Bore-induced macrovortices over a planar beach: the cross-sea condition case

Wave breaking over submerged topographic obstacles leads to vorticity generation and, at times, to the generation of strong offshore-directed rip currents. The generation of finite-length breakers may also be induced by the positive interaction of wave trains propagating to shore with a relative angle. Such an interaction gives rise to a short-crested system, this, in turn, generating both breakers of finite crossflow length and an intense associated vorticity. We here analyze such a vorticity generation mechanism specifically focusing on the location where wave breaking occurs. To this purpose we both derive a simple theory, based on the well-known theory of wave ray propagation, and perform ad-hoc numerical simulations, using a NSWE (Nonlinear Shallow Water Equations) solver. A fairly good comparison between such preliminary theoretical and numerical results suggests that the present work be used as the basis for future analyses of vorticity generation by cross-seas.