Hydropeaking mitigation project on a multi-purpose hydro-scheme on Valsura River in South Tyrol/Italy

A hydropeaking mitigation project on Valsura River in the Italians Alps is described. The project is of particular interest due to several aspects. First of all, the Valsura torrent has unique morphological braiding characteristics, which are unique in the reach of Adige valley between Merano and Bolzano, and has a good reproduction potential for fish, especially in the terminal stretch along a biotope before its confluence with Adige River. Moreover, the Valsura hydropower cascade, which overall consists of six high-head hydropower plants, has an exceptional economic importance for the local hydropower industry. Lastly, the last HPP on the cascade is a multipurpose plant, so that interesting interactions between hydropeaking mitigation, irrigation supply and peak energy production are considered. The project started from a hydrological and a limnological measuring campaign and from an energetic, hydraulic and legislative framework analysis. The ecological findings are combined into a deficit analysis, founding the basis for the definition of a hydrological target state, which points to achieve a good natural reproduction for brown trout in the hydropeaked stretch, fulfilling at the same time the human safety conditions. Finally, mitigation Measures are described that at the same time comply with the following manifold aspects: a. maintenance of the requested target limits for fish reproduction; b. maintenance of the water release for the agricultural irrigation; c. enhancement of the flexibility of the hydropower plant's operation; d. reduction of the risk for local population. The paper compares operational and constructive mitigation measures and shows that constructive hydropeaking mitigation measures, for the present case study, can combine the positive effects of ecological improvement with higher safety standards and more flexible energy production.