The Three Gorges Dam: Part IV, Will It Work?

On the night of August 27, 1993, a dam burst high in a remote western province of China , sending torrents of water crashing down on nearby villages, killing more than 200 people, and rendering thousands more homeless. Though no official reason has been given for this latest human-made disaster in a country plagued by them, one government spokesperson admitted that a destructive earthquake which hit the region of the Gouhou dam in 1990 "may have had some effect" in causing the dam to collapse under this year's flood waters. The Three Gorges Dam is situated near six active fault lines and above 15 million people. A dam burst at Three Gorges would, says engineer Philip Williams, president of the San Francisco-based International Rivers Network, "rank as one of history's worst man-made disasters." Perhaps saving the lives of the thousands of people annually killed by floods could justify the environmental and cultural costs, if the dam works, yet early inspections by international teams of engineers indicate otherwise. An international team of engineers who assessed the dam said, "the chosen approach to the design and implementation of the coffer dam appears to us to indicate a surprisingly cavalier attitude to risk." The dam is built to withstand earthquakes up to 7.0 on the richter scale, and the largest recent earthquakes have been below 6.0. However, filling the reservoir behind the dam creates seismic pressure which triggers earthquakes. In fact, earthquakes between 6.0 and 6.5 are expected once the reservoir is filled in 2009. One of the dams designed to hold back sedimentation farther up is subject to even worse seismic problems. "The Jinsha has bad geological conditions, and there is a more severe seismic area upriver from Xiangjiaba," said a Chinese geologist in Sichuan. He added that near this site, dam projects "should not be encouraged." Should the Jinsha dam hold out, .5 on the Richter scale is not a large margin of error, and earthquakes are not the dam's biggest problem. In 1992, the expert group identified 260 landslides and collapses containing at least 100,000 cubic metres of rock and earth; 140 of these had a volume of 1 million cubic metres or more. At least 14 landslides are considered likely to be activated by the filling of the reservoir. Already major cracks have developed in the dam, and even after extensive repairs, they have reappeared. Pan Jiazheng, one of China's top engineers recently acknowledged, "It appears that during the concrete pouring, we put too much emphasis on the goal of achieving a very high degree of strength. But it has turned out that a high degree of strength does not necessarily mean good quality in a concrete dam. We have achieved an unnecessarily high degree of strength and a lot of cracks in the dam by pouring too much concrete and spending a great deal of money. "I feel that it's too early to be proud of ourselves, and we have a long way to go. As we enter the third phase of the dam construction, I hope we will do our best to build a first-class project rather than a dam with 10-metre-long cracks!" In addition to problems with the strength of the dam, all three of the dam's principal benefits, flood control, power generation, and improved navigation, depend on a solution to the problem of reservoir sedimentation. Over 700 million tons of sediment are deposited into the Yangtze annually, making it the fourth largest sediment carrier in the world. The Chinese officials have decided to halt the flow of sediment higher up in the Yangtze tributaries by building four smaller dams, including one that will be second only to the Three Gorges in size. What will happen when sediment builds up behind these dams? There is little to address the primary source of flooding: the loss of forest cover in the Yangtze watershed, and the loss of 13,000 square km of lakes which stored excess water but now contain the topsoil from the lost forest cover. Probe International recommends dykes, channel improvements, overflow area designation, better zoning, flood proofing, and flood warning systems instead of more dams. Some question whether it will even be possible to accomplish all the purposes of the dam. Flood control requires the reservoir to maintain low levels of water to allow for the inflow of flood waters, while power generation requires high levels of water in the reservoir.