Lagrangian algorithms for bedload transport in streams: An analysis of relative force importance, inter-particle collisions and other features

Numerical models using the point-particle approach to simulate the saltation motion of particles near the bed in turbulent open-channel flows have been developed in recent decades. Although widely used, there are several differences in the details of such models for diverse ranges of particle size. Some of the discrepancies are related to the different forces used to characterize the particle motion in between collisions with the bed. In this work we show the relative importance of each force related to the total net force subjected to a single particle moving in saltating mode. First a generalized 3D algorithm that follows saltating particles is presented, including a unique treatment for the Basset force. The model conserves linear and angular momentum, and uses geometric considerations and stochastic parameters to represent inter-particle collisions and collisions with the wall. The model is then validated with experimental results within the sand range, for average saltation height and length. Later on, we examine the relative weight of the forces, and assess their importance for the model. Implications for the diffusion of particles in the transverse direction are discussed as well.