South in the Saas Valley is the largest earth dam in Europe, the Mattmark Dam. The dam, which is used to generate electricity, is a real place of power and fascinates with its technical details and its wild and romantic location. The dam can be reached as a winter hike, snowshoe tour, or ski tour in winter.
On August 30, 1965, two million cubic metres of ice and debris broke off the Allalin glacier in canton Valais, engulfing the Mattmark dam construction site. Eighty-eight people lost their lives. Many questions remain unanswered about the worst disaster in recent Swiss history.
Except for the Zermeiggern pumping station, the facilities of Kraftwerke Mattmark AG were built between 1958 and 1966. The Zermeiggern pumping station was built between 1983 and 1987 after the advance of the Allalin glacier destroyed some of the water catchments below the glacier, making it impossible for the glacier streams to flow into the Mattmark reservoir. With the first full damming in 1969, the Mattmark reservoir was handed over to commercial power plant operation. It held 100 million m3 of water and was built for the sole purpose of generating electricity. In 2001, the Mattmark dam was converted into a multi-purpose reservoir to protect the Saas Valley and Rhone Valley, based on the findings from the floods in 1990. From this point on, the canton of Valais has a flood retention volume of 3.6 million m3 at its disposal in Mattmark.
Additionally, the natural catchment area of 37.1 km2, the left- and right-bank side streams of the Saas Vispa, with a catchment area of 51.1 km2, are fed into the Mattmark reservoir. The catchment area is 45% glaciated.
The water stored in the Mattmark reservoir is used in the two power plants, Zermeiggern (Saas Almagell) and Stalden, over a maximum head of 459 m for the Mattmark-Zermeiggern stage and 1029 m for the Zermeiggern-Stalden stage. The inflows from the intermediate catchment area of 74.2 km2, which are stored in the Zermeiggern equalisation basin, can be turbined in the Stalden cavern control centre and pumped into the Mattmark reservoir through the Zermeiggern pumps. The Saas-Fee power station with the Feevispa water intake is used exclusively for doping the Saas Vispa.
The average annual production is 649 million kWh, of which 298 million kWh are generated in the winter half-year and 351 million kWh in the summer half-year.