Marmot Dam, which generated hydropower on the Sandy River for nearly a century, is no more. The dam’s removal was completed in October 2007, and the Sandy River was restored to a wild, free-flowing river from Mt. Hood to the Pacific.
Now it’s hard to tell where the Marmot Dam once stood. Stakeholders in the process have been pleasantly surprised to discover that sediment flowed down river and disbursed even faster than anticipated, settling into evenly sloping riverbeds and gravel bars ideal for fish passage and spawning.
Closure viewed as most cost-effective option
PGE first announced in 1999 it would close its Bull Run hydro operation and remove Marmot and Little Sandy dams and related equipment. The company chose to use other power sources, given the expense of maintaining aging equipment and making costly fish passage upgrades. The decision meant improved habitat for threatened fish and wildlife and expanded public recreation opportunities.
The Bull Run hydro project included the 47-foot-high Marmot Dam; a concrete-lined canal that took water from Marmot Dam through three tunnels to the Little Sandy River; the 16-foot-high Little Sandy Dam; a three-mile wooden-box flume; Roslyn Lake; and a 22-megawatt powerhouse.
A decommissioning plan was developed in 2002 by a diverse coalition, including PGE and 22 environmental organizations, state and federal resource agencies, local government and businesses.
Concrete dam demolished, then earthen dam
The historic demolition of Marmot Dam began in July 2007 with the detonation of 4,400 pounds of ammonium nitrate and dynamite to remove the top of the dam. By September, blasting and concrete demolition was completed. The debris was recycled for road surfacing. A remaining earthen or coffer dam, built to give crews a dry workspace, was breached Oct. 19, 2007, restoring the Sandy to a free-flowing river for the first time since 1912.
Within hours of the coffer dam breaching, the Sandy River resumed the appearance of a natural river. Torrents of water carried hundreds of thousands of yards of sediment downstream, helping create natural bends, bars and logjams indicative of a free-flowing river. In 2008, PGE removed the wooden flume and dam on the Little Sandy River, opening that river to unimpeded flow.
PGE biologists are continuing to monitoring streamside vegetation and fish passage on the rivers.
PGE donating land for recreation area
PGE is giving about 1,500 acres of Bull Run project land and other nearby holdings to the Western Rivers Conservancy without receiving a tax deduction. This land will form the foundation of a natural resource and recreation area in the Sandy River Basin. Ultimately covering more than 9,000 acres, the area will be owned and managed by the federal Bureau of Land Management.
See our River History section for a book-length history of the river and its salmon and steelhead runs over the centuries.