Dams and Earthquakes

Fan Xiao addresses dam concerns

June 19, 2008

In response to many press inquiries about China’s deadly May 12, 2008 earthquake, China’s Fan Xiao, chief engineer of the Regional Geology Investigation Team of the Sichuan Geology and Mineral Bureau, answers the following questions.

In response to many press inquiries about China’s deadly May 12, 2008 earthquake, China’s Fan Xiao, chief engineer of the Regional Geology Investigation Team of the Sichuan Geology and Mineral Bureau, answers the following questions.

Q: How badly would the recent China earthquake and its aftershocks have structurally weakened dams in and around the epicentre?

Fan Xiao: Dams in and around the epicentre have been damaged to different degrees: some have been distorted or cracked; buildings and equipment in power plants have been damaged; in some cases the sluice gates cannot be opened, and also parts of power stations have been hit and covered by debris from the landslides, and so forth. For example, the authority planned to blast at least three dams — Yingxiuwan (or Yingxiu), Taipingyi, and Yuzixi upstream of the Zipingpu dam on the upper Min, because their sluice gates were damaged and unable to open. But there has been no further public report on whether the blast was carried out or not and the course of action taken by the authorities remains unclear. In the case of Zipingpu, the dam structure was cracked and the sluice gates could not be opened, putting the area downstream of the dam in danger at that time. Emergency rescue work was carried out and the sluice gates were successfully opened and the water level was lowered in the reservoir.

Q: To what extent will monsoon rains further weaken these dams?

Fan Xiao: It is true that Sichuan entered the rainy season in June. First, the damaged dams will be challenged when the floodwaters come from upstream because the reservoirs will have trouble running with high water levels and performing their normal flood-control function. Second, the earthquake lakes and the seriously damaged dams upstream present double risks to dams downstream, which themselves may be damaged. Third, rainstorms, typical in the rainy season, are likely to trigger massive geological disasters such as landslides and mud-rock flows and so on, posing a great threat to the safety of dams in this area.

Q: How many people are in danger of flooding from collapsed dams and are Chinese authorities reacting swiftly enough to the problem?

Fan Xiao: So far the government has announced that there are at least 34 earthquake lakes in the area, though some of which have been removed from the dangerous list. We don’t know exactly how many people are affected by the earthquake lakes. The government has taken measures such as digging diversion channels and dispersing people living in the downstream areas.

Q: What effect will this have on the ongoing construction and flooding of the Three Gorges dam?

Fan Xiao: I don’t think there will be a significant effect on the ongoing construction of the project, but I do believe much greater attention should be paid to geological disasters in general, and specifically to reservoir-induced seismic activity, especially after the Three Gorges reservoir is filled to 175 metres.

Q: To what extent could vast reservoirs have induced the earthquake as has been claimed in some media reports?

Fan Xiao: Globally, the greatest recorded reservoir-induce seismicity (RIS) occurred in India, with a magnitude of 6.5. So far, globally, almost all RIS with a magnitude above 6.0 has occurred in areas with weak seismic activities, not in seismically active fault belts. In my opinion, the possibility that the Zipingpu reservoir induced the May 12 earthquake cannot be ruled out. If further studies confirm this, then Zipingpu would become a new and really important case of the RIS in the world.

Q: Should China proceed with the construction of dams in earthquake-prone zones?

Fan Xiao: Currently, there is no sign to indicate that construction of hydro dams in earthquake-prone areas will be suspended. In the west of China, for example, a great number of high dams and huge reservoirs are under construction in seismically active fault belts. The cascade of dams on the Dadu River (a tributary of the Yangtze) have been and will be built in both the Xianshuihe and Anninghe seismic belts, the cascade of dams on the Yalong River (a tributary of the Yangtze) have been and will be built in the Xianshuihe seismic belt, and the cascade of dams on the middle and lower Jinsha River (main channel of the upper Yangtze) will be built in both the Mabian-Zhaotong and Dongchuan-Songming seismic belts, and so forth.

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