On August 7, a large mudslide occurred in Zhouqu county, in Gansu province, north-western China. More than 1,000 people were rescued, but over 1,000 people were also killed and over 600 are still missing, according to officials.
What was the cause of such a big disaster? At the moment no one seems to be sure.
Tao Qingfa, from the Ministry of Land and Resources, offered one explanation to Xinhua news agency. First, he said, the high mountains, steep slopes and deep valleys of the region have very little vegetation -- the environment is dominated by slate, sandstone and other soft, easily fragmented rocks. A great deal of weathering and erosion makes the area prone to landslides, avalanches and mudslides. Second, he said, Zhouqu county was one of the areas hit by the Wenchuan earthquake in May 2008. The earthquake loosened the mountainsides and increased cracks in the rocks. Third, the region is semi-arid. Avalanches, landslide and mudslides are more likely to occur when dry rock-soil comes into contact with water, which adds to the source of mudslides. Finally, sudden rainstorms and continuous rainfall -- which has occured recently -- cause mudslides.
But other people have different views. Fan Xiao, a geological expert and chief engineer of the Regional Geological Survey Brigade in Sichuan, told China Economic Times: "The impact of large-scale human engineering exacerbates the risk of disaster."
Fan believes that these mudslides are related to decades of serious soil erosion. From 1950 until the beginning of this century, there was serious local deforestation. The forest area upstream at Bailong River decreased by about 700,000 mu (about 467 square kilometres) and land with a slope of less than 40 degrees were mostly cleared, causing an increase in soil erosion and the emergence of large amounts of loose sediment.
Fan said there was not enough evidence to say that dam construction is the direct cause of this disaster. But he believes that the impacts hydropower and other large-scale human engineering activities have on local geological conditions cannot be ignored, as it increases soil erosion as well as the size and frequency of these kinds of disasters.
Fan said that the development of hydropower on the trunk stream of Bailong River had been quite intensive. Just at the section of the river in Zhouqu county alone, there are seven dams built or under construction. Public information released between 2003 and 2007 appeared to show that of the 41 hydropower station projects under construction or already built on the river, there was a total surface area disturbance of 322.83 hectares, spoil disposal reaching 38.348 million cubic metres and 749,000 tonnes of soil erosion.
Since 2003, the Zhouqu county government has vigorously embraced hydropower building. From 2003 to 2007, a total of 53 contracts for hydropower development and construction were signed.
Ma Jun, director of the Institute of Public and Environmental Affairs, said that south-western China is not suitable for such large-scale hydropower development because of its fragile geology. After the Wenchuan earthquake, some environmental organisations and individuals wrote a joint letter that raised the issue of dam safety in the geologically unstable southwest. Large-scale digging of slopes and reconstruction of roads and tunnels may damage rock formations along reservoirs, causing worse landslides, mudslides and flooding when an earthquake occurs, it said. But currently, Bailong River is still being developed,one hydro plant after another.
Ma Dongtao, from the Institute of Mountain Hazards and Environment at the Chinese Academy of Sciences in Chengdu, who warned about the danger of mudslides 13 years ago, believes that there is only a small chance that the earthquake in 2008, or man-made factors, caused this disaster.
Ma wrote in a paper in August 1997 that if a large landslide were to occur in “Three Eyed Valley” in Zhouqu, it would result in much more serious losses than in 1992, when a mudslide killed 87 people.
Ma told Caixin that perhaps this disaster was unavoidable, but active measures should have been taken, such as effective monitoring and early-warning measures. By formulating a plan for disaster prevention, rationally planning for urban construction, population distribution and dredging of the drainage channel, the scale and hazards of disasters can be reduced.
He said that the urban population in Zhouqu increased from 21,400 in 1996 to more than 40,000 in 2010, meaning increased losses when disasters strike.