Impacts of Impervious Surface Cover on Stream Hydrology and Stream-Reach Morphology, Northern Georgia A thesis presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Master of Arts Benjamin J. Young June 2010 © 2010 Benjamin J. Young. All Rights Reserved. 2 This thesis titled Impacts of Impervious Surface Cover on Stream Hydrology and Stream-Reach Morphology, Northern Georgia by BENJAMIN J. YOUNG has been approved for the Department of Geography and the College of Arts and Sciences by Dorothy Sack Professor of Georgraphy Benjamin M. Ogles Dean, College of Arts and Sciences 3 ABSTRACT YOUNG, BENJAMIN, J., M.A., June 2010, Geography Impacts of Impervious Surface Cover on Stream Hydrology and Stream-Reach Morphology, Northern Georgia (91 pp.) Director of Thesis: Dorothy Sack Urban development significantly alters the hydrologic and morphologic characteristics of stream channels. Previous research cites impervious surface cover as a primary driving force behind fluvial geomorphic alterations associated with urban development, yet questions remain about the amount of total impervious area (TIA) responsible for subsequent geomorphic modifications of stream systems and about the nature of those modifications. This research compares selected characteristics of 29 rural and 23 urban streams in northern Georgia to determine significant differences in stream hydrology and morphology associated with the expansion of impervious surface cover. Compared to rural (pre-urban) streams, urban streams were found to exhibit greater mean and flood discharges, but no difference in flood stage recurrence interval was found between the two sample groups. Analysis of the urban stream data suggests that a watershed TIA of 14-16% may be an amount of impervious surface cover above which channels become unstable. It is important to establish the level of impervious surface cover associated with alterations to the fluvial system in an attempt to offset the negative fluvial effects of urban development. Approved: _____________________________________________________________ Dorothy Sack Professor of Geography 4 ACKNOWLEDGMENTS First and foremost, I would like to thank my advisor, Dr. Dorothy Sack. For the past six years she has been a constant source of knowledge, inspiration, and support during my tenure as a student at Ohio University. I would like to thank her for initially sparking my interest in geography, helping to create my appreciation for the physical processes that shape our world and the landforms that comprise the geographic landscape. I can think of no one more influential in my educational experience than she, and for that, I owe her a tremendous debt of gratitude. I would like to thank my thesis committee members Dr. James Lein and Dr. Gaurav Sinha for their time and effort as educators and in assisting me throughout the research process. I would like to thank Dr. Lein for putting up with my incessant and rudimentary questions over the statistical analysis of my research data. Also, I would like to extend my gratitude to Dr. Sinha who was instrumental in my graduate education, helping to form my knowledge of geospatial technologies and the science and philosophy behind them. Dr. Sinha’s brilliance is only matched by his ability as a teacher to make the most intellectually challenging concepts understandable to his students. No educator ever challenged me the way he did, forcing me to think about the fundamental fabric of my mental framework, for which I am extremely grateful. I would also like to thank all the faculty of Ohio University who impacted me during my undergraduate and graduate career, shaping me into the student and person I am today. Particularly, I wish to thank Dr. Margaret Pearce, whose enthusiasm for cartography instilled in me a fascination and deep appreciation for the beautiful and 5 artistic nature of cartographic representations and Dr. Hugh L. Bloemer, for his passion as an educator, his love of geography, and for demanding the best out of his students. Also, I would like to thank the Ohio University Department of Geography for providing me with a two-year teaching assistantship that allowed me to make an impact in the lives of undergraduate students by educating and imparting on them my knowledge of and passion for geographic concepts. Lastly, my appreciation goes out to my fellow graduate students for being an educational and emotional support at a time when both became extremely necessary. 6 For Bobbi. You are forever in my mind and heart. For God did not give us a spirit of fear, but of power, love, and self-control. II Timothy 1:7 7 TABLE OF CONTENTS Page Abstract ............................................................................................................................... 3 Acknowledgments............................................................................................................... 4 List of Tables ...................................................................................................................... 9 List of Figures ................................................................................................................... 10 Chapter 1: Introduction ..................................................................................................... 11 Chapter 2: Literature Review ............................................................................................ 15 2.1 Importance of Imperviousness ................................................................................ 16 2.3 Geomorphic Thresholds .......................................................................................... 20 2.4 Experimental Design ............................................................................................... 22 Chapter 3: Study Area ....................................................................................................... 24 3.1 Site Selection .......................................................................................................... 24 3.2 Metropolitan Atlanta ............................................................................................... 29 3.3 Physiographic Provinces ......................................................................................... 30 Chapter 4: Methodology ................................................................................................... 32 4.1 Data Sources ........................................................................................................... 34 4.2 Drainage Basin Variables ....................................................................................... 36 4.2.1 Drainage Area .................................................................................................. 36 4.2.2 Total Impervious Area ..................................................................................... 39 4.2.3 Topographic Texture ........................................................................................ 42 4.3 Stream Morphology Variables ................................................................................ 42 4.4 Hydrologic Variables .............................................................................................. 45 4.5 Possible Sources of Error ........................................................................................ 47 4.5.1 Drainage Area .................................................................................................. 48 4.5.2 Total Impervious Area ..................................................................................... 50 4.5.3 NHD-derived Variables ................................................................................... 51 4.5.4 Hydrologic Variables ....................................................................................... 52 4.6 Statistical Analyses ................................................................................................. 53 Chapter 5: Results ............................................................................................................. 58 5.1 Pre-Urban versus Urban Watershed Characteristics ............................................... 58 8 5.2 Associations between Variables ............................................................................. 61 5.3 Cluster Analysis ...................................................................................................... 68 Chapter 6: Discussion ....................................................................................................... 76 Chapter 7: Conclusion....................................................................................................... 82 References Cited ............................................................................................................... 86 9 LIST OF TABLES Page Table 1: Pre-Urban study site labels and corresponding watershed name .......................... .........................................................................................................................................26 Table 2: Urban study site labels and corresponding watershed name ............................27 Table 3: Research variables ............................................................................................33 Table 4: Types of error defined by Collins and Smith (1994 .........................................48 Table 5: Expected research outcomes for pre-urban versus urban watersheds