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Research

Scientific Portrait of the Largest Dam Removal in U.S. History



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The effects of dam removal are better known as a result of several new studies released in February 2015 by government, tribal, and university researchers. The scientists worked together to examine and report the effects of removing two large dams from the Elwha River in Washington State, the largest dam-removal project in U.S. history (see “Elwha River Restoration”). New findings suggest that dam removal can change landscape features of river and coasts, affecting ecosystems downstream of former dam sites.

“These studies not only give us a better understanding of the effects of dam removal, but show the importance of collaborative science across disciplines and institutions,” said Suzette Kimball, Acting Director of the U.S. Geological Survey (USGS).

Aerial photographs of the Elwha River mouth before and during dam removal
Above: Aerial photographs of the Elwha River mouth before and during dam removal. A, the river mouth wetlands before dam removal; B, the turbid coastal plume that was present during much of the dam removal project; and C, the expansion of the river mouth delta by sediment deposition. Photograph A by Ian Miller of Washington Sea Grant; B by Jonathan Felis of USGS; and C by Neal and Linda Chism, volunteers with LightHawk. [larger version]

Five peer-reviewed papers, with authors from the USGS, the Bureau of Reclamation, the National Park Service, Washington Sea Grant, National Oceanic and Atmospheric Administration (NOAA) Fisheries, the Lower Elwha Klallam Tribe, and the University of Washington, provide detailed observations and insights about changes in the river’s landforms, waters, and coastal zone during the first 2 years of dam removal. During this time, massive amounts of sediment were eroded from the drained reservoirs and transported downstream through the river and to the coast. 

One finding that intrigued scientists was how efficiently the river eroded and moved sediment from the former reservoirs; more than a third of the 27 million cubic yards of reservoir sediment, equivalent to the volume of about 3,000 Olympic-size swimming pools, was eroded into the river during the first 2 years, even though the river’s water discharge and peak flows were moderate compared with historical gaging records. 

This sediment release altered the river’s clarity and reshaped its channel while adding new habitats in the river and at the coast. In fact, the vast majority of the new sediment was discharged into the coastal waters of the Strait of Juan de Fuca, where the river mouth delta expanded seaward by hundreds of feet. 

Map of Elwha River watershed
Above: Map of Elwha River watershed (darker shading), showing locations of the Elwha and Glines Canyon dams, the lakes they used to impound, USGS river-gaging stations (numbered triangles), the regional setting (inset), and other boundaries. Slightly modified from figure 1C of “Large-scale dam removal on the Elwha River, Washington, USA: Source-to-sink sediment budget and synthesis” by Jonathan Warrick and others, 2015. [larger version]

“The expansion of the river mouth delta is very exciting, because we are seeing the rebuilding of an estuary and coast that were rapidly eroding prior to dam removal,” said USGS research scientist and lead author of the synthesis paper Jonathan Warrick

Although the primary goal of the dam-removal project is to reintroduce spawning salmon runs to the pristine upper reaches of the Elwha River within Olympic National Park, the new studies suggest that dam removal can also have ecological effects downstream of the former dam sites. These effects include a renewal of sand, gravel, and wood supplies to the river and to the coast, restoring critical processes for maintaining salmon habitat to river, estuarine, and coastal ecosystems.

“These changes to sediment and wood supplies are important to understand because they affect the river channel form, and the channel form provides important habitat to numerous species of the region,” stated USGS research scientist and river study lead author Amy East.

The final stages of dam removal occurred during the summer of 2014. Some erosion of sediment from the former reservoirs will likely continue. Research teams are continuing to monitor how quickly the river returns to its long-term restored condition.

“We look forward to seeing when the sediment supplies approach background levels,” said Bureau of Reclamation engineer and co-author Jennifer Bountry, “because this will help us understand the length of time during which dam-removal effects will occur.” 

USGS researchers retrieve instrumentation to measure sediment concentration from the Elwha River
Above: USGS researchers Raegan Huffman (left) and Chris Curran retrieve instrumentation to measure sediment concentration from the Elwha River, Washington, on April 2, 2012, during the incremental removal of two large dams from 2011 to 2013. The USGS sampled sediment from the river during the dam-removal project to quantify the magnitude and timing of sediment released during the restoration project. More than a third of the 27 million cubic yards of reservoir sediment, equivalent to the volume of about 3,000 Olympic-size swimming pools, was eroded into the river during the first 2 years of dam removal. USGS photograph by Jon Czuba. [larger version]

The five new papers have been published in Elsevier’s peer-reviewed journal Geomorphology, and they focus on the following aspects of the large-scale dam removal on the Elwha River, Washington: 

A public lecture about some of these findings was presented in February 2015 at the USGS campus in Menlo Park, California, by USGS research geologist Amy East. Read about it in “Undamming Washington’s Elwha River—Public Lecture on Largest Dam Removal in U.S. History,” Sound Waves, this issue; view an archived video of the lecture on the USGS Evening Public Lecture Series website (click “Video Archives” in bar at top of page).


Related Sound Waves Stories
Undamming Washington’s Elwha River—Public Lecture on Largest Dam Removal in U.S. History
Jan. / Feb. 2015
Elwha Dam Removal Begins—Long-Planned Project Will Restore Ecosystem, Salmon Runs
Nov./Dec. 2011
Final Beach-Erosion Survey of the Elwha River Delta Before Dam Removal
Sept./Oct. 2011
USGS Postdoctoral Researcher Studying Effects of Dam Removal on Marine Ecosystems
Mar. / Apr. 2013
New Video Shows a Virtual Fly-Through Along the Lower Elwha River, Washington, Using Recently Acquired Ground-Based Lidar Data
Mar. / Apr. 2012
Publications Explain Elwha River Restoration to Scientists, General Public
Sept./Oct. 2011
Studying the Elwha River, Washington, in Preparation for Dam Removal
Nov./Dec. 2006

Related Websites
USGS Science to Support the Elwha River Restoration Project
USGS
Elwha River Dam Removal—Rebirth of a River (USGS Fact Sheet 2011–3097)
USGS
Elwha River Restoration
NPS
Geomorphology
Elsevier
Large-scale dam removal on the Elwha River, Washington, USA: Erosion of reservoir sediment
Geomorphology
Large-scale dam removal on the Elwha River, Washington, USA: Fluvial sediment load
Geomorphology
Large-scale dam removal on the Elwha River, Washington, USA: River channel and floodplain geomorphic change
Geomorphology
Large-scale dam removal on the Elwha River, Washington, USA: Coastal geomorphic change
Geomorphology
Large-scale dam removal on the Elwha River, Washington, USA: Source-to-sink sediment budget and synthesis
Geomorphology

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in this issue:

Research
Virus Calculated as Culprit Killing Sea Stars

Scientific Portrait of the Largest Dam Removal in U.S. History

California Seafloor Mapping Program Reaches Milestone

Future Wave and Wind Effects on Pacific Islands

Fieldwork
California’s Sea Otter Numbers Holding Steady

New USGS Research Vessel in the Great Lakes

Spotlight on Sandy
Five New USGS Oceanographic Datasets Published Online

Outreach
Explore Coastal and Seafloor Images along U.S. Coasts

Getting Out of Harm’s Way—Evacuation from Tsunamis

USGS at the 2014 St. Petersburg Science Festival in Florida

Tribal GIS Training in the Northeast U.S.

Undamming Washington’s Elwha River—Public Lecture

Awards
Geologist Brian Atwater Receives Communications Award

Publications
Frozen Heat—New International Report on Methane Hydrates

Jan. / Feb. Publications

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