Coastal Processes and Influence on Damage to Urban Structures during Hurricane Irma (St-Martin & St-Barthélemy, French West Indies)

Abstract

This study aims to better understand coastal processes associated with extreme cyclonic events through the study of the coastal changes, flooding and damage that resulted from the passage of a category 5 hurricane (Irma) on 6 September 2017 over the islands of Saint-Martin and Saint-Barthélemy in the Lesser Antilles. Hurricane Irma was contextualized from tropical cyclone track data and local weather observations collected by Météo-France, as well as high-resolution numerical modelling. Field work involved the study of accretion coasts through qualitative observations, topo-morphological and sedimentary surveys, as well as image acquisition with Unmanned Aerial Vehicle (UAV) surveys during two trips that were made 2 and 8 months after the catastrophe. Wave propagation and flood numerical models are presented and compared to field data. Our field analysis also reports on the devastating impacts of storm surges and waves, which reached 4 and 10 meters height, respectively, especially along east-facing shores. The approaches reveal a variety of morpho-sedimentary responses over both natural and highly urbanized coasts. The analysis shows the effects of coastal structures and streets on flow channeling, on the amplification of some erosion types, and on water level increase. Positive spatial correlation is found between damage intensity and marine flood depth. The signatures of ocean-induced damage are clear and tend to validate the relevance of the intensity scale used in this study.

A 30-m scale modeling of extreme gusts during Hurricane Irma (2017) landfall on very small mountainous islands in the Lesser Antilles

“…The simulations are initialized with the hybrid ETKF-3DVAR assimilation (Wang et al, 2008) in the outermost domain (7.5 km scale), in the same way as in Jury et al (2019) and Rey et al (2019). A parametric Holland vortex (Holland, 1980, Krien et al, 2018 is assimilated using equal weights for the static covariance and the ensemble covariance.…”

“…The two islands are separated by a distance of 20 km. Saint Martin island is splitted into two political entities: on the southern side, the Netherlands territory called Sint Maarten; on the northern side, the French territory called Saint-Martin (Rey at al., 2019). The entire island covers an area of 90 km 2 with a maximum width of 15 km.…”

“…With peak maximum sustained winds of 80 m s -1 and a minimum pressure of hPa, Hurricane Irma (2017) was the strongest Atlantic hurricane ever recorded outside the Caribbean Sea and Gulf of Mexico (Cangialosi et al, 2018, Rey et al, 2019. On 6 September 2017, this category 5 hurricane hit the Lesser Antilles islands, landfalling with this maximum wind speed on Barbuda, Saint Barthélemy and Saint Martin, at respective times 05:45, 09:30, and 10:30 UTC.…”

“…Irma caused 15 deaths and damaged most of the urban structures in the island of Saint Martin. The total cost of the insured damage was estimated at 1.17 billion EUR for the Saint Martin French part (FR) and 823 millions EUR for Saint Barthélemy (Rey et al, 2019). The extreme gusts that occurred during the Irma landfall over Saint Barthélemy and Saint Martin islands were examined with numerical simulations reaching the maximum resolution of 280 m (Duvat et al 2019;Pillet et al, 2019;Rey et al, 2019).…”

“…The total cost of the insured damage was estimated at 1.17 billion EUR for the Saint Martin French part (FR) and 823 millions EUR for Saint Barthélemy (Rey et al, 2019). The extreme gusts that occurred during the Irma landfall over Saint Barthélemy and Saint Martin islands were examined with numerical simulations reaching the maximum resolution of 280 m (Duvat et al 2019;Pillet et al, 2019;Rey et al, 2019). But this subkilometer scale corresponding to the numerical region gap in turbulence modeling, usually called "turbulence gray zone" or "terra incognita" (Wyngaard, 2004), may lead to erroneous simulated winds.…”