Influence of storms on coastal retreat in SW Spain

Natural and anthropogenic controls contribute to coastal change at diverse temporal and spatial scales. This study presents an analysis of storminess and a correlation with the medium-term shoreline erosion rates in two sand spits of the Gulf of Cadiz (SW Spain). Recession rates were assessed by means of aerial photographs and orthophotographs considering the dune foot as an appropriate proxy. Storm events were obtained from a combination of coastal wave buoy data and the hindcast database of the HIPOCAS project. The characteristics of the storms were compared with shoreline changes determined using the aerial photographs, and the correlation between them was estimated and discussed. The best agreement between storms and shoreline change was observed in section 1 of Sancti Petri sand spit, while Valdelagrana sand spit showed a lower dependence between shoreline erosion and storminess. This is related to the contrasting exposure of both sites, with Sancti Petri being more exposed and thus more sensitive to storm impact. It is suggested that the main causes of retreat in Valdelagrana are human interventions performed on the coast and in the nearby rivers (breakwaters, jetties and dams). Nevertheless, storminess contributes to modulate recession rate, so that erosion rates increase when the number of storms is higher.