Dams and Landslides

Major landslides hit Three Gorges region

(December 1, 2008) On November 29, a major landslide hit Wu Gorge, one of the deepest canyons upstream of the Three Gorges dam on the Yangtze River, Xinhua reported on December 1.

The local county’s disaster office in Wushan confirmed there were no human casualties, injuries or damages to property in the area, which is known as Houzibao (Monkey Hill) on the north bank of Wu Gorge.

Officials said the slide poses no immediate threat to boats moving through the area but experts are concerned that an even bigger slide may follow. The Yangtze marine department has placed warning signs in the area as a precaution.

The landslide extended 60 metres in length, 120 metres in width, and five metres in height (for a volume of 15,000 to 20,000 cubic metres) but only about 20 percent of its mass slumped into the reservoir.

According to experts who investigated the incident, the November 29 landslide is part of a much larger slide waiting to happen, which covers an area 100 metres in length and 400 metres in width, with an estimated total volume of as much as 100,000 cubic metres. The experts found cracks around the bigger slide mass and are concerned the latest incident will trigger another much larger slide.

Commenting on the incident, Li Yankun, a senior engineer with Chongqing-based Nanjiang (South River) Geological Team, said that the steep slope of the mountain (40 degrees), a combination of loose and weathered rock and soil, and the filling of the Three Gorges reservoir, which changed the mountain’s physical mechanics, created the conditions for the landslide.

Mr. Li explained that most of the slip mass piled up by the riverbank and therefore wouldn’t slide into the Yangtze very soon, and posed no imminent threat to boats on the river. The Yangtze marine department has placed signs warning vessels not to navigate close to the area. When the local government sent a group of people to the scene, they were not allowed to enter the danger zone.

The November 29 incident is the second major slide to occur in the same area within one week. Around 16:40 on November 23, 2008, a landslide occurred at the entrance of the Wu Gorge on the north bank, just three kilometres upstream from the latest incident. With a volume of 50,000 cubic metres, the entire slip mass slumped into the Yangtze, spreading dust everywhere and causing a huge wave that violently rocked boats docked at the Wushan county port two kilometres away. One passenger boat named Jiangshan (River and Mountain) was pushed far away from the port by the waves.

For the safety of boats in the area, all shipping was temporarily suspended. By the afternoon of November 25, the slip mass appeared relatively stable but the area remains under emergency regulation, with boats guided [by the local waterway management department] to safer areas. To ensure the channel is safe for boats to go through, the department has sent a team of workers to measure the water depth in the affected river section, and the Wushan government has sent experts to investigate the cause and nature of the landslide.

Xinhua, December 1, 2008

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