Flood hazard area of the Veyre Basin (63DDT19980007) approved on 22-12-2008 — Puy-de-Dôme

Hazard maps determine flooded areas in terms of perimeter and flood intensity. Three hazard levels (low, medium and strong) are defined according to the physical parameters of the flood that can be translated in terms of severity for people and damage to property. These parameters are water heights and flow velocities: —strong hazard, for water heights exceeding 1 metre, and/or flow velocities exceeding 1 metre per second, —average hazard for water heights between 0.5 and 1 metre and speeds of less than 1 metre per second, or speeds between 0.5 and 1 metre per second and heights of less than 1 metre, —low hazard for water heights of less than 0.5 meters, and speeds of less than 0.5 meters per second. The intensity of the hazards is related to the possibilities of moving people according to water height and flow velocities. The hazard map is the result of the study of hazards whose objective is to assess the intensity of each hazard at any point in the study area. The assessment method is specific to each type of hazard. It leads to the delimitation of a set of zones on the study perimeter constituting a graduated zoning according to the level 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 and its degree of intensity. For multi-random PPRNs, each zone is usually identified on the hazard map by a code for each hazard to which it is exposed. All hazard areas shown on the hazard map are included. Areas protected by protective works must be represented (possibly in a specific way) because they are always considered subject to hazard (case of rupture or insufficiency of the structure). Hazard zones can be described as elaborated data to the extent that they result from a synthesis using several calculated, modelled or observed hazard data sources. 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 perimeter are considered “zero or insignificant hazard areas”. These are the areas where the hazard has been studied and is zero. These areas are not included in the object class and do not have to be represented as hazard zones. However, in the case of natural PPRs, regulatory zoning may classify certain areas not exposed to hazard as a prescribing zone (see definition of PPR Zone class).