Postnourishment Evolution of Beach Profiles in a Low-Energy Sandy Beach with a Submerged Berm

摘要

Submerged berms are an increasingly used coastal defense structure for beach nourishment because of their eco-friendly nature. A beach-nourishment project that included sand placement on the beach and in the nearshore area as a submerged berm was carried out in the winter of 2010 on West Beach in Qinhuangdao, China. West Beach is a low-energy beach characterized by small wave heights, a small tidal range, and low tidal-flow velocities. An analysis of the postnourishment beach profile evolution was conducted based on beach profile surveys from 2011 to 2014. The analysis showed that the most active parts of the profiles were the berm and the submerged berm, whereas the remaining parts of the profiles remained relatively stable. The cross-shore profiles of the submerged berm evolved significantly from roughly symmetrical shapes to asymmetrical shapes, which can be explained by applying the concept of equilibrium wave-energy dissipation per unit of water to a low-energy beach with a submerged berm. Empirical orthogonal function analysis was conducted on the beach profile surveys, which confirmed the features of the background-berms pattern gained from the evolution analysis. The first three eigenfunctions corresponded to the mean beach profile, the volume changes of the berm and the submerged berm, and the change in the submerged berm from roughly symmetrical to asymmetrical in shape, respectively. Finally, a new equilibrium beach profile (EBP) form was developed to represent low-energy sandy beaches with submerged berms. The findings in this paper contribute to the understanding of cross-shore beach morphodynamics and can provide a reference for beach nourishment under similar conditions.