Effect of submerged breakwaters construction on XBeach modeling - a case study: Bongpo beach

This study investigates the key parameters of the XBeach model to predict morphological changes at beaches with submerged breakwaters. Since the default setting of its parameters tends to overestimate coastal erosion, the optimal parameter combination has been empirically found using a trial-and-error method. For beaches with submerged breakwaters, studies on the applicability of this model are insufficient owing to an increase in the nonlinearity of breaking and incident waves. To overcome these shortcomings, this study analyzed the combination of the most suitable parameters for XBeach simulation at beaches with submerged breakwaters using the generalized likelihood uncertainty estimation. The optimal values of three parameters ( facua, gamma , and bedfriccoef ) that have the greatest influence on XBeach modeling were analyzed, as well as the sensitivity and distribution tendency of each parameter. The optimal combination of the parameters of the XBeach in the presence of submerged breakwaters was found using waves and morphology data observed at Bongpo Beach in Korea. Regardless of the presence or absence of the submerged breakwaters, facua showed the highest sensitivity, followed by gamma and bedfriccoef . Also, the probability distribution of facua was greater than 80 % in the range of 0.3–0.5 in the presence of the submerged breakwaters and the range of 0.2–0.4 in their absence, indicating that the default setting of facua =0.1 is not suitable for predicting coastal erosion. Likewise, for gamma , the probability distribution was greater than 80 % in the range of 0.4–0.7 in the presence of the submerged breakwaters and in the range of 0.6–0.9 in their absence. For more than 80 % probability distribution, the range of facua increased by approximately 25 % and that of gamma decreased by approximately 30 % in the presence of submerged breakwaters compared to the case without the submerged breakwater. This is likely because the construction of submerged breakwaters increased the spatial variability of wave nonlinearity and wave breaking characteristics.