The application of environmental flow regulations to small hydropower plants in alpine areas

within a framework of conflicting needs and under water scarcity scenarios, environmental issues are assuming more and more relevance in water cycle management. An important role in this context is played by the minimum discharge release downstream of diversion structures, the so-called “environmental flow”, aiming at assuring acceptable ecological conditions along natural watercourses. In this paper the regulation criteria adopted in several European alpine countries will be briefly discussed. The implementation of environmental flow regulations to small hydropower plants in the province of Brescia (Northern Italy), which is one of the most relevant Italian district in terms of number of hydropower plants, installed capacity and energy production, will be presented. In particular, the prevailing environmental flow release devices and their main technical characteristics, operating features and design criteria are briefly discussed. The introduction of environmental flow legislation entails both benefits and disadvantages which are often difficult to quantify. This paper gives a contribution to this costs-benefits analysis, by estimating the loss of energy producibility for a small alpine hydropower plant, related to the enforcement of environmental flow regulations and to the design criteria of the release devices.