Mianyang, China Water poured from a massive lake formed by China's deadly earthquake in a carefully engineered diversion Saturday to ease the threat of flooding for a million people in the sprawling disaster zone.
After two weeks of frantic work by engineers and soldiers, waters flowed into the hurriedly built spillway, but at a rate too slow to cause the lake's level to drop. Military engineers dynamited boulders and soldiers used excavators to deepen the channel to accelerate the flow, state media said.
"The lake was still dangerous despite the draining," the official Xinhua News Agency quoted Minister of Water Resources Chen Lei as saying late Saturday.
The Tangjiashan lake, created when a landslide dammed the Tongkou River, has become a priority for a government, hoping to head off another catastrophe even as it cares for millions left homeless from the May 12 quake that killed nearly 70,000 people. More than
1.3 million people live down river from Tangjiashan, 250,000 of them have been evacuated.
News that the draining had started sent ripples of anticipation through some of the cramped evacuation centers that have sprouted in hilly Sichuan province.
"I wish the water would hurry up so we can go home," said Wang Jing, a 25-year-old nurse, packed with an estimated 9,500 others into the branch campus of the Sichuan Music School in Mianyang city. "My house is fine."
Government experts, quoted by state media, downplayed the threat of imminent flooding, saying Tangjiashan's landslide-created dam should hold. But state media and officials estimated it would be a week before the evacuees could return home, even if all goes well.
"We can't have any more deaths," said Liu Xulong, a propaganda official in Mianyang, the main city in the area. Liu was helping out at the city's Jiuzhou Stadium, a refugee camp where 4,000 people, mostly from devastated Beichuan County, remain nearly four weeks after the quake.
The official death toll crept up Saturday to 69,134 people, with 17,681 still missing.
Engineering the draining of lakes created by landslides is challenging, experts said. They can burst through their unstable sides, causing massive flooding downstream.
A powerful quake in 1786 in another part of Sichuan dammed the Dadu River, which burst through the landslide 10 days later, killing more than 100,000 people, according to research published in 2005 in the scientific journal Geomorphology.
The Tangjiashan lake is the largest of more than 30 created by last month's quake, and draining it safely will depend on controlling the outflow of water, said David Petley, a professor of geography at Britain's Durham University.
If water flows too slowly from the lake, pressure will continue to build up behind the dam. If the flow is too fast, it could erode the 1,550-foot drainage channel constructed by the government, creating a steeper, narrower course that would pull in water more rapidly, potentially causing the dam to collapse, Petley said.
"The Chinese government have responded to this in an impressive manner," said Petley. "I don't believe that much more could have been done. Unfortunately the scale of the problem means that management is very challenging."