Experimental interpretation of the seaward boundary condition parameter in dam-break induced swash models

Physical interpretation of the seaward boundary condition (SBC) parameter $k$ proposed by Guard and Baldock (2007) in dam-break induced swash models is still unclear in experiments. In this study, a series of dam-break laboratory experiments were conducted to reveal such interpretation of the parameter $k$. Different nondimensional upstream reservoir lengths $L$ were applied to examine the relationship between parameters $L$ and $k$ with respect to the temporal variation characteristics of the local water depth. It is found that time-varying histories of the nondimensional water depth are almost identical among different cases when $L$ is the same (irrelevant to the initial water heads). Meanwhile, parameters $L$ and $k$ play analogous roles in determining the local swash features. Based on the maximum water depth, the rise time of the water depth, and its time ratio at a specified position, the one-on-one and averaged $L$-$k$ relationships were established. The $L$-$k$ relationship was then validated at other slope positions, confirming its applicability across the swash extension. In addition, the one-on-one $L$-$k$ relationship presents better agreement between model and experiment than the averaged $L$-$k$ relationship. These findings help to clarify the physical interpretation of the SBC parameter with the actual swash hydrodynamic conditions.