National audienceThe Val nantais, which is the flood plain of the Loire River 20 kilometres upstream Nantes City, has been protected from the waters by a levee in the middle of the XIX th century. Since this date, two processes has resulted in a metamorphosis : first, several agricultural revolutions during the XIX th and the XX th centuries and secondly, the urban extensions. Nowadays, economic and human vulnerability to floods have strongly increased with more than 4 000 inhabitants and 1 600 houses exposed to hydrological hazards of this temperate hydrosystem. Processes and actors of this land management will be studied in this paper. The aim of this contribution is to present how promethean society faces up natural hazards. This provide...