During their Federal Energy Regulatory Commission (FERC) relicensing process, Portland General Electric (PGE) decided to decommission their Bull Run Project and remove Marmot and Little Sandy dams on the Sandy and Little Sandy rivers, respectively. The Sandy River drains into the Columbia River and is located about 30 miles east of Portland, OR. Marmot Dam is located on the Sandy River at River Mile (RM) 30, and the impoundment formed by the dam is currently filled to near the dam's crest with approximately 980,000 yd3 of sediment. Little Sandy Dam is located 1.7 miles upstream of the confluence with the Bull Run River. Approximately 4,500 yd3 of mostly coarse (>2 mm) sediment is stored behind Little Sandy Dam.

Stillwater Sciences worked with a diverse stakeholder group of local, state and federal agencies, tribes, and non-governmental organizations to analyze the potential downstream effects of sediment release following dam removal. The analysis included modeling transport dynamics occurring under several different dam removal alternatives and hydrologic scenarios and then evaluating the geomorphic implications for the channel downstream and the potential effects on salmonid habitats and populations.

Stillwater Sciences developed numerical models for gravel and sand transport, based on existing bedload equations, to assess the geomorphic and biological effects of removing these dams. This pioneering modeling approach used state-of-the-art methods to route sand and gravel through the 30-mile reach of the Sandy River downstream of Marmot Dam following a simulated dam removal. The model is unique in its ability to provide predictions of sediment transport and deposition over large temporal and spatial scales, to allow comparison of various dam-removal alternatives, and to provide a basis for evaluating the potential downstream impacts of sediment release under these alternatives.

Stillwater Sciences used the model predictions in combination with field reconnaissance and interpretation of maps and aerial photographs to describe potential three-dimensional sediment deposition patterns and the potential resulting geomorphic effects and effects to anadromous salmonid habitats and populations. Our rigorous peer review process entailed circulating the report to several experts in the field of sediment transport modeling and fluvial geomorphology, resulting in a widely accepted analysis that served as the basis for decision-making. All parties in the process felt that the independent and sound scientific analysis conducted by Stillwater Sciences gave the group confidence in designing the removal methods. The dam is slated for removal beginning in 2007.