Call for Hydropower Dam Safety Reassessment

The Zipingpu hydropower dam in Sichuan was built in 2002 and completed in 2006, soon after the reservoir was filled and put in operation, on May 12, 2008, a massive earthquake, magnitude 7.9 hit the region and reportedly killed 69,000 people, rendering anywhere from 4.8 to 11 millions people homeless.

China and the world were shocked by the stunning catastrophe, in July 8, 2008, a group of Chinese environmentalists and scholars submitted the appeal to the Chinese government for dam safety assessments in geologically unstable south-west China. The petition was first reported on in the First Business Daily (Diyi caijing bao) on June 12, 2008 and translated by Three Gorges Probe. The petition is summarized below:

Chinese environmentalists and scholars appeal for dam safety assessments in geologically unstable south-west China.

One of the most glaring problems revealed by the disaster is that of dam safety. The Wenchuan earthquake has exposed three important issues regarding the construction of dams in southwest China:

• Whether it is appropriate to build big reservoirs and high dams in areas where there are seismic belts?

• Whether there is a possibility that mistakes were made in the assessment of seismic intensities during the planning stages of the dam?

• Whether the construction of big reservoirs and high dams in fault belts could trigger powerful earthquakes?

We hope that the relevant government departments will give serious consideration to these questions.

Dam safety is one of the most serious problems exposed by this disaster. In the fifteenth news conference on May 25, the deputy minister of Water Resources revealed that 2,380 reservoirs throughout eight provinces and cities including Sichuan, Chongqing and Shaanxi had been placed in danger because of the earthquake. The main problems included: dam cracking, dam sliding, destroyed spillways, collapsed outlets, breakwater walls broken, collapsed reservoir embankments, and so on. In Sichuan province alone, 69 dams are in danger of collapse, 310 have been deemed high risk, and 1,424 pose a moderate risk.

The damage resulting from the earthquake itself has been extensive, but if anything were to go wrong with the dams and reservoirs as a result of the earthquake, the whole area downstream would be inundated, and the casualties and property loss would be greater than those caused by the earthquake itself.

Now, apart from investigating the damage to dams and ensuring their safety, which is a little like mending the fold after the sheep have escaped, it is imperative to re-examine the plans to develop water resources in an unprecedented scale in the southwest region of China. The Wenchuan earthquake has highlighted three very important questions about dam construction in the southwest of China, all of which merit serious consideration.

1. Whether it is appropriate to build big reservoirs and high dams in areas where there are geological fault belts?

The southwest of China is geologically complex and affected by movement of the tectonic plates, especially on the eastern edge of the Qinghai-Tibetan Plateau bordering on Sichuan and the mountains and gorges in the northwest of Yunnan, which are products of the violent lifting and splitting of the earth’s crust. Areas such as this contain the most abundant water resources in China and have become the most important hydroelectric generating areas. Of the 13 hydropower development zones1 in China’s planned hydro-electricity generation program, the three most important are the Jinsha River, Yalong River and Dadu River zones, which are in western Sichuan and northwest of Yunnan. The zones on the upper reaches of the Yangtze River, as well as the Nanpan River and Hongshui River hydroelectric zones all straddle the provinces of Sichuan and Yunnan, and the Lancang River and Nu River hydroelectric zones are in the northwest part of Yunnan. (See Figure 1: Map of Yunnan Seismic Faults and Dam locations on The Lancang-Maekong)

Consider also that both Sichuan and Yunnan are the two provinces where the most earthquakes have occurred in China. They are part of the Sichuan-Yunnan earthquake zone of the north-south earthquake belts, where the magnitude and frequency of earthquakes in China is highest. Many of the cascade of hydro dams already built or planned to be built in the southwest will be built in earthquake zones. For example, the cascade of hydropower plants in the upper reaches of the Min River are located in the Songfan and Longmenshan seismic belts; the cascade of dams on the Dadu River (tributary of the Yangtze) have been and will be built in the Xianshuihe seismic belt; the cascade of dams built on the Yalong River (tributary of the Yangtze) are very close to the Anninghe-Zemuhe seismic belt; the Xiluodu dam on the Jinsha River (main channel of the upper Yangtze) is being built in the Yongshan seismic belt, and the dam projects proposed in the Lancang-Mekong and Nu rivers are located in the Three Parallel Rivers tectonic active belt.

The southwest area of China is geologically fragile and mud-rock-flows and landslides are common. Building a series of big reservoirs and high dams with a height over 100 metres -- and even over 300 metres -- is dangerous. Destruction of the rock mass along the reservoir is likely to occur as a result of large scale excavations of embankment slopes and large scale construction of highways and tunnels after the reservoir is filled. In the event of a strong earthquake, the above activities would exaggerate landslides, mud-rock-flows and landmass collapses, and even result in secondary disasters such as severe flooding or collapses caused by earthquake lakes. Thus we have to pay more serious attention to the hidden troubles and risks created for people living along the banks of rivers.

2. Whether there is a possibility that mistakes were made in the assessment of seismic intensities during the planning stages of the dam?

When questioned about the safety issue on the cascade of hydro dams built in the geologically unstable areas of southwest China, both the government and power companies usually responded in a confident way, emphasizing how the design of the big reservoirs and high dams was scientifically examined through the feasibility study, and how sound the choice of seismic intensity was to ensure the dams could withstand earthquakes and ensure safety. The Wenchuan earthquake, however, has demonstrated that there were flaws in the assessment of the risk of seismic activity related to dam building in this area.

Zipingpu Dam, the largest reservoir on the upper reaches of the Min River is a good example. Located 9 kilometres upstream of Dujiangyan, with a storage capacity of 1.1 billion cubic metres and a 156-metre high dam, the Zipingpu is a gigantic project. So it is no wonder that, as water experts described, the reservoir is “like a huge basin of water hanging over the heads of millions of people living in Chengdu and surrounding area.” As seismology and water resources experts revealed, in the feasibility study for Zipingpu, scientists anticipated a maximum seismic intensity of 7 in the dam site area, but the actual seismic intensity at the dam site was much higher than that because the dam site is only 17 kilometres away from the earthquake’s epicentre. As a specialist in earthquake prevention related to hydro dams said, “given such a high seismic intensity at the epicentre and the distance between the epicentre and the dam site, the seismic intensity at Zipingpu should have been between 8 and 9, which was a totally unforeseen event.”

Located high above the Chengdu Plain, close to the world heritage-listed Dujiangyan diversion and irrigation system, and as one of the key dam projects in the campaign of “Grand Development in the West,” the plan to build the Zipingpu dam attracted a wide range of debate even from the beginning of its feasibility study. And what worried a number of people in the country most was concern about the geological instability in the area, where it was proposed Zipingpu be built.

It has turned out that mistakes were made in the feasibility study of the Zipingpu dam, which now makes people uneasy and ask the question, if such mistakes could be made in such a key dam project as Zipingpu, how about the other cascade dams built in the geological fault belts of the same Min valley? Could the same mistakes have been made with those other cascade of dams in the Min valley? And does the same problem exist with big hydro dams which have been and will be built in other rivers such as the Dadu, Yalong, Jinsha, Lancang-Mekong and Nu rivers?

3. Whether the construction of big reservoirs and high dams in fault belts could trigger powerful earthquakes?

The epicentre of the huge Wenchuan earthquake was only five and a half kilometres away from the shoreline of Zipingpu reservoir. Based on studies by experts, the Zipingpu reservoir is located in an area of geological instability, with the notorious Longmenshan fault belts cutting right through the reservoir and surrounding area. Thus there are good reasons for people to wonder if the big reservoir induced such a record-breaking earthquake along the Longmenshan fault belts, which occurred after the reservoir had been filled.

As a disaster induced by human engineering projects, RIS (reservoir-induced seismicity) has caused wide attention around the world. According to data provided by experts from the Changjiang Water Resources Commission of the Ministry of Water Resources at the conferences of the feasibility study for the Three Gorges project, reservoirs with a dam height over 100 metres have a 7 percent chance of RIS in China; globally, reservoirs with a dam height over 200 metres would have a 34 percent likelihood of RIS. Worldwide, even though there are only four examples of dam and reservoir project construction having caused earthquakes with a magnitude over 6 (and the one with the highest magnitude was 6.5), these four dams were all located in areas of geological stability, which began with a low risk of naturally occurring earthquakes.

Not only is the Zipingpu dam built in an earthquake zone and an area with an active fault belt, but more and more hydro dam projects have been built and are planned for west Sichuan and northwest Yunnan, an area of high mountains and deep gorges, where new tectonic movement is occurring and seismic activity is frequent. While conducting the feasibility study for the Three Gorges project, experts from the departments of geology and seismology acknowledged that, “Currently, there are neither proper theories, nor methods of assessing and predicting RIS. And studies on the mechanism of how RIS occurs is still in the hypothetical stage.” In such circumstances, therefore, we simply must consider the risks of rashly going ahead with the development of hydroelectric power on an unprecedented scale, in such a geologically unstable area.