a north-south orientation. Combined surface area was 
about 43,000 m 2 . The net change from 1920/21 to 1983 has been an increase in 
surface area of 18,000 m 2 . The banks are probably an exposed portion of the 
North Edisto River Inlet ebb-tidal delta. Changes outlined here illustrate 
the dynamic nature of ebb deltas in response to changing environmental 
conditions . 
Captain Sams Inlet (Map 10) 

128. The 1854 survey does not indicate any inlet in the shoreline, but 
by 1921, Captain Sams Inlet was approximately 1,340 m wide, with two small 
islands between. Since 1921, the northeast side of the inlet has been advanc- 
ing in alongshore direction southwestward. The northeast side (spit) grew 
1,150 m between 1921 and 1933 (97 m/year) . Between 1933 and 1964, it grew at 
only 6 m/year, but this rate increased to approximately 44 m/year between 1964 
and 1983. Net elongation from 1921 to 1983 was approximately 2,200 m. During 
this same time, southwest erosion occurred alongshore as the inlet migrated 
southwest. From 1921 to 1933, erosion on the southwest side was approximately 
305 m, which was a slower pace than updrift side accretion. As a result, the 
inlet narrowed. Downdrift erosion and inlet narrowing continued to 1983, when 
the net result was approximately 1,800 m of southwest erosion and 400 m of 
narrowing. The inlet was at its narrowest in 1964 and 1970, when it was only 
about 120 m wide . 

Stono Inlet (Map 11) 

129. Stono Inlet is large with several islands in it, including Bird 
Key. Kiawah Island, southwest of the Inlet, accreted seaward rapidly between 
1862/64 and 1921 (1,500 m) adding about 90,000 m 2 /year. From 1921 to 1955, it 
eroded back slightly (60 m) and broadened. Since 1955, it remained fairly 
stable, having had a net increase in area of 5.7 x 10 6 m 2 since 1862/64. Sub- 
aerial shoals seaward of the inlet, present in 1862/64, were not evident on 
the 1921 survey, having perhaps migrated onto Kiawah Island and contributed to 
its seaward growth. 

109 



130. Folly Island, northeast of the inlet, has eroded landward and 
alongshore to the northeast over the duration of these data. From 1854/58 to 
1921, it retreated over 1,080 m in alongshore direction (16 m/year) . Along- 
shore retreat continued to 1983, although at a reduced rate (2.5 to 3.4 m/ 
year). Net change between 1854/58 and 1983 was alongshore erosion of approxi- 
mately 1,200 m. Coincident with rapid erosion of Folly Island between 1854/58 
and 1921 was the development of Bird Key between Folly and Kiawah Islands. It 
was first mapped on the 1921 survey, where it had an area of 0.2 x 10 6 m 2 . 

Its surficial area has waxed and waned dramatically between 1921 and 1983. 
Between 1921 and 1933, it lost 183,000 m 2 and then gained 1.1 x 10 6 m 2 by 1955. 
The 1964 survey shows a tiny island only 7,000 m 2 in size, representing a 
1.2 x 10 6 m 2 loss since 1955. In 1983, the key was 244,000 m 2 in area, repre- 
senting a net increase of 48,700 m 2 since 1921. Small changes in position, 
orientation, and shape accompanied these area changes. 

131. As a result of changes in Kiawah and Folly Islands and Bird Key, 
throat width changed from 1,525 m in 1854/58, to a maximum of 2,560 m in 1921, 
down to 1,700 m in 1955, and back up to 2,010 m in 1983. A net width increase 
of roughly 500 m from 1854/58 to 1983 was due mainly to erosion of Folly 
Island. 

Lighthouse Inlet (Map 13) 

132. Most changes that have occurred at Lighthouse Inlet are the result 
of rapid shoreline erosion along Morris Island since completion of the 
Charleston Harbor jetties. Net erosion rate between 1857/58 and 1983 is over 
10 m/year for the southern end of Morris Island. Folly Island, south of the 
inlet has also eroded landward since 1857/58, but the magnitude of change is 
small compared with Morris Island. A prominent seaward offset of Folly Island 
has resulted. The southern terminus of Morris Island has moved alongshore 
only slightly during this period. Net change from 1857/58 to 1983 has been 
about 60 m of southwest extension. Folly Island eroded southwest about 275 m 
during this same interval; however, because of landward retreat of Morris 
Island, the inlet throat retreated upstream and decreased in width by 120 m 
over the study duration. 

Charleston Harbor (Map 13) 

133. The northwest side of Charleston Harbor entrance is formed by 
Sullivans Island. Accretion in the vicinity of Fort Moultrie has been ade- 
quately measured by the shoreline mapping technique. Southwest of Charleston 

110 



Harbor is Cummings Point, on Morris Island. From 1857/58 to 1900, Cummings 
Point retreated alongshore approximately 600 m. This coincided with landward 
erosion of the entire northern portion of Morris Island, prior to jetty com- 
pletion in 1895. From 1900 to 1955, Cummings Point grew northward into the 
harbor approximately 600 m. From 1955 to 1983, there was no net change. Net 
change from 1857/58 to 1983 was a slight increase in length of approximately 
60 m. 
Breach Inlet (Map 13) 

134. The northeastern side of Breach Inlet has been accreting both sea- 
ward and alongshore to the southwest since first surveyed in 1875. Net change 
between 1875 and 1983 was approximately 180 m (1.7 m/year) with maximum 
advance (5 m/year) occurring between 1921 and 1933/34. Southwest of the 
inlet, alongshore erosion occurred during the data interval. Net change on 
the southwest side has been approximately 120 m (1.1 m/year) of erosion 
between 1875 and 1983. This erosion trend was punctuated by a period of no 
net change between 1921 and 1933/34 and 60 m of accretion between 1933/34 and 
1962/64. Inlet throat width decreased from 300 m in 1875 to 180 m in 1962/64 
and increased to 210 m by 1983. 

Dewees Inlet (Map 14) 

135. The southwest side of Dewees Inlet had numerous, but small, 
changes between 1856/57 and 1983. Its maximum mapped seaward extent was in 
1921, but as of 1983, it was 150 m landward of that position. The northeast 
side of the inlet is bounded by Dewees Island. Dewees Island has experienced 
rapid onshore erosion along its southern end and accretion along its northern 
shoreline, resulting in reorientation of the shoreline from north-south in 
1856/57 to northeast- southwest in 1983. A net loss in surface area of 2.0 x 
10 6 m 2 over the 1856/57 to 1983 period resulted. Rate of loss varied from 
30,000 to 60,000 m 2 /year, except during 1921 to 1934, when there was a net 
accretion of 157,000 m 2 . The new shoreline of Dewees Island is roughly paral- 
lel to Isle of Palms and Capers Island but landward of the former and seaward 
of the latter. Erosion on the south end of Dewees Island and small changes 
noted to Isle of Palms have resulted in a net widening of Dewees Inlet from 
approximately 430 to 550 m between 1856/57 and 1983. 

Capers Inlet (Map 14) 

136. Previously discussed changes on Dewees Island, particularly accre- 
tion on the north end, have influenced Capers Inlet. Northeast of the inlet, 

111 



alongshore erosion with seaward advance occurred between 1856/57 and 1875. 
However, net change between 1856/57 and 1983 has been alongshore (550 m) and 
landward erosion. A prominent spit extended southwestward in the late 1800 's 
forcing Capers Inlet southwest. However, over 700 m (12 m/year) of alongshore 
erosion removed the spit by the 1921 survey. Between 1934 and 1983, the pat- 
terns reversed, and accretion occurred (240 m) to the southwest again, 
although landward of its former position. This coincided with accretion on 
Dewees Island resulting in a switch from a updrift offset inlet to a downdrift 
offset inlet. The inlet throat, approximately 600 m wide in 1856/57, 
increased to approximately 670 m in 1875 and then decreased steadily to 
approximately 300 m wide by 1983. 
Price Inlet (Maps 14 and 15) 

137. The 1856/57 survey for the southwest side of Price Inlet is incom- 
plete, but it suggests approximately 1,400 m of northwestward spit accretion 
by 1875. The 1875 survey shows a well-formed spit with a small bay behind. 
Between 1875 and 1983, spit length remained constant, as did position of the 
inlet. Inlet width decreased from 1875 (300 m) to 1934 (240 m) , but remained 
constant between 1934 and 1983. However, despite alongshore consistency, the 
seaward shoreline of Capers Island advanced and retreated considerably in the 
inlet vicinity. The southwest shoreline eroded from 1875 to 1921, accreted 
from 1921 to 1934, eroded from 1934 to 1962/63, and finally, accreted between 
1962/63 and 1983. Northeast of the inlet, fairly stable alongshore shorelines 
had a similar, although inverted, history of cross-shore shoreline change. 
The shoreline accreted from 1875 to 1921, eroded from 1921 to 1934, accreted 
to its maximum seaward position by 1962/63, and eroded slightly between 
1962/63 and 1983. Observed 180-deg out-of -phase relationship of onshore/ 
offshore erosion/accretion has been discussed by FitzGerald (1984) , who 
attributes it to e~bb channel migration and associated welding of ebb delta 
features onto adjacent shorelines. 

Bull Bay (Maps 15. 16 and 17) 

138. Northeast Point forms the southwestern boundary of Bull Bay. Bull 
Island has been undergoing rapid erosion on its eastern end, driving it in a 
landward direction since 1875. Losses resulting from erosion have ranged from 
20,000 to 35,000 m 2 /year over the interval of data. Despite overall losses by 
erosion, Northeast Point accreted alongshore approximately 790 m between 1875 



112 



and 1921 and another 180 m from 1921 to 1962. Between 1962 and 1983, the 
Point broadened westward, but did not accrete farther into Bull Bay. 

139. Bird Island, which lies within Bull Bay, is included in this anal- 
ysis since it could not be adequately measured by the shoreline mapping tech- 
nique. Bird Island first appears on the 1921 survey. Its subaerial surface 
area was approximately 244,000 m 2 , and it was oriented in a northeast - 
southwest direction with a length of approximately 1,460 m. It is not evident 
on the 1934 survey, but by 1962, the island increased 1,150 m over its 1921 
length, and area increased 232,000 m 2 . The 1983 survey shows an additional 
increase in length of 180 m, but a decrease in surface area of 24,000 m 2 . Net 
change from 1921 to 1983 was a 207,000-m 2 increase of surface area. Accom- 
panying island length and area changes were position changes. The island as a 
whole moved approximately 600 m northeast from 1921 to 1964 and 550 m south- 
west by 1983. In 1983, it was approximately 250 m landward of its 1921 
position. 

140. Sandy Point Beach forms the northeast side of Bull Bay. It has 
experienced continuous onshore erosion since the 1875 survey. However, from 
1875 to 1934, the spit tip accreted southwest approximately 610 m. Between 
1934 and 1962, there was a dramatic reversal when the spit eroded 670 m along- 
shore. Erosion continued from 1962 to 1983 (180 m) . Net change over the 
range of data was 240 m of erosion. 

Key Inlet (Map 17) 

141. Key Inlet was a small, narrow (60 m wide) inlet during the 1875 
survey. Landward shoreline erosion combined with eastward inlet migration and 
westside erosion between 1875 and 1934. Net alongshore change west of the 
inlet was a loss of approximately 50 m. Inlet width doubled by the 1925 sur- 
vey, doubled again by 1934, and again by 1962. By 1983, inlet width had 
increased to approximately 550 m. Also, by 1983, a long, narrow spit extended 
from the east end of Lighthouse Island, which protected Key Inlet from direct 
wave attack. The east side of the inlet rapidly eroded into Lighthouse Island 
from 1875 to 1925, but only eroded a small additional amount by 1983. 
Lighthouse Island/Cape Romain (Maps 17 and 18) 

142. Shoreline position changes at Cape Romain are responsible for 
changes in surficial area and shoreline orientation on adjacent Lighthouse 
Island. In 1874, Cape Romain was at its most seaward (easterly) extent, with 
a small hook extending roughly 600 m southwest. The 1925 survey shows about 

113 



900 m of westward cape erosion with approximately 500 m of southerly accretion 
since 1874. The cape tip was broad and blunt. From 1925 to 1934, westward 
erosion continued at a reduced rate, and the cape retreated northward approxi- 
mately 180 m. Both bay and oceanside erosion resulted in narrowing of Cape 
Island in the vicinity of Cape Romain. A narrow east-west oriented spit about 
600 m long formed the cape terminus. By the 1962/63 survey, Cape Romain had 
retreated an additional 480 m northward. Westward erosion resulted in the 
1934 bay shoreline and 1962/63 ocean shoreline being in similar positions. 
The terminal spit elongated westward so that it was approximately 3,500 m long 
in 1962/63. This resulted in a longer Romain River outlet and protection of 
most of Lighthouse Island from direct wave attack. Additional landward 
retreat of both sides of the cape continued to 1983 (roughly 500 m north and 
500 m west) . The long east-west spit attached to the Cape Romain in 1962/63 
was apparently breached by the Romain River. Sediment downdrift of the breach 
appears to have moved landward and welded onto Lighthouse Island, which in 
1983 shows a long spit extending 4,250 m westward, past Key Inlet. That spit 
portion remaining on Cape Romain (800 m long) migrated landward about 500 m. 

143. Between 1874 and 1962/63, Lighthouse Island accreted rapidly at 
its southeast end. From 1874 to 1925, island surface area dropped from 10.7 x 
10 6 m 2 to 8.9 x 10 6 m 2 ; but by 1934, it had increased to 11.2 x 10 6 m 2 . Accre- 
tion continued through 1983 when island area was 16 . 9 x 10 6 m 2 . Island growth 
appears to correlate with spit growth on the tip of Cape Romain. A large 
increase in area (197,000 m 2 /year) came between 1962/63 and 1983 when the spit 
was breached and part of it appears to have welded onto Lighthouse Island. 
Net change between 1874 and 1983 was an increase in area of 6.2 x 106 m 2 . 
Southeasterly island growth and spit movements on Cape Romain have resulted in 
long-term narrowing of the Romain River Inlet from approximately 1,800 m wide 
in 1874 down to 180 m wide in 1983. 

Cape Romain Harbor (Map 18) 

144. Cape Island extends north to form the southern side of Cape Romain 
Harbor. The island's north end has accreted alongshore north-northeast since 
1873/74. Rate of accretion was approximately 34 m/year between 1873/74 and 
1934. From 1934 to 1983, accretion rate decreased to approximately 29 m/year. 
Net elongation of the island tip over survey duration is approximately 

3,600 m. Alongshore growth to the north has been accompanied by landward 
shoreline erosion. Shoreward erosion was particularly severe toward Cape 

114 



Romain; however, between 1873/74 and 1983 overall surface area of Cape Island 
increased from 12.2 x 10 6 m 2 to 15.3 x 10 6 m 2 , a net increase of 28,000 m 2 / 
year. Erosion on the south and accretion north have resulted in a net north- 
erly migration of Cape Island over the period of record. 

145. Murphy Island, north of Cape Romain Harbor, has accreted since 
1873/74. The largest increase came between 1962/63 and 1983. These changes 
are represented by the shoreline mapping procedure (Figure 39) . Accretion on 
both sides of Cape Romain Harbor entrance has resulted in its narrowing from 
approximately 2,700 m wide in 1873/74, to 2,050 m in 1934, to approximately 
975 m wide in 1983. 

South Santee River Inlet (Map 18) 

146. Cedar Island forms the northeast side of South Santee River Inlet. 
The island terminal spit accreted 850 m alongshore to the southwest at an 
approximate rate of 14 m/year between 1873/74 and 1934. Jetties at Winyah Bay 
to the north were completed about 1900. From the 1934 to 1962/63 survey, 
rapid spit erosion occurred (2,300 m, 83 m/yr) alongshore. Then from 1962/63 
to 1983, the spit accreted 420 m again. Net change was a loss in length from 
1873/74 to 1983 of roughly 900 m. A reversal of alongshore drift between 1934 
and 1962/63 is evidenced by a rapid rate of erosion during that time, plus 
development of a small spit extending east and north from the eroded tip of 
Cedar Island. This spit was not present on 1934 or 1983 surveys. 

147. Murphy Island on the west side of the inlet eroded alongshore from 
1873/74 to 1934 as the inlet migrated to the southwest. The width of the 
inlet throat decreased from 550 to 300 m during this interval. Reversal of 
the drift between 1934 and 1962/63 caused only mild accretion on Murphy Island 
and widening of the inlet to over 600 m. Return of the drift to its normal 
southerly direction by 1983 resulted in accretion on both sides of the inlet 
and a decrease of over 100 m in inlet width. 

North Santee Bay Inlet (Map 20) 

148. Santee Point, on the northeast side of North Santee Bay Inlet, 
grew southward from 1872/73 to 1925 a distance of approximately 900 m. The 
1925 survey shows several large islands seaward of South Island, which 
appeared to have formed a platform for seaward and alongshore (500 m) accre- 
tion of Santee Point by 1934. As with South Santee Inlet between 1934 and 
1962/63, alongshore erosion removed 550 m from the length of Santee Point. 
Net shoreline change by 1983 was minimal. The inlet's southwest side accreted 

115 



from 1872/73 to 1934, eroded from 1934 to 1962/63, and accreted slightly to 
1983. As a consequence of changes on both sides of the inlet, inlet width 
decreased from 800 to 360 m between 1872/73 and 1934, increased to 550 m wide 
in 1962/63, and decreased to 420 m wide in 1983. 
Winyah Bay Entrance (Map 20) 

149. Jetties at Winyah Bay Entrance were completed around 1900. North 
Island, north of the inlet, built alongshore to the south to 1962/63. Net 
change in subaerial surface area of North Island was an increase of 

2.2 x 106 m 2 from 1857/58 to 1962/63. Between 1962 and 1983, erosion resulted 
in area losses of roughly 439,000 m 2 . Net change in length of North Island 
was an increase of 1,280 m between 1857/58 and 1983. South of the jetties, 
South Island has undergone major changes in shoreline position, probably 
related to jetty construction. Between 1872/73 and 1925, South Island did not 
change drastically except that a long (4,500 m) , thin, arcuate -shaped island 
formed from the jetty southward, roughly paralleling South Island's coastline. 
This thin island was up to 3,100 m offshore of South Island. The 1934 
shoreline on South Island was similar to previous dates, except near Santee 
Point. The offshore island, however, changed to a "V" shape, with one leg 
anchored around the jetty. Maximum southwest elongation is approximately 
1,100 m, and it moved about 300 m landward since 1925. The 1962/63 survey 
shows formation of a large island positioned inland of the 1934 island and 
2,000 m of accretion on South Island's shoreline. This new island was 
primarily south of the jetty, but a small spit extended north (700 m) . By 
1983, area behind the 1962/63 island had filled in, leaving only a small tidal 
channel. The 1983 shoreline of South Island immediately south of the jetty 
was about 180 m landward of the 1962/63 small island shoreline. Farther 
south, shorelines show no offset. The 1983 south jetty survey shows a large 
spit (over 2,000 m long) extending into Winyah Bay. By 1983, a small 1962/63 
spit extending north of the south jetty increased in area by 2.1 x 10 6 m 2 . 
South Island area changes south of the jetty are presented in Table 12. 
North Inlet (Map 21) 

150. South of North Inlet, a long spit projected north in 1872. This 
spit eroded alongshore south approximately 1,600 m by 1925/26. Between 
1925/26 and 1983, net alongshore change south of the inlet was approximately 
200 m of northward accretion. Alongshore drift reversal prior to 1962 is evi- 
dent by extension of a small northward trending spit from the 1962 shoreline. 

116 



Table 12 
Area Changes South of the Wlnyah Bay Jetties 



Dates 



1872/73-1925 

1925-1934 

1934-1962/63 

1962/63-1983 

1872/73-1983 



Area Difference 
m 3 

+232,000 

-585,000 

+9,500,000 

+4,800,000 

+13,800,000 



Rate of Change 
m 2 /year 

+4,700 

-49,000 

+327,000 

+227,000 

+124,000 



Reversal at this inlet, South Santee River Inlet, and others may be due to 
local reversal in littoral drift around ebb- tidal deltas as described by Fitz- 
Gerald, Hubbard, and Nummedal (1978). However, this mechanism does not 
explain why drift reversals occur in the 1934 to 1962 time frame. In this 
case, it appears ebb delta landward migration by 1983 extended the shoreline 
seaward 300 m from its 1872 position. 

151. The north side of North Inlet extended approximately 120 m along- 
shore from 1872 to 1925/26 to form a small spit. Also, a small island formed, 
effectively creating two adjacent inlets. From 1925/26 to 1934 the spit 
showed a net erosion of 300 m (232,000 m 2 ) followed by rapid southward accre- 
tion of 1,900 m (1.3 x 10 6 m 2 ) by 1962. Spit growth protected the island from 
direct wave attack and returned morphology to a single inlet. Spit length in 
1983 was equal to its length in 1962; however, landward shoreline erosion and 
island incorporation resulted in a 1.4 x 10 6 m 2 increase in area. Net change 
between 1872 and 1983 north of the inlet was approximately 1,700 m of along- 
shore growth and a 2.7 x 10 6 m 2 growth in area. 

152. Inlet width was over 1,000 m in 1872 decreasing to 850 m total for 
two inlets that formed in 1925/26 through spit growth and island formation. 
Island erosion and spit retreat widened the inlet to 1,250 m by 1934. The 
1962 survey shows one inlet again approximately 975 m wide, narrowing to 730 m 
wide in 1983 by spit accretion on the south side. 

Unnamed inlet (Map 22) 

153. A small, unnamed inlet lies between Debidue Beach and Pawleys 
Island. The inlet's north side grew consistently southwest from 1872 to 



117 



1962/63. Rate of accretion varied from 15 m/year up to 46 m/year during the 
1926 to 1934 period. This resulted in a southerly inlet migration with cor- 
responding downdrift erosion. Inlet throat width decreased from approximately 
180 m in 1872 to 90 m in 1962/63. Between 1962/63 and 1983 surveys, the 
inlet's northeast side eroded, reducing spit length approximately 490 m. 
South side accretion kept the inlet throat around 100 m wide. 
Midway Inlet (Map 22) 

154. The northern side of Midway Inlet eroded 180 m alongshore between 
1872 and 1926. This northeastward erosion was followed by rapid southwestward 
accretion (240 m) between 1926 and 1934. A more modest rate of accretion 

(11 to 15 m/year) continued to 1983 for a net (1872-1983) southwest growth of 
670 m. Inlet changes on the south side are inversed, with accretion of over 
300 m between 1872 and 1926 and steady erosion (690 m) between 1926 and 1983. 
Inlet throat width narrowed from 275 m in 1872 to 150 m in 1926 and then 
increased to over 1,000 m in 1934. From 1934 to 1983, throat width decreased 
steadily to only 60 m. Net change from 1872 to 1983 was a narrowing of the 
inlet by just over 200 m. 
Murrells Inlet (Map 23) 

155. Murrells Inlet 1872 survey shows a long northeast trending spit 
extending southwest. The inlet throat, about 300 m wide in 1872, is in its 
most southerly position. Between 1872 and 1926, the long spit severely eroded 
northeasterly (1,950 m) while a new spit grew (2,280 m) toward the northeast 
from a southerly point along Magnolia Beach. This resulted in shoal accretion 
south of the inlet. Inlet throat width increased to 850 m as Murrells Inlet 
migrated to a northerly position. From 1926 to 1934, this south side spit 
continued to advance northeastward approximately 300 m. North side accretion 
(180 m) resulted in narrowing of the inlet to 300 m by 1934. From 1934 to 
1963, erosion/accretion patterns reversed, with over 850 ra of alongshore ero- 
sion south of the inlet and 580-m growth of a new spit on the north side. 
Inlet width increased to 670 m as it migrated south. South side erosion and 
north side accretion continued to the 1969/70 survey. Jetty construction 
occurred in 1977-1980. The 1983 survey shows no change in north side spit 
length since 1969/70, with mild accretion to the south (30 m) . Throat width 
decreased slightly from 640 m in 1969/70 to 580 m in 1983. 



118 



Futch Beach Inlet (Maps 26 and 27) 

156. Futch Beach Inlet was closed between 1934 and 1962/63. Tidal 
creek flow was diverted to nearby Hog Inlet. From 1873 to 1934, the inlet's 
northeast side accreted approximately 1,100 m southwest. The south side 
eroded approximately 1,150 m as inlet width increased roughly 50 m. 

Hog Inlet (Map 27) 

157. The northeast side of Hog Inlet accreted alongshore roughly 600 m 
from 1873 to 1933/34. Inlet throat width remained constant (90 m) as erosion 
on the southwest side kept pace with northeast side accretion. Between 
1933/34 and 1962/63, the pattern reversed. Northeast of the inlet, there was 
420 m of spit erosion, and there was 360 m of accretion on the southwest side. 
Throat width increased to 180 m and up to 300 m by 1969/70. From 1962/63 to 
1969/70, northeast side erosion continued while the southwest side remained 
fairly stable. Both sides accreted 60 m between 1969/70 and 1983, reducing 
inlet throat size to approximately 120 m. Between 1873 and 1983, net change 
northeast of Hog Inlet was approximately 120 m of accretion, and the southwest 
side had 240 m of erosion. Throat width was just over 200 m in 1983. 

Little River Inlet (Map 27) 

158. Little River Inlet and adjacent Mad Inlet are separated by Bird 
Island to form two inlets. Jetty construction on Little River Inlet was com- 
pleted in 1983. The west side of Little River Inlet advanced alongshore 
1,200 m from 1873 to 1924/26, while Bird Island moved eastward. During this 
time interval of eastward migration of the inlet, Bird Island increased from 
1,830 m long to 2,930 m long. No measurable alongshore changes occurred 
between 1924/26 and 1933/34, but from 1933/34 to 1969/70, alongshore erosion 
of the westside spit occurred (850 m) . Bird Island also decreased in length 
from 2,930 m in 1924/26 to 1,525 m in 1969/70 as inlet width increased from 
300 m in 1924/26 to 1,460 m in 1969/70. The 1969/70 to 1983 period saw a 
decrease in inlet width to approximately 600 m as the southwest side accreted 
490 m and Bird Island grew in length to 2,250 m. 

159. By 1969/70, Bird Island was no longer a true island, having welded 
to the mainland on its northeast corner. From 1873 to 1969/70, island area 
increased steadily from a surface area of 1.0 x 10 6 m 2 to 2.9 x 10 6 m 2 . This 
represents a net yearly increase in area of approximately 19,000 m 2 /year. 



119 



Mad Inlet (Map 27) 

160. Position of the west side of Mad Inlet is controlled by changes in 

position and aerial extent of Bird Island described above. The inlet's east 

< 
side eroded rapidly (1,890 m, 37 m/year) from 1873 to 1924/26 and then 

accreted slightly (120 m, 14 m/year) from 1924/26 to 1933/34. Another period 

of erosion (240 m, 8 m/year) followed from 1933/34 to 1962/63. From 1962/63 

to 1969/70, rapid accretion (420 m, 60 m/year) followed. Accretion patterns 

continued (150 m, 11 m/year) to 1983. Inlet throat width increased from 275 m 

in 1873 to a maximum of almost 400 m in 1933/34 and then narrowed to 120 m in 

1969/70 and 1983. 

Tubbs Inlet (Map 28) 

161. The earliest survey date available for Tubbs Inlet is 1924. From 
1924 to 1962/63, the inlet's east side accreted (1,300 m) west quite rapidly, 
up to 68 m/year. Land west of the inlet lost 975 m of length during this time 
interval. Inlet throat width narrowed from 550 m in 1924 to approximately 
300 m in 1962/63. From 1962/63 to 1983, patterns reversed with east of the 
inlet eroding approximately 1,200 m (up to 157 m/year). Inlet width increased 
to 360 m by 1983. In 1983, Tubbs Inlet appeared as two inlets separated by an 
island approximately 300 m long. 

Shallotte Sound (Maps 28 and 29) 

162. East of Shallotte Sound inlet, alongshore accretion added 480 m 
(up to 8.4 m/year) between 1857/59 and 1962/63. No substantial changes in 
length occurred between 1962/63 and 1983. The inlet's west side eroded 300 m 
from 1857/59 to 1924, accreted 90 m from 1924 to 1933, and eroded 210 m 

(7.4 m/year) from 1933 to 1962/63. From 1962/63 to 1969/70, it maintained its 
length, but eroded an additional 120 m by 1983. Net changes (1857/59 to 1983) 
include an east side length increase of 480 m, a west side length decrease of 
550 m, and an increase of inlet width from approximately 400 m in 1857/59 to 
approximately 480 m in 1983. Maximum inlet width (580 m) occurred in 1924. 
Lockwood Folly Inlet (Map 30) 

163. Since the earliest survey date (1856/57), Lockwood Folly Inlet has 
migrated west. Between 1856/57 and 1924, east side accretion added 730 m 
while west side erosion removed 550 m in length. Between 1924 and 1969/70, 
the east side eroded slightly (up to 3 m/year) or remained stable. The west 
side eroded slightly (up to 3 m/year) from 1924 to 1962, but accreted 

(13 m/year) from 1962 to 1969/70. From 1969 to 1983, east side accretion 

120 



(180 m) coincided with west side erosion (90 m) . Net change (1856/57 to 1983) 
was 850 m of east side accretion and 610 m of west side erosion. Inlet throat 
width decreased from 360 m in 1856/57 to 150 m in 1983. 
Cape Fear (Map 32) 

164. Shoreline position changes near Fort Caswell and Bald Head on Cape 
Fear River (Map 31) have been measured by the shoreline mapping procedure 
(Figure 47). Likewise, onshore -offshore changes on both sides of Cape Fear 
have been presented. 

165. Cape Fear was most seaward on the 1878 field survey, but retreated 
north-northwest 1,400 m by 1914. No substantial changes occurred at the cape 
tip between 1914 and 1923, but by 1933/34, it had accreted 300 m to the south- 
east. It retreated due north 240 m by the 1972/75 survey and moved east an 
additional 180 m by 1983. Net change between 1878 and 1983 of the tip of Cape 
Fear has been approximately 1,100 m of north-northwest erosion. Cape area has 
been steadily decreasing, as evidenced in Table 13; however, rate of loss has 
steadily decreased since 1878. 

Table 13 
Subaerial Surface Area Changes at Cape Fear 

Difference in Area Rate of Area Change 
Dates mf m 2 /year 

1878-1914 -3.2 x 10 6 -88,000 

1914-1923 -0.5 x 10 6 -50,000 

1923-1933/34 -0.2 x 10 6 -16,000 

1933/34-1972/75 -0.2 x 10 6 -6,000 

1972/75-1983 -85,000 -8,000 



New Inlet (Map 32) 

166. New Inlet is north of Cape Fear, along a north- south trending 
coastline. In 1878, there were two long, thin islands (1,750 and 4,050 m) 
composing the shoreline just north of a 360-m-long spit extending northerly 
from East Beach on Smith Island. As a result, there were two inlets (60 and 
670 m wide), both south of the 1983 position of New Inlet. By 1914, either 
these two inlets had closed and a new inlet opened farther north, or a new 
inlet had formed from northward migration of the larger inlet and small inlet 



121 



closure. New Inlet in 1914 continued to move north as its south side accreted 
790 m alongshore. The north side eroded 1,150 m between 1914 and 1923 and 
then accreted 600 m from 1923 to 1972/75. From 1972/75 to 1983, 180 m of 
south side erosion accompanied 30 m of north side erosion. Inlet width 
reached its maximum in 1983 at 480 m. Minimum width was measured on the 
1972/75 survey at 240 m. 



122 



PART V: PRESENT AND FUTURE SHORELINE CHANGES 
Analysis of Present Shoreline Positions 

167. The shoreline is defined by the zone of intersection of land, sea, 
and air. Shoreline position at any point in time is a function of complex 
interaction of five principal factors: sea level, sea energy, sediment sup- 
ply, geology, and human involvement. These factors operate over very short to 
very long time scales . Sea level includes daily tides , surges , annual tide 
variations, climate and geologically controlled water-level changes, and other 
naturally produced changes to ocean water levels. Little opportunity was 
available to evaluate sea level effects within the study area beyond what has 
already been discussed in previous sections. Sea energy is manifested in 
waves and currents that reach the shoreline. The WIS data were used to 
examine waves as a factor in controlling shoreline position. Previous 
research described in Part II indicates most sediment for South Carolina's 
beaches comes from exhumed pre-Holocene coastal sediments. No quantifiable 
data exist on sediment supply reaching beaches to allow evaluation of this 
factor as a control on shoreline position. Nearshore shelf bathymetry, depth 
to pre-Holocene semiconsolidated sediments, and antecedent topography are 
geological influences on shoreline position. A brief evaluation of bathymetry 
and depth to pre-Holocene sediment was conducted in the study area. Human 
intervention has affected shoreline position in several locations within the 
study area. At most locations of human intervention, time frames for 
intervention have been short. However, at Charleston Harbor and Winyah Bay, 
humans have had an impact for roughly two -thirds of the time embraced by this 
study. Effects of this intervention on the coastline at Morris Island, South 
Island, and other locations have been described previously in the shoreline 
change data analysis. 

168. To compare large amounts of shoreline data generated in this anal- 
ysis to shoreline orientation, bathymetry, and depth to pre-Holocene material, 
data were summarized for 282 coastal segments defined in the original mapping 
procedure (Figures 22a and b) . A summary of shoreline change for each section 
of each map is included in Appendix A. Since original selection of segments 
was based solely on the straightness of shoreline and not directly on its 
erosion/accretion history, the following results can be considered only 

123 



preliminary. A more rigorous approach, which will define shoreline segments 
based on records of erosion and/or accretion, is planned for future reports by 
the authors. Comparison of wave and erosion/accretion data for each segment 
was additionally complicated since WIS data are summarized only in 16-km-long 
blocks. Therefore, erosion/accretion data had to be further grouped to match 
16-km WIS spacing. 



Waves 



169. Using power spectrum analysis and principal component analysis, 
May (1983) compared WIS data for the North Carolina coast to eight shore zone 
attributes, including shoreline change. For most of North Carolina, there was 
no correlation between wave climate and shore zone rate of change. In a few 
areas, however, low-period, high- amplitude waves correlated with high erosion. 
Wave height 

170. Average net shoreline change was calculated for every 16-km seg- 
ment of coastline defined by WIS. Average shoreline change was compared with 
average wave height, maximum significant wave height, and occurrence of sig- 
nificant wave height greater than 1 and 2 m. Each of these wave height param- 
eters was further compared with maximum shoreline change (the envelope of 
change between the two most divergent shorelines irrespective of their dates) 
for each 16-km section of shoreline. 

171. Average wave height, which ranged between 0.48 and . 74 m along 
the coast, showed no apparent trends when compared with average shoreline 
change. Likewise, average shoreline change versus maximum significant wave 
height (2.6 - 5 . 3 m) and occurrence of significant wave heights greater than 
1 m, showed no apparent relationship. Average shoreline change versus occur- 
rence of significant wave heights (Hs) greater than 2 m does show some trends 
(Figure 54) . Data suggest less erosion and more accretion as occurrence of 
waves greater than 2 m decreases. Generally, in those areas where large waves 
(Hs > 2 m) hit the shoreline relatively often, average rates of erosion are 
expected to be larger. 

172. Maximum shoreline change versus significant wave heights in excess 
of 1 and 2 m showed no apparent organization. Maximum shoreline change versus 
average significant wave height (Figure 55) showed a very weak suggestion of 
increasing shoreline movement with increasing average height; however, there 

124 



AVG. CHANGE VS OCCURANCE OF Hs>2 m 









PER WIS SEGMENT 


























3.3 - 












a 




3.2 - 
















3.1 - 
















3 - 






D 










2.9 - 














□ 


2.8 - 
















2.7 - 






□ 




a 






2.6 - 
















2.5 - 


a 














2.4 - 
2.3 - 




D 


□ 

□ 










2.2 - 

2.1 - 

2 - 

1.9 - 

1.8 - 






D 

D 
D 


□ 
D 

a 
□ 


D 


a 




1.7 - 


a 




□ 










1.6 


i i i 




1 1 


i 




i 


r 



AVG. SHORELINE MOVEMENT (MAR) 

Figure 54. Average net shoreline change versus 

occurrence of significant wave heights greater 

than 2 m 



ENVELOPE OF CHANGE VS AVG. WAVE HEIGHT 



0.74 
0.72 

0.7 
0.68 
0.66 
0.64 
0.62 

0.6 
0.58 
0.56 
0.54 
0.52 

0.5 
0.48 



PER WIS SEGMENT 



□ □ 



200 400 

MAX. SHORELINE MOVEMENT (M) 



Figure 55. Maximum net shoreline change versus average 
significant wave height 



125 



was considerable data scatter at higher average significant wave heights and 
larger shoreline movements. The trend between maximum shoreline change and 
maximum significant wave height is clear (Figure 56) . Shoreline movement 
increases with increasing maximum height. Figure 4 shows that maximum signif- 
icant wave height is greatest along the barrier island and cuspate delta geo- 
morphic zones and least along the arcuate strand. Likewise, spatial 
distribution of erosion is greater in the barrier island and cuspate delta 
zones than in the arcuate strand (Figure 52) . 

173. Figures 54 through 56 suggest that shoreline change along South 
Carolina's coast is dependent on incidence of large waves at the shoreline. 
This in turn suggests that long-term erosional history of the coast may depend 
heavily on storm frequency and magnitude. Data presented by Simpson and Miles 
(1971) suggest a decreasing probability of tropical storm occurrence from 
south to north in the study area. It is difficult to attribute shoreline ero- 
sion or accretion at every segment to presence or absence of large waves since 
other factors influence effectiveness of waves in changing the shoreline. 
Orientation of the coast relative to direction of wave approach, nearshore 
slope, and sediment composition of beach and nearshore are factors that can 
greatly modify effects of waves on shoreline change. 

174. In addition to wave height, wave period (T) was examined relative 
to average and maximum shoreline movements. Occurrence of waves with periods 
greater than 4, 7, 8, and 11 sec were compared with shoreline change data. No 
relationship was apparent between average shoreline change and any wave period 
data. Data points were widely scattered (e.g. Figure 57). Comparisons of 
maximum shoreline movement and wave period do not show any trends except at 
periods greater than 11 sec (Figure 58). Three distinct groups are evident 
related to percentage of time that waves of T > 11 sec occur. Within each 
group, there appears to be no correlation between maximum movement and T > 

11 sec . Examination of the three groups shows a division based on shoreline 
orientation. The four east-west trending WIS segments west of Cape Fear 
receive fewest T > 11 sec waves. These four WIS segments roughly coincided 
with reaches 6 and 7, which have the most stable shorelines (Figure 52). 
Northeast- southwest trending barriers form the middle grouping. The segment 
of coast receiving most T > 11 sec waves is north- south trending zones north 
of Cape Romain and near Tybee Island. This corresponds with reaches 5 and 1 
respectively, which have the largest amount of erosion of all reaches 

126 



ENVELOPE OF CHANGE VS MAX. WAVE HEIGHT 

PER WIS SEGMENT 




200 400 600 

MAX. SHORELINE MOVEMENT. (M) 

Figure 56. Maximum net shoreline change versus maximum 
significant wave height 

AVG. CHANGE VS WAVES WITH T>4 

PER WIS SEGMENT 



81 - 


D 








D 


a 


80 - 














79 - 














78 - 
77 - 


D 

a 






D 






76 - 


a 


D 


□ 








75 - 






a 








74 - 














73 - 


n o 


D 

D 






□ 




72 - 














71 - 














70 - 




□ 










69 - 






□ D 








sa - 














67 - 


D 












66 - 














.. 








n 








1 1 1 I I 








i 





AVG. SHOREUNE MOVEMENT (MAR) 



Figure 57. Typical example of data scatter for average 
shoreline change versus wave period 



127 



MAX. CHANGE VS WAVES WITH T> 1 1 



PER WIS SEGMENT 




200 400 600 

MAX. SHORELINE MOVEMENT (M) 

Figure 58. Maximum net shoreline movement versus occur- 
rence of waves with a period greater than 11 sec 

(Figures 26 and 42). May (1983) noted that 55 to 60 percent of the energy 
supplied to the coast of North Carolina was from swell waves. The data point 
in each group that shows largest shoreline movement is the WIS segment immedi- 
ately south of a Cape. Where T > 11 sec occurrence is low, the WIS segment 
south of Cape Fear has largest shoreline changes. Of the northeast -southwest 
trending shoreline group, the WIS segment just south of Cape Romain has 
largest shoreline changes. In the group of high percent occurrence of T > 
11 sec , Tybee Island (which is capelike in morphology) has most shoreline 
movement. These data do not demonstrate any relationship between wave period 
and maximum shoreline movements, but they do hint that shoreline orientation 
plays an interactive role with waves in affecting erosion/accretion of the 
shoreline. 
Shoreline orientation 

175. Shoreline orientation with respect to predominant average and 
storm wave approach affects wave and current conditions in the littoral zone 
and, thus, may contribute to shoreline changes. To examine this factor, 
orientation of each coastal segment (Figures 22a and b) in the study area was 
determined, and scatter plots of orientation versus average annual and maximum 
shoreline change were prepared. 



128 



176. Figure 59 shows percentage of segments with orientations in speci- 
fied degree categories. Shorelines in 64 percent of the segments are aligned 
in a general northeast- southwest direction between 30 and 90 deg. 

177. Scatter plots showing shoreline orientation versus average annual 
and maximum shoreline change for all segments were completed (Figure 60) . 
These did not show a significant trend that might indicate a direct relation- 
ship between shoreline orientation and shoreline movement. Separate plots 
were made for each of the seven coastal reaches to see if trends occurred in 
certain geomorphic areas. None of the reach plots indicated the existence of 
significant correlation. Figure 61 showing data spread for reach 2 is 
typical. 

178. Absence of trends indicating a relationship between shoreline 
movement and shoreline orientation suggests that orientation to approaching 
waves by itself does not have a substantial effect on shoreline changes. The 
previous section indicated that orientation was a significant factor in recep- 
tion of large period waves; however, no correlation was evident between wave 
period and shoreline change. None the less, the east-west arcuate strand, 
which has fewest T > 11 sec waves, has the most stable coastline, and north- 
south oriented reaches 1, 2, and the segment of reach 7 north of Cape Fear 
have widespread erosion. 

Bathymetry 

179. Nearshore bottom slopes and historical shoreline changes were com- 
pared to determine if there was any correlation. For this purpose, distance 
from the shoreline midpoint of each coastal segment to the 1.8-m, 5.5-m, and 
9.1-m depth contours was measured on 1:80,000 scale NOS hydrographic charts. 
Corresponding slopes were calculated. Average yearly shoreline change and 
maximum shoreline change were compared with slope for each coastal segment. 

180. Scatter plots of nearshore slope angles versus average and maximum 
shoreline changes in each segment were constructed (e.g. Figure 62). In gen- 
eral, the scatter plots show that there is little apparent correlation between 
nearshore slopes and either maximum or average annual shoreline change. To 
further examine the data, scatter plots were made for each of the seven 
reaches. However, there appeared to be little correlation between nearshore 
slopes and shoreline change in any individual reaches. 

181. Figure 63 showing data for reach 6 indicates increasing shoreline 
movement with gentler slopes; however, there are too few data points at 

129 



SUMMARY OF ALL SEGMENTS 



150-180 Degrees (7.6%) 
120-149 Degrees (6.5%) 

90-119 Degrees (9.1%) 



0-29 Degrees (12.7%) 




30-59 Degrees (32.7%) 



60-89 Degrees (31.3%) 



Figure 59. Division of shoreline segments into specified 
orientation categories 

gentler slopes for confirmation. Gentle slopes have greater horizontal dis- 
placement of shoreline per unit vertical change in sea level. 

182. On Figures 62 and 63, it can be noted that although there is no 
apparent linear correlation, a large number of data points are clustered where 
comparatively steep slopes correspond to low values for shoreline change. 
Inspection of shoreline change maps and data for individual reaches indicates 
that the largest number of data points are derived from reaches 6 and 7 , which 
extend from Winyah Bay to Cape Fear. Comparing data from reaches 6 and 7 with 
data from reaches to the south shows significant differences in nearshore 
slopes and shoreline movement between these two areas. 

183. Table 14 shows percentage of coastal segments in each area that 
have nearshore slopes steeper than specified values. This figure shows near- 
shore slopes on-the-whole are steeper in reaches 6 and 7 than in southern 
reaches. Figures 64 and 65 compare cumulative percentage of segments with 
maximum and average annual shoreline movement greater than specified values. 
Both figures indicate in reaches 6 and 7 shoreline movement has, overall, been 
substantially less than in reaches 1 through 5. Figures 66 and 67 compare 
maximum and average annual shoreline movements of segments that have nearshore 

130 



SHORELINE ORIENTATION VS AVERAGE CHANGE 



PER We SECTION, ALL COASTAL SEGMENTS 



190 -r 
180- 
170 - 
160 - 
130 - 
140 - 
130 - 
120- 
110- 
100- 
90- 
80- 
70- 
60- 

ao- 

40- 
30- 
20 - 

10 - 
- 




t r~ 

7 



AVERACE SHORELINE CHANGE (M/TR) 



ENVELOPE OF CHANGE VS ORIENTATION 

ALL COASTAL SEGMENTS 



190- 












180- 


n°n° a ° „ 










170- 


D 




a 






180- 
130- 


rfl ° 

° off 

° a a ° 




a 




a 


140- 


cc a 










130- 


CO no ° 

a q an 


□ 


a ° 






120 H 


□a _ a rf 3 










110 - 


a% n °n 










100 - 


"ff" ° 


a a 








90 -I 


■ftd 


a 

0° 








SOH 

70 - 


-fi n U'ltftJ u a a c 


a 

a a 


a 


c 


80 - 


$BJ^ D D ° DD =<i° = 


a 
_ a 




a 


30 - 


oT," - no aa _ 


□ 






40 - 
30- 
20- 


jBff_ nop a a 


a 


a 


8 
a 

D 


_ □ 


10 - 


no a o „„ D o 


a 
a 




a 


□ 


- 


1 1 1 1 ■? — 


— I— I 


1 — i 


i 


1 ! i 


( 


) 02 OA 


aa 


aa 


i 


1.2 1. 






fThouaonds) 








UAUU4JU SHORELINE CHANGE (U) 







Figure 60. Shoreline orientation versus average and 
maximum net shoreline movement 



131 



SHORELINE ORIENTATION VS AVERAGE CHANGE 







PER IMP SECTION. COASTAL SEGMENT 2 














180- 






a 




170- 
160- 


a 




a 

a 
a 




130- 










140- 
130- 




D 


D 
D D 




120- 




D 






110- 
100- 




«f D 


B 




90- 
80- 
70- 
60- 
30- 
40- 


a 


D 
C 

q n 
n a q „ o 

D 


a o 

off 

a a 


a 


30- 
20- 
10- 


D 


a 


a 
a 

a 






r- i i 


I I i i I I 







AMERACE SHORELINE CHANGE (U/TN) 



ENVELOPE OF CHANGE VS ORIENTATION 

COASTAL SBDUEKT 2 



190- 
180- 












a 


















170- 








a 






















160- 








a 




a 












D 






130- 






























140-1 










□ 




□ 
















130- 














□ 






a 










120- 












□ 


















110^ 














n„ 
















100- 




a 


□ 








D 




a a 












90i 


3 
















a 












80- 
70- 






a 


□ 


a 

D 


a 




a 
















"^j 
























60- 




D 




D 


a 


a 





a 




a 






D 




30 - 




D 




a 




















40- 
















a 




n D 










30- 




















a 










20- 








□ 














D 






a 


10- 


















D 












- 






" 


- 1 — 


i 




i 


i 


i 


i i 


I 


1 


1 





0.7 



OJ 



IMMUUM SHORELINE CHANCE (U) 

Figure 61. Shoreline orientation versus average and maximum 
net shoreline movement in reach 2 



132 



SHORELINE CHANGE VS NEARSHORE SLOPE 

PER MAP SECTION 



3 - 



el 



5*£ 1-3- 



Pi 



*£ 



a u 



|q a 

D 



J 



D 

d a 



□ 



% 



t 1 ! 1 : 1 r 

-7 -5 -3 



nan n 

Hj on □ 

i 1 1 1 1 1 r 




AVERAGE SHOREUNE CHANGE (M/YR) 



MAX. CHANGE VS NEARSHORE SLOPE TO -5.5 







PER MAP 


SECTION. ALL COASTAL SEGMENTS 




3.4 - 
3J - 








D 










3 - 




C D 














2JJ - 










a 








2.8 -i 




□P 


a 












2.4 - 




o 


□ 












2J2 - 




D 














2 - 


D 


Dn o 


D 




a 


□ 


n 




1.8 - 

1.6 - 


D 


dP° 














1.4 - 

1.2 - 

1 - 


D 
D 

1 


DO 

* D 
D 


D 

s 

a 




D 

a 


□ 

D 


D 


D 



OJ - 

cue - 

OA 
0.2 






03. 



—I 1 1 1 1— 

O.S 0.8 

(Thouacrrtd*) 

MAX. SHORELINE CHANGE (M) 



Figure 62. Average and maximum net shoreline change versus 
nearshore slope out to -5.5 m mean low water (MLW) 



133 











PER MAP SECTION. COASTAL SEGMENT 6 




320 - 








D 




300 - 












280 - 








D 




260 - 








□ 


D 


240 - 








D 




220 - 












200 - 






D 






180 - 






D 


D 
D 




160 - 




D 








140 - 
















CD 


D D 












a 




120 - 


D 
□D 






D 




100 - 


a 

m 




D 

a 






80 - 


D D 

DUD 

as 




D 






60 - 


D D 












Da 


LI 


D 






40 - 












20 - 


















1 


1 v i I 


1 



200 400 600 

MAX. SHORELINE CHANGE (M) 

Figure 63. Maximum net shoreline change versus nearshore slope 
out to -5.5 m MLW for reach 6 

Table 14 

Cumulative Percentage of Total Shoreline .Distance with Nearshore Slopes 

to -1.8. -5.5. and -9.1 m MLW Steeper than Designated Values 



Slope 



Reaches 



1 through 5 
6 and 7 



1 through 5 
6 and 7 



1 through 5 
6 and 7 



<1:100 



9.3 
72.7 



0.0 

53.7 



0.0 
0.0 



<1:200 



<1:300 



<1:400 <1:500 <1:600 <1:900 





to 


-1.8 m 


MLW 








58.0 




65.7 


74.8 


76.6 


80.7 




97.3 


to 


98.9 

-5.5 m 


100.0 
MLW 


100.0 


100.0 


100.0 


1.3 




1.3 


2.4 


5.9 


17.0 


60.6 


89.3 


to 


93.9 
-9.1 m 


100.0 
MLW 


100.0 


100.0 


100.0 


0.0 




0.0 


0.0 


0.0 


5.8 


33.2 


11.9 




26.6 


31.6 


48.1 


64.6 


98.2 



134 



100 
90 
80 
70 
60 - 
50 
40 
30 
20 - 
10 - 



[771 REACHES 1 THRU 5 
IV^l REACHES 6 AND 7 






2a 



2SL 



>200 >300 >400 

MAXIMUM SHOREUNE CHANGE (m) 



Figure 64. Cumulative percentage of total shoreline distance versus 
maximum shoreline change greater than specified values 




W\ REACHES 1 THRU 5 
IV\I REACHES 6 AND 7 






>2.0 >3.0 

AVERAGE NET CHANGE (m/yr) 



Figure 65. Cumulative percentage of total shoreline distance versus 
average net shoreline changes greater than specified value 



135 



100 
90- 
80 - 
70- 
60- 
50 

40 4 
30 

20-1 
10 



1 



1771 ROCHES 1 THRU 9 
IV3 ROCHES 8 AMD 7 



% 



%. 



zm 



Li 



1 1 



m 



>2.0 >10 >4.0 

AVERAGE NET CHANGE fm/yr) 



100 
90 
60 
70 

604 
30 

40 -I 
30 

20-| 
10 






^ 



1771 REACHES 1 THRU 5 
[TSJ REACHES 6 AND 7 



1 




CcL 



^ 



2S 



^ Y/y 



>200 >300 >400 

MAXIMUM SHOREUNE CHANGE (m) 



>500 



Figure 66. Cumulative percentage of shoreline distance of segments 
having slopes steeper than 1:300 to -1.8 m MLW versus average and 
maximum net shoreline changes greater than specified values 



136 



100 
90 - 
80 - 
70 - 



60 - 
50 - 

40 
30 
20 

10 



m 



1771 R«och«» 1-5. 5.5 m 
Raoctiaa 6*7. 5.5 m 



fc>^ Raactwa 1-5. 9 



Raochaa 6*7. 9 



n 



/ 
/ 



a. 



E 



a 



>10 



>4.0 



AVERAGE NET SHORELINE CHANGE fm/yr) 




>300 



MOO 



MAXIMUM SHORELINE CHANGE (m) 

Figure 67. Cumulative percentage of shoreline distance of segments 
having slopes steeper than 1:900 to -5.5 and -9 m MLW versus 
average and maximum net changes greater than specified values 



137 



bottom slopes of specified values. Figure 66 compares data for segments with 
nearshore slopes to the 1.8-m depth contour of 1 on 300 or steeper. This fig- 
ure shows that even with comparable steepness values there is substantially 
less shoreline movement in reaches 6 and 7 than in coastal segments farther 
south. Figure 67 compares shoreline movement for segments having nearshore 
slopes to 5.5- and 9.1-m depth contours of 1 on 900 or steeper. A consider- 
able difference is evident in shoreline movement between the two areas compar- 
able to data in Figure 66. 

184. Figures 68 and 69 demonstrate graphically the contrast between 
reaches 6 and 7 and other reaches by means of scatter diagrams having a common 
scale. These diagrams clearly show consistent grouping of data points in 
reaches 6 and 7 contrasted to wide scatter of data points for reaches 1 
through 5. Reasons for these differences are not apparent. Differences in 
wave climate, geology, sediment supply, orientation, coastal morphology, and 
the fewer number of inlets in reaches 6 and 7 may have a combined influence 
with nearshore slopes on shoreline stability. 

Geology 

185. The study area is located along the seaward margin of the Atlantic 
Coastal Plain Province. Both emerged and submerged portions of the coastal 
plain are topographically subdued and have a gentle seaward slope. Surficial 
lower coastal plain deposits consist of a fringe of Holocene beach and back- 
barrier sediments backed by a broad zone of Pleistocene sediments. These give 
way inland to outcrops of Cretaceous and Tertiary formations. A complete geo- 
logic description of the area is presented in Part II. 

186. Core data from the inner continental shelf between Cape Fear and 
Cape Romain show that in many places older deposits either outcrop or lie 
close beneath the shelf surface (Meisburger 1979, Frankenburg 1987, unpub- 
lished CERC data) . Figure 70 shows positions of cores containing ancient 
deposits and downhole depth to pre-Holocene deposits. Except for Eocene age 
biogenic carbonate sediments near Cape Fear, these deposits are of Cretaceous 
and Paleocene age . 

187. Shallow depth of these formations on the shelf suggests they may 
lie close beneath the shoreface and beach in some areas, particularly along 
the predominantly mainland arcuate strand shoreline between New River Inlet 
and Cape Fear. Shoreface cores from the immediate vicinity of Myrtle Beach, 
South Carolina, encountered hard substrate at shallow depth (Frankenburg 

138 



COASTAL REACHES 1 - 5 






□ n n 



a n 

D 



a a 
□ 



n a n 



—I ! 1 1 1 1 1 r - 

9 -7 -5 -3 -1 




AVG. SHORELINE MOVEMENT (MA") 



l~ 



*€ 





COASTAL REACHES 6 ft 7 


3 - 






2.3 - 






a- 






1.3 - 






1 - 




5 
□ 


0.5 - 






- 


«£ 

i i i i i i i i 


n □ n a 

1 T 1 1 1 1 i 



-9 -7-5-3-1 1 3 5 7 

AVG. SHORELINE MOVEMENT (MAR) 

Figure 68. Average net shoreline change versus nearshore slope 
to -5.5 m MLW for reaches 1 through 5 and 6 and 7 



139 



MAX. CHANGE VS NEARSHORE SLOPE -5.5 



i~ 



*e 







COASTAL REACHES 


1 - 5 










a 










3 - 


D° 












2.5 - 


a 


Q 

D 


a 








2 - 


D 
DO 

a a 


D 


D 


D 


D 




1 J - 
1 - 

0.5 - 


D tP 

a 

d d n ? 


D 
8 

a 


a 

D 



a* 
a 


a 

D 
D 

a 


a 

D 

D 


a 

a 

D 




D 

D CD 


D° 




D D 








1 1 1 1 


i 


i i 


I I 


I l 


I 1 



0.2 0.4 0.B 0.0 1 1.2 

(Thousands) 
MAX SHORELINE MOVEMENT (M) 



*£ 





COASTAL REACHES 6*7 


3 - 




2J - 




2 - 




1.5 - 




1 - 


D 


0.5 - 




- 


CD B Dp ° n 


i i i i i i i i i r— i i i 1 



0.2 0.4 0^ 0.8 1 1.2 1.4 

(Thousands) 
MAX. SHORELINE MOVEMENT (M) 

Figure 69. Maximum net shoreline change versus nearshore slope 
to -5.5 m MLW for reaches 1 through 5 and 6 and 7 



140 



NORTH CAROLINA 
Long Beach 



SOUTH CAROLINA 




ATLANTIC OCEAN 



Figure 70. Map showing locations of inner continental shelf cores 

containing pre-Holocene sediment. Numbers indicate downhole depth 

in metres to the pre-Holocene contact 

1987) ; rock fragments up to cobble size were observed on Myrtle Beach and 
other arcuate strand beaches during visits by one of the authors in 1981 and 
1985. 

188. Presence of pre-Holocene material near the surface of the arcuate 
strand geomorphic zone may be partially responsible for its relative stability 
over the long term. Semiconsolidated sands and clays would be more resistant 
to erosion than loosely consolidated sands. FitzGerald, Hubbard, and Nummedal 
(1978) noted that many South Carolina inlets that were not migrating rapidly 
through time were apparently anchored in pre-Holocene sediments. Inner shelf 
cores are not available for South Carolina south of Cape Romain. Depth to 
pre-Holocene sediments along the cuspate delta or barrier island geomorphic 
zones is unknown, but based on coring data in the literature (e.g. Barwis 
1976, Hubbard and Barwis 1976), it appears deeper than in the arcuate strand 
zone . 

Inlets 

189. Previous sections of this report have discussed the role of inlets 
in affecting shoreline change. This fact was noted by numerous authors (e.g. 



141 



Hubbard et al . 1977, Fitzgerald and Hayes 1980) for various subreaches of the 
South Carolina coast. This data set, which includes the entire coast, empha- 
sizes the role of inlets in controlling shoreline change history. Average 
shoreline change is consistently most variable, and maximum shoreline change 
is greatest in the vicinity of inlets. It is not implied that every inlet- 
adjacent shoreline is highly variable, but a majority do influence shoreline 
position for several kilometres up and down drift. 

Future Shoreline Changes 

190. If an old geologic axiom is reworded slightly to "the present is 
the key to the future," results of this study can be carefully applied to pre- 
dict future shoreline changes between Tybee Island, Georgia, and Cape Fear, 
North Carolina. This assumes that factors which have controlled past shore- 
line erosion/accretion will operate in the same way with the same magnitude in 
the future. Rates of change given in Appendix A and within various figures 
and tables throughout this report can be applied to near future estimation of 
shoreline change. However, accuracy of predictions decreases with increasing 
projection into the future and/or projection into shoreline areas that have 
been historically variable. Sea level, sea energy, geology, sediment supply, 
and human intervention are the variables that control present and future 
shoreline positions. This report indicates storm waves are important in 
affecting the shoreline; however, prediction of number and frequency of future 
storms is impossible. Bathymetry and shoreline orientation have some effect 
on erosion/accretion also, but through time, these are constantly being modi- 
fied by waves and currents. Sea level is another important factor determining 
future shoreline change rates. Over the last 20 million years, sea level has 
been episodically dropping along South Carolina. Over the last 15,000 years, 
sea level has risen. Rate of rise has decreased perceptibly over the last 
4,000 years, although modern tide gages still detect an overall trend of ris- 
ing sea level. Predictions for the future (Gorman, in preparation) include 
rapid increases in sea level as the result of climatic warming from human 
intervention. 

191. Unpredictability of these and other long-term factors coupled with 
variability of short-term factors such as inlets means prediction of future 
shoreline change cannot be very accurate with increasing temporal spacing from 

142 



present. Some observations of present characteristics of the study area, how- 
ever, can be made to allow estimates of future shoreline position. 

192. The arcuate strand, which has slowest erosion/accretion rates, 
will probably remain the least variable geomorphic zone in the near future. 
Its sheltered orientation to storm waves, the presence of pre-Holocene semi- 
consolidated sediments near the surface, and general lack of inlets will all 
combine to keep this coastline relatively stable. Sea level rise, if acceler- 
ated in the future, could have a dramatic effect since elevation of this 
shoreline is low. 

193. The cuspate delta shoreline can be expected to continue as an 
erosional area into the future. Erosion results from loss of sediment from 
damming and diversion plus its nearly north- south orientation, which makes it 
susceptible to storm waves. An additional factor is the considerable amounts 
of fine sediments that compose the marshes behind cuspate delta barrier 
beaches. As beaches transgress over marshes, the finer sediments will be eas- 
ily removed, thus accelerating rates of erosion. 

194. Bull Bay and other large bays will continue to show only mild 
erosion/accretion. Their natural protection from storm and wave attack means 
the most influential factors are sediment supply and sea level changes. 
Changes in these two factors are generally slow, so the immediate future of 
Bull Bay and other large bays is not likely to be different from its recent 
history. 

195. Shoreline movement in the barrier island geomorphic zone is vari- 
able spatially and temporally. Frequent inlets, human interference, open ori- 
entation to wave attack, and variable nearshore bathymetry all contribute to 
shoreline position variability in this reach. Bathymetry and orientation are 
not likely to change significantly in the near future. Disequilibrium created 
by human intervention will slowly readjust to a new equilibrium if no further 
harmful intervention occurs. Therefore, areas of high erosion south of 
Charleston and accretion to the north will gradually abate. Areas immediately 
adjacent to most South Carolina inlets, however, may be subject to rapid 
changes at any time. Radical changes at inlets and adjacent shorelines can 
occur over very short periods, making change prediction difficult. The 
remaining barrier island geomorphic zone will continue into the near future as 
it is presently, stable to slightly eroding near midsections of barriers with 
increasing variability toward inlets. 

143 



196. If the South Carolina coastline is examined through time specify- 
ing that any landward movement, no matter how small, is erosion and any sea- 
ward movement is accretion, then shoreline trends are toward erosion. However, 
temporal division of data shows no one shoreline segment has eroded signifi- 
cantly faster than adjacent segments given a sufficient length of time. Ero- 
sion and accretion appear to dynamically alternate spatially and temporally 
with the present net effect of shoreline erosion. Specific locations, such as 
northern Kiawah Island, have been accreting steadily, and other areas have 
been eroding steadily over the 130 years of survey data; but overall there 
appears to be a dynamic balance favoring erosion. In the distant future, as 
sea level rise changes or climatic changes affect storm properties, the 
dynamic balance may swing toward more erosion or accretion. 



144 



PART VI: SUMMARY AND CONCLUSIONS 

198. This is the third and final report in a series of shoreline change 
studies undertaken cooperatively between NOS and CERC. Additional funding for 
map production was provided by the Division of Research and Statistical 
Services of the State of South Carolina. All survey data reduction, quality 
control, and publication of shoreline change maps were performed by NOS; data 
analysis and preparation of this report were completed by CERC. The study 
area comprises the northern coast of Tybee Island, Georgia, the entire 
coastline of South Carolina, and the contiguous coastline of North Carolina to 
Cape Fear (Figure 1) . Changes in ocean shoreline position were evaluated from 
1851 to 1983 using survey data from NOS. 

199. Shoreline change maps, Tybee Island, Georgia, to Cape Fear, North 
Carolina, are included as a separate enclosure to this report. Thirty- two 

1 : 24,000-scale USGS quadrangles were selected as base maps for this project. 
They were revised with 1: 24,000-scale color aerial photography taken in 
1982/83. Historical data obtained from NOS topographic surveys were compiled, 
rectified, and transferred to the base maps. The final composite shoreline 
position maps were used by CERC to evaluate shoreline changes within the study 
area. 

200. Using a digitizing procedure, average and maximum net shoreline 
change was quantified every 50 m along the open coast. Shoreline change rates 
are presented in graphical form at 50 -m intervals and have been summarized in 
tabular and graphical format for various along-the-coast intervals. Shoreline 
change data were compared with various environmental factors to evaluate 
causes for observed changes and to predict shoreline change rates for future 
years. The following characteristics of shoreline change within the study 
area can be concluded from this study: 

a. During every time interval examined, spatial distribution of 
shoreline change varied greatly. Mainland beaches of the 
arcuate strand geomorphic zone were least variable and had 
lowest shoreline change rates. Barrier island beaches were 
most variable spatially and had highest change rates. 

b. Spatial variability in shoreline change rates was influenced 
most by proximity to inlets. Shoreline change rates were 
largest and most variable immediately adjacent to inlets and 
decreased with distance from any inlet. Coastline centrally 
located between inlets had least variability and lowest 



145 



shoreline change rates. The arcuate strand has relatively few 
inlets . 

Dramatic alongshore changes in the shoreline occurred in the 
vicinity of inlets. Inlet formation and migration and changes 
in inlet ebb- tidal delta morphology not only affect cross- 
shore position of the shoreline, but also control growth and 
decay of spits and barriers in an alongshore direction. 
Changes in inlet width of over 1,000 m and aerial changes on 
the order of 110,000 m 2 /year to adjacent spits were observed. 
Temporal examination of alongshore changes at inlets suggests 
they result from continuous changes in inlet and ebb delta 
morphology driven by changes in environmental factors such as 
reversals in drift direction. 

Shoreline change rates have varied greatly from one period to 
another. Some segments of shoreline are temporally consistent 
in change direction, but most alternate between periods of 
erosion and accretion. Through 130 years of survey data, net 
change has been in favor of erosion. Temporal variations and 
difficulties encountered in trying to account for them prevent 
accurate quantitative forecasts of shoreline change decades 
into the future . 

The east-west oriented arcuate strand geomorphic zone, extend- 
ing from North Inlet to Cape Fear River, is the most stable 
shoreline examined. Approximately 87 percent of this shore- 
line has changed ±1 m/year or less over the duration of survey 
data. The remaining shoreline is divided equally between ero- 
sion and accretion in excess of ±1 m/year. 

Bull Bay, which is protected in several ways from a full range 
of wave conditions experienced by the rest of the coast, has a 
stable shoreline. Approximately 82 percent of Bull Bay has 
changed ±1 m/year or less over the duration of survey data. 
The most sheltered segments of shoreline (4 percent) have 
accreted more than 1 m/year, and shoreline open to waves from 
the northeast (14 percent) has been eroding in excess of 
1 m/year. 

Segments of shoreline predominantly showing erosion (more than 
50 percent of shoreline is eroding greater than 1 m/year) were 
the barrier island shoreline between Tybee Island and 
St. Helena Sound, the cuspate delta geomorphic zone centered 
around the Santee River delta, and north of Cape Fear. 
Although no correlation was evident between shoreline orienta- 
tion and shoreline change, these three reaches are the most 
north- south oriented reaches in the study area. Examination 
of wave data suggested north- south shoreline segments received 
highest percentages of swell waves. 

The only segment of shoreline in which accretion (greater than 
1 m/year) dominated was between Charleston Harbor and Bull 
Bay. Approximately 45 percent of this shoreline was accret- 
ing, while 30 percent was eroding and 25 percent changed 
±1 m/year or less. The dominance of accretion in this area is 



146 



due in large measure to trapping of alongshore drift north of 
the Charleston Harbor jetties. 

Human impact has resulted in rapid erosion along Morris 
Island, south of the Charleston Harbor jetties, and contrib- 
uted to wide distribution of erosion in the cuspate delta 
region. The Santee River had the fourth largest discharge of 
east coast rivers prior to damming and diversion in 1942. 
Loss of sediment supply to the coast has contributed to high 
erosion rates in this area. 

Summarizing shoreline change for the entire study area coast- 
line shows approximately 51 percent has been stable with 
±1 m/year or less change, approximately 31 percent has eroded 
faster than 1 m/year, and 18 percent has accreted faster than 
1 m/year over the 130 -year span of survey data. 

Maximum significant wave height correlates well with maximum 
net shoreline change. Maximum change occurs where maximum 
significant wave heights are greatest. Maximum significant 
wave heights are lowest along the arcuate strand and highest 
near Tybee Island, Charleston, and Cape Romain. 

Nearshore slopes were compared with shoreline changes, but no 
direct correlations were evident. However, even where near- 
shore slopes had similar steepness, shoreline changes in the 
arcuate strand were consistently lowest, suggesting factors 
other than bathymetry were controlling shoreline movements. 

Coastal stability in the arcuate strand geomorphic zone 
appears related in part to geology. Throughout this area, 
pre-Holocene semiconsolidated materials lie at or close to 
beach and nearshore surfaces. The proximity of these sedi- 
ments to the surface and their increased resistance to erosion 
may contribute to the reduced potential for erosion. Stable 
inlets along this coast have been found by others to be 
anchored in pre-Holocene sediments. 



147 



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152 



APPENDIX A: SUMMARY OF SHORELINE CHANGE DATA PER SEGMENT 



Column Legend 

MAP = number identifying one map within the. enclosed set of National 
Ocean Service (NOS) maps. Refer to Figure 18. 

SEGMENT = number identifying a small stretch of coastline within a 
particular map. Segment numbers are listed on Figure 22. 

A T MOVE = average total (net) movement; within each segment of each 
map, data were collected along shore -perpendicular transects located 50 m 
apart along the coastline. Total net shoreline movement for each transect was 
used to calculate the average total (net) movement for the segment. Units = 
metres, "-" = erosion. 

M T MOVE = maximum total (net) movement; within each segment of each 
map, data were collected along shore -perpendicular transects located 50 m 
apart along the coastline. Net shoreline change at the transect with maximum 
movement within the segment is listed in this column. Units = metres, "-" = 
erosion. 

A SH CHG = average shoreline change; the average total (net) movement 
for all transects within a segment, divided by the number of years between the 
first and last shoreline data set. Units = metres/year, "-" = erosion. 

M STD DEV = maximum standard deviation; standard deviation of shoreline 
change for the transect within a segment showing maximum variability in 
shoreline position over the measured interval of time. Units are in ± metres 
around the average shoreline change of that transect. These data are intended 
to give the reader a rough indication of just how variable the long-term 
shoreline change can be within a given segment of coastline. 

NUMBER OF TRANSECTS ERODING . STABLE . AND ACCRETING = within each segment 
of each map, shoreline change data were collected along shore -perpendicular 
transects located 50 m apart along the coastline. Within a segment, the 
number of transects eroding (>1 m/year landward movement) , accreting (>1 
m/year seaward movement), and/or stable (<1 m/year movement) were totaled. 
These data can be used to calculate the percentage of each segment within each 
of the three shoreline change categories. 

REACH = the entire study coastline was divided into seven zones 
(reaches) of similar geomorphic characteristics. Refer to Figure 21. 



Al 



MAP SEGMENT A T MOVE M T MOVE A SH CHG M STD DEV 



NUMBER OF TRANSECTS 
ERODE STABLE ACCRETE 



REACH 1 



1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

1 

1 

2 

3 

4 

5 



9 

10 

11 

12 

13 

14 

1 

2 

3 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 



76.8 

■274.5 

■277.6 

-70.6 

373.1 

-67.8 

85.7 

209.1 

-160.1 

-332.6 

-211.8 

-260.4 

-301.8 

-211.7 

-58 

627 

371 

183 

-115 

32 

122 

-21.9 

-147.6 

-224.9 

-282.7 

-184.5 

-1.3 

36.8 

46.8 

57.0 

21.2 

-36.7 

-166.7 

-256.4 

-222.9 

-136.8 

2.7 

-67.2 

-11.7 

136.0 

52.0 

11.3 

-221.9 

-672.4 

-697.3 

-532.5 

-261.9 

-423.1 



129. 
-497. 
-363. 
-139. 

991. 

-85. 

472. 

420. 
-364. 
-359. 
-247. 
-298. 
-314. 
-286. 
-134. 

856. 

432. 

262. 

-180. 

67. 

148. 
-111. 
-214. 
-248. 
-313. 
-290. 

-78. 
55. 
56. 
73. 
45. 

-91. 
-246. 
-337. 
-396. 
-282. 
29. 
-151. 

206. 

200. 
70. 
-172. 
-374. 
-970. 
-792. 
-606. 
-339. 
-444. 



0.69 
•2.47 
■2.83 
-0.68 



18 
35 
32 
68 
32 
70 
72 
18 
45 



■1.77 

■0.47 

5.32 

3.02 

1.49 

-0.94 

0.26 

1.00 

-0.18 

-1.20 

-1.83 

-2.30 

-1.52 

-0.01 

0.30 

0.38 

0.46 

0.17 

-0.30 

-1.35 

-2.09 

-1.80 

-1.11 

0.02 

-0.55 

-0.02 

1.13 

0.42 

0.09 



80 
60 
76 
33 

13 
46 



4.21 





3.57 


17 


2.76 


10 


9.47 


6 


11.67 


3 


2.49 


5 


2.59 


2 


4.29 





3.00 


41 


1.73 


5 


1.98 


39 


1.74 


17 


2.43 


13 


1.18 


22 


1.38 


2 


32.80 





19.24 





8.53 





4.30 


24 


2.12 





5.07 





1.68 





1.53 


18 


1.58 


21 


1.69 


60 


4.03 


32 


1.68 





1.71 





1.91 





1.07 





1.72 





2.89 





3.66 


25 


3.03 


24 


2.31 


64 


2.20 


5 


1.50 





7.05 


3 


6.89 


5 


6.88 





7.89 





14.48 


4 


11.86 


26 


8.19 


14 


5.32 


36 


4.58 


6 


2.73 


7 


2.46 


15 



16 

6 



6 





3 

4 

26 











14 





3 

23 

22 

32 

29 

3 





6 

32 

8 

6 

5 

5 

33 

8 

1 



4 

12 

7 

6 

7 

11 

37 

8 

2 





1 





5 




22 


11 
8 








16 

16 

11 



38 

















4 

12 











A2 



NUMBER OF TRANSECTS 



AP 


SEGMENT 


A T MOVE 


M T MOVE 


A SH CHG 


M STD DEV 


ERODE 


STABLE 


ACCRETE 


6 


1 


-396.7 


-428. 


-3.20 


2.44 


39 








6 


2 


-258.9 


-318. 


-2.11 


1.83 


16 


1 





6 


3 


-248.5 


-320. 


-2.04 


3.40 


11 








6 


4 


-6.7 


274. 


-0.05 


4.17 


10 


24 


9 


6 


5 


216.9 


345. 


1.75 


9.73 





9 


31 


6 


6 


322.5 


566. 


2.60 


11.13 








10 


6 


7 


-298.3 


-501. 


-2.41 


6.32 


95 








6 


8 


-731.6 


-1018. 


-5.91 


3.19 


31 








6 


9 


851.2 


1343. 


6.90 


11.58 








13 



10 



■23.0 
-11.8 



-30. 
-34. 



■0.36 
■0.53 



1.70 
2.60 



REACH 2 



8 

9 

9 

9 

9 

9 

9 

9 

9 

9 

10 

10 

10 

10 

10 

10 

11 



2 
3 
4 
5 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
1 
2 
3 
4 
5 
6 
7 
8 
9 
1 
2 
3 
4 
5 
6 
1 



137.8 

256.0 

384.7 

393.7 

-10.8 

112.3 

365.3 

381.4 

243.9 

-128.3 

-103.0 

95.5 

461.8 

203.8 

189.7 

377.5 

402. 

419. 

388, 

-49, 

-248. 

-446.6 

-661.5 



•1023. 

-791. 

-498. 
306, 
549, 
667 
117, 

-161. 

-122.0 

31.1 

239.0 

234.4 

360.8 



232. 

442. 

423. 

419. 

408. 

403. 

389. 

481. 

316. 
-145. 
-108. 

448. 

655. 

309. 

433. 

415. 

486. 

431. 

409. 

376. 
-286. 
-553. 
-886. 
-1254. 
-925. 
-693. 

750. 

704. 

918. 

392. 
-203. 
-187. 

120. 

315. 

257, 

615, 



0.67 

2.32 

3.03 

3.10 

■0.08 

0.86 

2.79 

2.99 

1.86 

-0.98 

-0.79 

0.73 

3.53 

1.85 

1.45 

2.88 

3.07 

3.20 

2.97 

-0.38 

-1.95 

-3.41 

-5.05 

-8.15 



04 
81 
34 



4.20 
5.10 
0.91 
-1.25 
-0.94 
0.24 
1.85 
1.82 
2.79 



2.73 


1 


4.17 





3.54 





3.30 





3.84 


12 


6.65 


2 


6.93 





8.98 





8.31 





3.17 


3 


2.89 





6.11 





9.93 





1.83 





2.79 





4.83 





5.28 





4.87 





4.46 





2.98 


29 


2.41 


14 


3.17 


49 


7.82 


66 


.0.10 


22 


8.78 


10 


6.34 


6 


4.82 





5.69 





6.82 





6.03 





2.78 


39 


2.69 


23 


3.31 





3.99 





3.20 





9.24 








1 



6 
4 



4 
3 
11 


7 




73 






5 


34 
10 
29 
36 
1 

4 



5 

6 

6 

10 

9 

5 

3 

7 

8 





6 

31 

6 

21 

4 

7 

3 

6 

13 













10 

17 

26 

31 







42 

12 

34 



A3 



NUMBER OF TRANSECTS 



MAP 


SEGMENT 


A T MOVE 


M T MOVE 


A SH CHG 


M STD DEV 


ERODE 


STABLE 


ACCRETE 


11 


2 


-1014.3 


-1148. 


-8.01 


7.96 


7 








11 


3 


-545.7 


-598. 


-4.20 


4.80 


6 








11 


4 


-314.4 


-441. 


-2.42 


3.74 


50 








11 


5 


-99.5 


-229. 


-0.77 


1.73 


11 


60 





11 


6 


-119.4 


-136. 


-0.92 


2.57 


6 


12 





11 


7 


-38.1 


-99. 


-0.30 


4.25 





15 





13 


1 


47.1 


84. 


0.38 


9.21 





32 





13 


2 


44.3 


69. 


0.35 


9.43 





4 





13 


3 


-182.5 


-243. 


-1.46 


4.39 


3 


1 





13 


4 


-835.1 


-1231. 


-6.74 


15.06 


91 








13 


5 


-161.2 


-216. 


-1.30 


14.38 


10 


3 





13 


6 
REACH 3 


-27.1 


-82. 


-0.22 


9.15 





7 





13 


6 


-27.1 


-82. 


-0.22 


9.15 





7 





13 


7 


226.6 


367. 


3.65 


5.07 





2 


15 


13 


8 


293.3 


339. 


4.73 


1.52 








6 


13 


9 


172.6 


242. 


2.79 


1.95 





1 


12 


13 


10 


70.1 


90. 


1.13 


3.34 





4 


16 


13 


11 


114.9 


186. 


1.85 


3.20 





4 


25 


13 


12 


90.0 


159. 


0.95 


1.92 





4 


2 


13 


13 


-9.7 


-141. 


-0.09 


1.79 


2 


11 





13 


14 


288.7 


301. 


2.67 


1.53 








3 


13 


15 


267.3 


301. 


2.90 


3.52 








7 


13 


16 


144.9 


238. 


1.55 


1.33 





1 


65 


14 


1 


178.2 


214. 


1.67 


2.31 








27 


14 


2 


130.6 


159. 


1.21 


2.31 





4 


25 


14 


3 


17.6 


-65. 


0.16 


3.91 





27 





14 


4 


73.9 


140. 


0.68 


4.33 





5 


3 


14 


5 


92.8 


132. 


0.86 


6.94 





26 


3 


14 


6 


69.8 


95. 


0.65 


5.44 





4 





14 


7 


5.5 


29. 


0.05 


3.77 





4 





14 


8 


-27.4 


-80. 


-0.25 


2.16 





8 





14 


9 


-417.2 


-932. 


-3.29 


8.95 


34 


3 


10 


14 


10 


-675.4 


-709. 


-5.32 


8.01 


5 








14 


11 


-506.1 


-843. 


-4.06 


15.53 


79 


3 


5 


15 


1 


297.3 


416. 


2.75 


12.07 








48 


15 


2 


100.9 


192. 


0.93 


3.36 





25 


20 


15 


3 


-114.7 


-206. 


-1.06 


2.85 


24 


23 





15 


4 


-188.3 


-249. 


-1.82 


2.62 


6 


1 





15 


5 


-273.4 


-369. 


-2.78 


2.13 


7 








15 


6 


-730.8 


-869. 


-6.77 


3.14 


41 









REACH 4 



15 


7 


-44.9 


-113. 


-0.41 


2.03 


1 


6 





15 


8 


18.0 


28. 


0.17 


2.27 





4 





15 


9 


32.7 


56. 


0.30 


0.62 





3 





15 


10 


-28.5 


-62. 


-0.26 


1.43 





15 






A4 



NUMBER OF TRANSECTS 



MAP 


SEGMENT 


A T MOVE 


M T MOVE 


A SH CHG 


M STD DEV 


ERODE 


STABLE 


ACCRETE 


15 


11 


15.9 


49. 


0.15 


1.06 





8 





15 


12 


-13.8 


-33. 


-0.13 


0.77 





4 





15 


13 


-31.7 


-44. 


-0.29 


1.21 





10 





15 


14 


-18.7 


-34. 


-0.17 


0.90 





3 





15 


15 


-93.1 


-151. 


-0.86 


1.18 


9 


19 





15 


16 


-196.1 


-323. 


-1.94 


1.99 


7 








15 


17 


-202.7 


-289. 


-1.96 


1.59 


24 








15 


18 


-126.5 


-210. 


-1.49 


1.76 


3 


1 





15 


19 


-76.8 


-122. 


-0.75 


2.15 


2 


3 





15 


20 


-126.7 


-219. 


-1.17 


1.87 


15 


7 





15 


21 


-55.2 


-112. 


-0.52 


2.58 


3 


7 





15 


22 


-9.0 


-54. 


-0.08 


0.83 





15 





15 


23 


-62.0 


-84. 


-0.62 


0.81 





9 





16 


1 


-5.0 


68. 


-0.04 


3.08 





27 





16 


2 


-6.1 


50. 


-0.06 


1.52 





21 





16 


3 


-2.4 


-15. 


-0.02 


0.99 





7 





16 


4 


3.5 


15. 


0.04 


0.95 





4 





16 


5 


-30.2 


-60. 


-0.28 


1.15 





20 





16 


6 


-20.3 


-70. 


-0.19 


1.34 





12 





16 


7 


-22.6 


-29. 


-0.21 


2.33 





5 





16 


8 


-24.6 


-62. 


-0.23 


1.77 





18 





16 


9 


-15.8 


-55. 


-0.15 


1.43 





5 





16 


10 


2.9 


-67. 


0.03 


2.16 





16 





16 


11 


-32.7 


-47. 


-0.30 


1.67 





12 





16 


12 


-17.3 


-36. 


-0.16 


1.22 





6 





16 


13 


-5.8 


-32. 


-0.05 


1.20 





15 





16 


14 


-8.0 


-15. 


-0.11 


0.66 





3 





16 


15 


-0.5 


54. 


-0.06 


1.59 





6 





16 


16 


-34.5 


-77. 


-0.32 


1.97 





10 





16 


17 


-13.6 


-24. 


-0.13 


1.04 





7 





16 


18 


-2.1 


29. 


-0.02 


1.34 





9 





16 


19 


9.4 


35. 


0.10 


1.38 





11 





16 


20 


-8.5 


-28. 


-0.08 


0.92 





4 





16 


21 


35.0 


46. 


0.32 


0.66 





3 





16 


22 


34.4 


66. 


0.32 


1.04 





8 





16 


23 


46.2 


72. 


0.43 


1.03 





6 





16 


24 


9.6 


38. 


0.09 


2.08 





7 





16 


25 


91.7 


224. 


0.84 


3.12 





19 


16 


16 


26 


88.2 


130. 


0.81 


0.75 





4 


2 



REACH 5 



16 


27 


-944.8 


-1237. 


-8.67 


8.00 


9 








17 


1 


-748.0 


-822. 


-6.96 


2.79 


96 








17 


2 


-644.4 


-789. 


-5.99 


5.32 


56 








18 


1 


-597.1 


-1318. 


-5.50 


6.20 


82 


4 





18 


2 


-213.0 


-293. 


-3.68 


2.99 


20 


1 





18 


3 


511.0 


685. 


4.69 


5.93 








21 


18 


4 


566.8 


652. 


5.20 


6.70 








11 


18 


5 


625.6 


849. 


5.74 


8.45 








19 



A5 



MAP 



SEGMENT A T MOVE M T MOVE A SH CHG M STD DEV 



NUMBER OF TRANSECTS 
ERODE STABLE ACCRETE 



18 
18 



794.3 
747.2 



822. 
834. 



7.29 
6.86 



10.56 
8.99 



16 
23 



18 


8 


-122.7 


-764. 


-1.13 


10.90 


31 


10 


18 


18 


9 


-29.6 


-188. 


-0.28 


4.02 


8 


10 


3 


18 


10 


-126.1 


-170. 


-1.17 


5.07 


20 


9 





20 


1 


-93.6 


-155. 


-3.16 


7.69 


4 


3 





20 


2 


-102.6 


-186. 


-0.92 


7.21 


10 


16 





20 


3 


580.1 


864. 


5.41 


35.43 








73 


20 


4 


92.5 


135. 


0.74 


2.06 





30 


2 


20 


5 


74.0 


87. 


0.59 


1.87 





17 





20 


6 


38.0 


75. 


0.30 


1.40 





21 





21 


1 


-9.2 


-24. 


-0.07 


1.32 





12 





21 


2 
REACH 6 


-254.5 


-526. 


-2.11 


3.76 


84 


32 





21 


3 


-65.8 


-294. 


-0.78 


6.44 


1 


12 





21 


4 


91.3 


172. 


0.82 


5.02 





14 


13 


21 


5 


121.1 


156. 


1.09 


1.86 





5 


9 


22 


1 


41.5 


77. 


0.49 


3.75 





34 


9 


22 


2 


2.6 


54. 


0.02 


1.46 





80 





22 


3 


-25.6 


-43. 


-0.23 


2.80 





23 





22 


4 


-38.8 


-60. 


-0.35 


0.63 





22 





22 


5 


-55.1 


-69. 


-0.50 


0.62 





29 





22 


6 


-45.8 


-60. 


-0.41 


1.62 





30 





22 


7 


22.3 


48. 


0.20 


1.65 





23 





23 


1 


54.9 


62. 


0.49 


3.35 





10 





23 


2 


69.5 


92. 


0.62 


4.00 





11 





23 


3 


111.2 


134. 


1.01 


6.29 





10 


13 


23 


4 


-45.7 


-188. 


-0.41 


8.15 


5 


10 


1 


23 


5 


251.7 


512. 


2.25 


13.92 





4 


21 


23 


6 


-14.6 


-75. 


-0.13 


7.69 





24 





23 


7 


-106.9 


-134. 


-0.97 


2.89 


13 


11 





23 


8 


-76.9 


-127. 


-0.69 


1.58 


8 


37 





23 


9 


-4.1 


-26. 


-0.04 


0.92 





65 





23 


10 


10.8 


27. 


0.10 


1.20 





77 





24 


1 


3.1 


16. 


0.02 


1.16 





26 





24 


2 


19.5 


38. 


0.18 


1.09 





31 





24 


3 


14.7 


33. 


0.14 


1.27 





43 





24 


4 


-7.7 


-28. 


-0.07 


1.32 





31 





24 


5 


-23.6 


-43. 


-0.22 


0.88 





37 





24 


6 


-14.7 


-28. 


-0.13 


0.88 





15 





24 


7 


-36.1 


-53. 


-0.33 


2.10 





33 





25 


1 


-14.4 


-35. 


-0.13 


2.38 





46 





25 


2 


-11.0 


-38. 


-0.10 


1.82 





88 





25 


3 


-14.7 


-40. 


-0.13 


1.68 





67 





25 


4 


-24.4 


-54. 


-0.22 


2.10 





45 





25 


5 


-25.9 


-46. 


-0.24 


1.07 





25 





25 


6 


-7.9 


-23. 


-0.07 


1.28 





32 





26 


1 


-4.6 


50. 


-0.04 


2.97 





54 






A6 



MAP 



SEGMENT A T MOVE M T MOVE A SH CHG M STD DEV 



NUMBER OF TRANSECTS 
ERODE STABLE ACCRETE 



26 
26 
26 



1.5 

14.4 



■1.3 



21, 
■27, 



■31. 



0.01 
■0.13 



■0.01 



1.64 
1.81 



2.09 



42 
46 



46 



26 


5 


-6.0 


-21. 


-0.06 


1.42 





26 





26 


6 


9.3 


24. 


0.08 


1.83 





23 





26 


7 


-86.9 


-159. 


-0.80 


5.61 


10 


13 





27 


1 


-69.6 


-188. 


-0.56 


3.47 


12 


21 





27 


2 


-24.9 


-41. 


-0.23 


3.88 





28 





27 


3 

REACH 7 


17.8 


67. 


0.16 


5.41 





27 





27 


4 


-7.9 


-55. 


-0.07 


5.41 





20 





27 


5 


61.1 


99. 


0.88 


8.68 





7 


6 


27 


6 


55.2 


113. 


1.65 


12.22 





4 


1 


28 


1 


16.5 


57. 


0.29 


22.40 





20 





28 


2 


1.9 


-29. 


0.03 


2.08 





39 





28 


3 


-112.6 


-148. 


-0.90 


1.74 


29 


66 





28 


4 


42.2 


149. 


0.34 


1.88 





17 


3 


28 


5 


180.2 


197. 


1.46 


4.90 








10 


28 


6 


160.1 


211. 


1.28 


5.97 





3 


6 


28 


7 


53.3 


97. 


0.43 


5.12 





4 





29 


1 


-33.9 


-60. 


-0.27 


3.28 





9 





29 


2 


6.5 


82. 


0.05 


4.10 





32 





29 


3 


-49.8 


-74. 


-0.40 


1.23 





32 





29 


4 


69.5 


290. 


0.55 


2.41 





15 


10 


29 


5 


-85.1 


-104. 


-0.67 


3.12 





47 





29 


6 


-79.9 


-101. 


-0.64 


2.97 





39 





29 


7 


-94.5 


-113. 


-0.76 


1.53 





38 





29 


8 


-96.7 


-108. 


-0.77 


2.14 





12 





30 


1 


-94.1 


-104. 


-0.74 


3.68 





10 





30 


2 


-112.9 


-157. 


-0.89 


3.77 


2 


6 





30 


3 


-23.5 


-67. 


-0.18 


1.58 





80 





30 


4 


-38.1 


-64. 


-0.30 


1.68 





38 





30 


5 


-60.0 


-73. 


-0.47 


1.10 





22 





30 


6 


-87.9 


-110. 


-0.69 


1.03 





27 





30 


7 


-102.5 


-130. 


-0.81 


1.05 


1 


16 





31 


1 


-11.0 


-34. 


-0.19 


1.68 





50 





31 


2 


-58.0 


-76. 


-0.98 


2.29 


18 


12 





31 


3 


9.7 


253. 


-0.06 


5.83 


35 


62 


20 


31 


4 


298.8 


322. 


2.85 


2.65 








6 


31 


5 


302.5 


333. 


2.88 


2.48 








6 


31 


6 


223.5 


419. 


2.13 


2.76 





2 


6 


31 


7 


-42.1 


-147. 


-0.61 


2.68 


6 


5 


1 


31 


8 


115.4 


162. 


1.67 


2.60 








5 


31 


9 


254.7 


346. 


3.69 


8.34 








12 


31 


10 


252.1 


303. 


3.66 


7.64 








14 


31 


11 


144.3 


200. 


2.09 


4.71 








6 


32 


1 


162.1 


235. 


1.54 


3.87 





7 


18 


32 


2 


-195.0 


-451. 


-1.86 


4.52 


32 


14 






A7 



NUMBER OF TRANSECTS 

MAP SEGMENT A T MOVE M T MOVE A SH CHG M STD DEV ERODE STABLE ACCRETE 

32 3 -500.2 -623. -4.77 9.43 107 2 

32 4 -348.1 -529. -3.23 7.33 11 3 1 

32 5 -157.3 -311. -1.58 6.94 39 7 7 

32 6 240.1 272. 2.29 6.40 34 

32 7 118.3 475. 1.48 6.48 5 6 25 



A8 



i \ 



LIBRARY 

Woods Hole Oceanog 

institution