Assessment of the Nearshore Zone at St. Marys Inlet, Florida

by Laurel T. Gorman, US Army Engineer Waterways, Experiment Station, Vicksburg, United States,

Document Type: Proceeding Paper

Part of: Coastal Zone '91


St. Marys Inlet connects Cumberland Sound from the Atlantic Ocean and actually forms the coastline border between Georgia and Florida. Drumstick shaped barriers are located to the north (Cumberland Island) and to the south (Amelia Island). The mean tidal range is 1.8 m and wave heights average 0.6 m. Southerly directed longshore sediment transport is dominant due to alongshore wave energy increasing to the southeast. Nearshore processes, sediment distribution patterns, and ebb-tidal delta morphology are all being measured and used to document temporal change in the physical and environmental parameters of St. Marys Inlet. This investigation is ongoing and part of a five-year monitoring program sponsored by the U.S. Navy. This paper discusses wave, bathymetric profiles, and sediment data sets collected during August 1988 and August 1989. Inshore wave conditions during April-October 1989 ranged between 0.27 and 1.76 m for significant wave height and between 4.3 and 14.2 seconds for wave period. Spatial changes in nearshore subbottom elevation were evaluated within six distinct morphologic features. Bathymetric contours of the nearshore zone to the -10 m contour indicates three large areas of sediment storage and two embayment areas where sediments are moved alongshore and offshore. The average mean grain size generally decreased along both islands within the beach and nearshore zones between the summer of 1988 and summer 1989. This change is attributed to several factors: storm activity, beach nourishment activity on Amelia Island, and alongshore sediment movement.

Subject Headings: Nearshore | Inlets (waterway) | Sediment transport | Tides | Islands | Bathymetry | Barrier islands | Littoral drift | United States | Florida | Atlantic Ocean | Georgia

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