MODELING OVERWASH VULNERABILITY ALONG MIXED SAND-GRAVEL COASTS WITH XBEACH-G CASE STUDY OF PLAYA GRANADA, SOUTHERN SPAIN

Abstract

This work aims to calibrate the XBeach-G model on a mixed sand-gravel deltaic coast (Playa Granada, southern Spain) and apply it to address the overwash vulnerability. Field surveys, consisting of topographical measurements and sediment sampling in two selected areas, were performed before and after two extreme southwesterly storms. A calibrated wave propagation model (Delft3D-WAVE) was used to obtain the inshore conditions required to drive the XBeach-G model. The XBeach-G results for the coarse gravel fraction, a sediment friction factor of 0.03 and a Nielsen's boundary layer phase lag of 20º were found to provide the best fits to the observed morphological changes of the beach profile. This indicates that the morphodynamic response of the beach is dominated by the coarse gravel fraction, which is in agreement with previous experimental and numerical works carried out in the study site. The obtained brier skill scores and root-mean-square errors were higher than 0.89 and lower than 0.18 m, respectively, highlighting that the XBeach-G model is capable of reproducing the profile response under southwesterly storm conditions. The model was used to compute the required water level to generate overwash as a function of the wave height and direction, and results show how the application of XBeach-G can be used to address issues of storm-induced coastal vulnerability on gravel-dominated coasts.