How long are these huge dams, like the Hoover Dam, engineered to last? How would we go about replacing it if it began to weaken or became obsolete? What’s the largest dam ever to fail? –Craig S., Jacksonville, Florida
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Don’t sweat the big dams, chum. It’s the little ones you should worry about. Most of the small and medium-size dams in this country were built to last just 50 years. (Nowadays, from what structural engineers tell me, the typical design life is more like 100 years.) According to the U.S. Army Corps of Engineers, about 30 percent of the more than 76,000 dams in the United States are older than 50 years–and by 2020, that number will increase to more than 80 percent. That’s a lot of old dams, some of which hold back not just water but toxic sediments from early industrial operations. Once they start to go, a lot of people are going to be in deep . . . OK, maybe not raw sewage. But some mighty unpleasant stuff.
Plenty of bad things can happen to a dam, without it collapsing. The spillways and pipes may erode, the sluice gates and valves may fail, or, if it’s a hydroelectric dam, the powerhouse equipment may (excuse me, will) wear out. The reservoir may silt up–some predict the Three Gorges Dam will become choked with silt in just 50 years. (Lake Mead, formed by the Hoover Dam, lost about 15 percent of its capacity between 1936 and 1964 due to silting–more than five million acre-feet.)
