Year Established: 2015 Start Date: 2015-03-01 End Date: 2016-02-28
Total Federal Funds: $27,500 Total Non-Federal Funds: $55,000
Principal Investigators: John Petrie, Balasingam Muhunthan
Abstract: Confluences are important features of river networks providing diverse flow conditions that influence physical and biological processes. Anthropogenic alterations to river systems are often in direct conflict with fluvial and ecological processes. Nowhere is this conflict more evident than the confluence of the Snake and Clearwater Rivers, where a complex web of challenges has emerged. The presence of a dam downstream of the confluence produces sediment deposition. This sedimentation has adverse effects on the navigability of shipping channels and the capacity of the rivers to pass floods. The historical solution to sedimentation at this location has been dredging. Questions regarding the environmental impacts of dredging, particularly with respect to national water quality standards and endangered species, led to a lawsuit in 2002. The response to the lawsuit was a programmatic management strategy that embraces a range of approaches to address sediment-related problems. Sound science is now needed to evaluate remediation options and support decision making. By quantifying sediment dynamics at the confluence of the Snake and Clearwater Rivers, this project will contribute to improved sediment management and, ultimately, improved water quality thereby directly addressing the priority topic of riparian ecosystem function. The long-term goal is to improve understanding of the relationship between flow and sediment dynamics and channel morphology at the confluence of large rivers. Current knowledge of morphology at confluences is informed primarily by studies in small channels (channel width<10 m). Field data have recently been collected at confluences of large rivers (channel width>100 m) that exhibit significant differences in flow and sediment processes when compared to small channels. These findings suggest that scale plays an important role in determining confluence morphology. This project addresses an important research need by using state-of-the-art technology and innovative field procedures to directly measure three-dimensional flow velocity and bedload transport—coarse sediment moving along the riverbed. Due to a lack of field measurements, little is presently known about bedload dynamics in large river confluences. The results of these measurements support (i) the development of predictive models for flow and bedload transport in large confluences 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, along with subsequent projects anticipated by the PIs, will contribute to fundamental knowledge of flow and sediment dynamics at the confluence of large rivers as well as support solutions to the complex challenges facing the lower Snake River system. This project will fund one MS student and directly contribute to the student’s thesis. In the near-term, the student will present the results at a scientific conference and produce one publication to be submitted to a peer-reviewed journal. This proposal also assists a junior faculty in establishing a research program under mentoring and guidance from a senior faculty. The work performed will provide the basis for subsequent publications and funding proposals investigating morphological processes at large river confluences. The findings of this and future studies will be disseminated to stakeholders through relationships fostered in the present project.