September 5, 2003
Leading Chinese hydrologist Lu Qinkan has written a third petition to top authorities in Beijing, raising the alarm about three potentially disastrous problems related to the Three Gorges dam.
In the document, signed by 42 other Chinese scientists and engineers, Prof. Lu warns against the plan to seal 22 outlets at the base of the dam in 2005-06. He believes this will lead to a dangerous accumulation of sediment in the Three Gorges reservoir and actually worsen flooding problems in Chongqing.
“The outlets are crucial to the process of releasing silt from the reservoir,” insists Prof. Lu, now retired from his post as deputy chief engineer in the Ministry of Water Resources and Electric Power.
Sediment accumulation raises a riverbed, causing floodwater to spill out onto adjacent land. In addition to warning about this increased risk of flooding, Prof. Lu picks holes in the calculations that determined the level above which Chongqing residents could remain in their old homes on the shores of the rising reservoir.
Those calculations were based on the water level that would be expected in the reservoir during a flood of a size that normally occurs once every 20 years, he writes. But typically in flood-control planning on the Yangtze River, the more severe one-in-100-year flood is used to determine the safe zone.
Prof. Lu suggests that many thousands of people in Chongqing, the huge city at the tail of the reservoir, will find themselves living in a high-risk, flood-prone area.
His analysis lends credence to the view that the official Three Gorges resettlement figure of 1.13 million will prove to be a gross underestimation of the number of people who need to be moved to safety.
“The guidelines and methods used to calculate the number of people destined to be affected in Chongqing are neither legal nor reasonable,” he concludes, and recommends “a new plan to resettle more migrants should be considered.”
In his latest petition, dated March 18, 2003, Prof. Lu also cites the project’s vulnerability to military attack as another compelling reason to keep the final water level in the reservoir lower than currently planned.
He did not raise this security issue in his two previous petitions, which were submitted to Chinese leaders in March and June 2000. But in this document, written after the September 2001 terrorist attacks in the United States, he does address the hideous possibility of an attack on the world’s biggest dam, located in a densely inhabited part of the world’s most populous country.
Keeping the “normal pool level” of the Three Gorges reservoir at 156 metres above sea level “will result in less damage and loss if the worst-case scenario [of a dam burst] does occur,” he writes. The current plan is to raise the reservoir to 175 metres in 2009.
In his two earlier petitions, Prof. Lu also urged that the reservoir be kept at 156 metres for a lengthy evaluation period. This would allow time to monitor potentially hazardous impacts of the project, such as the build-up of sediment on the reservoir bed.
In fact, this was official policy at the outset of construction in 1993, when there were no plans to raise the reservoir level to 175 metres before 2013. However, by 1997, dam officials appear to have discarded this more cautious approach in order to maximize the project’s power output. The Three Gorges reservoir, which was filled to 135 metres in June of this year, is now scheduled to rise to 156 metres in 2006, and to 175 metres three years later.
In his third petition, Prof. Lu warns against repeating the calamitous mistake made in the late 1950s by the builders of the Sanmenxia dam on the Yellow River, who ignored plans that called for silt-discharging tubes to be constructed near the base of the dam. Sanmenxia was completed in 1960, but by the third year of operation five billion tons of sediment had collected in its reservoir, waterlogging farmland and threatening the major city of Xian with disastrous flooding.
Sanmenxia had to be rebuilt at enormous expense. In her book Mao’s War against Nature [PDF], American University professor Judith Shapiro writes: “The dam was repeatedly reconstructed with tubes at the base to increase silt discharge capacity, but in 1969, again there were floods in Xian. Eventually, the dam was so pierced with holes that it became virtually worthless for either flood control or electricity generation.”
Twenty-two bottom outlets have been built into the Three Gorges dam at an elevation of 56 metres above sea level. They lie below the dam’s 23 sluice gates, which are at 90 metres above sea level.
Rather than permanently sealing the bottom outlets with concrete as planned, Prof. Lu advises that these low-elevation tunnels should be kept fully open during the summer flood season to help discharge the large amount of sediment that is carried by onrushing floodwater.
“It is clear that bottom outlets are important for flushing out silt,” he writes. “And it is very difficult to reopen them once they are sealed.”
Project officials counter that four more megadams that are planned for the upper reaches of the Yangtze will help block some of the silt that now flows toward the Three Gorges project. And they are concerned that the structural integrity of the dam could be undermined if the bottom outlets are not sealed.
Prof. Lu predicts that with the reservoir kept at 175 metres, sediment accumulation will raise the river and force as many as 200,000 more people on the Yangtze’s main channel to move, as well as others living along tributaries. And Chongqing, located more than 600 kilometres upstream of the dam, will face severe flooding and navigation problems.
In Damming the Three Gorges, a critique published by Probe International of the Canadian-backed feasibility study carried out for the dam in the 1980s, U.S. hydrologist Philip Williams writes: “The Yangtze is not only a river of water, it is also a river of sediment. The flow of the Yangtze carries with it the fifth-largest sediment discharge of any river in the world.”
On the Three Gorges scheme, he concludes that: “The type of operation and design proposed to minimize sedimentation has not been successfully demonstrated on such a large dam project. … The only previous attempt to manage sediment flows of this magnitude was at the Sanmenxia dam on the Yellow River, which is widely acknowledged outside China to have been a costly failure due to unanticipated sedimentation problems.”
The Three Gorges project, he writes, is “a gigantic experiment in river management.”
For the full text of Lu Qinkan’s March 2003 petition, see Keep the reservoir level at 156 metres.
Categories: Three Gorges Probe