Coastal & Marine Geology Program > National Assessment of Coastal Change Hazards > Open File Report 03-337

An Overview of Coastal Land Loss: With Emphasis on the Southeastern United States

USGS Open File Report 03-337

by: Robert A. Morton

Summary Introduction Physical Agents of Land Loss: Waves, Currents, & Storm Surges Landslides & Cliff Retreat Sediment Budget Relative Sea Level Climate & Land Loss Role of Shoreline Characteristics: Composition, Induration, & Saturation Coastal Morphology & Vegetation Role of Human Activities: Introduction Transportation Coastal Construction River Modification Hydrocarbon & Groundwater Extraction Climate Alteration Coastal Excavation Wetland Losses Acknowledgments References

Introduction To many people, coastal land loss is synonymous with beach erosion. Coastal land loss includes beach erosion, but it is a much broader term because it also includes land losses along bluffs and losses of wetlands around interior bays and estuaries. The most important causes of coastal land loss (Fig. 1) are erosion, inadequate sediment supply to beaches and wetlands, and coastal submergence (relative rise in sea level). Any one of these causes may be responsible for most of the land loss at a particular site, or the land loss may be the result of several factors acting in concert (Fig. 2). Figure 1. Common physical and anthropogenic causes of coastal land loss. Primary Causes of Coastal Land Loss Natural Processes Agent Examples Erosion waves and currents storms landslides Sediment Reduction climate change stream avulsion source depletion Submergence land subsidence sea-level rise Wetland Deterioration herbivory freezes fires saltwater intrusion Human Activities Agent Examples Transportation boat wakes, altered water circulation Coastal Construction sediment deprivation (bluff retention) coastal structures (jetties, groins, seawalls) River Modification control and diversion (dams, levees) Fluid Extraction water, oil, gas, sulfur Climate Alteration global warming and ocean expansion increased frequency and intensity of storms Excavation dredging (canal, pipelines, drainage) mineral extraction (sand, shell, heavy mins.) Wetland Destruction pollutant discharge traffic failed reclamation burning The primary causes of coastal land loss include both natural processes and human activities (Fig. 1). These primary causes determine where land will be lost whereas other factors, such as shoreline characteristics, control the rate of land loss. Some agents affecting land loss, such as wave energy, are common to all coasts, whereas other agents, such as vegetative cover, are only of local importance. In most coastal settings, the exact causes of land loss are uncertain, so it is necessary to evaluate all reasonable causes in order to predict what the coast might look like in the future and to understand how land loss will impact coastal communities. Figure 2. Interactions of factors that influence land loss. Modified from Morton (1977). [larger version] Physical agents affect land losses in all coastal environments, but wetlands are also subject to biochemical reactions and altered water circulation patterns. Because wetlands are unique organic environments, the causes of their deterioration and destruction (Fig. 1) are discussed in a separate section. This report represents a general overview of the primary causes and consequences of coastal land loss. Most of the examples and references are from states bordering the Gulf of Mexico and the Atlantic Ocean where the largest magnitudes and highest rates of coastal land losses in the United States are recorded (Dahl, 2000). The report serves as an introductory guide to the topics and literature on coastal land loss, and acts as a link to ongoing research being conducted by the U.S. Geological Survey. continue to Waves, Currents, & Storm Surges

Coastal & Marine Geology Program > National Assessment of Coastal Change Hazards > Open File Report 03-337