The influence of hydroelectricity multireservoir systems on the peak discharge in rivers during floods can be significant. When the surfaces drained by the accumulation reservoirs and their own available storage volume before the flood are important, the reservoir routing effect can reduce the flood damages along the water courses downstream. However, the reduction of the peak flow during such events strongly depends on the water releases through turbines, bottom outlets or spillways achieved by the dam operators.
In order to optimize the protection effect due to reservoir routing during floods, the use of a discharge forecast system gives the required information about the hydrological situation in the catchment area and provides to the decision-maker a general view and a predicted evolution of the discharges in the river network. When coupled to an optimization tool, it is possible to directly highlight the keyvariables of the system and to decide which release or storage operations at the reservoirs have to be made.
A new tool for forecast and management of floods was developed for the Upper Rhone River basin in Switzerland. The goals of the system are to provide the decision-maker relevant information about the meteorological and hydrological situation and to propose an optimal preventive operating strategy for the existing hydropower schemes in the catchment area. The functioning of the tool is presented with the example of a flood alert delivered in September 2006 by MeteoSwiss.