Boussinesq Modeling of Alongshore Swash Zone Currents

The report documents the theoretical and numerical investigations on wave propagation over porous beds as well as on alongshore surf and swash currents. The study has been carried out in the framework of wave-resolving Boussinesq-type models. First, we have derived a new set of Boussinesq-type equations for nonlinear waves and surf-zone currents over a permeable beach (Chen 2006). A Stokes-type analysis and rational expansions were carried out to examine the fundamental damping and dispersion properties of the new set of equations (Cruz and Chen 2006a). The vortical properties of the new and pre-existing Boussinesq equations have been carefully investigated (Gobbi et al 2006). Second, numerical implementation of porous effects into a one-dimensional Boussinesq wave model has been completed. Preliminary results were documented in Cruz and Chen (2004). We have tested the numerical model against laboratory experiments on wave transformation over heterogeneous porous beds and submerged rubble mounds. The results have been published in Cruz and Chen (2006b). Third, efforts have been devoted to the extension and testing of the Boussinesq wave model, FUNWAVE 2D, with respect to surf zone currents and swash motions. We have examined three different schemes for the treatment of a moving shoreline with an emphasis on the swash velocity. Tests of the improved FUNWAVE model against analytical, laboratory and field data of swash and surf zone currents have been carried out (Chen and Briganti 2006). Fourth, Lagrangian descriptions of the fluid motion have been employed to study the mixing of surf zone currents, which serves as an alternative to Eulerian analyses of the flow field (Briganti et al. 2006). The enhanced numerical model, tested under the SandyDuck field conditions, has produced fairly good results. Insight into the capability of predicting the alongshore drift velocity of the water mass in the swash zone was gained.