Two‐Layer Model of Saline Wedge. I: Entrainment and Interfacial Friction

Abstract

The arrested saline wedge geometry is characterized by two major internal demarcation lines, the density interface and the zero velocity line (ZVL). As a complement to earlier two‐layer model formulations that are based upon the density interface, a two‐layer model using the ZVL is developed. The advantage of this model is that it divides the flow into an active upper zone with high kinetic energy content and a passive lower zone as suggested by detailed experiments. Net entrainment across the ZVL drives the flow in the passive salt zone. An entrainment model is developed on the basis of stability theory and similarity theory for turbulent buoyant shear flows but includes an empirical transition to purely laminar flow in the low Reynolds number range. The model depends on two local parameters, a bulk Richardson number (or densimetric Froude number) and a bulk Reynolds number. Predicted entrainment rates agree well with available data over the range of parameters. Furthermore, the model can be extended to predict the interfacial shear in the complementary formulation that is based on the density interface and, again, shows good agreement with published data. In part 2, the proposed model is applied to the prediction of overall wedge properties, i.e., length, shape, and internal circulation, in estuary flows.