Small dams causing ecosystem disruption

An underlying assumption that small hydropower systems
pose fewer ecological concerns than large dams is not universally valid,
scientists said in the report. A five-year study, one of the first of its type,
concluded that for certain environmental impacts the cumulative damage caused
by small dams is worse than their larger counterparts. 

The findings were reported by scientists from Oregon
State University in the journal Water Resources Research, in work supported by
the National Science Foundation.

The conclusions were based on studies of the Nu River
system in China but are relevant to national energy policies in many nations or
regions – India, Turkey, Latin America – that seek to expand hydroelectric
power generation.

Hydropower is generally favoured over coal in many
developing areas because it uses a renewable resource and does not contribute
to global warming. Also, the social and environmental problems caused by large
dam projects have resulted in a recent trend toward increased construction of
small dams. 

"The Kyoto Protocol, under Clean Development
Mechanism, is funding the construction of some of these small hydroelectric
projects, with the goal of creating renewable energy that's not based on fossil
fuels," said Desiree Tullos, an associate professor in the OSU Department of
Biological and Ecological Engineering. 

"The energy may be renewable, but this research
raises serious questions about whether or not the overall process is
sustainable," Tullos said. 

"There is damage to streams, fisheries, wildlife,
threatened species and communities," she said. "Furthermore, the projects are
often located in areas where poverty and illiteracy are high. The benefit to
these local people is not always clear, as some of the small hydropower
stations are connected to the national grid, indicating that the electricity is
being sent outside of the local region. 

"The result can be profound and unrecognized
impacts." 

This study was one of the first of its type to look
at the complete range of impacts caused by multiple, small hydroelectric
projects, both in a biophysical, ecological and geopolitical basis, and compare
them to large dam projects. It focused on the remote Nu River in China's Yunnan
Province, where many small dams producing 50 megawatts of power or less are
built on tributaries that fall rapidly out of steep mountains. There are
already 750,000 dams in China and researchers say that about one new dam is
being built every day.

Among the
findings of the report as it relates to this region of China: 

• The
  cumulative amount of energy produced by small hydroelectric projects can be
  significant, but so can the ecological concerns they raise in this area known
  to be a "hotspot" of biological diversity. 
• Per
  megawatt of energy produced, small tributary dams in some cases can have
  negative environmental impacts that are many times greater than large, main
  stem dams. 
• Many dams
  in China are built as part of a state-mandated policy to "Send Western Energy
  East" toward the larger population and manufacturing centers. 
• Small dams
  can have significant impacts on habitat loss when a river's entire flow is
  diverted into channels or pipes, leaving large sections of a river with no
  water at all. 
• Fish,
  wildlife, water quality and riparian zones are all affected by water diversion,
  and changes in nearby land use and habitat fragmentation can lead to further
  species loss. 
• The
  cumulative effect on habitat diversity can be 100 times larger for small dams
  than large dams. 
• Policies
  encouraging more construction of small dams are often developed at the national
  or international level, but construction and management of the projects happen
  at the local level. 
• As a
  result, mitigation actions and governance structures that would limit social
  and environmental impacts of small hydropower stations are not adequately
  implemented.

"One of the things we found generally with small dams
is that there was much less oversight and governance with the construction,
operation and monitoring of small hydropower," Tullos said. "On the large, main
stem dams, people pay attention to what's going on. On a small hydropower
project, no one notices if minimum flows are being maintained. Or if a pump
breaks, the hydropower station might sit idle for long periods of time." 

Researchers said the key finding of the research,
contrary to prevailing but unproven belief, is that "biophysical impacts of
small hydropower may exceed those of large hydropower, particular with regard
to habitat and hydrologic change."