Beach cusp dynamics on a reflective beach

Beach cusps are common feature of steep reflective and intermediate beaches. However very few observations reported double coupled cusp systems. Here we present a data set of observations of a beach exhibiting two sets of beach cusps. Data were collected at Grand Popo Beach (Benin, West Africa) in February 2013. Daily topographic survey along a 380m long stretch of shore allowed observing the dynamic of the two set of beach cusps. At the beginning of the field survey, we clearly observe two sets of cusps : the upper beach cusps system is relatively asymetric with a typical wavelength of about 45 m while the lower beach cusps system is relatively symmetric with a typical wave length slightly shorter (about 35 m). After two days, we measured the total destruction of the lower set of beach cusps while the upper set of beach cusps was only partially des tructed. Data suggest that destruction of the lowerbeach cusp system may be related to persistent accretions conditions and/or calm conditions but probably also to the transition from wave- driven circulation dominated by weak alongshore currents with flash and swash rips, to a second period characterized by dominant longshore current further increasing in speed, and rare swash rips. On the other hand the disappearance of the western upper beach cusp might be related to an accretion pattern and to the merging of two individual features. Our observations, consistent with previous works, suggest that beach cusps certainly arise as a result of some combination of erosion and accretion.