Scour of Bed Material in Very Rough Channels

Abstract

Experiments with densely packed uniform spheres have confirmed that the initiation of motion of bed material is affected by the relative roughness of the channel. At shallow depths, larger values of the shields. parameter are required to initiate the motion. This was explained by the reduction of nondimentional velocities, u / u * , at the bed level with the increase of d / h . The effective values of the instantaneous flow velocity are thus achieved at higher bed shear stresses in comparison with flows at mild slopes.