SEATTLE, WA, May 1, 2015 -- A new study published by the U.S. Geological Survey (USGS) and its partners has found that rivers are resilient and respond relatively quickly after a dam is removed. This report was released in light of the fact that more than 1,000 dams have been removed across the United States because of safety concerns, sediment buildup, inefficiency, or having otherwise outlived usefulness.
"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 USGS. "Rivers quickly erode sediment accumulated in former reservoirs and redistribute it downstream, commonly returning the river to conditions similar to those prior to impoundment."
Dam removal and the resulting river ecosystem restoration is being studied by scientists from several universities and government agencies, including the USGS and U.S. Forest Service, as part of a national effort to document the effects of removing dams. Studies show that most river channels stabilize within months or years, not decades, particularly when dams are removed rapidly.
"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."
Sponsored by the USGS John Wesley Powell Center for Analysis and Synthesis, a working group of 22 scientists compiled a database of research and studies involving more than 125 dam removals. Researchers have determined common patterns and controls affecting how rivers and their ecosystems respond to dam removal. Important factors include the size of the dam, volume and type of sediment accumulated in the reservoir, and overall watershed characteristics and history.
See also:
"USDA invests $73M to fund critical dam rehabilitations, assessments in 23 states"
"New studies shed light on effects of dam removal on waterway landscapes"
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