STORY HIGHLIGHTS
- Drainage of Tangjiashan "quake lake" in Sichuan Province has gone smoothly since Saturday.
- Engineering soldiers have fired missiles to blast boulders in a man-made sluice channel.
- The water level in the lake stood at 741.70 meters above the sea level at 9 a.m. on Sunday.
MIANYANG, Sichuan Province, June 8 (Xinhua) -- The water level of the Tangjiashan "quake lake" in southwest China was continuing to rise dangerously on Sunday despite the operation of a manmade drainage channel since Saturday morning.
"The drainage plus natural leakage of the lake is about 25 cubic meters per second, while the inflow is 4.6 times more than that, but its impact on the lake dam is not obvious," said Zhang Ting, head of the Sichuan provincial hydro-meteorological bureau.
The water level in the lake stood at 741.82 meters above sea level at midday on Sunday, still 1.45 meters higher than the sluice, and the lake's volume exceeded 240 million cubic meters.
"Controlling the lake outflow is critical for the dam's safety," Zhang. "If the water flows out too slowly, the accumulating inflow will increase pressure on the barrier, but too strong an outflow will also erode the diversion channel and lead to the dam collapse."
A moderate rainfall hit the lake at 6:50 p.m., and a minute later a strong aftershock rocked the dam for about 20 seconds and caused massive landslides on surrounding mountains, a Xinhua reporter at the dam said.
The 4.8-magnitude aftershock jolted Beichuan County at 6:51 p.m., according to the China Earthquake Administration.
The aftershock's impact on the dam is being monitored.
The sluice appeared to be still operating smoothly after the aftershock and rain, the reporter said.
In addition, military engineers have fired missiles to blast boulders in the channel to accelerate drainage.
The water flow through the sluice channel has widened from less than five meters to about eight meters.
"Generally speaking, construction of the lake's drainage projects is going well, but the lake remains dangerous for hundreds of thousands of people 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 of the lake," said the general.
Some 600 armed police and soldiers worked for six days and nights to dig a 475-meter channel to divert water from the lake.
Soldiers are still widening and deepening the sluice channel with the help of 30 bulldozers and excavators. They are also digging a second sluice channel on another side of the lake barrier.
The soldiers had finished building a third of the new channel, which required the removal of about 60,000 cubic meters of earth and stone, said Liu Yongjian, a PLA officer in charge of the channel.
"We have also prepared underwater blasts to deepen the channels for accelerated drainage," said Liu.
Rao Xiping, head of the Beichuan hydro-meteorological station, said the lake dam remained stable as the drainage continued.
"We have found no obvious expansion of the sluice holes nor fissures in the dam. There is no sign of dam collapse either," said Rao. The staff of his station and soldiers are keeping 24-hour patrol along the dam.
Water Resources Minister Chen Lei warned that increasing rainfall, aftershocks, landslides and leakage were still threatening the barrier.
Rainfall of 400 mm or 500 mm, well above normal levels, was forecast upstream in June and July, posing a risk for the swollen lake, he said.
Landslides could pour another 17 million cubic meters of rock and earth into the lake, threatening a dam burst and workers on the barrier could be swept away, he said.
Editor: Bi Mingxin