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Sediment Routing Through Channel Confluences: Arp Ticle Tracing in a Gravel-Bed River Headwaters

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Sediment Routing Through Channel Confluences: Arp Ticle Tracing in a Gravel-Bed River Headwaters University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 2015 Sediment routing through channel confluences: arP ticle tracing in a gravel-bed river headwaters Kurt Imhoff University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Part of the Geomorphology Commons, and the Hydrology Commons Let us know how access to this document benefits ou.y Recommended Citation Imhoff, Kurt Sherman, "Sediment routing through channel confluences: arP ticle tracing in a gravel-bed river headwaters" (2015). Theses, Dissertations, Professional Papers. This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. SEDIMENT ROUTING THROUGH CHANNEL CONFLUENCES: PARTICLE TRACING IN A GRAVEL-BED RIVER HEADWATERS By KURT SHERMAN IMHOFF Bachelor of Science, Oregon State University, Corvallis, OR 97330 Thesis Presented in partial fulfillment of requirements of the degree of Master of Science in Geosciences The University of Montana Missoula, MT Summer 2015 Approved by: Sandy Ross, Dean of the Graduate School Graduate School Dr. Andrew C. Wilcox, Chair Department of Geosciences Dr. Marco P. Maneta Department of Geosciences Dr. Lisa A. Eby Department of Ecosystem and Conservation Sciences Acknowledgements There are many people and organizations whose assistance made this project possible. I would first like to thank my advisor, Andrew Wilcox, for his guidance and encouragement during the entirety of this project. I thank my committee members Lisa Eby and Marco Maneta, for valuable insight and perspective provided throughout. Thank you to my lab group members for valuable advice, technical help, field assistance, and constructive criticism on my thesis – Sharon Bywater-Reyes, April Sawyer, Erika Colaiacomo, Michael Jahnke, and Rebecca Manners. Thanks to my field assistants – Dylan Davis, Austin Maphis, and Pierre-Allain Duvillard – for valuable assistance during the 2014 field season. Thank you to Marwan Hassan, who aided the conceptual development of this project. Thank you to Nate Bradley, for help in setting up and analyzing the sediment transport model runs in my study. Thank you to Carl Legleiter, for insight into coordinate transformation coding. Thank you to Colin Phillips for assistance in developing and considering the dimensionless impulse analyses. Thank you to the Bitterroot National Forest for access to conduct this research. Thank you to Loreene Skeel and Christine Foster, for guidance through various logistical hoops. This material is based on work supported by the Montana Institute on Ecosystems’ award from the National Science Foundation EPSCoR Track-1 program under Grant # EPS-1101342. This work was also supported by grants from the Montana Geological Society, the Geological Society of America, and the Northwest Scientific Association. Any opinions, findings, conclusions, or recommendations presented in the material below are those of the authors and do not necessarily reflect the views of funding agencies or the Bitterroot National Forest. i Imhoff, Kurt, M.S., Summer 2015 Geosciences Sediment routing through channel confluences: Particle tracing in a gravel-bed river headwaters Committee Chairperson: Andrew Wilcox Abstract Sediment routing in gravel-bed rivers refers to the intermittent transport and storage of bedload particles, where short-duration steps are separated by periods of inactivity. Channel morphology governs sediment routing, but morphologic effects on routing in headwater systems are not well understood compared to lowland systems. RFID tracers are a valuable tool that can be employed to characterize routing processes in headwater channels through individual particle tracking. I present research on coarse sediment transport and dispersion through confluences using sediment tracers in the East Fork Bitterroot River basin, MT. I investigate the following questions: (1) How do sediment routing patterns through headwater confluences compare to those in low- gradient gravel bed river systems? (2) How does routing through confluences compare with theory and field analysis regarding dispersive behavior in non-confluence channel morphologies? I address these questions with tracer displacement data, topographic surveys, and flow measurements through two coarse-bedded headwater confluences. Within the confluence zone, transport occurs along scour hole margins in narrow, efficient transport corridors. Bedload transport is size-dependent in the plane- bed control reach, but not for tracers moving through the confluence zone. At the reach scale, data suggest that particle dispersion is enhanced through confluences relative to non-confluence channels. These results suggest that geomorphically-significant confluences may influence the dispersive evolution of bedload particles across headwater basins. ii Table of Contents Acknowledgements………………………………………………………………………..……i Abstract……………………………………………………………………………………..……ii List of Figures……………………………………………………………………...……...........iv List of Tables………………………………………………………………………….....….…...v INTRODUCTION…………………………………………………………………..…...….……1 METHODS………………………………...………………………………………..…...….…...7 Study area………………………………………………………………………………………..7 Channel Surveying………………………………………………………………….………......9 Streamflow Measurements…………………………………………………………………...10 Tracer Preparation…………………………………………………………………................10 Tracer Deployment and Recovery…………………….…………………………................12 Analyses…………………………………………………………………………....................13 RESULTS………………………………...………………………………………..….....…….17 Hydrology..………………………………………………………………………….................17 Tracer Displacement……………………………………………………………....................18 Transport Analyses……………………………………...………………………...................24 DISCUSSION………………………...……………..………………………..………………..31 Confluence Morphodynamics.…...…………………………………………........................31 Confluences and Sediment Transport……………………………………..........................32 The Big Picture……………………………………………..................................................36 CONCLUSION……………………...……………..………………………..………………....38 REFERENCES……………………...……………..………………………..………………...39 Appendix A: Study Site Characterization…………………………………………..……47 Appendix B: Tracer Data……………………………………………………………………59 Appendix C: Analyses……………………………………………………………………….70 iii List of Figures Figure 1. Headwater channel morphologies and characteristics…..………………………2 Figure 2. Effects of confluence deposits on channel morphology…………………………4 Figure 3. Confluence morphology and hydraulic variables……..………………...……......6 Figure 4. Study area map………………………………………………………………………8 Figure 5. Photographs study reaches…………………………………………………………9 Figure 6. Grain-size distribution of bed and tracers across study site…………………...11 Figure 7. Photographic cross-section of PIT-tagged tracer particle……………………...11 Figure 8. Tracer recovery method photographs……….………………………………..….12 Figure 9. Dimensionless impulse conceptual figure……………………………………….16 Figure 10. 2014 flood hydrograph at the East Fork Bitterroot River……………………..17 Figure 11. Initial and final tracer positions ………………………………………..………..19 Figure 12. Digitized patch maps at the upper and lower confluences……………….…..20 Figure 13. Particle size and depositional locations within confluences…..…………......21 Figure 14. Travel distance plotted against grain size……………………………………...22 Figure 15. Transport relation between scaled travel distance and particle size………..23 Figure 16. Travel distance as a function of starting position……………………………...24 Figure 17. Spatial distribution of tracer positions over time.……………………………...25 Figure 18. Dimensionless step length distributions………………………………………..26 Figure 19. Cumulative exceedance distributions of travel distance ……….………...…..26 Figure 20. Stochastic transport model fits……….………………………………………….28 Figure 21. Magnitude-frequency distribution of shear velocities …………………………29 Figure 22. Transport mean and variance against dimensionless impulse……………....30 Figure 23. Modal displacement against dimensionless peak shear velocity……………34 Figure 24. Proposed relation between displacement and impulse…………………….…35 Figure 25. Conceptualization of basin shape effects on dispersive pattern………….….37 iv List of Tables Table 1. Physical attribute data from each study reach……..….……………………..…..10 Table 2. Tracer transport statistics………………………….………………………...….….18 Table 3. Sediment transport model parameters and fits…..…………………..…...….….27 Table 4. Comparison of field data and model-derived transport statistics……......….….27 Table 5. Estimated critical Shields numbers………………………………………………..30 Table 6. Critical shear velocity and impulse results………………………………………..30 v 1 INTRODUCTION 2 3 Rivers act as conveyor belts that move water and sediment through their respective 4 catchments, linking terrestrial and marine environments. Geomorphic processes 5 responsible for storing and transporting sediment have been researched over a range of 6 spatial scales, from bulk denudation and erosion-driven uplift (e.g. Molnar and England, 7 1990; Whipple et al., 1999; Whipple, 2009) to particle-specific motion and patch-scale 8 bed evolution (e.g. Hassan et al., 1991; Lenzi et al., 2006; Scheingross et al., 2013). 9 Linking small-scale physical processes
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