The Colorado River at Kremmling. @bberwyn photo.
Study findings will help river restoration efforts
Staff Report
FRISCO — Scientists say rivers recover quickly when dams are removed. In some cases, it only takes a few months or years, rather than decades, for most river channels to stabilize, particularly when dams are removed rapidly.
The new study, published in Science, came after the research team compiled a database of research and studies involving more than 125 dam removals. Important factors include the size of the dam, the volume and type of sediment accumulated in the reservoir, and overall watershed characteristics and history.
“The apparent success of dam removal as a means of river restoration is reflected in the increasing number of dams coming down, more than 1,000 in the last 40 years,” said lead author of the study Jim O’Connor, geologist with the U.S. Geological Survey. “Rivers quickly erode sediment accumulated in former reservoirs and redistribute it downstream, commonly returning the river to conditions similar to those prior to impoundment.”
More than 1,000 dams have been removed across the United States because of safety concerns, sediment buildup, inefficiency or having otherwise outlived usefulness.
“In many cases, fish and other biological aspects of river ecosystems also respond quickly to dam removal,” said co-author of the study Jeff Duda, an ecologist with USGS. “When given the chance, salmon and other migratory fish will move upstream and utilize newly opened habitat.”
The increase in the number of dam removals, both nationally and internationally, has spurred the effort to understand the consequences and help guide future dam removals.
“As existing dams age and outlive usefulness, dam removal is becoming more common, particularly where it can benefit riverine ecosystems,” said Gordon Grant, Forest Service hydrologist. “But it can be a complicated decision with significant economic and ecologic consequences. Better understanding of outcomes enables better decisions about which dams might be good candidates for removal and what the river might look like as a result.”
The research was sponsored by the USGS John Wesley Powell Center for Analysis and Synthesis.
