Quake lake still poses big threat
Updated: 2008-06-09 08:35
MIANYANG, Sichuan: Water in the Tangjiashan quake lake in Sichuan province was rising Monday despite the increased outflow through a channel.
 A bird's eye view of the Tangjiashan quake lake, where soldiers and engineers widened and deepened the diversion channel on Saturday so that water could flow out more rapidly. Inset: An explosion is triggered in the diversion channel of the lake to clear debris and allow freer flow of water. [China Daily] |
Rescue workers completed widening and deepening the drainage channel early on Saturday.
But "the drainage plus natural leakage from the lake is about 25 cu m per second, while the inflow is 4.6 times greater", said Zhang Ting, head of the Sichuan provincial hydro-meteorological bureau.
"The impact of the inflow on the lake dam is not obvious, though." The water level yesterday evening was 742.11 m above the sea level, still 1.74 m above the sluice, and the volume exceeded 242 million cu m.
"Increasing the outflow of water is critical for the dam's safety," Zhang said. "If the water flows too slowly, the inflow will increase the pressure on the dam. But again, too voluminous an outflow can erode the diversion channel and cause the dam to collapse."
A moderate rainfall around 6:50 pm was followed by a 4.8 magnitude aftershock a minute later yesterday. The tremors that lasted 20 seconds caused massive landslides on the surrounding mountains, a Xinhua reporter at the dam said.
Experts are trying to determine the impact of the aftershock on the dam, though there was no apparent change in the flow of water, the reporter said.
Earlier, military engineers fired missiles to blast the boulders in the channel to increase the flow of water from the lake.
The quake lake was formed when landslides triggered by the May 12 quake blocked the flow of the Jianjiang River.
"Generally speaking, work on the lake's drainage is going well, but it still poses a danger to the hundreds of thousands of people living downstream," said General Ge Zhenfeng, deputy chief of the General Staff of the People's Liberation Army (PLA), who is supervising the project.
"It will take us a few days to eliminate the potential danger," he said.
Rao Xiping, head of the Beichuan hydro-meteorological station, however, said the lake dam was stable as water continued to flow out.
"We have not detected any obvious expansion in the mouth of the sluice or fissures in the dam," said Rao. His station staff and the soldiers working under him have been monitoring the dam day and night.
About 600 armed policemen and soldiers worked for six days and nights to complete the 475-m diversion channel. Some soldiers are still working with 30 bulldozers and excavators to widen and deepen the sluice further.
They have dug a second channel, and are working on a third, for which about 60,000 cu m of earth and boulders had to be cleared, said Liu Yongjian, a PLA officer, in charge of the channel work.
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