Preliminary evaluations of the impact of a pumped storage plant on the hypolimnetic circulation of a deep subalpine italian lake

Lake Iseo is an eutrophic lake located in northern Italy, having a surface of 61 km2 and a volume of about 8 billion m3. One of the most important hydrodynamic processes characterizing this deep subalpine lake is the water vertical overturn at the end of the limnological winter. This process has important physical, chemical and biological effects on the whole lake ecosystem. The gradual increase of average winter temperatures over the last decades has considerably hindered this process and, as a consequence, an increasing oxygen depletion has affected the hypolimnion of lake Iseo to the point that an evolution toward meromixis has been postulated. Although at different extent, the same problem has been observed in different lakes in the world and, when their dimension is not too large, forced circulation projects have sometimes been implemented as a tentative counteracting measure. Although the considerable dimension of the hypolimnion of lake Iseo poses an economic issue to this type of intervention, a recent debate regarding the possible construction of a pumped storage plant suggests the opportunity to use the withdrawal-discharge cycle of this plant as a way to force hypolimnetic circulation. This opens the way to a wide set of environmental questions, as a consequence of different possible plant layouts and production strategies. In this contribution we present some preliminary evaluations on the effectiveness of the operation of such a plant on lake circulation by using a 3-D model.