3D Calculations of Equilibrium Conditions in Loose-Bed Open Channels with Significant Suspended Sediment Load

Abstract

The flow, sediment transport, and bathymetry at equilibrium conditions in loose-bed open channels are predicted using a fully three-dimensional (3D) Reynolds-Averaged Navier-Stokes model that was validated for cases in which the bed-load transport is dominant. The paper focuses on two test cases corresponding to laboratory experiments performed in an S-shaped channel in which the suspended sediment load is comparable to the bed load. A modified version of the original model that accounts for gravitational force effects due to the total sediment load is proposed. It is shown that the way bed-slope effects are accounted for plays a major role in improving the predictive capabilities of the model for a case in which the equilibrium bathymetry is characterized by relatively large values and sharp variations of the transverse slope. The model is then used to qualitatively and quantitatively analyze the distributions of several flow variables that are difficult to measure in the laboratory. They include the distributions of the bed-shear stress and of a Chezy-type friction coefficient assumed to be constant by most lower-order (e.g., two-dimensional depth-averaged) models.