Numerical modeling of wave overwash on low-crested sand barriers

For management of coastal breaching hazards it is critical to be able to assess the potential of coastal barrier breaching as a result of wave actions during storm surges (wave overwash). This phenomenon is known as the breach initiation phase; the mechanisms behind this are not very well understood. In the present study, laboratory experiments of mobile-bed (sand) barrier were carried out to increase the understanding of the processes of the barrier response during storm surges and also to generate data for calibrating a new numerical overwash model. A numerical model of the barrier response, which integrates the processes of beach and dune erosion and of wave overwash, has been developed. The approach of the UNIBEST-TC model (Bosboom et al., 2000) was adopted for modelling the processes of beach and dune erosion. For modeling wave overwash new overtopping parameters are introduced, based on the approach of Tuan et al. (2006). The model is capable of simulating the time-dependent barrier response during storm surges with occurrence of moderate to severe overwash. Overwash-induced effects on the cross-shore transport processes are also effectively incorporated. The model has been calibrated with the laboratory data on the barrier response (the barrier profile response and the overwash channel development). The process of the barrier response together with its major morphological features was fairly well predicted