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Thesis Braided River Response to Eight Decades THESIS BRAIDED RIVER RESPONSE TO EIGHT DECADES OF HUMAN DISTURBANCE, DENALI NATIONAL PARK AND PRESERVE, AK Submitted by Mariah Richards Department of Geosciences In partial fulfillment of the requirements For the Degree of Master of Science Colorado State University Fort Collins, Colorado Summer 2016 Master’s Committee: Advisor: Sara Rathburn Derek Booth Peter Nelson Ellen Wohl Copyright by Mariah Ellis Richards 2016 All Rights Reserved ABSTRACT BRAIDED RIVER RESPONSE TO EIGHT DECADES OF HUMAN DISTURBANCE, DENALI NATIONAL PARK AND PRESERVE, AK The spatial complexity and stochastic nature of braided rivers complicate our ability to quantify natural rates of sediment transport and limit our understanding of braided river response to human disturbance. The Toklat River in Denali National Park and Preserve, a braided tributary of the Kantishna River draining the north-facing slopes of the Alaska Range, exemplifies these challenges. Eight decades of localized channel confinement due to installation of a causeway in the 1930’s and over three decades of gravel extraction since the 1980’s have occurred on the Toklat River adjacent to the Denali Park Road. A unique, multi-scalar and temporally diverse dataset records the responses of the river over a 10-km reach. I evaluated trends in short-term sediment storage through LiDAR differencing and analyzed long-term planform change using braiding index, braiding beltwidth and topographic ruggedness derived from aerial photographs. Two reference reaches along comparable adjacent braided rivers, with varying levels of confinement and no gravel extraction, illuminate the relative influence of these human disturbances on channel and planform change. Comparisons of 2009 and 2011 LiDAR-derived DEMs showed a statistically significant volumetric loss of -30,300 ± 27,600 m3 over 4 km of active braidplain within the study reach. Braidplain sediment loss adjacent to the channel-confining Denali Park Road bridge crossing was comparable to that removed biennially through gravel extraction downstream (17,100 m3). Upstream of both the gravel extraction site and the bridge crossing, the braiding beltwidth decreased by 400 m and the braiding index lowered from eight to one between 1988 and 2011. ii The reference reaches did not display such noticeable morphologic adjustments, implying upstream migration of gravel extraction and confinement impacts, which can significantly alter flow character, leading to increased localized stream power, degradation and infrastructure damage. These results are relevant to assessing the variety and spatial extent of human disturbance on braided river systems in general. iii ACKNOWLEDGMENTS Funding was provided by Denali National Park and Preserve, Federal Highways Adminsitration, GSA QG&G, and Warner College of Natural Resources. Thank you to my advisor, Sara Rathburn, committee members, Derek Booth, Ellen Wohl and Peter Nelson, and National Park Service supervisor Denny Capps. Grateful acknowledgement to Dave Schirokauer, Paul Franke, Brad Ebel, Stephanie Moret, Pamela Sousannes, Andrew Collins, Shannon Coykendall, Britta Schroeder, Joseph Mangano, Daniel Brogan, Peter Ashmore, Janet Curran, Ken Karle, David Dust, Fisher Ankney, and the entire Fluvial Geomorphology Group. Thank you to my Uncle Chris and Aunt Lise for all the wisdom and good meals and red wine you’ve shared. Thanks to my parents, sister and Jonathan for your humor, encouragement and patience. iv TABLE OF CONTENTS ABSTRACT .................................................................................................................................... ii ACKNOWLEDGMENTS ............................................................................................................. iv LIST OF FIGURES ...................................................................................................................... vii 1. INTRODUCTION ...................................................................................................................... 1 1.1 Braided River Processes ............................................................................................... 1 1.2 Braided River Process Quantification ........................................................................... 2 1.2.1 Difficulties and Limitations ........................................................................... 2 1.2.2 Remote Sensing Techniques .......................................................................... 3 1.2.3 Morphologic Metrics ..................................................................................... 4 1.3 Humans and Braided Rivers ......................................................................................... 6 1.4 Study Goals ................................................................................................................... 9 2. STUDY AREA ......................................................................................................................... 11 2.1 Denali National Park and Preserve ............................................................................. 11 2.2 Bedrock Lithology of the Toklat Basin ...................................................................... 12 2.3 Climatology................................................................................................................. 13 2.4 Human Impacts ........................................................................................................... 14 2.4.1 Causeway and Revetments .......................................................................... 14 2.4.2 Gravel Extraction ......................................................................................... 18 2.5 Bedload Estimations ................................................................................................... 20 2.6 Reference Reaches ...................................................................................................... 22 3. METHODS ............................................................................................................................... 25 3.1 Volumetric Change Detection..................................................................................... 26 3.2 Morphologic Change Detection .................................................................................. 29 3.2.1 Braiding Index ............................................................................................. 30 3.2.2 Braiding Beltwidth ....................................................................................... 31 3.2.3 Ruggedness .................................................................................................. 33 3.2.4 Slope ............................................................................................................ 34 3.2.5 Width-to-Depth Ratios ................................................................................. 34 3.2.6 Grain Size..................................................................................................... 36 3.2.7 Stage Measurements .................................................................................... 36 3.2.8 Repeat Oblique Photographs ........................................................................ 36 v 3.2.9 Federal Highways Bridge Elevation Data .................................................... 36 3.2.10 Weather Station Data ................................................................................. 37 4. RESULTS ................................................................................................................................. 38 4.1 Volumetric Change Detection..................................................................................... 39 4.2 Morphologic Change Detection .................................................................................. 44 4.2.1 Braiding Index ............................................................................................. 45 4.2.2 Braiding Beltwidths ..................................................................................... 48 4.2.3 Ruggedness .................................................................................................. 51 4.2.4 Slope ............................................................................................................ 53 4.2.5 Width-to-Depth Ratios ................................................................................. 55 4.2.6 Grain Size..................................................................................................... 56 4.2.7 Repeat Oblique Photos ................................................................................. 57 5. DISCUSSION ........................................................................................................................... 61 5.1 Toklat River Response to Human Disturbance ........................................................... 61 5.1.1 Upstream Subreach ...................................................................................... 63 5.1.2 Bridge Subreach ........................................................................................... 65 5.1.3 Downstream Subreach ................................................................................. 66 5.1.4 Comparison to Reference Reaches .............................................................. 67 5.2 Review of Methodologies ........................................................................................... 68 5.3 Revisiting Hypotheses and Research Objectives
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