Flood threat averted after China quake

As aftershocks of the May 12 earthquake in Sichuan continue to take their toll on China, rising water levels in newly formed lakes behind “landslide dams” are proving to be a critical issue. These “quake lakes” formed when landslides induced by the May 12 earthquake and its aftershocks dammed up rivers. More than 30 such lakes have already formed. Inherently unstable and prone to overflowing or breaking at any time, the reservoirs threaten villages located downstream. On Tuesday, workers made significant strides in the battle against these lakes.

More than 250,000 people evacuated Mianyang City and the surrounding area in the last couple days due to the looming threat of a giant quake lake, according to Xinhua, the state news agency. Tangjiashan Lake, formed by a landslide into the Tongkou River, is the largest of the quake lakes. If the dam holding back the lake were to fail, more than 1.3 million people living downstream of the lake would be at risk.
 
To prevent flooding or tsunamis, the government is draining Tangjiashan and other quake lakes. Efforts to drain Tangjiashan include construction of a 475-meter channel designed to divert the lake water elsewhere and decrease pressure on the dam. According to Xinhua, more than 200 police officers and soldiers have been working for four days, utilizing short-range missiles and more than three tons of dynamite to blast apart boulders responsible for slowing water flow through the channel. Because many of the area's roads are blocked by debris, the government has had to fly in equipment such as drilling machines and bulldozers.

But aftershocks in the Sichuan region are complicating this work. Seven aftershocks above magnitude 5.0 have struck Sichuan in the last two days alone, according to the U.S. Geological Survey. The aftershocks initiated landslides in nearby mountains, causing more rocks and dirt to fall into the lake, adding even more pressure to the precarious dam.

Despite the setbacks from the aftershocks, workers have completed a second channel and started a third. By Tuesday morning, the water level in the lake finally fell as water gushed out via the new channels, and by the end of the day, more than half the water behind the dam had drained, according to Xinhua. Cities downstream, including Mianyang, were on alert for floods, but only minor flooding and damage occurred, and the number of people in danger dropped to 50,000. Liu Qibao, Communist Party chief of the southwestern Sichuan Province, called the news a "decisive victory."

More than 69,000 people are dead and 17,000 are still missing from the May 12 quake.

Elaine Tu
Geotimes contributing writer

Links:
Aftershock warnings continue to shake up China, Geotimes online, Web Extra, May 21, 2008
Quake rocks central China, Geotimes online, Web Extra, May 12, 2008
News story on CNN.com
News story from Xinhua

Back to top