Ecological impacts of hydroelectric power production on the River Ticino. Part 1: Thermal effects

Abstract

As a consequence of widespread hydroelectric power production, the temperature regime of most major rivers in Switzerland is severely altered. This study was conducted to describe the impacts of a complex, yet typical hydroelectric power scheme in the Swiss Alps on the temperature regime of the utilised river. Between September 1998 and October 2001, temperature was continuously recorded at 20 different locations along the River Ticino (i.e. upstream, downstream, and in the water outlet of every major hydropower installation). Average temperatures on water abstraction sections were higher than natural during summer and lower than natural during winter, but annual temperature sum remained unaltered. Temperature amplitudes exceeded the natural situation in both seasons. Below water releases, in contrast, average temperature was somewhat higher than natural in winter, but much cooler than natural in summer, resulting in a substantial (-59%) annual heat deficit. Temperature fluctuations were weak but much more frequent than natural. It is suggested to assess the thermal impact of hydroelectric power production using the frequency of these temperature fluctuations.