Simulation of river water temperatures during various hydro-peaking regimes

Hydro-peaking is a type of hydropower operation characterized by rapid and frequent changes in flow, possibly also leading to similar changes in water temperature - http://www.nrk.no/tures ('thermo-peaking'). This study examines water temperature variations caused by the present hydro-peaking regime in Nidelva River (Norway), and the impacts that future changes in the operations of the hydropower system might introduce. The simulated future scenarios indicate that only limited changes are expected to happen compared to the present situation, measured as changes in accumulated degree-days. The model simulations predict a reduction in the range of 50 degree-days for two of the scenarios and an increase in approximately 40 degree-days for the third scenario. These results are further transformed into changes in salmon egg development and time of hatching, which corresponds to a few days delay in hatching in all three scenarios, and also a slight delay in swim-up for two of the three scenarios.