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Chongqing Youchou HPP

Chongqing Youchou HPP, located at Youyang County of Chongqing Municipality, is 73km away from Youyang County Town. The basin area of the Youshui River is 18,530km2, and the catchment area above Youchou dam site is 4,775km2, accounting for 25.8% of the basin area. The project has an installed capacity of 120MW and is categorized as a Rank 2 Large (2) project.
The project is mainly for power generation and concurrently for better navigation and tourism in the reservoir area. The reservoir, a seasonal regulation one, has a NPL of 335.00m, corresponding to 128 million m3 of storage, a total storage of 152 million m3, and an effective storage of 54 million m3.
The project lies in a limestone area characterized by developed karst. The overburden is thin in the dam area, and bedrocks are exposed, mainly of medium weathered rocks. The exposed formation is quite unitary and is of upper group of Middle Cambrian. The reservoir area is of monocline at the southeast wing of Youchou anticline.
The project is mainly composed of a RCC gravity dam, surface overflow bays in the dam body, stilling basins, a dam-type intake, steel-lined reinforced concrete pipes, a powerhouse at dam toe and a switch station.
The retaining structure is a RCC solid gravity dam with a dam axis length of 186.92m, crest elevation of 337.60m and maximum height of 62.60m. The release structure is of five surface overflow bays in the dam body. The maximum discharge capacity of the overflow dam section is 11,100m3/s, and the maximum crest unit discharge 170.8m3/(sm). Energy dissipation by flaring pier combined with hydraulic jump is adopted. Continuous end sills were furnished at the end of stilling basin. The headrace dam section was situated at dam sections 5 and 6 on the left bank, and a manner of taking water before the dam with one pipe for one unit was adoped. The powerhouse was arranged at the toe of dam sections 5 to 7 on the left bank.
The construction of the project was commenced in December 2004, the impoundment was started in October 2008, the two units were put into operation in December 2008 and January 2009, respectively, and the project was basically completed in April 2009.
Main Technical Features and Key Technical Issues:
Firstly, the project area is located on the upper reaches of a narrow river in mountainous area, and the catchment area above the dam site is small. Although the dam height is lower than 70.00m, the peak discharge is great.
Secondly, the reservoir has incomplete seasonal regulation capacity, and the power station mainly takes on the peaking task in the system.
Thirdly, the dam site is narrow topographically, and the conditions for construction site and access arrangement are poor.