Random-Walk suspended sediment transport and settling model

This paper describes a particle-based approach to simulate entrainment, transport, and settling of non-cohesive sediments in rivers and the coastal zone where the velocity distribution is characterized by a fully-developed turbulent boundary layer extending from the bed. Sediment distributions are modeled as a set of particles that are tracked on an individual basis by solving Lagrangian transport equations that account for advection by the mean flow, settling, and random turbulent motions. The vertical distribution of the mean flow is modeled by a power law, and turbulent motions are modeled as a random walk that is scaled by the turbulent diffusivity analogous to random molecular motions that constitute Fickian diffusion. Because it is not feasible to track individual sediment grains, each particle accounts for a large number of sediment grains of a single size and settling velocity. A suite of particles is used to account for a spectrum of grain sizes. The model resolves the vertical distribution of particles consistent with Rouse profiles for a wide range of Rouse numbers. Using an entrainment relationship from literature, model predictions of sediment loads compare favorably to established empirical models. The model is applied to predict the collection efficiency of a sedimentation basin in Ballona Creek, California, highlighting the effectiveness of the basin at collecting coarse sands but not finer grained material.