The is a concrete arch-gravity dam

Arch-gravity dam

An arch-gravity dam, curved-gravity dam or arched dam is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam...

 on the Tadami River

Tadami River

The is a major tributary of the Agano River in Japan. Its basin covers and its main stem is extensively regulated and developed for hydroelectric power...

, 17 km (11 mi) southwest of Tadami

Tadami, Fukushima

is a town located in Minamiaizu District, Fukushima, Japan. It is famous locally for its own Snow Festival, where huge sculptures and replicas of monuments are cut out of Tadami's abundant snow....

 in Fukushima Prefecture

Fukushima Prefecture

is a prefecture of Japan located in the Tōhoku region on the island of Honshu. The capital is the city of Fukushima.-History:Until the Meiji Restoration, the area of Fukushima prefecture was known as Mutsu Province....

, Japan. The primary purpose of the dam is hydroelectric power generation and it supports a 182 MW power station. The power station contains two Kaplan turbine

Kaplan turbine

The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was developed in 1913 by the Austrian professor Viktor Kaplan, who combined automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and...

-generators. Unit 1 (95 MW) was commissioned on 20 November 1963 while Unit 2 (87 MW) was commissioned on 7 June 2003 as part of a power plant expansion project that included an additional 200 MW generator at Okutadami Dam

Okutadami Dam

The Okutadami Dam is a concrete gravity dam on the Tadami River, east of Uonuma on the border of Niigata and Fukushima Prefectures, Japan. The primary purpose of the dam is hydroelectric power generation and it supports a 560 MW power station which is the largest conventional hydroelectric power...

 upstream. The dam is 83 m (272 ft) tall and 188 m (617 ft) long. Its reservoir

Reservoir

A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...

 has a 15800000 cubic metre capacity of which 5000000 cubic metre is active (or "useful") for power generation. The reservoir has a catchment area

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 of 656.9 km² (254 sq mi) and surface area of 89 ha (220 acre). Of the two generators, Unit 1 has a maximum effective hydraulic head

Hydraulic head

Hydraulic head or piezometric head is a specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer...

 of 50.8 m (167 ft) and Unit 2 is afforded 48.1 m (158 ft). The design flood discharge of the dam is 2200 m3/s and its service spillway is controlled by three tainter gate

Tainter gate

The Tainter gate is a type of radial arm floodgate used in dams and canal locks to control water flow. It is named for Wisconsin structural engineer Jeremiah Burnham Tainter....

s.