The Formation of a Turbidity Maximum in an Estuaryby Kathryn Pickens, Univ of California, Santa Barbara, United States,
Zenitha Chroneer, Univ of California, Santa Barbara, United States,
Poorvi Patel, Univ of California, Santa Barbara, United States,
Wilbert Lick, (M.ASCE), Univ of California, Santa Barbara, United States,
Abstract: In the present study, a numerical model is used to investigate the transport of sediments in a stratified estuary. The model includes sediment resuspension and deposition as well as three-dimensional, time-dependent descriptions of the hydrodynamics, sediment transport, and sediment bed dynamics. The purpose of the modeling is to examine the basic physical processes which cause the formation of a turbidity maximum in an estuary. Specific examples of stratified flows which are illustrated here are (a) a constant depth, steady-state flow, (b) a variable depth, steady-state flow, and (c) a variable depth, time-dependent flow as forced by tidal oscillations. The formation of a turbidity maximum can be shown to be dependent on the incoming flow rates in the river, the turbulent mixing and stratification of the flow in the estuary, the settling speeds of the solid particles, the bathymetry, and the magnitude of the tidal amplitudes. The magnitude and location of the turbidity maximum vary with the phase of the tidal cycle, while the magnitude of the turbidity maximum increases with an increase in the tidal amplitude. The tides enhance the turbidity maximum due to (a) the increased vertical velocities near the salt water wedge that are caused by the tidal oscillations, and (b) the deposition of sediments during slack periods and the subsequent resuspension of these recently deposited, low density, and easily-resuspendable sediments during high flow periods.
Subject Headings: Tides | Oscillatory flow | Flow duration | Sediment transport | Turbidity | Estuaries | Water flow | Fluid flow
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