Differential short- and medium-term behavior of two sections of an urban beach

The present study aims to identify factors that control the different morphological evolution of two sections of an urban beach. The study area is the Victoria Beach in Cadiz city (SW Spain). The beach comprises two sectors: Cortadura zone (CZ) and Victoria zone (VZ), both subject to the same offshore wave conditions. The area is a typical low energy coast with dissipative beach morphology, where storm conditions are generally recorded in the winter season. Variability of beach profiles was analyzed through the use of empirical orthogonal functions (EOF). For short-scale processes, nearshore wave and current measurements were collected simultaneously at both zones during a tidal cycle. Additionally, medium term beach evolution from the last 50 years was evaluated using aerial photos. Results of medium term beach changes show a clear retreat that in fact led to several artificial nourishments of the beach over the last years. Erosion observed in CZ was greater than in VZ. In the short term, VZ presented greater morphological variability than CZ, which only experienced some changes in beach volume. Wave and current measurements showed a higher wave height and longshore current velocity in CZ under the same offshore wave conditions, which might account for the higher erosive trend in this area and development of a more dissipative profile. The reason for this differential behavior is related to the different characteristics of wave propagation in the outer surf and shoaling zone of both sections.