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
CountryJapan
Location Totsukawa
Coordinates 34°7′4″N135°49′16″E / 34.11778°N 135.82111°E / 34.11778; 135.82111 Coordinates: 34°7′4″N135°49′16″E / 34.11778°N 135.82111°E / 34.11778; 135.82111
StatusOperational
Construction began1971
Opening date1980
Owner(s) Kansai Electric Power Company (KEPCO)
Upper reservoir
CreatesSeto Reservoir
Total capacity1,685,000,000 m3 (1,366,000 acre⋅ft)
Lower reservoir
CreatesAsahi Reservoir
Total capacity1,692,000,000 m3 (1,372,000 acre⋅ft)
Power Station
Hydraulic head 505 m (1,657 ft) [1]
Pump-generators6 x 201 MW (270,000 hp) Francis pump-turbines [2]
Installed capacity 1,206 MW (1,617,000 hp)

The Okuyoshino Pumped Storage Power Station (奥吉野発電所) is located 15 kilometres (9.3 mi) north of Totsukawa in Nara Prefecture, Japan. Using the pumped-storage hydroelectric method, the power plant has an installed capacity of 1,206 megawatts (1,617,000 hp). 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]

Nara Prefecture Prefecture of Japan

Nara Prefecture is a prefecture in the Kansai region of Japan. The capital is the city of Nara. Nara Prefecture has the distinction of having more UNESCO World Heritage Listings than any other prefecture.

Sediment Particulate solid matter that is deposited on the surface of land

Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation and if buried, may eventually become sandstone and siltstone.

Turbidity The cloudiness of a fluid caused by large numbers of particles that are generally invisible to the naked eye

Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.

Contents

Design and operation

Intake and outflow structure for the power station, located on the northern edge of Asahi Reservoir Asahi Dam (Totsukawa, Nara) intake.jpg
Intake and outflow structure for the power station, located on the northern edge of Asahi Reservoir

Asahi Dam

The lower reservoir is created by the Asahi Dam which is a 86.1 metres (282 ft) tall and 199.41 metres (654.2 ft) long arch dam on the Asahi River of the Shingu River system. Its catchment area covers an area of 39.2 square kilometres (15.1 sq mi) and the surface of the reservoir covers 52 hectares (130 acres). The lower reservoir's storage capacity is 1,685,000,000 cubic metres (1,366,000 acre⋅ft) of which 1,250,000,000 cubic metres (1,010,000 acre⋅ft) is active (or usable) for pumping up to the lower reservoir.

Arch dam solid dam made of concrete that is curved upstream in plan

An arch dam is a concrete dam that is curved upstream in plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, compressing and strengthening the structure as it pushes into its foundation or abutments. An arch dam is most suitable for narrow canyons or gorges with steep walls of stable rock to support the structure and stresses. Since they are thinner than any other dam type, they require much less construction material, making them economical and practical in remote areas.

Asahi River river in Japan

The Asahi River is a river in Okayama Prefecture, Japan.

Drainage basin Area of land where precipitation collects and drains off into a common outlet

A drainage basin is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water. The drainage basin includes all the surface water from rain runoff, snowmelt, and nearby streams that run downslope towards the shared outlet, as well as the groundwater underneath the earth's surface. Drainage basins connect into other drainage basins at lower elevations in a hierarchical pattern, with smaller sub-drainage basins, which in turn drain into another common outlet.

Seto Dam

Creating the upper reservoir in a valley above the lower is the Seto Dam. It is a 110.5-metre (363 ft) tall and 342.8-metre (1,125 ft) long rock-fill embankment dam with 3,740,000 cubic metres (4,890,000 cu yd) of fill. Its catchment area covers a much smaller area of 2.9 square kilometres (1.1 sq mi) and its surface covers 52 hectares (130 acres). The upper reservoir has a storage capacity of 1,692,000,000 cubic metres (1,372,000 acre⋅ft) of which 1,250,000,000 cubic metres (1,010,000 acre⋅ft) is useful for power generation down at the power station. [3] [4] [5]

Embankment dam large artificial dam

An embankment dam is a large artificial dam. It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay, or rock. It has a semi-pervious waterproof natural covering for its surface and a dense, impervious core. This makes such a dam impervious to surface or seepage erosion. Such a dam is composed of fragmented independent material particles. The friction and interaction of particles binds the particles together into a stable mass rather than by the use of a cementing substance.

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 megawatts (270,000 hp) 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 metres (1,657 ft). [3]

Hydraulic head Specific measurement of liquid pressure above a geodetic datum

Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum.

Sediment bypass tunnel

To allow sediment to pass the lower Seto Reservoir, a bypass tunnel was constructed. The tunnel itself is hood-shaped and 2,350 metres (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 metres (44 ft) tall and 45 metres (148 ft) long weir located 2.5 metres (8 ft 2 in) 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 cubic metres per second (4,900 cu ft/s) of water and discharges downstream of the Seto Dam. [3]

Weir barrier across a river designed to alter its flow characteristics

A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. There are many designs of weir, but commonly water flows freely over the top of the weir crest before cascading down to a lower level.

See also

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References

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