U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2004-1043

National Assessment Of Shoreline Change: Part 1

Historical Shoreline Changes And Associated 

Coastal Land Loss Along The U.S. Gulf Of Mexico

Robert A. Morton, Tara L. Miller, and Laura J. Moore
National Assessment Of Shoreline Change: Part 1

Historical Shoreline Changes And Associated 

Coastal Land Loss Along The U.S. Gulf Of Mexico

Robert A. Morton, Tara L. Miller, and Laura J. Moore

Open File Report 2004-1043

U.S. Geological Survey

Center for Coastal and Watershed Studies

St. Petersburg, FL 33701

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. 

Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S.Government.

Morton, Robert A., Miller, Tara L., and Moore, Laura J., 2004, National assessment of shoreline change: Part 1: 

Historical shoreline changes and associated coastal land loss along the U.S. Gulf of Mexico: 

U.S. Geological Survey Open-file Report 2004-1043, 45p.

U.S. Department of the Interior

U.S. Geological Survey
Open-File Report 2004-1043 i

Contents

EXECUTIVE SUMMARY..............................................................................................................................................................................4

INTRODUCTION ..........................................................................................................................................................................................4

U.S. Geological Survey National Assessment of Shoreline Change.........................................................................................4

Disclaimer...........................................................................................................................................................................................5

Acknowledgments.............................................................................................................................................................................5

THE ROLE OF STATE AND FEDERAL GOVERNMENTS..........................................................................................................................5

PRIOR NATIONAL AND GULF COAST SHORELINE ASSESSMENTS..................................................................................................6

METHODS OF ANALYZING SHORELINE CHANGE.................................................................................................................................6

Compilation of Historical Shorelines ..............................................................................................................................................6

Delineation of a Modern (lidar-derived) Shoreline ......................................................................................................................7

Geographic Information System (GIS) Procedures .....................................................................................................................9

Calculation and Presentation of Rates of Change .....................................................................................................................10

Shoreline Definitions and Beach Alterations that Influence Rates of Change ..................................................................... 11

Shoreline Definitions.............................................................................................................................................................. 11

Human Activities.....................................................................................................................................................................12

Reliability of the Results .................................................................................................................................................................12

GEOMORPHOLOGY OF THE GULF COAST REGION.............................................................................................................................14

Gulf of Mexico Mainland Shores ..................................................................................................................................................16

Bays and Lagoons ...........................................................................................................................................................................16

Barrier Islands..................................................................................................................................................................................16

Origin and Evolution of Barriers ...........................................................................................................................................16

Morphologies of Gulf Coast Barrier Islands.......................................................................................................................18

Chenier Plain ....................................................................................................................................................................................20

Tidal Inlets.........................................................................................................................................................................................20

GEOLOGIC HISTORY AND SETTING ......................................................................................................................................................20

Climate...............................................................................................................................................................................................21

Coastal Processes...........................................................................................................................................................................21

Sand Sources ...................................................................................................................................................................................24

GENERAL CHARACTERISTICS OF THE GULF SHORES BY STATE.....................................................................................................25

HISTORY OF INFRASTRUCTURE DEVELOPMENT ...............................................................................................................................26

SHORELINE CHANGE AND COASTAL LAND LOSS .............................................................................................................................27

West Florida......................................................................................................................................................................................27

Alabama ............................................................................................................................................................................................29

Mississippi ........................................................................................................................................................................................29

Louisiana ........................................................................................................................................................................................... 31

Texas ............................................................................................................................................................................................... 31

HUMAN RESPONSES TO COASTAL EROSION AND LAND LOSS.....................................................................................................32

DISCUSSION AND FURTHER CONSIDERATIONS ...............................................................................................................................38

Summary of Shoreline Changes....................................................................................................................................................38

Planned Updates and Related Research.....................................................................................................................................38

Influence of Human Activities .......................................................................................................................................................39

REFERENCES ............................................................................................................................................................................................39
Open-File Report 2004-1043 ii 

Figures

Figure 1. Example of a lidar profile from September 26, 1997 at Kitty Hawk, North Carolina for (a) the entire 

cross-shore region and (b) an expanded view of the foreshore region. .....................................................................9

Figure 2. Examples of common conditions where transects are eliminated in the absence of 

four shoreline intersections. .............................................................................................................................................. 11

Figure 3. Index map of the Gulf Coast region...................................................................................................................................15

Figure 4. Common coastal landforms of the Gulf Coast region. ...................................................................................................16

Figure 5. Conceptual diagram showing possible origins of barrier islands. ..............................................................................17

Figure 6. Sea level curve during the past 150,000 years that depicts the general magnitude and timing of 

sea level changes in the Gulf of Mexico. Modified from Moore (1982). .....................................................................18

Figure 7. Geomorphological characteristics of high and low profile barrier islands. Modified from 

White and others (1978). .....................................................................................................................................................19

Figure 8. Long linear ridges and swales that characterize some Gulf Coast barrier islands, such as San Jose Island, 

Texas mark the former positions of the Gulf shoreline. ................................................................................................22

Figure 9. Fields of migrating sand dunes on North Padre Island, Texas may contribute to erosion by removing 

sand from the beach. ..........................................................................................................................................................22

Figure 10. Long-term trends in average annual sea level at selected tide gauges in the Gulf of Mexico. Data are 

from the National Ocean Service. .....................................................................................................................................23

Figure 11. A coastal subdivision of nearly 200 homes near Houston, Texas was submerged as a result of subsidence 

induced by ground-water production...............................................................................................................................24

Figure 12. Tracks of some of the most deadly and destructive Atlantic and Gulf hurricanes in the 20th century. 

Data are from the National Hurricane Center..................................................................................................................24

Figure 13. Property damage near Panama City, Florida caused by Hurricane Eloise in 1975. From Morton (1976)...............25

Figure 14. Erosion of the Gulf shore eventually destroyed this beach house at Captiva Island, Florida.................................28

Figure 15. Even where wave energy is normally low, episodic erosion during storms is capable of 

destroying roads and eliminating the beach. This example of erosion along the low energy coast 

is from Lighthouse Point, Florida. ......................................................................................................................................28

Figure 16. This narrow eroding beach in front of a seawall near Clearwater, Florida was used for recreation 

before beach nourishment. ...............................................................................................................................................29

Figure 17. Many nourished beaches along the west Florida coast, such as this one on Sand Key, have steep 

erosional escarpments early in the history of the project. ...........................................................................................30

Figure 18. A beach nourishment project near Gulf Shores, Alabama. Accelerated erosion in front of the beach 

houses was attributed to construction of an artificial channel and jetties................................................................30

Figure 19. The seawall along U.S. 90 at Biloxi, Mississippi extends for nearly 27 miles............................................................ 31

Figure 20. Long-term Gulf shoreline erosion at Sargent Beach, Texas.........................................................................................32

Figure 21. Multiple structures including a seawall, riprap, and failed groin field have been unable to stop erosion at 

Longboat Key, Florida. Later these structures were removed and the beach was nourished. ..............................33

Figure 22. The breakwater at Redington Shores, Florida has protected the beach fill but has aggravated erosion of 

adjacent sand beaches.......................................................................................................................................................33

Figure 23. Rock revetments and groins have been used to control beach erosion at Fort Gaines on the east end of 

Dauphin Island, Alabama....................................................................................................................................................34

Figure 24. Storm waves in the Gulf of Mexico destroyed the interlocking block revetment constructed to protect 

Louisiana State Highway 82 near Peveto Beach (Fig. 3). The revetment structure was replaced with 85 

segmented breakwaters. ...................................................................................................................................................35

Figure 25. West end of the seawall at Galveston, Texas. ...............................................................................................................36

Figure 26. Visitor’s center at Padre Island National Seashore, Texas in 1982 and 1992. The concrete reinforced 

structure built on the beach was torn down and a wooden structure was built landward of the dunes.............37
Open-File Report 2004-1043 iii

Table 1. Prior reports of long-term historical shoreline movement................................................................................................7

Table 2. Providers and original sources of historical shorelines....................................................................................................8

Table 3. Dates of compiled shorelines for selected periods............................................................................................................8

Table 4. List of tide gauge measurements used to calculate mean high water elevation........................................................10

Table 5. Horizontal and vertical differences between high water and mean high water shorelines. ....................................12

Table 6. Maximum estimated measurement errors for Gulf of Mexico shorelines....................................................................13

Table 7a. Long-term shoreline change trends, 1800s to post-1998.................................................................................................14

Table 7b. Short-term shoreline change trends, 1970s to post-1998................................................................................................14

Table 8. Historical hurricane inlet openings and associated surge elevations, west coast of Florida. .................................21

Table 9. Technical responses to erosion and land loss in the Gulf Coast region. ......................................................................32

Tables
Open-File Report 2004-1043 4

EXECUTIVE SUMMARY

Beach erosion is a chronic problem along most openocean shores of the United States. As coastal populations continue to grow and community infrastructures are threatened 

by erosion, there is increased demand for accurate information regarding past and present trends and rates of shoreline movement. There is also a need for a comprehensive 

analysis of shoreline movement that is consistent from one 

coastal region to another. To meet these national needs, the 

U.S. Geological Survey is conducting an analysis of historical shoreline changes along open-ocean sandy shores of the 

conterminous United States and parts of Hawaii and Alaska. 

One purpose of this work is to develop standard repeatable 

methods for mapping and analyzing shoreline movement so 

that periodic updates regarding coastal erosion and land loss 

can be made nationally that are systematic and internally 

consistent. 

This report on states bordering the Gulf of Mexico 

(Florida, Alabama, Mississippi, Louisiana, and Texas) represents the first in a series that will eventually include the 

Atlantic Coast, Pacific Coast, and parts of Hawaii and Alaska. 

The report summarizes the methods of analysis, interprets 

the results, provides explanations regarding the historical and 

present trends and rates of change, and describes how different coastal communities are responding to coastal erosion. 

Shoreline change evaluations are based on comparing three 

historical shorelines with a recent shoreline derived from lidar 

(Light Detection and Ranging) topographic surveys. The historical shorelines generally represent the following periods: 

1800s, 1920s-1930s, and 1970s, whereas the lidar shoreline 

is 1998-2002. Long-term rates of change are calculated using 

all four shorelines (1800s to lidar shoreline), whereas shortterm rates of change are calculated for the most recent period 

(1970s to lidar shoreline). The historical rates of change 

presented in this report represent past conditions and therefore are not intended for predicting future shoreline positions 

or rates of change.

Rates of erosion for the Gulf of Mexico region are generally highest in Louisiana along barrier island and headland 

shores associated with the Mississippi delta. Erosion is also 

rapid along some barrier islands and headlands in Texas, and 

barrier islands in Mississippi are migrating laterally. Highest 

rates of erosion in Florida are generally localized around tidal 

inlets. The most stable Gulf beaches are along the west coast 

of Florida where low wave energy and frequent beach nourishment minimize erosion. Some beach segments in Texas 

have accreted as a result of net longshore drift convergence, 

and around tidal inlets that have been stabilized by long jetties. 

Seawalls and riprap revetments were constructed in all 

the Gulf Coast states as initial community responses to longterm beach erosion. Although some states, such as Florida, 

still permit shoreline stabilization structures, beach nourishment has become the preferred method of mitigating longterm erosion.

INTRODUCTION

U.S. Geological Survey National Assessment of 

Shoreline Change

Sandy ocean beaches of the United States represent 

some of the most popular tourist and recreational destinations, 

and they also constitute some of the most valuable real estate 

in the country. These ephemeral interfaces between water 

and land are the sites of intense residential and commercial 

development even though they are frequently subjected to 

natural hazards including flooding, storm impacts, and coastal 

erosion. Because population centers continue to shift toward 

the coast where valuable coastal property is vulnerable to 

erosion, the U.S. Geological Survey (USGS) is conducting a 

National Assessment of Coastal Change. One aspect of this 

effort, the National Assessment of Shoreline Change, uses 

shoreline position as a proxy for coastal change because 

shoreline position is one of the most commonly monitored 

indicators of environmental change (Morton, 1996), and it 

is easily understood by those who are interested in historical 

movement of beaches.

A principal purpose of the USGS shoreline change 

research is to develop a repeatable surveying methodology 

so that shorelines for the continental U.S., and portions of 

Hawaii, and Alaska can be periodically and systematically 

updated in an internally consistent manner. In addition, new 

methods for developing datum based shorelines and assessing 

coastal change will provide the opportunity to achieve more 

comprehensive assessments of error in the future. USGS primary objectives of this project are: (1) to develop and implement improved methods of assessing and monitoring shoreline movement, (2) to obtain a better understanding of the 

processes controlling shoreline movement, and (3) to enter 

into strategic partnerships to facilitate data dissemination. 

Achieving these ongoing long-term objectives requires 

research that (1) examines the original sources of shoreline 

data (maps, air photos, global positioning system (GPS), 

lidar), (2) evaluates the utility of different shoreline proxies (geomorphic feature, water mark, tidal datum, elevation) 

including the errors associated with each method, (3) investigates the bias and potential errors associated with integrating 

different shoreline proxies from different sources, (4) develops standard uniform methods of shoreline change analysis, 

(5) determines the effects of human activities on shoreline 

movement and rates of change, and (6) investigates alterna-
Open-File Report 2004-1043 5 

tive mathematical methods for calculating historical rates of 

change and forecasting future rates of change.

This report summarizes historical changes in the Gulf 

of Mexico shoreline, both accretion and erosion, but emphasizes the erosion hazard because it impacts natural resources 

and the economy. Shoreline erosion is also presented in the 

context of coastal land loss (http://pubs.usgs.gov/of/2003/

of03-337/), which is a much broader issue than beach erosion because it also includes bluff retreat, and erosion and 

submergence of wetlands around interior bays and estuaries. 

The brief accounts of coastal land loss for each state provide 

a more comprehensive view of coastal processes and key 

references that can be used to learn more about coastal 

change in a broader context.

Disclaimer

Results of the National Assessment of Shoreline 

Change are organized by coastal regions. This report for the 

Gulf of Mexico region is the first in a series of reports that 

will include text summarizing methods, results, and implications of the results in addition to maps, via Internet Map 

Server (IMS), illustrating rates of shoreline change. Rates 

of shoreline change are being published for the purpose 

of regional characterization. The shoreline change results 

and products prepared by the USGS are not intended for 

comprehensive detailed site specific analysis of shoreline 

movement, nor are they intended to replace any official 

sources of shoreline change information identified by local 

or state government agencies, or other federal entities that 

are used for regulatory purposes. Rates of shoreline change 

presented herein may differ from other published rates, but 

differences do not necessarily indicate that the other rates 

are inaccurate. Some discrepancies are expected, considering the many possible ways of determining rates of change, 

and the inherent uncertainty in calculating these rates. Rates 

of shoreline change presented in this report represent shoreline movement under past conditions. The results are not 

intended for predicting future shoreline positions or rates of 

shoreline change.

This publication was prepared by an agency of the 

United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes 

any legal responsibility for the accuracy, completeness, or 

usefulness of any information apparatus, product, or process 

disclosed in the report, or represents that its use would not 

infringe privately owned rights. Reference to any specific 

commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or 

favoring by the United States Government or any agency 

thereof. Any views and opinions of authors expressed herein 

do not necessarily state or reflect those of the United States 

Government or any agency thereof.

Acknowledgments

This report was made possible by the hard work and 

generous cooperation of many individuals. We owe a debt 

of gratitude to Scott Douglass (Alabama), Emmett Foster 

(Florida), Jim Gibeaut (Texas), Shea Penland (Louisiana), 

and Barbara Yassin (Mississippi) for providing electronic 

historical shorelines and accompanying metadata for their 

respective states, Mike Rink (NOAA) for providing digital 

historical shorelines and scans of selected T-sheets, David 

Doyle (NOAA) for providing datum corrections so that 

T-sheets could be rectified before they were digitized by 

the USGS, and Matt Stutz (Duke University) for providing information about beach nourishment projects. An 

enthusiastic and untiring USGS team was responsible for 

developing the methods and computer codes for calculating 

operational mean high water elevations and extracting the 

lidar shorelines. The lidar research and development team 

included Abby Sallenger, Jeff List, Karen Morgan, Eric 

Nelson, Hillary Stockdon, and Kathy Webber. Rob Thieler 

worked closely with TPMC Environmental Services to 

develop and improve the Digital Shoreline Analysis System 

(DSAS) code for shoreline change measurement. Kristy Guy 

spent countless hours testing the DSAS code and suggesting improvements. She also contributed to the layout for the 

maps depicting rates of shoreline change. Lindsey Kraatz 

and Heather Kaminsky provided tremendous assistance by 

digitizing and georectifiying maps and preparing metadata. 

Betsy Boynton prepared the colorful illustrations, and Valerie Paskevich created the IMS. Critical reviews that greatly 

improved the technical content and clarity of the report 

were provided by John Haines, Cheryl Hapke, Jeff List, 

Bruce Richmond, Peter Ruggiero, Abby Sallenger, and Rob 

Thieler of the USGS; Spencer Rogers of North Carolina Sea 

Grant; Jim OʼConnell of Woods Hole Oceanographic Institution Sea Grant; Steve Jones and Bob Mink of the Geological Survey of Alabama; Rebecca Beavers of the National 

Park Service; and Chris Parrish, Maryellen Sault, and Jason 

Woolard of the National Oceanographic and Atmospheric 

Administration (NOAA).

THE ROLE OF STATE AND FEDERAL 

GOVERNMENTS

One reason for conducting this National Assessment 

of Shoreline Change is that there is no widely accepted 

standardized method of analyzing shoreline changes. Each 

state has its own data needs and coastal zone management responsibilities (eg. construction set-back lines, dune 

protection zones), and therefore each state uses a different 

technique and standard to compile shorelines and to calculate rates of shoreline movement. Consequently, calculated 

rates of shoreline change and projected shoreline positions 

are inconsistent from state to state and cannot be compared 
Open-File Report 2004-1043 6

directly. These inconsistencies were clearly demonstrated 

by the Federal Emergency Management Agency (FEMA) 

sponsored erosion studies (Crowell and Leatherman, 1999) 

that were used as the basis for evaluating erosion hazards 

(The Heinz Center, 2000). The USGS National Assessment 

of Shoreline Change represents the first time that shorelines 

from original data sources have been compiled and rates of 

shoreline change have been calculated on a national scale 

using internally consistent methods. The results of this 

analysis allow direct comparison of rates of change from 

one coastal segment to another and form the basis for future 

comparison of shoreline position.

Several federal agencies (USGS, FEMA, NOAA, U.S. 

Army Corps of Engineers (USACE)) have regulatory or 

administrative responsibilities pertaining to shorelines. Yet 

these responsibilities are quite different, requiring different approaches and offering substantial opportunities for 

cooperation. For example, the USACE is authorized and 

funded by Congress to report on the economic and environmental implications of shoreline change and the costs of 

erosion mitigation. Their National Shoreline Management 

Study (Stauble and Brumbaugh, 2003) is being conducted 

using existing shoreline data. The USGS will share data and 

information, such as the lidar-derived shoreline and rates of 

change, in support of their effort. NOAA has the mandate 

to establish the official shoreline boundary for the nation 

using tidal datums. Their emphasis is on safe navigation and 

using the shoreline to generate nautical charts. NOAA also 

has a developing program (V datum), which will greatly 

assist other agencies in establishing alternative shorelines 

for a variety of purposes where the official shoreline is 

inappropriate. Congress authorized and funded FEMA to 

report on the economic impact of erosion hazards on coastal 

communities, and on claims to the National Flood Insurance 

Fund. To accomplish this, FEMA contracted state agencies 

and academic researchers to conduct a pilot study of erosion hazards that included shoreline change data for limited 

geographic areas. The USGS is responsible for conducting 

research pertaining to coastal change hazards including 

shoreline change, understanding the processes that cause 

coastal change, and developing models to predict future 

change. The USGS is the only government agency that has 

a dedicated program to monitor coastal change into the 

future using consistent methods nationwide. Such a program 

is critically important to assess national issues, such as the 

coastal impacts of sea level rise.

PRIOR NATIONAL AND GULF COAST 

SHORELINE ASSESSMENTS

The USACE (1971) conducted the first national assessment of coastal erosion that included the Gulf of Mexico 

Region. That study identified areas of critical and noncritical erosion on the basis of economic development and 

potential for property loss, but rates of shoreline movement 

were not evaluated. Dolan and others (1985) conducted a 

comprehensive analysis of shoreline changes for the U.S. 

Their analysis was based on compilation of rates of shoreline change provided by other contributors and derived from 

their own studies of the middle Atlantic region. Rates of 

change were presented on maps, and the long-term trends of 

erosion and accretion were summarized in an accompanying 

text. 

A previous quantitative analysis of shoreline movement 

that focused entirely on the U.S. shores bordering the Gulf 

of Mexico was conducted for the Environmental Protection 

Agency (EPA) Gulf of Mexico Program. From that study, a 

map entitled “Historical Shoreline Change in the Northern 

Gulf of Mexico” was published in 1991. The map (scale 

1:2,000,000) depicted rates of shoreline change that were 

prepared by a contributor for each state. The EPA map was 

revised and reissued in 1996 (Coastal Erosion Subcommittee, 1996). There have been numerous local studies of 

shoreline movement in each of the Gulf Coast states. Rather 

than attempting to summarize all of these studies, Table 1 

recognizes most statewide or regional studies and provides 

appropriate references. 

Since the work of Dolan and others (1985), methods of 

obtaining, analyzing, displaying, and storing shoreline data 

have improved substantially, and coastal change has continued. Furthermore, coastal scientists have not agreed on standard methods for analyzing and reporting shoreline changes, 

nor have they identified rigorous mathematical tests that 

are widely accepted for quantifying the change and associated errors. Consequently, there are critical needs for (1) a 

nationwide compilation of reliable shoreline data including 

the most recent shoreline position, and (2) a standardization 

of methods for obtaining and comparing shoreline positions 

and mathematically analyzing the trends.

METHODS OF ANALYZING 

SHORELINE CHANGE

Compilation of Historical Shorelines

Coastal scientists in universities and government agencies have been quantifying rates of shoreline movement 

and studying coastal change for decades. Before GPS and 

lidar technologies were developed, the most commonly used 

sources of historical shoreline position were NOAA Topographic Sheets (T-sheets, see Shalowitz, 1964) and aerial 

photographs. Ideally, extraction of shoreline position from 

these data sources involves geo-referencing and removing 

distortions from maps or aerial photographs, followed by 

digitizing shoreline position. Depending on coastal location, data source, and scientific preference, different proxies 

for shoreline position are used to document coastal change, 

including the high water line (for discussion of the high 

water line (HWL) see Shalowitz, 1964), wet-dry line, veg-
Open-File Report 2004-1043 7 

etation line, dune toe or crest, toe of the beach, cliff base or 

top, and the line of mean high water (MHWL). 

In addition to deriving a modern shoreline from lidar 

data, the USGS National Assessment of Shoreline Change 

Project incorporates shoreline positions from pre-existing 

historical shoreline databases. Numerous organizations and 

individuals have provided the USGS with digital shoreline 

data (Table 2). To maintain consistency at a national scale, 

shorelines from four periods (mid- to late1800s, 1920s1930s, 1970s, and post-1998) were selected for analysis 

regardless of the number of shorelines available from existing data sets. Any remaining data gaps were filled using 

scans of historical T-sheets provided by the NOAA Vectorization Project.

Shorelines were compiled for each state following 

the guidelines established for selected periods (mid- to late 

1800s, 1920s-1930s, 1970s, and post-1998) as closely as 

possible. Table 3 lists the final range of years for shorelines 

compiled for each period by state. A few notable exceptions 

include a second-period shoreline for Florida covering years 

up to 1953, a second-period shoreline for Alabama covering 

years up to 1957, and a third-period shoreline for Mississippi covering the years 1986-1987. The Florida shoreline 

incorporates a small segment in West Florida dated 1957 

and a few additional segments from the early 1940s due to 

a lack of alternatives for those specific areas. In Alabama, a 

1917 shoreline for the westernmost 8 km of Dauphin Island 

was disregarded because the island was severely impacted 

by a storm in 1917. A 1957 shoreline segment was included 

as an alternative. The 1980s Mississippi shoreline was 

selected due to a lack of alternatives closer to the 1970s 

period.

Delineation of a Modern (lidar-derived) 

Shoreline

The most recent shoreline used in this National Assessment (post-1998) was derived from lidar (light detection and 

ranging) data. The USGS, in collaboration with NASA, has 

been using the NASA Airborne Topographic Mapper (ATM) 

to map coastal areas since 1997 (Krabill and others, 2000; 

Sallenger and others, 2003). The ATM surveys ground 

elevation using an elliptically rotating blue-green laser. GPS 

(global positioning system) positions and inertial navigation systems are used to correct for aircraft pitch, roll, and 

heading, providing ground elevations with accuracies of 

about ±15 cm (Sallenger and others, 2003). Most of the lidar 

surveys used to extract shorelines for this report were conducted in 2001 (Table 3). This includes the NASA surveys 

as well as additional lidar data for the Texas coast, which 

was provided by The University of Texas at Austin Bureau 

of Economic Geology (Table 2). 

To compare with historical shorelines, an operational 

MHW shoreline was extracted from the lidar surveys using 

a method developed by Stockdon and others (2002)(Fig. 1). 

Shorelines were extracted from cross-shore profiles which 

consist of bands of lidar data 2-4 m wide in the alongshore 

direction and spaced every 20 m along the coast. A leastsquares linear regression line is passed through the cluster of 

data that encompasses the operational MHW datum (Table 

4) and is limited to the seaward-sloping beach foreshore. 

The regression equation is then used to derive the horizontal 

intersection of the operational MHW datum with the profile, 

giving the shoreline position for that profile. Repeating 

this procedure at successive profiles 20 m apart generates a 

continuous shoreline. 

To determine the operational MHW elevation, the Gulf 

of Mexico region was divided into 3 subregions. For each 

subregion, the operational MHW elevation represents an 

average of MHW elevations from individual open-ocean or 

a

 Primarily compilation of rates of change provided by other investigators

b

 Compilation of rates of change provided by state contributors

Region References

Gulf Coast states Dolan and others, 1985a, Coastal Erosion Subcommittee, 1996b;

West Florida Clark, 1991; Dean and others, 1998

Alabama Hardin and others, 1976, Sanchez and Douglass, 1994

Mississippi Waller and Malbrough, 1976; Byrnes and others, 1991;

Louisiana Morgan and Larimore, 1957; McBride and others, 1992

Texas Morton, 1977a; Paine and Morton, 1989; Morton, 1997

Table 1. Prior reports of quantitative regional analyses of long-term historical shoreline movement that used shorelines derived 

from T-sheets and aerial photographs.
Open-File Report 2004-1043 8

near open-ocean tide gauges. A list of tide gauges and MHW 

elevations used in each subregion is presented in Table 4. 

The lidar-extracted MHW shoreline is not the same as a 

MHW shoreline surveyed by a licensed land surveyor. This 

is because the operational MHW elevation used for the lidar 

shoreline is an average of the MHW elevations at several 

tide gauges. Furthermore, the lidar-extracted shoreline is 

intended only as a reference feature for measuring shoreline 

change. It is not intended to establish legal boundaries.

Because wetlands generally are not suitable sites for 

extraction of a lidar shoreline, extensive wetland areas 

such as the mangrove swamps of south Florida, Big Bend 

marsh of Florida, and much of the Mississippi delta were 

not included in the shoreline change analysis. Also, lidar 

surveys were not available for sandy beaches in west Florida 

from Cape Romano to Sanibel Island, and along the chenier 

plain in southwestern Louisiana. When lidar data are available for these gaps, the shoreline change analyses will be 

conducted and provided in future reports and as on-line 

updates.

Texas University of Texas at Austin

Bureau of Economic Geology

NOAA T-sheets, aerial

photographs, lidar Entire Coast

Louisiana University of New Orleans Department of

Geology and Geophysics

NOAA T-sheets, aerial

photographs Entire Coast

University of South Alabama Department

of Civil Engineering T-Sheets Fort Morgan to Gulf Shores

NOAA Coastal Services Center Scanned NOAA T-sheets Dauphin Island

NOAA Vectorization Project NOAA T-sheets Entire Coast

Alabama

Mississippi Office of Geology Photo and Map Shorelines Dauphin Island, Fort Morgan

Mississippi Office of Geology Photo and Map Shorelines Entire Coast

Mississippi

NOAA Vectorization Project NOAA T-sheets Entire Coast

Department of Environmental Protection, NOAA T-sheets Entire Coast

Florida Pinellas County Public Works NOAA T-sheets Egmont Key

NOAA Vectorization Project NOAA T-sheets Panhandle: Escambia to Bay County

West Coast: Pinellas to Lee County

State Organization Original Data Source Spatial Coverage

Table 2. Providers and original sources of historical shorelines for each Gulf Coast state.

Selected Periods

State mid- to late- 1800s 1920s - 1930s 1970s post-1998

Florida 1855-1895 1926-1953 1976-1979 1998-2001

Alabama 1849-1867 1918-1957 1978-1981 2001

Mississippi 1850 1917 1986-1987 2001

Louisiana 1855-1887 1922-1934 1973-1978 2001

Texas 1850-1883 1930-1938 1970-1975 2000-2001

Table 3. Dates of compiled shorelines for selected periods.
Open-File Report 2004-1043 9 

Geographic Information System (GIS) 

Procedures

Digital shorelines for each selected period were 

compiled as ESRI ArcView shapefiles and a quality assessment was performed. Shoreline gaps for each period were 

identified and NOAA T-sheet indexes were used to determine T-sheet availability for those areas. T-sheets were then 

requested from NOAA and received as scanned TIF images.

T-sheets were rectified using Erdas Imagine geographic 

imaging software by placing at least 6 well-spaced ground 

control points (GCPs) on selected T-sheet graticules in 

geographic coordinates. Some T-sheets produced before 

1930 required additional coordinate transformation information from NOAA to convert from the United States Standard Datum (USSD) to the North American Datum of 1927 

(NAD27). The datum transformation was applied to T-sheet 

graticule coordinates prior to rectification. Total Root Mean 

Square (RMS) error for the rectification process was maintained below 1 pixel, which is approximately 4 m at a scale 

of 1:20,000 and approximately 1.5 m at a scale of 1:10,000. 

Typically the resulting RMS was much lower than one pixel. 

Newly geo-referenced T-sheets were loaded in ArcView 

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Figure 1. Example of a lidar profile from September 26, 1997 at Kitty Hawk, North Carolina for (a) the entire crossshore region and (b) an expanded view of the foreshore region. (a) Laser returns off of the water’s surface are 

seen as the noisy signal seaward of x = 350 m. Bold symbols indicate data points within ± 0.5 m of the operational 

MHW datum. (b) The asterisk marks the cross-shore position of the shoreline on the foreshore. The horizontal 

error bar represents the 95% confidence interval about the estimate. From Stockdon and others (2002).
Open-File Report 2004-1043 10

and shorelines were digitized. Completed shoreline vectors 

were finally converted to the Universal Transverse Mercator 

(UTM) projection with the North American Datum of 1983 

(NAD83).

Shorelines from all sources were merged to produce a 

single shoreline for each of the 4 time periods by state. Final 

shorelines were coded with 6 attribute fields (ID, Type, 

Date, Description, Source, and Accuracy) to prepare for 

calculating shoreline change rates with the Digital Shoreline 

Analysis System (DSAS). The attributes include the original 

survey year in the Date field and the source of the data in 

the Source field. 

Calculation and Presentation of Rates of 

Change

Rates of long-term shoreline change were generated in 

a GIS with the Digital Shoreline Analysis System (DSAS) 

version 2.0, an ArcView extension developed by the USGS 

in cooperation with TPMC Environmental Services. The 

extension is designed to efficiently lead a user through the 

major steps of shoreline change analysis. This extension 

to ArcView contains three main components that define a 

baseline, generate orthogonal transects at a user-defined 

separation along the coast, and calculate rates of change 

(linear regression, endpoint rate, average of rates, average 

of endpoints, jackknife). The extension utilizes the Avenue 

code to develop transects and rates, and uses the Avenue 

programming environment to automate and customize the 

user interface.

Baselines were constructed seaward of, and parallel 

to, the general trend of the four shorelines. Using DSAS, 

transects were spaced 50 m apart. Transects were manually 

eliminated to prevent calculation of rates in areas where 

less than four shorelines were intersected. Fewer than four 

shorelines can result from one or more of the following 

conditions (Fig. 2): 1) an inlet eliminated one or more of 

the shorelines, 2) shoreline segments were missing (data 

gaps), 3) a barrier island migrated laterally (no overlap of 

shorelines and/or misrepresentation of rates), 4) a shoreline 

disappeared over time. 

Long-term rates of shoreline change were calculated 

at each transect using linear regression applied to all four 

shoreline positions from the earliest (1800s) to the most 

recent (derived from lidar). Linear regression was selected 

because it has been shown to be the most statistically robust 

quantitative method when a limited number of shorelines 

are available (Crowell and others, 1997). It is also the 

most commonly applied statistical technique for expressing 

shoreline movement and estimating rates of change (Crowell and Leatherman, 1999). Short-term rates of shoreline 

change were calculated using the endpoint method comparing the 1970s and most recent (lidar-derived) shoreline 

positions. Long-term rates and short-term rates of shoreline 

change, as defined here, are used throughout the report. 

Site Name

MHW above NAVD88

(m) (m)

Average of MHW

Corpus Christi, TX 0.281

Galveston Pleasure Pier, TX 0.369 0.37

Grand Isle, LA 0.468

Gulfport Harbor, MS 0.318

Dauphin Island, AL 0.24

Navarre Beach, FL 0.22

St. Andrews State Park, FL 0.216 0.23

Mexico Beach, FL 0.18

Cape San Blas, FL 0.16

Alligator Point, FL 0.27

Baileys Bluff, FL 0.17

Clearwater Beach, FL 0.14

Indian Rocks Beach, FL 0.09

St. Petersburg Beach, FL 0.065 0.09

Venice, FL 0.067

Captiva Island, FL 0.024

Naples, FL 0.09

Marco Island, FL 0.11

Table 4. List of tide gauge measurements used to calculate mean high water elevation.
Open-File Report 2004-1043 11 

Both long-term and short-term rates of shoreline change 

calculated for each transect (50 m alongshore spacing) were 

color coded according to class interval with green colors 

indicating accretion and red colors indicating erosion. The 

shoreline change rates and individual shoreline data layers 

were compiled into an ArcIMS, or Arc Internet Map Server, 

viewable at http://coastalmap.marine.usgs.gov/.

Shoreline Definitions and Beach Alterations 

that Influence Rates of Change

Shoreline Definitions

Inclusion of a lidar-derived shoreline represents a new 

approach to the investigation of shoreline change. The three 

pre-lidar historical shorelines come from topographic maps 

and aerial photographs that use the HWL as the shoreline 

proxy. For more than 150 years the HWL has served as the 

authoritative shoreline because it could be visually identified in the field. With advanced technologies, such as GPS 

and lidar, it is possible to define the shoreline on the basis of 

an elevation or a tidal datum, such as MHW. Changing the 

shoreline definition from a physical feature that is uncontrolled in terms of an elevation datum to a shoreline defined 

by an elevation has important implications with regard to 

inferred changes in shoreline position and calculated rates of 

change. 

Published and unpublished data were compiled to 

evaluate the horizontal and vertical differences in HWL 

determined from beach profiles, aerial photographs, or GPS 

surveys, and the MHWL derived from beach profiles, GPS 

surveys, or lidar surveys (Table 5). The HWL and MHWL 

positions were established at the same time, or within a few 

weeks of one another at multiple sites around the U.S. where 

the beach and wave characteristics are diverse. Comparing 

these HWL and MHWL positions assumes that the observed 

offsets are entirely artifacts of shoreline definition and are 

not related to actual changes in the beach profile between 

the survey dates. This is a relatively safe assumption considering the short intervals between surveys or the knowledge 

that a particular shoreline segment is relatively stable.

Table 5 shows that average absolute horizontal and 

vertical offsets between the HWL and MHWL range from a 

few meters to more than 50 m, and vertical offsets can be as 

much as 2 m. Most of the horizontal offsets are less than 20 

landward

seaward

landward

seaward

A Inlet Openings B Missing Data

C Barrier Migration D Shoreline Loss

offshore baseline offshore baseline

offshore baseline offshore baseline

Shorelines Transects

eliminated

1800s used for calculation

2000s

1970s

1930s

transect/shoreline

intersection

Figure 2. Examples of common conditions where transects are eliminated in the absence of four shoreline intersections.
Open-File Report 2004-1043 12

m, and most of the vertical offsets are less than 1 m. Offsets 

are greatest on relatively flat beaches where high waves produce high wave runup (southwest Washington). Conversely, 

offsets are least where beaches are relatively steep and wave 

runup is low (west coast of Florida). Because breaking 

waves run up on the beach, the MHWL is most commonly 

seaward of the HWL (Morton and Speed, 1998). For the 

data we analyzed, the MHWL was seaward of the HWL at 

more than 90% of the transects (Table 5). Because we are 

using a MHWL shoreline for the latest period, this nearly 

systematic horizontal offset between the HWL and the 

MHWL could cause shoreline positions and calculated rates 

of change to imply slower erosion, a change from erosion to 

accretion, or faster accretion depending on actual changes at 

a given site. 

Human Activities

Attempts to stabilize the shore can also greatly influence the rates of shoreline change. Activities such as beach 

nourishment or emplacement of shoreline stabilization 

structures tend to alter coastal processes, sediment transport, 

and shoreline position. For example, beach nourishment 

artificially causes rapid, temporary shoreline accretion. 

Depending on the frequency of beach nourishment, the 

placement of large volumes of sand on the beach will bias 

the rates of observed shoreline change toward accretion or 

stability, even though the natural beach, in the absence of 

nourishment, would be eroding.

Trembanis and Pilkey (1998) prepared a summary of 

identifiable beach nourishment projects in the Gulf Coast 

region that had been conducted before 1996. These records 

were used to identify shoreline segments that had been 

influenced by beach nourishment. Additional information 

regarding beach nourishment was provided by Steve Jones 

of the Alabama Geological Survey, Scott Douglass of the 

University of South Alabama, and Ralph Clark of the Florida Department of Environmental Protection. Only projects 

that pre-date the lidar shoreline were included. There is no 

distinction made between large volume, continuous projects 

and small volume, finite projects. According to Trembanis 

and Pilkey (1998), beaches along the west coast of Florida 

are some of the most frequently nourished beaches in the 

U.S. The frequent nourishment is reflected in the slow rates 

of shoreline retreat or stability, even though the natural rates 

of erosion may be higher. Differentiating between natural 

rates of erosion and the influences of beach nourishment is 

difficult because experiments have not been conducted to 

specifically address this issue. In addition, available data 

may be inadequate to address this issue because there are 

not enough shoreline positions immediately before, after, 

and between nourishment projects. Human responses to 

coastal erosion in each state, including beach nourishment 

and emplacement of structures, are discussed in more detail 

in a later section.

Reliability of the Results

Documented trends and calculated rates of shoreline 

change are only as reliable as: (1) measurement errors that 

determine the accuracy of each shoreline position, (2) sampling errors that account for the variability of shoreline posiLocation

Survey Date

HWL

Survey

Date

MHWL

Length of

Shore

(km)

Number of

Observations

Average

Horizontal

Offset

(m)

Average

Vertical

Offset

(m)

% MHWL

with

Seaward

Offset Data Source or Reference

1 Simultaneous measurement of HWL and MHWL at beach profiles coordinated with tide gauge measurements

2 Video camera projections of HWL for 111 days during a three-year period and MHWL from generalized beach profiles

3 Nearly simultaneous aerial photographs (HWL) and GPS surveys (MHWL)

4 Nearly simultaneous GPS (HWL) and lidar surveys (MHWL)

Galveston Is., TX1 01-27-95 01-27-95 Point 1 18 0.6 100

08-16-95 08-16-95 1.6 6 8 0.4 100

09-14-95 09-14-95 1.6 6 8 0.2 100

09-28-95 09-28-95 1.6 6 12 0.2 100

North Padre Is., TX1

10-06-95 10-06-95 1.6 6 6 0.3 100

Morton and Speed, 1998

Duck, NC2 1994-19962 Point 111 40 2.0 100 Pajak and Leatherman, 2002

05-26-99 05-28-99 3.0 171 22 0.5 100 Klipsan, WA3

09-21-99 09-24-99 3.0 171 52 0.8 100

05-26-99 05-28-99 4.0 200 23 1.0 100

Ocean Shores, WA 07-27-99 07-22-99 4.0 200 8 0.2 100 3

05-06-01 05-07-01 4.0 200 30 1.0 100

Oysterville, WA3 09-21-99 09-10-99 3.5 201 49 0.9 100

Ruggiero and others, 2003

03-16-98 & 03-17-98 04-03-98 58.6 1172 11 0.7 99

09-29-99 & 10-28-99 10-01-99 60.0 1200 20 1.6 100

06-13-01 & 06-14-01 06-05-01 52.4 1049 8 0.6 92

National Park Service (M. Duffy) Assateague Is., MD/ VA4

10-01-02 09-12-02 47.7 953 22 1.4 98 Coastal Research and Engineering, Inc. (M. Byrnes)

Table 5. Absolute horizontal and vertical differences between high water and mean high water shorelines.
Open-File Report 2004-1043 13 

tion, and (3) statistical errors associated with compiling and 

comparing shoreline positions. Anders and Byrnes (1991), 

Crowell and others (1991), Thieler and Danforth (1994), 

and Moore (2000), provided general estimates of the typical measurement errors associated with mapping methods 

and materials for historical shorelines, registry of shoreline 

position relative to geographic coordinates, and shoreline 

digitizing. The largest errors were positioning errors of 

±10 m, which were attributed to scales and inaccuracies 

in the original surveys (T-sheets and aerial photographs). 

However, the influence of large shoreline position errors 

on long-term rates of change can be reduced because the 

period of analysis is so long (>100 yrs). Stockdon and others 

(2002) provided estimates of GPS positioning errors (±1 m) 

and regression errors (±1.5 m) associated with shorelines 

derived from lidar data. 

Estimates of the maximum measurement errors for 

this study are provided in Table 6 to show how each error 

contributes to uncertainty in the shoreline position and 

in the rates of change. A total shoreline position error 

(Esp)(equation 1) incorporates all of the measurement errors 

by taking the square root of the sum of the squares of: rectification error (Er

), digitizing error (Ed), T-sheet survey error 

(Et), shoreline proxy offset (Eo), and lidar position error (El). 

Rectification error represents the elected maximum acceptable RMS error for T-sheets at a scale of 1:20,000 in this 

study. We assume data from outside sources conforms to 

similar standards. The rectification error is applied to the 

historical shorelines only. Digitizing error reflects the maximum digitizing error specified in past studies (Anders and 

Byrnes, 1991; Crowell and others, 1991; Moore, 2000). The 

digitizing error is applied to the historical shorelines only. 

The maximum T-sheet survey error, determined by Shalowitz (1964), incorporates all of the errors associated with 

the mapping process including distance to rodded points, 

plane table position, and identification of the HWL. The 

T-sheet survey error is applied only to historical shorelines 

from time periods 1 and 2 (1800s shoreline and 1920-1930s 

shoreline, respectively), as it is assumed that more recent 

shorelines are derived from aerial photos or other sources. 

The shoreline proxy offset reflects the maximum horizontal 

offset between high water and mean high water shorelines 

in the Gulf of Mexico (see Table 5). The offset error pertains 

only to the lidar-derived shoreline. Lidar position error 

reflects the maximum error associated with the derivation 

of a lidar shoreline (Stockdon and others, 2002). The lidar 

position error is applied only to the lidar-derived shoreline. 

Thus, total shoreline position error is expressed by equation 1:

A separate Esp can be calculated for each period. 

Finally, the position errors for each period can be incorporated into an error for each transect. That value can be 

annualized to provide an error estimation for the shoreline 

change rate at any given transect. The annualized error (Ea) 

is expressed by equation 2:

The maximum annualized error using best estimates for 

Gulf of Mexico shorelines is 0.2 m/yr (Table 6).

Sampling errors relating to the local short-term variability of true shoreline positions (Morton, 1991; Douglas 

and Crowell, 2000) are less well known. Temporally dense 

data are required to evaluate short-term shoreline variability 

resulting from seasonal cycles and from rapid storm erosion 

and subsequent recovery. Moreover, most data sets include 

some apparent shoreline movement caused by changes in 

water level (HWL) and not changes in sediment volume 

(Morton, 1991). Lack of reliable high frequency data regarding short-term variability of true shoreline position at most 

coastal sites limits the ability to quantify and incorporate 

the associated uncertainty into the overall shoreline position 

uncertainty. An exception is the 20-year record of beach 

profiles surveyed by the COE at Duck, N.C. Using 460 

shoreline positions from the Duck profile data, Barton and 

*Time periods: 1=1800s; 2=1920s-1930s; 3=1970s; 4=post-1995

Time Period*

Measurement Errors (m) 1 2 3 4

Rectification error (Er) 4 4 4 0

Digitizing error (Ed) 1 1 1 0

T-sheet survey error (Et

) 10 10 0 0

Shoreline proxy offset (Eo) 0 0 0 18

Lidar position error (El) 0 0 0 1.5

Total shoreline position error (Esp) (m) 10.8 10.8 4.1 18.1

Annualized transect error (Ea) (m/yr) 0.2

Table 6. Maximum estimated measurement errors for Gulf of Mexico shorelines.
Open-File Report 2004-1043 14 

others (2003) showed that the envelope (range) of shoreline 

positions even around a relatively stable shoreline was about 

±20 m. 

Linear regression is the most commonly applied 

statistical technique for expressing shoreline movement 

and estimating rates of change (Crowell and Leatherman, 

1999). Linear regression assumes linear behavior, which 

technically is incorrect (Morton, 1991; Barton and others, 

2003), but is adequate for a first approximation. Because 

linear regression fails to recognize the potential for temporal differences in trend (trend reversals) and accelerations 

or decelerations (Morton, 1991; 1996), average trends and 

rates of shoreline change in this study were calculated for 

long-term (entire period) and short-term (most recent) time 

scales. Long-term rates of shoreline change were determined at each transect by taking the slope of the regression 

line applied to all four shoreline positions. The resulting 

rate is reported in units of m/yr (Table 7). Uncertainties for 

the long-term rates (± values in Table 7) are also reported 

in units of m/yr. The reported uncertainties represent a 90% 

confidence interval for the slope of the regression line. This 

means with 90% statistical confidence that the true rate 

of shoreline change falls within the range defined by the 

reported value plus or minus the error value. The variability 

around the trend line reflects both measurement and sampling errors. 

Field observations and prior studies of shoreline movement within each State bordering the Gulf of Mexico (Table 

1) suggest that the trends and relative rates of change presented in this study are reasonably accurate. Reliability of 

the mapped results increases as both the persistence of the 

trend and rates of change increase. Stated another way, confidence in the analytical results is greatest where the rates 

of shoreline erosion or accretion are high and the trend has 

persisted for decades. On the other hand, confidence in the 

absolute results decreases where the shoreline is relatively 

stable and the rates of change are low. This is because minor 

differences in historical or lidar shoreline positions can alter 

substantially the regression line and the calculated results. 

Data confidence also decreases in areas where frequent 

trends reversals occur.

Advanced technology such as GPS and lidar can better 

constrain shoreline positions, reduce the methodological 

errors, and improve the accuracy (reduce the error) of future 

historical shorelines. Establishing a datum-based shoreline (lidar derived MHWL) as the standard for comparison 

provides, for the first time, the ability to perform an error 

analysis that is both quantitative and meaningful, in terms of 

its application. In the future, each electronic MHWL shoreline could be presented with an accompanying error bar that 

would define the alongshore envelope of confidence. Subsequent shorelines and associated confidence envelopes would 

provide a more precise basis for determining the statistical 

significance of observed shoreline change. Unfortunately, 

the use of lidar or any other shoreline mapping technology 

will still require distinguishing between short-term variability in shoreline position and the long-term trend of shoreline 

change.

GEOMORPHOLOGY OF THE GULF 

COAST REGION

The Gulf Coast region encompasses west Florida, Alabama, Mississippi, Louisiana, and Texas (Fig. 3). This lowlying area comprises a variety of coastal features including 

mainland shores, bays and lagoons, deltaic plains, chenier 

plains, barrier islands and peninsulas, and tidal inlets (Fig. 

4). The physical characteristics and geologic framework 

of each of these features partly determine the trends and 

rates of shoreline movement and related coastal changes 

of the region. In the following descriptions, the numbers in 

parentheses following a geographic location or feature refer 

to Figure 3.

Table 7a. Long-term shoreline change trends, derived from linear regression rates using 4 shorelines.

Erosion Rates (m/yr) Accretion Rates (m/yr)

State Number of Transects

Mean Shoreline Change

Rate (m/yr) % Erosion Max Mean % Accretion Max Mean

Florida 10,644 -0.1 ± 0.1 58 -7.7 ± 3.4 -0.8 ± 0.9 42 7.6 ± 8.5 0.9 ± 1.2

Alabama 1,294 -0.4 ± 0.8 75 -2.8 ± 1.9 -0.8 ± 0.8 25 2.2 ± 0.5 0.5 ± 0.9

Mississippi 724 -2.3 ± 1.9 80 -13.5 ± 3.3 -3.1 ± 1.8 20 3.0 ± 3.1 1.0 ± 2.2

Louisiana 2,490 -7.1 ± 4.5 91 -36.8 ± 14.2 -8.2 ± 4.4 9 7.2 ± 12.0 2.5 ± 5.2

Texas 10,626 -0.7 ± 1.7 64 -9.2 ± 5.1 -1.8 ± 1.3 36 14.9 ± 18.6 1.2 ± 2.4

Table 7b. Short-term shoreline change trends, derived from end-point rates using 2 recent shorelines.

Erosion Rates (m/yr) Accretion Rates (m/yr)

State Number of Transects

Mean Shoreline Change

Rate (m/yr) % Erosion Max Mean % Accretion Max Mean

Florida 11,116 0.2 54 -21.3 -1.5 46 37.3 2.2

Alabama 1,466 0.3 42 -9.2 -1.5 58 10.4 1.5

Mississippi 968 -2.1 63 -46.4 -5.8 37 19.4 4.4

Louisiana 2,924 -10.1 88 -78.6 -12.0 12 19.1 3.9

Texas 10,912 -0.1 48 -25.1 -2.6 52 48.2 2.2

Table 7a. Long-term shoreline change trends, derived from linear regression rates using four shorelines.

Table 7b. Short-term shoreline change trends, derived from end-point rates using two recent shorelines.
Open-File Report 2004-1043 15 Figure 3. Index map of the Gulf Coast region. 68 67 66 65 64 62 61 60 5958 57 56 54 55 63 53 52 51 50 48 47 46 45 44 43 4241 40 37 39 36 35 33 32 31 28 27 26 25 23 24 21 20 19 18 171513 16 12 14 11

9

10

8

7

6

5

4

2

3

1

30

29

34

38

22

49

GULF OF MEXICO

TX

LA

MS AL 

FL

Texas53. Sabine Pass54. Bolivar Peninsula55. Galveston Bay56. Galveston Island57. Follets Island58. Brazos River59. Sargent Beach60. Matagorda Peninsula61. Matagorda Island62. San Jose Island63. Corpus Christi Bay64. Mustang Island

65. North Padre Island66. Central Padre Island67. South Padre Island68. Rio Grande

Louisiana43. Chandeleur Islands44. Curlew, Grand Gosier, and Breton Islands45. Mississippi River46. Grand Isle47. Caminada-Moreau headland48. Timbalier Island49. Isle Derniere-Racoon Island50. Atchfalaya River and Bay51. Grand Chenier52. Holly-Peveto-Constance Beaches

Mississippi36. Horn Island37. Ship Island38. Cat Island39. Mississippi Sound40. Pascagoula41. Biloxi42. Bay St.Louis

Alabama32. Gulf Shores33. Morgan Peninsula34. Mobile Bay35. Dauphin Island

Florida1. Key West2. Marco Island3. Naples4. Sanibel Island5. Captiva Island6. Manasota Key7. Venice8. Siesta Key-Sarasota Bay

9. Longboat Key10. Egmont Key11. Tampa Bay12. Sand Key-St. Petersburg13. Redington Shores-Indian Rocks14. Clearwater15. Caladesi Island (Hog Island)16. Honeymoon Island (Hog Island)17. Anclote Key18. Tarpon Springs19. Crystal River20. Lighthouse Point21. St. Georges Island and Sound22. Apalachicola River and Delta23. Cape San Blas24. St. Joseph Peninsula25. Mexico Beach26. Panama City27. Destin28. Ft. Walton Beach29. Santa Rosa Island and Sound30. Pensacola Bay31. Perdido Key and Bay
Open-File Report 2004-1043 16 

Gulf of Mexico Mainland Shores

The U.S. coast bordering the Gulf of Mexico consists mainly of barrier islands, but there are some segments where the mainland shore meets the Gulf without an 

intervening bay or lagoon. For example, in Florida sandy 

mainland shores are exposed to Gulf waves near Mexico 

Beach (25), Venice (7), and Naples (3); a sandy bluff shore 

extends from Panama City (26) to Ft. Walton Beach (28); 

and a marsh shore is found from Tarpon Springs (18) to 

Apalachicola (22). The only mainland shore in Alabama is 

a sandy stretch of beach near Gulf Shores (32). In Mississippi, sandy and marsh mainland shores extend from 

Pascagoula (40) westward to the Louisiana state line. There 

are mainland shores along the Caminada-Moreau headland 

(47) and chenier plain (51) of southwestern Louisiana. In 

Texas, Gulf mainland shores are located between Sabine 

Pass (53) and Bolivar Peninsula (54), between Follets Island 

(57) and Matagorda Peninsula (60), and near the mouth of 

the Rio Grande (68). The mainland Gulf shores in Louisiana 

and Texas generally are locally underlain with mud and the 

beaches are narrow.

Bays and Lagoons

Most large coastal bays bordering the Gulf of Mexico 

are drowned river valleys that have remained unfilled 

because the rivers emptying into the bays are transporting 

very little sediment. Bays are oriented perpendicular to the 

Gulf shoreline, whereas lagoons are parallel to the Gulf 

shoreline. Some lagoons are locally named bays or sounds 

such as Sarasota Bay, Florida (8) and Santa Rosa Sound, 

Florida (29). The coastal lagoons formed when the uplands 

between the river valleys were flooded by rising sea level, 

so the lagoons separate the barrier islands from the mainland.

Bay and lagoon shores account for the longest stretches 

of eroding shoreline (Smith, 1990; Doyle and others, 1984; 

Canis and others, 1985; Morton and Paine, 1990; Penland 

and others, 1990). They are also the most complex in terms 

of land loss because they have different orientations and 

relief, and they cut across sediments with different elevations and resistance to erosion. Bay shores can be composed 

of sand, shell, or mud and they can form low beaches, tall 

bluffs, or marshes. Analyses of shoreline changes in bays 

and lagoons are not included because the focus of this report 

is on the Gulf shoreline.

Barrier Islands

Origin and Evolution of Barriers

The origins and related morphologies of barrier islands 

can influence shoreline movement because the thicknesses 

River

Bayhead Delta Mainland

Shore

Peninsula

Tidal Inlet

Bay

(estuary)

River

Delta plain

Lagoon

Barrier

Island

Tidal Inlet

Waves

Longshore

Currents

Chenier plain

Figure 4. Common coastal landforms of the Gulf Coast region.
Open-File Report 2004-1043 17

and volumes of sand stored in the barriers are related to 

the processes that formed them. Barrier islands commonly 

form the outer fringes of low-lying coastal plains throughout the world. As their name implies, they are surrounded 

by water and are separated from the adjacent mainland by 

lagoons, bays, or marshes and from neighboring islands by 

tidal inlets. Barrier islands are long and narrow mounds of 

sand deposited by waves and wind over millenia. In general, 

they are produced by long-term submergence of the lowgradient coast. Three independent mechanisms (Fig. 5) 

have been proposed for the origins of barrier islands: (1) 

dune drowning (McGee, 1890), (2) spit accretion (Gilbert, 

1885), and (3) shoal emergence (De Beaumont, 1845). Each 

mechanism explains the origin of some barriers (Hoyt, 

1967), but no single cause explains the origins of all barriers 

(Schwartz, 1971). 

Barrier islands can form by dune drowning (Fig. 5A) 

when a relative rise in sea level partly inundates the mainland ridge of coastal dunes. The rising water encompasses 

the sand dunes along the beach and eventually floods the 

seaward sloping coastal plain between the dunes and upland, 

forming a lagoon.

Spit accretion (Fig. 5B) refers to lateral barrier extension along the prevailing trend of the beach. Sand transported along the coast by longshore currents is deposited on 

the flanks of headlands or at the downdrift ends of existing 

barrier islands. Spit accretion is a widely observed process 

whereby barriers are originally constructed across embayments forming lagoons, or previously formed barriers are 

enlarged in a downdrift direction. Recurved beach ridges 

are diagnostic field evidence of spit accretion. This type of 

barrier formation generally occurs under stable sea-level 

conditions and/or a surplus of sand supply.

Shoal emergence (Fig. 5C) involves the upward growth 

of a submerged bar where sand is supplied by erosion and 

redistribution of sediment on the sea floor. The vertical 

accumulation of sand causes the bar to eventually rise above 

the ocean level so that the emergent bar forms a barrier 

island. Shoal emergence is aided by a slight lowering of 

relative sea level, such as after a storm, and it also requires a 

local surplus of sand to maintain the barrier. 

All three origin scenarios are represented in the barriers of the northern Gulf of Mexico. Many of the barriers 

(Sanibel Island, Florida (4); Horn Island, Mississippi (36); 

A. Dune Drowning B. Spit Accretion C. Shoal Emergence

Time 1 Time 

2

Time 

3

Dune

Ridge

Sea Level

Dune

Ridge

Sea Level

Dune

Ridge

Sea Level

Sea Level

Sea Level

Sea Level

Headland

Headland

Headland

Embayment

Embayment

Lagoon

Ocean

Ocean

Ocean

Figure 5. Conceptual diagram showing possible origins of barrier islands.
Open-File Report 2004-1043 18 

Galveston Island, Texas (56)) were originally migrating 

across the continental shelf and then began to grow seaward 

when the rise in sea level slowed about 5,000 years ago 

(Fig. 6). Some barriers have grown laterally as spits attached 

to the mainland shore (St. Joseph Peninsula, Florida (24); 

Bolivar Peninsula, Texas (54)) and other barriers formed 

around an island core of older barrier deposits left over from 

a previous time when sea level was at about the same level 

as today (east Dauphin Island (35) and Morgan Peninsula 

(33), Alabama). Still other barriers (Mississippi Sound (39) 

barriers and Anclote Key, Florida (17)) may have emerged 

from offshore sand shoals (Otvos, 1979; Davis and others 

1985). This upbuilding of barriers occurs most commonly 

in shallow water where wave energy is low, where the slope 

of the continental shelf is very gentle, and where a rapid 

accumulation of sand deposited by storms can drastically 

alter nearshore currents and wave patterns. These conditions 

are particularly applicable to the west coast of Florida.

Today the highest barrier elevations and largest sand 

dunes are present on the sand-rich aggradational (upward 

building) and progradational (seaward building) barrier islands such as Central Padre Island, Texas (66); east 

Dauphin Island, Alabama (35); and St. Joseph Peninsula, 

Florida (24). Much of the coastal sand that was washed 

ashore as sea level reached its present position is stored in 

these high-profile barriers (Fig. 7) and they typically have 

lower erosion rates because of the abundant sand. Migrating 

and landward retreating barriers, such as St. George Island, 

Florida (21); Chandeleur Islands, Louisiana (43); and South 

Padre Island, Texas (67), typically have higher erosion rates 

because they are located away from major sources of sand.

Morphologies of Gulf Coast Barrier Islands

Barrier islands make up more than two-thirds of the 

northern Gulf of Mexico shore. Each of the barriers is either 

high-profile or low-profile (Fig. 7) depending on the elevations and morphology of the island. The height and continuity of these elevations determine the ability of the barriers to 

withstand storm surge flooding and overwash. The origins 

0

20

40

60

80

100

120

140

0 50,000 100,000 150,000

Years before present

 SEA LEVEL

Depth below present sea level (m)

Figure 6. Sea level curve during the past 150,000 years that depicts the general magnitude and timing of 

sea level changes in the Gulf of Mexico. Modified from Moore (1982).
Open-File Report 2004-1043 19

and profiles of the barriers also partly determine the stability 

of the shoreline (Morton, 1979).

Low-profile barriers, such as South Padre Island, Texas 

(67), the Chandeleur Islands of Louisiana (43), western 

Dauphin Island, Alabama (35), and St. George Island, 

Florida (21), are typically narrow and characterized by 

discontinuous frontal dunes that are lower than and inundated by extreme storm surges. This makes the entire barrier 

subject to frequent overwash during storms. Overwash 

also creates channels and fans that transfer sand from the 

ocean onto the barrier or into the adjacent lagoon. Barrier 

upbuilding is a response to a rise in relative sea level, and 

the transfer of sand from the ocean to the lagoon is how the 

barrier migrates landward and still retains its general shape 

and sand volume. Island migration is enhanced if there is a 

deficit in the sand supply or if there is a rapid rise in relative 

sea level. However, if the rate of sea level rise is too great, 

then the barrier island is drowned in place and left as a submerged sand shoal on the continental shelf.

High-profile barriers, such as Sanibel Island, Florida 

(4), Matagorda Island, Texas (61), and Central Padre Island, 

Texas (66) are the result of abundant sand supply for thousands of years. These barriers are typically wide and have 

continuous, well-vegetated dune ridges. The high elevations 

effectively block storm surges and prevent island overwash, 

even during the most severe storms. For high-profile barriers, enough sand is stored in the dunes that they are able to 

withstand prolonged erosion without being breached, which 

High-Profile Barrier Island

Low-Profile Barrier Island

OceanFore beachBack beachHummocky vegetated

fore -island dunes

Foredune ridgeIntervening swale

Foredune ridge

Vegetated barrier flat

Marsh

Lagoon

OceanFore beachBack beachHummocky 

 discontinuous dunes

Overwash fans

Lagoon

Figure 7. Geomorphological characteristics of high and low profile barrier islands. Modified 

from White and others (1978).
Open-File Report 2004-1043 20 

would allow flooding of the barrier core. However, flooding 

of high-profile barriers can occur from the lagoon side or 

from the ocean through artificial breaks in the dune ridge, 

such as beach access roads or areas where dunes have been 

destroyed by coastal construction.

Chenier Plain

The chenier plain of southwestern Louisiana and southeastern Texas (51-53) is the western extension of the Mississippi delta. It consists of topographically high beach ridges 

composed of sand and shell separated by low swales of 

marsh filled with muddy organic-rich sediments (Gould and 

McFarlan, 1959). The sandy beach ridges represent periods of slow delta construction and possibly slightly higher 

sea levels when the coastal plain sediments were reworked 

by waves and concentrated along the shore. The intervening swales represent periods of mud deposition and delta 

advancement when the supply and accumulation of muddy 

sediments was greater than the erosional capacity of the 

waves. Although the chenier plain was actively prograding 

several hundred years ago, the shore is presently eroding.

Tidal Inlets

Tidal inlets, also referred to as passes, are the primary 

channels separating the barrier islands (Fig. 4). They also 

allow the exchange of water and migration of marine organisms between the Gulf and adjacent bays. Shorelines near 

unstabilized inlets are commonly sites of high variability 

and rapid erosion due to inlet migration and high current 

velocities. Long-term rates of change and their associated 

uncertainties at sites near inlets can be useful in conveying 

the variable nature of the shoreline and the derived risks 

from a coastal hazards perspective. For this study, some of 

this variability may be minimized in the rates and uncertainties around inlets because of the decision to maintain 

consistent routines by deleting transects in cases where less 

than four shorelines were present.

Most large inlets are used for navigation into and out of 

the coastal bays and ports. These navigable inlets have been 

modified for maintenance of deep-draft shipping channels, 

and many of the channels are lined by long, rock jetties. 

Where they are unmodified, sand banks and beaches line the 

inlets. Several man-made inlets through Gulf Coast barrier 

islands have altered water circulation patterns, longshore 

currents, and littoral drift and have locally caused or contributed to both beach erosion and accretion (Morton, 1977b; 

Dean and OʼBrian, 1987).

Some tidal inlets are opened during storms and remain 

open for long periods. For example, in 1969 Hurricane 

Camille breached Ship Island, Mississippi (37), forming 

Camille Cut, and the 1926 hurricane opened Hurricane Pass 

between Caladesi Island (15) and Honeymoon Island (16), 

Florida (Davis, 1994). Barrier breaching commonly reoccurs after narrow spits or peninsulas attach to headlands. 

Breaching is also common where substantial downdrift inlet 

migration has over time produced a low barrier segment and 

a long ebb channel that is hydrodynamically inefficient.

Long, narrow microtidal barrier island segments that 

have low relief (maximum dune elevations of less than 2 

m) and that are far from existing tidal inlets are the most 

susceptible to breaching and new inlet construction during 

inundation by an extreme storm. Inlet formation may occur 

when fast moving hurricanes tracking near the coast produce 

oceanic storm surges that exceed the dune heights. When 

there is insufficient time for lagoon water levels to respond 

to elevated open ocean water levels, a hydraulic head can 

be created driving flows landward across the narrow barrier and incising channels (Morton, 2002). The west coast 

of Florida has been the site of numerous historical inlet 

openings or reactivation of closed inlets and is particularly 

vulnerable to this extreme storm response (Table 8).

GEOLOGIC HISTORY AND SETTING

River deltas, marshes, and barrier islands built the 

broad coastal plain bordering the northern Gulf of Mexico 

during two periods when sea level was relatively high. The 

highest coastal plain elevations were formed about 130,000 

years ago during a late Pleistocene interglacial period when 

sea level was about 6 to 8 m higher than today (Fig. 6). 

The lower coastal plain elevations associated with modern 

marshes and barrier islands formed when sea level reached 

its present position about 5,000 years ago. Between these 

periods, the shape and origin of the present Gulf Coast was 

greatly influenced by changes in sea level due to expansion 

and melting of continental glaciers. The present-day shape 

of the Gulf Coast, and the origin of many of the distinctive 

coastal features found today, reflects these fluctuations in 

sea level that alternately exposed and submerged the coastal 

plain. 

About 18,000 years ago, at the end of the last glacial 

epoch, sea level was about 130 m lower than today (Fig. 6). 

This lower sea level caused coastal plain rivers to cut deep 

valleys across the continental shelf. As the glaciers melted 

and sea level rose to its current position, these valleys were 

drowned and most were only partly filled with sediment. 

The unfilled remnants of former river valleys that rim the 

Gulf of Mexico are the major bays, such as Galveston Bay, 

Mobile Bay, and Pensacola Bay. Only large rivers, such as 

the Rio Grande and Brazos River in Texas, the Mississippi 

River in Louisiana, and the Apalachicola River in Florida 

carried enough sediment to fill their valleys and build deltas 

into the Gulf of Mexico. 

Post-glacial changes from a cooler and wetter climate 

to todayʼs warmer and drier conditions had dramatic effects 

on the amount of water and sediment transported by the 

coastal plain rivers draining into the Gulf of Mexico. As 

rainfall decreased so did stream flow and sediment load, 
Open-File Report 2004-1043 21

which caused some river deltas (Rio Grande and Brazos 

in Texas) to retreat (Morton, 1979). While the deltas were 

retreating, some adjacent beaches and barrier islands that 

had been migrating landward began to build seaward as a 

result of locally abundant sand supply. The sand that built 

the accreting shores was supplied by erosion of adjacent 

deltas or mainland shores and reworking of Pleistocene 

barrier islands that were submerged on the continental shelf 

by the rising sea. Numerous beach ridges that mark successive former positions of the Gulf shoreline at Sanibel Island, 

Florida; Morgan Peninsula, Alabama; Cat Island, Mississippi; and San Jose Island, Texas (Fig. 8), and many other 

islands, are evidence of the abundant supply of older sand. 

Climate

Differences in rainfall distribution along the Gulf 

Coast create a distinct east-to-west climatic gradient that is 

reflected in the vegetation and geologic processes of each 

sub-region. From Florida to southeast Texas, annual rainfall 

is abundant and the climate is subhumid. Here salt-water 

marshes are widespread, maritime forests occupy the higher 

coastal elevations, and eolian processes are limited in their 

capacity to modify the landscape. At the dry end of the 

spectrum are the semi-arid conditions of South Padre Island, 

Texas where evapo-transpiration exceeds precipitation. In 

areas of low rainfall, salt-water marshes are rare, forests are 

absent, grasses are the climax vegetation on barrier islands, 

and large active dunes cover the landscape, signifying the 

importance of eolian processes. On average, the amount 

of rainfall and evaporation are about equal near Corpus 

Christi, Texas. Areas south and west of Corpus Christi are 

susceptible to prolonged droughts that weaken or kill the 

vegetation and create large active dune fields (Fig. 9). From 

a beach erosion perspective, these dune fields represent vast 

quantities of sand that are derived from the beach, transported across the barrier islands, and deposited either in the 

adjacent lagoons or on the mainland forming a vast sheet of 

wind-blown sand.

Coastal Processes

The Gulf Coast is a microtidal (less than 0.5 m tidal 

amplitude) storm-dominated region that is constantly changing as a result of active coastal processes that are directly 

linked to meteorological events. Wind-driven waves and 

currents are the most important geological agents controlling sediment transport and evolution of the Gulf shores. 

Wind directions and intensities vary seasonally with 

southerly winds prevailing most of the year. During the 

winter months, wind-circulation patterns and low barometric pressures preceding the passage of cold fronts cause 

strong onshore winds and high waves that typically erode 

the beach. After each frontal system passes the coast, wind 

direction shifts and strong northerly winds can generate 

waves that erode the backbarrier shores at many locations. 

Astronomical tides in the Gulf of Mexico are diurnal or mixed and typically have a range of less than 1 m. 

Water levels vary only about 0.5 m between high and low 

tide during an average tidal cycle. Tide records around the 

Gulf since the turn of the century all show the same general 

variations in sea level (Fig. 10). Annual variations are controlled by meteorological and oceanographic factors (Hicks, 

1968), some of which coincide with droughts and periods 

of abnormally high rainfall (Morton, 1994). Averaging of 

the tide records shows that some areas, such as the west 

coast of Florida, are relatively stable because the underlying hard limestone substrates are stable. Other tide records 

Storm Date Inlet Name Barrier Segment Barrier

Width

(m)

Nearest

Inlet

(km)

Category/

Rank

Max.

Surge

(m)

Storm

Quadrant

Sept. 1848 Johns Pass Sand Key 125 5.5 NR 4.6 ?

Sept. 1848 New Pass Longboat Key 200 5.0 NR 4.6 RF flood

Oct. 1921 Hurricane Pass Hog Island 150 4.5 3/39 2.9 RF flood

Oct. 1921 Midnight Pass Siesta Key 120 9.5 3/39 2.1 RF flood

Oct. 1921 Redfish Pass Captiva Island 50 6.1 3/39 2.0 RF flood

Oct. 1926 unnamed Indian Rocks 75 1.6 4/12 -1.8 RF ebb

Elena 1985 Willy's Cut Caladesi Island 100 0.9 3/56 1.5 RF flood

Table 8. Historical hurricane inlet openings and associated surge elevations, west coast of Florida. Information regarding inlet 

openings and closings is summarized in Davis and Gibeaut (1990) and Barnard (1998). Storm categories (Saffir-Simpson scale), 

rankings, and surge elevations are from National Hurricane Center archives and the U.S. Army Corps of Engineers (1984). Rank 

refers to the intensity of each hurricane compared to the most intense hurricanes of record. NR is not ranked. Quadrant refers 

to geographic location with respect to the storms center. RF is right front (looking onshore) where the storm surge is greatest. 

Flood and ebb refer to the direction of water flowing onshore (flood) or offshore (ebb) from the shoreline.
Open-File Report 2004-1043 22 

Figure 8. Long linear ridges and swales that characterize some Gulf Coast barrier islands, such as San Jose 

Island, Texas mark the former positions of the Gulf shoreline. These features record shoreline accretion at time 

scales of thousands of years.

Figure 9. Fields of migrating sand dunes on North Padre Island, Texas may contribute to erosion by removing 

sand from the beach. Dunes are activated when the stabilizing vegetation is destroyed either as a result of natural causes (droughts, grass fires) or as a result of human activities (off-road vehicles, overgrazing, construction).
Open-File Report 2004-1043 23

at Galveston Island, Texas and Grand Isle, Louisiana show 

a relative rise in sea level of about 0.3 to 0.6 m during the 

20th century (Lyles and others, 1988). This rate of rise is 

about 3 times faster than the global rise in sea level, which 

recently has averaged about 0.18 m per century (Gornitz and 

Lebedeff, 1987). 

The difference between recorded rates of submergence 

along the Gulf Coast and the global rate of sea level rise is 

caused mostly by subsidence (Swanson and Thurlow, 1973). 

Releveling surveys show that the subsidence is related to 

regional tilting of the coastal plain; areas near and seaward 

of the shoreline are sinking while inland areas are being 

uplifted (Swanson and Thurlow, 1973, Holdahl and Morrison, 1974, and Jurkowski and others, 1984). Within the 

regional trend are areas where subsidence rates are high, 

such as the Houston-Galveston area (Fig. 11) and the Mississippi delta where accelerated sinking is attributed respectively to ground-water withdrawal (Gabrysch, 1984), and 

sediment compaction and oil and gas production (Roberts 

and others, 1994; Morton and others, 2002). 

Fair-weather waves in the Gulf of Mexico are normally 

less than 0.6 m high (Bretschneider, 1954; U.S. Army Corps 

of Engineers, 1983). The largest waves and highest sustained wind speeds in the Gulf of Mexico accompany major 

hurricanes. They also are responsible for the most property 

damage and loss of lives. Hurricanes entering or originating in the Gulf normally follow a northward or westward 

path (Fig. 12). The preferred paths of the storms determine 

the likelihood that a storm will make landfall at a particular 

site. Using historical sites of hurricane landfall, the National 

Hurricane Center has shown that the areas at greatest risk 

are around Galveston, Texas, southeastern Louisiana, and 

the Mississippi/Alabama coast (Simpson and Lawrence, 

1971). Because hurricanes seldom recurve and make landfall near St. Petersburg Florida, this part of the west Florida 

coast has the lowest probability of a storm in any year. 

However, because of the high density of development and 

population, this area has one of the highest potentials for a 

storm-related catastrophe.

Before crossing the northern Gulf Coast, the counterclockwise circulation of hurricane wind drives nearshore 

currents and large volumes of beach and shoreface sand 

alongshore. High tides, large waves, and strong currents that 

accompany the storms can leave semi-permanent marks on 

the barrier islands and beaches. For example, the erosional 

escarpment carved by Hurricane Elena in 1985 is still visible along the northern shore of St. George Sound, Florida. 

Storm channels that breached Dauphin Island, Alabama 

in the early 1900s and again in 1948 were reoccupied in 

1979 when Hurricane Frederic completely washed over 

1905 1925 1945 1965 1985 2005

Year

Sea Level (mm)

6600

6800

7000

7200

7400

7600

7800

Key West, FL

Pensacola, FL

Galveston, TX

Grand Isle, LA

Figure 10. Long-term trends in average annual sea level at selected tide gauges in the Gulf of Mexico. Data are from the National 

Ocean Service.
Open-File Report 2004-1043 24 

the island destroying the causeway that links the island to 

the mainland. During the next year (1980) Hurricane Allen 

reoccupied more than 60 washover channels through South 

Padre Island, Texas destroying, in several places, the main 

road that runs the length of the island. In Florida, even 

relatively weak storms have destroyed piers, seawalls, dune 

walkovers, swimming pools, roads, houses, motels, and 

other buildings because structures were poorly sited and the 

beach did not recover from storm erosion before the next 

storm arrived (Clark, 1986). The hard lessons of Hurricanes 

Camille, Frederic, and Eloise (Fig. 13) were not heeded by 

coastal residents of Mississippi, Alabama, and Florida who 

rebuilt in the same place after each of these major storms.

Sand Sources

Eroding mainland shores and the continental shelf are 

the primary sources of sand for maintaining the Gulf Coast 

barriers and beaches. Gulf Coast rivers generally do not contribute significantly to the present sand budget of Gulf Coast 

beaches. A few rivers, such as the Rio Grande and Brazos 

in Texas, add sand directly to the littoral system, but most 

of the rivers empty into estuaries and deposit their sediment 

loads far inland from the shoreline. The Mississippi River in 

Louisiana deposits its load of fine-grained sediments at the 

edge of the continental shelf in relatively deep water where 

it is unavailable to build beaches and barriers. 

Natural reductions in sand supply during the past few 

thousand years were further aggravated by recent human 

Figure 11. A coastal subdivision of nearly 200 homes near Houston, Texas was submerged as a result of subsidence induced by ground-water production.

1938

1900

1928Camille (1969)

Carla (1961) 1919 Betsy (1965)

Figure 12. Tracks of some of the most deadly and destructive 

Atlantic and Gulf hurricanes in the 20th century. Data are from 

the National Hurricane Center.
Open-File Report 2004-1043 25

activities such as damming rivers, dredging channels, and 

constructing jetties. Flood-control structures caused most 

rivers to lose their capacity to transport sediment, thus 

dramatically decreasing the amount of sediment delivered 

directly to the Gulf shoreline or the bayhead deltas. Even 

if some river-borne sediment reaches the Gulf shore, the 

jetties at inlets disrupt the longshore currents and compartmentalize the coast, preventing sediment exchange from one 

coastal segment to another. Before the littoral drift system 

was altered, sand was naturally bypassed around tidal 

inlets and shared between neighboring coastal segments. 

Now there are many coastal compartments isolated by long 

impermeable jetties or deep navigation channels like those 

maintained at the entrance to Tampa, Mobile, Galveston, 

and Corpus Christi Bays. This human interference with littoral drift has caused some formerly accreting or stable shores 

to begin eroding (Morton, 1979).

GENERAL CHARACTERISTICS OF THE 

GULF SHORES BY STATE

The southwest, west, and panhandle coasts of Florida 

offer a rich diversity of shoreline types, compositions, and 

degrees of economic development. This coastal region 

contains mangrove swamps, sandy barriers and mainland 

beaches, irregular drowned karst topography, and marshes. 

Barrier islands occupy much of the shore from Marcos 

Island to Anclote Key and from Destin to Perdido Key (Fig. 

3). Exceptions are the topographically high sandy uplands 

that extend from Marco Island to Sanibel Island and from 

St. Joseph Peninsula to Destin. Barrier islands also fringe 

the Apalachicola Delta, but it forms a large promontory 

that abruptly changes the shoreline orientation. The delta 

also marks the northern limit of the low wave-energy coast, 

which coincides with the drowned karst topography that 

extends southward to Anclote Key (Price, 1953; Tanner, 

1960). Marsh and upland hammocks cover the drowned 

limestone segment. It lacks well-developed surface drainage, and the tidal creeks are largely controlled by fracture 

patterns in the underlying limestone bedrock. Streams in this 

karst region do not transport any significant load of sediment suitable for building or maintaining beaches. Large 

linear oyster reefs grow in the Gulf of Mexico where brackish salinities are maintained by freshwater inflows from 

underground springs and surface streams such as the Crystal 

River in Florida. The few pocket beaches fronting marsh of 

the low wave-energy coast are composed mostly of broken 

shells derived from the oyster reefs and offshore shoals 

(Davis and others, 1985).

Alabama has the least amount of ocean shore of the 

Gulf Coast states. In terms of landforms, the Alabama coast 

is similar to that of Texas and Florida where sandy barrier 

islands (Dauphin Island, Morgan Peninsula, Perdido Key) 

are close to but separated from the mainland by lagoons. 

Other features in Alabama that are similar to the other coasts 

are the unfilled river valleys (Mobile Bay, Perdido Bay) that 

dominate the landscape.

Figure 13. Property damage near Panama City, Florida caused by Hurricane Eloise in 1975. From Morton (1976).
Open-File Report 2004-1043 26 

The Mississippi coast is composed of a chain of barrier islands separated by wide tidal inlets, mainland bluffs 

covered by dense pine forests, and small marshes crossed 

by tidal creeks and bayous. It is a unique coast in that it has 

two open shores, the one fronting the barrier islands and the 

mainland shore bordering Mississippi Sound. The barrier 

islands are low, narrow, and generally migrating to the west 

due to the westerly alongshore currents. Sand that maintains 

the Mississippi barriers is derived from the east or from 

the sandy platform underlying the barriers (Otvos, 1979). 

Although Mississippi barriers are low and the intervening 

tidal inlets are wide, they absorb most of the wave energy 

generated in the Gulf before it reaches the mainland. Exceptions are during large hurricanes, such as Camille (category 

5), that completely overtop the barriers and directly impact 

the mainland shore. Hurricane channels periodically cut 

Mississippi coast barriers, such as in 1969 when Camille 

Cut bisected Ship Island. 

The modern birdfoot delta and older delta lobes of the 

Mississippi River dominate the Louisiana coast. Because 

the delta is composed predominantly of mud, most beaches 

are only veneers of sand that are retreating over the delta 

plain. Barrier islands fringing the delta represent thin 

wedges of reworked sand that are also retreating landward at 

high rates. These low, relatively narrow barriers are frequently overwashed by storm surges that erode sand from 

the Gulf side and deposit it in adjacent bays and sounds, 

resulting in landward migration of the barriers (McBride 

and others, 1992). Chandeleur, Grand Gosier, Curlew, and 

Breton Islands make up an eastern arc of migrating barriers 

that outline the abandoned and foundering lobe of the St. 

Bernard subdelta. Eroding sandy beaches and short barriers typify the shore on the west flank of the birdfoot delta. 

These beaches extend westward to Grand Isle, which is a 

barrier attached to the abandoned Lafourche lobe of the 

delta. Narrow sandy beaches form the Caminada-Moreau 

headland shore of the Lafourche subdelta, whereas the 

Timbalier Islands and the Isles Dernieres are narrow, low 

migrating barriers that formed on an older, more rapidly 

subsiding part of the Lafourche subdelta. From the Isles 

Dernieres westward to Grand Chenier the Gulf shore consists of marshes and mud bars. The mud bars are supplied by 

westward flowing littoral currents and the Atchafalya River 

that empties into Atchafalya Bay. Western coastal Louisiana 

consists of high sandy beach ridges with intervening marsh 

swales that together make up a headland known as the chenier plain. Sandy beaches of the chenier plain extend from 

Grand Chenier into southeastern Texas.

The beaches and barriers of the Texas coast are 

arranged in an orderly pattern with respect to the Holocene 

river deltas (Brazos-Colorado and Rio Grande) and Pleistocene mainland shores (Morton, 1979). All these mainland 

shores, which are composed of muddy deltaic sediments, 

form moderately large promontories in the Gulf of Mexico. 

The promontories focus wave energy and have been eroding for the past few thousand years. The lack of abundant 

sand along the rapidly eroding mainland shores prevents the 

growth of sand dunes; consequently, the highest elevations 

along the mainland shores coincide with a narrow terrace of 

washover deposits composed of sand and shell. Between the 

mainland shores, littoral currents converged and deposited their sand load. The result was construction of the 

high-profile barriers (Bolivar Peninsula, Galveston Island, 

Matagorda Island, San Jose Island, Mustang Island, North 

and Central Padre Island) and their large foredunes. The 

low-profile transgressive barriers (Follets Island, Matagorda 

Peninsula, South Padre Island) formed on the flanks of the 

mainland shores as they continued to retreat. Shores of the 

Texas bays and lagoons are also varied in their composition 

and susceptibility to land loss. 

HISTORY OF INFRASTRUCTURE 

DEVELOPMENT

Since their discovery by French and Spanish explorers, 

the Gulf Coast barriers and mainland shores have served 

as safe harbors that promoted early economic development 

related to shipping and other maritime activities. Barriers 

strategically located at the mouths of major bays were the 

sites of quarantine stations, supply docks, military installations, and trading posts. Early resort development of most 

Gulf Coast barriers was slowed because of their remoteness, 

and in some areas, such as Mississippi and Texas, there was 

a lack of fresh water and adequate building materials. 

The west Florida coast experienced high-density development during the post World War II building boom, and 

many of the building practices and codes were not suitable 

for coastal construction. Many of these construction deficiencies were exposed shortly after development began, but 

some of the consequences are still being experienced. For 

example, beach houses built in the 1950s near Panama City, 

Florida were sited on the dunes using slab-on-grade foundations. This standard building practice is used extensively 

at inland sites and it did not present a problem at the coast 

until 1975 when Hurricane Eloise destroyed long seawalls, 

undermined the dunes, and caused many buildings to collapse (Fig. 13). In 1992, Hurricane Andrew and its impact 

in south Florida revealed again that adequate building codes 

and code enforcement are generally lacking.

The only community development of a Mississippi 

barrier was on the Isle of Caprice in the 1920s (Canis and 

others, 1985). This small ephemeral sand shoal was unstable 

and the resort development did not survive. Both the shoal 

and development declined in later years.

Because most of coastal Louisiana is extremely low 

and flooded frequently, economic development has been 

greatly limited and restricted to a few areas. Exceptions are 

local infrastructures that were built to support the widespread petroleum production activities. Grand Isle is the 

only barrier island in Louisiana that has roads and both 

residential and commercial development. The development 
Open-File Report 2004-1043 27

began as recreational fishing camps and facilities that serviced the offshore petroleum industry. More recently, Grand 

Isle has been developed for permanent residents and as a 

destination for tourists. The coastal communities of Holly 

Beach and Peveto Beach are located in the chenier plain 

south of Cameron, Louisiana. These unplanned developments bordering the Gulf of Mexico consist of small beach 

houses that were constructed in the 1960s before the threat 

of beach erosion was well understood.

The Gulf Coast barriers have always had a strong 

military presence beginning with early construction of forts 

and continuing today with its Naval Stations and Air Force 

bases. In fact, fortifications and training facilities represent 

the earliest occupation of some Gulf Coast barrier islands. 

Construction of most of the forts was begun in the early to 

the mid 1800s. Many of the barriers were bombing ranges 

during World War II and some were used for target practice 

through the Vietnam War. None of the active military bases 

are currently threatened by coastal erosion because facilities near the water are armored by hard structures. Some of 

the training facilities have been closed or dismantled, but 

most of the land has remained in the public domain and is 

controlled by state or federal agencies and will not be developed for commercial purposes.

Some of the oldest landmarks, like lighthouses and 

forts, are especially vulnerable to erosion because these aids 

to navigation and military defense were built on the tips 

of barrier islands or on points of land that provided unobstructed visibility. These structures also provide a basis for 

determining long-term shoreline change. For example, the 

Cape San Blas, Florida lighthouse has been relocated six 

times because of continued erosion and shifting of the Cape 

(Tanner, 1975). The lighthouse at the entrance to Mobile 

Bay also stands as a testament to the shifting sands of time. 

This structure was built on Sand Island, but the island 

migrated westward more than 3 km, leaving the lighthouse 

exposed to wave attack. The lighthouse is now surrounded 

by water and protected by a rock revetment that prevents 

it from being completely undermined and destroyed. The 

history of Fort Massachusetts on Ship Island, Mississippi 

involves another story of island migration. When it was built 

in 1856, the Fort was centrally located on the island about 

120 m from Mississippi Sound, the Gulf of Mexico, and 

the western end of the island. More than 140 years later, the 

Sound side of the island has eroded, flooding the foundation 

of the Fort, which is more than 1100 m from the western 

end of the island (Boone, 1973). Although continued migration of Ship Island to the west is not likely because a ship 

channel at the western end of the island is maintained by 

dredging, there is a continuing threat of Sound side erosion.

Most of the Gulf beaches front private property. The 

longest publicly owned beaches belong to the National 

Park Service. The NPS is responsible for managing Padre 

Island National Seashore in Texas and Gulf Islands National 

Seashore, which includes all of the barriers in Mississippi 

(including parts of Cat Island), and part of Santa Rosa Island 

and Perdido Key in Florida. In addition to these federal 

holdings, the Gulf States have many state and local parks 

that account for a significant percentage of the non-private 

Gulf-front property.

SHORELINE CHANGE AND COASTAL 

LAND LOSS

In this section shoreline changes are presented with an 

emphasis on shoreline erosion, because it is an important 

natural coastal hazard along many Gulf of Mexico beaches. 

Table 7 summarizes both long-term and short-term rates 

of shoreline change as averages of all the changes, including both erosion and accretion, and as averages of only the 

erosion values and only the accretion values. Distinguishing 

between erosion and accretion provides more quantitative 

detail to the results.

The summary discussion includes references to 

shoreline erosion and to the broader issue of coastal land 

loss in order to provide a more complete perspective of 

coastal change. In the Gulf Coast states coastal land loss is 

occurring primarily because of episodic high wave energy, 

natural changes in the coastal system, and as a consequence 

of human activities (Clark, 1990; Morton and Paine, 1990; 

Penland and others, 1990; Smith, 1990). Additional information about coastal land loss is available in a USGS Open 

File Report at http://pubs.usgs.gov/of/2003/of03-337/.

West Florida

Land losses for west Florida are primarily associated 

with erosion of sandy beaches and barrier islands, especially around inlets (Clark, 1991) where swift tidal currents 

easily remove the loose sand that forms the ends of the 

barriers. Land loss in the bays and lagoons of west Florida 

is minor because these water bodies are generally small or 

are already protected by erosion control structures such as 

bulkheads (Doyle and others, 1984). 

Compared to shoreline erosion in some other Gulf 

Coast states, the average long-term erosion rate of -0.8 ± 0.9 

m/yr for west Florida (Table 7a) is low, primarily because 

wave energy is low. Even though erosion rates are generally low, more than 50% of the shoreline is experiencing 

both long-term and short-term erosion. The highest rates 

of erosion in west Florida are typically located near tidal 

inlets. Long-term and short-term trends and rates of shoreline change are similar where there has been little or no 

alteration of the sediment supply or littoral system (see Dog 

Island, St. George Island, and St. Joseph Peninsula). Conversely, trends and rates of change have shifted from longterm erosion to short-term stability or accretion where beach 

nourishment is common (see Longboat Key, Anna Maria 

Island, Sand Key, and Clearwater, Panama City Beach, and 

Perdido Key). A shift from long-term relative stability to 
Open-File Report 2004-1043 28 

Figure 15. Even where wave energy is normally low, episodic erosion during storms is capable of 

destroying roads and eliminating the beach. This example of erosion along the low energy coast is from 

Lighthouse Point, Florida.

Figure 14. Erosion of the Gulf shore eventually destroyed this beach house at Captiva Island, Florida.
Open-File Report 2004-1043 29

short-term erosion occurred on Santa Rosa Island, probably 

as a result of beach erosion and overwash deposition associated with Hurricane Opal in October 1995. 

Slow but chronic erosion along the west coast of 

Florida eventually results in narrowing of the Stateʼs valuable recreational beaches (Figs. 14-16), and many highly 

developed beaches retain no dunes to protect buildings from 

large storm waves and flooding. Lighthouse Point, south of 

Tallahassee, presents a good example. Situated in the low 

energy sector of the coast, past storms have still destroyed 

park facilities and some roads (Fig. 15) that are now protected by rock revetments. In places where beach erosion is 

chronic, these structures have replaced the beaches (Fig. 16) 

except where artificially nourished (Fig. 17). 

Alabama

In Alabama, coastal land loss is caused primarily by 

beach and bluff erosion. Other mechanisms for loss, such 

as submergence, appear to be minor. Slope failure accounts 

for much of the land loss along the east and west shores of 

Mobile Bay (Smith, 1990). Although bay shorelines were 

not analyzed in this study, Smith (1990) reported that high 

bluffs on the eastern side of the bay are retreating at rates 

of -1 to -1.5 m/yr. Along the Alabama Gulf shoreline, the 

western half of Dauphin Island is experiencing short-term 

erosion of as much as -4.7 m/yr. An exception is the westernmost 3 km of the island, which is accreting as the island 

lengthens to the west. Stumps of former pine trees exposed 

on the beach at the Dauphin Island Public Beach are evidence of long-term beach erosion. Just east of the park is a 

large, active dune complex that is migrating into the pine 

forest and burying the trees. Although the reason for this 

dune migration is unclear, it is likely that this dune sand 

would reduce beach erosion to the west if it were available 

to the littoral system. Elsewhere along the Alabama Gulf 

shore, Morgan Peninsula and Perdido Key are relatively 

stable owing to a sufficient supply of sand by longshore 

transport to the west and local beach nourishment (Fig. 18).

Mississippi

Long-term rates of land loss for Mississippi mainland 

shores are relatively low. Extensive armoring and periodic 

beach nourishment around Mississippi Sound (Fig. 19) have 

greatly slowed land losses along these shores (Canis and 

others, 1985). However, the barrier island shores are eroding 

rapidly. Long-term rates show that 80% of the shoreline 

has experienced erosion at an average rate of -3.1 ± 1.8 

m/yr (Table 7a). Short-term erosion is even more rapid 

with over 60% of the shoreline eroding at an average rate 

of -5.8 m/yr (Table 7b). Erosion is most pronounced at the 

eastern (updrift) ends of the barriers where short-term rates 

of erosion average -8.3 m/yr and long-term rates average 

-4.6 ± 1.6 m/yr. The systematic pattern of updrift erosion 

and downdrift deposition that transfers sand from east to 

west and promotes westward migration has also reduced the 

island areas by about one third since the 1850s (Byrnes and 

others, 1991). 

The most dramatic example of coastal erosion and land 

loss in Mississippi was the formation and destruction of 

the Isle of Caprice. This relatively small sand shoal formed 

Figure 16. This narrow eroding beach in front of a seawall near Clearwater, Florida was used for recreation 

before beach nourishment. 
Open-File Report 2004-1043 30 

Figure 17. Many nourished beaches along the west Florida coast, such as this one on Sand Key, have 

steep erosional escarpments early in the history of the project.

Figure 18. A beach nourishment project near Gulf Shores, Alabama. Accelerated erosion in front of the beach 

houses was attributed to construction of an artificial channel and jetties.
Open-File Report 2004-1043 31

in Mississippi Sound between Horn and Ship Islands as a 

result of barrier migration and changes in current patterns 

within the adjacent tidal inlet. The Isle of Caprice emerged 

between 1917 and 1924 when sand deposited between 

two channels caused several small sand shoals to coalesce 

(Rucker and Snowden, 1988). In the mid 1920s, during the 

Prohibition Era, it was developed into an entertainment 

center with cabanas, a gambling casino, restaurant, artesian potable water supply, electric power plant, and a ferry 

landing (Rucker and Snowden, 1988). By 1932, all of these 

assets had been completely destroyed by the Gulf waters 

and there was no evidence of the Isle of Caprice.

Louisiana

The highest rates of laterally continuous shoreline 

retreat and land loss in the Gulf of Mexico are found in 

coastal Louisiana. While land loss associated with shoreline 

change along the Gulf shore and around the margins of large 

coastal bays is severe, loss of the interior wetlands is also 

extensive due to submergence and destruction of the Mississippi River delta plain (Penland and others, 1990). Subsidence and coastal erosion are functions of both natural and 

human induced processes. The natural delta cycle begins 

with construction of a delta lobe. Eventually that lobe is 

abandoned as the river system relocates to another area. 

Following abandonment, the delta lobe subsides as sediments compact and the area becomes submerged because 

no additional sediment is available to offset the subsidence. Sediment supply to the delta also has been artificially 

reduced by controlling the Mississippi River and preventing 

it from flowing into the Atchafalya Basin. Recent studies 

have also suggested that hydrocarbon production has been 

partly responsible for accelerated subsidence and wetland 

loss (Morton and others, 2002).

About 90% of the Louisiana Gulf shoreline is experiencing erosion, which increased from an average of -8.2 ±

4.4 m/yr in the long-term to an average of -12.0 m/yr in the 

short term (Tables 7a and b). Short sections of the shoreline are accreting as a result of lateral island migration. The 

highest rates of Gulf shoreline erosion in Louisiana coincide 

with subsiding marshes and migrating barrier islands such 

as the Chandeleur Islands, Caminada-Moreau headland, 

and the Isles Dernieres. The frequent breaching of the 

Chandeleur Islands makes shoreline delineation difficult at 

many locations and prevents calculation of accurate rates 

of change along some barrier segments. The change from 

long-term erosion to short-term accretion on the west end of 

Grand Isle is related to frequent beach nourishment efforts. 

Elsewhere, beach nourishment along the Caminada headland and the Isles Dernieres, and a rock revetment along 

East Timbalier Island have not substantially reduced the 

rates of erosion at those locations.

Texas

In Texas, a combination of erosion and submergence 

contribute to land loss, which is concentrated along the Gulf 

shoreline and along bay marshes and bluffs (Morton and 

Paine, 1990). Wetland losses, which constitute about 75% 

Figure 19. The seawall along U.S. 90 at Biloxi, Mississippi extends for nearly 27 miles. This reinforced 

concrete structure provides protection from minor storms and high water but it was unable to prevent 

massive destruction and death caused by Hurricane Camille in 1969.
Open-File Report 2004-1043 32 

of the total land losses, have dramatically accelerated both 

directly in response to human activities or indirectly as a 

result of modifications to the coastal system. Rates of land 

loss around bays are highest near the heads of the largest 

bays where long wave fetch and high bluff elevations produce unstable conditions. Wave erosion at the base of bluffs 

causes slumping and bluff retreat at rates of -0.6 to -1.2 m/yr 

(Morton and Paine, 1990) that threatens houses, power lines, 

and pipelines.

Erosion of Gulf beaches in Texas is concentrated 

between Sabine Pass and High Island, downdrift (southwest) 

of the Galveston Island seawall, near Sargent Beach and 

Matagorda Peninsula, and along South Padre Island. The 

most stable or accreting beaches in Texas are on southwestern Bolivar Peninsula, Matagorda Island, San Jose Island, 

and central Padre Island. 

Long-term erosion at an average rate of -1.8 ± 1.3 m/yr 

characterizes 64% of the Texas Gulf shoreline (Table 7a). 

Although only 48% of the shoreline experienced short-term 

erosion, the average short-term erosion rate of -2.6 m/yr 

is higher than the long-term rate, indicating accelerated 

erosion in some areas. Sargent Beach (Fig. 20) is a good 

example of accelerated erosion. Since the mid-1800s, 

Sargent Beach has retreated almost 700 m at an average rate 

of -4.4 ± 2.2 m/yr. That rate has increased to -6.4 m/yr since 

the 1970s. Here the beach is steep, narrow, and composed of 

many clam and oyster shells that normally grow in the bays 

but not in the open Gulf. The absence of dunes and presence 

of a low overwash terrace that forms the backbeach are clear 

indicators of the rapid erosion and frequent storm waves that 

are responsible for the rapid land loss. Sargent Beach is far 

from sand sources and engineering projects and yet there is 

an unmistakable connection between updrift activities and 

the accelerated erosion. In 1929, the mouth of the Brazos 

River was relocated so that the entrance to Freeport Harbor would not shoal when the river flooded. After the river 

diversion, a delta formed at the river mouth and trapped 

the sand that normally would have flowed toward Sargent 

Beach.

HUMAN RESPONSES TO COASTAL 

EROSION AND LAND LOSS

Each Gulf Coast state uses a different combination of 

technical and regulatory responses to combat beach erosion 

and to mitigate land loss. The technical responses include 

hard structures, beach nourishment, sand bypassing at inlets, 

and retreat (Table 9). Many developed bay shores exhibit a 

patchwork of relatively low-cost structures such as wooden 

and metal bulkheads, concrete seawalls, revetments, and 

small groins. Common bay shoreline structures are rubble 

revetments composed of various materials including large 

rocks, broken masses of concrete, rubber tires, household 

appliances, and trash. These low-cost structures typically 

become ineffective in less than 20 years because the structures deteriorate and are unable to withstand the repeated 

forces of storm waves. Bulkheads or seawalls are used to 

protect portions of nearly all of the Gulf shore communities. 

These structures have little effect on beach stability where 

sand supply is plentiful, but on eroding beaches they can 

accelerate beach loss by reducing beach width and preventing the growth of dunes (Morton, 1988).

The following statements illustrate the types of community and individual responses to shoreline erosion in the 

Gulf of Mexico. They provide typical examples rather than 

a comprehensive review of shoreline protection projects 

within each state. The examples also reveal some of the 

unintended consequences of shoreline development and 

subsequent modification.

Hard structures such as seawalls, rock revetments, 

bulkheads, and groins are common along the west coast of 

 Structural Non-structural 

Seawalls Grass planting

Bulkheads Horizontal Relocation

Breakwaters

Revetments

 Structural Non-structural 

Groins River Diversion

Perched Beaches Beach Replenishment

Sand Bypassing

Beach Scraping

Dune Restoration

Submerged Berms

Artificial Seaweed

 Structural Non-structural 

Seawalls Vertical Relocation

Dikes and Levees Land Reclamation

1. Protect Shore from Wave and Current Energy

2. Maintain or Increase Sediment Supply

3. Nullify Sea-Level Rise

Figure 20. Long-term Gulf shoreline erosion at Sargent Beach, 

Texas.

Table 9. Technical responses to erosion and land loss in the 

Gulf Coast region.
Open-File Report 2004-1043 33

Figure 21. Multiple structures including a seawall, riprap, and failed groin field have been unable to stop 

erosion at Longboat Key, Florida. Later these structures were removed and the beach was nourished.

Figure 22. The breakwater at Redington Shores, Florida has protected the beach fill but has aggravated erosion of adjacent sand beaches.
Open-File Report 2004-1043 34 

Florida (Figs. 16 and 21) where high-density development 

has existed for more than 40 years. The submerged breakwater at Redington Shores, Florida (Fig. 22) is an example 

of unexpected environmental and social costs resulting from 

construction of a hard structure. When it was built in 1985, 

this rubble mound breakwater and beach fill were designed 

to create a recreation beach and to protect a seawall without causing additional downdrift erosion (Dean and Pope, 

1987). The breakwater was built 90 m offshore in about 

2.5 m of water and is about 80 m long. About 46,000 m3

of fill material was dredged from a nearby tidal inlet and 

stockpiled for beach fill, but after Hurricane Elena only half 

of the dredged material remained for beach nourishment 

(Dean and Pope, 1987). After the beach fill was added, the 

nourished beach responded to the lowered wave energy by 

building toward the breakwater. This created a safety hazard 

since swimmers were attracted to the breakwater because it 

was in shallow water and close to the beach. The submerged 

rock mounds have protected the artificial beach and seawall, 

but they increased downdrift beach erosion and created 

unusually deep scour holes around the mounds that contributed to at least five deaths by drowning. 

 In both Alabama and Florida, bulkheads are built to 

protect the foundations of hotels and condominiums on the 

Gulf, but the beach is wide enough that these structures currently are not directly interfering with beach processes. The 

most common hard structures used to mitigate beach erosion 

in Alabama are rock revetments and riprap. At the eastern 

end of Dauphin Island, the beach adjacent to Fort Gaines 

continues to erode even though several attempts have been 

made to stabilize it with groins and large blocks of riprap 

(Fig. 23). 

The mainland shore of Mississippi is almost completely armored by low bulkheads, revetments, and seawalls 

in combination with other structures such as groins and 

riprap. The 40-km long stepped seawall (Fig. 19) extending from Bay St. Louis to Biloxi covers the entire length of 

Harrison County. A beach is maintained along this relatively low-energy shore by periodic pumping of sand from 

Mississippi Sound. Some of the seawall was built along 

Mississippi Sound after the 1915 hurricane to protect the 

upland homes from being destroyed as the Pleistocene bluff 

retreated. In 1951, about 7 million m3 of sand dredged from 

the Sound was pumped up creating an artificial beach to 

protect the seawall and to provide recreational areas. Sand 

fences and grass plantings have been used along this nourished beach to encourage the development of sand dunes 

and to reduce the sand blowing across U.S. 90 (Fig. 19).

The rapidly retreating beaches of Louisiana were 

largely unaltered by hard structures until recently, but the 

high rates of wetland loss and concern for the future of the 

delta plain resources and petroleum industry infrastructure 

have led to the construction of several shoreline stabilization projects. Riprap revetments were constructed along the 

Caminada-Moreau headland. Rock revetments were also 

built to try to stabilize East Timbalier Island, but the subsidence and erosion were so severe that the rip rap structure 

was stranded in the Gulf of Mexico as the barrier continued to retreat landward. Six segmented breakwaters were 

constructed along the Isles Dernieres for a demonstration 

project and the construction of others along the island have 

Figure 23. Rock revetments and groins have been used to control beach erosion at Fort Gaines on the 

east end of Dauphin Island, Alabama.
Open-File Report 2004-1043 35

been proposed. Perhaps the longest breakwater project in 

the U.S. is the 12 km stretch of 85 segmented breakwaters 

between Holly Beach and Constance Beach of the chenier 

plain. The breakwaters were built to replace a failed 

revetment (Fig. 24) intended to protect Louisiana Highway 

82 from storm damage.

Little of the Texas Gulf shoreline is stabilized by 

hard structures. Long seawalls have been constructed on 

Galveston, North Padre, and South Padre Islands, and these 

seawalls have caused some additional erosion of downdrift beaches (Morton, 1988). The most famous shoreline 

protection structure in Texas is the Galveston seawall, which 

stretches for more than 16 km. The seawall was built in 

response to the enormous death and destruction caused by 

the 1900 hurricane. Construction first began in 1902 and 

continued sporadically until 1961 when the last section was 

completed. The crest of the wall was built 5 m above sea 

level to protect the city and residents from flooding by large 

storms. This high elevation required raising much of the city 

by jacking up the buildings on pilings and pumping sand 

beneath them. The seawall accelerated erosion in front of 

the wall and as the beach narrowed, the unprotected beach 

downdrift of the end of the seawall began to erode more 

rapidly. The ramp at the end of the wall is clear evidence 

of the erosion (Fig. 25). The ramp once served as the beach 

access road; now it is barricaded to prevent unsuspecting 

visitors from driving into the Gulf of Mexico. Because of 

the depleted recreational beach in front of the seawall, the 

City of Galveston spent about $6 million in 1995 to restore 

the sand beach and to reduce erosion. 

Rarely are coastal engineering structures removed for 

any reason and they are usually either left to deteriorate, or 

less commonly, are maintained indefinitely. Exceptions to 

this general statement include the removal of the jetties in 

Alabama, a failed seawall on South Padre Island, Texas, and 

a failed groin field on Longboat Key, Florida (Fig. 21). 

Beach nourishment (Figs. 17 and 18) is becoming a 

more popular alternative to structural erosion control in 

the Gulf of Mexico. Florida has spent the most money to 

nourish beaches and has the greatest number of projects, 

whereas Texas has the fewest nourished beaches. Trembanis 

and Pilkey (1998) reviewed beach nourishment data for the 

Gulf of Mexico through 1989 and reported that more than 

80% of the projects were implemented to restore beaches 

of the west Florida coast, mainly between Clearwater and 

St. Petersburg. Sand has been trucked and hydraulically 

emplaced to nourish beaches and to reconstruct dunes at 

several sites in Texas including Bolivar Peninsula, Galveston Island, and Sargent Beach. These small, low-volume 

projects have provided only temporary relief. The largest 

beach nourishment projects in Texas were in front of the 

Galveston seawall and at the south end of South Padre 

Island.

One of the most successful beach nourishment projects 

in the Gulf (Fig. 19) has been along the mainland shore near 

Biloxi, Mississippi (Dixon and Pilkey, 1991). The beach fill 

has lasted an average of 15 to 20 years because it is partially 

Figure 24. Storm waves in the Gulf of Mexico destroyed the interlocking block revetment constructed to 

protect Louisiana State Highway 82 near Peveto Beach (Fig. 3). The revetment structure was replaced 

with 85 segmented breakwaters between Constance Beach and Holly Beach (Fig. 3).
Open-File Report 2004-1043 36 

protected by the barrier islands. Another durable nourished 

beach is at Captiva Island, Florida where fill is obtained 

from maintenance dredging of a nearby inlet. In general, 

nourished beaches last longer in the Gulf of Mexico than 

on either the Atlantic or Pacific shores because of the lower 

wave energy. Even though beach nourishment is a favored 

method of controlling beach erosion, it can lead to some 

unfavorable results, such as steep scarps (Fig. 17) and shelly 

or rocky beach material. A specific example of undesirable 

consequences of beach nourishment is the Egmont Key, 

Florida project that derived its fill from maintenance dredging of a nearby tidal inlet (Egmont Channel). The beach fill 

material was composed mostly of broken shell, which is 

less suitable than sand for beach durability and recreational 

comfort. 

Sand bypassing is another engineering response to 

beach erosion at inlets where jetties are constructed to 

help maintain the inlet for boat traffic. At Perdido Key and 

Mexico Beach, Florida, small fixed bypassing plants have 

been constructed to transfer sand from the updrift side to 

the downdrift side of the inlet. Although these bypassing 

operations may reduce erosion at the inlets, they are unable 

to transfer the sand as efficiently as the natural unimpeded 

waves and currents. Therefore, sand bypassing does not 

entirely compensate for the erosion caused by the channel 

dredging and jetty construction.

Submerged berms (Table 9) are non-structural solutions to beach erosion near tidal inlets. They are constructed 

of sediment dredged from navigation channels and are 

currently being promoted as a solution to two problems, disposal of dredged spoil and mitigation of beach erosion. The 

dredged material is deposited under water in a low mound 

parallel to the beach and in relatively shallow water. The 

berm acts as a submerged breakwater causing large waves 

to break offshore, thus reducing storm beach erosion. If the 

berms are oriented properly and built in shallow water, the 

waves may transfer some of the sand onshore and add to the 

forebeach. In the Gulf of Mexico, the Corps of Engineers 

has constructed submerged berms to reduce erosion and 

storm damage of Dauphin Island, Alabama and South Padre 

Island, Texas. These projects are not as efficient in controlling beach erosion as direct placement of the dredged material on the beach, but they are also less costly than beach 

nourishment.

Deliberate relocation of buildings is not a common 

response to beach erosion and attendant coastal land loss 

in the Gulf Coast region. Nevertheless, there are several 

examples of voluntary relocation. Relocation of the visitorʼs 

center at Padre Island National Seashore (Fig. 26A and B) is 

a classic example of what happens when conventional wisdom is ignored at the coast. Optimistic planners projected 

that many visitors would come to Padre Island National 

Seashore each year. In response, a large visitorʼs center was 

built that included bathhouses, observation decks, offices, 

a restaurant, and a nature display describing the processes 

and ecology of the barrier island. Park officials, ignoring the 

possible consequences of building too close to the water, 

constructed the large concrete pile-supported building on the 

beach so that beach users would not be inconvenienced. Furthermore, the tall sand dunes that formed the highest barrier 

island elevations were destroyed to construct a parking lot 

and to provide access to the facilities. After about 20 years 

Figure 25. West end of the seawall at Galveston, Texas. The concrete ramp (right foreground) was the 

road leading to the beach in the mid 1960s. Since then the beach has eroded more than 150 m.
Open-File Report 2004-1043 37

A

B

Figure 26. Visitor’s center at Padre Island National Seashore, Texas in 1982 and 1992. The concrete 

reinforced structure built on the beach was torn down and a wooden structure was built landward of the 

dunes.
Open-File Report 2004-1043 38 

and a major hurricane it was discovered that the pilings that 

supported the visitors center were structurally damaged. The 

facilities were declared a hazard to public safety, torn down, 

and a new building was constructed landward of the position 

of the former dune ridge (Fig. 26).

In some Gulf Coast states, involuntary retreat from the 

eroding shoreline has been the result of both physical and 

legal forces. The resulting landward relocation of houses 

and highways is designed to maintain a coastal presence 

while recognizing the inevitability of future coastal erosion. In Texas, several lawsuits resulted in the removal of 

a restaurant and a house from the Gulf beach because the 

buildings interfered with the publicʼs use of the beach. Both 

structures were relocated to lots farther inland on the barrier 

islands. 

DISCUSSION AND FURTHER 

CONSIDERATIONS

Summary of Shoreline Changes

According to measurements by the National Ocean 

Service, states bordering the Gulf of Mexico have 2610 km 

of open ocean coastline (Shalowitz, 1964). In this report, 

rates of shoreline change are provided for 1370 km, or 52% 

of the total length of shore. Shoreline change analyses were 

not conducted for approximately 42% of the Gulf shore that 

is characterized by predominantly muddy shores and where 

a lidar-derived shoreline was unavailable (mangrove islands 

of southwest Florida, marshes of Florida Big Bend, and 

marsh-dominated segments of the Mississippi delta), and 

for 6% of the Gulf shore where all four shorelines were not 

present (Fig. 1).

Of the Gulf shoreline where rates of change were 

quantified, at least 830 km (61%) is eroding with average 

long-term rates as high as 36.8 ± 14.2 m/yr. Short-term rates 

of change are comparable with about 750 km (55%) of the 

evaluated shore eroding in spite of beach nourishment and 

other attempts to stabilize the shore. The length and percentage of eroding shore would be even higher if the mangrove 

islands and marshes of Florida and Mississippi delta segments were included (see Hine and Belknap, 1986; Penland 

and others, 2000 respectively).

Rates of erosion for the Gulf of Mexico region are 

generally highest in Louisiana along barrier island and 

headland shores associated with the Mississippi delta. Both 

the highest long-term and short-term rates of erosion are 

anomalous and locally the result of barrier rotation or the 

shoreline crossing open water between two land features. 

Neither of these conditions could be sustained indefinitely, 

so the highest retreat rates could not be sustained. Erosion 

is also rapid along some barrier islands and headlands in 

Texas, and barrier islands in Mississippi are migrating laterally. High rates of erosion in Florida are generally localized 

around tidal inlets. Gulf shoreline change is greatly reduced 

along the west coast of Florida where low wave energy and 

frequent beach nourishment minimize erosion. Some beach 

segments in Texas have accreted as a result of net longshore 

drift convergence, and around tidal inlets that have been 

stabilized by long jetties.

Comparing long-term and short-term summary values 

for each state (Table 7a and 7b) shows a systematic decrease 

in the length (percent) of eroding shore. The decrease in 

eroding shore and complementary increase in accreting 

shore may partly be related to the systematic seaward offset 

in the lidar shoreline. 

Planned Updates and Related Research

The USGS plans to revise and report on rates of 

shoreline change for the Gulf of Mexico every 5 to 10 years. 

The revision interval will depend on the need for updated 

information and technological advances that will allow 

relatively rapid shoreline position acquisition, processing, 

and dissemination. Future revisions will also incorporate 

the results of ongoing shoreline research. For example, we 

plan to evaluate the advantages and disadvantages of using 

the MHWL to determine if another datum-based shoreline 

would be more suitable for historical analysis. We will also 

explore other approaches to reduce shoreline positioning 

uncertainty (spatial errors) and shoreline sampling uncertainty (temporal variability). GPS technology has so greatly 

reduced positioning errors that they are no longer a significant component of the uncertainty analysis like they were in 

the past. GPS and lidar also eliminate the need for digitization and introduction of their associated positioning errors. 

Switching from the HWL to the operational MHWL will 

reduce some of the apparent short-term sampling variability that limits the reliability of the results. A datum-based 

shoreline that is higher on the beach profile than the operational MHWL might further reduce some of the short-term 

sampling variability by taking advantage of the more stable 

portion of the beach profile. The dynamics of sandy beaches 

ensure that short-term shoreline fluctuations will not be 

eliminated entirely from future shoreline positions, but data 

being collected in various coastal regions as part of the 

USGS regional studies will provide quantitative assessments 

of seasonal and interannual changes in shoreline position. 

These assessments will provide a means to determine if the 

detected shoreline change is within the expected range of 

movement and allow us to further constrain the uncertainties.

Another ongoing topic of research involves non-linear 

analysis of shoreline movement. It has been shown that time 

averaged linear methods of estimating future rates of shoreline movement (the existing paradigm) may not be appropriate for future predictions of shoreline position because 

coastal dynamics are non-linear. However, time series 

analyses based on non-linear theories require numerous 
Open-File Report 2004-1043 39

shoreline positions (high sampling frequency) that generally 

are unavailable for most coastal areas.

Influence of Human Activities

As coastal communities expand along eroding shores 

of the Gulf of Mexico, potential conflicts may arise between 

preservation of upland property (typically privately owned) 

and conservation of the beach (typically publicly owned). 

Past social responses indicate that these conflicts most likely 

will be resolved through a combination of beach nourishment projects and shoreline protection structures. Both 

of these engineering responses to erosion alter the natural 

beach processes and eventually lead to shoreline positions 

that are not related to the natural unaltered rates of beach 

erosion. 

Adding sand to eroding beaches is the most common method to mitigate storm damage and to maintain a 

Clark, R., 1986, The impact of Hurricane Elena and tropical storm Juan on coastal construction in Florida: Florida 

Department of Natural Resources, Division of Beaches 

and Shores, Report 85-3, 140p.

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