Because of its turbulent history, Alsace is one of French regions where the historic floods are the most underestimated. The damages connected to the wars (on 1870, 1914 - 1918, 1939 - 1945), the particular classification of archives and, especially, their writing in German during several periods of the recent history, is rebuffing numerous specialists Located in the same geographical area (the Rhine Graben), but by the other side of the the border constituted by the Rhine, the land of Bade is, him too, confronted with the problem of the misunderstanding of the historic floods, because of the destructions of the war also, but especially because of the harmful absence, for archives production, of a strong centralized state until the German unification after 1870. Hence the idea to set up a multidisciplinary French – German research program, to establish compared floods chronologies over several centuries in the Rhine Graben, both in France and in Germany, by associating historians, geographers, anthropologists and specialists of the languages from the universities of Mulhouse (France) and Freiburg in Breisgau (Germany). This program (called “TRANSRISK” 2008 - 2010), financed by the « Agence Nationale de la Recherche » and the « Deutsche Forschungsgemeinschaft , has multiple objectives: - filling the gaps in the knowledge of the floods in France and in Germany - building a common geohistory of the floods - optimizing the prevention and the information about the floods, thanks to the classification, the reconstruction and the mapping of the extreme phenomena - understanding the role of rivers developments responsible for an different floods evolution on both sides of the Rhine - contributing to the implementation of flood risk observatories on a French – German basis. These works join the logic of the “European Directive 2007/60/EC on the assessment and management of flood risks” come into effects in november 2009 and will allow both regions, previously late, to take place in the forefront of innovation in knowledge on flood risks, including for small streams, and in mapping, two objectives were fixed for 2011 and 2013 by the European Directive. The first results are already spectacular because they are not less than 600 floods in Alsace and 400 in Bade who were able to be counted during the last 5 centuries, bringing to light, on one hand, totally forgotten extreme phenomena, and on the other hand significant breaks in compared floods chronologies, giving evidence of the essential role of the anthropological developments in the decrease or increase of flood risk... and in the production of archives.