On The Role of Swash-Swash Interaction in Swash Zone Dynamics

The swash zone is the nearshore region characterized by shallow and transient flows where boundary layer dynamics are controlled by surface-injected and near-bed turbulence. Recent laboratory and numerical studies have increased our understanding on the dynamics in this region for the case of a single (dam-break driven) swash event. However, under natural conditions the interaction between inundating and receding wave driven flows contribute to the local and convective budget of hydrodynamic quantities. Thus, the study of swash-swash interactions is needed to improve our understanding on boundary layer and sediment transport mechanisms occurring in this region. The present study employs a validated 2D numerical model, solving the Reynolds-Averaged Navier-Stokes equations with a VOF-tracking scheme and a κ-ε turbulence closure, to investigate different scenarios of swash-swash interaction. Two moving gates are implemented in the model (see Figure 1a). The timing between the release of fluid from each reservoir can be adjusted to alter swash interaction type. Numerical experiments are conducted to investigate the mean and turbulence properties of the flow for three distinct conditions: i) swash overtake, ii) weak backwash - bore, and iii) strong backwash - bore interaction (as shown for turbulence kinetic energy κ in Figure 1b-d, correspondingly). The comparative analysis focuses on the mean vorticity field, turbulence budget, and bed shear stress in a normalized temporal-spatial framework. Differences with respect to previous work conducted for a single swash event suggests the importance of swash-swash interaction in sediment transport. This work was funded by the Instituto de Ingenieria UNAM, through the International Collaborative Research project with the University of Delaware, and the DGAPA UNAM (PAPIIT IN107315).