Tamahara Dam

Tanbara Dam is a rock-fill embankment dam impounding the headwaters of the Hotchi River, a Tone River tributary in Gunma Prefecture of Japan. It is located 14 kilometres north of Numata. It creates the upper reservoir for the 1,200 megawatts Tamahara Pumped Storage Power Station. Construction began in 1973 and the dam was complete in 1981 while the power station was commissioned in 1986. It is 116 metres tall and withholds a reservoir with a storage capacity of 14,800,000 m³. Of that capacity, 13,000,000 cubic metres is active for power generation. The lower reservoir for the pumped-storage power station is created by the Fujiwara Dam, located 4 km to the northwest on another Tone River tributary. Power is generated during periods of high energy demand and pumping occurs during times when energy demand is low such as at night. The power station contains four 300 megawatts reversible Francis turbine pump-generators which serve to both pump water and generate electricity. The upper Tamahara Reservoir is at an elevation of 1,177 metres and the lower Fujiwara Reservoir is at 651 metres which affords the power station an effective hydraulic head of 518 metres. When pumping, the pump-generators can move up to 210 cubic metres per second of water and when generating, they discharge up to 276 cubic metres per second. ()