Coastal storm characterization and morphological impacts on sandy coasts

Abstract

The present work deals with storm classification, using the Storm Power Index, and beach morphological response to storm events in the Gulf of Cadiz (SW Spain). Over the 1958–2001 period, 377 events divided into five classes ranging from ‘weak’ to ‘extreme’ were characterized. Classes I (weak) and II (moderate) accounted for 60% and 23% of events, respectively. Class III (significant), were 9% of the recorded events and Classes IV (severe) and V (extreme) accounted for 5% and 2%, respectively. The probability of storm occurrence per year ranged from 93% for Class I to 15% for Class V. In order to characterize beach response to storm events, 214 beach profiles carried out with a monthly periodicity over the 1996–1998 period along the Chipiona-Rota littoral were analysed, as well as published data. Different beach types were observed: (i) ‘Intermediate’ beaches underwent important vertical relief changes ranging from 0.3m to 1.33m associated with average slope changes from tan b = 0.06 to tan b = 0.03; (ii) the ‘dissipative’ beaches were characterized by smaller and homogeneous foreshore vertical changes, from c. 0.36m to 0.65 m, according to the parallel retreat mechanism characterized by small slope variations (from tan b = 0.025 to tan b = 0.035); and (iii) ‘intermediate with rock shore platform’ experienced small morphological and foreshore slope variations, related to both beach pivoting and parallel retreat mechanisms. The most important morphological changes were due to the impact of usually ‘weak’ and ‘moderate’ events during October and November that produced berm erosion and upper foreshore lowering, and the impact of ‘severe’, ‘significant’ and ‘extreme’ events in December and January which produced dune escarpment, overwash and/or damage to coastal structures.