Three-dimensional numerical modelling of the wave-induced rip currents under irregular bathymetry

A process-based 3-D hydrodynamic model is established to simulate the rip current structures under irregular bathymetry. The depth-varying wave-induced residual momentum, the surface rollers, the turbulent mixing and the wave-current interactions are considered. Experimental datasets are used to validate the model, and it is shown that the model can effectively describe the 3-D structures of the rip currents in both normal and oblique wave incident cases. The flow patterns of the rip currents see various characteristics for different incident wave directions. In the normal incident case, pairs of counter-rotating primary circulation cells are formed, and an offshore rip flow occurs in the embayment troughs. The peak seaward velocities occur at the top of the bed boundary layer, and the undertow is incorporated in addition to the rip currents. In the oblique incident case, the longshore currents are dominant, which result in a meandering flow along the depth contour, and the undertow is weaker compared to that in the normal incident condition.