Sediment routing in gravel-bed rivers following dam removal

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Fundamental knowledge of how rivers respond to changes in sediment supply is essential to the management of issues associated with the removal of large dams. Dam removal also creates an opportunity for learning about the response to large sediment pulses, which is critical for planning and stream restoration. This project will examine the 2008 removal of Milltown Dam on the Clark Fork River, MT, to develop new insights into sedimentary and geomorphic processes, including how quickly sediment pulses move through rivers, where they deposit, the extent to which they infiltrate into gravel river beds, how far they propagate, and how they affect channel morphology. This will be achieved through measurements of bedload transport; sampling of bed material to assess textural changes, infiltration dynamics, and contaminant transport; and repeat surveys of river bed, bar and floodplain topography to identify spatial and temporal patterns of sediment deposition and erosion. Field efforts will be complemented by laboratory analysis of sediment geochemistry, to fingerprint fine sediment and investigate transport of metal-laden reservoir sediments, and modeling of flow and sediment transport processes.This research, by developing a comprehensive dataset on geomorphic response to a large dam removal and generalizing those results beyond the study area, will contribute to emerging efforts to develop more predictive science for informing dam removals and river restoration. This research will also represent a field-scale experiment into the movement and fate of sediment pulses in gravel-bed rivers that will be used to evaluate how theory and data from flumes and smaller streams can be applied to larger rivers. The dam removal investigated here is especially significant in light of the quantity (approximately 3 million cubic meters) and quality (varying degrees of mining-derived contamination) of reservoir sediments potentially available for downstream transport. This project will build on data collected immediately before and after the Milltown dam removal under a NSF Small Grant for Exploratory Research. Outreach efforts will include workshops about river processes and dam removal for students from Montana Tribal Colleges and for K-8 teachers participating in the Big Sky Science Partnership. Education and outreach will also be achieved through the University of Montana?s Center for Riverine Science and Stream Renaturalization conferences and support for graduate and undergraduate students.