Characteristics and dynamics of crescentic bar events at Castelldefels beach

Abstract

Crescentic sand bars have been studied intensively in the last decades, resulting in good knowledge of some of their characteristics, but the processes behind their formation and destruction are not yet clear. This study aims to increase our understanding of the dynamics of crescentic bars at an open, dissipative Mediterranean beach (Castelldefels, 20 km southwest of Barcelona). Their dynamics have been analysed using a 4.25-year dataset of video images. The crescentic bar events have been identified using visual analysis, including the formation and destruction moments. The results show that crescentic bars hardly occurred when the sandbar was located close to the beach, whilst they developed often when the sandbar was further offshore. Wave conditions during crescentic bar formation were low- to intermediate-energy waves with both oblique and shore-normal angles of incidence. Sandbar straightening was preferably observed for oblique waves (of both intermediate and high energy). The alongshore wavelength and cross- shore amplitude of the crescentic bars have been also quantified, giving some 245 m and 10 m on average, respectively.