"Climate Change Complicates the Whole Dam Debate"

"Demolishing dams helps many fish but threatens waters where some native species shelter from drought and invasive predators"

"With California now on track to have the rainiest year in its history—on the heels of its worst drought in 500 years—the state has become a daily reminder that extreme weather events are on the rise. And the recent near-collapse of the spillway at California’s massive Oroville Dam put an exclamation point on the potentially catastrophic risks.

More than 4,000 dams in the U.S. are now rated unsafe because of structural or other deficiencies. Bringing the entire system of 90,000 dams up to current standards would cost about $79 billion, according to the Association of State Dam Safety Officials. Hence, it has become increasingly common to demolish problematic dams, mainly for economic and public safety reasons, and less often to open up old habitats to native fish. About 700 dams have been taken down across the U.S. over the past decade, with overwhelmingly beneficial results for river species and ecosystems.

Now, however, a new study in Biological Conservation takes the science of dam removal in an unexpected direction. Although acknowledging that reopening rivers usually leads to “increased species richness, abundance and biomass,” a team of South African and Australian authors argues that in some cases threatened species may actually benefit from keeping existing dams intact."

Richard Conniff reports for Scientific American March 14, 2017.