8 • The Southwest Portland Post
Dear EarthTalk: How is it that dams
actually hurt rivers?
– Missy Davenport, Boulder, CO
Dams are a symbol of human ingenu-
ity and engineering prowess—control-
ling the flow of a wild rushing river is
no small feat.
But in this day and age of environ-
mental awareness, more and more peo-
ple are questioning whether generating
a little hydroelectric power is worth
destroying riparian ecosystems from
their headwaters in the mountains to
their mouths at the ocean and beyond.
According to the non-profit American
Rivers, over 1,000 dams across the U.S.
have been removed to date.
And the biggest dam removal project
in history in now well underway in
Olympic National Park in Washington
State where two century-old dams
along the Elwha River are coming out.
But why go to all the trouble and
expense of removing dams, especially
FEATURES
if they contribute much-needed renew-
able, pollution-free electricity to our
power grids?
The decision usually comes down
to a cost/benefit analysis taking into
account how much power a given
dam generates and how much harm
its existence is doing to its host river’s
environment.
Removing the dams on the Elwha
River was a no-brainer, given that they
produced very little usable electricity
and blocked fish passage on one of the
region’s premiere salmon rivers. Other
cases aren’t so clear cut.
According to the Hydropower Re-
form Coalition (HRC), a consortium of
150 groups concerned about the impact
of dams, degraded water quality is one
of the chief concerns.
Organic materials from within and
outside the river that would normally
wash downstream get built up behind
dams and start to consume a large
amount of oxygen as they decompose.
In some cases this triggers algae
blooms which, in turn, create oxygen-
starved “dead zones” incapable of sup-
porting river life of any kind.
Also, water temperatures in dam
reservoirs can differ greatly between the
surface and depths, further complicat-
ing survival for marine life evolved to
handle natural temperature cycling.
And when dam operators release
oxygen-deprived water with unnatural
temperatures into the river below, they
May 2012
harm downstream
environments as
well.
Dammed riv-
ers also lack the
natural transport
of sediment cru-
cial to maintaining
healthy organic ri-
parian channels.
Rocks, wood,
sand and other
natural materials
build up at the
mouth of the res- Dams have a deleterious affect on water quality and on fish
ervoir instead of habitat and passage. Pictured is the world famous Hoover
dispersing through Dam, built in 1936. (Photo courtesy of iStockPhoto/Think-
the river ’s mean- stock)
dering channel.
tury ago.
“Downstream of a dam, the river is
While the U.S. government has
starved of its structural materials and
resisted taking down any major hy-
cannot provide habitat,” reports HRC.
droelectric dam along the Columbia
Fish passage is also a concern. “Most
system, political pressure is mounting.
dams don’t simply draw a line in the
No doubt all concerned parties will be
water; they eliminate habitat in their
paying close attention to the ecosystem
reservoirs and in the river below,”
and salmon recovery on the Elwha
says HRC.
River as it unfolds over the next few
Migratory fish like salmon, which
decades.
are born upstream and may or may not
CONTACTS: American Rivers,
survive their downstream trip around,
www.americanrivers.org; HRC, www.
over or through a dam, stand an even
hydroreform.org.
poorer chance of completing the round
EarthTalk® is written and edited by
trip to spawn.
Roddy Scheer and Doug Moss and is a reg-
Indeed, wild salmon numbers in the
istered trademark of E - The Environmental
Pacific Northwest’s Columbia River
Magazine (www.emagazine.com). Send
basin are down some 85 percent since
questions to: earthtalk@emagazine.com.
the big dams went in there a half cen-
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