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Sand transport in a salt marsh estuary near Sapelo Island, Georgia, is in a net seaward direction. Bed forms migrate seaward at rates that vary with both their wave height and the tidal amplitude, and they maintain an ebb orientation through both the ebb and flood portions of the tidal cycle. Analysis of the energy flux through the estuary delineates the close interrelation between sand transport and hydrodynamics. The average rate of tidal-energy dissipation over the entire estuary-salt marsh system was determined from the difference in energy flux at the seaward and headward ends of the estuary. Estimates of the energy-dissipation rate within the estuary proper were obtained from measurements of bottom shear stress recorded at intervals over a tidal cycle. Comparison of these energy-dissipation rates indicates that the rate of energy loss in the total estuary-salt marsh system is several orders of magnitude larger than within the estuary proper. Most of the tidal energy loss is due to frictional dissipation around the Spartina grass in the marsh.
An important result of this is the "storage" of water at high tide in the marsh creating a large phase lag in the ebb flow between the headward and seaward ends of the estuary. The resulting large ebb-water slope (pressure gradient) induces ebb currents and bottom frictional forces which dominate over the flood phase. This result is directly reflected in the ebb-dominated bed-form geometry and sand transport.
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