Laboratory validation of SWASH longshore current modelling

Abstract

In this paper, the ability of the numerical phase resolving model SWASH (Simulating WAves till SHore) to hindcast wave-induced longshore currents is evaluated. Using default settings for all processes modelled, highly accurate results are found for wave heights, mean water levels and longshore currents. While wave current interaction is intrinsically modelled, insights into the spatial variation of wave driven longshore currents are found. Additionally, vertical variations of modelled longshore currents have been compared. Depth uniform profiles of longshore current within surf zone are noted on plane beaches under regular waves, except for minor deviations near the shoreline. The apparent validity of a depth-uniform longshore current encourages the use of a depth-averaged moment balance equation to compute the longshore current. A simpler model is shown to also be able to predict a proper magnitude of longshore current, although the cross-shore distribution – in contrast with SWASH - needs tuning for the eddy viscosity and the bottom friction coefficient, since the distribution of the wave-induced longshore current heavily depends on lateral mixing.