Châlons-en-Champagne flood risk prevention plan — Aval sector of the CAC — map of hazards

Area exposed to one or more hazards represented on the hazard map used for risk analysis of flood RPP. The hazard map is the result of hydraulic modelling carried out in 2003 by Royal Haskoning France, whose objective was to assess the intensity of the hazard at any point in the study area. The assessment method led to the delimitation of a set of areas on the study perimeter, constituting a graduated zoning based on the level of water heights of the hazard. The assignment of a hazard level at a given point in the territory takes into account the probability of occurrence of the dangerous phenomenon (the centennial flood) and the natural terrain of the area. All hazard areas shown on the hazard map are included. Areas protected by protective structures are represented (possibly in a specific way) because they are always considered subject to hazard (case of breakage or inadequacy of the structure), here we speak of hydraulic transparency. In addition to this hydraulic modelling of the Marne watercourse, four additional areas have been identified and selected to perfect the hazard map. These areas, involving small tributaries of the Marne River, have not been modelled. The four areas, from the Atlas of the Highest Waters in the Marne Valley (PHEC) of 2001, can inflate in contact with the Marne in flood (dam effect), a check made with the rainy episodes of February 2008. Hazard zones can be described as developed data to the extent that they result from a synthesis using multiple sources of calculated, modelled or observed hazard data. These source data are not concerned by this class of objects but by another standard dealing with the knowledge of hazards. Some areas of the study area are considered “zero, insignificant or white zones”. These are the areas where the hazard has been studied and is nil. These areas are not included in the object class and do not have to be represented as hazard zones. Furthermore, these areas are not included in the regulatory zoning as they do not constitute exposure to hazard. Genealogy: The boundaries of a hazard zone are shown on the hazard map depending on the level of the hazard. In other words, the polygon objects representing the hazard zones form a partial coverage of the area studied, each of which is a closed polygon in which hazards have the same intensity level. In other words, the criterion for dividing the hazard zones is the level of the hazard.