Suspended sediment variability on seasonal and tidal time scales in the Winyah Bay estuary, South Carolina, USA

Abstract

A transient estuarine turbidity maximum (ETM) was observed in Winyah Bay during field sampling in 1996. The core of this turbidity maximum migrated 8 km seaward of its traditional location at the salt–freshwater interface in response to very high river discharge events in 1996. In response to the semidiurnal tidal cycle, there was a well-defined variation in the suspended sediment concentration within the turbidity maximum zone between ebb and flood tides as a result of differences in tidal velocities. The suspended sediment inventory in the water column during the flood tide was greater than suspended sediment inventory during the ebb tide. During slack water, the water column was characterized by 0.03 kg m −3 sediment concentrations whereas at times of maximum boundary shear stress near the bottom, the water column was highly turbid, indicating that bottom sediments were resuspended by the strong tidal currents typical of the bay. Throughout a tidal cycle, the vertical extension of high suspended sediment concentration in the water column within the ETM was well developed during the flood tide and inhibited during the ebb tide. Internal tidal asymmetry, with well-mixed conditions during the flood tide near the bottom, and with stratification in the water column during the ebb tide, was probably the process responsible for the enhancement of turbulence during the flood tide and inhibition of turbulence during the ebb tide with implications for the ETM.