Since the end of the World War 2, the municipality of Lièpvre (Alsace, France – located along the Lièpvrette river) knew an intense urbanization of its flooded areas. The risk of floods (and the vulnerability of the municipality) increased until that time, mainly because of a lack of protection. To quantify this vulnerability we develop an innovative method based on geohistory (to collect data on past events) and modelling of past hydraulic conditions. This study allows us to quantify the risk in an economic way to order the factors at risk. The results allow us to analyze the risk evolution in time and space. This study was done within the ANR-DFG-TRANSRISKS 2 project.