A new report concludes that a global push for small hydropower projects, supported by various nations and also the Kyoto Protocol to reduce greenhouse gas emissions, may cause unanticipated and potentially significant losses of habitat and biodiversity. The 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 said to be relevant to national energy policies in many nations or regions -- India, Turkey, Latin America -- that seek to expand hydroelectric power generation. The social and environmental problems caused by large dam projects have resulted in a recent trend toward increased construction of small dams.
Besides the damage to streams, fisheries, wildlife, threatened species and communities, 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.
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 about one new dam is being built every day, researchers say.
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 found generally with small dams was that there was much less oversight and governance with the construction, operation and monitoring of small hydropower. 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, said a team member.