Numerical Prediction of Rip Currents on Barred Beaches

The time-dependent evolution of rip currents is investigated in this paper using a numerical model based on Boussinesq-type equations. A numerical wave basin was set up to reproduce the laboratory experiments of Haller et al.. The bathymetry consists of a barred beach with two rip channels. Waves propagating over the bar break on the bar while those propagating through the gap break closer to the shoreline. This sets up a spatial variation of the wave-induced excess momentum flux and drives a time-varying circulation pattern. Large-scale horizontal eddies are also generated at the edges of the rip channels and advected offshore. Time histories of the measured velocities have been compared with the Boussinesq model predictions. The numerical model reproduces the overall trend in the unsteady behavior of the rip current but pronounced differences are observed in the flow exiting the rip channel.