A suspended sediment stratification correction for combined wave and current flows

TLDR

The study presents a simple model for near‑bottom combined wave and current flow over a movable sediment bed. The model extends Grant and Madsen’s framework by incorporating movable‑bed roughness effects and solves coupled unsteady momentum and sediment‑mass equations with an eddy‑diffusivity closure to compute velocity, suspended‑sediment concentration, and transport profiles. The results indicate that self‑stratification can be significant for fine to medium sands during storms, driven by wave‑induced sediment suspension and enhanced turbulent mixing, and the theory can be readily extended to a full Ekman‑layer model.

Abstract

A simple model for the near‐bottom combined wave and current flow over a moveable sediment bed is presented. The model is an extension of the Grant and Madsen (1979) combined wave and current model, with moveable bed effects on the physical bottom roughness included as by Grant and Madsen (1982). The unsteady conservation of fluid momentum and sediment mass equations, which are coupled through an eddy diffusivity closure scheme, are solved for the wave and current velocity profiles, along with the suspended sediment concentration and transport profiles. Sample runs are presented to illustrate the effect of varying wave conditions on the current, the mean sediment concentration, and the mean sediment transport. Results show that for fine to medium sands, self‐stratification of the flow can be important during storms owing to the large amount of sediment suspended by the waves and the enhanced turbulent mixing associated with the wave‐current interaction. The theory easily can be generalized for inclusion in a full Ekman layer model.