Lateral circulation and suspended sediment transport in a curved estuarine channel: Winyah Bay, SC, USA

Shipborne vertical profiles of flow and suspended sediment concentration collected on a transect, across a curved, nonsymmetrical estuarine channel are presented. Analysis of the transient cross‐channel momentum balance equation shows that the lateral circulation pattern is controlled by the interaction between centrifugal and lateral baroclinic forcings although those two might not be necessarily in balance as suggested earlier by Seim and Gregg (1997). Instead, differential along‐channel advection and local acceleration appear to influence greatly lateral circulation dynamics. During ebb when the water column is highly stratified, the interaction between centrifugal acceleration and opposite‐directed lateral baroclinic forcing results in weak lateral flows. During flood, lateral flows are dominated by centrifugal acceleration, which is directed toward the outside of the curvature at the mid‐depth because of the nonlogarithmic current profile, and reinforced by lateral baroclinic forcing. This results in strong two‐layer clockwise circulation (looking up‐estuary) during flood. The eastward‐directed bottom currents during ebb deliver only a small amount of suspended sediment from the relatively narrow western shoal to the channel bed. During flood, the west‐directed near‐bed currents deliver a significant amount of sediments from the gentle, broad eastern shoal, which in conjunction with the locally resuspended sediment load promotes the development of the estuarine turbidity maximum. Increased lateral advection of sediments during flood reinforces a tidal asymmetry in the development of turbidity maximum. Decomposition analysis of lateral sediment fluxes averaged over a tidal cycle suggests convergence of sediment toward the center of the channel is driven mainly by the oscillatory tidal component.