Power plant Loetschen and reservoir Ferden


After about 50 years the power plants Gampel I and Gampel II were reaching their end of life. To let them in service, an enormous personnel deployment was necessary. So they started studies to see, how the power plants could be replaced with only one power plant. In 1968 a project was worked out. The new power plant envisaged a concrete dam near Ferden. Through a 7 km long pressure tunnel the water would reach the Central in Steg, where it should be turbined.

To build the concrete dam, first the river Lonza had to be diverted. For this, a diversion tunnel was excavated. After completion of the diversion tunnel, the former bed of the river Lonza was drained and the construction works for the concrete dam could begin. At the same time, a small tunnel drilling machine broke out the future pressure tunnel. After finishing the concrete dam, the diversion tunnel was closed and the filling the reservoir started. In November 1975, the first time water flowed through the pressure tunnel and was turbined in Steg. After that, the three power plants Gampel I to Gampel III were shut down.

The concrete dam is 67 meter high and has a crest length of 162 meters. The reservoir is almost 1300 meters long and has a volume of approximately. 1.89 million m3. Through the 6.85 km long pressure tunnel the water flows until Laden, from where it falls down about 600 meters into the turbines. There are two turbines, which could produce up to 330 GWh every year.

Incidents
In winter 1999, there were extreme snowfalls and thus a high number of avalanches in the Loetschental. The Faldum avalanche hit the concrete dam and destroyed all railings and foot bridges at the outside. Also the operation-gallery was badly damaged. The avalanche snow, about 250000 to 300000 m3, filled the valley below the concrete dam almost up to the control-bridge. Thus, the bottom outlet was closed. The snow, hard as concrete, had to be removed by dredging. Only two and a half months later, the normal operation resumed.

On October 10 2011, the Loetschental was hit by a devastating storm. After massive snowfalls in height and persistent rain in the lowlands it gets surprisingly warm and the snow melted again. As a result, several rivulets burst their banks and brought gravel from a height of almost 2500 meters down to the valley. On several places, the road was washed away. The gravel flowed down into the reservoir. Mud, gravel and tons of wood blocked the bottom outlet, so the water and lot of the wood flown over the dam down to Goppenstein and Gampel into the river Rhone. After the bottom outlet was cleared and the lake could be drained, the mud was removed from the reservoir. Because the Central in Steg was under water as well, the power plant was out of service for about half a year.