Cusp morphodynamics in a micro-tidal exposed beach

Abstract

Beach cusps have attracted the focus of several studies due to their effect on sediment transport and their rhythmic presence in the midst of complex nearshore interactions among waves, currents and sediment. In this paper, cusp evolution is investigated to determine the factors which influence them within Maracas Bay, Trinidad, in the micro-tidal environment of the southern Caribbean. Data on beach profiles, beach sediment, coastal processes, and cusp dimensions were collected using standard geomorphological techniques across daily, weekly and seasonal time-scales. Results indicate that beach cusp dimensions are predominantly determined by beach volume and beach angle. These two parameters in turn are influenced by wave energy. In both the wet and dry seasons, periods of lower wave energy promote accretion, leading to the formation of smaller beach cusps; conversely, periods of higher wave energy and the associated increase in erosion result in the formation of larger beach cusps. There was agreement with the self-organization theory since cusps were always present along the beach, constantly changing morphologically but never completely being erased and recreated anew. Beach cusps form an integral part of the total sediment deposited and retained on beaches over tidal and seasonal cycles, with implications for nearshore currents and beach safety. As such, a proper understanding of their dynamics will help support planning and management of beaches as they go through cyclic phases annually.