Envelopes approached with Potential Floods of the rivers of Auvergne-Rhône-Alpes

As part of the Preliminary Flood Risk Assessment (EPRI), DREAL Rhône-Alpes in connection with DREAL Bourgogne, Franche-Comté, Languedoc-Roussillon and PACA have carried out over the entire Rhône-Mediterranean basin of Envelopes approaching potential floods (EAIP) taking into account 2 phenomena: flooding by river overflows (EAIPce) flooding by Marine Submersions (EAIPsm) These envelopes have been developed with a view to approaching the contours of extreme events. In this sense, the effect of hydraulic structures (dams and protective dikes) is not considered. Except in particular cases, the protective dikes shall be considered transparent. EAIP “ce” represents the potential for overflows of all streams, including small and intermittent streams, torrents, talweg bottoms. Since the dikes are not taken into account, the right-of-way obtained can be considered, in the first approximation, as incorporating the effect of the failure of the protective structures. Nevertheless, it does not integrate pouring runoffs (sludge flows and localised runoffs outside the talwegs), nor the specific phenomena related to the local saturation of urban sanitation networks. EAIPs are intended to be the subject of a more precise analysis of the phenomena during the next stages of the Flood Directive for the territories concerned by a IRR or a local strategy. The method used to build EAIPs has led to the merging of information sources varying scale and precision. It generates uncertainties that can be punctually significant (overestimating right-of-way or, on the contrary, under estimation). Therefore, EAIPs do not constitute a mapping of flood areas and should not be confused with: plans to prevent foreseeable natural hazards from floods or coastlines; atlases of flood or submersible areas; mapping Submersible Surfaces and Flood Risks of the Important Flood Risk Territories (TRI). EAIPs cannot be used to identify flood areas in administrative or regulatory procedures. Moreover, given the scales of the data mobilised, their graphic exploitation only makes sense for scales above 1/100 000e.