Warning issued in advance by the departmental flood forecasting services. In the event of heavy rainfall or hydrological alert, a flood warning is sent to the Prefect, who then alerts the mayors of the catchment areas concerned.
Warning issued in advance by a special state service (flood forecasting service). In the event of a rainfall or hydrological alert (triggering when thresholds are exceeded), the flood forecasting service offers the Prefect the alert of the mayors of the watersheds concerned. As a severe overflow flood, the flood warning service broadcasts, for prefects and mayors, hydrological situation bulletins and information on the evolution of water levels . In 1994, 54 flood warning services monitored 16,000 km of waterways in France using automated measurement networks.