Dams and Landslides

Chinese dam played role in deadly landslide

(July 9, 2010) An exclusive report for Probe International from Fan Xiao, chief engineer of the Regional Geology Investigation Team of the Sichuan Geology and Mineral Bureau, detailing the potential role a nearby dam played in a deadly landslide in China’s southwest Guizhou Province.

By Fan Xiao
Probe International
July 5, 2010

A Probe International Exclusive

In the early afternoon of June 28, 99 people were buried in a landslide in the Dazhai Village, Gangwu Township of Guanling County, Guizhou Province in southwest China—making it the deadliest geological disaster this year.[1] The reported cause of the landslide was heavy rainfall, with as much as 257 mm of precipitation having fallen on the city the previous day. This was certainly a heavy rainfall, and it played a role in the landslide. But we need to examine what happened more carefully in order to learn lessons and prevent similar geological disasters from happening in future.

According to the media, the villagers are quick to point to the nearby Guangzhao hydropower station as the real culprit behind the landslide. Many of the villagers reported feeling earthquake-like tremors before the landslide, like a series of dynamite blasts—in fact, a number of houses in the village showed visible cracks as a result of the tremors. Villagers also reported that last year, the landslide site showed signs of cracking and that higher authorities were warned, but they did nothing.

With a height of 200.5 metres, a total storage capacity of 3.245 billion cubic meters and an installed capacity of 1.04 million kilowatts, the Guangzhao hydropower station is the largest and “head” dam of a cascade of dams on the Beipanjiang River. At its Normal Pool Level (NPL) of 745 meters above sea level, the Guangzhao Reservoir covers 51.54 square km. The Dazhai Village, where the landslide occurred, sits on the left bank of the Beipanjiang River on the Guangzhao reservoir. The debris from the landslide has since spilled into the reservoir.

The western Guizhou Province—where the Guangzhao hydropower station is located—is home to a number of karst mountains and valleys, with geological disaster-prone areas such as sinkholes and underground rivers—making it prone to gravity collapses, dissolution collapses, landslides and other geological disasters. High dams and large reservoirs significantly impact this geological environment—for example, because dams require repeated changes in water levels, they destroy the reservoir shoreline, destabilize mountains and cause changes in the groundwater regime in this karst area. The result is not only seismic activity, but also other geological disasters such as landslides, land subsidence, mountain collapse and so on.

Construction of the Guangzhao dam began in 2004, while the filling of the reservoir occurred in 2007 and full operation commenced in 2008. The risk that the dam could cause reservoir induced seismicity (RIS) was known to be high—indeed, one of the highest in the region—so a seismic monitoring network was built and put into operation in May 2007. According to data published by experts, both the intensity and frequency of seismic activity increased as the dam operators began filling the reservoir. As many as 1,299 earthquakes were recorded between December 2007 and August 31, 2008. Of those, 20 were large enough to be felt by local citizens, with the largest measuring 3.2 on the Richter scale.

It is likely that the Guangzhao dam negatively affected the geological environment of the region and created an impending geological disaster. Both the seismic activity and the fluctuating water levels might have played a role in causing the landslide in the Dazhi Village.

Because of the dam’s potential role in the landslide, further studies are needed to determine the relationship between the reservoir and the landslide. The landslide should also provide experts with an opportunity to find new and more effective ways to monitor and manage geological disasters that occur because of reservoirs. Further studies may be particularly important in regards to the Guangzhao dam, as, at this point in its lifespan, it is likely to produce significant seismic activity and other geological disasters.

Since the rainy season began this year, a series of severe geological disasters—including landslides, collapses and mud-rock flows—have occurred in southern China. While heavy rainstorms are the direct cause of such disturbances, many of them are also associated with human activities. On May 23 for example, the K859 passenger train on the Shanghai-Kunming Railway derailed in Jiangxi Province, killing 19 people; and on June 14, a landslide occurred at the dam site of the Jinping Hydropower Station in Kangding County of Sichuan Province, killing 23 people. These incidents, and many others, while sparked by particularly heavy rainfall, are also a result of excavation, debris-dumping and other construction activities.

In recent years, large scale construction projects have been initiated in nearly every region across China—and because of this construction frenzy, the hidden dangers and risks of induced geological disasters have also been on the rise. On my field trip to the Dadu River, a tributary of the Yangtze where a cascade of hydropower dams and highways are being constructed, I discovered the steep mountain slopes in the area were excavated and a number of dregs were directly dumped into the Dadu River. The amount of soil erosion and the destruction of forests and other vegetation was shocking. Two serious disasters occurred in 2009 along the Dadu River—the first, a mud-rock flow at the dam site of the Changheba dam in Kangding County in Sichuan Province on July 23, and the second, a mountain collapse at the construction site of a road for the Pubugou dam in Hanyuan County in Sichuan on August 6. Both of the disasters were a direct result of man-made activity.

It’s also worth noting that the places experiencing some of the worst geological disasters have never been identified as high-risk zones in need of monitoring. Nor have any measures been taken to manage these risks in the interest of public safety.

What we can take away from these cases is that human activity is likely to exacerbate known geological risks and create new risks where none existed before. The cases also show that, to date, officials have failed to properly monitor these situations and to heed the warning signs.

Because of the potential disasters that can be induced by these projects, officials need to do better scientific analysis and feasibility assessments before forging ahead with them. They also need to better monitor the construction and operation of the projects—and, in the process, establish a system of accountability for both the owners and builders of such projects, while heeding the concerns of local citizens.

Fan Xiao is the chief engineer of the Regional Geology Investigation Team of the Sichuan Geology and Mineral Bureau

BACK TO POST: 1. According to a July 4, 2010, Xinhua report, 42 bodies have been recovered. Fifty-seven remain missing and are presumed dead.

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