USGS: Dam Removal Study Reveals River Resiliency
U.S. Department of the Interior
1 May 2015
U.S. Department of the Interior, U.S. Geological
Survey, Office of Communications and Publishing, 12201
Sunrise Valley Dr, MS 119,
Reston, VA 20192
Jeff Duda, USGS, Grant Gordon, USFS, Ryan
Seattle, Wash. — More than 1,000 dams have been removed across the
United States because of safety concerns, sediment buildup,
inefficiency or having otherwise outlived usefulness. A paper
published today in Science finds that rivers are resilient and
respond relatively quickly after a dam is removed.
“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.”
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, the volume and type of
sediment accumulated in the reservoir, and overall watershed
characteristics and history.