he purpose of regulation is to save water, and thus energy, from the spring flood period for use during the next winter season. This maximises the production of energy during the winter when the demand is highest and the profit is the best. To be able to accommodate the spring flood the lowering of the reservoirs during the winter has to be adapted to the expected volume of the spring flood. Reservoir operators intend to keep the 90% level of the reservoirs over the summer to guarantee maximum possible energy production. Thus an overestimation of the spring flood may result in an reservoir level below the capacity level at the end of the filling period (decreasing efficiency and causes economic losses) and an underestimation of the spring flood would result in an overload of the reservoir which causes serious safety issues within the dam (e.g. dam break) and downstream flooding (due to uncontrolled water releases). But also the timing of the reservoir lowering is important, since reservoir managers want to avoid a too early release of water which could be used for power production especially after the low flow period and intend an optimal refilling schedule of the reservoir.