Silt accumulation has always been an obstacle in the construction of water dams or reservoirs, and China is a leader in this area of research, said Zhang Chaoran, chief engineer of the China Yangtze Three Gorges Project Development Co., adding that "we believe the Three Gorges dam will provide a good model for future projects."

Experts anticipate that upon completion, the reservoir at Three Gorges could accumulate an average of 530 million tons of silt each year, something which would constitute a major threat to the normal functioning of the hydroelectric plant as a whole.

Scientists have found a solution which consists of discharging the silt through a series of big holes in a strategic part of the dam, said Prof. Ji Xuewu, a prestigious expert in silt research. This solution proved successful in the case of the Sanmenxia Dam in the middle reaches of the Yellow River, restoring it to normal operation.

There will be approximately 23 holes, 7m X 9m in diameter, which will allow the passage of silt during the rainy season, during which the water has a high silt content. During this period, between June and September, the water level will remain at about 145 meters. At the end of October, the dam will start to store water containing less sediments.

Zheng Shouren, chief engineer of the Yangtze River Water Resources Committee and an academician of the Chinese Academy of Engineering, said this solution permits the elimination of the large part of the silt from the upper reaches of the Yangtze River and will therefore guarantee its smooth operation in the long run.

It will also be essential to set up auxiliary silt-cleaning facilities in the area of the Three Gorges in order to oversee the operation of the water route and power station, said the expert.

In order to evaluate real results, the China Yangtze Three Gorges Project Development Co. has funded a 200 million yuan (US$24 million) project in which the Yangtze River Hydroelectric Plant will monitor the real-time situation of silt in the river from now until 2009.

Meanwhile, the Chinese government has allocated a combined sum of 2 billion yuan (US$241 million) into the project in an effort to protect the soil and water in the upper reaches and has also beefed up financial support for an ambitious tree-planting project along the Yangtze River valley. Statistics indicate that soil erosion has been dropping by one percent annually in the area of the Three Gorges, as suggested by the latest monitoring findings.

According to the Yangtze River Water Resources Committee, the State Council has developed a long-term comprehensive scheme to ensure the balanced development of the river, including the construction of a number of water reservoirs.

Two large reservoirs are planned to be built on the turbulent Jinsha river, one of the leading tributaries of the Yangtze's upper reaches. These will steadily reduce silt accumulation by about 46 percent upon completion, said Chief Engineer Zhang Chaoran.

Lu Youmei, general manager of the China Yangtze Three Gorges Project Development Co., said the Three Gorges reservoir will begin storing water gradually, and consequently, the silt treatment will be carried out in different phases in line with theevolving situation in the river.

(Xinhua News Agency November 1, 2002)