Modification of Stokes Drift in Coastal Areas due to Surface Wave, Current and Topography Interactions

Surface gravity waves cause floating particles to undergo a slow drift in the direction of wave propagation. This forward drift, commonly known as the Stokes drift, plays a crucial role in transporting various tracer parcels, from sediments to pollutants, in the marine environment. In the classical analysis, the effect of mean current and sea-bed undulations are not factored in while calculating Stokes drift. We find that in the nearshore region, Stokes drift is non-trivially affected by alongshore current and sea-bed undulations. We theoretically show that the time-independent particular solution, arising from mean-current and bottom-ripple interactions, leads to additional terms in the Stokes drift. Next, using High-order Spectral method, we numerically simulate wave-current-topography interactions in a 3D setting and compute the Lagrangian drift. We find that the resulting drift in the presence and absence of sea-bed corrugations have significant differences. Topographic interactions are inevitable in the nearshore region, and our study reveals that sea-bed corrugations can significantly affect cross-shelf exchange of microplastics and other nearshore tracers like pathogens, contaminants, nutrients, larvae, and sediments.