Monday, March 19, 2012

How long is the lifespan of a dam?

With its human history stretching back thousands of years and its vast canyons formed over millennia, Hasankeyf is a place that demands long-term thinking. If it is to be submerged under the waters of the Ilısu Dam, it only makes sense to ask how many years of benefit would be gained from the trade-off. Answering this question, though, poses a real challenge.

The Rindge Dam in Southern California: built in 1926 and filled with sediment by around 1950
Advocacy groups such as Doğa Derneği say the Ilısu Dam’s lifespan would be just 70 years, a blip in Hasankeyf’s history, but a number with no clear citation. In a statement to Congress in 2010, the American Society of Civil Engineers described 50 years as “the typical useful lifespan” of a dam. But there can be dramatic variations on either side of that average. According to International Rivers:

“Dams age at different rates and in a different way, depending on a variety of circumstances. Some dams may remain safe for a thousand years, others may start to crack and leak after less than a decade.”

To give just two examples from either end of the spectrum, the Grand Anicut (Kallanai) in India, an irrigation dam built from unhewn stone in the 2nd century A.D., is still in use nearly 2,000 years later, while the Laoying reservoir in China had to be abandoned even before dam construction was completed due to excessive siltation.

The Grand Anicut dam in India
Various factors come into play in determining how long a dam will remain usable, including its design and construction materials, the composition of the foundation rock, how well the dam is maintained, local temperature and humidity levels, the risk of earthquakes and other natural hazards, and the sediment levels of feeder rivers.

As we have yet to come across a comprehensive assessment of how these and other factors would affect Ilısu’s expected lifespan, we are issuing a call to knowledgeable engineers to make such an estimate and share it with us in order to better inform the public. Turkish-language submissions welcomed. Please spread the word!


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