Prepared in cooperation with the 

South Carolina Sea Grant Consortium 

Coastal Change Along the Shore of Northeastern South 

Carolina—The South Carolina Coastal Erosion Study

Circular 1339

U.S. Department of the Interior

U.S. Geological Survey
Cover. Photograph showing geologists towing a subbottom profiler (yellow pontoons) in shallow water near the beach.
Coastal Change Along the Shore of 

Northeastern South Carolina—

The South Carolina Coastal Erosion Study

Edited by Walter A. Barnhardt

Contributing authors: 

W.C. Schwab1, P.T. Gayes2, R.A. Morton3, N.W. Driscoll4, W.E. Baldwin1, 

W.A. Barnhardt1, J.F. Denny1, M.S. Harris5, M.P. Katuna5, T.R. Putney6, 

G. Voulgaris7, J.C. Warner1, and E.E. Wright2

1

U.S. Geological Survey, Woods Hole, MA

2

Coastal Carolina University, Conway, SC

3

U.S. Geological Survey, St. Petersburg, FL

4

Scripps Institution of Oceanography, La Jolla, CA

5

College of Charleston, Charleston, SC

6

General Engineering and Environmental, LLC, Charleston, SC 

7

University of South Carolina, Columbia, SC

Prepared in cooperation with the

South Carolina Sea Grant Consortium

Circular 1339

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

This circular supersedes U.S. Geological Survey Open-File Report 2008–1206

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

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To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Barnhardt, W.A. (ed.), 2009, Coastal change along the shore of northeastern South Carolina—the South Carolina 

coastal erosion study: U.S. Geological Survey Circular 1339, 77 p.

Library of Congress Cataloging-in-Publication Data

Coastal change along the shore of northeastern South Carolina : the South Carolina coastal erosion study / edited by 

Walter A. Barnhardt; contributing authors: W.C. Schwab ... [et al.] ; prepared in cooperation with the South Carolina 

Sea Grant Consortium.

 p. cm. -- (Circular ; 1339)

 Includes bibliographical references.

 ISBN 978-1-4113-2538-8 (alk. paper)

 1. Coast changes--South Carolina. 2. Beach erosion--South Carolina. 3. Shore protection--South Carolina. 

I. Barnhardt, Walter A., 1960- II. Schwab, William C. III. South Carolina Sea Grant Consortium. 

 GB459.5.C63 2009

 551.45’7--dc22

200903633

Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, 

or subcontractors, make any warranty, express or implied, nor assume any legal responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use 

would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no 

responsibility is assumed by the USGS in the use of these data or related materials.
iii
iv

Acknowledgments

Funding for this research was provided by the Coastal and Marine Geology Program of the 

U.S. Geological Survey (USGS) and the South Carolina Sea Grant Consortium (SCSGC). We 

thank M. Richard (Rick) Devoe, Director of the SCSGC, for his encouragement and support 

of coastal research. William Danforth, David Nichols, Thomas O’Brien, Barry Irwin, Kenneth 

Parolski, Charles Worley, Shawn Dadisman (USGS), and Paul Byham (SEA Ltd.) provided support 

during data acquisition and processing. Neal Gielstra, Jenna Hill, Elizabeth Johnstone, German 

Ojeda, Jamie Phillips, Beth Sharrer, Triniti Dufrene, Melody van der Linde, Trent P. Tinker, 

Amanda Windsor, Elizabeth Gherman, and Heather Young (Coastal Carolina University) provided 

invaluable logistical and technical assistance. Sarah Kruse (University of South Florida) and 

Steven Forman (University of Illinois at Chicago) provided scientific analyses and interpretations. 

Jennifer Martin arranged this document in HTML. We also thank the captains and crews of the 

R/V Atlantic Surveyor, R/V Megan Miller, and R/V Coastal II. This report greatly benefited from 

reviews by C. Wiley Poag, E. Robert Thieler, and Eric Grossman.
v

Contents

Section 1: Coastal Change: Implications for the Grand Strand................ 2

Section 2: Mapping Coastal Change .............................................................18

Section 3: Geologic Framework.....................................................................32

Section 4: Shoreline Change ..........................................................................46

Section 5: Sediment Budget and Ocean Processes.......................................58

Section 6: An Effective Strategy for Understanding Coastal Change........70

Section 7: References Cited............................................................................72

Section 8: Glossary..........................................................................................76
vi

Conversion Factors and Abbreviations

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 0.3861 square mile (mi2)

Volume

cubic meter (m3) 1.308 cubic yard (yd3)

Flow rate

meter per second (m/s) 3.281 foot per second (ft/s)

meter per year (m/yr) 3.281 foot per year (ft/yr)

millimeter per year (mm/yr) 0.03937 inch per year (in/yr)

kilometer per second (km/s) 0.6214 mile per second (mi/s)

Mass

kilogram (kg) 2.205 pound avoirdupois (lb)

ACRONYMS DEFINITIONS

ATV All terrain vehicle

BERM Beach erosion and monitoring project

GIS Geographic information system

GPR Ground penetrating radar

LIDAR Light detection and ranging

MCPH Mid-Carolina Platform High

MSL mean sea level

NOS National Ocean Service (National Oceanographic and 

Atmospheric Administration)

OCRM Ocean and Coastal Resource Management (South Carolina 

Department of Health and Environmental Control)

SCCES South Carolina Coastal Erosion Study

SL Sea level

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey
Coastal Change Along the Shore of Northeastern 

South Carolina—The South Carolina Coastal 

Erosion Study

Edited by Walter A. Barnhardt

Abstract

The U.S. Geological Survey, in cooperation with the South Carolina Sea Grant Consortium, conducted a 

7-year, multidisciplinary study of coastal erosion in northeastern South Carolina. Shoreline behavior along 

the coast of Long Bay is dictated by waves, tidal currents, and sediment supply that act within the overall 

constraints of the regional geologic setting. Beaches are thin ribbons of sand that sit on top of layered 

sedimentary rocks, which have been deeply eroded by rivers and coastal processes over millions of years. 

Offshore of the beaches, these sedimentary rocks are exposed as hardgrounds over large expanses of 

shallow seafloor and are locally overlain by a discontinuous veneer of sandy sediment generally less than 

1 m thick. Rates of shoreline retreat largely depend on the geologic framework of the shoreface that 

is being excavated by ocean processes. Mainland-attached beaches have remained relatively stable, 

whereas barrier islands have experienced large shifts in shoreline position. In this sediment-limited region, 

erosion of the shoreface and inner shelf probably contributes a significant amount of new material to the 

beach system. Oceanographic studies and numerical modeling show that sediment transport varies along 

the coast, depending on the type and travel path of storms that impact Long Bay, but the long-term net 

transport direction is generally from north to south. Changes in storm activity that might accompany climate 

change, coupled with anticipated increases in sea-level rise, are expected to strongly affect low-lying, 

heavily developed areas of the coast.
2 Section 1: Coastal Change: Implications for the Grand Strand

1.1. Introduction

Coastal and nearshore marine environments 

are dynamic natural systems that continually evolve or change over time. In the United States, 

barrier islands that protect most of the Atlantic and 

Gulf Coasts have, on the whole, moved landward over 

many centuries. To a geologist or oceanographer, the 

landward migration is a natural response to storms, 

sea-level rise, and other processes that operate at the 

ocean’s edge. To an owner of beachfront property, 

however, this coastal change is simply erosion. By 

identifying the agents responsible for coastal change 

and determining the relative contribution of each 

agent, scientists and policy makers can address the 

underlying causes of beach erosion, wetland loss, and 

other challenging issues. The development and application of science-based management strategies will 

help to conserve coastal environments while ensuring that they remain places the public can continue to 

safely inhabit and enjoy.

Coastal change is a major concern along many 

segments of the world’s coastlines. Rapid population 

growth over recent decades has increased pressure on 

what remains of natural coastal environments. More 

than half the U.S. population lives in coastal counties, 

which account for only 17 percent of the land area of 

the nation (Beach, 2002). Most of these coastal areas 

are actively eroding or are otherwise vulnerable to 

rising sea level (Dolan and others, 1985; Thieler and 

Hammar-Klose, 1999, 2000a, 2000b). Human activities, such as seawall construction and channel dredging, have reduced sediment supply to beaches, interrupted the natural movement of sediment along the 

coast, and modified the normal flow of water through 

inlets and estuaries. Additionally, processes associated 

with storms and sea-level rise have profoundly shifted 

the position of the shoreline by eroding beaches and 

flooding low-lying areas (fig. 1.1). These processes 

act over different time scales to drive coastal change, 

which in turn threatens the infrastructure and economies of many coastal communities. 

An increase in the rate of sea-level rise is 

expected as a result of global warming over the 21st 

century, according to a report by the Intergovernmental Panel on Climate Change (IPCC, 2007). Projections of sea-level rise have been the topic of much 

debate, especially regarding the potential contributions made by melting of ice sheets in Greenland and 

Antarctica (CCSP, 2009). Conservative estimates call 

for at least 0.5 m of sea-level rise by the year 2100, 

but plausible scenarios range up to 2 m higher than 

present depending on rates of ice loss (Rahmstorf, 

2007; Pfeffer and others, 2008). Even the low end 

of these estimates is considerably faster than the rate 

observed over the previous 100 years (Douglas, 1997). 

Global warming is also expected to produce higher 

sea-surface temperatures, which have been linked 

to more frequent and more powerful hurricanes 

(Emanuel, 2005; Webster and others, 2005). If this 

linkage is real, years of relatively quiet storm 

activity will come to an end for many coastal areas. 

Beach towns might face severe societal and 

Figure 1.1. The beach at Folly Island taken before (top) 

and after (bottom) Hurricane Hugo struck the coast of 

South Carolina in October 1989. Published by permission 

of the National Oceanic and Atmospheric Administration 

Photo Library (accessed online July 1, 2007, at http://www.

photolib.noaa.gov).
3

3

economic upheaval such as that recently experienced 

by residents of the Gulf Coast during active hurricane 

seasons. The scientific community generally lacks 

the ability to predict these effects on time scales short 

enough to be useful in making land-use decisions 

such as locating new construction or issuing permits 

for other activities. However, resource managers and 

policy makers need reliable information to predict 

when, where, and how much the coast will change. 

Changes in the morphology of coastal landforms 

and patterns of sediment movement have been studied for over a century, but, in general, scientists have 

only a rudimentary understanding of the processes 

that drive coastal change. For example, we know that 

the shapes of sandy shorelines are largely dictated by 

waves, tides, and currents that act across a wide spectrum of spatial and temporal scales. Whereas a single 

storm can dramatically transform a section of coastline overnight, the impacts of sea-level rise take place 

over decades or centuries. That storm might deeply 

erode a beach in only a few hours, but the sediment 

is not necessarily lost forever. Gentle swells from 

prolonged periods of fair weather following the storm 

typically return sediment to the beach (fig. 1.2). As the 

frequency and intensity of storms vary each year, so 

too does the condition of the beach.

The U.S. Geological Survey (USGS) conducts 

regional studies of coastal erosion to provide impartial 

scientific information necessary for the protection and 

management of valuable coastal resources. This report 

summarizes the results of a multidisciplinary study of 

the northeastern coast of South Carolina by the USGS 

in cooperation with the South Carolina Sea Grant 

Consortium (SCSGC) from 1999 to 2006. The main 

objective of the study was to determine the geologic 

and oceanographic processes that control sediment 

movement along the region’s shoreline and thereby 

improve projections of coastal change.

1.2. The Grand Strand

Physical Setting

The nearly continuous series of sandy beaches 

in northeastern South Carolina is commonly known 

as the “Grand Strand.” This arcuate segment of 

coast extends 100 km (62 mi) along the central and 

southern portions of Long Bay, a large embayment 

that lies between Cape Fear, North Carolina, and 

Cape Romain, South Carolina (fig. 1.3). The broad, 

crescent-shaped shoreline is characteristic of regions 

where seasonal changes in wind directions produce 

waves that move sediment alternately up and down 

the coast. Waves are more important than tides in 

moving sediment along the Grand Strand, which has 

a low mean tidal range of 1.5 m. These microtidal 

conditions typically result in narrow barrier islands 

that are separated by small tidal inlets (Hayes, 1994). 

Presently, beaches in the region receive little or no 

sediment from rivers. Sediment carried by the Pee 

Dee River, which discharges into Winyah Bay at the 

southern end of the Grand Strand, is trapped upstream 

behind dams or in the estuary before it reaches the 

coast (Patchineelam and others, 1999).

Barrier islands and spits are limited to the 

northern and southern ends of the Grand Strand and 

are not present in the center (fig. 1.3). Waites Island, 

a small undeveloped barrier island near the North 

Carolina border, is separated from the mainland by 

a narrow estuary and salt marshes. The central part 

of the Grand Strand consists of mainland-attached 

beaches with residential and commercial development 

built close to the beach (Lennon and others, 1996). No 

tidal inlets are present in the stretch of coast between 

Cherry Grove and Garden City Beach. Along this 

stretch, beaches directly abut the mainland shore, 

which reaches elevations as high as 11 m above local 

mean sea level. The character of the coast again 

changes between Murrells Inlet and Winyah Bay in 

the southwestern part of Long Bay, where short barrier 

islands and spits are separated from the mainland by 

narrow estuaries.

This study focuses on terrestrial and marine 

environments in a swath that extends 5 to 15 km 

landward and 10 km seaward of the Grand Strand 

coastline. Inland, the study area includes the 

popular resort cities of Myrtle Beach, North Myrtle 

Beach, Surfside Beach, and several smaller coastal 

communities. Seaward, it covers the nearshore portion 

of the Long Bay inner continental shelf from the surf 

zone to water depths of about 15 m. The low-relief 

seafloor slopes seaward at relatively steep gradients 

up to 4 m/km in nearshore areas (Denny and others, 

2007). Beyond the 7-m isobath, the slope decreases to 

1 m/km or less.
SECTION 1

4

Figure 1.2. The active beach system, which extends from the dunes to the inner edge of the continental shelf. (A) During 

fair weather, sediment is stored in the upper beach and dunes. The relatively broad, flat berm is dry at high tide. The 

intertidal beach is relatively narrow, and the seaward-sloping shoreface forms a concave-upward surface beneath the 

waves. (B) During stormy weather, waves and currents erode the berm and dunes. Sediment is transported offshore into 

deeper water (red arrow) and produces a broader, more gently sloping intertidal beach and shoreface. Sediment temporarily 

stored offshore typically moves back onto the beach in the weeks and months following a storm.

Shoreface

Intertidal

beach

ACTIVE BEACH SYSTEM

Upper

Dunes beach

Low tide

High tide

Intertidal

beach

High tide

Low tide

Fair-weather profile

Sediment stored

on lower shoreface

Erosional

scarp

Berm

FAIR-WEATHER BEACH

STORM-ERODED BEACH

A

B

Continental

shelf

VERTICAL SCALE GREATLY EXAGGERATED
5

5 SECTION 1

Figure 1.3. (A) The location of the Grand Strand study area on the North and South Carolina coasts. Published by 

permission of the National Aeronautics and Space Administration–Visible Earth program accessed July 1, 2007, online at 

http://visibleearth.nasa.gov/. (B) Physiographic and geographic features of the Grand Strand. Types of coastal landforms 

are indicated by the color-coded bands parallel to the coast.

NORTH CAROLINA

SOUTH CAROLINA

79°20' W 79°10' 79°00'

34°00'

78°50'

33°55' 33°50'

79°00' 78°50' 78°40' 78°30'

33°10' 33°15' N

EXPLANATION

Long Bay

Winyah

Bay

Cape

Romain

Cape

Fear

Cape

Lookout

Long

Bay

Onslow

Bay

N

Cape

Hatteras Raleigh

Bay

Wilmington

Charleston

GRAND

STRAND

50 KILOMETERS

50 MILES

0

0

Folly

Island

Waites

Island

Cherry

Grove

Atlantic Beach,

Crescent Beach

Little River

Inlet Myrtle Beach

Surfside

Beach

Garden

City

Murrells

Inlet

Huntington

Beach State

Park

Great Pee Waccamaw River

Dee River

Pawleys

Island

North Inlet

Debidue

Beach

North

Island

N

Intracoastal waterway

North

Myrtle

Beach

10 KILOMETERS

10 MILES

0

0

Land

Wetland

Water

Barrier island

Barrier spit

Mainland-attached beach

Inlet or swash area

A

B
SECTION 1

6

Population, Economy, and Development

The sandy beaches of the Grand Strand have 

attracted year-round residents and recreational visitors since the mid-1800s, when coastal development 

first began in the region. Since that time the Grand 

Strand has become increasingly popular as a tourist 

destination and as a home for many new residents. 

The population of Horry and Georgetown Counties 

was recently estimated at almost 300,000 (U.S. Census Bureau, 2008). The 36.5-percent increase in the 

number of year-round residents during the past decade 

(1990–2000) has made the two counties together the 

13th fastest growing metropolitan area in the nation. 

A robust tourism industry annually draws about 

14 million visitors and generates over $2 billion in 

direct visitor expenditures (Myrtle Beach Area 

Chamber of Commerce, 2008). Tourism revenues produced along the Grand Strand account for more than 

30 percent of the annual statewide total (2000–04); 

this revenue represents an economic boon for the 

region as well as an important source of income for 

the State.

A dramatic increase in residential, commercial, 

and infrastructure development (fig. 1.4) has accompanied this growth surge and has underscored the 

vulnerability of the Grand Strand to the perils of its 

coastal location. The continued economic success of 

the region and the quality of life that local residents 

enjoy are inherently tied to the integrity and quality 

of maintenance of local beaches. The beaches provide 

the recreational potential that drives the local tourism 

economy and, more importantly, protection from the 

impacts of storms and coastal erosion. With ongoing 

sea-level rise, beach erosion is expected to continue or 

possibly worsen, jeopardizing the future of the Grand 

Strand as a premier seaside resort.

1.3. Coastal Hazards

Sea Level

Global sea level has fluctuated widely due to climate changes and tectonic influences. Sea level falls 

during glacial periods, commonly referred to as Ice 

Ages, because large volumes of water evaporate from 

the oceans and become incorporated into ice sheets 

(see Box #1). The opposite occurs during interglacial 

periods such as today, when the climate is warmer, 

and melting ice returns water to the oceans. Warmer 

ocean water also expands, causing additional sea-level 

rise. In response to these changes in sea level, coastal 

systems have migrated across the continental shelf 

and coastal plain of South Carolina (fig. 1.5). These 

landscapes are flat and gently sloping, so a small rise 

in sea level can inundate a broad area of land. The 

shoreline moves landward as sea level rises. When sea 

level reaches its maximum elevation, movement of the 

shoreline slows to a stop. Sediment has more time to 

accumulate while the coast remains in one position, 

so barrier islands and other shoreline deposits develop 

and grow.

The Atlantic Ocean has flooded nearly all of the 

South Carolina coastal plain during the geologic past 

during repeated cycles of sea-level rise and fall. The 

generally flat coastal plain steps down toward the 

ocean in a series of terraces that are aligned northeastsouthwest, roughly parallel to the Grand Strand coast. 

The terraces are separated by erosional escarpments 

and low linear hills that represent ancient shorelines 

(fig. 1.6). The shoreline features formed at times of 

high sea level over the last 3–4 million years. The 

Orangeburg Scarp, the oldest shoreline, lies more than 

100 km landward of Myrtle Beach. It was formed by 

wave erosion when the coast was west of the cities of Florence and Sumter. These erosional scarps 

and shoreline deposits progressively decrease in age 

and elevation towards the modern coast (DuBar and 

others, 1974; Colquhoun and others, 1991), where a 

new escarpment is currently forming along the Grand 

Strand. Although these ancient shoreline features are 

indicative of sea-level changes in the distant past, the 

record that they provide is largely incomplete. Old 

shorelines also formed seaward of the modern coast 

when sea level was lower than present, but most evidence has been eroded away by ocean processes.

Sea level has slowly continued to rise over the 

course of our lifetimes. Tide-gauge records from 

around the world indicate that global sea level 

increased at an average rate of about 2 mm/yr during 

the 19th and 20th centuries (Douglas, 1997). Longterm records from Charleston show that the rate of 

sea-level rise is considerably higher along the 

South Carolina coastline, where it is estimated at 

3.28 mm/yr. As sea level slowly continues to rise, lowlying coastal areas will be inundated, and the beaches, 

barriers, and marshes of the Grand Strand coastal 

system will continue to migrate landward. Waves and 
7

7 SECTION 1

Figure 1.4. Views of the Grand Strand before and after high-density oceanfront development. (A) Picture postcard of Myrtle 

Beach Pavilion area with boardwalk and small structures behind a natural dune. Photograph taken by W.C. Johnson around 

1927 and published by permission of the Lake County (IL) Discovery Museum, Curt Teich Postcard Archives. (B) Picture 

postcard of the Crescent Beach and Ocean Drive Beach sections of North Myrtle Beach around 1955. Published by permission 

of the South Caroliniana Library, University of South Carolina–Columbia. During this period, single-family cottages represented 

most of the development, and, although structures did stand close to the shoreline, the integrity of coastal dunes was 

preserved. (C) Photograph of oceanfront along the downtown section of Myrtle Beach around 2000 (published by permission 

of the Myrtle Beach Area Convention and Visitors Bureau). High-rise condominiums and hotels now dominate development 

along the Grand Strand. In many areas, structures stand directly adjacent to the beach and frontal dunes are absent. Locations 

shown on figure 1.3B.

B

C

A
SECTION 1

8

BOX #1: SEA-LEVEL CHANGE

A. EVENT SCALE (hours to days). 

The tide gauge at Charleston Harbor shows variations 

in water levels due to tides and an anomalously high 

tide when Hurricane Hugo made landfall at midnight on 

September 21, 1989. The storm surge rose 2.6 m (8.0 ft) 

above mean sea level (MSL) at Charleston and over 6 m 

(20 ft) above MSL in coastal areas 20 mi to the north 

(Brennan, 2001). Data from NOAA National Ocean Service 

(http://tidesonline.nos.noaa.gov/).

B. HISTORICAL SCALE (decades to centuries). 

Tide-gauge records depict fluctuations in the elevation 

of mean high water (MHW) from 1900 to 2005. Monthly 

averages (black dots) are overlain with a curve showing 

the annual average (red line). The long-term trend in 

sea-level rise is about 3.3 mm/year (1.1 ft/century). Data 

from NOAA National Ocean Service (http://tidesonline.nos.

noaa.gov/).

C. GEOLOGICAL SCALE (thousands of years). 

Large changes in global sea level have occurred because 

of glacial cycles and changes in continent-based ice 

volumes. Geologic evidence shows that about 

120,000 years ago sea level was at or above its present 

elevation. Barrier islands existed along the South Carolina 

coast, much like today. Sea level later fell as glaciers 

grew during the last Ice Age and, about 21,000 years ago, 

the shoreline was far out on the continental shelf. Since 

that time, climate warming and melting glaciers have 

driven the ongoing rise in sea level and general landward 

migration of the shoreline to its present position. Figure 

modified from Lambeck and Chappell (2001, their 

figure 1B).

Graphs A through C illustrate sea-level changes that occur over different time and spatial scales. 

0

-20

-40

-60

-80

-100

-120

-140

120 100 80 60 40 20 0

YEARS BEFORE PRESENT (x 1,000)

140

10

0.2

0.4

0.6

0.8

1.2

1900 1920 1940 1960 1980 2000

MSL

YEAR

no data

-1.5

-1.0

-0.5

MSL

0.5

1.0

1.5

2.0

2.5

3.0

9/18 9/19 9/20 9/21 9/22 9/23 9/24 9/25

DATE, IN MONTH/DAY, 1989

Hurricane Hugo

High sea level

(interglacial period)

Low sea level

(glacial period)

WATER LEVEL, IN METERS

ABOVE MEAN SEA LEVEL AT CHARLESTON

WATER LEVEL, IN METERS

ABOVE DATUM

SEA LEVEL, IN METERS

ABOVE DATUM

B

C

A

1.0
9

9 SECTION 1

D. STORM SURGE (hours to days). 

Image showing areas of the Grand Strand at risk of inundation 

from hurricanes. Differences in the height of surge from a given 

storm result from a site’s proximity to landfall, geometry of the 

coastline, and the depth of water offshore. Barrier islands in the 

northeastern and southwestern parts of the map are at highest risk 

from category 4 to 5 hurricanes. Mainland-attached beaches in the 

center near Myrtle Beach maintain relatively high elevations that 

provide a greater degree of protection. The image was developed by 

the U.S. Army Corps of Engineers using the Sea Lake and Overland 

Surges from Hurricanes (SLOSH) model, which was developed by 

the Federal Emergency Management Agency (FEMA), United States 

Army Corps of Engineers (USACE), and the National Weather 

Service (NWS).

E. SEA-LEVEL RISE (decades to centuries). 

Image showing the risk from sea-level rise along the North 

Carolina to Georgia coast. The risk is lowest in the vicinity of 

Cape Fear because of the relatively high slope of the upland 

adjacent to the coast. Modified from Thieler and HammarKlose (1999, their figure 10).

F. SEA-LEVEL CHANGE (thousands of years). 

Image of the southeastern United States showing a series of 

ancient shorelines that formed at previous highstands of sea 

level. The shoreline deposits are preserved on the middle to lower 

coastal plain. The 120-m depth contour (dashed blue line) shows 

the approximate position of the shoreline during the last Ice Age 

when sea level was lowest relative to today. Little evidence of 

shorelines marking lower sea levels exists owing to reworking of 

the continental shelf by terrestrial and marine processes. Figure 

modified from Winker and Howard (1977, figure 1).

Images D through F display the impacts of sea-level changes on coastal areas that range from local flooding due to 

storm surges to long-term migration of shorelines across the region due to climate-driven increases in sea level.

D

Open water

Category 1

Category 2

Category 3

Category 4

Category 5

100-year

flood plain

Myrtle

Beach

North

Myrtle Beach

Surfside

Beach

EXPLANATION

N

very low

Low

Moderate

High

Very high

Risk rank for 

sea-level rise

EXPLANATION

E

North Carolina

South Carolina Georgia

Grand

Strand

Charleston

Cape Fear

N

Rank Rate of sea-level rise (mm/yr)

Very low <1.8

Low 1.8–<2.5

Moderate 2.5–<2.95

High 2.95–3.16

Very high >3.16

300

320

340

820 800

120 m

Grand

Strand

Charleston

F

EXPLANATION

Ancient shorelines, 

beach ridges, and 

related features

River terraces

(undifferentiated)
SECTION 1

10

currents will erode and redistribute sediment from 

older deposits along the coast, providing much 

needed nourishment to the modern beaches of the 

Grand Strand.

Storms

Tropical cyclones (tropical storms and hurricanes) 

and northeasters are the greatest natural hazard facing South Carolina coastal communities. These severe 

storms generate strong winds and waves, heavy rainfall, and storm surges, which cause extensive erosion, 

flooding, and damage to infrastructure and development. If storms move slowly or stall at a single 

location, they might batter a stretch of coastline for 

several days and wreak great destruction. Historically, 

South Carolina has experienced direct landfalls of 

tropical storms and hurricanes relatively infrequently, 

averaging one every four to five years (see Box #2). 

Since 1871, 33 tropical storms and hurricanes have 

directly hit the state (SCDNR-SCO, 2007). Northeasters, informally called “Nor’easters,” are winter storms 

that affect the South Carolina coastline every year 

with strong winds that blow in a northeast to southwest direction. These storms can be ten times larger 

than a hurricane and thereby affect a broader stretch 

of coast at one time.

Figure 1.5. Typical response of shorelines to rising sea level. When sea level rises, the ocean advances over the land, 

and shorelines retreat or move landward. The red line shows the irregular rate of sea-level rise since the end of the last 

Ice Age (modified from Fairbanks, 1989). At that time, sea level was about 120 m below the present level, and the shoreline 

was at or near the edge of the continental shelf. The steep section of the red line between 12,000 and 8,000 years ago 

shows a rapid sea-level rise that caused shorelines to migrate landward at a faster rate. Even small increases in sea level 

can cause shorelines to retreat large distances across the gently sloping continental shelf and coastal plain. The rate of 

sea-level rise slowed about 6,000 years ago and thereby allowed shorelines to stabilize near their present location. Old 

shoreline deposits on the coastal plain (see figure 1.6) were formed at least 125,000 years ago when sea level was higher 

than it is today.

SEA LEVEL, IN METERS BELOW 

PRESENT SEA LEVEL

0 2 4 6 8 14 16

YEARS BEFORE PRESENT

(x1,000)

10 12 18

0

20

40

60

80

100

120

140

160

S E A - L E V E L R I S E

Continental shelf

Coastal

plain

Present sea level

8,000 years ago

12,000 years ago

18,000 years ago

Present

shoreline

Old shoreline
1111 SECTION 1

Figure 1.6. Barrier islands and other shoreline features on the coastal plain of the Long Bay region (modified from 

DuBar and others, 1974). Ancient shorelines (red lines) formed at former highstands of sea level that flooded the coastal 

plain multiple times over the last 3 to 4 million years. These shorelines step down in elevation and become progressively 

younger toward the modern coast, with the highest and oldest (Orangeburg Scarp) farthest inland. All the shoreline 

features have been heavily dissected by rivers and streams.

NORTH CAROLINA

SOUTH CAROLINA

Fayetteville

Florence

Hartsville

Marion

Surry

Scarp

Lake

Marion

Lake

Moultrie

Georgetown

Myrtle

Beach

Sumter

Cape

Fear

Winyah

Bay

Lumberton

1

1

2

3

4

5

5

6

7

8

L o n g

B a y

Orangeburg

Scarp

Mechanicsville Scarp

Pee De e River

Wilmington

Barrier Islands

Modern

Myrtle Beach

Jaluco–Cainhoy

Conway

Hakina–Pleasant Hill

Horry–Kingstree

Lakeview

Orrum

1

2

3

4

5

6

7

8

35o 

80o 

Cape Fear River

Santee River

34o

78o 79o

5

6

1

3

2

3

6

6

2

6 EXPLANATION

0 20 MILES

0 20 KILOMETERS
SECTION 1

12

Tropical cyclones, which include tropical storms and hurricanes, develop in the tropical and subtropical regions of 

the North Atlantic Ocean. They begin as tropical depressions, which are low-pressure systems that exhibit cyclonic 

(counterclockwise) circulation. In the presence of favorable atmospheric conditions, warm tropical waters can 

provide enough energy to allow these systems to organize and strengthen into more powerful storms. Upper-level 

winds and pressure systems steer these storms into higher latitudes, where some make landfall and wreak havoc 

along the coast. Others dissipate over the cooler waters of the North Atlantic.

BOX #2: TROPICAL CYCLONES

Map of the North Atlantic Ocean showing the area of hurricane and tropical-storm activity (light green). Tropical depressions (red 

symbols) form within or near the Intertropical Convergence Zone (ITCZ, light purple), a zone of low pressure near the equator where 

trade winds converge and cause moist air to become unstable and rise. Tropical depressions gain strength from warm surface 

waters and often intensify into tropical storms and hurricanes as they are forced westward by the trade winds and the anticyclonic 

(clockwise) rotation of the Bermuda High. The storm paths are also influenced by low-pressure systems that move eastward across

continental North America, generally causing the storms to recurve and change their heading towards the north and east.

Tropical cyclones occur during a season that extends from June 1 to November 30, with the most activity occurring between July and September. On the basis of the measure of sustained wind speeds near the centers of these 

storms, they are classified as tropical storms, 63 to 118 km/hr (39 to 73 mi/hr) or hurricanes, >119 km/hr (74 mi/hr). 

The Saffir-Simpson Scale (see next page) uses wind speed to further subdivide hurricanes into five categories of 

intensity and provides descriptions of the storm surge and types of damage that can be expected with each.

0°

60°

30°

90° 30° 

H

L

Southeast trade winds

Northeast trade winds

ITCZ

Bermuda

High

Northern westerly winds

Zones of tropicaldepression developmentGeneral zone of tropicalstorm and hurricane activityIntertropical 

Convergence

Zone (ITCZ)

Typical tracks of tropical

storms and hurricanes

EXPLANATION

0 1,000 KILOMETERS

0 1,000 MILES

Eastward moving

low pressure
1313 SECTION 1

Saffir-Simpson Scale

Category Wind speed Storm surge1 Potential damage

1 74–95 mi/hr

64–82 kts2

119–153 km/hr

4–5 ft

1.2–1.5 m

MINIMAL. Damage primarily to shrubbery, trees, and mobile homes. Low-lying coastal roads 

inundated, minor pier damage, small craft torn from moorings.

2 96–110 mi/hr

83–95 kts

154–177 km/hr

6–8 ft

1.8–2.4 m

MODERATE. Some trees blown down. Major damage to mobile homes, poorly constructed signs, and 

piers. Some damage to building roofs, windows, and doors. Flooding damages piers and marinas.

3 111–130 mi/hr

96–113 kts

178–209 km/hr

9–12 ft

2.7–3.7 m

EXTENSIVE. Many large trees and signs blown down. Some structural damage to small 

residences and utility buildings. Mobile homes destroyed. Serious flooding, possibly requiring 

evacuation of low-lying areas.

4 131–155 mi/hr

114–135 kts

210–249 km/hr

13–18 ft

4.0–5.5 m

EXTREME. Extensive damage to small buildings. Complete destruction of mobile homes. Major 

erosion of beaches. Flooding far inland, possibly requiring evacuation of areas near the shore.

5 >155 mi/hr

>135 kts

>249 km/hr

>18 ft

>5.6 m

CATASTROPHIC. Considerable damage to residences and industrial buildings; some complete 

structural failures. Extensive flooding possibly requiring evacuation within 5 to10 miles 

(8 to 16 km) of shore.

1 Storm-surge values are highly dependent on the slope of the continental shelf and the shape of the coastline.

2

 kts, knots (1 knot = 1.15 miles per hour).

Satellite image of Hurricane Hugo on September 21, 1989, 

just hours before making landfall on the South Carolina 

coast. Source: NOAA National Hurricane Center.

Image of hurricane tracks that hit or passed 

near the South Carolina coast from 1851 

to 2005. Thin gray lines indicate tropical 

storms and minor hurricanes (categories 

1–2). Black lines indicate major hurricanes 

(categories 3–5). Red line indicates 

Hurricane Hugo. Source: NOAA National 

Hurricane Center.

In September 1989, Hurricane Hugo slammed into the 

South Carolina coast near Charleston as a strong category-4 storm. Large waves severely eroded beaches 

and dunes in several southeastern States. A maximum 

storm surge of 6 m (20 ft) completely submerged some 

low-lying barrier islands north of Charleston. At the 

time, Hugo was the costliest hurricane to ever hit the 

U.S. mainland. It remained at category-1 strength all the 

way to Charlotte, N.C., about 300 km (180 mi) inland 

from the coast, and destroyed many homes, trees, and 

farms. In South Carolina alone, 29 people were killed, 

and property damages were estimated at $6 billion.

Hurricane Hugo was only one of many hurricanes to 

impact the South Carolina coast during historical time. 

From 1871 to 2008, a total of 33 tropical storms and hurricanes made direct hits on the State, including six major 

hurricanes of category 3 or higher. 

Additional reading: 

Brennan, J.W., 2001, Meteorological 

summary of Hurricane Hugo: Journal of 

Coastal Research, Special Issue 8, p. 1–12.

Hazel (1954)

Diana (1984)

Fran (1996)

Hugo (1989)

Grand

Strand

N
SECTION 1

14

Strong winds associated with storms accentuate 

high tides by piling ocean water along the coast 

and not allowing it to recede during a subsequent 

low tide. If this situation persists over multiple 

tidal cycles, extreme coastal flooding results. Such 

storms do not need to make direct landfall in order to 

affect the coastline significantly. Whether they make 

landfall elsewhere and pass through the state or pass 

close to the coast offshore, they can still produce 

violent winds, waves, and storm surge. Storms that 

pass farther offshore might actually be beneficial 

by generating long-period swells that move sandy 

sediment towards Grand Strand beaches.

1.4. Beachfront Management

Prior to 1988, regulation of development along 

the coast of South Carolina was limited, and seawalls 

were routinely permitted on beaches. Most hard stabilization structures (fig. 1.7) were emplaced during the 

late 1970s and 1980s under the guidelines of the South 

Carolina Coastal Zone Management Act. This legislation established the Critical Line as a benchmark from 

which to regulate oceanfront development. The line 

was defined as either the scarp line or the seaward toe 

of the primary dune. The State had no jurisdiction to 

regulate development in areas landward of the line. 

Much of the new oceanfront construction during this 

period was placed too close to the coast and thus was 

at immediate risk of damage by storms.

Recognizing that the existing laws had failed 

to preserve the integrity of the beach/dune system, 

the State legislature passed the South Carolina 

Beachfront Management Act (SCBMA) in 1988 (see 

Box #3). With further amendments added in 1990, 

this legislation improved coastal management in 

two important ways. First, it mandated the Office of 

Ocean and Coastal Resource Management (OCRM) to 

regulate coastal development activities on a statewide 

basis. Second, it largely prohibited seawalls and 

promoted use of soft erosion-management solutions 

such as beach nourishment. Every ten years, the 

statewide base line is updated to account for shoreline 

changes over that time period. South Carolina’s 

beaches are monitored by OCRM, which publishes 

assessments entitled “State of the Beach” in annual 

reports (SCDHEC-OCRM, 1995–2006). Because most 

of the State’s coast is eroding, the base line moves 

landward in step with the retreating shoreline. In this 

way, properties originally located landward of the base 

line can fall under the jurisdiction of the SCBMA.

Whereas many agree with the long-term objective 

of beach management, application in the short 

term has proven difficult. The State’s beachfrontmanagement policy has been challenged, and one 

case (Lucas v. South Carolina Coastal Council) 

was ultimately considered by the U.S. Supreme 

Court. Regardless of legal outcomes, the shoreline 

continues to move, and the migration brings coastal 

infrastructure into conflict with the relentless natural 

processes that shape beaches. The inevitable result of 

the policy, when viewed in the context of the State’s 

chronically eroding beaches, is one of retreat from the 

coast. South Carolina has effectively chosen to retreat 

but struggles to accomplish this feat and, at the same 

time, solve the significant economic problems that the 

strategy creates.

As in many coastal states, beach nourishment 

has been the predominant strategy for slowing the 

effects of coastal erosion and thereby delaying 

implementation of long-term policies. After Hurricane 

Hugo struck in 1989, the City of Myrtle Beach began 

an expensive program to renourish its beaches with 

sand trucked from inland borrow pits. By the mid1990s, the demand for sand had increased, and the 

city opted for mining offshore sources to maintain the 

beaches. Identification of additional sand sources in 

offshore areas has become a priority issue to supply 

future nourishment projects, which are projected to be 

repeated every 8 to 10 years along the Grand Strand.

1.5. South Carolina Coastal Erosion Study

The USGS Coastal and Marine Geology Program 

and the SCSGC began scientific investigations of 

coastal erosion along the Grand Strand in 1999. The 

South Carolina Coastal Erosion Study (SCCES) 

is one of the most comprehensive regional studies 

undertaken to date and has provided critical 

information for management of the State’s coastal 

resources. The cooperative effort involves the 

USGS Coastal and Marine Geology Program, 

Coastal Carolina University, University of South 

Carolina, College of Charleston, Georgia Institute of 

Technology, Scripps Institution of Oceanography, and 

South Carolina Sea Grant.
1515 SECTION 1

The SCCES attempts to understand the full range 

of factors and processes that control sediment transport and coastal morphology along the Grand Strand. 

Knowledge of how the coastal system functions 

enhances our ability to predict coastal change ranging 

from the short-term effects of a single storm (hours 

to days) to the long-term effects of sea-level rise 

(decades to centuries). The interdisciplinary nature of 

the study has required cooperation among geologists, 

geophysicists, physical oceanographers, and numerical modelers. Our systematic approach consists of 

three phases:

1. Describe the regional geologic framework, which 

refers to the structure, composition, and distribution of rocks and sediment that compose the coast, 

shoreface, and inner continental shelf. 

2. Determine seasonal and longer term patterns of 

shoreline change by surveying beaches at regular 

intervals over several years.

3. Quantify the physical processes that drive coastal 

erosion through a combination of field measurements and numerical-modeling simulations. 

This report synthesizes the geologic and 

oceanographic factors that control sediment 

movement along the Grand Strand inner shelf and 

beaches. Ultimately, the three-part research strategy 

applied in this study will improve the prediction of 

shoreline behavior and guide efforts in other regions 

where limited sediment availability on the inner shelf 

is linked to coastal erosion.

Figure 1.7. Effects of engineering structures on South Carolina’s beaches: (A) Seawall at Garden City Beach in February 2007; see 

figure 1.3B for location. Seawalls are constructed to protect structures from being undermined as the shoreline migrates landward. 

This image highlights the dilemma between saving structures and maintaining a usable beach. Published by permission of M. Scott

Harris, College of Charleston, Charleston, South Carolina. (B) Southern end of the seawall at Debordieu Island in June 2005; see 

figure 3.2 for location. The adjacent unarmored section of coast is left free to migrate and leaves the seawall-protected property in a 

precarious position seaward of the natural shoreline. Beach nourishment has been used at this site to prevent failure of the seawall and 

temporarily provide some beach function. Published by permission of Paul Gayes, Coastal Carolina University, Conway, South Carolina.

A B
SECTION 1

16

The South Carolina Beachfront Management Act (SCBMA) 

is designed to protect coastal resources while also promoting responsible development in the State’s coastal 

zone. The SCBMA was adopted in 1988 and established a 

jurisdictional base line typically placed at the crest of the 

primary dune, if present. The SCBMA called for developers to locate new construction at a minimum distance 

landward of the base line. This minimum distance, 

delineated by the setback line, is established where the 

base line is calculated to be in 40 years (that is, a distance 

equal to 40 times the annual erosion rate). The annual 

erosion rate is determined from analysis of aerial photographs and beach profiles. Because the rate of erosion 

varies along the coast, the distance to the setback line is 

not the same for every section of beach. Also under the 

SCBMA, no new seawall construction is allowed, but older 

erosion-control structures can be maintained. If an existing structure is heavily damaged or destroyed, however, 

it must be removed by the owner. Specific provisions 

include:

• No construction is allowed seaward of the base line. 

The law was amended in 1990 and again in 2002 

to allow for special permits on a case-by-case basis. 

The special permits, if issued, strictly limit the size 

and design of new construction.

• Development is heavily regulated between the 

base line and the setback line. If an existing property in this area is damaged beyond 50 percent, it 

cannot be rebuilt.

Inlet systems locally complicate pathways of sand movement, and beaches adjacent to inlets are particularly 

dynamic. As a result, the SCBMA classified sections of the 

coast as “standard zones” and “inlet hazard zones” (see 

examples below). Standard zones are those areas away 

from the influence of inlets; these zones are defined by 

having shore-parallel depth contours. In standard zones, 

the base line is defined as the crest of the primary dune 

identified by beach surveys. Inlet hazard zones are those 

areas adjacent to tidal inlets where depth contours are 

oblique to the coast due to the influence of inlet-associated shoals and nearshore sand bars. In inlet hazard zones, 

the base line is defined by the most landward position of 

the shoreline in the previous 40 years as identified from 

aerial photographs.

The SCBMA also recognized that engineering structures, where they exist, strongly modify beach processes and 

behavior. As a result, standard zones are further divided into “natural” and “armored” areas. For armored areas, the 

primary dune crest no longer exists as a marker to determine the base line. Instead, an idealized-dune crest is projected landward of the shore-protection structure on an equivalent-volume basis (see example below). Inlet hazard

zones are similarly divided into “stabilized” and “unstabilized” areas. In the vicinity of jetties and other structures, 

profiles from adjacent nonengineered beaches are used to project the base line along the coast.

Aerial photographs showing examples of the jurisdictional 

base line (red line) established in 2000. (A) Inlet hazard zone 

in Garden City, South Carolina. The base line in this area is 

defined by the landward-most erosion of vegetation as seen 

on aerial photography over the last 40 years. (B) Standard zone 

in Myrtle Beach, South Carolina. The base line in this area is 

defined by the crest of the primary dunes as determined by 

beach-profiling surveys.

BOX #3: LINES IN THE SAND

Base line

A

0

0

500 METERS

1,500 FEET

Inlet hazard

zone

Standard

zone

Base line

B

500 METERS

1,500 FEET

0

0
1717 SECTION 1

Aerial photograph (C) of high-rise buildings along the beach at Garden City, South Carolina. The base line (red line) runs through 

the structures which are very close to the beach and fronted by a seawall (D) and would not meet present development standards. 

No dune crest exists, so the location of the base line is determined by fitting an undisturbed-beach profile (E, dashed line) to the 

existing armored-beach profile (E, solid line) so that there is an equivalent sand volume between the two profiles. The base line is 

set at the idealized-dune crest, which is landward of the seawall.

Seawall

0 100 METERS

0 300 FEET

C

Base line

Seawall

D

0

3

-3

0 200 400

Seawall

600

Idealized-dune crest

E

ELEVATION, IN METERS ABOVE

 MEAN SEA LEVEL

DISTANCE, IN METERS
18 Section 2: Mapping Coastal Change

directions. Some sound energy is reflected back to the 

sonar and precisely recorded. The angle, intensity, and 

traveltime of these reflected signals are used to calculate water depth along the swath. As the vessel moves 

forward, continuous depth measurements are collected 

and used to generate detailed bathymetric maps of the 

seafloor (fig. 2.3).

Surficial Geology

Sidescan or side-looking sonar systems are used 

to image wide areas (tens of meters to kilometers) of 

the seafloor (fig. 2.1). These systems emit a series of 

acoustic pulses, or pings, that insonify the seafloor 

along a ribbon-like swath perpendicular to the direction of travel. Sound scatters in all directions as it 

intersects the seafloor, with some percentage reflected 

back to the sonar. The traveltime and intensity of these 

reflections are recorded, and their relative intensity 

(backscatter) provides information about the type of 

material that covers the seafloor. As the research vessel moves forward, continuous pings insonify a swath 

along the seafloor much as a lawnmower cuts through 

grass. To obtain full coverage of the bottom, the ship 

sails back and forth as though it were mowing the 

lawn along a closely spaced series of parallel tracklines, with each swath overlapping adjacent swaths. 

Finally, the data are stitched together to form a composite sidescan-sonar image (figs. 2.4 and 2.5).

Subsurface Geology

Subbottom-profiling systems are used to image 

the internal structure of the seafloor (fig. 2.1). Similar 

to swath bathymetric and sidescan-sonar systems, 

subbottom profilers emit pulses of sound and then 

measure the intensity and traveltime of the return 

signals. In this case, however, more power is used 

to generate an acoustic pulse that penetrates into the 

subsurface and travels through rock and sediment. 

When the acoustic pulse moves across a boundary 

marking a contrast in physical properties, such as the 

upper surface of rocks buried beneath a sheet of sand 

or internal layering within individual deposits 

(fig. 2.6), some of the sound energy is reflected back 

to surface receivers and recorded.

2.1. Introduction

Scientists within the USGS Coastal and Marine 

Geology Program conduct research and mapping investigations designed to understand fundamental processes that create, modify, and maintain coastal 

and nearshore marine systems. The following sections 

describe methods used by the SCCES to map the geologic framework, assess historic shoreline change, and 

define the modern oceanographic processes influencing sediment transport along the coast of northeastern 

South Carolina. 

2.2. Mapping the Geologic Framework

The geologic framework forms the foundation of 

the coastal system and is shaped by the cumulative 

effects of tectonics, storms, sea-level change, and 

human activities. The geologic framework is defined 

by identifying three primary components: (1) seafloor 

topography (bathymetry), (2) texture and distribution 

of sediment on the seafloor, and (3) structure and 

composition of older rocks and sediment that underlie 

the seafloor, beach, and lower coastal plain. To map 

these components, a suite of remote-sensing and 

sampling techniques are employed both at sea and on 

land (figs. 2.1, 2.2A and B). 

To see beneath the ocean surface and image 

seafloor environments, sound (acoustics) energy 

is used. Sound travels efficiently in water and can 

penetrate deep into the ocean to provide detailed 

views of the seafloor; these views are comparable 

to topographic maps or aerial photographs on land. 

During the SCCES, different types of sonar systems 

were deployed that bounce sound waves off the 

seafloor and underlying rocks and sediment (fig. 2.1). 

Return signals, or reflections, are measured by the 

sonar systems and are used to produce sound images 

of the seafloor terrain and subsurface geology.

Seafloor Topography

Swath-bathymetric systems measure water depth 

in a narrow band, or swath, perpendicular to the 

direction of ship travel (fig. 2.1). The systems emit 

a series of acoustic pulses that insonify the seafloor 

beneath the survey vessel and scatter sound in many 
1919 Figure 2.1. The different techniques used to investigate the active beach system along the Grand Strand. Acoustic instruments (sidescan-sonar, swath- bathymetry, and subbottom profilers) provide information on the distribution of sediments, topography, and underlying structure of the shallow seafloor adjacent to the beach. On land, ground-penetrating radar (GPR) determines the thickness and structure of sediment beneath the beach and dunes. Sediment- grain size, composition, and age are determined by direct sampling of offshore and onshore deposits. To monitor short-term changes in beach morphology, precise elevation measurements are collected from the dune to the edge of the inner shelf by using all-terrain vehicles (ATVs) on land and small boats offshore as part of the Beach Erosion Research and Monitoring (BERM) program. Aerial photography and LIght Detection and Ranging (LIDAR) are used to survey and quantify changes along the coast. Differential Global Positioning Systems (DGPSs) are used to accurately position all of the data. Swath bathymetryResearch vessel Seismic source Hydrophone Sidescan sonar Echosounder Sampling BERM Aerial photographs and LIDAR DGPS GPR Onshore sampling (GeoProbe)
SECTION 2

20

Figure 2.2A. Mapping operations of the SCCES include (A) research vessel at dock preparing for departure, (B) small research vessel 

at dock with subbottom profiler towed from the stern, (C) subbottom profiler towed by rigid-hull inflatable boat directly off the beach, 

(D) subbottom profiler towed in very shallow water away from the beach, (E) sidescan-sonar system, (F) subbottom profiler, (G) subbottom 

profiler deployed off the stern of small coastal research vessel, (H) swath-bathymetric system configured as a side mount, (I) swathbathymetric transducer deployed off the bow of a small vessel, and (J) all-terrain vehicle (ATV) towing a ground-penetrating radar sled 

across the beach.

Offshore geologic mapping by

large- and small-boat operations

Geologic-mapping techniques

A

B

D

C

E

G

F

H

I

J
2121 SECTION 2

Figure 2.2B. Mapping operations of the SCCES include (A) collection of sediment core on the beach, (B) large coring rig for deep sampling, 

(C) video camera used to collect images of the seafloor, (D1) grab sampler used to collect sediment from the seafloor, (D2) sediment samples 

stored in bags for laboratory analysis, (E1) photograph of a sediment core, (E2) collection of offshore sediment with Vibracores, (F1) rigidhull inflatable boat measuring beach profiles in nearshore area, (F2) ATV measuring beach profiles onshore, (G) aerial photograph used in 

shoreline-change analysis of North Myrtle Beach, (H) LIDAR systems rapidly map topography over extensive areas of coast, and (I) and (J)

deployment of oceanographic instruments on a tripod (rigid three-leg structure) that will be anchored to the seafloor.

Battery Packs

Sensors

Measuring shoreline change

Onshore and offshore sampling techniques

Measuring sediment transport

A

D1

B

F1

G

Overlapping swaths

Direction 

of flight

H

I

C

E1

J

D2

E2

F2
SECTION 2

22

Figure 2.3. Bathymetry offshore of the Grand Strand. Water depths in the survey area range from 2 to 14 m. MLLW, mean lower low water.

N

9

7

8

9

9 10

8

10

9

7

8

10

11

Water depth, in meters relative to mean lower low water (MLLW)

Bathymetric contour (1-meter interval)

- 2

-14

11

EXPLANATION

0 10 KILOMETERS

10 MILES 0

WaccamawRiver

33°55' 33°50'

78°30' 78°40' 78°50' 79°00'

33°15' 33°10'

79°20' 79°10' 79°00'

34°00'

78°50'

WaitesIsland

North Myrtle Beach North Myrtle Beach

Little River

Inlet

Little River

Inlet

Myrtle Beach Myrtle Beach Intracoastal waterway Murrells Inlet Murrells Inlet

WaccamawRiver

Pawleys

Inlet

Pawleys

Inlet North

Inlet North Island Winyah

Bay

Black River

Great Pee Dee River
2323 SECTION 2

Figure 2.4. Acoustic-backscatter intensity, as measured with sidescan sonar, on the shallow seafloor of Long Bay. Backscatter intensity is a measure of the hardness and roughness of the seafloor. In general, higher values (light tones) represent rock, coarse sand, and gravel. Lower values (dark tones) generally represent fine sand and muddy sediment. Backscatter values are represented as digital numbers (DN) that are assigned to the pixels within the imagery and range from 0 (black) to 255 (white). Backscatter data combined with data from laboratory analyses of sediment samples are used to interpret the surficial geology of the seafloor. Locations where the data were collected for the images in figures 2.5, 2.6, and 2.7 are shown.

Backscatter, in digital number (DN)

High (255)Low (0)

EXPLANATION

0 10 KILOMETERS

10 MILES 0

Pawleys

Inlet North

Inlet North

Island

Murrells

Inlet

Myrtle Beach

WaitesIsland

North Myrtle Beach

Little River

Inlet Waites

Island

North Myrtle Beach

Little River

Inlet

Myrtle Beach

Murrells

Inlet

Pawleys

Inlet North

Inlet North

Island

33°55' 33°50'

78°30' 78°40' 78°50' 79°00'

33°15' 33°10'

79°20' 79°10' 79°00'

34°00'

78°50'

Intracoastal waterway

Winyah

Bay

Figure 2.5 Figure 2.7 Figure 2.6

N

Intracoastal waterway

Winyah

Bay

WaccamawRiver WaccamawRiver

Black River

Great Pee Dee River
SECTION 2

24

Ground-penetrating radar (GPR) is used to image 

the subsurface geology beneath the beach and other 

land areas. Instead of sound energy, GPR emits pulses 

of FM-frequency radio waves from an antenna traveling across the ground surface (fig. 2.1). When the 

outgoing signal travels across boundaries marking a 

change in the physical and chemical properties of the 

underlying deposits, some energy is reflected back 

to the surface. As with subbottom profiling, the time 

it takes a signal to travel from the antenna into the 

ground and back is precisely measured and converted 

to distance. Numerous closely spaced soundings are 

combined to form an image of the subsurface and used 

to measure the thickness of beach sand over rock, 

for example, or to locate buried channels formed by 

ancient streams or tidal inlets (fig. 2.7).

Seafloor Sediment

The geophysical techniques described above 

allow us to see through ocean waters and deep below 

the land surface to image the surficial and subsurface geology; however, it is difficult to determine the 

physical characteristics, such as grain size, of seafloor 

sediment and subsurface deposits on the sole basis of 

these remote images. In order to fully understand what 

the imagery represents, we need to collect physical 

samples of rocks and sediment and analyze them in 

the laboratory. A variety of techniques, such as coring and grab sampling, are used to sample sediment 

deposits (fig. 2.2B). Additional techniques, such as 

photography and video, are also used to verify interpretations of seafloor geology.

Figure 2.5. Enlarged section of the sidescan-sonar image in figure 2.4 shows the complexities of the shallow seafloor 

offshore of Myrtle Beach (location shown in figure 1.3B). Intricate patterns of high backscatter (light tones) and low 

backscatter (dark tones) represent exposures of rock and fine-sand deposits, respectively. Backscatter values are 

represented as digital numbers (DN) that are assigned to the pixels within the imagery and range from 0 (black) to 

255 (white). See figure 2.4 for location of section.

N

0 1 KILOMETER

Backscatter, in 0 1 MILE

digital number (DN)

High (255)

Low (0)

EXPLANATION
2525 SECTION 2

Figure 2.6. Subbottom profiles collected with three different systems along the same trackline offshore of 

Murrells Inlet (location shown in figure 2.4). A constant seismic velocity of 1.5 km/s was used to convert traveltime 

to depth. Modified from Baldwin and others (2004). 

A

B

C

TWO-WAY TRAVELTIME, IN MILLISECONDS

 DEPTH, IN METERS BELOW MEAN SEA LEVEL

0

10

20

30

20

0

10

0

10

20

30

0

10

20

30

20

0

10

20

0

10

0 1 KILOMETER

0 1 MILE

Chirp subbottom profile (Benthos SIS-1000; collected in 1999) 

Boomer subbottom profile (Huntec Boomer; collected in 1999) 

Chirp subbottom profile (Edgetech SB-512; collected in 2001)

VERTICAL SCALE GREATLY EXAGGERATED
SECTION 2

26

Figure 2.7. TOP: Aerial photograph of Myrtle Beach (location in figure 2.4) showing transect of ground-penetrating radar profile at Hurl Rock Park. BOTTOM: Profile showing Pleistocene beachrock buried 1 to 2 m beneath the beach. These rocks are episodically exposed when storms erode the surface of the beach (see photograph in figure 4.4B).

Reflections from

Pleistocene beachrock

Holocene beach and dune 

deposits and nourishment fill

Pleistocene beachrock

Holocene beach and dune 

deposits and nourishment fill

DEPTH, IN METERS BELOW MEAN SEA LEVEL0123456

7

N

0 50 100 METERS

FEET 500 250 0

Hurl Rock Park

Benchmark

5320

A A'

A A'

0 METERS

50 FEET

10

0
2727 SECTION 2

2.3. Mapping Shorelines

Sandy shorelines are dynamic systems that 

change in response to natural processes or human 

modifications to the coast. Change is measured by 

comparing shoreline positions at different points in 

time from days to many years apart. The shoreline at 

any particular beach is established from features visible in the field or on aerial photographs (for example, 

wet-dry line, vegetation line), features measured from 

beach profiles (for example, crest of the primary 

dune), or elevation contours extracted from topographic surfaces (for example, mean high water).

Beach Profiling

Beaches in South Carolina have been monitored 

since 1993 by using beach profiles taken at established benchmarks along the entire coast. In its simplest form, a beach profile is constructed by a survey 

crew who use leveling instruments to determine the 

elevation of a series of points along a line. Profiles 

generally begin at the dune, cross the dry beach, and 

end in the surf zone at wading depths of less than 2 m. 

Survey results are presented as a graph of land elevation relative to distance along the profile (fig. 2.8). 

Surveys along the same profile are collected at regular time intervals so that changes in the shape of the 

Figure 2.8. Beach profiles measured at Myrtle Beach (location shown in figure 2.4) over a 10-year period showing changes in 

beach shape. Blue lines represent the beach before and after Hurricane Hugo struck in 1989, causing extensive erosion. The 1997

prenourishment profile shows limited amounts of mobile sediment overlying beachrock and sedimentary rock, which commonly 

were exposed along the beach and shoreface. Later that year, a large amount of new sediment was pumped onto the beach and 

buried the rocky outcrops beneath a wide, sandy berm. Ten years after the nourishment, the beach fill has eroded but continues to 

cover the rocks. See figure 4.5 for location of transect.

-2

0

2

4

6

DISTANCE, IN METERS FROM BENCHMARK 5320

ELEVATION, IN METERS RELATIVE TO MEAN SEA LEVEL

0 50 100 150 200 250

Mobile sand

Beachrock

Sedimentary

rock

Mobile sand

Sedimentary

rock

Myrtle Beach

Benchmark 5320

1989 pre-Hugo

1989 post-Hugo

1997 postnourishment

1997 prenourishment

10-year postnourishment

(2007)
SECTION 2

28

beach can be monitored on a seasonal or yearly basis. 

Changes in beach shape indicate erosion (loss) or 

accretion (gain) of sediment over that time period.

Geologists at Coastal Carolina University and 

USGS have improved traditional beach-profiling 

techniques by extending cross-shore profiles beyond 

wading depths to water depths of about 8 m. Different techniques are used on land and in the water. 

To survey the dry beach, Global Positioning System 

(GPS) navigation receivers are mounted on an allterrain vehicle (ATV) or carried in backpacks on foot. 

Precise position and elevation data are collected at 

low tide while surveyors drive or walk along survey 

lines. To survey in deeper water, surveyors mount a 

fathometer on a small, rigid-hull inflatable boat that is 

precisely tracked by GPS (fig. 2.2B). At high tide, the 

boat drives as close as possible to the beach, thereby 

overlapping the area covered in land-based surveys. 

Data from the two surveys are then merged to form a 

single profile.

Historical Shoreline Analysis

Analysis of field surveys, historical maps, and 

aerial photographs reveals long-term trends in shoreline change (Shalowitz, 1964; Anders and Byrnes, 

1991). A widely used source for establishing historic 

shoreline positions is the National Ocean Service 

(NOS) topographic sheet, or T-sheet. Dating back to 

the mid-1800s, T-sheets are usually the oldest reliable source of shoreline data and provide a long-term 

record for most areas of the U.S. coast. Aerial photographs dating from the mid-1900s help to better 

define long-term trends in shoreline variability. Aerial 

photography allows rapid surveying of large sections 

of coast (fig. 2.9) and thereby provides snapshots of 

the shoreline at more frequent intervals.

In recent years, the use of laser-based techniques 

for mapping topography has revolutionized shoreline 

mapping. LIght Detection And Ranging (LIDAR) 

systems are deployed from airplanes and can rapidly 

survey extensive areas of the coast (fig. 2.2B). LIDAR 

systems bounce a laser beam off the ground hundreds 

of times per second across a wide swath beneath the 

airplane. The time it takes the laser beam to reach the 

ground surface and bounce back (or to be reflected) 

to the airplane is used to calculate elevation. LIDAR 

systems can map hundreds of kilometers of coast in 

a few hours and are able to acquire data every few 

meters (fig. 2.10). The large number of closely spaced 

topographic measurements is used to establish shoreline positions (Sallenger and others, 2003). Frequent 

surveying enables examination of shorter term trends 

in shoreline change, such as the effects of a single 

storm (Stockdon and others, 2002).

2.4. Mapping Sediment Movement

To understand fully how sediment moves within 

the coastal system, scientists placed oceanographic 

instruments on the shallow seafloor offshore of the 

Grand Strand beaches. Current meters, sediment traps, 

wave-height sensors, and other instruments were 

attached to sturdy metal frames (tripods) and anchored 

to the seafloor (fig. 2.11). At regular intervals over a 

six-month period, these tripods collected time-series 

measurements of water flow, sea level, seafloor 

bedforms (ripples), near-bottom turbulence, suspended 

sediment concentrations, salinity, and temperature 

(Sullivan and others, 2005). Supplemental data 

such as wind speed and direction, air temperature, 

barometric pressure, and streamflow measurements 

were also collected.

2.5. Summary

A suite of high-resolution remote-sensing 

and sampling techniques were used to define the 

geologic framework, assess historic shoreline change, 

and identify oceanographic processes influencing 

sediment transport along the Grand Strand. Swathbathymetry, sidescan-sonar, and seismic systems 

describe three primary components of the geologic 

framework, which forms the foundation of the 

coastal system; seafloor topography, the distribution 

of rocks and sediment on the seafloor, and structure 

and composition of underlying geology. Historical 

shoreline analysis allows monitoring of short- and 

long-term trends in shoreline change. Knowledge of 

the geologic framework and shoreline change is used 

to site oceanographic studies that measure winds, 

waves, and currents. This multiphase approach helps 

us to better understand the mechanisms influencing 

coastal change along the Grand Strand.
2929 SECTION 2

Figure 2.9. (A) Diagram showing the flight path for an aerial photographic survey that followed the coastline in 

North Myrtle Beach (location shown in figure 2.4). Surveys were conducted at low tide and consisted of adjacent, 

overlapping photographs to allow for continuous coverage. (B) Example of aerial photograph showing coastal 

development and shoreline morphology at Cherry Grove (location shown in figure 1.3B). (C) Enlarged area of the 

photograph showing prominent features such as the sand fence, wet-dry line, and low-tide line. The wet-dry line is 

typically used to delineate shoreline position on aerial photographs. Successive surveys are compared to assess 

changes in shoreline position over time. Sand fences are constructed of evenly spaced, wooden vertical slats 

approximately four feet in height, and are designed to build sand dunes by trapping wind-blown sand and to protect 

existing dunes and vegetation. 

A

B

C

Cherry Grove

North Myrtle Beach

Survey 

aircraft

Sand 

fence

Wet-dry 

line

Low-tide

line
SECTION 2

30

Figure 2.10. Aerial photographs overlain with Light Detection and Ranging (LIDAR) topography show (A) dense coastal development at Myrtle Beach and (B) undeveloped beach and dunes at Waites Island. Data were collected in 2006 as part of the National Coastal Mapping Program by the U.S. Army Corps of Engineers. Frequent surveys allow geologists to assess short-term change to the shoreline, such as the immediate impact of large storms. Locations shown in figure 1.3B.

100

0

Elevation, in meters above sea level

100

0

Elevation, in meters above sea level

N

N

0 2 KILOMETERS

2 MILES 0

0 2 KILOMETERS

2 MILES 0

EXPLANATION

EXPLANATION

A

B

Waites Island

Hog Inlet

Springmaid Pier

Myrtle Beach Airport

Benchmark5320

Hurl RockPark

Benchmark5260

Myrtle BeachState Park

Benchmark5960

Palace Resort

South Ocean Boulevard

LandmarkResort
3131 SECTION 2

Figure 2.11. (A) Diagram showing oceanographic instruments deployed offshore of Myrtle Beach (locations shown in 

figure 5.5) as part of the South Carolina Coastal Erosion Study (SCCES). The tripod frame and instruments were anchored to 

the seafloor, collecting data at regular intervals over a six-month period. ADCP, Acoustic Doppler current profiler. Modified 

from Bothner and Butman (2007). (B) Graphs showing data for wind speed and direction (top), wave height (center), and 

suspended sediment concentrations in the water column (bottom). Red box indicates a period of strong winds and high 

waves on February 26 to 27, 2004, which mobilized sediment from the seafloor and suspended it in the water column. 

02/08/04 02/15/04 02/22/04 02/29/04

−10

0

10

02/08/04 02/15/04 02/22/04 02/29/04

0

0.5

1

1.5

2

WAVE HEIGHT,

IN METERS

02/08/04 02/15/04 02/22/04 02/29/04

0

50

100

5

10

15

ELEVATION ABOVE 

SEAFLOOR, IN CENTIMETERS

Warm Front Tropical Storm Cold Front

WIND SPEED,

IN METERS PER SECOND

SUSPENDED SEDIMENT 

CONCENTRATION, 

IN KILOGRAMS PER 

CUBIC METER

Tripod

 Approximately 10 meters

ADCP

Currents

Temperature

Salinity

Suspended sediment

concentrations

Waves

Bedforms

Marker buoy

Radar

reflector

Marine light

Not to scale

Strong 

winds

High 

waves

High concentration

of sediment in 

water column

B

A

DATE
32 Section 3: Geologic Framework

3.1. Introduction

The Grand Strand geologic framework consists 

of an ancient sedimentary-rock foundation 

that is overlain by younger unconsolidated sediment 

(fig. 3.1). Unconsolidated sediments measure up to 

30 m thick landward of the shoreline but thin significantly in offshore areas. Modern sediment is largely 

absent across much of the shallow seafloor of Long 

Bay, and exposures of older sedimentary rock are 

common (fig. 3.2). The framework components have 

been eroded to various degrees, and the remains of 

these components provide a fragmented geologic 

record that spans about 70 million years (table 3.1).

3.2. Framework Components

Cretaceous and Tertiary Sedimentary Rocks

The layered succession of sedimentary rocks 

underlying the region was deposited between about 

70 and 55 million years ago during the Cretaceous 

and Tertiary Periods (table 3.1; fig. 3.1A). Fossilized 

remains of marine organisms indicate that the rocks 

were originally deposited as sandy and muddy sediment in continental-shelf settings. Over time, a combination of biochemical and geochemical processes 

cemented the loose particles of sediment together to 

form sandstones, siltstones, and mudstones (fig. 3.3). 

Erosion has sharply truncated the rocks since their 

deposition and created a broad, low-relief surface that 

slopes gently seaward across the region. Locally, rivers and streams eroded deep channels into the rocks 

during times of lower sea level (figs. 3.2, 3.4). These 

paleochannels differ in size and shape (fig. 3.5A), 

indicating that they were formed by different types of 

fluvial systems, including large rivers, small tributaries, marsh creeks, and tidal inlets. The eroded upper 

surface of the rocks represents an unconformity, which 

is a gap in the geologic record caused by a combination of erosion and nondeposition. The unconformity 

represents a time span of about 70 million years in 

locations where Cretaceous rocks crop out on the 

seafloor (fig. 3.2).

Pleistocene Sediment

After the long hiatus represented by the 

unconformity, sediments began to accumulate on top 

of the eroded sedimentary rocks about 1.8 million 

years ago during the Pleistocene Epoch (table 3.1; 

fig. 3.1B). Deeply buried Pleistocene sediments 

consisting of sands and gravels fill the network of 

paleochannels incised into the underlying foundation. 

These channel-fill deposits are truncated by a second 

regionally extensive erosional unconformity which 

has formed in part during the ongoing rise in sea level 

(figs. 3.2, 3.4).

Pleistocene sediments also compose ancient 

shoreline deposits that form the coastal upland landward of Grand Strand beaches (fig. 1.6). These shoreline deposits consist of sediments that accumulated 

in ancient salt-marsh, estuarine, dune, beach, barrierisland, tidal-inlet, and nearshore-marine settings, and 

their preservation is irregular along the coast (fig. 3.2). 

South of Surfside Beach, the old shoreline deposits 

are relatively well preserved landward of modern 

barrier systems such as North, Debordieu, and 

Pawleys Islands. To the north, however, where there 

are no protective barriers, the deposits have been 

eroded landward of the shoreline. Storm-related erosion periodically exposes semiconsolidated parcels of 

the shoreline deposits on the beach and upper shoreface, where they form low-relief pavements in places 

like Hurl Rock Park.

Holocene Sediment

The modern coastal system includes shoreline 

and inner-shelf sediment that is actively moved by 

waves and currents. These mobile, generally sandy 

deposits are composed of Holocene sediment that 

has been accumulating since about 7,000 years ago 

(fig. 3.1C). The deposits lie above the regionally 

extensive erosional unconformity (figs. 3.2, 3.4), so 

they are easily distinguishable from older underlying 

rocks and channel fills. Holocene shoreline deposits 

are distributed unevenly in a narrow wedge along 

the coast (fig. 3.2). South of Murrells Inlet and north 

of North Myrtle Beach, relatively thick and wide 

accumulations form salt marshes, barrier islands, and 

spits that lie seaward of the Pleistocene upland. No 

barrier islands line the Myrtle Beach section of the 
3333 Figure 3.1. The Murrells Inlet area showing the primary components of the Grand Strand geologic framework, from the deepest and oldest to the shallowest and youngest. See figure 3.2 for the location of this area. (A) Layered units of tilted Cretaceous and Tertiary sedimentary rocks underlie the entire coastal system. Relief map shows large channels deeply incised by rivers and streams at times of lower sea level. Elevations are shown relative to mean sea level. (B) Pleistocene channel fills are regionally truncated by a low-relief erosional unconformity. Pleistocene shoreline deposits form the core of the coastal upland. (C) Holocene shoreline and inner-shelf sediments overlie the regionally extensive erosional unconformity. Wedge-shaped shoreline deposits lie above and adjacent to the eroded remains of older Pleistocene shoreline deposits and thin considerably across the shoreface onto the inner shelf. Rocks and channel fills are exposed at the seafloor over extensive areas lacking Holocene sediment cover. Deposits up to 6 m (20 ft) thick are primarily associated with tidal inlets. (D) A composite view of the framework beneath the coastline and seafloor. Black line indicates the location of the seismic-reflection profile in figure 3.4. Red lines in diagrams A–C indicate erosional unconformities. The onshore land image was compiled from 1999 digital-orthophoto quarter quadrangles provided by the South Carolina Department of Natural Resources. D Composite framework ~ 20 km ~ 10 km

~25 meters

VERTICAL EXAGGERATION

Approximately 100 :1 

Profile in Figure 3.4

A Cretaceous and Tertiary sedimentary rocks

Deep

paleochannels

Eroded

upper

surface Dipping rock

layers

Base of Quaternary sediments, elevation in meters relativeto mean sea level

6

Deeper than -21

Murrells

Inlet

B Pleistocene sediment

Pleistocene

shoreline

deposits

Pleistocene

channel-fill

deposits

Holocene sediment thickness, in meters

0.56

C Holocene sediment

Holocene

shoreline

deposits

Holocene

inner-shelf

sediments Exposed 

channel fill

Exposed 

sedimentary

rock

EXPLANATIONEXPLANATION
SECTION 3

34

Figure 3.2. Surficial geologic map and geologic cross sections showing the regional geologic framework of the Grand Strand 

coast and Long Bay inner shelf. The underlying foundation is composed of Cretaceous and Tertiary sedimentary rocks, which 

are incised by deep channels of the ancestral Pee Dee River. Landward of the shoreline (section A–A’), channel-fill deposits 

are overlain by a section of Quaternary shoreline units between about 10 and 30 m thick. On the inner shelf (section B–B’), 

sedimentary rocks and Pleistocene channel fills are regionally truncated by a low-relief erosional unconformity and overlain by

a thin, patchy layer of unconsolidated Holocene sediment. Onshore geology is generalized from McCartan and others (1984) and 

Owens (1989). Offshore geology is from Baldwin and others (2007). Cross section A–A’ is modified from Putney and others (2004), 

and B–B’ is from interpretation of seismic-reflection profiles. The background shaded-relief imagery was constructed by using the 

NOAA-NGDC coastal-relief model. 

Figure 3.1

A A'

Myrtle

Beach Murrells Inlet Waites 

Island Debordieu

Island

0

ELEVATION, IN METERS

RELATIVE TO MEAN

SEA LEVEL

Vertical lines indicate borehole locations and depths

0 5 KILOMETERS

0 5 MILES

VERTICAL EXAGGERATION APPROXIMATELY 200:1

-25

-50

-75

Surfside

Beach North Myrtle

Beach

-5

-10

-15

-20

B B'

Myrtle

Beach Murrells Inlet Waites 

Island

Debordieu

Island

ELEVATION, IN METERS

RELATIVE TO MEAN

SEA LEVEL

0 5 KILOMETERS

0 5 MILES

VERTICAL EXAGGERATION APPROXIMATELY 1,000:1

North

Island

Surfside

Beach

North Myrtle

Beach

B B'

A

A'

33°55' 33°50'

79°00' 78°50' 78°40' 78°30'

33°10' 33°15'

79°20' 79°10' 79°00'

34°00'

78°50'

0 10 KILOMETERS

0 10 MILES

Waites

Island

North

Myrtle Beach

Little 

River

Inlet

Myrtle Beach Surfside Beach

Intracoastal waterway

Murrells

Inlet

Waccamaw River

Great Pee Dee River

Pawleys

Debordieu Inlet

Island North

Inlet Winyah

Bay North

Island

Hog

Inlet

N

Pawleys

Island

Early Tertiary (between approximately 65 and 55 million years old)

Late Cretaceous (between approximately 90 and 65 million years old)

Sedimentary rocks Unconsolidated sediments

Quaternary (approximately 1.8 million years old to present)

Pleistocene (between approximately 1.8 million and 120,000 years old)

Holocene (approximately 10,000 years old to present)

EXPLANATION

Black River

Long Bay
3535 SECTION 3

Table 3.1. Geologic time scale from the Jurassic Period to the 

present day. 

[Stippled patterns indicate long segments of geologic time not represented by 

deposits in the Grand Strand region (that is, times of erosion or nondeposition). 

Simplified from Palmer and Geissman (1999). Ma, million years before present]

Quaternary

Tertiary

Cretaceous

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Period Epoch Age

Jurassic

EraMesozoic Cenozoic

Late

Early

Early

Middle

Late

0.01 Ma

1.8 Ma

5 Ma

24 Ma

34 Ma

55 Ma

65 Ma

144 Ma

206 Ma

99 Ma

159 Ma

180 Ma

coast, where limited amounts of Holocene sediment 

form thin, narrow beaches that are directly attached to 

the eroded mainland.

The wedge of Holocene beach sediment thins 

seaward and forms a discontinuous veneer on the 

shoreface and inner shelf of Long Bay. Holocene 

sediments are less than 0.5 m thick or absent across 

most of the inner shelf (an area of about 530 km2); 

as a result, the seafloor largely consists of broad 

exposures of older rocks and channel-fill deposits 

(figs. 3.2, 3.5B). Inner-shelf sediments generally 

increase in abundance toward the southwest. The 

thickest accumulations (up to 6 m) primarily form 

low-relief linear ridges and shoal complexes that lie 

seaward of modern tidal inlets and estuaries, including 

Little River Inlet, Hog Inlet, Murrells Inlet, Pawleys 

Inlet, North Inlet, and Winyah Bay (fig. 3.5B).

Figure 3.3. Upper Cretaceous 

sedimentary rock excavated 

during engineering work 

offshore of northern Myrtle 

Beach (published by permission 

of James Daigle, Sunland 

Construction, Inc., Eunice, 

Louisiana).
SECTION 3

36

The evolution of the Grand Strand region is 

viewed in the broad context of continental-margin 

development, climate-driven changes in sea level, 

and oceanographic and fluvial processes acting 

along the northeastern South Carolina coast. This 

perspective emphasizes how broad-scale changes in 

the framework have influenced processes that act over 

increasingly small, local scales. The general scales of 

influence over Grand Strand geologic evolution (table 

3.2) are designated in this report as margin, platform, 

and coastal, on the basis of their geographic extent 

and the time periods over which they occurred.

Margin Scale

Margin-scale influences (scales of 1,000 km and 

1,000,000 yr) are related to the position of the Grand 

Strand region within the wider geologic framework of 

the U.S. Atlantic continental margin (table 3.2). The 

Figure 3.4. Seismic-reflection profile offshore of the Murrells Inlet area. TOP: Original data showing vertical slice through the upper 

20 m of the seafloor. BOTTOM: Interpreted profile showing the primary framework components underlying the inner shelf. Location 

is indicated in figure 3.1D. A constant seismic velocity of 1.5 km/s was used to convert two-way traveltime to depth (modified from 

Baldwin and others, 2006). 

3.3. Evolution of the Geologic Framework

The geologic framework underlying the Grand 

Strand has evolved over millions of years of Earth history, and it continues to influence the development of 

the region’s modern coastal system. The present study 

has revealed three basic elements of the framework 

that highlight the most important aspects of Grand 

Strand evolution. First, numerous unconformities and 

extensively eroded geologic units indicate that periods 

of nondeposition and erosion have been frequent and 

prolonged. Second, networks of ancient shorelines and 

deeply-incised paleochannels reveal linkages between 

cyclical sea-level change, fluvial-system evolution, 

and changes in sediment supply. Third, narrow and 

irregularly distributed modern shoreline and innershelf deposits indicate that sediment supply has been 

particularly limited during the Holocene.

0

10

20

0

10

20

VERTICAL EXAGGERATION APPROXIMATELY 150:1

Seafloor

Inlet shoals

DEPTH, IN METERS BELOW MEAN SEA LEVEL

0

10

20

30

0

10

20

30

TWO-WAY TRAVELTIME, IN MILLISECONDS

Regional erosional

unconformity

Dipping sedimentary

rock layers

Data

gaps

Erosional

unconformitiy

Tertiary sedimentary rocks

(approximately 55 million 

years old)

Pleistocene channel-fill sediment

(approximately 1.8 million to

120,000 years old)

Holocene inner-shelf sediment 

(less than 7,000 years old to present)

0

0

1 KILOMETER

1 MILE

EXPLANATION
3737 SECTION 3

Figure 3.5. (A) Topography on top of Cretaceous and Tertiary sedimentary rocks (base of Quaternary elevation) beneath the Grand 

Strand. Elongate depressions (shown in the darkest blue colors) crossing this generally low-relief surface represent paleochannels 

incised by fluvial systems since the Late Pliocene (about 2.1 million years ago). The largest paleochannels were produced by the 

Pee Dee River, which has occupied multiple courses across the region during the geologic past (see figure 3.9). Modified from 

Putney and others (2004) and Baldwin and others (2007). (B) Map showing thickness of Holocene inner-shelf sediments, which 

generally increase in abundance from north to south. Holocene sediments are less than 0.5 m thick or absent over large areas. The 

largest accumulations (up to 6 m thick) generally form shoal complexes that extend seaward from tidal inlets. A notable exception 

is a shore-oblique shoal offshore of Myrtle Beach. Modified from Baldwin and others (2007). The background shaded-relief imagery 

was constructed by using the NOAA-NGDC coastal-relief model and USGS hydrography data.

Long Bay

Long Bay

0 10 KILOMETERS

0 10 MILES

Myrtle Beach

Waccamaw

River Great Pee

Dee River

Great Pee

Dee River

Murrells

Inlet Pawleys

Inlet

Hog

Inlet

Little 

River

Inlet

Waites

Island

Surfside Beach

Myrtle Beach North

Debordieu

Island

North

Inlet North

Island

Intracoastal waterway

Waites

Island

Myrtle Beach Surfside Beach

Intracoastal waterway

Murrells

Pawleys Inlet

Inlet

Debordieu

North Island

Inlet

Winyah

Bay

North

Island

Hog

Inlet

N

33°55' 33°50'

79°00' 78°50' 78°40' 78°30'

33°10' 33°15'

79°20' 79°10' 79°00'

34°00'

78°50'

Myrtle Beach

North

Little 

River

Inlet

0 10 KILOMETERS

0 10 MILES

Waites

Island

Myrtle Beach Surfside Beach

Intracoastal waterway

Murrells

Inlet Pawleys

Debordieu Inlet

Island

North

Inlet

Winyah

Bay

North

Island Hog

Inlet

N

33°55' 33°50'

79°00' 78°50' 78°40' 78°30'

33°10' 33°15' 

79°20' 79°10' 79°00'

34°00'

78°50'

Myrtle Beach North

Little 

River

Inlet

Base of Quaternary sediments,

elevation in meters relative

to mean sea level

Greater than 3

Less than -21

Deep paleochannels

Deep 

paleochannels

EXPLANATION

A

Holocene sediments, 

thickness in meters

0.5

6

B

Shoal

complexes

Linear

ridges

EXPLANATION

Black River Great Pee

Dee River

Waccamaw

River

Black River Great Pee

Dee River

Waccamaw

River
SECTION 3

38

Table 3.2. Three general scales of influence on the geologic evolution of the Grand Strand.

Scale Margin Platform Coastal

Spatial influence U.S. Atlantic Margin (thousands of 

kilometers)

Carolina Platform (hundreds of 

kilometers)

Coastal Zone (less than 

hundreds of kilometers)

Temporal influence Millions of years Tens to hundreds of thousand years Less than ten thousand years

Geologic and geomorphologic influenceMargin basement structures (platforms and embayments); longterm patterns of infill and erosionEmergence-submergence; repeated 

subaerial and marine erosion; Pee 

Dee River migration; changes in 

sediment supply

Coastal landforms and 

morphologies; changes in 

sediment supply

Dominant processes Differential subsidence caused by 

tectonic changes; global climate 

and sea-level changes

Global climate and sea-level changes; 

fluvial, tidal, current, and wave 

energy; differential erosion

Tidal, current and wave energy; 

differential erosion

Grand Strand framework characteristicsPredisposition to sediment limitation; 

shallow, truncated Cretaceous and 

Tertiary sedimentary rocks

Pleistocene shoreline units; paleochannels and fills; erosional unconformitiesHolocene shoreline units; 

modern coastal features; 

erosional unconformities

following description of margin evolution is based on 

studies by Owens and Gohn (1985), Popenoe (1985), 

Popenoe and others (1990), Klitgord and others 

(1988), Riggs and Belknap (1988), and Gohn (1988).

About 210 million years ago the continents of 

North America and Africa began to pull apart, or rift, 

creating a narrow seaway that eventually widened 

to become the North Atlantic Ocean. During rifting, 

the continental crust that formed the margin was 

faulted into a series of coherent blocks. While the 

ocean basin widened, the crustal blocks deformed 

and differentially subsided as they cooled and were 

buried by massive amounts of sediment. These 

tectonic adjustments warped the basement rocks 

into a series of structural highs and lows. The highs, 

called platforms and arches, formed where the 

crust subsided least. The lows, called embayments, 

basins, and troughs, formed where it subsided most. 

Northeastern South Carolina overlies a prominent 

structural high called the Carolina Platform (fig. 3.6). 

Interactions between this structure, global sea level, 

and oceanographic currents have strongly influenced 

patterns of deposition and erosion since the Late 

Jurassic (table 3.1). Sediment deposits are as thick as 

3 km within the adjacent Albemarle and Southeast 

Georgia Embayments but thin to less than 500 m 

across the shallowest, most stable portion of the 

Carolina Platform, which is called the Cape Fear Arch 

or Mid-Carolina Platform High (MCPH).

The Grand Strand region was predisposed to 

long-term sediment limitation early during margin 

development because of its location near the apex 

of the MCPH. The region was a depositional center 

during the Late Cretaceous and early Tertiary, 

when global climate was warm and sea levels were 

generally much higher than present (fig. 3.7A). Thick 

sediments accumulated across calm continental 

shelves, roughly paralleling the topography of the 

underlying structure (fig. 3.6B). Nondeposition and 

erosion became dominant during the Middle to Late 

Eocene (between about 50 and 34 million years 

ago; table 3.1), when an ancient equivalent of the 

Gulf Stream current temporarily flowed across the 

MCPH (fig. 3.6A). The current prevented deposition, 

removed earlier Eocene deposits, and truncated Lower 

Tertiary and Upper Cretaceous units. A cooler global 

climate and the formation of polar ice sheets generally 

lowered sea level throughout the remainder of the 

Tertiary Period (fig. 3.7A). As sea level fell, sediment 

mostly continued to accumulate across the relatively 

low-relief embayments and areas farther seaward, 

while minimal deposition and erosion prevailed across 

the MCPH.

The shallow burial and truncation of sedimentary 

rocks that form the foundation of the Grand Strand 

resulted from the unique history of structural development, deposition, and erosion along this portion of the 

margin. The slight downward tilt, or dip, of the rock 

layers away from the apex of the MCPH reflects how 
3939 SECTION 3

Figure 3.6. (A) Major structure and physiography of the southeast U.S. continental margin. Yellow contour lines indicate depth to the base of Cretaceous sedimentary rocks (adapted from Horton and others, 1991). Seaward-bulging contours indicate relatively thin post-Cretaceous deposits across the Carolina Platform, a major structural high that underlies the coastal plain and continental shelf. The Grand Strand is near the apex of the Mid-Carolina Platform High (MCPH), which is the shallowest, most stable portion of the Carolina Platform. Gray arrows indicate the direction of an ancient ocean current like the modern Gulf Stream that flowed across the MCPH during the Middle to Late Eocene and caused prolonged nondeposition and erosion (generalized from Popenoe, 1985). (B) Geologic cross section constructed from deep-borehole data (black dots #1–9) along the coast (red line in part A). Cretaceous rocks are at or near the surface along the Grand Strand but more deeply buried by younger deposits within the Albemarle and Southeast Georgia Embayments, structural lows that bound the Carolina Platform on either side. Figure adapted from Gohn (1988).

1 2 3 4 5 6 7 8 9

1

2

3

4

5

6

7

8

9

Carol ni a P al t of

mr

Florida

-300

-600

-900 -1,200 -1,500

-300 -600 -900 -1,200 -3,000 -1,500 Albemarle

Embayment

SE Georgia 

Embayment

M

C

P

H

Virginia

Raleigh

Columbia

North Carolina

Georgia Coastal plain

Continental shelf

Fall Line

A t l a n t i c

O c e a n

Albemarle

Embayment

Base of Cretaceousrocks (in meters

Grand Strand region

below mean sea level)

Direction of Middle toLate Eocene Gulf Stream

80o 75o

35o30o

N

Georgia South Carolina North Carolina

Grand

Strand

South East Georgia

Embayment

Albemarle

Embayment

MCPH

Basement rocks

Carolina Platform

0

500

1,000

1,500

DEPTH, IN

METERS

BELOW SEA

LEVEL

DEPTH, IN

METERS

BELOW SEA

LEVEL

0

5001,0001,5002,0002,5003,0003,500

B

Quaternary and late Tertiary(Miocene and Pliocene)Early and middle Tertiary(Paleocene, Eocene, and Oligocene)Late Cretaceous

Early CretaceousLate Jurassic

0 100 KILOMETERS

0 100 MILES

EXPLANATION

EXPLANATION

-300

South Carolina
SECTION 3

40

Figure 3.7. (A) Global sea level and general climate conditions over the past 100 million years. Grey box indicates 

ongoing period of high-frequency sea-level changes caused by ice-volume fluctuations over the past 3 million years. 

(B) Section showing sea level over the last 3 million years enlarged from the graph in part A. Sea-level curves simplified 

from Miller and others (2005); climate and glacial-ice information generalized from Moran and others (2006). Color coded 

bars along the bottom of each part indicate geologic time: Kl, Late Cretaceous; Tp, Paleocene; Te, Eocene; To, Oligocene; 

Tm, Miocene; Tpl, Pliocene; Q, Quaternary; Qp, Pleistocene; and Qh, Holocene.

MILLIONS OF YEARS BEFORE PRESENT

-150

-100

-50

0

50

100

150

100 90 80 70 60 50 40 30 20 10 0

Present sea level

SEA LEVEL, IN METERS RELATIVE TO PRESENT SEA LEVEL

A

Kl Tp Te To Tm Tpl Q

Warmer global climate Cooler global climate

Polar ice sheets

High-frequency

Arctic polar ice

fluctuation

Time period

displayed in

part B

3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2

Qh

Tpl Qp

-140

-100

-80

0

-20

20

40

-40

-60

-120

Present sea level

B

0
4141 SECTION 3

others, 2004; Baldwin and others, 2006). The 

migration was primarily driven by the formation of 

Pleistocene shorelines during periods when sea level 

was higher than at the present time. These ridgelike, elongate landforms were deposited across the 

lower coastal plain over successive submergences, 

and their orientations rotated from generally eastwest to northeast-southwest trends. Each newly 

formed shoreline deflected the river to the southwest 

and forced it to carve a new course during the 

subsequent period of emergence. During the most 

recent highstand of sea level about 120,000 years 

ago, deposition of the Myrtle Beach Barrier caused 

extreme deflection of the river and eventually forced 

it to flow parallel to the shoreline (fig. 3.9). This 

deflection caused the river mouth to move from the 

central part of the Grand Strand near Murrells Inlet 

to its southernmost extent at Winyah Bay and thus 

significantly reduced the role of the Pee Dee River 

as a source of regional sediment supply. During the 

Holocene, sediment transported by the river has 

contributed minimally to shoreline development 

along the Grand Strand because most of it has been 

deposited in Winyah Bay (Hayes, 1994; Patchineelam 

and others, 1999). Beach sediment is now primarily 

supplied through erosion of older geologic units along 

the coast and inner shelf. Dominant southwestward 

sediment transport within Long Bay causes this 

sediment to preferentially accumulate in southern 

parts of the region.

Over the past 3 million years, platform-scale 

changes have profoundly influenced Grand Strand 

evolution. Fluvial systems that incised the network of 

paleochannels into the sedimentary-rock foundation 

caused localized topographic variation across the 

foundation’s otherwise low-relief surface beneath the 

coast and inner shelf (fig. 3.5A). Differential erosion 

across the foundation clearly influenced the spatial 

patterns of this fluvial incision, as Tertiary units south 

of Surfside Beach are more extensively incised than 

the more resistant Cretaceous units to the north 

(fig. 3.2). Additionally, the potential for differential 

erosion increased as more erodible channel-fill 

deposits were embedded across the width of the 

rocky foundation. Alternating periods of subaerial 

and marine erosion caused continual excavation and 

gradually deepened the regional unconformity that 

defines the upper surfaces of channel-fill deposits 

and sedimentary rocks. Although this long-term 

their deposition generally conformed to the underlying structural trend (figs. 3.4 and 3.6B). The rocks are 

rather erosion resistant, but cementation differs from 

layer to layer. Truncation has exposed the dipping layers as parallel units across the surface of the foundation. As a result, erosional resistance differs slightly 

across the width of the rocky foundation because 

weakly cemented units are more susceptible to erosion 

than adjacent, well cemented units.

Platform Scale

Platform-scale changes (scales of 100 km and 

10,000–100,000 yr) have occurred as fluctuations in 

sea level forced shoreline migrations back and forth 

across the Carolina Platform (table 3.2). Since about 

3 million years ago (during the Pliocene Epoch; 

table 3.1), changes in the volume of Arctic polar ice 

sheets have caused sea level to repeatedly rise and fall 

as much as 25 m above and 120 m below its present 

elevation (fig. 3.7; Box #1). During times of lower sea 

level, the exposed coastal plain and continental shelf 

underwent broad subaerial erosion and deep fluvial 

incision while shoreline deposits accumulated at lower 

elevations seaward of the modern coast (fig. 3.8). 

When rising sea level submerged the coastal plain 

over relatively brief periods, the shoreline was forced 

to migrate landward and develop at higher elevations. 

As the shoreline migrated back and forth, wave and 

current energy continually eroded coastal landforms, 

redistributed sediment, and generally flattened the 

landscape. The history of these emergences and 

submergences is partially preserved across the 

coastal plain in a series of remnant shoreline deposits 

(fig. 1.6; Colquhoun and others, 1991; Colquhoun, 

1995). The ancient shorelines were deposited during 

submergences that reached progressively lower 

elevations over time, and thus decrease in age and 

elevation toward the modern coast.

Coastal deposits across northeastern South 

Carolina are primarily composed of sediment supplied 

by the Pee Dee River, which has transported large 

volumes of material eroded from the Blue Ridge 

Mountains, Piedmont, and coastal plain to the 

coast (Brown, 1980; Meade, 1982; Hayes, 1994). 

Seven groups of large paleochannels underlying 

the Grand Strand record a regional southwestward 

migration of the Pee Dee River between the Late 

Pliocene and present (figs. 3.5A, 3.9; Putney and 
SECTION 3

42

Figure 3.8. A three-phase conceptual model showing evolution of the Grand Strand region over a cycle of emergencesubmergence driven by relative sea-level changes. Diagrams illustrate shoreline migration seaward and landward across 

the coastal plain and continental shelf. (A) Initial sea level is high; stable shoreline deposits develop at relatively high 

elevation. (B) Sea level falls and shoreline migrates seaward. Inner shelf emerges, leaving older shoreline stranded high on 

the coastal plain. Unconformity produced by broad subaerial erosion and deep fluvial incision of the exposed coastal plain. 

(C) Sea level rises and shoreline migrates landward. Eroded remnants of lowstand shoreline stranded on the continental 

shelf. Erosion by waves and currents generally flattens the landscape and partially truncates older highstand shoreline. As 

sea level stabilizes, shoreline deposits accumulate at higher elevations and cause river mouth to migrate downdrift.

A Initial sea level

Shoreline 

position 1 Inner-shelf

deposition

Sea level 1 

Sea level 3

Sea level 2 

B Lowered sea level—emergence

Seaward migration of shoreline

and coastal-plain emergence

Landward migration of shoreline

and coastal-plain submergence

Stranded ancient

shoreline 

Shoreline

position 2

Deep fluvial

incision Subaerial erosion

Not to scale

C Elevated sea level—submergence

Shoreline

position 3 Paleochannel

fill Eroded, flattened

shoreline remnant

 Partial truncation

of ancient shoreline

Marine erosion

River deflected

in downdrift

direction

Continental shelf

Coastal

plain
4343 SECTION 3

erosion tended to flatten the landscape, some subtle 

topography remains across the unconformity. It is 

notable that younger channel fills south of Murrells 

Inlet are less flattened than older features to the 

north because they have undergone fewer periods 

of emergence and submergence (fig. 3.2). Except 

for channel-fill deposition, the Grand Strand mostly 

underwent erosion or nondeposition until about 

400,000 years ago. Since that time, successive 

submergences culminated at elevations near the 

present shoreline and resulted in the consecutive 

deposition and partial erosion of Pleistocene shoreline 

units that compose the coastal upland and Holocene 

shoreline units that form the modern coast (figs. 3.2, 

3.9). Over this time period, platform-scale influences 

overlapped with smaller, coastal-scale influences 

and caused the late Pleistocene shift in the dominant 

mode of regional sediment supply. The shift from a 

high-volume fluvial source supplied by the Pee Dee 

River to a lower volume erosional source supplied 

by coastal and inner-shelf erosion has strongly 

influenced subsequent coastal-scale changes, which 

have determined the distribution, configuration, and 

preservation of shoreline units along the Grand Strand.

Figure 3.9. Perspective view of the Grand Strand region towards the northwest. Arrows indicate changing locations of the 

Pee Dee River over time (generalized from Baldwin and others, 2006). Progressive, southwestward deposition along ancient 

shorelines gradually deflected the river toward the southwest. Older (more landward) shorelines initially trended east-west, but 

rotated to northeast-southwest as they were deposited progressively closer to the modern coastline. Shaded relief of the regional 

surface defining the base of Quaternary sediments (also displayed in figure 3.5A) shows that the river carved at least seven 

distinct courses across the region prior to arriving at its current configuration, which flows through Winyah Bay. The backgroundshaded relief imagery was constructed by using the NOAA-NGDC coastal-relief model. 

N

Pee Dee River system migration and coastal-plain shoreline deposits

EXPLANATION

Group 1 (North Myrtle Beach)

Group 2 (Atlantic Beach)

Group 3 (Cane North)

Group 6 (Pawleys Island)

Group 7 (North Island)

Modern

Group 4 (Cane South)

Group 5 (Murrells Inlet)

Group 1 Group 2

Group 3 Group 5 Group 4

Group 6 Group 7

Modern

Base of Quaternary sediments, elevation, 

in meters relative to mean sea level

Greater than 3 Less than -21

Horry

Barriers

Daisy Strand

Barriers

Kingstree Barriers

Conway 

Barriers

Cainhoy Barriers

Pleasant Hill Barriers

Jaluco

Barriers

Myrtle Beach Barriers

Myrtle Beach

Barriers

Myrtle Beach Barriers

Cainhoy Barriers

Little Pee Dee River

Great Pee Dee River

Great Pee Dee River

Holocene

0 10 KILOMETERS

0 10 MILES
SECTION 3

44

Coastal Scale

Coastal-scale changes (scales less than 100 km 

and 10,000 years) occur as rivers and streams, winds, 

waves, and currents expend energy across the coastal 

upland, beach, and nearshore-marine zone (table 3.2). 

These processes create and modify coastal features 

such as barrier islands, spits, tidal inlets, marshes, and 

mud flats, as well as sand ridges and shoals on the 

inner shelf. Significant coastal deposition has occurred 

across northeastern South Carolina only when sea 

level has been relatively high, like today, and slowly 

rising or falling. During these periods of relative 

stability, the development of coastal features is determined by the interaction among nearshore processes 

(wave and current energy), sediment supply, and 

preexisting geologic framework. Progressive southwestward deposition along the shorelines of northeastern South Carolina suggests a consistent, long-term 

pattern of domination by wave-driven currents and the 

resulting longshore transport of sediment. This pattern has apparently remained constant over periods of 

submergence since the Pleistocene. The growth of the 

North Island spit across the mouth of Winyah Bay and 

the concentration of inner-shelf sediment across the 

southern portion of the region (fig. 3.5B) show that 

these southerly directed, sediment-transport processes 

continue to dominate today.

Like older Pleistocene shorelines across the lower 

coastal plain (fig. 1.6), the late Pleistocene Myrtle 

Beach Barrier is expansive compared to the Holocene 

shoreline units that line the modern coast (fig. 3.9). 

The Myrtle Beach Barrier formed while sediment 

transported by the Pee Dee River was delivered to the 

central portion of the Grand Strand, where it could be 

distributed over a large portion of the coastline. After 

the mouth of the Pee Dee River migrated southward 

in the late Pleistocene, its importance as a sediment 

source was significantly diminished. The river now 

discharges into Winyah Bay, and little to none of 

the sediment that it delivers reaches adjacent Grand 

Strand beaches. As a result, the modern coastal system 

is sand limited with thin layers of Holocene shoreline and inner-shelf sediment perched on top of older 

geologic units. The conditions and extents of shoreline 

units along the Grand Strand coast clearly illustrate 

the dominant effects of wave and current energy after 

the late Pleistocene shift in sediment supply 

(figs. 3.2, 3.9). Older shoreline deposits that lie 

behind the modern beach have been significantly 

eroded north of Surfside Beach. Predominant southwestward longshore transport has generally prevented 

sediment deposition along this portion of the coast, 

and only thin Holocene beaches have developed. In 

contrast, the Myrtle Beach Barrier is well preserved 

south of Surfside Beach, where it has been protected 

by modern barrier islands and spits.

Large, well developed shorelines formed during 

periods of relatively high sea level when abundant 

sediment was delivered to Long Bay by the ancestral 

Pee Dee River. As each successive shoreline formed, 

topographic relief on the lower coastal plain increased 

and thereby enhanced the difference in slope between 

the coastal plain and the adjacent, flat-lying inner 

shelf. Longshore topographic variability has influenced the shapes of successive shorelines. Waves and 

currents have differentially eroded the old shorelines 

and redistributed sediment across lower lying areas. 

Shorelines have preferentially eroded adjacent to 

locations where paleochannel fills are embedded into 

the underlying sedimentary-rock foundation, and this 

erosional pattern has regionally controlled coastal 

drainage patterns (fig. 3.2). Salt-marsh creeks and 

coastal swashes that occupy these depressions drain 

runoff from higher areas of the coastal upland, and 

tidal inlets allow for vigorous exchange of tidally 

driven flow between the depressions and the coastal 

ocean. The largest accumulations of Holocene innershelf sediments also overlie embedded paleochannel 

fills because of a combination of inner-shelf erosion 

and the tendency of adjacent tidal inlets to 

concentrate sediment. 
4545 SECTION 3

3.4. Summary

Despite being primarily composed of eroded 

geologic units that provide a fragmented record, the 

Grand Strand geologic framework embodies a wealth 

of information about how geologic, oceanographic, 

and fluvial processes have influenced its long- and 

short-term evolution. The present coast has been 

shaped by the cumulative effect of these processes, 

which have acted over very different spatial and 

temporal scales. The scales of these interrelated 

processes can be placed into three broad categories: 

margin, platform, and coastal. 

At the margin scale, the Grand Strand has been 

predisposed to sediment limitation over millions of 

years because of its location within the structural 

configuration of the U.S. Atlantic continental margin. 

At the platform scale, widely fluctuating sea levels 

between the Late Pliocene and present have caused 

alternating periods of subaerial and marine erosion. 

At the coastal scale, nearshore marine processes 

have forced the southwestward migration of the 

Pee Dee River; this shift diminished its role as the 

dominant source of regional sediment supply. As 

coastal processes continued to shape the region 

during the Holocene, erosion of shoreline and innershelf deposits became the more important mode of 

regional sediment supply. Driven by coastal wave 

and current energy, predominant southwestward 

sediment transport has generally prevented significant 

deposition along the northern and central portions of 

the Grand Strand and caused concentrated deposition 

in the southwestern part of the region. Differential 

erosion across the geologic framework has influenced 

the distribution and extent of coastal features and 

the overall shape of the shoreline. The geologic 

framework continues to control coastal evolution as 

sea level slowly rises, and coastal processes continue 

to erode sediments along the coast and inner shelf.
46 Section 4: Shoreline Change

4.1. Introduction

Dry sandy areas such as the berm and dunes 

represent only a small part of the active 

beach system. Most sediment movement occurs 

underwater on the shoreface, a narrow, relatively 

steep surface seaward of the low tide line (fig. 1.2). 

This energetic zone extends offshore to deeper water 

where waves and currents generally do not move 

sediment. The width and depth of the shoreface vary 

along the coast, depending on wave climate, sediment 

supply, and the nature of the underlying geology. The 

overall shape of the beach/shoreface system changes 

seasonally as eroded sediment is stored offshore during stormy weather and later returned to the beach in 

fair weather. 

The rates of shoreline retreat and the responses 

of a beach to storms largely depend on the geologic 

framework of the shoreface that is being excavated 

by ocean processes. Coastal engineers who design 

stabilization or nourishment projects typically assume 

that the shoreface is a pile of loose sediment with 

a uniform grain size. In their forecasts of beach 

behavior, waves acting on this idealized shoreface 

produce a predictably smooth, concave-up profile 

of equilibrium that retains its general shape as the 

shoreline changes position (Dean, 1991; Thieler 

and others, 2000a). In South Carolina, however, 

framework components beneath the shoreface widely 

differ in their resistance to erosion. Assuming that 

physical and biological processes are uniform across 

the region, we can reasonably expect a greater rate of 

change where less resistant materials (that is, loose 

sandy sediment) underlie the shoreface (Park and 

others, 2009). Conversely, a section of coast underlain 

by more resistant materials (that is, sedimentary rock) 

is likely to be relatively stable. 

4.2. Beaches on the Move

Shoreline change over different time scales is 

quantified by comparing a series of maps, aerial 

photographs, or physical surveys made months, years, 

or decades apart (fig. 4.1). The measured shoreline 

has been variously defined as a specific contour 

elevation (that is, mean high water), a wet-dry line 

visible on aerial photographs, or a surveyed crest of 

the primary dune. Lateral movement of a shoreline 

over a specified period of time is typically shown as 

a series of colored-coded bands on a map (fig. 4.2A). 

Maps of this type reduce a complex coastal system to 

a single line when, in fact, the active beach covers a 

broad zone that extends a distance both landward and 

seaward of the shoreline. Accurate data are difficult 

to collect from submerged parts of the beach system 

where waves and currents are energetic. Most landbased surveying techniques end in shallow wading 

depths of about 1.5 m, and marine-based surveys 

stay well offshore of the surf zone where ships can 

safely navigate. As a result, considerable areas of the 

active beach are poorly represented in most coastalerosion studies. Early studies typically provided only 

long-term trends because they relied on sparse data 

generated over many years. Beach profiles were collected more often, usually once or twice per year, but 

localized areas of high erosion rates commonly went 

undetected in gaps between widely spaced profiles.

Rates of shoreline change have varied widely 

along the Grand Strand since the middle of the 

19th century (Hubbard and others, 1977a, 1977b; 

Anders and others, 1990; Morton and Miller, 2005). 

To quantify these changes better, the SCCES compiled 

several sources of data into a geographic information 

system (GIS). Paper maps originally produced 

by Anders and others (1990) were digitized and 

rectified to provide shoreline positions from 1851 to 

1983. Shorelines determined from annual airborne 

topographic surveys (see Section 2) between 1996 

and 2000 were provided by NOAA. Shoreline-change 

rates were calculated over two time scales, historical 

and short term (fig. 4.2). Mainland-attached beaches 

have remained relatively stable, with rates of retreat 

generally less than 0.5 m/yr. Barrier islands, however, 

have undergone large shifts in shoreline position, 

especially deposits in the vicinity of tidal inlets 

because they commonly migrate along the coast in 

response to longshore currents. Inlet migration causes 

alternating periods of accretion and erosion on the 

ends of adjacent barrier islands. In addition, new inlets 

open and old inlets close over time. Moving landward 

and seaward at rates up to 10 m/yr since the 1850s, 

segments of shoreline adjacent to large inlets (North, 

Murrells, and Little River Inlets) have changed the 

most. Because of this dynamic process, construction 

and other activities planned for areas adjacent to inlets 

are managed differently by the State than activities in 

areas not influenced by inlets (see Section 1, Box #3).
4747

Figure 4.1. Aerial photograph showing historical shorelines from 1856 to 1983 around 

Waites Island and Little River Inlet. Shore-normal transects (gray lines), starting at a base 

line 500 m offshore (red line) and extending inland for 2,000 m, were drawn every 25 m along 

the coast. Where a transect intersected a former shoreline position (colored dots), the 

distance from the base line was used to calculate the average rate of shoreline change over 

that time period. See figure 4.2 for location.

1969

1962

1923

1856

1933

1983

1933

base line

N

Little River

Inlet

Waites Island

1 KILOMETER

1 MILE

0

0 Transects

Former shorelines

(colored dots) and year

EXPLANATION
SECTION 4

48

Figure 4.2. (A) Map view of the Grand Strand showing rates of shoreline change as color-coded bands parallel to the 

coast. Historical rates were based on shoreline positions derived from maps, charts, and air photographs. Short-term 

rates were based on shoreline positions measured by LIDAR surveys. Rates were calculated by using the linear rate-ofregression method (Thieler and others, 2003), which runs a best-fit line through all available data points. (B) Graph showing 

historical rates of shoreline change (green line) from the 1850s to 1980s. Highest rates of change were in the vicinity of 

inlets; lowest rates were along mainland-attached beaches. Standard error (red line) of the measurements indicates 

variability in shoreline positions through time. If the shoreline at a particular area shows high variability (that is, it moves 

back and forth a lot), standard error is high. Shoreline positions have higher variability along inlets and barrier islands, and 

lower variability along mainland-attached beaches. (C) Graph showing short-term rates of shoreline change between 1996 

and 2000. Shoreline positions along smaller inlets, swashes, and the beach nourishment project at Myrtle Beach show the 

largest amount of variation at this time scale.

Short-term rates (1996–2000)

A

Murrells

Inlet

Winyah

North Inlet

Bay

North

Island

RATE OF SHORELINE CHANGE,

IN METERS PER YEAR

-8.0

-10.0

-4.0-2.0-1.0-0.5-0.3-0.1

0.00.10.30.51.02.04.08.0

10.0

Landward (erosion) Seaward (accretion)

Long Bay

10 KILOMETERS

10 MILES

0

0

Historical rates (1850s to 1980s)

Myrtle Beach

(Figure 4.5)

Waites Island

(Figures 4.1 and 4.6)

33°55' 33°50'

79°00' 78°50' 78°40' 78°30'

33°10' 33°15'

79°20' 79°10' 79°00'

34°00'

78°50'
4949 SECTION 4

0 10 20 30 40 50 60 70 80 90 100

15

10

5

0

-5

-10

-15

spit barrier islands

North

Inlet

Murrells

Inlet

mainland-attached beaches barrier islands

50

45

40

35

30

25

20

15

10

5

0

Little River

Inlet

swashes

0 10 20 30 40 50 60 70 80 90 100

RATES OF SHORELINE CHANGE, 

IN METERS PER YEAR

0

20

40

60

80

100

-20

-40

-60

-80

-100 0

100

200

300

400

500

600

700

800

900

STANDARD ERROR,

IN METERS PER YEAR

beach

nourishment

B

C

DISTANCE FROM WINYAH BAY, IN KILOMETERS

STANDARD ERROR,

IN METERS PER YEAR

RATES OF SHORELINE CHANGE, 

IN METERS PER YEAR
SECTION 4

50

shallow submerged areas adjacent to the beach 

(fig. 4.3). The lower shoreface at Myrtle Beach, 

measured at the 6-m depth contour, has migrated 

landward at an average rate of 0.8 m/yr. At Waites 

Island, the 5-m depth contour has migrated landward 

at an average rate of 2.3 m/yr. As a result, nearshore 

water depths at these locations are slowly increasing, 

and beach profiles are becoming steeper over time. 

Steepening at Myrtle Beach can be attributed to beach 

nourishment pushing the upper profile seaward and 

erosion driving landward migration of the lower 

shoreface, albeit slowed by the presence of hard rocky 

substrate. The cause of steepening at Waites Island is 

not known but might be related to sediment trapping 

by jetties at Little River Inlet. Whatever the cause, 

as water depths in front of a beach increase, wave 

impacts on the shoreline also increase.

4.4. Framework Controls on Beaches

Grand Strand beaches sit on top of a framework 

of layered sedimentary rocks, which have been deeply 

eroded over the last few million years (see Section 3). 

The upper surface of these units is widely exposed on 

the shoreface and inner shelf, especially offshore of 

mainland-attached beaches in the central part of the 

study area. The erosion-resistant materials lie at shallow depths beneath the region’s beaches (fig. 4.4A) 

and provide firm foundations for high-rise buildings. 

Outcrops of cemented beach deposits are also sporadically exposed and buried by movement of modern 

beach sands at Hurl Rock Park in Myrtle Beach 

(fig. 4.4B). Near tidal inlets in the northern and southern parts of the Grand Strand, however, thicker deposits of modern sediment completely bury the rocks.

The shoreface profile and stability of beaches 

over time are very different where sediment is abundant, such as Waites Island, relative to areas where 

sediment is scarce, such as Myrtle Beach. The following sections describe representative examples of 

sediment-limited and sediment-rich areas of the Grand 

Strand. In these two examples, the relative abundance 

of modern sediment on the shoreface determines the 

overall shape of adjacent beaches and local rates of 

coastal erosion.

4.3. Monitoring South Carolina’s Beaches

In 1993 the USGS, OCRM, and SCSGC formed 

a cooperative program to survey beaches statewide. 

The program, named Project BERM (Beach Erosion 

Research and Monitoring), has developed new 

methods to document change across the entire active 

beach (see figure 1 and Section 2.3). Frequent surveys 

(up to four times per year at selected locations) of 

beach shape have revealed short-term fluctuations that 

aid in constructing a record of seasonal and chronic 

changes. The ongoing program has continued to 

characterize the coast on a regional scale through at 

least 2008. More information on shoreline change 

can be found at the Project BERM web site 

http://www.coastal.edu/cmws/berm/index.html.

Beach profiles vary in shape along the length of 

the Grand Strand, largely depending on the volume of 

sediment available in a particular location. Beaches 

with little sediment exhibit steeper, more irregular 

profiles relative to beaches with abundant sediment. 

Representative profiles at two sites were chosen to 

illustrate the differences in profile shape:

1. Along the central Grand Strand at Myrtle Beach, 

the beach system is sediment limited. Older rocky 

deposits are exposed as ledges and scarps that 

create subtle relief on the shoreface. The beach 

profile is relatively steep, and water depths are 

more than 6 m at a distance of 342 m offshore of 

the +1-m contour (fig. 4.3A).

2. Along the northern Grand Strand at Waites Island, 

the beach system contains abundant loose sediment. Sediment shoals near the ends of the island 

are related to Hog and Little River Inlets. The 

beach profile is less steep than at Myrtle Beach, 

and water depths are about 6 m at a distance of 

849 m offshore of the +1-m contour (fig. 4.3B).

Average rates of shoreline retreat from the 1850s 

to the 1980s are 0.2 m/yr at the site of the Myrtle 

Beach profile and 0.9 m/yr at the Waites Island profile 

(fig. 4.2). Even though long-term shoreline movement 

has been relatively slow, profiles collected 14 years 

apart show that more rapid changes are occurring in 
5151 SECTION 4

Figure 4.3. (A) Typical profile at Myrtle Beach is relatively steep and interrupted by rocky ledges and scarps. 

This area was nourished in 1998, and a small wedge of beach fill remains visible in the 2007 profile. (B) Typical 

profile at Waites Island is more gently sloping because of abundant sand associated with inlet shoals. The 

profile has steepened in both locations because of continued erosion and landward migration (that is, retreat) of 

the middle to lower shoreface (red arrows). See figures 4.5 and 4.6 for locations of the profiles.

-2

0

2

4

-4

-6

-8

6

Waites Island, Benchmark 5960

0 100 200 300

Beach profiles (year surveyed)

Northern Grand Strand:

Sediment-rich framework

Sandy shoals

400

DISTANCE, IN METERS

Myrtle Beach, Benchmark 5340

0 100 200 300

6

1993

2007

Central Grand Strand:

Sediment-limited framework 

Hardbottom with

ledges and scarps

Beach profiles (year surveyed)

B

A

Beach fill

Frontal dune

400

1993

2007

At the -6 meter contour, 

average rate = -0.7 months per year

(retreated 10 meters in 14 years)

At the +1 meter contour, 

average rate = +2.0 months per year 

(advanced 28 meters in 14 years)

At the +1 meter contour, 

average rate = -0.3 months per year

(retreated 4.3 meters in 14 years)

At the -5 meter contour, 

average rate = -1.6 months per year

(retreated 22 meters in 14 years)

ELEVATION, IN METERS -2

0

2

4

-4

-6

-8
SECTION 4

52

Central Grand Strand: Sediment-Limited 

Framework 

The central part of the Grand Strand, occupied in 

part by the City of Myrtle Beach, is one of the longest 

stretches of seaboard that is not protected by barrier 

islands in the eastern United States. For a distance of 

more than 50 km, open-ocean processes act directly 

on the mainland. Landward of the beaches, adjacent 

upland elevations rise quickly to more than 

10 m above local mean sea level, putting most of the 

city above the flood zone. Average rates of shoreline 

change in this area are relatively low, except around 

swashes where the shoreline is migrating across 

small fluvial valleys that drain the adjacent upland 

(fig. 4.2B). The relative stability of the Myrtle Beach 

coastline is largely controlled by sedimentary rock and 

erosion-resistant deposits of ancient shorelines that 

underlie the area. 

The central Grand Strand area represents an endmember shoreline segment where older sedimentary 

rocks dominate the shoreface. Offshore of Myrtle 

Beach, the shoreface is characterized by a series of 

low-relief scarps and ledges formed by layers of rock 

exposed at the seafloor. Subbottom profiles collected 

along the beach just seaward of the surf zone show 

that rocks also compose the shallow subsurface 

(fig. 4.5, profiles A–D). The shape and position of the 

beach and shoreface change relatively little in areas 

where modern processes act on these erosion-resistant 

deposits. This area has exhibited only modest changes 

in beach profile during large erosional events such 

as Hurricane Hugo in 1989 (Nelson, 1991) and during the years following such storms (fig. 2.8). The 

most significant change resulted from a regional 

beach-nourishment project in 1997 that pumped large 

amounts of sediment from borrow sites offshore onto 

the beach. At that time (prior to the SCCES), little 

information on the location and volume of offshore 

sediment resources was available to guide dredge 

operations. Instead of hitting soft sediment, dredges 

often scraped rocky parts of the seafloor even though 

large deposits of high-quality sand existed nearby.

Figure 4.4. (A) Large boulders excavated during construction 

of stormwater outfall near 52nd Avenue North, Myrtle Beach 

(published by permission of James Daigle, Sunland Construction, 

Inc., Eunice, Louisiana). The boulders came from rocky deposits 

at shallow depths beneath Grand Strand beaches. (B) Rocks 

indicated by arrows exposed by beach erosion at Hurl Rock 

Park, Myrtle Beach (published by permission of Paul Gayes, 

Coastal Carolina University, Conway, South Carolina.) Sediment 

removed by storms typically returns in times of fair weather and 

rebuilds the beach.

B

A
5353 SECTION 4

Figure 4.5. Shoreface geology along the central Grand Strand at Myrtle Beach. Perspective view shows a complex pattern of 

acoustic backscatter on the shallow seafloor (top). High backscatter (light shades) generally indicates coarse sand, gravel, and rock. 

Low backscatter (darker shades) generally indicates sandy or muddy sediment. Interpreted subbottom profiles A–A’, B–B’, C–C’, and 

D–D’ show the geologic framework underlying the shoreface. See figure 4.2A for location.

0

10

20

DEPTH, IN METERS

BELOW MEAN SEA LEVEL

0

10

20

DEPTH, IN METERS

BELOW MEAN SEA LEVEL

A B C D

C

0

10

20

DEPTH, IN METERS

BELOW MEAN SEA LEVEL

D

0

10

20

DEPTH, IN METERS

BELOW MEAN SEA LEVEL

B

A'

B’ C’ D’

no data

AA

BB CC DD

Smooth shoreface

underlain by

channel-fill deposits

Irregular shoreface

underlain by rock

Channel-fill deposits

(1.8 million to 10,000 years old)

Sedimentary rock

(approximately 70 million 

years old)

Modern sediment

(less than 10,000 years old)

Irregular shoreface

underlain by rock

A' A'

Myrtle Beach Airport Myrtle Beach Airport

Beach profile

(Figure 2.8)

Beach profile

(Figure 2.8)

VERTICAL EXAGGERATION APPROXIMATELY 50:1

Beach profile

(Figure 4.3A)

Beach profile

(Figure 4.3A)

N

B’ B’ C’ C’ D’ D’

EXPLANATION

0 1 KILOMETER

0 1 MILE

500 METERS

1,500 FEET

0

0

VERTICAL EXAGGERATION APPROXIMATELY 10:1

200 METERS

600 FEET

0

0

200 METERS

600 FEET

0

0

200 METERS

600 FEET

0

0
SECTION 4

54

construction at Little River Inlet. Sediment captured 

by the jetties has accumulated along the north end 

of the island. The mid-to-lower shoreface, however, 

has not grown seaward in the same way as the upper 

beach. Measured at a depth of 5 m, the shoreface has 

progressively migrated landward, thereby creating a 

steeper slope over time.

4.5. Exposure and Burial of Hardbottom 

Areas

Sediments that compose the shoreface of the 

Grand Strand vary in thickness and constantly shift 

across an irregular, rocky surface. In the short term, 

fair-weather conditions promote landward transport 

of sediment from the lower shoreface to the upper 

shoreface and beach system. The wide, elevated berm 

formed by these mobile sediments remains dry at 

mean high tide and is a favorite spot for beachgoers. 

Just offshore, however, sediment is scarce, and rock 

is exposed on the shallow seafloor (fig. 4.7). Erosion 

of these exposed hardbottoms provides relatively 

small but significant quantities of new sediment that 

is incorporated in the active beach (Riggs and others, 1998). Over the long term, repeated cycles of 

exposure wear down the erosion-resistant rocks of the 

shoreface and effectively increase water depths just 

offshore of the beach.

During storms, waves and currents remove 

sediment stored in the dunes and beach and transport 

it offshore (fig. 4.7). The seasonal movement of 

sediment away from the beach temporarily buries 

the hardbottom areas on the shoreface. Stripped of 

sediment cover, the rocks on the upper shoreface 

are eroded and contribute some new sediment to the 

active beach. When fair weather returns, sediment on 

the shoreface is driven back onto the upper shoreface 

and beach, reestablishing the berm and dunes. This 

onshore-offshore shifting of sediment alternately 

buries and exposes rocks on the beach and shoreface. 

The balance of this process, along with gains and 

losses from longshore transport, determines whether 

there is erosion or accretion of a particular stretch of 

beach. As a result of this constant shifting, the beach 

and its underlying rocky foundation wear away, and 

the beach and shoreface migrate landward as a system.

Low-relief rocky outcrops do not characterize 

the entire shoreface of the central Grand Strand. In 

some areas, the cross-shore beach profile is much 

smoother and steeper than in adjacent rocky areas; the 

smooth profiles coincide with the locations of ancient 

river channels eroded into older sedimentary rocks 

(fig. 4.5, profile C). Deposits filling the channels are 

younger, relatively weaker, and therefore less resistant 

to erosion than sedimentary rock. The smooth, steeply 

sloping shoreface reflects the relative ease by 

which channel-fill deposits can be eroded by waves 

and currents. 

Northern Grand Strand: Sediment-Rich 

Framework

At the northern and southern ends of the Grand 

Strand, barrier islands have formed instead of the 

mainland-attached beaches that characterize the 

central section. Waites Island, at the northern end 

(fig. 4.2A), is the first in a chain of small barrier 

islands that extend north along the coast of Long Bay 

to Cape Fear, North Carolina. Sandy barriers of similar shape and size also extend south from Garden City 

to Winyah Bay. As is typical for barrier islands, their 

shape and behavior are strongly influenced by waves 

hitting the beach and tidal currents moving in and out 

of inlets. 

Unlike areas closer to the center of the Grand 

Strand, the shoreface and inner shelf along Waites 

Island contain abundant sand. Erosion-resistant 

sedimentary rocks are more deeply buried by 

Holocene sediment at this location (fig. 4.6). The 

shape and position of the shoreline are strongly 

modified by storage of modern sediment in tidal 

shoals associated with Little River and Hog Inlets. 

The inlet-related sand bodies are up to 6 m thick and 

together represent one of the largest accumulations of 

modern sediment along the coast. 

The shoreface along Waites Island generally 

forms a smooth concave-up profile, the characteristic 

shape of beaches with abundant mobile sediment 

(fig. 4.3B). Along most of the island, significant 

amounts of sediment have accumulated in the upper 

beach system. Beach ridges have expanded seaward 

over the last 20 years, probably because of jetty 
5555 SECTION 4

Figure 4.6. Shoreface geology along the northern Grand Strand at Waites Island. Perspective view shows a 

complex pattern of acoustic backscatter on the shallow seafloor (top). High backscatter (light shades) generally 

indicates coarse sand, gravel, and rock. Low backscatter (darker shades) generally indicates sandy or muddy 

sediment. Interpreted subbottom profiles A–A’ and B–B’ show the geologic framework underlying the shoreface. 

See figure 4.2A for location.

0

10

20

0

10

DEPTH, IN METERS

20

BELOW MEAN SEA LEVEL

0 B

10

20

0

10

20

DEPTH, IN METERS

BELOW MEAN SEA LEVEL

DEPTH, IN METERS

BELOW MEAN SEA LEVEL

DEPTH, IN METERS

BELOW MEAN SEA LEVEL

A

no data

AA

BB

Channel-fill deposits

(1.8 million to 10,000 years old)

Sedimentary rock

(approximately 70 million

years old)

Modern sediment

(less than 10,000 years old)

A’ Beach profile

(Figure 4.3B) (Figure 4.3B)

no data

Hog Inlet Hog Inlet

Little River

Inlet

Little River

Inlet

Waites Island

small channels

B

unconformity

unconformity

N

A'

B’

VERTICAL EXAGGERATION APPROXIMATELY 10:1

B’ B’

VERTICAL EXAGGERATION APPROXIMATELY 50:1

EXPLANATION

500 METERS

1,500 FEET

0

0

200 METERS

600 FEET

0

0

0 1 KILOMETERS

0 1 MILE
SECTION 4

56

Figure 4.7. Seasonal changes in a sediment-limited beach typical of the central Grand Strand. (A) During times of fair weather, 

sediment is transported landward from the shoreface and stored in the dunes and berm. Upper surface of erosion-resistant 

sedimentary rock is exposed in shallow-water areas adjacent to the beach. (B) During times of stormy weather, the beach is 

eroded, and sedimentary rock is locally exposed on the broad intertidal beach. The eroded sediment is transported offshore, where 

it buries rocky areas and produces a relatively smooth, sandy shoreface.

High tide

Low tide

Rocks exposed

on beach

Fair-weather profile

Intertidal

beach

Sediment stored

on lower shoreface

Erosional

scarp

ACTIVE BEACH SYSTEM

Low tide

Intertidal

beach

High tide

Rocks exposed

on shoreface

Dunes

Hardbottom

(rock)

Layered

sedimentary

rocks

STORM BEACH,

SEDIMENT-LIMITED

FAIR-WEATHER BEACH,

SEDIMENT-LIMITED

Modern

sediment

A

B

Shoreface

Upper

beach Continental

shelf

VERTICAL SCALE GREATLY EXAGGERATED
5757 SECTION 4

4.6. Summary

The uniquely detailed record of shoreline 

behavior from the SCCES provides guidance for 

land-use and development decisions along the Grand 

Strand. It also helps us understand the linkages 

between subaerial coastal lands, which may be eroded 

in the near future, and adjacent submerged lands of 

the continental shelf where sediment moves freely on, 

off, and along the shore. As the beach and shoreface 

migrate, they contact different materials underlying 

the modern coastal system. The degree of resistance of 

the materials to erosion depends on their composition 

(percent sand, silt, clay) and mechanical properties 

(degree of cementation or compactness). Erosion 

proceeds at different rates; less resistant deposits 

are eroded more deeply, and more resistant deposits 

are eroded less deeply. This differential erosion has 

modified the morphology of the seafloor and, in some 

cases, probably altered sediment-dispersal pathways 

in nearshore areas. Because extensive development 

is located very near the coast throughout the region, 

even minor rates of coastal erosion pose a serious 

threat. The large number of engineered coastalstabilization structures along the Grand Strand is a 

testament to the pervasive erosion, and the distribution 

of these structures provides a general indication of 

the areas where the effects have been the greatest. 

In many instances, these so-called hard engineering 

solutions (fig. 1.7) have proven to further exacerbate 

erosion rather than alleviate the problem.
58 Section 5: Sediment Budget and Ocean Processes

5.1. Introduction

The constant shifting of sediment along shorelines presents a fundamental challenge for the 

prediction of beach behavior. A valuable approach to 

managing coastal resources is to consider the sediment 

that moves in and out of or is stored within a beach 

system in an annual sediment budget (Komar, 1996). 

A balanced sediment budget means that, over time, 

equal amounts of sediment are transported into and 

out of a coastal compartment. Ideally, annual losses 

are offset by annual gains, and the beach remains 

relatively stable; however, an imbalance in the 

amount of sediment gained or lost during the year 

destabilizes the beach and causes changes in its shape 

and (or) position. 

A good way to think of a sediment budget is in 

terms of a bank account: when more sediment is 

deposited than removed, the sediment budget has a 

surplus and the beach grows seaward. Conversely, 

when more sediment is removed than deposited, the 

sediment budget is in deficit and the beach retreats 

landward. Coastal erosion occurs when waves 

and currents remove sediment faster than it can be 

replaced. If a beach has a large positive balance of 

sediment, a small deficit will have a minor impact on 

its overall condition; however, if the initial balance is 

small (that is, the beach system stores little sediment), 

relatively minor losses can cause significant changes 

in the shape and/or position of the beach.

The major components of a sediment budget 

are sources that provide new sediment, sinks where 

sediment is lost to the active beach, and transport 

pathways along which sediment is exchanged between 

different parts of the coastal system (fig. 5.1). Sediment budgets typically are based on limited data that 

Figure 5.1. The components of a conceptual long-term sediment budget for the Grand Strand region (modified from Gayes and others, 

2003). Numbered arrows indicate the general direction of sediment movement. Sediment sinks include: 1. Winyah Bay, 2. North Island 

Spit, 3. North Inlet, 4. Murrells Inlet, 5. Hog Inlet, 6. Little River Inlet, and 7. loss offshore. Sediment sources include: 8. rivers, 9. beach 

and shoreface erosion, and 10. inner-shelf erosion. See table 5.1 for estimates of sediment volumes associated with each component. 

Land

Wetland

Water

Sediment sinks

Sediment sources

EXPLANATION

Long Bay Waites

Island

Little River

Inlet

Murrells

Inlet

Great Pee Waccamaw River

Dee River

North Inlet

Winyah

Bay

North

Island Spit

N

3

4

Hog

Inlet

7

1

2

8

9

10

6

5

33°55' 33°50'

79°00' 78°50' 78°40' 78°30'

33°10' 33°15'

79°20' 79°10' 79°00'

34°00'

78°50'

10 KILOMETERS

10 MILES

0

0
5959

include inherent uncertainties. Accurate estimates of 

sediment gains and losses are difficult to determine, 

particularly along coasts with numerous sources and 

sinks. The Grand Strand, however, is a sedimentlimited system that is relatively free of complications 

associated with inlets and estuaries. It provides an 

unusual opportunity to determine a first-order approximation of sediment losses and gains (table 5.1) and to 

identify transport pathways within a relatively simple 

coastal compartment. This section incorporates some 

text previously published by Gayes and others (2003) 

with new data and figures to provide an overview of 

sediment movement in the region.

5.2. Sediment Sources

Sediment in the active beach system is derived 

from (1) erosion of upland by rivers, (2) longshore 

transport from adjacent coastal compartments, 

(3) erosion of older beach and shoreface deposits, and 

(4) erosion of older deposits on the inner shelf. The 

sum of the deposits from all of these sources represents the input of new sediment into the active beach 

system. Although the amounts of sediment contributed 

by the sources are difficult to quantify accurately, we 

provide a general accounting of their contributions.

Sediment Delivered by Rivers

Fluvial input to the coastal system is limited 

to areas at the northern and southern boundaries of 

Long Bay. In the north, the Cape Fear River enters 

Long Bay at Cape Fear. In the south, the Great Pee 

Dee River coalesces with several smaller rivers near 

Georgetown to form a large estuary at Winyah Bay. 

Dams on these rivers largely block the movement 

of sediment, however, and most of the sediment that 

does makes it downstream is trapped in Winyah Bay 

before it reaches the coast (Meade and Trimball, 1974; 

Patchineelam and others, 1999). Extensive deposits of 

mud are dredged routinely to maintain shipping channels in upper parts of Winyah Bay and the Cape Fear 

River estuary. The limited amount of fluvial sediment 

that is transported beyond the estuaries appears to be 

incorporated into shoal complexes offshore of Cape 

Fear and Cape Romain.

Table 5.1. A conceptual sediment budget for the Grand Strand region.

[Table lists estimated volumes of mobile sediment lost annually to sinks and gained from different sources (modified from Gayes and others, 2003). 

Numbers in first column correspond to numbered arrows in figure 5.1. Dredging records are from C. Mack (U.S. Army Corps of Engineers, oral 

commun., 2003)]

Sediment sinks 

(losses)

Volume 

(cubic meters per year) Basis of estimate

1. Winyah Bay 284,000 1994–2002 dredging records

2. North Island Spit 79,000 Historic spit growth

3. North Inlet ?

4. Murrells Inlet 75,000 1974–1978 dredging records

5. Hog Inlet ?

6. Little River Inlet 57,000 1982–1995 dredging records

7. Loss offshore ?

Total sinks 495,000

Sediment sources 

(gains)

8. Rivers Very small Patchineelam and others (1999)

9. Beach and shoreface erosion 104,000 Beach-profile migration based on the long-term average erosion rate

10. Inner-shelf erosion 391,000 Difference between total losses (1–7) and gains from other source (8–9)

Total sources 495,000
SECTION 5

60

Sediment Delivered by Longshore Transport

Geomorphic evidence suggests that little or no 

sediment is exchanged around the capes that separate 

Long Bay from coastal compartments to the north and 

south. Extensive southerly spit growth at the Winyah 

Bay entrance indicates a dominance of southerly 

longshore transport, which limits any contribution of 

sediment moving north into Long Bay. Sand spits and 

the associated shoal complex offshore of Cape Fear 

appear to be the dominant regional sediment sinks, 

which effectively trap sediment that might enter Long 

Bay from the north (Denison, 1998).

Erosion of Beach and Shoreface Deposits

The contribution of sediment from beach and 

shoreface erosion was estimated by analyzing beachprofile geometries and historical erosion rates 

(Gayes and others, 2003). First, the coast was divided 

into about 950 segments that measured 100 m wide 

and extended along the entire Grand Strand coastline 

(fig. 5.2). Each segment was assigned the closest 

BERM profile, which typically had been measured 

within 200 m of each segment. The assigned profile 

for each segment was translated landward according 

to the long-term erosion rate for that segment of 

beach. The translated profile was assumed to maintain 

a constant shape over the long term (decades or 

longer), although slight variations probably occurred 

over the short term (months to years). The crosssectional areas between the translated and existing 

profiles in each segment were calculated and added 

for all segments to represent the volume of sediment 

derived by this idealized migration. On the basis of 

this analysis, erosion of the beach and shoreface along 

the entire Grand Strand has released an average of 

104,000 m3/yr of sediment. This volume of sand is 

a maximum estimate because deposits underlying 

large areas of the beach contain abundant muddy 

sediment, and its erosion yields relatively less sandsized sediment.

Erosion of Inner-Shelf Deposits

A considerable proportion of sediment in the 

modern coastal system is derived from the erosion of 

older materials underlying the inner shelf. Wehmiller 

and others (1995) provide evidence of this process by 

showing that up to 75 percent of clam shells found 

on beaches in the region are actually fossils. The 

clams lived more than 10,000 years ago and, after 

death, were preserved in rocky deposits that underlie 

parts of Long Bay. Biological and physical processes 

actively rework these deposits on the inner shelf, 

providing recycled sediment to the modern coast. 

Riggs and others (1998) calculated that bioerosion 

of hardbottoms in nearby Onslow Bay, North 

Carolina (fig. 1.3A), yields as much as 5.5 kg/m2 of 

new sediment each year. Large waves can excavate 

fragments of the rocky material from the inner shelf 

and wash them up onto Grand Strand beaches 

(fig. 5.3). Soft corals and other invertebrates are often 

still attached to the rock fragments on the beach after 

storms. These types of organisms typically live more 

than 1 km offshore of the surf zone; in this offshore 

area, waves and sediment abrasion are less intense. 

Their presence on the beach indicates inner-shelf 

erosion and onshore transport during intense storms. 

The volume of sediment derived from the inner 

shelf is estimated as 391,000 m3/yr. This value was 

indirectly calculated and represents the residual or 

remaining volume of sediment needed to balance the 

total losses in the budget (table 5.1).

The combination of processes that drive 

net onshore transport of sediment are not fully 

understood, but the estimated volume of inner-shelf 

sediment, at this regional scale, is not excessive. 

It represents only a fraction of the sediment that is 

available on the inner shelf as a potential source of 

beach sediment. On the basis of geologic mapping, 

at least 270 million m3 (353 million yd3) of mobile 

sediment is on the inner shelf (fig. 3.5B). This large 

reservoir of sediment can readily account for the 

deficit in the sediment budget.
6161 SECTION 5

Figure 5.2. Diagrams showing how volumes were calculated for sediment eroded from beach and shoreface deposits. 

(A) Plan view of a beach divided into 15 equal segments, each 100 m wide and extending from the dune crest to the 

shoreface. A BERM profile (A, B, or C) is assigned to nearby segments of beach. In this example, profile A (red line) 

represents segments 1 to 5. Profiles B and C represent segments 6 to 10 and 11 to 15, respectively. (B) The existing profile 

is moved landward based on the long-term erosion rate that has been established for each beach segment (fig. 4.2). The 

profile shape remains constant, and the area between the eroded profile and the existing profile represents the sediment 

released in one year. For example, if the beach in segment 1 is eroding rapidly at 8 m/yr, profile A is translated 8 m landward 

of its original position, and the region between the two profiles (diagonal-line pattern) represents the annual area of eroded 

sediment. Values are added for all segments to determine the volume of new sediment that is contributed to the regional 

sediment budget. ELEVATION RELATIVE TO MEAN SEA LEVEL, IN METERS

25 50 75 100 125 150

DISTANCE, IN METERS

0

-2

0

2

4

-4

-8

-6

6

Existing profile A

Eroded profile

8

meters

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

100 m

Profile A Profile B Profile C

ocean

beach

dune

A

B
SECTION 5

62

5.3. Sediment Sinks

On a regional scale, potential sinks for sediment 

from the beach system include adjacent coastal compartments, into which sediment is transported across 

the southern or northern boundary, and the inner shelf, 

to which sediment is transported from the shore. The 

sum of the sediment volumes lost into all of these 

sinks represents the total loss of sediment from the 

active beach system. Geologic mapping and analysis 

of dredging records provide estimates of the annual 

rate of sediment loss and information about transport 

pathways and probable sinks.

Losses Across the Southern Boundary

Significant sediment transport out of the Grand 

Strand is evident across the southern boundary at 

Winyah Bay. The bay lies behind North Island spit, a 

sandy peninsula about 5 km long and 1 km wide 

(figs. 5.1, 5.4A). Progressive elongation of the spit 

deflected the Winyah Bay entrance channel about 

1 km to the south between 1872 and 1983 (Anders and 

others, 1990; Morton and Miller, 2005). The estimated volume of the spit deposits is about 9 million 

m3 on the basis of data from cores, ground-penetrating 

radar, and topographic surveys. Over the 111 years of 

observed spit growth, an estimated 79,000 m3/yr of 

sediment was lost from the Grand Strand (table 5.1).

Sandy sediment also fills the entrance channel to 

Winyah Bay, where a jetty system was constructed 

to stabilize and maintain the shipping lanes into the 

Port of Georgetown. Regular dredging is required 

to keep the channel open for navigation. Logs from 

maintenance-dredging projects completed between 

1994 and 2002 indicate that the average annual 

rate of deposition in the channel and lower bay is 

284,000 m3/yr. Most of this material probably was 

delivered by southerly directed longshore transport in 

Long Bay (Patchineelam and others, 1999). 

Losses Across the Northern Boundary

The results of studies by the U.S. Army Corps 

of Engineers (USACE) indicate that longshore 

transport is small and more variable across the 

northern boundary of Long Bay at Little River Inlet. 

On the basis of measurements recorded over short 

time periods, the initial modeling reported limited 

net annual transport towards the northeast out of 

the Grand Strand system (Chasten, 1992). Some of 

the northward-transported sediment apparently is 

accumulating at Waites Island. The formation of beach 

ridges indicates seaward growth of the island and a 

Figure 5.3. Pieces of sedimentary rock (arrows) 

on Surfside Beach after a 1999 storm. The corals 

attached to these rock fragments typically live 

more than 1 km offshore of the beach (from 

Gayes and others, 2003).
6363 SECTION 5

Figure 5.4. (A) Aerial photograph of the North Island spit at the southern end of the Grand Strand, showing the 

positions of five historical shorelines. Prominent beach ridges (small white arrows) that predate the historical 

record were produced as the spit grew from north to south. (B) Ground-penetrating-radar profile showing the 

internal structure of the spit, which consists of sandy sediment over 10 m thick. Steeply dipping layers in the lower 

unit (orange) formed as sediment, carried by south-directed longshore currents, filled the channel at the entrance 

to Winyah Bay. Beaches and dunes later developed on top of the channel-fill sediment, producing an upper deposit 

of fine sand (yellow) that exhibits wavy, nearly flat-lying layers. The calculation of sediment volume stored in the 

spit from 1872 to 1983 (see table 5.1) is based on the prograding upper unit and underlying channel fill.

0 1 KILOMETER

0 1 MILE

A

B

0 50 100

VERTICAL EXAGGERATION APPROXIMATELY 7:1

0

10

5

0

10

5

Channel-fill sediment

0

10

5

0

10

5

DEPTH, IN METERS BELOW

MEAN SEA LEVEL

Dipping layers

Beach and dune sediment beach and dune sediment

150 200 250

DISTANCE, IN METERS

South North

Winyah Bay

GPR profile

(below)

1962–1963

1983

1933–1934

1923–1926

1872–1874

Historical shorelines

(years surveyed)

Jetty

Whitearrows

point to beach ridges

EXPLANATION

N
SECTION 5

64

net surplus of sand (fig. 4.3B). Dredging records from 

Little River Inlet prior to the construction of jetties in 

1982 show small net losses of sediment from Long 

Bay into Onslow Bay off the coast of North Carolina 

(fig. 1.3A). An average of 57,000 m3/yr of sediment 

was dredged from the navigation channel between 

1975 and 1982 (table 5.1). This value was used to 

estimate sediment lost across the northern boundary 

by longshore transport.

Losses at Tidal Inlets

Tidal inlets function as reservoirs that temporarily 

store and release sediment within the regional system. 

Net changes in the volumes of sediment contained 

in the inlet systems strongly affect the stability of 

adjacent beaches over the short term. In addition to 

inlets at the boundaries of the Grand Strand, Hog 

and Murrells Inlets are probably sites of net sediment 

loss from the beach system (fig. 5.1). On the basis of 

dredging records for 1974 to 1978, about 75,000 m3/yr 

of sediment was lost at Murrells Inlet (table 5.1). No 

dredging data were available for Hog Inlet to estimate 

sediment losses.

Losses Offshore to the Inner Shelf

Extensive areas of hardbottom dominate the inner 

shelf of Long Bay (figs. 2.4, 2.5). Seaward of Surfside 

Beach (fig. 1.3B), for example, is a nearly continuous 

area of rocky outcrops extending offshore for about 

10 km. Small lenses of loose sediment within this 

zone probably are derived from biological and 

mechanical erosion of the outcrops, as has been 

observed elsewhere in the region (Riggs and others, 

1998). The near-absence of modern sediment indicates 

that transport of sediment from the beach to the inner 

shelf may be small. Alternatively, the mobile sediment 

may be moved quickly into deeper water beyond the 

limit of the survey area.

5.4. Sediment-Transport Pathways

The relatively minor amount of mobile sediment 

in Long Bay is moved by waves and currents in 

a complex pattern. On a broad regional scale, 

seafloor mapping helps us infer the long-term 

directions of sediment transport on the basis of 

geomorphic evidence and sediment distribution. 

However, formulation of a quantitative sediment 

budget is not possible with mapping techniques 

alone. Most sediment movement occurs during 

short-lived, energetic storms. Direct observations of 

oceanographic processes (for example, the speed and 

direction of bottom currents) are needed to quantify 

how much and in what direction sediment is moved 

during a storm or series of storms. Knowledge of the 

actual rates and pathways of sediment transport can be 

used to predict patterns of erosion and accretion along 

the beach and determine the availability of sediment 

for planned beach-nourishment projects.

Transport Direction Inferred from Seafloor 

Mapping

Several lines of evidence indicate that sediment 

generally moves along the coast from north to south. 

First, the southerly migration of the Pee Dee River 

over a period of more than a million years (Baldwin 

and others, 2006) has shifted the major supply of 

fluvial sediment away from the center of the Grand 

Strand (fig. 3.9). Consequently, the central and 

northern parts of the Grand Strand now depend 

primarily on the reworking of relict-shoreline and 

inner-shelf deposits for sediment supply. Second, 

sediment-thickness mapping shows relatively little 

mobile sediment in the northern and central parts of 

the Grand Strand, with the largest accumulations in 

the south (fig. 3.5B). Third, the direction of longterm net sediment transport is inferred from lowrelief sand ridges on the inner shelf (fig. 5.5). Profile 

asymmetry and changes in sediment texture show 

current winnowing in the troughs between the sand 

bodies and support conceptual models of sediment 

moving south along the coast towards Winyah Bay. 

These characteristic patterns that indicative sedimenttransport pathways are being used to guide processoriented studies.

Offshore-directed losses of sediment from Grand 

Strand beaches are not assigned an estimate for this 

sediment budget. Sediment is probably transported 

offshore in some areas, but little data are available to 

prove that it moves across the shelf. Slightly elevated 

rocky ledges oriented nearly perpendicular to the 

shoreline (fig. 2.5) might divert sediment seaward 

and thereby contribute to locally high rates of erosion 

(Gayes and others, 2003). 
6565 SECTION 5

Figure 5.5. Perspective view of the inner shelf offshore of Myrtle Beach shows sidescan-sonar imagery draped over bathymetry (top). 

High backscatter values (light tones) generally represent rock, gravel, or coarse sand. Low backscatter values (dark tones) generally 

represent fine sand or muddy sediment. Oceanographic instruments were deployed at eight sites (red circles) on and near a large 

sandy shoal to determine the physical processes that control sediment transport around the feature. A bathymetric profile across a 

low-relief sand ridge shows the direction of net sediment transport (bottom). The steeper slope faces toward the southwest, and finer 

sediment winnowed from the trough and northeast-facing side of the ridge has left a lag of coarse sand and gravel. Fine sand has been 

deposited on the crest and southwest-facing side. Modified from Denny and others (2007).

0 5 KILOMETERS

0 5 MILES

-10.0

-10.2

-10.4

DISTANCE, IN METERS

ELEVATION, IN

METERS

0 200 400 600 800 1,000 1,200 1,400 1,600

Sediment deposited

on crest

(fine sand)

SW NE

Sediment winnowed

in trough

(coarse sand, gravel)

Inferred direction of sediment transport

Backscatter

255 (high)

0 (low) Sandy shoal

deposit North Myrtle Beach

Myrtle Beach

Myrtle Beach

Crest of low-relief

sand ridge

(in profile below)

Low-relief sand ridge Low-relief sand ridge

Sites of

oceanographic

measurements
SECTION 5

66

Direct Observations of Sediment Transport

An initial study in 2001 measured waves and 

currents for periods of over 30 days at six locations in 

Long Bay. The data were helpful in determining the 

general circulation in the bay and the response of the 

system to local winds (Gutierrez and others, 2006). 

In a second study, instruments were deployed from 

October 2003 to April 2004 offshore of Myrtle Beach 

to investigate sediment movement on the inner shelf 

(fig. 5.5). Measurements of winds, currents, waves, 

and suspended sediment concentrations were collected 

at eight sites in the vicinity of a large sandy shoal that 

lies in water depths of about 10 m. Given the importance of finding sand resources for beach nourishment, 

this deposit might be suitable for sand extraction. 

Before dredging the deposit, however, some important 

questions need to be addressed. Is the resource renewable? Will inner-shelf processes replace sediment that 

is mined? Will dredging change the distribution of 

wave energy along nearby stretches of coastline and 

cause unwanted erosion? 

Preliminary results show that locally high winds 

strongly correlate with peaks in wave energy. As 

wind strength increases during a storm, wave heights 

increase (fig. 2.11). Large waves create orbital 

motions at the sea surface that propagate downward 

and oscillate along the seafloor. These motions erode 

bottom sediment and suspend it in the water column 

during storms. Suspended sediment concentrations are 

increased only when there are large waves; tidal currents alone are not strong enough to mobilize the sediment. A combination of wind-driven surface currents 

and near-bottom circulation determines the direction 

and magnitude of sediment transport within Long Bay. 

Details of the site locations, equipment specifications, 

all the processed data, and the processing tools are 

described in Sullivan and others (2005).

5.5. Numerical Modeling

Numerical models developed as part of the 

SCCES show that offshore bathymetric features, such 

as the sandy shoal seaward of Myrtle Beach (fig. 5.5), 

affect nearshore processes through the modification of 

waves that pass over them. The direction and magnitude of sediment transport on the inner shelf are influenced by different patterns of storms that pass through 

South Carolina: (1) tropical cyclones (that is, tropical 

storms and hurricanes), (2) cold fronts, and (3) warm 

fronts (fig. 5.6). Storms develop around atmospheric 

regions of high and low pressure that move across 

North America. Winds blow counterclockwise around 

low-pressure systems, bringing cooler air to the south 

and warmer air to the north. As these air masses move, 

they create a cold front to the south of the low pressure and a warm front that extends to the east from the 

low pressure.

•	 TROPICAL CYCLONE: Low pressure is 

southwest of Long Bay and moving to the 

north. As it passes offshore of the coast, winds 

initially blow out of the northeast (dashed 

arrow) and shift to the northwest (solid arrow). 

Strong winds, waves, and currents are directed 

generally towards the south throughout the 

storm. Net sediment flux along the coast is 

towards the southwest.

•	 COLD FRONT: Low pressure is northwest of 

Long Bay and moving to the east. A trailing 

cold front crosses the region and is accompanied by a change in wind direction. Wind 

initially blows out of the southwest (dashed 

arrow) and shifts to the northeast (solid arrow). 

More sediment is transported when the wind 

blows from the southwest because the larger 

fetch, or the area of the open ocean over which 

wind blows in constant speed and direction, 

generates stronger waves. Net sediment flux 

along the coast is towards the northeast.

•	 WARM FRONT: Low pressure is west of 

Long Bay and moving to the north. An extending warm front crosses the region and is 

accompanied by a rapid change in wind direction. Wind initially blows out of the northeast 

(dashed arrow) and shifts to the southwest 

(solid arrow). Even though the wind pattern 

of the warm front is opposite to that of a cold 

front, the fetch is larger when the winds are 

from the southwest. Net sediment flux along the 

coast is also towards the northeast.

The duration, magnitude, and frequency of 

the different storm types dictate the long-term 

sediment flux in the region. Cold fronts and warm 

fronts generally drive sediment transport toward the 

northeast; tropical storms generally drive it to the 

southwest (fig. 5.6). If transport is roughly equal in 

both directions, it provides a potential mechanism for 

partially preserving the sandy shoal, which somehow 
6767 SECTION 5

Figure 5.6. (A) Measurements of wind speed and direction collected offshore of Myrtle Beach from February 8 to 29, 

2004. Additional data for this time period are shown in figure 2.11B. (B) Weather maps on the left show three different 

storm patterns crossing the region. Simulation results for each storm on the right show the general direction of sediment 

transport (arrows) and predicted areas of sediment erosion and deposition on the inner shelf (colors). The 8-m bathymetric 

contour is displayed in red. See main text for description of storms and predicted movement of shelf sediment.

02/08/04 02/15/04 02/22/04 02/29/04

−10

0

10

Warm Front Cold Front Tropical Cyclone

WIND SPEED, IN

METERS PER SECOND

Warm Front

−5

−4

−3

−2

−1

0

1

2

3

4

5

BED ELEVATION CHANGE, IN MM

DEPOSITION

net sediment flux

EROSION

Daily weather map for February 11, 2004 Simulation results 

78°54'W 78°48' 78°42' 78°36' 78°30'

33°48'N 33°42' 33°36' 33°30'

Cold Front

−5

−4

−3

−2

−1

0

1

2

3

4

5

DEPOSITION EROSION

net sediment flux

Daily weather map for February 21, 2004 Simulation results 

78°54'W 78°48' 78°42' 78°36' 78°30'

33°48'N 33°42' 33°36' 33°30'

BED ELEVATION CHANGE, IN MM

78°54'W 78°48' 78°42' 78°36' 78°30'

33°48'N

Tropical Cyclone

Daily weather map for February 26, 2004 

−5

−4

−3

−2

−1

0

1

2

3

4

5

BED ELEVATION CHANGE, IN MM

DEPOSITION EROSION

net sediment flux

Simulation results 

Myrtle Beach

Myrtle Beach

Myrtle Beach

33°42' 33°36' 33°30'

L

L

L

Long Bay

Long Bay

Long Bay

Long Bay

A

B
SECTION 5

68

has survived erosion over the last 5,000 years or so 

since it was formed (Barnhardt and others, 2007). 

Instead of storms moving sediment in one consistent 

direction and eventually eroding the shoal, these 

observations suggest that storms could have shifted 

sediment back and forth across the shelf. Additional 

modeling will help us identify the oceanographic 

processes responsible for maintaining the shoal 

and explore the possible natural sediment pathways 

connecting the shoal to the beach.

5.6. Summary

In most places along the Grand Strand, the modern beach is a thin veneer of sand. As a result, it is 

sensitive to relatively small changes in the annual balance between sediment gains and losses. A sediment 

budget was constructed to determine the directions 

and annual rates of sediment movement within the 

coastal system. South of Murrells Inlet, there is clear 

evidence of long-term net longshore transport towards 

the south. North of Murrells Inlet net transport 

appears to be more variable. Large losses occur where 

sediment moving longshore is trapped by tidal inlets 

(Murrells and Little River), accumulates in a large spit 

complex (North Island), or exits the coastal compartment at the southern boundary (Winyah Bay).

Two important assumptions underlie our sediment-budget calculations. First, the budget is balanced 

so that the total volume of sediment in the Long Bay 

system remains constant. Losses of sediment must be 

offset by gains of new sediment. Second, the coastal 

system is closed and receives no sediment from 

adjacent coastal compartments to the north and south. 

Sediment is not transferred around the shoals at Cape 

Fear and Cape Romain. Lacking significant fluvial 

or longshore input, the only potential sources of new 

sediment are internal to the system, primarily erosion 

of older deposits within Long Bay. These potential 

sources include beach and shoreface deposits, which 

have been closely monitored by beach profiling, and 

inner-shelf deposits, which lie offshore in deeper, less 

accessible areas. Estimates of sediment derived from 

beach and shoreface erosion (table 5.1) are based on 

an idealized beach profile and are maximum values 

that are based on the assumed steady landward migration of sediment (fig. 5.2). If erosion across the idealized beach profile is uneven (fig. 4.3), however, the 

volume of new sediment might be significantly lower 

and more sediment would be assumed to originate 

from inner-shelf erosion to balance the budget. In 

either case, total sediment losses greatly exceed the 

estimates of new sediment derived from beach and 

shoreface erosion. Although the absolute amounts 

of sediment moving out of the beach system are 

unknown, erosion of the inner shelf must be an important contribution to the regional sediment budget.

Experiments using moored instruments have 

shown that shelf sediment responds to storms in a 

variety of ways. Depending on the type and path of 

given storm, waves and currents of differing intensity 

and direction can be expected. Some storms drive 

sediment towards the northern boundary of the system, and some drive sediment towards the southern 

boundary. The net result over a given year or decade 

will depend on the relative frequency and intensity 

of the different types of storms. Continued improvement of models of sediment transport within the Bay 

will aid us in refining the regional sediment budget 

and predicting future coastal response. The potential 

for shifts in storm frequency, intensity, and tracks that 

may accompany climate change can be expected to 

strongly affect sediment movement in the area.
6969 SECTION 5
70 Section 6: An Effective Strategy for Understanding Coastal Change

Sandy beaches represent a public resource 

that is vitally important to the economic 

and environmental health of coastal communities. 

In northeastern South Carolina, however, the 

natural coastal system has been widely disturbed by 

human activities. The dynamic and mobile beach 

is progressively colliding with static infrastructure, 

which prevents it from migrating landward in an 

orderly fashion. The direct and indirect effects 

of shoreline migration on development in this 

complex system likely will increase as a result of 

global warming and accelerated rates of sea-level 

rise. Beach nourishment is the preferred method of 

erosion control, but experience shows that nearly all 

nourished beaches have a limited lifespan, so repeated 

infusions of new sediment are required (NRC, 1995; 

Trembanis and others, 1999). The long-term need 

for beach fill in the Grand Strand region will require 

improved projections of coastal-erosion rates and the 

identification of new sediment sources. 

The SCCES has developed a comprehensive 

strategy to determine the factors and processes that 

control sediment movement in the coastal zone. The 

strategy consists of three distinct parts. The first part 

is to map the geologic framework of Grand Strand 

beaches and adjacent areas of shallow seafloor. The 

second part is to document both long-term and shortterm fluctuations in shoreline position over time. The 

third part is to develop a conceptual sediment budget 

for the coastal system, measure sediment transport 

at selected sites, and ultimately construct numerical 

models of sediment flux in the nearshore area.

Part 1 - Geologic Mapping. The geologic 

framework of the Grand Strand exerts strong control 

on the production, movement, and ultimate deposition 

of sediment. The degree to which geology controls 

sediment movement along the coast was difficult 

to measure until recently, because collecting data 

in energetic areas adjacent to the beach was not 

feasible; however, improvements in technology now 

provide efficient methods to explore and map the 

shallow seafloor. High-resolution maps of seafloor 

topography and sediment texture support conceptual 

models of sediment generally moving from northeast 

to southwest along the coast. The Pee Dee River has 

migrated southward for millions of years, too, as 

shown by a series of buried river channels mapped 

beneath the seafloor. This migration has shifted the 

major supply of fluvial sediment away from the center 

of the Grand Strand and thereby produced a generally 

sediment-limited inner shelf dominated by rocky 

outcrops. Geologic mapping of the inner shelf has 

identified large sandy deposits that represent potential 

sources of beach-nourishment sediment in the future.

Part 2 - Shoreline Change. Aerial photography 

and beach-profile measurements showed that the 

active beach system has been migrating landward 

but at different rates at different sites along the 

coast. Also, the rate of retreat at any single site has 

not been uniform over time. In Myrtle Beach, for 

example, substantial variations in beach-fill stability 

were observed where a large beach-nourishment 

project was completed in 1998. Areas of low stability 

coincided with extensive rocky outcrops mapped 

in shallow water just seaward of the reconstructed 

beaches. The outcrops appeared to interrupt sedimentdispersal pathways and alter patterns of sediment 

accumulation along the beach; the result was localized 

areas of enhanced erosion. The monitoring period 

(1988–present) includes some of the largest storms 

to affect the region, such as Hurricane Hugo (1989) 

and the storm named “The Storm of the Century” 

(1993). These storms were major erosional events 

that removed the thin veneer of beach sediment to the 

greatest extent of any storms over the last 20 years. 

Beach profiles measured when the beach was most 

deeply eroded documented the base of the active 

sediment layer where it overlay a rocky substrate. In 

many places, sediment on the modern beach is less 

than 1 m thick, even though nourishment projects 
7171

have repeatedly placed large amounts of new sediment 

on the beach.

Part 3 - Ocean Processes and Sediment Budget.

Ongoing efforts aim to quantify the volume of 

sediment moving through the coastal system and 

determine the role of coastal oceanographic processes 

that cause erosion. Time-series measurements of 

ocean processes help us to address questions raised by 

geologic mapping. For example, what is the precise 

role of the large sandy shoal offshore of Myrtle 

Beach in controlling the distribution of wave power 

along the shoreline? Mining the shoal to rebuild 

the beach might alter the height and direction of 

waves approaching the beach and thereby locally 

increase the vulnerability of the beach to erosion. 

Data collected during oceanographic experiments 

are being used to determine the sediment-transport 

processes responsible for shaping the shoal and 

adjacent shoreline. Eventually, observational data and 

numerical models will be used to determine regional 

circulation dynamics and to predict patterns of 

sediment flux around the shoal and adjacent surf zone.

The results of this integrated approach 

to investigating coastal erosion have helped 

municipalities and government agencies protect public 

health and stabilize beaches. For example, the City 

of North Myrtle Beach used geologic maps produced 

by the SCCES to design stormwater outfalls, which 

extend offshore so that discharge will not circulate 

back onto the beach and affect water quality. The 

results of this study generated substantial cost savings 

for the construction of 12 outfalls by obviating the 

need for expensive surveys at many potential sites. 

Instead, the city accessed the geologic maps and 

information to determine suitable locations. Every 

major beach-nourishment project in South Carolina 

over the past 10 years has relied on beach-profile data 

and mapping products from the SCCES (Park and 

others, 2009). The USACE has reduced expenses by 

as much as $50,000 per year per project, depending 

on the shoreline length, by incorporating the study 

results as part of its planning process. The City of 

Myrtle Beach and Horry County similarly use the 

data to generate annual maintenance reports for 

nourishment projects. In this sediment-limited region, 

South Carolina is committed to beach nourishment 

to mitigate coastal erosion, and sediment is already 

being mined from borrow areas beyond the 3-mile 

limit of State waters. The regionally comprehensive 

framework approach described in this report supports 

efforts to efficiently manage coastal sediment and 

reliably project the long-term availability and cost of 

these resources.

Mapping products and data generated by the 

SCCES have led scientists to challenge some 

long-held assumptions about how beaches evolve, 

especially how they respond to storms and rising 

sea level. Most models of coastal change are based 

on the assumptions that waves and currents are 

acting on homogeneous deposits of unconsolidated 

sediment, and that beaches maintain a constant 

geometry (smooth and concave up) over time as 

they migrate landward. The degree to which these 

assumptions are violated along the Grand Strand was 

initially identified by the long time series of beach 

profiles collected in this study. The profiles clearly 

show that older, erosion-resistant deposits underlie 

the beach and inner shelf. Rock ledges exposed on 

the shoreface interrupt the standard concave-up 

profile used in the traditional models. Integration of 

shoreline-change studies with geologic-framework 

mapping conclusively demonstrates that, in many 

places along the Grand Strand, virtually no modern 

sediment is present on the shallow seafloor adjacent to 

the beach. The absence of this sediment highlights the 

relative importance of the actively eroding inner shelf 

and shoreface as major components of the regional 

sediment budget.
72 Section 7: References Cited

Anders, F.J., and Byrnes, M.R., 1991, Accuracy of 

shoreline change rates as determined from maps and 

aerial photographs: Shore and Beach, v. 59, no. 1, 

p. 17–26.

Anders, F.J., Reed, D.W., and Meisburger, E.P., 1990, 

Shoreline movements—Report 2, Tybee Island, 

Georgia, to Cape Fear, North Carolina, 1851–1983: 

USACE Technical Report, CERC–83–1, 164 p.

Anderson, K.E., Cahoon, D.R., Gill, S.K., Gutierrez, 

B.T., Thieler, E.R., Titus, J.G., and Williams, S.J., 

2009: Executive summary in Coastal sensitivity to 

sea-level rise—A focus on the mid-Atlantic region. A 

report by the U.S. Climate Change Science Program 

and the Subcommittee on Global Change Research. 

[J.G. Titus (coordinating lead author), K.E. Anderson, 

D.R. Cahoon, D.B. Gesch, S.K. Gill, B.T. Gutierrez, 

E.R. Thieler, and S.J. Williams (lead authors)]: U.S. 

Environmental Protection Agency, Washington, D.C., 

USA, pp. 1–8.

Baldwin, W.E., Denny, J.F., Schwab, W.C., Gayes, P.T., 

Morton, R.A., and Driscoll, N.W., 2007, Geologic 

framework studies of South Carolina’s Long Bay from 

Little River Inlet to Winyah Bay, 1999–2003—

Geospatial data release: U.S. Geological Survey 

Open-File Report 05–1346, 1 DVD-ROM, accessed 

online July 1, 2007, at http://woodshole.er.usgs.gov/

pubs/of2005-1346/.

Baldwin, W.E., Morton, R.A., Denny, J.F., Dadisman, 

S.V., Schwab, W.C., Gayes, P.T., and Driscoll, N.W., 

2004, Maps showing the stratigraphic framework of 

South Carolina’s Long Bay from Little River to 

Winyah Bay: U.S. Geological Survey Open-File 

Report 04–1013, accessed online July 1, 2007, at 

http://pubs.usgs.gov/of/2004/1013/.

Baldwin, W.E., Morton, R.A., Putney, T.R., Katuna, 

M.P., Harris, M.S., Gayes, P.T., Driscoll, N.W., Denny, 

J.F., and Schwab, W.C., 2006, Migration of the Pee 

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76 Section 8: Glossary

A

acoustics The study of sound, particularly the generation, 

propagation, and reception of mechanical waves and 

vibrations. 

B

backscatter The scattering of acoustic energy.

bathymetry The measurement of depths of bodies of water 

(in this report, seafloor topography).

barrier island An elongated sandy island that is roughly 

parallel to the mainland shore.

beachrock Partially cemented sedimentary rock that consists 

of sandy sediment and shell fragments and forms in the 

intertidal zone.

berm A sandy, nearly horizontal step-like feature on the 

backshore of a beach.

C

coastal compartment A geographically defined segment of 

coastline in which sediment gains and losses are estimated for 

the purpose of calculating sediment budgets.

coastal plain The relatively flat, low-lying physiographic 

province that extends landward of the shoreline to the 

Piedmont physiographic province along the U.S. Atlantic 

Margin.

continental crust The solid, outermost layer or shell of the 

Earth that underlies the continents and continental shelves.

continental margin The ocean floor that is between the 

shoreline and the abyssal floor, including the continental shelf, 

slope, and rise.

continental shelf The submerged, gently sloping portion of 

the continental margin that extends seaward of the shoreline to 

the continental slope.

D

dip The angular tilt or incline of a geologic feature or units.

dune A low mound, ridge, or hill composed of wind-blown 

sediment.

E

escarpment A relatively straight, cliff-like face or steep 

slope of considerable linear extent formed by faulting or 

erosion.

estuary A water body located at the intersection of a river 

or stream with the sea, where freshwater mixes with saltwater 

and tidal effects are evident.

F

fault A fracture or zone of fractures within rocks that show 

evidence of relative movement.

fetch The area of the open ocean over which wind blows at a 

constant speed and direction, creating a wave system.

fluvial Refers to rivers and streams.

G

geographic information system (GIS) A computer-based 

system for capturing, storing, analyzing, managing, and 

presenting geospatial data.

geologic framework Refers to the underlying geologic 

setting, structure, and lithology (rock/sediment type) in a 

given area.

geomorphology The study of landforms and the processes 

that create them.

ground-penetrating radar (GPR) A geophysical method that 

uses pulses of electromagnetic energy to image the subsurface. 

H

hardbottom Rocky areas of seafloor with little to no 

sediment cover.

hiatus A break or interruption in the continuity of the 

geologic record, such as the time interval not represented by 

rocks or sediments along an unconformity.

highstand The uppermost topographic position or elevation 

on land reached by sea level during a specific period in time.

I

insonify To illuminate an area of the seafloor with sound 

energy, as with a sonar.

L

light detection and ranging (LIDAR) A method of 

topographic surveying, generally from aircraft, that uses 

pulses of laser light.

longshore current A shore-parallel current formed by 

breaking waves that approach the coast at an angle. 

longshore transport The movement of sediment driven 

parallel to the shoreline by longshore currents.
7777

M

mainland-attached beach A beach that is backed by dry 

land; not separated from the mainland by a open body of 

water.

microtidal Tidal range of less than 2 m.

N

nearshore marine The portion of the inner continental shelf 

that extends from the shoreline to water depths of about 10 m.

P

paleochannel An ancient incision that was cut by a stream 

or river and filled by younger sediments.

profile of equilibrium A theoretical term that that describes 

a generally concave-up surface formed by waves breaking 

across a bed of uniform, unconsolidated sediment.

R

rift A long, narrow zone where the Earth’s crust and 

lithosphere are being pulled apart.

S

salt marsh Vegetated intertidal wetlands that form in 

protected environments, such as behind barrier islands.

sand fence Evenly spaced, wooden vertical slats that are 

approximately four feet in height, and are designed to build 

sand dunes by trapping windblown sand and to protect existing 

dunes and vegetation.

scarp Abbreviated form of escarpment.

seawall An artificial structure built along a coast to 

protect buildings and infrastructure from coastal erosion, but 

commonly resulting in loss of the dry beach.

sediment budget An inventory or accounting of the inputs 

(gains), outputs (losses), and storage of sediment within a 

coastal compartment.

sedimentary rock A major group of rocks, including 

limestone, sandstone, conglomerate, and shale, that generally 

form by the cementation of layered deposits of sediment.

shoal A submerged ridge, bank, or bar that consists of or is 

covered by sandy, unconsolidated sediment and stands in relief 

on the seafloor.

shoreface The narrow, shallow part of the inner continental 

shelf adjacent to shore. Waves regularly agitate the bottom 

within the shoreface.

sonar Acronym for SOund Navigation And Ranging. A 

method that uses sound waves to detect the presence and 

location of submerged objects.

spit A small point, low tongue, or narrow embankment 

of land that extends from the mainland, or an island that is 

composed of sand deposited by longshore sediment transport.

storm surge An abnormal, sudden rise in sea level generated 

by large waves and low atmospheric pressure that accompany 

a storm at landfall.

swash Flat, gently sloping areas of beach over which waves 

uprush and backwash. In South Carolina, swashes are broad, 

low-relief channels that drain water from the upland across 

the beach.

subaerial erosion Erosion by wind, rain, and other processes 

that operate in the open air or immediately adjacent to the land 

surface.

T

tectonics A field of geologic study concerned with 

structures within the Earth’s crust and the particular forces and 

movements that create them.

tidal inlet An opening in the shoreline, such as between 

two barrier islands, that connects bays or lagoons to the open 

ocean and is maintained by tidal currents. 

topographic sheet (T-Sheet) Surveys of the topography of a 

land surface; typically depicts the mean high-water line, which 

is used to define historical shoreline positions.

topography The general configuration of any part of the 

Earth’s surface, including relief and the position of natural and 

artificial features.

truncation The eroding or beveling of the top of a geologic 

unit or landform.

two-way traveltime The time it takes an outgoing acoustic 

(or radar) pulse to travel from the source to the target and back 

to the receiver. 

U

unconformity A substantial break or gap in the geologic 

record where a surface of erosion or nondeposition separates 

geologic units of different ages.

unconsolidated Loose sediment; particles not cemented 

together.
Prepared by the Pembroke Publishing Service Center.

Edited by Mary S. Ashman.

Graphics by Christine T. Mendelsohn and Mark V. Bonito.

Layout and design by Ann Marie Squillacci.

For more information concerning this report, contact:

U.S. Geological Survey

Woods Hole Coastal and Marine Science Center

384 Woods Hole Road

Quissett Campus

Woods Hole, MA 02543

wbarnhardt@usgs.gov

or visit our Web site at:

http://woodshole.er.usgs.gov/
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Barnhardt and others—Coastal Change Along the Shore of Northeastern South Carolina—The South Carolina Coastal Erosion Study—Circular 1339