Development of a drought forecasting system and reservoir management model for water supply: Case-study of the Arzal Dam (Brittany, France)

The IAV is in charge of the management of the Arzal dam located in Brittany (France), which, in summer periods, supplies drinking water for 1 million people. The implementation of an operational hydrometeorological forecasting system is considered a priority for the next years. Such a system is expected to add value to recent research developments and open opportunities for new products in operational water-reservoir management. The Arzal dam regulates a 50 Mm3 single reservoir downstream the Vilaine River Basin (10,000 km²) in the Northwestern part of France. Built in 1970 to avoid flooding due to the concomitance of a flood in the river and high sea level, it has gained in importance over the years in the regional water management system. Today its water reservoir plays a central role in water supply for drinking and irrigation, sailing and fish by-passing. During summer periods, conflicts among water users may arise. The development of a low-flow forecasting and reservoir management model to improve management decisions started in 2013 within the framework of the Interreg IVB NWE project DROP. It includes a drought forecasting model, a reservoir water balance model, and the development of an efficient visualization of the forecast outputs to support decision making in seasonal forecasting and to anticipate water use conflicts. The results obtained so far will be presented and illustrated in this communication. Particular attention will be given to the performance of raw and bias corrected seasonal precipitation and
streamflow forecasts, as well as to the first assessment of reservoir management variables.