SPRING-NEAP VARIATIONS OF LATERAL SEDIMENT TRAPPING PROCESSES IN A MODEL OF THE HUDSON RIVER ESTUARY

Previous field investigations and modeling studies of sediment transport in the Hudson River estuary have identified an estuarine turbidity maximum (ETM) at the intermediate salinity portion of the estuary. The sediment trapping processes in the ETM are influenced significantly by cross channel flows. Near the channel bottom, these flows are directed to the shallower western side as a result of the transverse baroclinic pressure gradient set up during flooding currents. This creates a convergence of flow resulting in higher suspended sediment concentrations and more rapid accumulation of sediment on the shallow western side of the channel. This study examines results from a three dimensional, numerical model in order to study the variations in the transverse pressure gradients, flows, and sediment fluxes during spring and neap tidal cycles in the region of the ETM. Preliminary results show significant cross-channel variability in stratification and sediment concentrations during spring tides, with the maximum gradients occurring at the end of the flood and higher concentrations on the shallow western side of the channel. The transverse salinity gradient is significantly diminished during neap tides and stratification is nearly uniform across the channel. Overall sediment concentrations and fluxes in the ETM are lower during the neap tide, and, unlike spring tide conditions, the suspended sediment concentrations are greatest in the deeper eastern side of the channel.