2003), Effects of wave-current interaction on shear instabilities of longshore currents

[1] We examine the effects of wave-current interaction on the dynamics of instabilities of the surf zone longshore current. We utilize coupled models for the simulation of the incident waves and the wave-induced nearshore circulation. The coupling between the models occurs through radiation stress gradient terms (accounting for the generation of nearshore circulation) and through wave-current interaction terms (leading to the modification of the wave field by the generated circulation field). Simulations are carried out with a realistic barred beach configuration and obliquely incident waves for two frictional regimes. The results show that the shear instabilities of the longshore current have a significantly altered finite amplitude behavior when wave-current interaction effects are included for beaches with relatively high frictional damping. The primary effects are a reduction of the offshore extent of the motions and a delay of the onset of instabilities. In addition, the energy content of the motions within two surf zone widths is reduced, the propagation speed increases, and tendency to form offshore directed jets is reduced. The horizontal mixing induced by the instabilities is also reduced when wave-current interaction is considered, leading to a larger peak mean longshore current and