USDA Forest Service
 

Pacific Northwest Research Station

 
 
Pacific Northwest Research Station
1220 SW 3rd Ave.
Portland, OR 97204

(503) 808-2100

US Forest Service

Newsroom

News Releases: 2012

2012 | 2011 | 2010 | 2009 | 2008 | 2007 | 2006 | 2005 | 2004 | 2003 | 2002 |

[Image]: Forest Service Shield.

Marmot Dam removal publication reveals how rivers change after dams are removed, providing guidance for future removals

 

US Geological Survey/USDA Forest Service
Pacific Northwest Research Station

Portland, OR: June 14, 2012

Contacts: Jon Major, jjmajor@usgs.gov, 360-993-8927; Gordon Grant, ggrant@fs.fed.us, 541-750-7328.

Media contact: S. Richardson Dodge, (503) 808-2137, srichardsondodge@fs.fed.us; Yasmeen Sands, ysands@fs.fed.us, (360) 753-7716.

Marmot coffer dam breach. USFS scientist Gordon Grant points to rapidly eroding knickpoint following the breach. Credit: USDA-FS Jon Major.
Marmot coffer dam breach. USFS scientist Gordon Grant points to rapidly eroding knickpoint following the breach. Credit: USDA-FS Jon Major.

PORTLAND, Ore. June 14, 2012. Over the past decade, both the number and size of dams removed on rivers across the United States has been increasing. Dam removal typically involves release of at least some of the sediment stored in the reservoir behind the former dam. As released sediment moves downstream, it has the potential to dramatically change the form and behavior of the downstream channel. Nowhere has this been more closely studied than on the Sandy River, outside Portland, Oregon, following the removal of Marmot Dam in 2007. At the time, its removal produced the largest intentional release of sediment from any dam removal in history.

A newly published U.S. Geological Survey (USGS) report describes how the Sandy River responded to the release of sediment over the next 2 years. It documents the rapid and dramatic changes in channel form, profile, and sediment transport close to the dam site.

For more than 90 years, Marmot Dam blocked the Sandy River, providing hydroelectric power by diverting water into Roslyn Lake where generations of Portlanders fished and swam. But a combination of economic and environmental issues resulted in the dam’s owner, Portland General Electric, surrendering its operating license and removing the dam. Similar issues are prompting dam removals across the country.

“ An important management issue associated with dam removal is the fate of sediment accumulated in reservoir pools,” explained Jon Major, the report’s lead author and a hydrologist with the USGS. “Concerns over dam removal are sharpened where stored sediment may be contaminated by decades of upstream land-use actions.”

“ Removal of Marmot Dam provided the research community with an exceptional laboratory for studying how powerful rivers digest large quantities of coarse sediment,” says coauthor Gordon Grant, a hydrologist with the U.S. Forest Service. “Our study of physical response of the river system to the dam removal confirmed some pre-removal predictions, but also revealed some surprises, and the lessons learned have broad implications for helping to guide future removals.”

Key findings:

• An energetic river can rapidly incise and remove large volumes of unconsolidated stored sediment, even under very modest flows.
• Channel change is initially quite rapid but diminishes over time as sediment sources diminish.
• Allowing rivers to naturally process stored sediment rather than manually removing it before dam removal may be a tractable option for coarse, clean sediment in cases where sediment deposition will not create a flood risk downstream.

The report, “Geomorphic Response of the Sandy River, Oregon, to Removal of Marmot Dam,” was recently published by the USGS. It is coauthored by Jon Major and Jim O’Connor (USGS), Charles Podolak (Johns Hopkins University), Mackenzie Keith (USGS), Gordon Grant (USDA Forest Service), and others.

Read the report online at http://pubs.usgs.gov/pp/1792/pp1792_text.pdf.

USGS scientist Jon Major readies a time-lapse camera to capture the breaching of Marmot Dam. Credit: USGS scientists/interns.
USGS scientist Jon Major readies a time-lapse camera to capture the breaching of Marmot Dam. Credit: USGS scientists/interns.

 

USGS scientists and interns from the National Center for Earth Surface Dynamics process gravel samples to measure grain size distributions. Credit: USGS.
USGS scientists and interns from the National Center for Earth Surface Dynamics process gravel samples to measure grain size distributions. Credit: USGS.

 

 

 

 

 

 

 

____________________________________________________________________
The PNW Research Station is headquartered in Portland, Oregon. It has 11 laboratories and centers located in Alaska, Oregon, and Washington and about 425 employees.


US Forest Service - Pacific Northwest Research Station
Last Modified: Tuesday,10September2013 at17:35:04CDT


USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.