Quasi-three-dimensional modelling of the morphology of longshore bars

A morphological quasi-three-dimensional (Q3D) area model for bar-red coasts has been developed. The model combines a two-dimensional depth integrated model for wave-driven currents with a model for under-tow circulation currents. The combined model makes a simultaneous simulation of the bar-forming processes associated with the undertow and the horizontal wave-driven circulation currents, which may cause instabilities of the bar and the formation of rip channels. Situations with normal and oblique wave incidence are considered. Compared to the depth integrated approach the Q3D model produces less pronounced alongshore irregularities for obliquely incident waves. For normal incident waves the Q3D model produces a crescentic bar while the depth integrated model predicts almost straight sections of the bar interrupted by rip channels. The sensitivity to variation of wave angle and beach slope is further investigated.