Trade wind intensification and hurricanes on a Caribbean beach, MartiniqueIsland: A comparison of their morphological impacts from field experimentsand numerical simulations

The impacts of Trade Wind intensification and moderate hurricanes on beach sediment balance have been analysed from a study of time variations of the sediment volume of Bagasse Beach and its shoreface, on the island of Martin ique (French West Indies). Field experiments (wave characteristics, longsho re current velocity, bathymetric and topographic surveys) conducted at diff erent time scales show a negative dry season sediment budget and a slightly positive annual budget for this microtidal beach. Volumetric variations co mputed for one day of Trade Wind intensification appear to represent about twice those for one dry season. This analysis reveals that the influence of moderate hurricanes (coastal wave heights less than 2.5 m) on the long-ter m (2 yr) sediment balance is weak. In order to compare these high-energy events, numerical simulations have be en carried out. Comparison between moderate hurricane conditions and a Trad e Wind intensification event shows that the latter is responsible for more important volumetric erosion by about 23%. At a daily scale, moderate hurri canes have a larger power of erosion, 40 m(3) m(-1) day(-1) versus 28 m(3) m(-1) day(-1) for a Trade Wind intensification event. However, hurricane wa ves last only a few hours to 2 days, while waves generated by Trade Winds l ast, on average, 3-4 days. This study clearly highlights the importance of Trade Wind intensification events on the short-term (order of days) evoluti on of this beach.