Morphodynamic model for low-energy exposed beaches. Application to Vistahermosa Beach (Cádiz Bay)

Abstract

Four years of a monthly monitoring was carried out in a South Atlantic spanish beach, in a low-energy environment where beaches change slowly, following a typical seasonal behaviour. In this word a two-dimensional study of beach morphological variations has been made, related to the incident wave fluctuant conditions. After applying classical morphodynamic parameters to the field data, poor or null representative results were obtained. It was then necessary to design another energetic characterisation of the incident wave energy. A new index, named wave erosivity factor, was introduced in this sense. The resulting ratio between beach gradient and wave erosivity expresses the equilibrium state of the beach for any given energy level. The departure from the equilibrium curve is largest in the intermediate situations, while at the extremes the points are better adjusted to asymptotic tendencies towards equilibrium: on reflective states, small increases in the wave erosivity will produce important beach changes; on dissipative beaches, important increases in the wave erosivity will not produce significant morphological modifications.