Environmental Engineering Reference
In-Depth Information
Figure 2.4
Percentage of dams more than fi fty years old by 2020, EOS (American Geophysical Union),
December 1, 2009
.
more than 400 dams in three states.
53
Clearly many of the nation's dams
are disasters waiting to happen. About 500 have been torn down in the
past few decades for structural or environmental reasons, such as the
blocking of sediment to downstream areas and blocking of fi sh passage.
Dam removal averages about one-third the cost of repair to structurally
defi cient dams.
54
In the past decade or so, the rate of dam removal has
exceeded the rate of dam construction.
55
More than half of the dams are privately owned, which is one
reason dams are among the nation's most dangerous structures (fi gure
2.5).
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Many private owners cannot afford to repair aging dams; some
resist spending the necessary money by tying up governmental repair
demands in court or campaigning to weaken state dam safety laws.
Thousands of dams have been abandoned by their owners, and over
time, title to them has become obscure. Fifteen percent of the listings
in America's National Inventory of Dams have no known owner.
