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| The Teton dam, an earthen dam on the Teton River in Idaho Source unknown |
On February 21, 2011 the New York Times had an article about the decaying infrastructure of some of the 85,000 dams on rivers in the U.S. According to the Association of State Dam Safety Officials, more than 4,400 are considered susceptible to failure for various reasons. The cost of repairing all of these dams would be billions, money not freely at hand in this fiscal climate. As far as I can tell, this does not include privately-owned dams, of which there are a significant number. The "Great Flood of 1889" in Johnstown, PA, was the result of the failure of a privately owned dam. In that case, a group of speculators had purchased an abandoned reservoir to convert it into a recreational lake for the wealthy associates of Carnegie Steel of Pittsburgh. The South Fork Fishing and Hunting Club became an exclusive retreat for 50+ Pittsburgh industrial tycoons. A major storm deluged the region with 6-10 inches in 24 hours, causing the dam to fail, resulting in 2200 deaths, surpassed only by the 1900 Galveston hurricane and then the 9/11 attacks.
Construction of dams has been a human enterprise since nearly our prehistory, with evidence for manipulation of the Nile thousands of years ago. Dams have been used to manage floods, to harness water as hydropower, to irrigate fields or be used in industry, to supply drinking water, and to provide lakes for recreation. But in the second half of the 20th century it became a major enterprise, and now there are few rivers not severely impacted by dams and megadams. Half of the world's rivers have at least one large dam, and many have sequences along their full length. (A major source of information on dams is The World Commission on Dams (WCD), www.dams.org.)
According to the WCD, a "large dam" is 15 m high or more from its foundation, and any dam between 5-15 m in height that has a reservoir volume of more than 3 million cubic meters is also a "large dam." By this classification, there are more than 45,000 large dams around the world. These dams provide growing populations and economies with water to be used in many ways. Many of them are on rivers that are subject to disputes amongst neighboring countries who argue over water rights of rivers on their boundaries. Competing needs amongst agriculture, industry, and municipal uses continue to draw on a limited supply of water.
The causes of concern about aging dams are numerous. In some cases, new information has come to light about the geologic setting, e.g., an unknown fault discovered. There is danger of internal seepage, or of overtopping if extreme floods occur. There have also been decades of accumulation of knowledge about environmental effects that range from induced earthquakes to habitat destruction.
Interestingly, the World Commission on Dams report focuses to a large extent on documenting past expectations and performances of dams, and dam building practices. I could find relatively little dealing with the problems of maintaining infrastructure on the century time-scale. Perhaps someone can help?
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