Shin-Takasegawa Pumped Storage Station

The Shin-Takasegawa Pumped Storage Station (新高瀬川発電所) uses the Takase River (a tributary of the Shinano River) to operate a pumped storage hydroelectric scheme about 12 km west of Ōmachi in Nagano Prefecture, Japan. Part of the system is within Chūbu-Sangaku National Park.

Construction on the complex began in 1971, concluded in 1978 and the power station was commissioned in 1980. The power plant has a 1280 MW installed capacity and its upper reservoir is created by the Takase Dam, a rock-fill dam — which at 176 m in height is the tallest of its type in Japan. It is also the second tallest dam in Japan, next to Kurobe Dam.

Design and operation
When energy demand is low and therefore electricity less expensive, the turbines reverse and pump water from the lower reservoir back into the upper reservoir. This process repeats depending upon energy demand and water availability. Water released from the lower reservoir is used to power the Nakanosawa Power Station which uses 140.8 m of hydraulic head to power a single 42 MW Francis turbine generator. It was commissioned in May 1980.

Takase Dam
Creating the upper reservoir is the Takase Dam which is a 176 m tall and 362 m long rock-fill embankment dam with a structural volume of 11586000 m3. The Takase Reservoir has a 76200000 m3 capacity of which only 16200000 m3 is active (or "useful") for power generation. The low active capacity of the reservoir is due to the high levels of silt in the Takase River which cause the reservoir to reserve 79 percent of its capacity for this purpose. During operation, the upper reservoir only draws down 10 m.

During periods of high energy demand, water from the Takase Reservoir is released down to the power station. After received by the intake, water initially travels along two 8 m diameter and 2600 m long head-race tunnels. At the terminus of these tunnels, they split into four 330 m long penstocks which drop down a 200 m deep shaft to the underground power station. At the power station, the water operates four 320 MW reversible Francis turbine-generators before being discharged into the lower reservoir, created by the Nanakura Dam.

Nanakura Dam
The Nanakura Dam is a 125 m tall and 340 m long rock-fill embankment dam with a structural volume of 7380000 m3. The reservoir created by the dam, the lower reservoir, has a 32500000 m3 capacity of which 16200000 m3 is active. To protect in against rapid draw-down in water levels (as much as 28 m), the top of the dam is coated in hard rock materials.