Nature | News
A damming assessment of Mekong development
Dams on tributaries worse for fish than those on the main river.
ï¿½ Jane Qiu
05 March 2012
Dams on the tributaries of the Mekong River could have a greater
negative effect on fish biodiversity and food security than those on
the main river, researchers say.
Hydropower developments on Mekong tributaries are not subject to the
same level of scrutiny as their counterparts on the main river. ï¿½Most
of the attention has been on proposed dams on the Mekong mainstream,
such as the highly controversial Xayaburi dam in Laos,ï¿½ says lead
author Guy Ziv, an environmental scientist now at Stanford University
in California. ï¿½The impact of tributary dams is little studied.ï¿½
The findings, published today in Proceedings of the National Academy
of Sciences1, ï¿½point to a desperate need to reconsider hydropower
development in the entire Mekong River basinï¿½, says Ame Trandem, the
Southeast Asia programme director for the environmental group
International Rivers in Bangkok.
With a watershed of 800,000 square kilometres, the Mekong River basin
supports the worldï¿½s largest inland fishery and is home to 65 million
people in six countries: China, Myanmar, Laos, Thailand, Vietnam and
Cambodia. ï¿½Most of the people are poor and get 81% of their protein
from subsistence fisheries,ï¿½ says Ziv.
The steep topography of the region makes the Mekong an attractive
place for hydropower development. Driven by increasing demand for
electricity and a desire for economic development, 11 dams are being
planned on the main river, with 41 on the tributaries expected to be
completed within the next 4 years. Another 10ï¿½37 tributary dams are
likely to be built between 2015 and 2030.
Using a fish migration model, Ziv and his colleagues found that if all
of the proposed dams were constructed, they would reduce fish
productivity by 51% and endanger 100 migratory fish species.
ï¿½ Dam controversy: Remaking the Mekong
ï¿½ China admits problems with Three Gorges Dam
ï¿½ Conservationists protest Mekong dam
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They then focused on the 27 tributary dams whose fate is yet to be
determined, and were surprised to find, says Ziv, that the losses in
fish biodiversity and production would be greater than for the
proposed dams on the upper reach of the lower Mekong River.
ï¿½Individual dams may not make a big difference,ï¿½ says Ziv. ï¿½But if you
add all 27 dams together, you may get a catastrophic impact.ï¿½ This is
not only because of the total area that will be blocked for fish
migration, but also because some regions are more important fish
passages than others, he says.
One area of particular importance, the study shows, is the 3S river
system in northeastern Cambodia, southern Laos and central Vietnam
that is dominated by three major Mekong tributaries ï¿½ the Se San, Se
Kong and Sre Pok Rivers. Dams in this region would hit fish migration
the hardest. The planned Lower Se San 2 Dam in Cambodia, for instance,
would cause a 9.3% drop in fish biomass basin-wide. ï¿½The impact would
be catastrophic,ï¿½ says Ziv.
ï¿½Dams at different locations have different trade-offs between power
generation and the loss in fish biodiversity and productivity,ï¿½ says
Ziv. ï¿½The Lower Se San 2 Dam will have the highest environmental cost
per unit of energy produced.ï¿½
The team has created a simple matrix for deciding which dams to build
throughout the basin. The tool estimates the loss of fish productivity
at different levels of total electricity generation and ranks each dam
in terms of its trade-offs. ï¿½Dams with better trade-offs can be built
first when the energy demand is relatively low,ï¿½ says Ziv. ï¿½And you
really should avoid building those with the worst trade-offs, such as
the Lower Se San 2 Dam.ï¿½
Ziv stresses that the study is just a ï¿½starting pointï¿½ and that other
aspects of potential impact, such as effects on sediment, agriculture
and the displacement of people and communities, must be incorporated
into the scheme for comprehensive trade-off analyses.
According to the 1995 agreement of the Mekong River Commission (MRC),
an international body responsible for the sustainable development of
the river, each member country is required to consult other nations
for any major development projects on the Mekong itself. But there is
no such requirement for projects on the tributaries.
To many, the latest findings call for a change in that policy. ï¿½Itï¿½s
really time for the MRC to take a basin-wide approach to assessing the
consequences of dams in the region,ï¿½ says Trandrem.
Ziv, G., Baran, E., Nam, S., Rodriguez-Iturbe, I. & Levin, S. A. Proc.
Natl Acad. Sci. USA. http://www.pnas.org/cgi/doi/10.1073/pnas.
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