State Water Resources Research Institute Program

Project ID: 2012MT267B
Title: Student Research Fellowship: Pool Response to Fine Sediment Loading from Dam Removal, White Salmon River, Washington
Project Type: Research
Start Date: 3/01/2012
End Date: 2/28/2013
Congressional District: at-large
Focus Categories: Geomorphological Processes
Keywords: reservoir, sediment, erosion
Principal Investigator: Colaiacomo, Erika
Federal Funds: $ 1,000
Non-Federal Matching Funds: $ 420
Abstract: On October 26, 2011, the 98-year-old Condit Dam on the White Salmon River was breached, releasing a mudflow downstream. Within hours, fine silt and sand had draped the 3.3 river miles between the dam site and the confluence with the Columbia River. Our study will investigate the spatial and temporal controls on geomorphic response to this fine sediment loading.

We will quantify the resultant erosion from pools by determining what flows create a boundary shear stress that exceeds the critical shear stress of fine pool sediment, thus creating the movement of particles are required to flush reservoir sediments from pools and return the river to viable fish habitat. We will complete hydraulic modeling of shear stress with the US Army Corps of Engineers Hydrologic Engineering Centers River Analysis System (HEC- RAS) sediment transport model and calibrate the models against repeat field measurements of pool bed elevation. We will use the model to explain how fine sediment responds to the annual hydrograph. Through modeling and repeat field measurements, we will quantify how sediment in pools respond to the high magnitude flows in the winter versus the lower magnitude flows the rest of the year. We can also model how the observed field response corresponded to flow. This will allow us to predict what flows would be required to produce a desired pool recovery.

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