The Avisio torrent is an Italian stream located in the central eastern part of the Alps and a left tributary of the Adige River. It is about 90 km long with an average gradient of 2.02%, has a basin with an area of 940 km2 and it feeds 4 hydroelectric power plants. Avisio is as an emissary of Fedaia lake (2054 m above s.l.), which receives the melting waters of the Marmolada glacier. The river runs through the valleys of Fassa, Fiemme and Cembra and flows into Adige River at a height of 196 m above s.l. in the town of Lavis, a few kilometers north of the city of Trento. In Fassa Valley, the stream receives its first tributary, the “Ruf de Contrin”, in the village of Penia. In Canazei village Avisio receives the “Ruf d'Antermont” tributary from mountain of Sella Group and, moving towards the valley, it greatly increases its reach thanks to the tributaries from Rosengarten group. After Soraga village the stream is barred from Pezzé Dam. In Fiemme Valley the water catchment area extends in its maximum amplitude, receiving numerous streams, such as Travignolo stream, the main tributary. Travignolo generates from a glacier and is barred in Paneveggio valley creating Forte Buso lake; it flows in Avisio torrent near Predazzo village. Moving downstream, after the village of Molina, the Avisio stream is dammed to create Stramentizzo Reservoir, and its waters are conveyed to the hydroelectric plant of San Floriano of Egna (Bolzano Province) and then returned directly to Adige river. Immediately after the artificial lake Stramentizzo, the stream (with significantly reduced flow rate because of withdrawals for hydroelectric purposes) enters into Cembra Valley, through a characteristic and winding canyon in the porphyry rock. The major tributaries in this reach are those of the left side of the basin. Lastly Avisio flows into the Adige River at Lavis, with a very broad delta (width about 1 km), forming a swampy zone that is a protected area, the biotope “Foci dell'Avisio”. From a geological point of view, moving from the Fassa Valley to the Fiemme Valley, Avisio gradually passes the from Dolomite region (with limestone rocks) to the porphyritic atesina platform (with siliceous rocks) and this affects the hydrology. In Cembra Valley, given the geological conformation of the territory (impermeable rocks) and the steep slopes, Avisio has a distinctly torrential character, with minimal flow rates of about 5 m3/s and flood events with over 1000 m3/s. With regard to the climate, Trentino has the characteristics of a typical alpine region, with cold and dry winters and cool and rainy summers. The mean annual precipitation for the Avisio basin settles around 993 mm (PGUAP data).
The two pilot sites on Avisio river are located around the hydroelectric reservoirs Pezzè (46°23'2.09"N - 11°39'50.62"E - Fassa Valley) and Stramentizzo (46°15'50.27"N - 11°22'24.81"E - Fiemme Valley). The reaches of interest are both upstream and downstream of the dams, and the main physical characteristics are described in the table below. With respect to the hydrological regime and the ecological state of the watercourse, both aspects are conditioned by the presence of the reservoirs.