The 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 XIXth century. Since this date, two processes has resulted in a metamorphosis : first, several agricultural revolutions during the XIXth and the XXth 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 provides new information ab...