Blasting of temporary dam all set

PUBLISHED : Tuesday, 06 June, 2006, 12:00am
UPDATED : Tuesday, 06 June, 2006, 12:00am

192 tonnes of dynamite will destroy the top 30 metres today

The top of the temporary 140-metre-high cofferdam built to hold water and generate power for the construction of the Three Gorges Dam will be demolished today.

About 192 tonnes of dynamite - enough to blow up 400 10-storey buildings - had been put in place to bring down the top 30 metres of the cofferdam, Xinhua reported.

The remaining 110 metres of the 580-metre-long cofferdam will be retained as a protective structure for the world's largest dam.

The explosives will be set off at 4pm, with 971 consecutive explosions around the cofferdam, taking about 12 seconds to complete. Debris will fall into the river.

The main dam would be able to stand the shock from the blast, according to Yu Ying, a technical expert from the Gezhouba Dam Group, which is in charge of the massive demolition in Hubei province .

Two layers of 'bubble curtains', resembling air bags in cars, would absorb the shock waves and pressure generated from the blast to reduce their energy by 50 to 70 per cent before they arrived at the main dam, Xinhua quoted Mr Yu as saying.

Experts have also piled sandbags and installed a steel cage around the top of the cofferdam to catch flying rubble.

According to the Xinhua report, the explosives to be used are environmentally friendly and do not contain any toxins, so the Yangtze would not be polluted by the operation.

The cofferdam was erected in 2003 to hold reservoir water and generate power for construction crews.

Construction of the Three Gorges Dam was completed on May 20, two years ahead of schedule.

It will now begin to hold water for flood-control purposes, with the water level behind the dam raised from its current 139 metres to 156 metres by October. Its first generators are expected to come on line next year.

The dam has been a controversial project that drew criticism from environmentalists for altering the natural landscape of the area and relocating more than 1 million inhabitants.