World's Largest Dam Withstands Yangtze Floodwaters

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Last updated at: (Beijing Time) Thursday, September 05, 2002

World's Largest Dam Withstands Yangtze Floodwaters

The gigantic Three Gorges Dam, the world's largest, has survived unscathed China's battle this summer against what was nearly its worst ever floods on its longest river, the Yangtze.

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The gigantic Three Gorges Dam, the world's largest, has survived unscathed China's battle this summer against what was nearly its worst ever floods on its longest river, the Yangtze.

The surging floodwaters, having shown their muscle and rivaled those of 1998, are now much subdued as they flow down to the sea, and the river now running sedately past the dam has peaked.

"Having been severely tested by the floods -- the most authoritative quality controller - the completed sections of the dam have made people rest assured," said the Austrian expert Robert, also general supervisor of engineering for the Three Gorges Project, the country's largest water conservancy project on the middle reaches of the Yangtze River.

Situated in the western part of Yichang area in central China's Hubei province, the project consists of a 2,309 meter-long by 185 meter-tall dam and 26 generating units with a combined capacity of18.2 million kilowatts.

Upon completion in 2009, the project will be able to generate 84.7 billion kilowatts of electric power annually. Its permanent locks will allow ships of more than 10,000 DWT (dead weight tonnage) to pass.

By the end of August, approximately 70 percent of the dam had been completed. According to the design plan, the dam is built to withstand the heaviest flood in a period of 10,000 years.

Since April this year, lingering rains in the upper Yangtze reaches and in the mammoth Three Gorges reservoir area caused river levels to keep rising, even above those of the 1998 floods, in the cities of Yichang, Shashi, and Hankou, part of the provincial capital of Hubei.

According to meteorologists, this season's drastic weather changes and high water levels of the Yangtze had seldom occurred in the past 50 years.

During the flooding, the cofferdams were demolished to test the dam's leak proof capability, and results proved to be very satisfactory.

The cofferdams had been built to allow normal navigation in the course of the 17-year construction period. When the main streams of the Yangtze River were blocked on November 8, 1997, cofferdams were constructed on the river's left bank to form a pit in which the dam and a powerhouse were built, experts said.

In mid May, water flows reached 21,000 cubic meters per second at the dam area, and rose above the warning level of 30,000 cubic meters per second on May 23. The raging current meant that a navigation limit was imposed on the water diversion canal, which is 3.7 km long and 350 meters wide and serves as the only navigable channel for ships and boats in a five-year period from 1997 to 2002. Small vessels had to try the alternative of passing through the temporary shiplock.

The flood crest arrived in the dam area on the early morning ofAug. 16, when flows increased to 45,000 cubic meters per second onthe canal, and navigation was suspended both on the canal and at the temporary shiplock.

Along with perpetual heavy rains and rising river waters, natural disasters like landslides, mud-rock flows and thunderstorms occurred occasionally in the area. But the dam and related constructions remained intact thanks to their successful design and careful anti-disaster measures, according to sources.

"The dam's design is absolutely safe, and when it is completely finished, it will be able to control floods effectively," said Zhang Chaoran, general engineer of the Three Gorges Development Company.

As soon as the flood season ends, the river will be dammed for a second time to pave the way for next year's three scheduled goals -- water storage, navigation and power generation, according to Zhang.

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