The Imaichi Dam (今市ダム) is a concrete gravity dam on the Togawa River located 4 kilometres (2.5 mi) west of Nikkō in Tochigi Prefecture, Japan. The dam serves as the lower reservoir for the 1,050 megawatts (1,410,000 hp) Imaichi Pumped Storage Power Station, while the Kuriyama Dam forms the upper. It is owned by TEPCO and was constructed between 1979 and 1986. The reservoir can store 9,100,000 cubic metres (7,400 acre⋅ft) of water. Of that storage volume, 6,200,000 cubic metres (5,000 acre⋅ft) can be used for power generation.

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Imaichi Dam
Location of Imaichi Dam in Japan
Country	Japan
Location	Nikkō, Tochigi Prefecture
Coordinates	36°49′31″N 139°39′58″E
Status	Operational
Construction began	1979
Opening date	1986
Owner(s)	TEPCO
Dam and spillways
Type of dam	Gravity, concrete
Impounds	Togawa River
Height	75.5 m (248 ft)
Length	177 m (581 ft)
Elevation at crest	551 m (1,808 ft)
Dam volume	192,000 m3 (251,127 cu yd)
Spillway capacity	1,620 m3/s (57,210 cu ft/s)
Reservoir
Total capacity	9,100,000 m3 (7,377 acre⋅ft)
Active capacity	6,200,000 m3 (5,026 acre⋅ft)
Catchment area	14.8 km2 (6 sq mi)
Surface area	380 m2 (0 acres)
Normal elevation	548.5 m (1,800 ft)
Power Station
Commission date	1988
Hydraulic head	524 m (1,719 ft)
Turbines	3 x 350 MW (470,000 hp) Francis pump turbines
Installed capacity	1,050 MW (1,410,000 hp)

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The power plant operates using the pumped storage hydroelectric method. During periods of high electricity demand, water is sent from the upper Kuriyama Reservoir to the power plant which contains 3 x 350 megawatts (470,000 hp) Francis pump turbines. Water discharged from the power plant then enters the Imaichi Reservoir. When demand is low, the pump-generators reverse mode and pump water from the lower reservoir back up to the upper. The process repeats as needed.^[1][2]

• List of dams and reservoirs in Japan