Phase‐resolved modeling of wave interference and its effects on nearshore circulation in a large ebb shoal‐beach system

A time-domain Boussinesq model was applied to modeling wave interference and its effects on nearshore circulation in San Francisco Bar and the adjacent Ocean Beach, CA. The model predicted the wave interference phenomena caused by the ebb shoal, with interference scales consistent with the radar observation and are persistent with nodal lines unchanged with time. Nearshore circulation predicted by the model shows small-scale flow structures tied with the wave modulation patterns. However, the small-scale modulation in the wave field seems not to generate alongshore variation in wave setup at similar scales. Therefore, in a large-scale view, the alongshore currents predicted by the Boussinesq model still keep the general features shown in a wave-averaged model, such as the flow divergence caused by the pressure gradient force associated with the alongshore variation of wave setup. The further analysis based on idealized short crest waves on a plane beach suggests that the alongshore pressure gradient is mainly balanced by the gradient of radiation stresses in the antinodal region, while by the flow advection in the nodal region. The rip current behavior is forced locally near breakers, rather than by gradients in wave setup close to shore. The time-domain Boussinesq model predicted the spatial variability of wave-induced processes. The alongshore-varying wave breakers caused by wave interference are the source of the vorticity generation, inducing energetic vortex eddies nearshore.