Impact of estuarine convergence on residual circulation in tidally energetic estuaries and inlets

Estuarine convergence (landward reduction of width and/or depth) is known to have the potential to significantly enhance estuarine circulation, a result theoretically derived under the assumption of constant eddy viscosity. Recent studies of longitudinally uniform energetic tidal channels indicate that tidal straining, a process driven by tidally varying eddy viscosity, is a major driver of estuarine circulation. The combined effect of estuarine convergence and tidal straining is investigated, for the first time, in this paper. The present idealized numerical study shows that estuarine convergence is reducing or even reversing tidal straining circulation in such a way that estuarine circulation can be weakened. This is a counterintuitive hydrodynamic effect of estuarine convergence, which may reduce (rather than increase) up-estuary particulate matter transport in estuaries and tidal inlets. Key Points <list list-type="bulleted"> <list-item id="grl51282-li-0001">It is a priori not clear if estuarine convergence enhances exchange flows <list-item id="grl51282-li-0002">Tidal straining is reversed by strong convergence <list-item id="grl51282-li-0003">Estuarine convergence tends to increase eddy viscosity during ebb