The project consists of drawing the flowing water of the River Sorba by a pick-up station at the altitude of 1.080 meter above sea level and discharge the same 1.135 meter downstream at an altitude of 900 meters above sea level the turbine that is positioned at the confluence of the River Sorba and the River Gronda.
The Installed Power of the Mini Hydro Power Station is very low (226kW) as the location of the plant is in the high part of the valley and the natural annual medium water flow of the river is only 0,745 cubic meter per second (745 liters per second).
The upper drawing station is designed to draw from the river the major flow and to guarantee according to local environmental law a Minimum Vital Runoff somewhere in between 0,1 to 0,2 cubic meter per second (100-200 liters per second) depending on the specific levels of normal flow.
The water deviated will be driven/channeled in a pipe and discharged 1135 meters downstream after having passed through the turbine to produce energy. The estimated yearly production is 1650 MWh. As the river runs in a deep gorge the upper station will be built by excavating a 12 meter deep trenc to reach the level of river bed.
The turbine and discharge station will be built in the green lot few meters from the Middle Age bridge, precisely at the confluence of the two rivers Sorba and Gronda as shown in the pic below.
The valley is protected under European Directive and it is included in the Natura 2000 scheme (“SIC” Site of Interest for the European Community and “ZPS” Zone of Special Protection) as the area is of undiscussed natural value and highly sensible under the environmental point of view. Due to its position the area is also subjected to geological and geomorphological risk. This means that all anthropic disturbances may create instability if not well designed and conceived and evaluated.
The main impacts due to the construction and operation of the plant are listed below:
the change of the morphology of the whole site can generate a risk for future geological instability;
the change of the morphology of the river bed can generate hydraulic risk in case of natural high flow (flooding) that we can say to be quite unpredictable due to climate change;
the drainage of water flow and the resulting minimal low flow for most of the year will easily damage the aquatic life endangering mainly the environment of the “trota fario” a specific and rare species of trout that is typical of this area;
the drainage of the flow especially in the warm season will have an impact on the use of the area for human outdoor activities such as fishing, kayaking, swimming, trekking;
the discharge station will have an impact due to continuous noise in the center of the village
the discharge station will occupy the green field at the confluence and will have a impact under the architectural and visual impact as it will be a building not in harmony with the local walser architecture;
Major of the village of Rassa (population of 62 inhabitants) is the plan's proposer stating that part of the economical incomes will be devolved to public works for the required infrastructures that we believe will not be possible due to the low redditivity of this specific project.