Race against the clock

PUBLISHED : Friday, 06 June, 2008, 12:00am
UPDATED : Friday, 06 June, 2008, 12:00am

The quake lake in Tangjiashan, the largest of the 35 lakes formed after the May 12 earthquake, threatens to cause another catastrophe. It is hoped that a controlled collapse of the dam will take place once water starts flowing through a channel dug by soldiers and police.

The lake:

Amount of water 210m cubic metres

Catchment area 3,350 sq km

Water level 738.8 metres

The dam

Width 800 metres

Thickness 611 metres

Height up to 740 metres

The channel

Length 500 metres

Maximum width 50 metres

Maximum depth 11 metres

By 5pm yesterday, water level 1.2 metres below drainage channel

Completed by more than 600 armed police and soldiers on Sunday

Engineers hope that when water starts flowing through channel - after expected rainfall - flow will widen channel and lead to collapse of one-third of dam and emptying of lake

Channel 11 metres deep and a minimum of 7 metres wide, becoming larger downstream

The dangers

Aftershocks: experts say tremor measuring 6 or more on Richter scale could collapse temporary dam and unleash deadly torrent

Rainfall: every 2mm of rainfall leads to 1 metre rise in level of lake, and heavy rainfall forecast for next few days. Sudden rise could increase pressure on dam

Beichuan county 3.2km downstream 150,000 evacuated