Damming Chinese rivers has been in the public consciousness for many years now, if for no other reason than for the impact the construction of the Three Gorges Dam had on the surrounding region: the 400 mile long reservoir of the Three Gorges Dam has flooded 13 cities, 140 towns, 1352 villages, and 100,000 acres of China’s most fertile farm land, according to some statistics.
Also, as an aside, the filling of the Three Gorges Dam also slowed the Earth’s rotation. Consider that for a moment.
However, new research by the National Science Foundation has found that the impact of small dams on Chinese rivers is actually a greater threat to the surrounding ecosystems than large dams, though I do not believe the scientists would have included Three Gorges Dam in that assessment.
Surveying habitat loss and damage at several dam sites along the Nu River and its tributaries in Yunan Province revealed environmental effects caused by the small dams as being often greater — to the point of several orders of magnitude in some cases — than effects 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.”
“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.”
Kibler investigated 31 small dams built on Nu River tributaries and 4 large dams proposed for the main stem of the Nu River and divided the effects into 14 categories. After evaluating the data collected from the field, in conjunction with hydrologic models, and Environmental Impact Assessment reports on the small dams, Kibler and Tullos found that the effects on the local environment of the small dams exceeded those of the large dams in 9 out of 14 categories.
“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.”