An experimental study of the interaction of two successive solitary waves in the swash: A strongly interacting case and a weakly interacting case

The interaction of successive solitary waves in the swash zone have been studied using large-scale experiments with a simple bathymetry of a constant depth region, where the water depth was 1.72 m, and a plane beach, whose slope was 1:12. Two wave cases were considered where two successive solitary waves of the same height were generated one after the other so that the wave crests were separated by the effective wavelength associated with a single solitary wave. In the weakly interacting case, the swash period associated with a single solitary wave is smaller than the time period separating the successive wave crests, which leads to similar run-ups for the first and second wave, whereas in the strongly interacting case, the swash period associated with a single solitary wave is larger than the time period separating the successive wave crests, which leads to a significant reduction in the run-up of the second wave. The degree to which there is an interaction between the swash uprush of the second wave and the downrush of the first wave is found to be related to the solitary wave slope parameter, which predicts breaker type of the first wave. Previous data from literature are found to support this claim. Measurements of bed shear stress, bed pressure, and the free-surface displacement at a location near the stillwater shoreline are used to describe how the dynamics of the boundary layer differ when the downrush of the first wave meets the incoming second wave in both cases.