An uncommon geomorphological crisis — Dominica Coastal systems response and adjustments in the Aftermath of Hurricane Maria (September 2017 episode)
Résumé
The 2017 Atlantic hurricane season is undoubtedly one of the most active and devastating ever recorded. Hurricane Maria ranks as the deadliest of the six strongest hurricanes of the season causing about 3,000 fatalities as recently reported. It started as a tropical wave off the West African coast before turning into a category 5 hurricane in less than 18 hours just before making landfall on the island of Dominica in the evening of the 18th of September 2017. It stroke the island going from the south-east to the north-west and wrecked considerably this small island developing state (1.3 billion American Dollars loss or 224% of the 2016 GDP). It affected seriously a population already made vulnerable by the passing of Hurricane Erika in 2015. Analysing the physical impact of Hurricane Maria on the Dominican coastline is relevant to the TIREX 2017 research project funded by the ANR OURAGANS - a national grant devoted to the study of hurricanes. TIREX refers to the use of scientific feedback to encourage better response and adjustment from the civilian population as well as the local and national authorities in a context of climate change ; it focuses on the north area of the West Indies during 2017 hurricane season. Physical impact is studied through a comparative and diachronic approach on several sediment cells and watersheds displaying different signs of anthropisation. Their resilience is assessed a year and a half after the event. The use of aerial footage and topomorphological data analysis made on field are put forward thanks to a cartographic translation in order to emphasize morphosedimentary response at different moments in time. Working on the ability to adjust as well as the physical (geomorphological changes) and social recovery (through reconstruction) is a priority when taking into account the territorial vulnerality at stake in Dominica in a context of climate change. Our results show that coast evolution is mainly due to fluvial processes rather than marine dynamics. Heavy rain caused major landslides and flooding while enabling organic materials and debris to flow downstream towards river mouths. This phenomenon of extreme sedimentation accounts for major morphological alterations such as land elevation, sedimentary progradation, and river alvulsion. Contrary to the idea according to which hurricanes generally make coastlines recede, in the case of Dominica island, large amounts of input materials of heterogenous granulometry have generally contributed to a sustained fattening/growth/development (t + 1 year) of sediment cells. The aggradation of the lower coastal area produced by the sudden dumping of waste materials brought about the destruction of most of the water crossing structures ; it also affected buildings located in the flood plain being completely carried away or buried. Large amounts of woody debris washed away into the sea and reshaped by the cyclonic swell intensified the impact of the waves on the coastline. Identifying Dominican specificities about hurricane Maria event should allow us to develop adjustment measures to reduce the cyclonic risk and improve the resilience of the island coastal systems.
Domaines
Géographie
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