Mud Banks, Sand Flux and Beach Morphodynamics: Montjoly Lagoon Beach, French Guiana

Abstract

Sandy beaches affected by mud in an open-coast, wave-dominated setting are rare. Such beaches can also show rapid response patterns where large mud banks affect the nearshore wave regime, as on the Amazon-influenced coast of French Guiana. The sand flux patterns and morphodynamic changes affecting Montjoly beach, in Cayenne, have been analysed from interpretation of beach plan-view patterns deduced from four satellite images (1986, 1996, 2003, 2011) and from topographic monitoring at a shorter timescale. The data show the prevalence of beach rotation induced by the gradual approach and alongshore migration of mud banks. An irregular rotation pattern is highlighted, commanded in part by regional-scale and global climatic and hydrodynamic influences on mud bank dynamics. This irregularity denotes the difficulties of elaborating a predictive temporal scheme of beach change.