In low visibility, helicopters yesterday airdropped bulldozers and excavators to dig a diversion channel for a quake lake in Beichuan county.

Diggers were using a dozen of the heavy machines to divert water from the swelling Tangjiashan lake - formed when a river was blocked after landslides - and prevent flooding downstream.

An 1,800-strong force, including PLA soldiers and armed police each carrying 10 kg of dynamite, are already on the scene. They plan to blast a channel if the excavators are not able to.

"I feel relieved this morning after they reached the area," said Minister of Water Resources Chen Lei, who is in Mianyang city supervising the handling of 35 quake lakes in Sichuan.

Yesterday in Tangjiashan, visibility was only 2 km, much less than the 5 km required for flying helicopters.

Chen hoped the weather relents to allow helicopters deliver more heavy machinery.

"But we can start dealing with the swelling lake now," he said.

Experts estimate that digging a diversion ditch in 10 days, as planned, needs 80 machines, CCTV reported.

The quake lake is 3.2 km upstream from the Beichuan county seat, from which thousands of quake survivors have been evacuated since Wednesday.

Chen told local governments to evaluate the risks if the water overflows.

"We should work out the risk analysis reports as soon as possible because the rain upstream is raising the water level," he said.

The water level rose by almost 2 m on Saturday to 723 m, only 29 m below the lowest part of the barrier.

The risks have been heightened as thunderstorms are forecast for the area today, and after a strong aftershock of 6.4 magnitude hit the area on Sunday.

The lake is holding more than 130 million cu m of water and could cause a devastating flood threatening the lives of 1.3 million residents in adjacent areas if it bursts.

More than 30,000 residents downstream of Tangjiashan lake have been evacuated to higher ground, according to the Mianyang government.

(China Daily May 27, 2008)