| Plunging inflows in lakes and reservoirs are the result of higher density water flowing into an ambient body of lower density. As the denser fluid intrudes, it pushes the lighter fluid ahead. The lifting of the lighter water counters the momentum of the inflowing water and stops its progress. At this point the denser water plunges beneath the surface of the ambient fluid and eventually flows as a density current along the riverbed. Entrainment and mixing through the plunge zone has received little attention, although it is estimated that up to 80% of the total entrainment can occur in the plunge.; In this study plunge zones are investigated under a range of conditions that would influence mixing: inflow rate, geometry, and stratification. All of these plunge zones occurred in laterally-confined inflows that are typical of man-made lakes and reservoirs. Tracer studies are the primary investigative tool to determine mixing. Coupled with velocity profile data from acoustic Doppler instruments, tracer concentrations allowed mass balance estimates to be made on the tracer. Stratification conditions are defined with conductivity, temperature, and depth profilers (CTD) and with in situ thermistor chains.; These data, along with the limited data available in the literature, are used to create an algorithm to predict the location and amount of mixing in the plunge zone under the range of parameters normally encountered in the field. With the new mixing algorithm and previously established mixing coefficients for the density current, the point of neutral buoyancy can be better determined. The work provides better information on operational constraints on reservoirs to control release temperatures, and on the fate of any dissolved or suspended sediment carried by the inflowing water. (Abstract shortened by UMI.)... |
