Sign up to receive an email update when a new issue of Sound Waves is available.

close window

Link to USGS home page
Sound Waves Monthly Newsletter - Coastal Science and Research News from Across the USGS
Home || Sections: Cover Stories | Fieldwork | Research | Outreach | Meetings | Awards | Staff & Center News | Publications || Archives

 

Cover Story

Moving Mountains: Elwha River Still Changing Five Years After World’s Largest Dam-Removal Project



in this issue:
 next story

Starting in 2011, the National Park Service removed two obsolete dams from the Elwha River in Olympic National Park, Washington. It was the world’s largest dam-removal project to date. Over the next five years, water carrying newly freed rocks, sand, silt, and old tree trunks reshaped more than 13 miles of river and built a larger delta into the Pacific Ocean.

Animated map showing changes in sediment at the mouth of the Elwha River from 2011-2016
Above: Computer animation showing changes at the mouth of the Elwha River from 2011 through 2016. Brown-shaded areas are elevations above low tide; blue shades indicate seafloor depths below low tide. Watch the delta grow and change as millions of tons of sediment moved downstream from Olympic National Park to the Pacific Ocean. [larger version]

Scientists from the USGS and six research partners recently published a paper summarizing a half-decade of changes to the shape and sediment of the Elwha River after dam removal. Starting with 33 million tons of sediment trapped behind the dams, about 8 million tons resettled along the river or at the mouth, and another 14 million dispersed into the ocean. It would take more than 70 dump trucks running 24 hours a day for five years to move that much dirt and debris downstream. Piled up, the sediment would form a cone about one-third of a mile in diameter and taller than a 50-story building.

Graphic location map with labels, showing the Elwha River and surrounding area Diagram of Elwha River sediment showing the changes five years after dam removal began
Above: Map showing the Elwha River including the sites of two dams and their reservoirs, since removed. [larger version]

  Above: Diagram of Elwha River sediment changes five years after dam removal began. Mt = millions of metric tons (1,000 kilograms or 1.1 US tons). [larger version]

Aerial photo showing the Glines Canyon Dam on the Elwha River, during dam removal
Above: Glines Canyon Dam on the Elwha River, during dam removal. Photo credit: Jeff Duda, USGS. [larger version]

Illustration comparing the Statue of Liberty and a 50-story building to a hypothetical conical pile of Elwha River-dam sediment washed downstream.
Above: Illustration comparing the Statue of Liberty and a 50-story building to a hypothetical conical pile of Elwha River-dam sediment washed downstream. [larger version]

“It really emphasizes the power of water to move mountains,” said USGS geomorphologist Andy Ritchie, lead author on the peer-reviewed article in the journal Scientific Reports (see “Morphodynamic evolution following sediment release from the world’s largest dam removal.” “Five years later, the Elwha was more like an undammed river than a river choked with sediment. Even without exceptional flows, a river can recover very rapidly after removing a dam or two.”

Aerial photo showing sediment from the Elwha River flowing into the ocean after dam removal
Above: Sediment from the Elwha River flows into the ocean after dam removal. Photo credit: Jonathan Felis, USGS. [larger version]

Ritchie said 90 percent of the sediment released by the project flowed downstream to the river delta and into the ocean. Even after the main pulse of sediment had passed, the shoreline near the river’s mouth continued changing.

“I think it surprised everybody that the sediment moved out of the river as fast as it did,” said USGS research geologist and co-author Amy East. “We thought we'd be seeing major changes for 10 years or so. Instead, the peak disturbance only lasted about five months.” Yet the river continued to transform. A few years later there was a large flood on the Elwha; the river changed course in one area and heavily damaged a road and two campgrounds.

Researchers measured changes in the shape and sediment of the Elwha River and in the ocean offshore using a variety of techniques, including pre-dam survey records, GPS, and 3D lidar (laser pulse) surveys, air photos, and river gages. Scientists from the USGS, the National Park Service, the U.S. Bureau of Reclamation, Washington Sea Grant, NOAA Fisheries, the University of Washington, and the Lower Elwha Klallam Tribe worked together to collect, process, and analyze mountains of river data.

Photo collage of researchers surveying Elwha River elevations and depths
Above: Researchers survey Elwha River elevations and depths. Clockwise from upper left: setting up a traditional survey instrument above the river; measuring river depths from a kayak with sonar and GPS; walking the beach with GPS backpacks; and mapping offshore bathymetry using a personal watercraft with GPS and sonar. [larger version]

“The Elwha project has been one of the greatest examples of collaboration that I’ve ever been a part of,” said Ritchie. “But there’s still a tremendous amount to learn from the river.”

Related Sound Waves Stories
International Recognition for Historic Elwha River Restoration
Oct. - Dec. 2016
Scientific Portrait of the 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
Studying the Elwha River, Washington, in Preparation for Dam Removal
Nov. - Dec. 2006

Related Websites
Morphodynamic evolution following sediment release from the world’s largest dam removal
Scientific Reports
USGS science supporting the Elwha River Restoration Project
USGS
Elwha River Restoration
NPS
Coastal habitat and biological community response to dam removal on the Elwha River
Ecological Society of America

 next story

 

print this issue print this issue

in this issue:

Cover Story Moving Mountains: Elwha River Still Changing Five Years After Dam Removal

News Brief
News Briefs

Field Work
WHCMSC Aerial Imaging and Mapping Group Aids with Kīlauea Eruption

Recent Fieldwork

Awards
USGS Scientists Receive DOI Award for Elwha River Dam-Removal Study

Publications
Sept. Publications

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://soundwaves.usgs.gov/2018/09/index.html
Page Contact Information: Feedback
Page Last Modified: October 19, 2018 @ 12:22 PM