Experimental study of bore-driven swash–swash interactions on an impermeable rough slope

•Hydrodynamics of bore-driven swash–swash interactions on an impermeable rough slope•Investigates wave–capture interaction and weak wave–backwash interaction•Large-scale laboratory experiments measuring simultaneous depths and velocities•Yields measures of time-varying velocities and turbulence during interactions

Experimental measurements are obtained to investigate the detailed hydrodynamics of wave–wave interactions in the swash-zone. Two bores are generated using a double dam-break mechanism and interact on a 1:10 impermeable rough slope. Measurements of the hydrodynamics are obtained via acoustic displacement sensors and a combined particle image velocimetry and laser induced fluorescent system. Two types of interactions are investigated: wave capture, with the second bore reaching the first one during the uprush, and weak wave–backwash interactions when interaction happens during the backwash of the first wave. The relative strength of the bores at the initial shoreline and time between their arrivals determines the initial type of interaction, however the type as well as the intensity of the interaction may vary throughout the swash-zone for the same swash event. During wave capture and weak wave–backwash interactions, the fluid of the first bore is advected upwards, then mixed with the fluid of the second bore by intense shearing and highly turbulent vortices generated at the front of the second bore because of the relative velocity differences between the two bores. The details of the hydrodynamics during interaction confirm the potential of swash–swash interactions to suspend sediment and transport it shoreward or interrupt seaward sediment transport.