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

Physical Agents of Land Loss: Sediment Budget Introduction Sandy Coasts Rivers & Deltas Changes in Sediment Supply Changes in Sediment Supply Several thousand years ago the principal suppliers of sediment to most non-cliffed coasts were either rivers that delivered sand directly to the beach or nearshore currents that transported sand onshore from the continental shelf. Once at the coastline the sand was redistributed by alongshore currents. The presence of sandy beach-ridges and barrier islands on both Atlantic and Gulf coasts indicate that sand supply was plentiful and beaches were building seaward as sea level approached its current position several thousand years ago. Since then, sediment supplied by some coastal rivers and the continental shelf has naturally diminished as a result of climatic changes and adjustments of the inner shelf profile. Humans have also contributed significantly to the deficit in sediment supply by damming rivers, building seawalls, groins, and jetties, and dredging tidal inlets. These natural and artificial reductions in coastal sediment supply have resulted in the erosion of many beaches, barrier islands, and deltas. Today the only remaining source of sediment for many coastal compartments is local erosion of nearby beaches and bluffs. continue to Relative Sea Level

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