Saturation Concentrations of Suspended Fine Sediment

Computations with the Prandtl Mixing-Length Model

Report (1998)

Authors

Department
Hydraulic Engineering (CEG) (TU Delft)
Copyright: © 1998 TU Delft, Department of Hydraulic Engineering
Concentration Fine sediments Prandtl Mixing-length model Saturation concentration Damping functions Computations
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Published Date

01-01-1998

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Source:

Report no. 5-98

Faculty

Civil Engineering and Geosciences

Department

Hydraulic Engineering

Abstract

Adopting a 1DV numerical model including the standard k-eps turbulence model, Winterwerp et al. (1999) calculated a saturation concentration for an initially uniform distribution of fine sediment concentration in steady flow. At concentrations exceeding the saturation concentration the concentration profile collapsed and all sediment was deposited as fluid mud. In this report similar computations are presented using the Prandtl mixing-length model. New expressions for the damping functions accounting for buoyancy effects are derived from three conditions: 1) in the case of equilibrium the concentration should be bounded for all gradient Richardson numbers, 2) the mathematical model should be stable and 3) the relationship between flux Richardson number and gradient Richardson number should agree with empirical data. Numerical results obtained with this model, such as the saturation concentration, agree fairly well with those of Winterwerp et al. (1999). It is shown that the saturation concentration is sensitive to the coefficients in the damping functions. This concentration may increase markedly for values of these coefficients that differ from those selected herein.