Beaches Seasonal and Paroxysmal Morphosedimentary Dynamics: Results of 10 years Martinique Coastal Observation Network

ABSTRACT Dolique, F.; Sedrati, M.; Charpentier, J.; Jeanson, M.; Cohen, M.; Dupuy, L., and Alami, S., 2019. Beaches seasonal and paroxysmal morphosedimentary dynamics: Results of 10 years Martinique coastal observation network. In: Castelle, B. and Chaumillon, E. (eds.), Coastal Evolution under Climate Change along the Tropical Overseas and Temperate Metropolitan France. Journal of Coastal Research, Special Issue No. 88, pp. 172–184. Coconut Creek (Florida), ISSN 0749-0208. Coastlines are vulnerable to the effects of climate change and sea-level rise as well as modifications in the wave climate and, in particular, increased storminess. The coastal areas of islands form part of this scenario and the Martinique shoreline illustrates this intensification of shoreline retreat and coastal erosion. In the context of this critical situation, a coastal observation network was set up in 2010 to monitor the evolution of the coast of Martinique. This network includes 28 beaches along the coast of Martinique and is based on studies of shoreline evolution using aerial photographs and topographic surveys of 71 cross-shore transects. The main aim of this network is to characterize the modal and seasonal dynamics of these vulnerable beaches and to estimate their resilience capacity and trends in the context of the increasing frequency of hurricanes. Analysis of the measurements over the last ten years highlights a general acceleration of the shoreline retreat. Furthermore, in terms of seasonal coastal evolution processes, the results clearly show the weak effect of the longshore sediment transport component on the open beaches of Martinique Island. However, a predominant cross-shore sediment transport component is observed on smaler bay beaches, which represent the most numerous beach type on the island (including several pocket beaches). On the short-term scale, the results of hydrodynamic and morphodynamic measurements highlight variable and intensive beach dynamic responses with a determining role played by shoreface parameters and coral-lagoon complexes. While cyclones have a significant impact on reducing the slope of beach profiles, our measurements reveal a significant resilience of eroded beaches owing to constructive swell. We also demonstrate that the hurricane season is not the season with the strongest morphosedimentary impacts. This almost ten-year-old observation network, provides an overview of shoreline evolution on Martinique and is an efficient management tool for the Lesser Antilles coastal environments.