Abstract
Abstract. The French Riviera is very often threatened by flash floods. These hydro-meteorological events, which are fast and violent, have catastrophic consequences on life and property. The development of forecasting tools may help to limit the impacts of these extreme events. Our purpose here is to demonstrate the possibility of using b-flood (a subset of the Basilisk library http://basilisk.fr/, last access: 8 November 2021), which is a 2D tool based on the shallow-water equations and adaptive mesh refinement. The code is first validated using analytical test cases describing different flow regimes. It is then applied to the Toce river valley physical model produced by ENEL-HYDRO in the framework of the CADAM project and on a flash-flood case over the urbanized Toce area produced during the IMPACT project. Finally, b-flood is applied to the flash flood of October 2015 in Cannes in south-eastern France, which demonstrates the feasibility of using software based on the shallow-water equations and mesh refinement for flash-flood simulation in small watersheds (less than 100 km2) and on a predictive computational timescale.
Highlights
The south of France is very often affected by flash floods, strong and rapid events that arise in the summer and autumn due to slow-moving convective storms bringing moisture from the Mediterranean Sea, with the induced rainfall amplified by topographic influences (Sene, 2012)
The b-flood software takes advantage of the adaptive mesh refinement (AMR) technique developed on Basilisk by S.Popinet (Popinet, 2015)
We model the friction with Manning’s law, and we set Manning’s coefficient to n = 0.0162 m−1/3 s as recommended by the CADAM report
Summary
The south of France is very often affected by flash floods, strong and rapid events that arise in the summer and autumn due to slow-moving convective storms bringing moisture from the Mediterranean Sea, with the induced rainfall amplified by topographic influences (Sene, 2012). Watersheds located in the French Riviera are steep and generally cover less than 100 km, which induces short hydrological responses (from a few minutes to a few hours) On these watersheds, two types of flood can be defined (World Meteorological Organization, 2011): riverine flood, which is encountered in the upstream part of the river basin, and urban flood, which occurs in the downstream part of the watershed. Two types of flood can be defined (World Meteorological Organization, 2011): riverine flood, which is encountered in the upstream part of the river basin, and urban flood, which occurs in the downstream part of the watershed Most of these watersheds are densely urbanized, and this density is increasing over time (Fox et al, 2019), and people’s lives, property (Carrega, 2016; Saint-Martin et al, 2018), and even health (Jacq et al, 2016) are highly threatened by these hazardous climatic events. B-flood is applied to the flash flood of 3 October 2015 in Cannes in south-eastern France
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