Flood-forecasting and flood management for the Skienselva river system in Norway

Hydropower reservoirs can be useful tools for flood management in regulated rivers and can reduce or eliminate dangerous flood events by storing water during flood peaks and releasing it later in a controlled way. The operation of the reservoirs before and during such dramatic events can, however, be challenging, since the timing of reservoir operation must be based on uncertain predictions of future inflow and the effects of possible release strategies. This paper describes a flood modelling system developed for the lower part of the Skienselva river system in Norway. The natural flood conditions in the river are described, and how the hydropower system with its many reservoirs has reduced damaging floods. It is shown that the modelling system can be used to manage the balance between reducing flood risk and maintaining hydropower generation.