On the applicability of empirical formulas for natural salients to Sardinia (Italy) beaches

The paper presents an empirical analysis of the shoreline response to natural obstacles, either submerged reefs and islands, distributed along the Sardinian (Italy) coastlines exposed to different wave and wind climates. The study focuses on salient morphological features whose geometrical properties have been acquired through an extensive field and image-derived survey. The current analysis has been used to propose geometric predictive formulas for stable salients that overcome some limitations affecting previous works. A semi-probabilistic method based on well-known rate-of-change statistics is also presented to verify the equilibrium condition of salients. Analysis results suggest that site-specific wave transmission in the lee of submerged reefs requires a range of salient limiting B/S ratio values broader than those presented in the literature, B being the length of the obstacle and S the distance between undisturbed beach and obstacle. The B/S ratio has been proved to be the main dimensionless variable for predicting salient amplitude and basal width. In particular, the proposed predictive equation suggests an erosion condition for some combinations of B/Sand the “8 times rule” appears not to be applicable to natural salients.