Modeling of Sediment Transport in Steady Flow over Mobile Granular Bed

A multilayer system with bottom, intermediate, and upper zones is proposed in order to provide full, continuous sediment velocity and concentration profiles. The model is developed with respect to different physical processes that rule sediment transport at various distances from an immobile bed to the water surface. In particular, the variation of shear stress is proposed, characterized by the increase to a maximum value at the bed and its fade-out in the bed. Consequently, the participation of separate layers in total transport is different for various shear rates. Specifically, when bed flow is fully mobilized, the participation of the bottom layer in sediment transport is dominant, whereas its contribution is negligible under conditions close to incipient motion. Then, only the topmost grains of that layer are transported as bed load. The model works in a very wide range of grain mobility conditions, from incipient motion to a fully mobilized bed. The theoretical description was validated with a number of data sets for different grain diameters and densities.