On the development of large-scale cuspate features on a semi-re£ective beach: Carchuna beach, Southern Spain

Carchuna beach, located on the southeast coast of Spain, has a series of natural permanent horns of timedependent horizontal dimensions, which do not appear to be periodically spaced, and do not propagate alongshore. Until at present, it has been assumed that the permanency of these forms is related to the existence of bed rocks; nevertheless, analysis of the configuration of the depth contours and the bed sediment composition does not justify this hypothesis. This paper explores the formation of cuspate features by the effects of the wind wave dynamics and their development by nearshore circulation and infragravity waves, including edge waves. Three levels of wave energy flux conditions are considered. In all likelihood, wave refraction of severe storms on submerged fluvial valleys is the main cause for longshore variation of breaking wave height, which seems to be one of the initial conditions necessary for the cuspate to initiate. Moderate storms enhance the deepening of the embayments, whereas mild sea states are able to maintain the features by self-organization. The possibility of the occurrence of edge waves due to the nonlinear interaction between the components of a gravity wave spectrum approaching the shore under moderate storm conditions is explored. Preliminary analysis of video images taken by an Argus station seems to confirm this