Mixing Behavior of Density-Stratified Pools

Abstract

Numerous inland Australian streams contain density-stratified or saline pools. Saline pools consist of a layer of saline water underlying a layer of fresh water. They are associated with seasonal low flows and influxes of saline groundwater and have important water quality and environmental implications. A theoretical model of the dominant mixing process (flushing) associated with flows of fresh water across the top of the saline layer is presented. Laboratory results show that progressive removal of saline water from saline pools occurs because of a thin saline layer flowing up the downstream depression slope when the surface layer flows over the saline layer at a sufficiently high velocity. The behavior of this thin layer is controlled by a balance between shear and buoyancy forces that act on it. Experimental results describe the initiation of this outflow, the rate of the outflow, the composition of the outflow, and the range of scour hole geometries over which flushing is the dominant mixing process.