A transport model for sheetflow based on two-phase flow

This paper describes a model of the net sediment transport rate under linear and arbitrary nonlinear oscillatory flows in the sheetflow regime. The model is based on a two-phase flow description. The turbulent diffusivity was formulated to take into account phase-lag effects for different wave conditions and sediment properties. An introduction of a modifier to the turbulent diffusivity produced asymmetry in the concentration profiles, which qualitatively agrees with temporal and spatial distributions of the concentration profiles measured during laboratory visualization experiments. The model can predict transport rates in the sheetflow regime for combined waves and co-directional currents and for waves alone. The model is validated for a wide range of sediment median particle diameters, wave periods, and maximum flow velocities. Comparisons with experimental data on transport rates under linear and nonlinear waves, including velocity and acceleration asymmetric oscillations, were made and showed good agreement. Other comparisons encompassing combined waves and currents were conducted, also with good agreement.