Experiments on Saline Wedge

Abstract

Detailed measurements on the internal flow structure of the arrested saline wedge over a horizontal bottom have been performed together with observations of its overall appearance. The experiments covered a channel Reynolds number range between 4,000 and 10,000 and a densimetric Froude number range between 0.39 and 0.49. Measurements included overall shape, internal circulation, velocity, density and gradient Richardson number profiles, entrainment rates, and shear stresses. The major portion of the saline wedge, excluding the wedge tip and the exit regions, is a quasi‐equilibrium region in which internal flow properties are nearly similar. The flow dynamics are controlled by the turbulent freshwater overflow with a downward cascading process of energy toward the salt layer. Conditions at the two major internal dividing lines, the density interface and the zero velocity line, are elucidated. The density interface is a highly stable zone with intermittent wave breaking, mixing, and entrainment. The zone is in a state of marginal instability consistent with linear stability theory. Viscous and turbulent shear stresses are of about equal magnitude at the interface, while the net upward entrainment is small. The zero velocity line, in contrast, experiences a large upward entrainment of salt water but has small shear stresses.