Total exchange flow, entrainment and turbulent mixing in a partially stratified estuary

The linkage among isohaline transport, entrainment and turbulent mixing in salinity coordinate in estuaries is investigated. Under steady state, they have integral relationships between each other. With known exchange flow and stratification at the mouth and river discharge, the isohaline integrated entrainment and turbulent mixing in the interior estuary can be quantified. Through using a numerical model of the Hudson estuary, their temporal variability associated with the spring-neap cycle and the spatial variability due to realistic topography are also studied. During neap tides, TEF indicates a two-layer flow. Mixing mainly happens in the interface. During spring tide, TEF is mainly time-dependent due to weaker vertical structure and strong tidal advection of salt. Mixing mainly happens near the bottom. The topography influences the local features of TEF and mixing. Jet-sink flow makes TEF a little larger than other regions and the salt fronts induce strong mixing.