Okuyoshino Pumped Storage Power Station

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Okuyoshino Pumped Storage Power Station
Asahi Dam (Totsukawa, Nara).jpg
The Asahi Dam which forms the lower reservoir
Okuyoshino Pumped Storage Power Station is located in Japan
Okuyoshino Pumped Storage Power Station
Location of Okuyoshino Pumped Storage Power Station
Country Japan
Location Totsukawa
Coordinates 34°7′4″N 135°49′16″E / 34.11778°N 135.82111°E / 34.11778; 135.82111Coordinates: 34°7′4″N 135°49′16″E / 34.11778°N 135.82111°E / 34.11778; 135.82111
Status Operational
Construction began 1971
Commission date 1980
Owner(s) Kansai Electric Power Company (KEPCO)
Pumped-storage power station
Upper reservoir Seto Reservoir
Upper res. capacity 1,685,000,000 m3 (1,366,052 acre·ft)
Lower reservoir Asahi Reservoir
Lower res. capacity 1,692,000,000 m3 (1,371,727 acre·ft)
Hydraulic head 505 m (1,657 ft)[1]
Pump-generators 6 x 201 MW Francis pump-turbines[2]
Power generation
Nameplate capacity 1,206 MW

The Okuyoshino Pumped Storage Power Station (奥吉野発電所) is located 15 km (9 mi) north of Totsukawa in Nara Prefecture, Japan. Using the pumped-storage hydroelectric method, the power plant has an installed capacity of 1,206 MW. To accomplish power generation, the power station shifts water between two reservoirs, the lower Asahi Reservoir and the upper Seto Reservoir. Construction on both the Asahi and Seto Dams began in 1971 and was complete in 1978. The power station was commissioned in 1980. Due to heavy sediment and turbidity in the Seto Reservoir, caused by logging and landslides upstream, a sediment bypass tunnel was constructed between 1992 and 1998.[3]

Design and operation[edit]

Intake and outflow structure for the power station, located on the northern edge of Asahi Reservoir

The lower reservoir is created by the Asahi Dam which is a 86.1 m (282 ft) tall and 199.41 m (654 ft) long arch dam on the Asahi River of the Shingu River system. Its catchment area covers an area of 39.2 km2 (15 sq mi) and the surface of the reservoir covers 52 ha (128 acres). The lower reservoir's storage capacity is 1,685,000,000 m3 (1,366,052 acre·ft) of which 1,250,000,000 m3 (1,013,391 acre·ft) is active (or usable) for pumping up to the lower reservoir. Creating the upper reservoir in a valley above the lower is the Seto Dam. It is a 110.5 m (363 ft) tall and 342.8 m (1,125 ft) long rock-fill embankment dam with 3,740,000 m3 (4,891,735 cu yd) of fill. Its catchment area covers a much smaller area of 2.9 km2 (1 sq mi) and its surface covers 52 ha (128 acres). The upper reservoir has a storage capacity of 1,692,000,000 m3 (1,371,727 acre·ft) of which 1,250,000,000 m3 (1,013,391 acre·ft) is useful for power generation down at the power station.[3][4][5]

During periods of low demand when electricity is cheap, the power station pumps water from the lower reservoir to the upper. When energy demand is high, the water is released back down to the power station through the same tunnels to generate electricity. Additionally, the six 201 MW Francis pump-turbine-generators are reversible and serve to both pump water and generate electricity.[6] The pumping and generation process is repeated as needed and although the power station consumes more electricity pumping than it does generating, pumping occurs when electricity is cheap and generating when it is expensive; making the power station economical. The difference in elevation between the two reservoirs affords a hydraulic head of 505 m (1,657 ft).[3]

Sediment bypass tunnel[edit]

To allow sediment to pass the lower Seto Reservoir, a bypass tunnel was constructed. The tunnel itself is hood-shaped and 2,350 m (7,710 ft) long. It passes through rock on the north side of the reservoir. The intake for the tunnel is controlled by a 13.5 m (44 ft) tall and 45 m (148 ft) long weir located 2.5 m (8 ft) upstream of the dam. The weir is used to divert sediment-laden river water into the tunnel or to let it flow into the reservoir. The tunnel can divert a maximum of 140 m3/s (4,944 cu ft/s) of water and discharges downstream of the Seto Dam.[3]

See also[edit]


  1. ^ "Yoshino Power Plant" (in Japanese). Tourism Promotion Division Totsukawa village office. Retrieved 26 January 2012. 
  2. ^ "Case Study 05-01: Water Quality – Asahi Dam, Japan / IEA Hydropower Implementing Agreement Annex VIII". Hydropower Good Practices: Environmental Mitigation Measures and Benefits. IEA Hydro. Retrieved 26 January 2012. 
  3. ^ a b c d "Asahi Dam". BP Sample. IEA Hydro. September 2005. Retrieved 26 January 2012. 
  4. ^ "Asahi Dam" (in Japanese). Dam Net. Retrieved 26 January 2012. 
  5. ^ "Seto Dam" (in Japanese). Dam Net. Retrieved 26 January 2012. 
  6. ^ "Hydro Generators". Toshiba. Retrieved 26 January 2012.