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Silting in Three Gorges Dam less serious than expected

(Xinhua)
Updated: 2008-08-15 00:00

BEIJING -- The silting problem in China's mega Three Gorges project is much less serious than expected, said a senior dam official here Thursday.

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The volume of silt carried downriver to the dam area has been one third of that before the reservoir was impounded in 2003, said Cao Guangjing, vice general manager of the China Three Gorges Project Corporation (CTGPC), at a press conference here Thursday.

"Four major factors contributed to this," he said.

He noted that the environmental protection programs to control erosion and restore forests along the upper reach of the Yangtze River have worked.

Another reason is that sand is being taken out from the river bed to meet the need of large-scale infrastructure development in the upper reach, he said.

A number of new dams along the river's upper reach and main branches also holds up mud and sand, he said. "Several new dams are under construction in the region. We expect the volume of silt will continue to drop."

These new projects are part of the country's energy development. They are not built simply to reduce silting in the Three Gorges Dam, he added.

"In addition, the incidence of heavy rainfall in the region has been low in the past few years," he said.

Scientists and environmentalists worried that sediment would pile up behind the world's largest dam, 2,309 meters long and 185 meters high, threatening its safety and causing the river bed in this stretch of the river to rise.

"Silting is listed by the developers of the Three Gorges Project as one of the major technical problems that they face. A lot of investment has gone into resolving the problem," said Prof. Wang Jun, a Chinese water control specialist with the Yangtze River Water Resources Committee (YRWRC).

The project engineers have adopted a system to reduce silting by "storing water when it is clear but discharging it when it becomes muddy."

They have built 23 deep-set spillways in the Dam to wash silt by huge water flow during the flood season.

A YRWRC report issued last year said that 470 million tonnes of silt were piled in the reservoir between June 2003 and the end of 2006, less than expected.