On the influence of the improved seaward boundary condition on the shock wave induced frictional swash process

Following Antuono (2010), a frictional shock wave model with an improved seaward boundary condition (ISBC) was developed to simulate the bore-driven swash hydrodynamics in this study. It is found that bottom friction has a negligible effect when the shock wave propagates towards the original shoreline, whereas it plays important roles in the area near the swash tip and during the backwash. The ISBC increases the swash water depth and the onshore flow velocity, whereas it decreases the flow velocity during the backwash stage, thus the bottom friction effect. A comparison between the present shock wave model and the dam-break model was conducted, which indicates that these two models present similar swash hydrodynamics if the traditional seaward boundary condition is applied, whereas modifications of the water depth and flow velocity under different ISBCs are less significant for the present shock wave model compared to the dam-break model. Swash excursion increases with the ISBC in the shock wave model, which however keeps uniform in the dam-break model. Subsequently, model validation was conducted with respect to the experimental data of Kikkert et al. (2012). Comparing with the dam-break model result, swash hydrodynamics (water depth and flow velocity) in the uprush and early backwash stages could be better reproduced by the present shock wave model.