Numerical Model on Filtration Flows across a Beach Face and Sediment Transports in the Swash Zone

摘要

The importance of sediment transport in the swash zone has been widely recognized, however, the present understanding is not satisfactory. The main reason for this comes from the complexity of the sediment transport mechanism. One of the important and unsolved factors is the in-/ex-filtration effect on the hydrodynamics and the sediment transport. In this study, a numerical model is proposed by coupling an analysis on ground water flows in a sandy ground with an analysis on swash wave motion over a uniform slope by inserting an imaginary thin layer of high conductivity at the interface. The hydrodynamic properties of in-/ex-filtration flows across the beach face have been discussed. Next, using the obtained velocity fields over the permeable beach slope, the sediment transport mechanism has been investigated. For the stabilizing/destabilizing effects that the filtration flows act on the sediment transport, two opposing processes, modification of the effective weight of the sediment particle and to modification of the boundary layer thickness have been considered. These effects of the filtration flows on the sediment transport rate have been quantified based on a bed load transport model with a modified Shields parameter.