Monday, January 22, 2007

Old Dams Need Attention

The New York Times:
In 2005, the American Society of Civil Engineers gave United States dams a D, a grade that is still justified two years later.

For starters, the nation’s dam stock is rapidly aging. Most dams need major repairs 25 to 50 years after they’re built, and most United States dams are at least 25 years old; some... were built more than a century ago.

As dams age, their danger increases. This is a matter of not just advancing decrepitude, but “hazard creep” — the tendency of developers to build directly downstream from dams, in the path of floods that would follow dam failures. The result is that even though Americans now build few dams, more and more dams threaten people’s lives. Chiefly for this reason, the number of dams identified in one estimate as capable of causing death and in need of rehabilitation more than doubled from 1999 to 2006, from around 500 to nearly 1,400. The civil engineers’ 2005 report placed the number of unsafe dams much higher, at more than 3,500.