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dam-l Dams and greenhouse gases/LS




>From New Scientist magazine, 03 June 2000.

Raising a stink
Rotting vegetation in hydroelectric dams stokes global warming

FAR from being "green", many hydroelectric power schemes release more
greenhouse gases into the atmosphere than large coal-fired power stations,
because of the rotting vegetation they contain. So says the World
Commission on Dams, a group of scientists, engineers and environmentalists
supported by the World Bank, the world's biggest funder of large dams.


The report comes just as engineers are arguing that dams should qualify for
support as a "clean" technology under the Kyoto Protocol agreed in 1997.
The commission will report its findings later this month at a meeting in
Bonn to discuss the Clean Development Mechanism, a key part of the Protocol
aimed at reducing carbon emissions worldwide.

One surprise finding is that organic matter washed into a reservoir from
upstream generates much of the greenhouse gas. The decay of forests
submerged when the reservoirs fill up creates "only a fraction" of the gas.
This means that the emissions don't disappear when the flooded forest has
rotted away, but may continue for the lifetime of the reservoir.

Hydroelectric reservoirs cover an area of the world the size of France.
They release carbon dioxide and methane. Stagnant water produces the worst
emissions because the decaying vegetation generates methane. This is 20
times as potent a greenhouse gas as CO2, which is produced when there is
oxygen in the water. So a reservoir will produce more methane than the
river did before the dam was built.

Warnings about the gas emissions from reservoirs surfaced in the mid-1990s
(New Scientist, 4 May 1996, p 29). But what appeared at first to be a
problem for a handful of reservoirs now looks much more general.

"Tropical reservoirs that are shallow and uncleared of biomass [before
flooding] appear most at risk," says the commission. It names two
rainforest reservoirs as major planet-warmers. One is Balbina in Brazil,
which is just four metres deep in parts. Its generating capacity is 112
megawatts and it is estimated that it will produce 3 million tonnes of
carbon per year over its first 20 years. A coal-fired power station of the
same capacity would produce 0…35 million tonnes per year. Petit-Saut in
French Guyana, which has a similar capacity and powers the launch site for
Europe's Ariane rocket, will produce 0…9 million tonnes per year in its
first 20 years.

The report's authors have only studied a handful of reservoirs so far, in
just four countries, so they believe there may be many more offenders. They
warn, however, that emissions from reservoirs seem erratic and
unpredictable: one study of nine reservoirs in Brazil found that their
emissions per unit of electricity vary by a factor of 500.

"Greenhouse gases are emitted for decades from all dam reservoirs in the
boreal and tropical regions for which measurements have been made. This is
in contrast to the widespread assumption that such emissions are zero,"
says the commission. "There is no justification for claiming that
hydroelectricity does not contribute significantly to global warming."

Jamie Skinner, environmental adviser to the commission, which is based in
Cape Town, South Africa, says the report is significant because both dam
engineers and environmentalists agree on its conclusions.

Fred Pearce
---------------------
BBC Online, 31 May 2000
http://news.bbc.co.uk/hi/english/sci/tech/newsid_771000/771465.stm

Water power 'fuels climate change'

By environment correspondent Alex Kirby

   Hydro-electric power, often proclaimed as one of the greenest ways of
generating energy, can be more polluting than coal.
   This is because the reservoirs that power the dams can trap rotting
vegetation, which emits large amounts of greenhouse gases.
   But establishing just how much pollution a particular reservoir will
cause is very difficult, because they vary widely.
   The announcement of this cause of climate change comes shortly before the
next round of negotiations on how to tackle it.
   The discovery of the full greenhouse potential of hydro-electric schemes,
published in New Scientist magazine, was made by the World Commission on
Dams (WCD).

Clean claim

   The commission, a group of scientists, engineers and environmentalists,
is supported by the World Conservation Union and the World Bank, which is
the single biggest funder of large dams.
   Supporters of dams argue that they should qualify for support as a clean
technology under the 1997 Kyoto Protocol on tackling climate change.
   Many scientists believe there is strong evidence to suggest that the
earth's atmosphere is warming, and that human activities - chiefly the
burning of fossil fuels - are a significant cause.
   The WCD will report its findings at a meeting in the German city of Bonn
in June to discuss the Clean Development Mechanism, a key part of the Kyoto
Protocol.
   It says the decay of forests submerged when reservoirs are flooded
produces only a fraction of the two gases involved, carbon dioxide (CO2) and
methane.
   Much more is produced by organic matter washed into the reservoir from
further upstream, a process which may continue for the lifetime of the
reservoir.
   Methane is 20 times more potent as a greenhouse gas than CO2. It is given
off by stagnant water, while running water, which contains oxygen, produces
CO2.

Extensive problem

   So a reservoir will produce more methane than the river which ran before
the dam was built.
   The WCD, which believes the problem is far more widespread than first
thought, says the reservoirs that appear most at risk are shallow ones in
the tropics which have not been cleared of biomass before they were flooded.
   It says one particular cause for concern is the Balbina reservoir in
Brazil, which in parts is only four metres deep.
   Its generating capacity is 112 megawatts, and it is estimated to produce
three million tonnes of CO2 annually over its first 20 years.
   A coal-fired power station of the same capacity would produce 0.35m
tonnes of CO2 a year.
   In French Guyana the Petit-Saut reservoir, which has a similar capacity
and powers the launch site for Europe's Ariane rocket, is expected to
produce 0.9m tonnes of CO2 annually in its first 20 years.

Huge variation

   The WCD has looked at only a few dams in four countries, and thinks there
will be many similar examples.
   But it says one study of nine Brazilian reservoirs found their greenhouse
emissions varied per unit of electricity by a factor of 500.
   It says: "There is no justification for claiming that hydro-electricity
does not contribute significantly to global warming."

BBC Online, 31 May 2000
http://news.bbc.co.uk/hi/english/sci/tech/newsid_771000/771465.stm





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      Lori Pottinger, Director, Southern Africa Program,
        and Editor, World Rivers Review
           International Rivers Network
              1847 Berkeley Way, Berkeley, California 94703, USA
                  Tel. (510) 848 1155   Fax (510) 848 1008
                        http://www.irn.org
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