Detailed simulation of storage hydropower systems in large Alpine watersheds

Most mountain catchments worldwide are exploited for hydropower production causing significant alterations of their natural regime. Hydrological and water resources modelling in these catchments is challenging because the alterations of natural streamflow caused by hydropower production are often significant, while capturing their variability in space and time requires critical data concerning the hydraulic infrastructures and their operational schedules. These data are difficult to acquire, thereby hindering the possibility to correctly simulate the complex interaction between the natural hydrological cycle and water uses. To overcome these limitations we propose a framework that relies solely on publicly available data which provides accurate simulation of both streamflow and hydropower production. The proposed framework is illustrated by means of the HYPERstreamHS hydrological model applied to the Adige catchment, a large watershed of the south-eastern Alpine region whose streamflow is strongly impacted by 39 large hydropower systems, 22 of which connected to storage reservoirs, with an overall mean annual production that accounts for about 14% of the total Italian hydropower production. We analyzed the impact on modelled hydropower production of commonly adopted simplifications in the production schedule as well as of the hydropower systems, which are often characterized by a complex infrastructure with several interlinked derivations and conveyance intakes. Our simulations highlight how an accurate topological representation of hydraulic infrastructures is crucial to correctly represent water transfers, more important than capturing the operational schedules when reservoir oscillations are a small fraction of the total head. On the contrary, scheduling is important for systems in which reservoir oscillations account for a significant portion of the total head. Furthermore, we show that simplifications motivated by difficulties in data collection combine in a non-linear manner with an overall impact difficult to assess. We propose this framework for accurate modelling of hydropower production at regional and national scales, particularly in studies dealing with the projection of climate change and competing uses on water resources and renewable energy.