The Okutadami Dam is a concrete gravity 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...

, 26 km (16 mi) east of Uonuma

Uonuma, Niigata

is a city located in Niigata Prefecture, Japan. It has an area of 946.93 km² and a population of 41,894 .It is famous for its rice – the koshihikari rice grown in Uonuma is the most sought-after and most expensive rice in Japan...

 on the border of Niigata

Niigata Prefecture

is a prefecture of Japan located on the island of Honshū on the coast of the Sea of Japan. The capital is the city of Niigata. The name "Niigata" literally means "new lagoon".- History :...

 and 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....

s, 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 station in Japan. The dam also forms the second largest reservoir in Japan, next to that of the Tokuyama Dam

Tokuyama Dam

The is an embankment dam near Ibigawa, Ibi District, Gifu Prefecture in Japan. The dam was completed in 2008 and will support a 153 MW hydroelectric power station that is expected to be complete in 2014. The dam was originally intended to withhold the upper reservoir of a 400 MW...

.

Background

Construction on the dam began and its original 200 MW power station was commissioned 2 December 1960. The rest of the project was complete in 1961. Between 1999 and 2003, the power station was expanded, adding an additional 360 MW in installed capacity. In addition, a 2.7 MW generator was added to ensure a flow of 2.5 m3/s downstream for environmental purposes. Along with the same power plant upgrade, a second 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...

-generator was added to the 83 m (272 ft) tall Otori Dam

Otori Dam

The is a concrete arch-gravity dam on the Tadami River, southwest of Tadami in Fukushima Prefecture, 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-generators...

's power station downstream at 37°12′53"N 139°12′50"E. This generator has a 87 MW capacity in addition to the existing 95 MW unit, for an installed capacity of 182 MW.

Design

The Okutadami Dam is a 157 m (515 ft) tall and 475 m (1,558 ft) long concrete gravity dam with a structural volume of 1636000 m³ (2,139,807 cu yd). Sitting at the head of a 595 km² (230 sq mi) 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...

, the dam creates a 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...

 with a 601000000 cubic metre capacity of which 458000000 cubic metre is active (or "useful") storage. The reservoir has a surface area of 1150 ha (2,842 acre). The power station is underground and located on the right bank of the river next to the dam's abutment. It consists of two underground caverns, one for the original power station and another adjacent for the expansion. After being received by the dam's intake, water supplied to the original power plant travels down three penstock

Penstock

A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydraulic turbines and sewerage systems. It is a term that has been inherited from the technology of wooden watermills....

s 185–189 m (607–620.1 ft) in length before reaching an individual 200 MW Francis turbine

Francis turbine

The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts....

-generator. The 200 MW Francis turbine-generator receives water via a 280 m (919 ft) long penstock. After water is processed through the generators, its travels down two tailrace tunnels before being discharged over 3 km (2 mi) downstream at the upstream edge of the Otori Reservoir.