Numerical Simulation of Nearshore Hydrodynamics and Sediment Transport Downdrift of a Tidal Inlet

Abstract

Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a structured tidal inlet with complex bathymetry are investigated to determine the potential causes of downdrift beach erosion. A coupled wave and hydrodynamic model is used to simulate the nearshore hydrodynamics and morphodynamics. Near the inlet, the tidal-induced pressure gradient dominates the wave radiation stress gradient only in the first half of the flood duration. The nearshore hydrodynamic pattern for the rest of the tidal cycle is driven mainly by the wave-driven pressure gradient. The wave-driven pressure gradient results from alongshore variation of water surface elevation induced by nearshore wave focal points caused by wave refraction over irregular bathymetry (with ebb tidal shoals and nonparallel shoreline depth contours). The resulting alongshore sediment transport patterns suggest that the direction of the time-averaged alongshore sediment transport rate near the inlet and at the downdrift beach is against that of the larger-scale net sediment transport along the coast. The inlet-adjacent time-averaged alongshore sediment transport rate increases for waves with larger wave height and an incident angle closer to shore normal in contrast to expectations under the assumption of straight and parallel depth contours.