Abstract
Climate change and the needed reductions in the use of fossil fuels call for the development of renewable energy sources,
such as solar power and wind power, both being non-regulating energy sources. In order to secure sufficient and stable
supply of electricity to the consumers, an increased need for regulating energy production will raise, a service hydropower
can provide. Changes in operational strategies of the hydropower plants will most likely also introduce changes in the water
temperature regime of the receiving water bodies. Water temperature is recognized as a very important factor for many
biological processes in riverine ecosystems (e.g. Ward & Stanford , 1979 and Caissie, 2006 ). To what extent the water
temperature will change will depend on factors such as type of and degree of regulation, location of reservoir, operational
strategy, season and residual flow. Hydro-peaking is an extreme variant of hydro-power production introducing rapid and
frequent changes in the water flow possibly also causing similar rapid and frequent changes to the water temperature. The
aim of this study is to contribute to the understanding of ‘thermo-peaking’ (Zolezzi, et al. 2011 ) along a river stretch
exposed to hydro-peaking. Two case studies have been defined; the rivers Lundesokna and Nidelva, both located close to
Trondheim, Norway and downstream of hydro-peaked hydropower plant outlets. Lundesokna is a small tributary with a
typical low flow regime below 0.5 m3/sec and a production flow of 20 m3/s, while Nidelva is a much larger river with a
minimum low flow regime close to 30 m3/sec and a production flow up to 180 m3/s. The study is carried out by applying a
1-D hydraulic model with a water temperature module to the two rivers. Both the simulated water level data and the water
temperature data show very good correlation with the observed data. Based on the calibrated model for the two rivers, a set
of scenarios for future operational regimes of the hydropower plants have been defined and the changes in the downstream
water temperature regimes have been simulated. The simulation results form the basis for discussing the impacts on water
temperature regimes exposed to various types of thermo-peaking events in different types of rivers and how these results
can be used to assess biological impacts.
such as solar power and wind power, both being non-regulating energy sources. In order to secure sufficient and stable
supply of electricity to the consumers, an increased need for regulating energy production will raise, a service hydropower
can provide. Changes in operational strategies of the hydropower plants will most likely also introduce changes in the water
temperature regime of the receiving water bodies. Water temperature is recognized as a very important factor for many
biological processes in riverine ecosystems (e.g. Ward & Stanford , 1979 and Caissie, 2006 ). To what extent the water
temperature will change will depend on factors such as type of and degree of regulation, location of reservoir, operational
strategy, season and residual flow. Hydro-peaking is an extreme variant of hydro-power production introducing rapid and
frequent changes in the water flow possibly also causing similar rapid and frequent changes to the water temperature. The
aim of this study is to contribute to the understanding of ‘thermo-peaking’ (Zolezzi, et al. 2011 ) along a river stretch
exposed to hydro-peaking. Two case studies have been defined; the rivers Lundesokna and Nidelva, both located close to
Trondheim, Norway and downstream of hydro-peaked hydropower plant outlets. Lundesokna is a small tributary with a
typical low flow regime below 0.5 m3/sec and a production flow of 20 m3/s, while Nidelva is a much larger river with a
minimum low flow regime close to 30 m3/sec and a production flow up to 180 m3/s. The study is carried out by applying a
1-D hydraulic model with a water temperature module to the two rivers. Both the simulated water level data and the water
temperature data show very good correlation with the observed data. Based on the calibrated model for the two rivers, a set
of scenarios for future operational regimes of the hydropower plants have been defined and the changes in the downstream
water temperature regimes have been simulated. The simulation results form the basis for discussing the impacts on water
temperature regimes exposed to various types of thermo-peaking events in different types of rivers and how these results
can be used to assess biological impacts.