Suspension gravity currents (turbidity currents) occurring in lakes,
reservoirs, and the ocean are investigated theoretically. When the
turbid water, a mixture of suspended particles and clear water, is
introduced in a quiescent body of clear water, the turbid mixture flows
downslope due to its larger density. Turbidity currents derive this
driving force from the sediment in suspension. Such turbidity currents
are essentially non-uniform and in disequilibrium because of water
entrainment across the upper boundary of the flowing layer. Therefore,
turbidity currents can be erosive or depositive, accelerating or
decelerating as they travel over the sloping bed, exchanging sediment
between the bed and the flow. The governing equations which describe
the movement of gradually varied steady-state turbidity currents
occurring in sloping channels with constant as well as variable widths
are developed. In order to incorporate the mechanism of sediment
exchange into the model, the sediment entrainment function is derived by
utilizing data for suspended sediment transport in free-surface open
channel flows and is applied to the analysis. The model is also applied
to actual field sites. Such turbidity currents can be originated by
various processes when large amounts of sediment are put into
suspension. One mechanism investigated both theoretically and
experimentally is the direct inflow of dense river water into a
reservoir. This phenomenon is sometimes referred to as "plunging flow."
The results obtained herein are expected to be useful for
applications by geologists, oceanographers, and hydraulic engineers, who
are concerned with understanding the impact of turbidity currents on
natural environments, for example, the redistribution of sands in the
ocean, subsurface morphology, and with modeling of water quality and
transport of dissolved solids, suspended matter in lakes and reservoirs.
Minnesota Sea Grant Program, NOAA, Department of Commerce;
National Science Foundation;
Legislative Commission on Minnesota Resources
Akiyama, Juchiro; Stefan, Heinz G..
Gravity Currents in Lakes, Reservoirs and Coastal Regions: Two-Layer Stratified Flow Analysis.
St. Anthony Falls Hydraulic Laboratory.
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