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 Sandy Coasts Common sources of coastal sediment are rivers (e.g. Mississippi), eroding bluffs and dunes (e.g. Cape Cod), and the continental shelf (e.g. North Carolina Outer Banks). Sand is removed from the beach and stored in coastal dunes and storm washover deposits, as well as in tidal inlets and tidal deltas. Some sand eroded from the beach and shoreface during storms is transferred to the inner continental shelf where it is deposited in water so deep that fair-weather waves cannot return the sand to the beach. Under these conditions, the continental shelf is a permanent sand sink. Atlantic coast estuaries are large sinks for sand transported landward from the continental shelf and adjacent beaches (Meade, 1969). Along the tectonically active Pacific coast, other sediment sinks are deep submarine canyons that permanently intercept sand moving alongshore. Artificial channels and dredged inlets are also large sediment sinks that can cause imbalances in the sediment budget. Erosion along one stretch of sandy beach may be responsible for accretion or reduced erosion of a nearby beach in a downdrift direction if the sediment volume is sufficient and the available material is compatible with downdrift beaches. On the other hand, depletion of an updrift sediment source will initiate or accelerate retreat of downdrift beaches. The type of material eroded determines whether or not nearby beaches benefit from the erosion. For example, erosion of sandy beaches provides a ready source of sand for nourishment of downdrift beaches, whereas erosion of marshes and other muddy deposits usually does not contribute to the sand budget of adjacent beaches. continue to Rivers & Deltas

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