On the relation between the direction of the wave energy flux and the orientation of equilibrium beaches

The Equilibrium beach planform concept has been widely used in recent years as an engineering tool for modeling shoreline changes, designing new beaches and for stability studies of existing ones. It defines the final shape of a beach on a scale of years, which is important for solving erosion problems and for the design of nourishment projects. Throughout the literature, the planform final shape, hereinafter denoted as the Static Equilibrium Beach Orientation (SEBO), is obtained based on the direction of the mean wave energy flux of whole waves impinging on the coast. This paper investigates the effect of beach sediment size and the Shape of the Directional Distribution (SDD) of the energy flux of the wave climate on the direction that dictates the (SEBO). The study employs field data from 32 beaches along the Spanish coast and available long-term databases of directional wave climates. Initiation of sediment motion due to wave action is taken into account in order to filter the directional wave climate to consider only waves that are capable of moving the sediment. The results indicate that the direction of the mean energy flux of filtered waves is more appropriate for the determination of the (SEBO) than that of whole waves. Additionally, the results confirm the importance of both the filtration process of the local directional wave climate and the usage of the whole directional spectra in stability studies and coastal engineering practice.