The long-awaited drainage of China's Tangjiashan "quake lake" started on Saturday morning, as its water flowed into a man-made sluice channel.
Experts calculated that the flow volume has reached two cubic meters per second in the sluice channel.
Photo taken at the Tangjiashan "quake lake" on June 7, 2008
Rao Xiping, head of the Beichuan hydrometeorological station, said the water level of the lake is still rising due to the slowness of the water flow in the sluice channel.
The water level in the lake now stands at 740.85 meters above the sea level, 0.48 meters higher than the time when the quake lake started to overflow this morning.
"But the dam is safe now," said Rao, adding that no more spots of overflowing have emerged and he didn't think the dam would either collapse or cave-in.
Soldiers are still still widening and deepening the sluice channel to speed up the drainage, with the help of 30 bulldozers and excavators. They also also digging a second sluice channel.
The quake lake was enlarged by 13.5 million cubic meters, and has reached 229.5 million in total, according to experts at the Tangjiashan quake lake relief center.
The experts also said no strong rainfall is expected until June 16, which will be good for the quake relief work. The possibility of a strong aftershock measuring 6.0 or above on the Richter scale is also slim, they said.
The overflow had been expected to occur Friday night when water level reached the lowest point of the blockage, but it was delayed by a 0.6-meter-high temporary dam erected on Friday afternoon to protect workers dredging the sluice channel.
The swollen lake was formed by a massive landslide following the May 12 earthquake that jolted the country's southwest. It is posing a major threat to 1.3 million people downstream.
Some 600 armed police and soldiers worked for six days and nights to dig a 475-meter channel to divert water from the lake.
More than 250,000 people in low-lying areas in Mianyang have been relocated under a plan based on the assumption that a third of the lake volume breached its banks.
Two other plans require the relocation of 1.2 million people if half the lake volume is released or 1.3 million if the barrier fully opened.
The lake is also posing a threat to the Fujiang river bridge on the Baoji-Chengdu Railway, a critical part of the railway network in west China.
Liu Yongzhan, a pontoon bridge army colonel, told Xinhua that his men are ready to protect the bridge by intercepting, bombarding and salvaging large floaters that may be washed down by the flooding.
The bridge has been in smooth operation for passenger and cargo trains as of 2:00 p.m., Saturday.
Photo taken at the Tangjiashan "quake lake" on June 7, 2008
Real-time monitoring of the Tangjiashan "quake lake"
The swollen quake lake has also put China's longest oil pipeline at risk. The pipeline, winding from Lanzhou via Chengdu to Chongqing, was 60 kilometers downstream from the lake.
Liu Xiaozhong, director in charge of the pipeline protection work, said told Xinhua that the pipeline will not be disrupted according to the work plan on the quake lake.
More than 100 Petro China staff and 20 pieces of large equipment were assembled for protecting the pipeline.
With a capacity of transferring six million tons of oil each year, the pipeline provides 70 percent of product oil to Sichuan and neighboring Chongqing Municipality.
If the line was cut, refined oil in storage could only supply Sichuan for three days, whereas repair work would take 30 days.
