An experimental and numerical study of bimodal velocity profile of longshore currents over mild-slope barred beaches

• Investigate the laboratory experiments for mild slope and measure quantitatively second peak.
• Discuss the feasibility of the passive circulation system and alongshore uniformity of different period.
• The dependence of bimodal feature on wave height, wave period and beach slope on the longshore currents are discussed.
• Simulate measurement results and discuss the effects of parameters for mild slope.

A detailed description is given of the results of laboratory experiments on bimodal velocity profile of longshore currents over two mild-slope barred beaches. The objective is to examine the bimodal longshore current velocity profile for purely wave-driven currents, with emphasis on the second peak and ratio of two peaks. The research focus is on the locations, values and ratios of two velocity peaks for the cases of mild slope beaches. The dependence of its bimodal feature on wave height, wave period and beach slope on the longshore currents are discussed. The 2-D model based on vertically integrated equations (external mode) of Nearshore POM was performed to compute the measured velocity profile. The depth-varying wave-induced residual momentum, the surface rollers, and the lateral mixing the bottom friction are considered, and the effects of lateral mixing, surface rollers and bottom friction on numerical model are discussed.