Investigation and Discussion on the Beach Morphodynamic Response Under Storm Events Based on A Three-Dimensional Numerical Model

A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach, and a series of discussions were made on the surfzone hydro-sedimentological processes under calm and storm events. Model results revealed that the nearshore wave-induced current presents a significant 3D structure under stormy waves, where the undertow and longshore currents exist simultaneously, forming a spirallike circulation system in the surfzone. Continuous longshore sediment transport would shorten the sediment supply in the cross-shore direction, subsequently suppress the formation of sandbars, showing that a typical recovery profile under calm waves does not necessarily develop, but with a competing process of onshore drift, undertow and longshore currents. Sediment transport rate during storms reaches several hundreds of times as those under calm waves, and two storm events contribute approximately 60% to the beach erosion. Sediment transport pattern under calm waves is mainly bed load, but as the fine sands underneath begin to expose, the contribution of suspended load becomes significant.