Small Dams on Chinese River Harm Environment More Than Expected

Small Dams on Chinese River Harm Environment More Than Expected
National Science Foundation Press Release
May 28, 2013

http://nsf.gov/news/news_summ.jsp?cntn_id=128073&org=NSF

A fresh look at the environmental impacts of dams on an ecologically
diverse and partially protected river in China found that small dams can
pose a greater threat to ecosystems and natural landscapes than large dams.

Large dams have been considered more harmful than their smaller
counterparts.

But researchers' surveys of habitat loss and damage at several dam sites
on the Nu River and its tributaries in Yunnan Province revealed that the
environmental effects of small dams are often greater--sometimes by
several orders of magnitude--than of large dams.

"Small dams have hidden detrimental effects, particularly when effects
accumulate" through multiple dam sites, said Kelly Kibler, a water
resources engineer who led the study while at Oregon State University.

"That's one of the main outcomes, to demonstrate that the perceived
absence of negative effects from small hydropower is not always correct."

She and Desiree Tullos, also a water resources engineer at Oregon State,
report their findings in a paper accepted for publication in Water
Resources Research, a journal of the American Geophysical Union (AGU).

"These researchers have taken advantage of what is essentially a natural
experiment that allowed them to compare the effects of hydroelectric
dams of different sizes," said Tom Baerwald of the National Science
Foundation's (NSF) Directorate for Social, Behavioral & Economic
Sciences, which co-funded the research with other NSF directorates. "The
results are applicable beyond this region."

To compare the effects of small and large dams, Kibler investigated 31
small dams built on tributaries to China's Nu River and four large dams
proposed for the main stem of the Nu River.

She assessed the environmental effects of these dams in 14
categories--including the area and quality of habitat lost, the length
of river channel affected, the amount of conservation land affected, and
the landslide risk.

Because information regarding large dams is restricted under the Chinese
State Secrets Act, Kibler modeled the potential effects of the four
large dams using publicly-available information from hydropower
companies, development agencies, and academic literature.

After evaluating data from the field, hydrologic models, and
Environmental Impact Assessment reports on the small dams, Kibler and
Tullos concluded that effects of the small dams exceeded those of large
dams on nine out of the 14 characteristics they studied.

One particularly detrimental effect of the small dams is that they often
divert the flow of the river to hydropower stations, leaving several
kilometers of river bed dewatered, Kibler said.

From its headwaters in the Tibetan Plateau, the Nu River flows through
China, Myanmar (Burma) and Thailand.

"While the number of small hydropower dams in operation or planned for
tributaries to the Nu River is unreported," the authors state in their
paper, "our field surveys indicate that nearly one hundred small dams
currently exist within Nujiang Prefecture alone."

Thirteen large hydropower dams are proposed for the mainstem of the Nu
River in Tibet and Yunnan Province in China.

Environmental, social, and economic factors make the Nu River basin
extremely sensitive to hydropower installations.

In addition to supporting several protected species, the region is home
to a large proportion of ethnic minorities and valuable natural
resources, the authors report.

While large hydropower projects are managed by the central government,
and both large and small hydropower projects undergo environmental
impact assessments, decisions about small hydropower projects are made
at a provincial or other regional level and often receive less
oversight, Kibler and Tullos state.

The lack of regulation paired with a dearth of communication between
small dam projects in China allows for the effects to multiply and
accumulate through several dam sites, the authors write.

To mitigate the detrimental effects of small dams, there's a need for
comprehensive planning for low-impact energy development, said Kibler
and Tullos.

"The lack of analyses of the cumulative effects of small hydropower,"
Kibler said, "is a significant research gap with important policy
implications."
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