A three-dimensional distinct element model for bed-load transport

A three-dimensional model is developed to simulate bed-load transport using Distinct Element Method (DEM). The model describes the bed-load transport as dynamically interdependent motions of individual sediment particles under the flow action. A steady logarithmic velocity distribution over the flow depth is considered to represent fluid motion, while turbulent intensities are also included within the closure model. The present model accounts for both fluid-particle and particle-particle interactions, which are the predominant micro-mechanisms of bed-load transport under low and high tractive forces, respectively. Characteristic features of bed-load transport, previously reported by experimental observations, are numerically reproduced. The concept of vertical momentum transfer is exploited to describe features of concurrently present of saltation and sheet-flow layers. It is concluded that the vertical motion of particles is not significantly active in sheet-flow layer and the particle momentum is preserved. Consequently the interparticle collisions is the predominant mechanism of bed-load transport at high fluid tractive forces.