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, with the first generator commissioned in 1988. Its 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.
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.