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CHINA / National

Cofferdam of Three Gorges demolished in seconds
(Xinhua)
Updated: 2006-06-06 16:11

Fish dispelled away

Before the demolition operation, about 90 percent of fish stocks have been dispelled 500 meters away from the Three Gorges dam area, less than one hour before the explosion of the protective dam, according to ultrasonic monitoring result in the reservoir.

Two dispelling vessels drove in shore at around 3:00 p.m., as all navigation near the world's largest hydro-power project in the middle of Yangtze River was temporarily blocked off for the demolition of the cofferdam.

A total of 191.3 tons of explosives, enough to topple down 400 10-storey buildings, have been installed to demolish the concrete cofferdam, which is located 114 meters away from the just completed Three Gorges Dam, the world's largest concrete reservoir dam. Debris from the explosion will be measured at 180,000 cubic meters.

The detonators were triggered off at about 4:00 p.m. The whole demolition operation lasted around 12 seconds.

Professor Tan Xichang, who took in charge of the fish dispelling operation, said that nine biologists used electric devises to create high-pressure electric pulse in water to dispel fish schools near the cofferdam, including such rare species as Chinese sturgeon, river dolphins and mullet.

"Sturted animals won't return to the area at least for an hour, " said Tan, who referred to the experiment result from the previous trial operation.

Tan explained that the explosion and the accompanied shock waves would evitablely hurt some fish species.

"Our job is to dispel water species away from an area of 700 square meters close to the cofferdam before the designated explosion," said Tan.

Nine biologists from the Water Biological Engineering Institute under the Chinese Academy of Sciences took the two vessels loaded with sonar detectors and electric machineries to carry out the mission.

The team of experts have surveyed location of fish shoals within 600 meters of reaches from the cofferdam before the operation.

Professor Tan said that the dispelling method by using high-pressure electric pulse is China's patented scientific breakthrough, which proved effective in driving away creatures in water without hurting them.

The Three Gorges reservoir has become a natural habitat for many endangered freshwater species, since the cofferdam exerted its role to store water in the middle reaches of China's longest river of Yangtze in 2003.


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