HYDRODYNAMICS AND SEDIMENT TRANSPORT IN A SALT MARSH TIDAL CHANNEL

Abstract

Processes and sediment transport were investigated in a salt marsh drainage system at Kiawah Island, South Carolina. A general survey of the tidal current was done in the major tidal channel (Bass Creek) for a 10 tidal cycle period in August, 1977. Detailed determinations of current velocity, discharge, and suspended load were conducted during 15 tidal cycles in March, 1977 and again during 8 tidal cycles in July- August, 1977. For each of these periods, mass budget for the total suspended load were computed. The tidal currents have a pronounced time velocity asymmetry with the maximum current velocity occurring nearer high slack water and the peak ebb velocity being 20 - 30% stronger than the flood. Suspended load transport is significantly affected by the time velocity asymmetry. Peak current occurring nearer high slack water causes a net displacement of suspended material in an ebb or seaward direction under normal conditions. This process is enhanced by the stronger ebb currents. Mass budgets reflect the ebb dominance of the system showing a net export of combustible (organic) material during the March sampling period and a net export of both noncombustible (inorganic) and combustible material during the July-August period. Also important to suspended load transport in marsh systems are stressed meteorological conditions. High winds or heavy rains increase suspended load concentration and can cause significant import or export of fine-grained material.