In the present study, the impact of the storm event on the bed morphology of a typical Belgian coastal profile, is numerically simulated. The simulations are performed using the open-source model XBeach, which is capable of representing hydrodynamic and morphodynamic processes in coastal areas. The objective is to evaluate the performance of XBeach through a sensitivity analysis, in which various model parameter (numerical and physical) settings, are considered. It was found that the model's predictions are, in general, reasonable, while extensive grid resolution analysis led to suggestions for the optimal use of non-equidistant grids in the cross-shore direction.
The protection of coastal areas from eroding processes is an issue of high importance that has motivated many scientists and researchers to investigate in depth related processes, such as wave propagation, sediment transport and bed morphology evolution. Over the past few decades, tools for addressing the combined action of the aforementioned phenomena have been developed (e.g. Vellinga, 1986; Steetzel,1993; Larson et al., 2004). XBeach (Roelvink et al., 2009) is an open-source, process-based model, which was developed to represent hydrodynamic and morphodynamic processes and impacts on coastal areas. As for the hydrodynamics, XBeach includes the processes of short wave transformation (shoaling, refraction and breaking) and long wave transformation, while bed load and suspended sediment transport and avalanching are the main processes supported by the morphodynamic module of XBeach.
Two modes of XBeach are available, i.e. the hydrostatic and the nonhydrostatic mode. The hydrostatic mode is based on the solution of the time-dependent (instationary) version of wave-action balance equation for the calculation of short-wave forcing, which is introduced in the non-linear shallow water equations for the (low-frequency) flow calculation (Roelvink et al., 2009). In the non-hydrostatic mode, the calculation of short and long wave transformation is achieved by the non-linear shallow water equations, which include a dynamic pressure correction term following the procedure introduced by Zijlema et al. (2011). One of the main advantages of XBeach is the capability to account for the generation of long waves in the surf zone and therefore reproduce their impact on the bed morphology evolution close to the shoreline. As mentioned in Van Dongeren et al. (2003), these lowfrequency motions were confirmed to contain a significant portion of the total energy in the wave field, especially in shallower water, and has been hypothesized that they have important effect on the nearshore morphology.
