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A Century of Geomorphic Change of the San Rafael River and Implications for River Rehabilitation

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A Century of Geomorphic Change of the San Rafael River and Implications for River Rehabilitation Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 8-2015 A Century of Geomorphic Change of the San Rafael River and Implications for River Rehabilitation Stephen T. Fortney Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Life Sciences Commons Recommended Citation Fortney, Stephen T., "A Century of Geomorphic Change of the San Rafael River and Implications for River Rehabilitation" (2015). All Graduate Theses and Dissertations. 4363. https://digitalcommons.usu.edu/etd/4363 This Thesis is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. A CENTURY OF GEOMORPHIC CHANGE OF THE SAN RAFAEL RIVER AND IMPLICATIONS FOR RIVER REHABILITATION by Stephen T. Fortney A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Watershed Science Approved by: _________________________ __________________________ Dr. John C. Schmidt Dr. Janis L. Boettinger Major Professor Committee Member _________________________ __________________________ Dr. Joseph M. Wheaton Dr. Mark R. McLellan Committee Member Vice President for Research and Dean of the School of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2015 ii Copyright © Stephen Fortney 2015 All Rights Reserved iii ABSTRACT A Century of Geomorphic Change of the San Rafael River and Implications for River Rehabilitation by Stephen Tinley Fortney, Master of Science Utah State University, 2015 Major Professor: Dr. John C. Schmidt Department: Watershed Sciences Beginning in the early 20th century and continuing into the 21st century, the lower 87 km of the San Rafael River in central Utah underwent rapid geomorphic changes. Extensive water development in the headwaters, invasion of the non-native tamarisk shrub, and man-made perturbations to the channel-floodplain system have been responsible for the changes that we documented in this study. We used a combination of spatially robust and temporally precise methods to reconstruct the modern history of channel change and identify the processes responsible for those changes. These methods include analysis of historic aerial photographs, analysis of USGS gage data, dendrogeomorphic analysis of floodplain stratigraphy, and comparison of historic and modern longitudinal profiles. The San Rafael River changed from a wide, shallow, heterogeneous channel to a narrow, deep, homogeneous channel. Specifically, between 1938 and 2009, the San iv Rafael River along the length of the entire study area narrowed 83%. Additionally, the floodplain vertically accreted between 1.0 and 2.5 m. The majority of the channel narrowing occurred during two distinct time periods - 1952 to 1979 and 1987 to the present - when low, mean annual stream flow was low. Channel narrowing is primarily due to the reduction in transport capacity, but when coupled with tamarisk establishment, channel narrowing and floodplain aggradation has been rapid. We documented the spatial extent of channel bed changes over the course of the 20th century. We found that the channel bed aggraded in five segments, lowered in one segment, and remained the same in the other portions of the study area. Analysis of historic, precise measurements of bed elevation at the USGS gage 09328500 revealed that the channel bed incised between Hatt’s Ranch and MacMillan Lower Ranch Dam during two time periods: from 1952-1965 and 1983 to the present. Both episodes of incision were caused by unequal amounts of scour and fill. This imbalance in bed fluctuation was induced by human modification of the channel during the first episode and lowering of the local base control during the second episode of incision. The changes to the physical template of the San Rafael River have implications for the management of three endemic fish – the roundtail chub (Gila robusta robusta), the bluehead sucker (Catostomus discobolus), and the flannelmouth sucker (Catostomus Latipinnis) – which currently utilize the study area. Future management of the river will benefit from the results of our study, which reveal the physical processes that are responsible for the historic and current condition of the river. (211 pages) v PUBLIC ABSTRACT A Century of Geomorphic Change of the San Rafael River and Implications for River Rehabilitation Stephen T. Fortney Suspended-load rivers are subject to rapid geomorphic changes. In particular during the Holocene Epoch, arroyos of the Colorado Plateau experienced several periods of rapid erosion and aggradation. The most recent period of entrenchment occurred around the turn of the 20th century. The mechanisms responsible for the modern period of aggradation that has followed the most recent period of entrenchment have not been well documented. The research presented in this thesis reveals the mechanisms responsible for modern alluviation of the San Rafael River, which drains the Colorado Plateau The lower 87 km of the San Rafael River, which enters the Green River south of the town of Green River, UT has experienced rapid geomorphic changes during the last 100 years. To quantify these changes, we used a complement of temporally precise and spatially robust methods. By understanding the rates, magnitudes and types of geomorphic changes, we could then identify the mechanisms of these channel changes. The San Rafael River narrowed by 83% between 1938 and 2009 and the floodplain aggraded 1.0 to 2.5 m. Channel narrowing was caused by a reduction in the transport capacity of the river, and was accelerated by the establishment of vegetation, including the non-native tamarisk shrub, on active channel surfaces and the floodplain. Significant water withdrawals during the 20th century have primarily been responsible for the reduction in transport capacity by decreasing the magnitude and duration of the annual snowmelt flood. During this time period, monsoon floods continued to deliver large quantities of fine sediment to the channel. During the 20th century, the channel bed incised in one segment and aggraded in five segments. The two periods of incision that we documented were related to human modifications of the channel and floodplain. With the knowledge of the physical processes that have been responsible for the channel changes in the San Rafael River, prediction of future channel conditions can then be made. The changes to the physical template of the San Rafael River have implications for the management of three endemic fish – the roundtail chub (Gila robusta robusta), the bluehead sucker (Catostomus discobolus), and the flannelmouth sucker (Catostomus latipinnis) – which currently utilize the study area. vi ACKNOWLEDGMENTS I would like to thank the Natural Resources Conservation Services for funding this study. I would like to thank Jack Schmidt for giving me the opportunity to work on an amazing project in a beautiful part of the world. I cannot thank Jack enough for his guidance as well as his patience while I learned the skills that were necessary to complete the project. Jack’s knowledge of the Colorado Plateau and the hydrology and geomorphology of the rivers that cross this spectacular landscape is unsurpassed, and my work greatly benefited from this. Also, the excellent work that Jack’s former students have completed on projects similar to mine in places such as the Green River, Colorado River, Duchesne River, and Rio Grande River provided a great foundation of knowledge on which to build my work. During my time at Utah State University, I had the privilege of working among an amazing group of people that were Jack’s lab. In particular, my research greatly benefitted from the mentorship of my lab mates: Dave Dean, Milada Majerova, Susannah Erwin, and Rebecca Manners. Dave Dean deserves special attention, for he got me on track when I first started and he took the lead on digging and interpreting the Hatt’s Ranch trench. He also provided logistical support for my research as well as technical advice to me as I analyzed, what seemed like, an insurmountable amount of data. Other folks who deserve attention for either helping me in the field or conducting grain size analysis in the lab include Alan Saltzman, Ashton Montrone, Jon Harvey, Michelle Summa-Nelson, Ryan Dutson, Martin Schroeder, and Amrith Gardihewa. Also, I would like to thank my committee members Dr. Joseph Wheaton and Dr. Janis Boettinger for vii their unique perspectives on geomorphology and for providing friendship and professional support during my work. Dr. Peter Wilcock also provided guidance during the process of untangling the story of channel change of the San Rafael River. Our collaborators - USU Fish Ecology Lab, USU Luminescence Laboratory, Utah Division of Wildlife Resources, and Bureau of land Management - deserve recognition for their support and help with the project. Last but not least, I would like to thank my family who have been supportive of me (or at least faked it well enough for me to believe it) throughout the duration of the time that it took to complete my degree. My wife, Mijanou, deserves the most amount of appreciation. Finally, I want to thank my kids, Elias and Sally, for being wonderful. I look forward to the time when they get the opportunities to learn more than I know about the rivers and the places of this world. Stephen Fortney viii CONTENTS
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