The Minamiaiki Dam is a rock-fill embankment dam

Embankment dam

An embankment dam is a massive artificial water barrier. It is typically created by the emplacement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, and a dense, waterproof...

 on the Minamiaiki River in Minamiaiki, Nagano Prefecture

Nagano Prefecture

is a prefecture of Japan located in the Chūbu region of the island of Honshū. The capital is the city of Nagano.- History :Nagano was formerly known as the province of Shinano...

, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. Together with the Ueno Dam

Ueno Dam

Ueno Dam is a concrete gravity dam in the Gunma Prefecture of Japan. The dam serves as the lower reservoir of the Kannagawa Hydropower Plant.-References:...

, it provides water for the Kannagawa Hydropower Plant

Kannagawa Hydropower Plant

The Kannagawa Hydropower Plant is an under construction pumped-storage hydroelectric power plant near Minamiaiki in Nagano Prefecture and Gunma Prefecture, Japan. The power plant utilizes the Minamiaiki River along with an upper and lower reservoir created by two dams, the upper Minamiaiki Dam and...

 owned by the Tokyo Electric Power Company. The Minamiaiki dam is the higher of the two dams. When completed, the station will have the largest power output of any pump-storage power plant

Pumped-storage hydroelectricity

Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps...

 in the world at around 2.82 GW. Since 2005 Unit 1 with installed capacity of 470 kW is in commercial operation. Commercial operation of Unit 2 is planned in 2012, commercial operation of all six units as late as 2020.