Surface Roller Modeling for Mean Longshore Current over a Barred Beach in a Random Wave Environment

The effect of surface roller on mean longshore current, which depends strongly on the wave-breaking process, was investigated by applying various surface-roller models to a random wave-induced current-model system, incorporating a nearshore circulation model, SHORECIRC, and a random wave model, SWAN. The investigation was performed based on simulations of the SandyDuck field experiments, employing observed wave spectra and two-dimensional topography. The topography is characterized as a longshore variation caused by scouring because of bridge piers and a barred beach on a steep foreshore slope linked to a relatively broad bar formation on a seaward gentle slope. The experimental data show that before the waves intensely broke from a decrease in water depth on the steep slope, some partial breaking of random waves occurred in the wave-breaking process. The chosen surface-roller model was modified using the classification of the partial wave-breaking and intense wave-breaking regions. The mean longshore currents simulated using the modified surface-roller model was compared with the measurements as well as the results from the simulations using conventional surface-roller models. The modified simulations agreed with the measurements better than did those of the simulations.