Hydro- and morpho-dynamic modeling of breaking solitary waves over a fine sand beach. Part I: Experimental study

Abstract The objectives of this work are (1) to examine the mechanisms that influence tsunami erosion and deposition mechanisms in the littoral zone via physical simulations of breaking solitary waves over a fine sand beach, and (2) to provide experimental data for validation of numerical models to predict tsunami erosion and deposition processes. The experiments were carried out in a 48.8 m × 2.16 m × 2.1 m wave flume. The flume was instrumented to observe free surface elevations, cross-shore velocities, suspended sediment concentrations, vertical and cross-shore pore-pressure gradients near the shoreline, and morphological changes. In addition, wave–sediment interactions were observed via underwater video cameras. The results are systematically analyzed to investigate the roles of wave breaking, bore runup, wave drawdown, and wave-induced pore-pressure variations on tsunami erosion and deposition processes. The studies showed that the wave plunging on a thin layer of water prior to reaching the shoreline did not cause much sediment suspension, while the waterjet impinging directly on the beach entrained substantial amounts of sand. The suspended sediments were subsequently pushed up the slope by fluid momentum as the broken wave transformed to a turbulent bore. A small net deposition region was observed near the maximum runup point where both the flow velocity and the water depth were near zero. A significant amount of the sediment transport occurred during the wave drawdown in the form of thick sheet flow, which resulted in net erosion of the shore face and the beach. A hydraulic jump formed near the wave breaking region toward the end of the drawdown, which caused most of the suspended sand to deposit in the wave breaking region. Consequently, breaking solitary waves over a sloping fine sand beach led to net erosion of the shore face and the beach, net deposition in a small region immediately seaward of the max excursion point, and net deposition in the wave breaking zone.