FREQUENCY DOWN-SHIFT OF SWASH OSCILLATIONS COMPARED TO INCIDENT WAVES

The frequency down-shift of swash oscillations compared to incident waves is examined by laboratory experiments and numerical simulations in connection with the uprush-backwash interaction in the swash zone and the standing wave in the surf zone. The experimental and numerical results show that the interaction between uprush and backwash actually generates swash oscillations with the frequency lower than that of incident waves when the power of short waves or bores near the shoreline is large. When the power of the bores is weak, a group-induced standing wave is dominant in the swash oscillations.