More on the Three Gorges Dam’s flood control capabilities and its performance in one of the wettest seasons for China since the record-breaking El Niño event of 1997-98. In this report, The Economist concludes the country’s weakened river pulse is “in danger not only from floods but from its flood controls.”
From The Economist
At the world’s largest dam, the operation is successful but the patient is dying.
This season has been one of the wettest in China’s recent history, with 150 towns and cities suffering record amounts of rain. The Yangzi (or Yangtze) basin has been particularly hard hit. In the week to July 6th Wuhan, a giant city downstream from the dam, received 560mm (22 inches) of rain, its biggest ever downpour.
China’s most recent experience of weather like this was in 1998, which was also the last time El Niño, a shift in the weather patterns of the western Pacific, had a big impact on the world’s weather. That summer the Yangzi burst its banks, causing more than 1,300 deaths. So far this year fewer than 200 people have died in the river’s basin. [Continue at the publisher’s website here]
The Economist goes onto note that the “much-denounced dam seems to be passing its first big test as flood barrier” but that it “doesn’t necessarily justify the project”.
Grave concerns, says The Economist, include silt build-up, which, on the reckoning of the late Huang Wanli, a hydrologist at Tsinghua University in Beijing, will accumulate to such an extent the dam itself will have to be taken down, leaving the Yangzi basin worse off than “if the barrier had never been built.” Fears over the dam reservoir’s water weight and its impact on fault lines in a region known as “the world’s most seismically active” are another.
As a means of flood control, “the dam is a mixed blessing,” The Economist continues, citing Fan Xiao, an independent researcher and the author of several reports for Probe International. Incoming water stripped of silt by the dam rushes downstream hungry and seeks to replenish its sediment load by eroding the river’s bed and banks. According to Fan, that water has scraped away and lowered the Yangzi’s bed by as much as 11 metres, says The Economist. This, says Fan, has weakened downstream embankments as flood barriers and the capacity of nearby wetlands to act as sponges. [See: Astonishing changes in the life and environment of Chongqing: 20 years after the construction of the Three Gorges Dam]
The Economist compares Three Gorges Dam to a move by the American Army Corps of Engineers to prevent deadly flooding after a tropical hurricane in 1928 drowned 2,500 people in southern Florida. To prevent such a recurrence they drained much of the Everglades, and while no such disaster has struck since, the Everglades is now “a shadow of its former self” and in danger of disappearing. Similarly, “the Yangzi,” it writes “is in danger not only from floods but from its flood controls.”
For more on this
The limited benefits of flood control (An interview included in the original Chinese edition of Yangtze! Yangtze!)