Calibration and Assessment of Bed Evolution Model in an Embayed Beach with Submerged Breakwaters

An embayed beach is a common beach around the world and relatively stable over longer timescale except for high-energy wave event. A submerged breakwater is a structure that is effective in reducing coastal erosion by dissipating wave energy. Typhoon Lingling, which occurred in September 2019, affected the shoreline change in Korea. XBeach, process-based model, has been used to simulate nearshore hydrodynamics and morphological response to storm condition. XBeach has a variety of parameters, and provides default settings. However, parameter calibration is a process that must be performed to apply to a specific site. Parameter calibration has been carried out depending on the researchers' experience or through traditional trial-and-error, but more rigorous and systematic methods are required. In this study, parameter calibration in XBeach is performed for an embayed beach with submerged breakwaters under storm conditions. Seven hundred (700) parameter groups were generated using Monte-Carlo sampling and 700 simulations were performed for calibration and assessment using the Root Mean Square Error (RMSE) statistical method. The retreat distance of 20 cross-shore section extracted from the surveyed shoreline, and RMSE was calculated through comparison with the simulation results. As a result, there are difference between the default setting and the optimal setting, and the accuracy in the optimal setting was improved by about 30% compared to the default setting.