La géohistoire des inondations au service de l’évaluation critique du zonage du Plan de Prévention des Risques d’Inondation : l’exemple de Thann (Haut-Rhin, France)

Abstract

Thann, between the Vosges Mountains and the Alsace plain, is one of the first cities of Haut-Rhin to have been concerned by a Flood Risks Prevention Plan (PPRI). The town is indeed crossed by the Thur river, characterized by violent floods. However, the zoning of the PPRI mentions only a relatively small risk area. But the city has suffered in the past from destructive floods, as it is revealed by the TRANSRISK database. Among these events, the flood of December 1947, very well documented, allows, through a geo-historical approach (contextualization, transposition), the spatial confrontation of areas flooded in 1947 and flood areas designated by the PPRI. The results raise many questions about the quality of PPRI zoning that appears to present errors and omissions. And in the case of a 100-year flood, the damage would be catastrophic. If the re-enactment of the 1947 flood features a worst case scenario, this can also be the basis for a preparation for crisis management.

Keywords

• geohistory
• floods
• Risk mapping (PPRI)
• Alsace
• Thann