Dams and Landslides

Falling short: Three Gorges unable to prevent floods says engineer

(July 29, 2010) Three Gorges is unable to fill its flood-prevention promises, says one engineer.

The Three Gorges dam’s celebrated flood-storage capacities are facing renewed criticism in the wake of recent floods that have, again, highlighted its shortcomings.

According to Dr. Wang Weiluo, a Chinese engineer who participated in the Three Gorges feasibility study, the Three Gorges dam will never be able to work according to its original design to store flood waters—once a major selling point during the dam’s construction.

“Even with the Three Gorges dam, fierce flooding continues to occur in the Yangtze River and the dam project has yet to achieve the goals of its original design,” he said in a recent interview.

At 22.1 billion cubic meters, the dam’s official flood-storage capacity is too small—far below the 30 billion cubic meters requirement scientists working on the dam’s feasibility study had proposed. Yet, says Dr. Wang, even the official claim that the dam can store 22.1 billion cubic meters of floodwater may be a miscalculation.

He says the dam’s true flood storage capacity is likely less than 20 billion cubic meters and could be as low as 11.9 billion cubic meters.

In the past, officials have secretly admitted that the dam’s flood storage capacity was lower than the figures presented to the public. In 2001, Probe International published a number of leaked letters between government officials admitting as much, with stern warnings to, “never, ever let the public know this.”

To encourage decision makers to agree to the dam’s creation, Dr. Wang said officials, “started in 1991 to launch a series of propaganda campaigns … primarily focusing on the positive elements of the dam—with several benefits greatly exaggerated, especially flood control.”

One of the most glaring miscalculations by officials regarding the dam’s ability to prevent floods was their haste to overlook the fact that its reservoir would not be flat. Initially, officials drew a straight line from the dam to the top of the reservoir in the major city of Chongqing city, nearly 660 kilometres away, at 175 metres—marking the height of the reservoir at its peak. A flat reservoir helped to keep resettlement figures down.

A number of scientists disagreed, saying the reservoir would have a hydraulic slope with a gradient of 0.007 per cent—meaning the water would be seven metres higher every 100 kilometres.

And those scientists were right, says Dr. Wang, adding, “the Three Gorges reservoir has never been flat for a single day since the dam was filled for the first time in June 2003.”

He points to recent data to substantiate this claim. At the beginning of the month, when the reservoir’s height was 140 metres at the Three Gorges dam, “the difference in water level was as much as 40 meters between the dam site downstream and Chongqing city upstream … (with the reservoir) more than 190 meters above sea level in the city of Chongqing.”

Dr. Wang cautions against ignoring the importance of a sloping reservoir on flood control.

“To achieve the goal of flood control, the water level at the dam site of the Three Gorges should be raised to 175 meters from 145 meters above sea level,” he says.

But raising the dam to 175 metres would result in the flooding of Chongqing—which is currently not an option as more than 28,000 people still live on the reservoir’s edge, below that level.

Like many other critics of the dam, Dr. Wang says flood control on the Yangtze river could have been achieved—at far less cost—by “dikes and flood diversion areas.”

Brady Yauch, Probe International

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