Zillergründl Dam

The Zillergründl Dam is an arch dam on the Ziller River in the upper Ziller Valley of Tyrol state, Austria. It lies 16 km east of Mayrhofen. The primary purpose of the dam is hydroelectric power generation and it supports a 360 MW pumped-storage power station. As part of the Zemm-Ziller Development, construction on the dam began in 1981 and, along with the Häusling Pumped Storage Power Plant, it was completed in 1986. The power plant was fully commissioned by 1988. The dam is the second tallest in Austria.

Design and operation
At an elevation of 1850.7 m above sea level, the Zillergründl is a 186 m tall and 502 m long variable-radius arch dam with a structural volume of 1373000 m3. The dam is 6 m wide at its crest and 36 m at its base. Its reservoir has a capacity of 89500000 m3, of which 88800000 m3 is active (or "useful") capacity. At normal levels, the reservoir has a catchment area of 67 km2. The reservoir operates at elevations from 1850 m to 1740 m, which is the draw-down level.

Water released from the reservoir reaches the Häusling Power Plant 10 km downstream. The power plant is located at an elevation of 1060 m and contains two 180 MW Francis turbine-generators. It is afforded 744 m of hydraulic head given the difference in elevations. Using its pumped-storage capability, the power-station receives water from the Stillupp Reservoir 8 km to the west in an adjacent valley at 47.12139°N, 11.86611°W and pumps it up to the Zillergründl Reservoir. The pumping and replenishment of the reservoir occur at night, during low energy demand periods. The process is repeated; electricity is generated during high-demand periods and pumping occurs during low-demand periods when electricity is cheaper.