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Scope/Content: Abstract: Marmot Dam, located on the Sandy River near Portland, Oregon was removed in October 2007 to restore fish passage into the upstream watershed. Marmot Dam was a 14-m (40-foot) high concrete structure located approximately 30 river miles upstream from the confluence of the Sandy River with the Columbia River. The upstream reservoir had filled with sediment, which will now be eroded and transported downstream by the river during subsequent high flows. Previous sediment studies have evaluated the potential impacts to hydraulic and sediment processes of the Sandy River due to dam removal (Stillwater Sciences, 2000). Scientists involved in the dam removal identified a need to complete a continuous longitudinal profile of the Sandy River prior to dam removal in order to evaluate the effects of dam removal with more certainty. Topographic monitoring efforts for the dam removal include detailed cross section data collection in the reservoir and in some downstream river channel areas. A longitudinal profile of water surface elevation downstream of the dam was collected in 2004 during low flow to document baseline channel slopes. However, channel bed elevation data were not collected during this effort; furthermore, a large flood occurred in 2006 that was observed by locals to have filled in many of the pools that previously existed. In September 2007 and June 2009, the Sedimentation and River Hydraulics Group was funded through the Science and Technology branch of the Bureau of Reclamation (Grant #6284) to conduct a longitudinal profile of the Sandy River before and after the removal of Marmot Dam. This survey data can be used to evaluate predictions in sediment transport and monitor changes in river morphology after the dam is removed. Scope/Content: Height: 30 feet. Length: 4690 feet. Scope/Content: Date constructed: 1913. Date removed: 2007.
Pre- and post-project monitoring Sediment and channel dynamics Dams Dam retirement