From: Andy Soos, ENN
Published June 18, 2013 04:31 PM

Dams, The Whole Picture

Dams are good for hydroelectric power. But just like figuring how to reduce waste or improve energy efficiency, one has to look at the whole picture and all of the potential media effects. Researchers conclude in a new report that a global push for small hydro-power 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.


An underlying assumption that small hydro-power 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.

There are many potential effects on the environment from a dam such as fragmentation of river ecosystems, acting as a barrier between the upstream and downstream movement of migratory river animals, sedimentation changes, overall water temperature, and river line and coastal erosion.

In many developing countries the savanna and forest ecology of the floodplains depend on seasonal flooding from rivers. Also, flood recession cropping is practiced extensively whereby the land is cultivated taking advantage of the residual soil moisture after floods recede. Dams attenuate floods which may affect the ecology and agriculture seriously.

The new findings were reported by scientists from Oregon State University in the journal Water Resources Research.

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. Hydro-power is generally favored 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.

"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 hydro-power 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. 

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.

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.

"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 hydro-power," Tullos said. "On a small hydro-power project, no one notices if minimum flows are being maintained. Or if a pump breaks, the hydro-power station might sit idle for long periods of time."

Researchers said the key finding of the research, contrary to prevailing but unvalidated belief, is that "biophysical impacts of small hydro-power may exceed those of large hydro-power, particular with regard to habitat and hydrological change."

For further information see Small Dams.

Nu River image by Kelly Kibler, courtesy of Oregon State University

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