Rescuers to work non-stop to lower dangerous barrier lake in Yunnan quake zone
Rising waters threaten 39,000 residents and more than 2,700 hectares of farmland
Rescuers are digging a canal to divert water from a giant barrier lake, formed by landslides during the deadly earthquake in Yunnan province, which threatens to deluge villages and power stations.
The effort was to prevent massive casualty caused by possible burst of the lake. The 6.5-magnitude earthquake had left at least 615 people dead and another 114 missing; more than 3,143 people were injured, and 230,000 relocated.
After landslides blocked the Niulan River near Hongshiyan village, the barrier lake has swelled and threatened to flood nearby villages and seven hydropower stations downstream.
By yesterday morning, the lake had flooded 90 hectares of farmland, 368 houses and 7.4 kilometres of roads. Its overflow will affect 9,000 residents upstream and more than 30,000 residents downstream, as well as a total of more than 2,766 hectares of farmlands, according to the State Flood Control and Drought Relief Headquarters.
Authorities have relocated about 5,000 residents. Two hydropower stations downstream have reserved storage for the discharged lake water, the Water Resources Department of Yunnan province said.
The channel excavation requires 400 workers with 150 heavy machineries, including excavators, bulldozers and loaders, to work round the clock to meet the five-day deadline, state broadcaster China Central Television said.
Experts said the time frame was sufficient as the water’s sweeling had slowed down, but rains and landslides could increase the water level quickly, the official news website of Yunnan province said.
”This is a big barrier lake, and is ranked highest in risk level. In addition, the Niulan River is in its main flood season, and heavy rains may fall at any time. Once the barrier burst, it will cause huge damages,” Li Shengang, an expert from Ministry of Water Resources was quoted by Xinhua as saying.
The water level stood just 40 metres below the top of a 300-metre-long rock barrier that formed in the lake’s west, according to the disaster relief headquarters in the neighbouring Huize county.
The water rose 0.3 metres from the day before, much slower than an earlier rate of one metre per hour.
Excavating the barrier – made of large rocks and which prevents the water from flowing west – poses a challenge. The team will use explosives to blast the rocks into smaller pieces before bulldozers can take them away, Yue Xi, commander of the operation, told China National Radio.
Last night, hydropower engineers demolished 60 rocks on the barrier for the first time. Close to five tons of explosives were strapped next to the barrier by soldiers in the past two days.
Watch: Rescue scenes from Yunnan earthquake
A reservoir upstream from the barrier lake has shut down its flood gate to bar river waters from further flowing into the lake.
In 2008, Sichuan’s magnitude-8.0 earthquake that killed almost 70,000 people also caused a big barrier lake in Tangjiashan. The lake had a capacity of 145 million cubic metres of water, and was finally drained through a flood relief tunnel.
The storage capacity of the Hongshiyan barrier lake is 260 million cubic metres.
Yue said the Hongshiyan lake is much more difficult to deal with than the Tangjiashan lake in 2008 because of the presence of large rocks.
The barrier of Tangjiashan lake was formed mainly by earth, and could be removed directly by bulldozers.