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In this work, we conduct controlled experiments in a wave flume to represent different wave-wave interactions occurring in the swash zone. Using solitary waves as the forcing condition, we combined different wave amplitudes with separation times between the wave events. Experimental results show that interactions developing in the swash zone present three main stages: A jet slamming, an induced splash, and a region where the flow becomes fully 3D turbulent. We identified that the location where the interactions occur and the type of interaction depends on two main factors, the relationship between the wave amplitudes and the separation time between these wave events. Additionally, we were able to mimic the wave-wave interactions observed in real-case scenarios. Our goal is to relate these findings to the sediment transport processes in the swash zone, where interactions could develop a potential impact on the sediment transport mechanism and possible morphological changes. 

In fluid dynamics applications that involve flow adjacent to a porous medium, there exists some ambiguity in how to model the interface. Despite different developments, there is no agreed upon boundary condition that should be applied at the interface. We present a new analytical solution for laminar boundary layers over permeable beds driven by oscillatory free stream motion where flow in the permeable region follows Darcy's law. We study the fluid boundary layer for two different boundary conditions at the interface between the fluid and a permeable bed that was first introduced in the context of steady flows: a mixed boundary condition proposed by Beavers and Joseph [“Boundary conditions at a naturally permeable bed,” J. Fluid Mech. 30, 197–207 (1967)] and the velocity continuity condition proposed by Le Bars and Worster [“Interfacial conditions between a pure fluid and a porous medium: Implications for binary alloy solidification,” J. Fluid Mech. 550, 149–173 (2006)]. Our analytical solution based on the velocity continuity condition agrees very well with numerical results using the mixed boundary condition, suggesting that the simpler velocity boundary condition is able to accurately capture the flow physics near the interface. Furthermore, we compare our solution against experimental data in an oscillatory boundary layer generated by water waves propagating over a permeable bed and find good agreement. Our results show the existence of a transition zone below the interface, where the boundary layer flow still dominates. The depth of this transition zone scales with the grain diameter of the porous medium and is proportional to an empirical parameter that we fit to the available data.