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Wujiangdu HPP

Wujiangdu HPP, located in Zunyi City of Guizhou Province, has an arch gravity dam (165m high), and an installed capacity of 1130MW (including extension). It is the first large-scale hydropower project built in karst areas in China and was awarded national first prize for scientific and technological progress, and national gold prizes for excellent engineering investigation and for excellent engineering design.

The project is mainly for power generation and concurrently for flood control and navigation. Meanwhile, it plays the role of peaking and frequency modulation for Guizhou grid. It features in a NPL of 760.00m, a total storage of 2.14 billion m3, an installed capacity of 630MW, and an annual energy output of 3,340 GWh. The main structures were designed against 500-year flood and checked aginst 5000-year flood. Design flood discharge is 18360m3/s, and check flood discharge 21350m3/s. The project was commenced in 1970 and completed in December 1983, with all the three units being put into operation in March 1982.
Main Technical Features:
Wujiangdu HPP is a large-scale hydropower project completed in 1980s and has the following main technical features:
(1) The dam site lies in a V-shaped narrow valley with symmetrical high mountains and high slopes on both banks. The water surface is 50~70m wide in dry season and 100~120m wide in flood season. High water level and dry water level vary greatly, normally 35m and maximum 47m. Consequently, multilayer overlapping arrangement was adopted for the structures of dam, spillway, powerhouse, auxiliary plant and switch station, and the maximum overlapping height up to 98m. To fully utilize the thick water cushion on the downstream river bed in flood season, the outlets of release structures are stagger so as to make the nappe diffuse longitudinally along the river bed and keep it away from the scouring-prone shale.
(2) The project is in a karst developed area, so leakage control of dam foundation and both banks is a critical issue. Through scientific verification, the designer adopted a measure of connecting HP cement grout curtain to upper sandy shale confining layer and thus successfully solved the problem of reservoir leakage. In the scope of dam body the curtain was aligned parallel to the dam axis and was formed straightly downward from the foundation surface in the limestone of Yulong Mountain. As for the two banks, two major faults brought about shale offset and created leakage passages. Therefore, the impervious curtains on both banks bend toward upstream from the dam abutments and extend into the mountains. The dam foundation curtain has a total length of 1020m, deepest point at 200m below the riverbed, a total area of 189,000 m2, and a total length of grout holes about 190,000m. Non-flushing HP cement grouting was adopted, with maximum grouting pressure 6MPa and low limit of pressure no less than 2MPa. A 93m-long concrete diaphragm wall was built at El. 640-670m in the left-bank abutment bedrock adjacent to the dam foundation surface. A 242m-long cement grout curtain was provided along the lower side line and on both sides of the powerhouse. The big karst caves in riverbed were filled with concrete after being cleared, and those in deep were subject to HP grouting. After the treatment, the daily seepage from the dam foundation and both banks was 20m3 at a service head of 120m, and the actual uplift pressure was far less than the design value. The successful construction of the project has offered valuable experience for high dam building in karst areas.
(3) High unit discharge and high velocity for flood release. Vent grooves are commonly used for aeration and corrosion reduction of flood release structures with high-velocity flow. Aeration and corrosion reduction facilities were provided at eight points of the flood-release structures, i.e., ogee sections and their starting points of ski-jump spillways on the left and right banks, starting point of ogee section of left flood-release tunnel, inclined section and straight section of right flood-release tunnel, starting point of ogee section of surface bay spillway. Basically there is no cavitation at all the points during the operation.
(4) Design of an arch aqueduct with large discharge, high velocity and big span. A 72m-long arch aqueduct was arranged at the end of right flood-release tunnel, with a discharge up to 2100m3/s and a velocity of 35m/s.
(5) Equi-strength design principle employed for dam stability. Integral arch gravity dam was adopted to make the anti-sliding safety coefficients of riverbed and abutments of both banks approximately equal. Monolithic stability gravity dam for the upper dam body was employed for water retaining because of the poor foundation conditions, and thus the problem of building high dam in inhomogeneous foundation was solved according to the local conditions.
(6) Technological design of large artificial aggregate production system (annual output 2.00 million tons).
(7) 40m-high upper concrete arch cofferdam was built under flow condition by the technology of underwater concrete placement at one time.
(8) The project was awarded first prize for national scientific and technological progress, national gold prizes for excellent engineering investigation and for excellent engineering design, and national silver prize for high-quality.
Extension of Wujiangdu HPP was conducted at the end of last century. Two new units were installed (500MW in total), and the powerhouse for the extension project was an underground one on the left bank. The extension project was commenced in November 2000, the two new units were put into operation in August and November 2003, respectively, and the capacity of the original three units was increased by 120MW from 210MW. So far the total installed capacity of Wujiangdu Hydropower Station reached 1250MW, and the station has strongly supported the power and basin development of Guizhou Province.