Dams and Landslides

Dam’s flood control capacity overstated, experts say

(September 1, 2010) The flood control capacity of the Three Gorges dam continues to be questioned by analysts and former officials, writes Toh Han Shih in the South China Morning Post.

The flood control capacity of the Three Gorges Dam is substantially less than officially stated, analysts and former officials say.

The world’s largest hydroelectric project was designed to be able to hold back 22.1 billion cubic metres of floodwater, but the dam’s flood-control capacity will decrease to 18.7 billion cubic metres due to sedimentation in the reservoir, a report by Lu Qinkan , a former deputy chief engineer at the Ministry of Water Resources, said.

Another dam engineer, Wang Weiluo , who was involved in the dam’s planning in the 1980s and is now with an engineering firm in Germany, said the construction of the dam had resulted in the loss of natural flood-control capacity of rivers amounting to 10.2 billion cubic metres, possibly reducing the flood-control capacity to 11.9 billion cubic metres. Wang said the Three Gorges Dam “has virtually no natural flood-control capability, only man-made flood-control capability”.

In July, state media hailed the performance of the Three Gorges Dam in countering the floods of the Yangtze River.

Patricia Adams, executive director of Probe International, an independent environmental protection advocacy group, said the official claim that the dam came through an important test with flying colours was an exaggeration. Moreover, the dam had increased the chances of catastrophic flooding in various ways, she added.

Officials had not mentioned the fact that holding floodwaters behind the dam increased flooding. “To achieve the dam’s official gross flood-control capacity of 22.1 billion cubic metres, the Three Gorges reservoir level would have to be raised to 175 metres, which would cause flooding in Chongqing to be unacceptably high,” Adams said.

“Operating the dam at 175 metres would not only increase flooding upstream, it would also increase deadly landslides, potential tsunami in the reservoir and reservoir-induced seismicity.”

Lu and Wang both agreed. The officially stated reason for not raising the level to 175 metres was to prepare for future floods, but the actual reason was that if the reservoir’s water level rose to 175 metres, Chongqing’s water level would rise to 200 metres, Lu said in his report.

Globally, dams have a mixed record in flood control, said Peter Bosshard, policy director of International Rivers, an NGO focusing on environmental issues. “Dams can minimise some floods, but can also cause floods and make floods more destructive,” he said. In the US and Europe, there was consensus among experts and policymakers that a flood-control approach based on dams had not worked, Brosshard said, and a better approach was restoring rivers and wetlands, and defending vulnerable urban infrastructure with short embankments.

But John Briscoe, professor of environmental engineering at Harvard University, defended the project.

“The Three Gorges Dam has done exactly what it was designed to do – reduce peaks on floods and protect people in the lower Yangtze Basin,” Briscoe said. “There seems little doubt that the dam saved many lives and averted huge damage this year.”

Toh Han Shih, South China Morning Post

Further Reading from Probe International

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