Historical Coastal Morphodynamics at St. Marys Entrance and Vicinity, Florida, U.S.A.

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by Stephen C. Knowles, U.S. Army Engineer Waterways, Experiment Station, Vicksburg, United States,
Laurel T. Gorman, U.S. Army Engineer Waterways, Experiment Station, Vicksburg, United States,

Document Type: Proceeding Paper

Part of: Coastal Sediments:

Abstract: St. Marys Entrance is an Atlantic Ocean tidal inlel located on the Florida-Georgia state border. At the end of the nineteenth century rubble-mound jetties were constructed. Large-scale natural and jetty-induced morphologic changes have occurred in the area, including; fillet accretion adjacent to both jetties, landward migration of ebb-tidal shoals, and profile steepening of nearshore areas downdrift (south) of the inlet. Natural migration of the ebb-tidal shoal at the north end of Cumberland island and of shoals seaward of central Cumberland island have also occurred. Average shoreline position change from 1870 to 1974 along Cumberland and Amelia island was 1.5 m/yr and 0.3 m/yr, respectively. Preliminary analysis indicates 58 × 106 m3 of sediment accumulated in the St. Marys Inlet/Ebb-Delta Complex from 1924 to 1970's, implying a gross sediment transport of 1.2 × 106 m3/yr. Net southerly littoral transport is estimated to be 0.3 × 106 m3/yr. Nearshore volumetric losses have been significant along central Amelia Island, resulting in profile steepening along most of the island. Geomorphic response to jetty construction at St. Marys Entrance has been similar to other Atlantic coast tidal inlets. Relatively rapid, significant reconfiguration of the ebb-delta system was followed by more subtle, long-term changes farther up-and down-drift.

Subject Headings: Islands | Tides | Coastal environment | Sediment transport | Sea water | Inlets (waterway) | Jetties | Shoals | Nearshore | North America | Florida | United States | Atlantic Ocean

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