A BRIEF INTRODUCTION TO DACHAOSHAN HYDROPOWER PROJECT

　　The Lancang River flows through the west of Yunnan Province and then runs southwards.Its downstream reaches out of China are called the Mekong River. It is 1240km long with a total water drop of 1780m within the boundaries of Yunnan Province of China. Its mean annual discharge is 2180m³/s, hydroenergy potential is 25500MW and exploitable hydropower capacity is 23480MW. The cascade development of hydropower in the Lancang river basin is noted as a rare ricb hydropower mine for its prominent natural advantages in abundant and well-distributed runoff, large drops and less flooding losses of the reservoirs.

　　The Dachaoshan Hydropower Station located on the Lancang River at the border between Yun Xian County of Lincang Prefecture and Jindong Yi Autonomous County of Simao Prefecture in Yunnan Province is the downstream cascade hydropower station next to the Manwan Hydropower Station according to the planning of cascade hydropower developments along the medium and lower reaches of the Lancang River. Its dam site is 131km away from the completed Manwan Hydropower Station, and 600km away from Kunming City. the capital of Yunnan Province.

　　The Dachaoshan Hydropower Project is constructed solely for the power generation purpose. The water reservoir has its normal storage water level at EL. 899m and its total storage capacity of 940 million m³. It will Hood 12385mu(1mu=0.0667 hectares) of farm land, and affect 6100 people, of which, however, only 84 people are living below the proposed flooding line. The total installed capacity and firm capacity of the Project are 1350MW and 363.1MW respectively. Tke mean annual energy output is 5931 GWh and will reach 7021 GWh after the completion of its upsffeam reservoir for the Xiaowan Hydropower Station.

　　The Dachaoshan Hydropower Project consists of a roller compacted concrete (RCC) gravity dam, a right bank underground powerhouse and long tailrace tunnels.

　　The RCC gravity dam has a maximum height of 111m with its crest level at E1906m, and a total crest length of 460.4m, including 254m of dam section in the river bed. The designed concrete volume of the dam is 1.1267 million m³, out of which the RCC concrete volume is 756600 m³. The dam has five overflow crest outlets, three flood and sand discharge bottom outlets, and a sand-flushing bottom outlet.

　　The underground powerhouse system is composed of a main powerhouse, an auxiliary plant, a main transformer room, a bus bar gallery and other appurtenant chambers. The power tunnel system consists of pressure power tunnels, draft-tube tunnels, tailrace surge chambers and long tailrace tunnels. One penstock to one unit system is adopted, with six pressure power tunnels in total. The tail water goes into two long tailrace tunnels from the draft-tube tunnels through long-gallery-type tailrace surge chambers, and then empties into the Lancang River downstream. Three draft-tube tunnels share one tailrace surge chamber and one tailrace tunnel. forming a layout of two groups of three generating units, one chamber and one tailrace tunnel.

　　The river closure for the Dachaoshan Hydropower Project was carried out at one time. The river diversion is executed by means of the diversion tunnel in dry seasons. and the diversion tunnel jointly with overtopping of the cofferdams and the foundation pit in flood seasons. A diversion tunnel is arranged at the left bank. A RCC overtopping arch cofferdam is placed upstream, and a roller compacted concrete-faced earth-rockfill overtopping cofferdam is placed downstream.

Longitudinal section of power generation system

Typical cross-section of overflow dam section

Typical cross-section of dam

　　The Dachaoshan Hydropower Project started its initial construction preparations in 1993, was approved by the State as a state project to be ready for construction in 1994, and was approved to start construction on August 4, 1997. The river closore was completed successfully on November 101997. The first generating unit is scheduled to be put into operation in 2001, then three generating units shall be put into operation in 2002, and the last two generating units in 2003.

　　The Project is designed jointly by Beijing Hydroelectric Investigation Design & Research Institute and Kunming Hydroelectric Investigation Design & Research Institute.

Three-dimensional view of underground chambers

　　The Owner of the Project. Yunnan Dachaoshan Hydropower Co., Ltd. is a standardized large corporation set up based on Corporation Law of the People's Republic of China. The Corporation was established jointly by State Development and Investment Corporation, Yunnan Hongta Industrial Co., Ltd., Yunnan Development and Investment Corporation, and Yunnan Electric Power Group Co.,Ltd, in the share proponion of 5:3:1:1 in November, 1994. The registered capital of the Corporation is RMBY 1.77 billion. As an independent power plant, the Corporation is responsible for execution of integrated management of construction and operation of the Dachaoshan Hydropower Station, and has already signed an agreement for purchasing and selling electricity with Yunnan Electric Power Group Co.,Ltd, The Corporation exercises the general manager responsibility system under the leadership of the Board of Directors. In the construction of the Project, the project legal person responsibility system, competitive bidding system and engineering supervision system are implemented in an all-round way.

　　The total investment of the Project is RMB￥8.87 billion.

　　The main project data are given in the following table.