Anthropogenic alterations to river systems are often in direct conflict with fluvial and ecological processes, especially at river confluences. This conflict is especially evident at the confluence of the Snake and Clearwater Rivers. The presence of a dam downstream of the confluence produces sediment deposition, which has adverse effects on the shipping navigability and the capacity of the rivers to pass floods. The historical solution to sedimentation at this location has been dredging despite known environmental impacts. In response to a lawsuit in 2002, a programmatic management strategy was developed to address sediment-related problems. Sound science is now needed to evaluate remediation options and support decision making.
The long-term goal of the project is to improve the understanding of the relationship between flow and sediment dynamics and channel morphology at the confluence of large rivers and specifically improve sediment management and water quality for the Snake and Clearwater Rivers. This project used state-of-the-art field procedures to directly measure three-dimensional flow velocity and bedload transport of coarse sediment. The results of these measurements supported (i) the development of a predictive model for flow and bedload transport, and (ii) the identification of regions where coarse sediment is likely to be deposited downstream of the confluence of the Snake and Clearwater Rivers. This study will support future solutions to the complex challenges facing the lower Snake River system.
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