POSTED JAN 16, 2003
Colorado River water. Everybody wants some. Ever-expanding
California is using way beyond its share. The desert sin-'n-sun capital,
Las Vegas, is booming. And it needs precious river
water for those stupendous fountains. The water comes from the huge dams
blocking the Colorado River. Despite a treaty between the United States
and Mexico, barely a trickle reaches the river's mouth in the Sea of Cortez.
Economically, the Colorado River dams are critical
to the heavily-populated desert Southwest, and nobody is seriously considering
taking them down.
at Glen Canyon Dam, 1963. Environmentalists warned that the dam, by blocking
the Colorado River, would forever alter the ecology of the Grand Canyon.
Glen Canyon ain't coming down anytime soon, but other dams are - an estimated
63 dams in 2002 alone. Image: U.S.
Department of the Interior
It's a different story with "little, dinky dams."
Estimated to number 2 million (one measure of their ubiquitousness is
the fact that nobody knows the exact number), they are coming under attack
for economic, safety, and environmental reasons.
And they are coming down. American Rivers, an environmental
63 small dams were scheduled for removal in 2002, part of a trend
toward removing dams that have outlived their usefulness.
Rivers are, by definition, moving water, and dams interfere
with that flow - and with river ecology. Yet despite the many presumed
environmental benefits of removal, the real motivation is usually dollars
and cents. Old dams need repair, and that's expensive, especially when
the dam produces little or no benefit.
We can't help it. The Why Files is obsessing about
dams. What do they do to rivers? What happens when they are removed?
Dams are built for many reasons:
To control floods.
To make lakes for recreation.
To store water for drinking, industry or irrigation
To raise river levels for navigation (consider
the dam-studded Mississippi and Missouri Rivers, which are essentially
barge canals at this point).
To store water for hydroelectric power (in earlier
times, to power grain- or saw-mills.)
Many dams have overlapping justifications. The Glen
Canyon dam, built primarily for water storage and hydroelectric power,
created Lake Powell, a tourist attraction in the arid Southwest. (It also
starved the Grand Canyon of water and sediment, causing biological and
geological changes to the national park.)
A dam-buster caught red-handed on Koshkonong Creek, Wisconsin.
Whatever their purpose, dams regulate water flow.
And that can cause a series of upstream and downstream problems.
Constant water level prevents sediment from consolidating, turning banks
oxygen may fall, harming fish and shellfish.
Water may warm, injuring or killing fish that need cold water.
Wildlife habitat is flooded.
Fish are blocked from migrating and spawning (although the decline of
the salmon is blamed largely on dams in the Northwest, steelhead, striped
bass, sturgeon and alewife have similar spawning habits).
Silt in the dam impoundment can damage or destroy fish spawning grounds.
By regulating river flow, dams destroy habitat for organisms adapted
to rising and falling water.
River stay inside their banks, so floodplains no longer get deposits
of fertile sediment .
Dams block sediment flow, causing many changes downstream:
The river bottom becomes more rocky, as sediment no longer fills gaps
between larger stones.
Beaches on the nearby ocean are starved of sand normally carried in
the river, a particular problem in Southern California.
same starvation can affect wetlands. The many dams on the Mississippi-Missouri
rivers, for example, have deprived wetlands in the Gulf of Mexico
of sediment, exposing coastal Louisiana to devastating hurricanes.
Still, the impetus for dam removal comes not from environmental
damage, but from the simple fact that dams are getting long in the tooth:
25 percent of America's 2 million dams are older than 50 years.
Many of these codger dams have problems: They may
have cracks. Water may have undermined the foundation. They may be so
full of sediment that they cannot store water. They may have been built
for a purpose that no longer exists. Or they may endanger swimmers or
canoeists, who can get trapped and drown in "scour holes" that appear
downstream of dams.
The dam-removal process often begins when a state
inspector looks at a dam and insists on repairs. These often turn out
to cost far more than removal, so repair can only be justified if the
dam provides significant economic benefits. If a dam was built, for example,
to power a grain mill that is long gone, or is supplying only a small
amount of hydroelectricity, who would want to pay a million bucks to keep
it going, when it could be ripped out for $50,000 or $100,000?
The Amistad Dam, on the Rio Grande at the border between Mexico and the
United States, is used for flood control, water storage and electricity
generation. It also completely rewrites the ecology of the area.
Amistad Dam Project
Angela Bednarek, now at Colombia University's Earth Institute, queried state dam
safety officers about the motivations for removals, and learned that safety
and liability trumped environment. In Pennsylvania, where she focused
her research, the message was clear: owners were worried about lawsuits,
not fish habitat. Although she knew that dam safety officers would naturally
stress safety, she notes that they are responsible for approving removals
and thus in a good position to know the situation.
At first, Bednarek was surprised by the bottom-line
emphasis. "I was an ecologist interested in river restoration, so I assumed
the removals were occurring for environmental reasons. But after I thought
about it, I realized that would be rare for that to drive the process
completely; it would come down to balancing costs and benefits."
Unlike the cost of removal or repair, environmental
advantages are tough to enter into cost-benefit calculations. Still, she
says, "It's exciting that environmental reasons are playing a role, and
starting to play more of a role in many states."
Internationally, the effects of dam construction
are rather different. The World Commission
on Dams, in its 2000 report, said large dams had created enormous
The negative social impacts reflect a pervasive and systematic failure
to assess and account for the range of potential negative impacts on
displaced and resettled people as well as downstream communities. Estimates
suggest that some 40-80 million people have been displaced by dams worldwide
while the livelihoods of many more living downstream were affected but
not recognized. Mitigation, compensation or resettlement programs were
Here in the United States, however, the fate of
many small dams is being sealed by the fact that they are no longer needed.
And that could be good news for the environment.
Generalities, shmeneralities. Can you give
me some specifics?