In Europe, floods are the most damaging natural disaster in terms of cost and human lives. In France, many catastrophic flood events have occurred in the last ten years. In several cases, they showed the lack of efficient forecasting tools to provide reliable flood forecasts and warn populations with sufficient delay. Therefore the Ministries of Environment and Equipment, in collaboration with the Meteorological Services, supported initiatives to modernise the existing forecasting tools. The Oise basin (20 000 km2), an important tributary to the Seine River, is one of the catchments where catastrophic floods occurred in 1993 and 1995. It receives the water of the Aisne River basin (8 000 km2). Several cities are located along the river and it goes through the densely urbanised area of Paris before joining the Seine River. The basin is managed by the Entente Oise-Aisne an organisation which is in charge of improving the management of flood risk on this catchment. In 2001, Cemagref carried out a project in collaboration with the French consultancy SAFEGE to develop and implement an operational flood-forecasting tool for the Oise and the Aisne Rivers. The objective was to use rainfall-runoff models to make shortterm flood forecasts. The tool is now used by the forecast services. The study was completed in 2002 in order to apply the rainfall-runoff model downstream in the catch-ment for flood forecasting. The objective of this poster is to present: -The methodology carried out to select the modelling tools (rainfall-runoff models, updating procedures) -The modelling tools used in these studies, their accuracy and the software developed for operational services; -A comparative assessment of two updating techniques, one based on model parame ters and the other on model states. Tests were carried out at a daily time step. The results will be presented on 12 sub catchments of the Aisne and Oise Rivers ranging from 385 to 14 900 km2 .