MIXING BEHAVIOR OF DENSITY-STRATIFIED POOLS

Numerous inland Australian streams contain density-stratified or salin e 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 en vironmental implications. A theoretical model of the dominant mixing p rocess (flushing) associated with flows of fresh water across the top of the saline layer is presented. Laboratory results show that progres sive removal of saline water from saline pools occurs because of a thi n saline layer flowing up the downstream depression slope when the sur face layer flows over the saline layer at a sufficiently high velocity . The behavior of this thin layer is controlled by a balance between s hear and buoyancy forces that act on it. Experimental results describe the initiation of this outflow, the rate of the outflow, the composit ion of the outflow, and the range of scour hole geometries over which hushing is the dominant mixing process.