Simulation of the Alex Storm Flash-Flood in the Vésubie Catchment (South Eastern France) Using Telemac-2D Hydraulic Code

International audienceIn the south-east of France, flash floods due to particularly heavy rainfall on catchment areas with high relief represent a real threat to the population and buildings. On Friday 2 October 2020, an exceptional hydro-climatic event occurred in the inland region of Nice city (French Riviera). At present, the death toll is 9 victims and 9 missing persons (to November 12), and the costs provisionally estimated in the Alpes-Maritimes by the insurances exceed 1 billion euros. The Vésubie River Bassin (VRB) is particularly affected, with rainfall of 500 mm recorded at Saint-Martin-Vésubie in only several hours. Our purpose here is to simulate this event in the VRB thanks to the hydraulic computation code TELEMAC-2D (www.opentelemac.org), an open-source solver based on the shallow water equations on unstructured meshes. In this work, we will show the ability of TELEMAC-2D to consider the variability in time and space of the precipitation. The performance of the simulations will be evaluated by comparing simulated flood extent with observed damages (e.g., from the ICube-SERTIT impact maps) and the water elevations observed and estimated within the watershed and with results obtained with basilisk modelling tool