The power of Hutiaoxia1 February 2002
The Hutiaoxia hydroelectric project on the Jinshajiang river in China will play an important role in the transfer of electricity across China, as Zenghai Zhao reports
THE JINSHAJIANG river basin in China is estimated to reserve 113,000MW of hydroelectric energy in its main stem and tributaries, accounting for about 17% of the total in China. Hydro power resources in the river are concentrated in the middle and lower reaches which feature an exploitable installed capacity of about 60,000MW and an annual energy output of 274,000GWh.
These middle and lower river reaches are also conducive to development. For example, Hutiaoxia Grand Gorge, on the middle reaches of the river, is renowned for its natural landscapes of snow mountains and gorges, coupled with an enormous potential for hydro power. Topographically, construction of large dams on the river is feasible but conditions for reservoir impoundment are limited.
The live storage of the 11 cascades downstream of Hutiaoxia to Xiangjianba totals less than 20B m3. Generally, the cascades can only achieve seasonal regulation of storage, meaning hydroelectric energy in the Jingshajiang river will not be efficiently utilised. This is unfavourable for paving a competitive role in the power market and highlights the need for a key control reservoir to improve the situation.
Hutiaoxia is one of the most topographically suitable areas for building a high dam and large reservoir which will stand in a key control position among the Jingshajiang river cascades.
The China State Development Planning Commission has approved and initiated a fund for the preparatory works of a hydroelectric project at Hutiaoxia. The task of preparing a pre-feasibility study has been given the to Mid-South Design & Research Institute for Hydroelectric Projects and is is expected to be completed in 2004.
The main purpose of the Hutiaoxia project is to develop hydroelectric energy in the reaches upstream of the Hutiaoxia Gorge. The drainage area at the dam site is 218,400km2, accounting for 46.2% of the total Jinshajiang river basin. The mean annual flow at the dam site is 1410m3/sec and the mean annual runoff is 44.47B m3. Construction of the project will create live storage along a 170km long valley upstream of the Hutiaoxia gorge.
Studies undertaken during the planning stages of the project indicate that a normal pool level (NPL) of 1950m is needed. The created reservoir will have a total storage of 18.34B m3 with a live storage of 13.86B m3 and a storage coefficient of 0.312. The power plant will have a total installed capacity of 2800MW, with a firm output of 998MW and a mean annual energy output of 11,090GWh.
An underground power house arrangement will also be employed. The dam and discharge facilities will be located on the channel, with the underground power house and two power tunnels on the right bank, and power intakes upstream of the dam. The double curvature arch dam will be 216m high and the spillway is designed to have five surface bays and four emptying low level outlets arranged at the middle of the dam.
The total construction period is expected to be 9.25 years, affecting a total population of 65,800 and about 10,420ha of farmland.
The Hutiaoxia reservoir will have a large storage compensation capacity and play a decisive role in developing hydroelectric energy in the Jinshajiang river. Besides these benefits the Hutiaoxia project will be a multi-purpose scheme.
Central Yunnan and Kunming City are relatively well-developed regions of the Yunnan Province and are considered to have the most potential for agricultural development. However, insufficient water supply, due to short rainfall, has limited economic development. Yunnan authorities plan to divert 1.5B m3 of water a year from the Hutiaoxia reservoir to irrigate 80,000ha of farmland in Dali and Chuxiong prefectures and Kunming City, and to supply water for Dali, Chuxiong and Kunming cities.
The areas along the middle and lower reaches of the Yangtze river - downstream of Jinshajiang river - are often threatened by flooding. The Hutiaoxia reservoir will provide a flood control storage capacity of more than 5.2B m3 because of its large storage capacity and key control compensation capacity. Initial calculations have indicated that Hutiaoxia reservoir's flood storage volumes would exceed 4B m3 in the month of July, when severe floods often occur. Construction of the Hutiaoxia dam is also expected to boost the local recreation industry and promote development of the local social economy.
In addition to its own power benefits, it is expected to improve the dependability and stability of power exports and provide compensating regulation to the hydroelectric projects beyond the Jinshajiang basin.
With the rapid growth of China's national economy and an improving socialist market economy system, the programme of transferring electric power from the west to the east is becoming increasingly important. This means that the cost of power from the west has to be competitive. As the cascades on the middle and lower reaches of the Jinshajiang river are a distance from central and east China, the long transmission lines required will be costly.
In order to improve the cost-effectiveness of the transfer programme, the utilisation hours of the transmission line capacity should be extended as far as possible and the exported power should be increased in the dry season. At present, the Three Gorges project is under construction and its first group of units will be put into generation in 2003. Gezhouba hydro power plant has been in service for more than ten years. The Xiluodu and Xiangjiaba hydroelectric projects on the lower reaches of the Jinshajiang river are under feasibility study and expected to be the first group of projects to be developed on the main stem of the river. The power from these plants will mainly be transmitted to central and east China. The development of the Hutiaoxia key control reservoir is expected to substantially improve the benefits and quality of the energy produced by these projects.
Calculations show that without the Hutiaoxia reservoir, the joint operation of the four cascades of Xiluodu, Xiangjiaba, Three Gorges and Gezhouba will have a total firm output of 13,381MW and a total annual energy output of 188,260GWh (considering regulation capacity of the cascades on the Yalong river, a tributary of the Jingshajiang river).
With the Hutiaoxia reservoir however, operation is expected to increase to a firm output of 16,240MW and a total annual energy output of 192,520GWh. This increased energy will be produced during the dry season. In addition, a total of 5220GWh will be transferred from the wet to dry season, and a total of 9580GWh of energy output will be increased in dry seasons. The ratio of average outputs in wet seasons (June through October) and dry seasons (November through May) will rise from 1:0.58 to 1:0.68.
Electric power export is one of the pillar industries of the Yunnan Province. The cascades on the middle reaches of the Jinshajiang river, including Liangjiaren, Liyuan, A'hai, Jin'anqiao, Longkaikou, Ludila and Guanyinyan will form an important power export base for the province. Without the Hutiaoxia reservoir, the cascades will have a total installed capacity of 11,695MW, a total firm output of 3689MW, and a total annual energy output of 72,560GWh. The ratio of average outputs in wet and dry seasons will be 1:0.27.
With the Hutiaoxia reservoir, the cascades will have a firm output of 7676MW, increasing by 108% and a total annual energy output of 76,080GWh. The ratio of average outputs in wet and dry seasons is expected to increase to 1:0.54, thus transferring a large amount of electric energy from the wet to dry seasons.