Dams in the Amazon basin, such as Brazil's Tucuruí dam in Pará state,
must be carefully
planned to avoid disrupting the flow of nutrients from
headwaters in the Andes.
Out of some 151 dams proposed for the Amazon river system, more than
half will sever the connectivity between the Amazon lowlands and
headwaters in the Andes mountains, according to the latest study. The
unimpeded flow of the river over the past 10 million years is thought to
have fuelled the extraordinary biodiversity of the Amazon ecosystem.
The finding follows decisions to prioritize hydropower
development in the countries that share the Amazon tributaries,
including Bolivia, Columbia, Peru, Brazil and Ecuador. As many as 48
dams that produce at least two megawatts of power each are already in
place, and there are plans to triple that number by 2030. Peru,
especially, is aggressively pursuing hydropower in cooperation with
Brazil.
The study, published in the journal PLoS ONE2,
is the first to evaluate the impact of all proposed dams on the six
Amazon river basins across five countries, together with associated
projects to construct road and power lines. Previous impact assessments
focused only on individual projects and country-level impacts.
This kind of analysis “has been needed for a long time to
take a comprehensive view of the Amazon basin”, says Robert Naiman, a
river ecologist at the University of Washington in Seattle.
Dam data
The study began in 2010 when Matt Finer, a staff ecologist
at Save America’s Forests in Washington DC, and his colleague Clinton
Jenkins, of North Carolina State University in Raleigh, acquired data on
the locations of proposed dams from government ministries in all five
nations. The information included their power-generation capacities and
their requirements for roads and electric grids.
Finer and Jenkins plotted the locations of the dams using
maps from a global river database called HydroSHEDS, and developed five
criteria that could be applied across national boundaries to assess the
ecological impact. They looked at whether a new dam would fragment the
river, and decided that there would be no impact if the proposed dam is
within 25 kilometres of an existing large dam that has already altered
the river.
The other criteria consider whether the dams would be the
first disruption of the connectivity between the Andes and the Amazon;
whether the dams would need new roads and power lines; and whether there
could be miscellaneous environmental impacts, such as flooding of land
or blocks to migrating fish. A ‘yes’ to any of these would signify a
negative ecological impact.
Using this framework, the study finds that 47% of the proposed dams
are high impact, having at least three negative effects. About 20% are
low impact, with little or no ecological effect.
And 80% of the projects are situated at least 3 kilometres
away from the nearest roads or main power lines, meaning that forests
would have to be cleared to enable construction of this infrastructure.
“From an ecological perspective, having that many dams in
the headwaters is going to change the Amazon for several hundreds, if
not thousands, of kilometres downstream,” says Naiman.
John Matthews, an ecologist at Conservation International
in Arlington, Virginia, says that the framework could be adapted to
reflect changes to climate, using the HydroSHEDS database together with
other models. “A lot of this added investment in the upper Amazon is
going to be sensitive to climate change,” he says. “There’s been
indirect evidence that flows have been impacted, and that has impacted
the quantity of hydropower in the Andes.”
“It is important not to view all dams as bad or all dams
as good,” says Finer. Instead, the goal is to show governments the need
for strategic planning so that hydropower is developed as a network
across the entire basin, rather than as a series of isolated,
opportunistic projects, he says.
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