Abstract
The regulation of the Aurland water course due to hydropower development has significantly
altered the hydrological regime (both flow and water temperature) of the Vassbygdvatn lake and the
downstream Aurlandselva river. The water released from the hydropower plant is directly discharged in
Vassbygdvatn providing much colder water than prior to regulation, especially in late spring, summer and
early autumn. As a consequence Vassbygdvatn supplies Aurlandelsva with this colder water, giving
impacts on the biological system held by the river. An increase in water temperature of Aurlandselva
would, in specific, better meet the fish population’s need for ambient water temperature. The analysis of
the water temperature regime under the present manoeuvring of the hydropower system showed that
enhancing the formation of temperature stratification in Vassbygdvatn during the summer period is the
prioritised strategy to increase the water temperature in Aurlandselva. A continous production of the
hydropower plant in late spring and summer seems to affect the development of the seasonal stratification
in Vassbygdvatn, as the negative heat flux of the production water cools down the uppermost layers and
destabilize the vertical water temperature gradient developed by solar radiation.
altered the hydrological regime (both flow and water temperature) of the Vassbygdvatn lake and the
downstream Aurlandselva river. The water released from the hydropower plant is directly discharged in
Vassbygdvatn providing much colder water than prior to regulation, especially in late spring, summer and
early autumn. As a consequence Vassbygdvatn supplies Aurlandelsva with this colder water, giving
impacts on the biological system held by the river. An increase in water temperature of Aurlandselva
would, in specific, better meet the fish population’s need for ambient water temperature. The analysis of
the water temperature regime under the present manoeuvring of the hydropower system showed that
enhancing the formation of temperature stratification in Vassbygdvatn during the summer period is the
prioritised strategy to increase the water temperature in Aurlandselva. A continous production of the
hydropower plant in late spring and summer seems to affect the development of the seasonal stratification
in Vassbygdvatn, as the negative heat flux of the production water cools down the uppermost layers and
destabilize the vertical water temperature gradient developed by solar radiation.
