The Former Marmot Dam
Sandy River Following Marmot Dam Removal
Marmot Dam was a diversion dam on the Sandy River and a major component of the Bull Run Hydroelectric Project. The project owner, Portland General Electric (PGE), decided to decommission the dam and other project structures and facilities. Cornforth Consultants (CCI) was retained by PGE to develop decommissioning plans.CCI prepared preliminary plans and details for cofferdams and river diversion structures to remove not only the dam but also the sediment that had accumulated upstream of the dam. Materials removed included 13,000 cy of an original timber crib dam; 12,000 cy of roller-compacted concrete; and 20,000 cy of sediment immediately upstream of the dam. The plan also included various regulatory and permitting tasks, project scheduling, and evaluation of options for removal of an additional 230,000 cy of sediment in the reservoir. In addition, CCI developed conceptual plans for decommissioning other components of the project, including tunnels, flume structures, and the powerhouse forebay reservoir.