When author Edward Abbey famously wrote “The Monkey Wrench Gang” in 1975, he was roundly condemned for portraying eco-terrorists plotting to blow up Glen Canyon Dam on the Colorado River. Forty years later, the aging of the world’s dams, coupled with increasing awareness of their environmental costs, has brought dam decommissioning and re-operation to the attention of the scientific community, management agencies, and the general public. Just last month, a historic pulse of water released from the gates of Morelos Dam on the U.S.-Mexico border brought a rejuvenating shot of water to the parched Colorado River Delta for the one of the first times in many decades.

Flow experiments (FEs) - such as this experimental release from Glen Canyon Dam in 2013 - are intended to mimic some aspect of natural flooding. Photo courtesy of Western Power Administration (Lynn Weka).

Flow experiments (FEs) – such as this experimental release from Glen Canyon Dam in 2012 – are intended to mimic natural flooding for downstream areas. Photo courtesy of Western Power Administration (Lynn Weka).

Despite the attention dam releases receive, managing water resources for ecological outcomes is contentious; such actions are expensive and potentially forego other benefits. Just how common and successful are these massive experiments? In the latest issue of Frontiers in Ecology and the Environment, Julian Olden and colleagues from a NCEAS Working Group provide the first global assessment of large-scale flow experiments (FEs). After scouring the literature, they found that FEs have been used to evaluate the effects of alternative dam operations for rivers and their floodplains in over 20 countries worldwide. By scrutinizing more than100 studies, they showed that when clear objectives were articulated prior to conducting the experiment, FEs were twice as likely to achieve their stated objectives as compared to FEs without clearly articulated objectives. Furthermore, changes to dam operations were three times less likely when FEs were conducted primarily for scientific purposes. Despite the recognized importance of riverine flow regimes, four-fifths of FEs used only discrete flow events. Over three-quarters of FEs documented both abiotic and biotic outcomes, but only one-third examined multiple taxonomic responses, limiting how FE results can inform holistic dam management. In short, the authors found that although FEs are more commonplace in the lexicon of river management, there are still considerable challenges to ensuring that they succeed in advancing science and informing management decisions in the future.