Laboratory experiment and three-dimensional large eddy simulation of wave overtopping on gentle slope seawalls

Wave overtopping on gentle slope seawalls for both smooth and stepped front faces was investigated in a laboratory wave flume. Overtopping rates were measured by a catchment basin placed behind the seawall. Overtopping velocity and water depth at the top of the seawall were simultaneously measured by using a Laser Doppler Velocimeter and a wave gage. It was found that the velocity of overtopping water has a sharp peak just after initiation of each overtopping event. The water depth on the seawall crown shows relatively gradual decrease. A numerical model of three-dimensional Large Eddy Simulation was developed for evaluating the instantaneous overtopping discharge and compared to the experimental results. The calculated root-mean-square value of water surface elevation at the toe of the seawall agreed very well with the measured value, but large discrepancies were found for individual wave deformation in some waves. The magnitude of the calculated velocity on the top of seawall was generally smaller than that of the measured velocity. The calculated volume of the overtopping water was between the volumes measured for the smooth seawall and the stepped seawall. Since the two-dimensional Large Eddy Simulation model far overestimated the overtopping volume, it was considered that appropriate representation of three-dimensional large eddies generated by wave breaking is important for wave overtopping evaluation.