A Characterization of Urban Infiltration Capacities Through Measurement, Modeling, and Community Observation (Under the Direction of Dr
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ABSTRACT BERGESON, CHASE BENDER. Where Can the Water Go? A Characterization of Urban Infiltration Capacities Through Measurement, Modeling, and Community Observation (Under the direction of Dr. Katherine Martin). Increasingly urbanized watersheds are creating new challenges for stormwater management, as some relevant aspects of urban hydrology and their perceived impacts by communities are not well understood. Infiltration models commonly used in rainfall-runoff predictions are often based on relatively undisturbed soils; however, highly disturbed and compacted urban soils may function almost as impervious surfaces, with very low infiltration rates. When soils become highly altered, soil maps and land cover data alone may not be sufficient to estimate infiltration rates across an urban watershed. As a result, models may frequently do a poor job estimating runoff volumes in urban areas. Additionally, urbanites may perceive issues of stormwater flow within a watershed that differ spatially from those predicted by models. Our research addresses these gaps in understanding using a sociohydrological approach that will help prioritize stormwater management within an urban watershed. In this study, we tested three common infiltration models, by comparing modeled infiltration rates to infiltration rates measured at 89 locations around the Walnut Creek watershed in Raleigh, NC. Based on these measurements we assessed which factors: land use, ground cover, time since development, and soil texture had the greatest impact on soil infiltration. We also asked residents of the watershed about where and how they experience flooding and about the practices that they use to maintain their own properties. Collected data was used to assess how social and hydrological data could be used jointly to improve our knowledge about urban hydrology. We found that the commonly used, Horton, Green-Ampt, and Curve Number models typically underestimate soil infiltration rates in urban settings without inputs from field measurements. In this study, we propose an alternative model for predicting infiltration capacities based on a basin-wide random forest model. Results from field measurements show that urban forests and areas with forested ground covers have statistically significantly (p<0.05) higher infiltration capacities than other urban land. Additionally, urban residents perceive issues of flooding in their communities, often in publicly visible locations close to the areas that they frequent. Our results also indicate that although traditional infiltration models do a poor job in urban settings, urban soils in the Walnut Creek watershed are generally able to absorb the water from most precipitation events and may have high capability of infiltrating urban stormwater runoff. In the context of further reduction of stormwater runoff from impervious surfaces, the preservation of urban forests, especially adjacent to new development, could be important for maintaining and improving the ability of urban soils to absorb water. The prioritization of this and other stormwater control measures should be focused upstream of areas where residents find the most impacts from urban flooding and in areas with populations most vulnerable to flooding. © Copyright 2021 by Chase Bender Bergeson All Rights Reserved Where Does the Water Go? A Characterization of Urban Infiltration Capacities Through Measurement, Modeling, and Community Observation by Chase Bender Bergeson A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Natural Resources Raleigh, North Carolina 2021 APPROVED BY: _______________________________ _______________________________ Katherine Martin Bethany Cutts Committee Chair _______________________________ Barbara Doll DEDICATION This thesis is dedicated to the residents of the Walnut Creek watershed. ii BIOGRAPHY Growing up in Maryland on the shores of the Chesapeake Bay, I jumped in a canoe, went for a swim, or sat down with family and friends for a crab feast whenever I could. I was fortunate to grow up with my parents, siblings, cousins, and four loving grandparents nearby. In high school, my grandfather’s tireless work for the local environment got me interested in environmental studies, but it was not until my freshman year of college when the passionate professor of a geoscience course convinced me to make protection of the environment, specifically water resource conservation and restoration the goal of my studies and career. In 2013, I graduated from The University of North Carolina at Chapel Hill with a BS in Environmental Science, a minor in Geology, and new family, friends, and experiences that will forever bond me to North Carolina. After graduating, I moved back to Maryland and undertook a year of service with the Chesapeake Conservation Corps. Through this program, I worked with a great team at the Anne Arundel Watershed Stewards Academy, trying to improve the health of the Chesapeake Bay through the training of community leaders in stormwater management and pollution-reducing behavior change campaigns. While there, I learned a lot about working with diverse groups, environmental education, and the issues that face the Bay. I wanted to get more hands-on research experience, so I worked for almost 5 years at the University of Colorado at Boulder in the CIRES Center for Limnology, where I conducted field and lab studies on many of Colorado’s lakes and streams, before deciding to return to my studies, as well as friends and family back east and begin a Masters in Natural Resources at North Carolina State University. I hope my research will be useful to the field of urban hydrology generally and to residents of the Walnut Creek watershed specifically. iii ACKNOWLEDGMENTS So many people helped me on the journey to complete this research, I would specifically like to thank: My partner: Dr. Patrick Heenan My family: Jory Bender, Michael Bergeson, Melvin Bender, Judith Bender, Jesse Bergeson, Ryan Bergeson, Wyatt Bergeson, Amy Shera, Keller Shera, Rowen Shera, Anyka Bergeson-Keller, Jordan Bergeson-Keller, Sarah Heenan, Alan Malnak, Lisa Stuntz My committee members: Dr. Katherine Martin, Dr. Bethany Cutts, Dr. Barbara Doll Members of the Watershed Ecology Lab: Elly Gay, Katie McQuillan, Zhenzhen Zhang, Tatiana Height, Amanda Roberts, Dr. Dominic Libera and especially the urban hydrology field team: Logan Swope, Will Mangum, and Jordan Williams Members of the NC State community: Melinda Martinez, Dr. Ryan Emanuel, Dr. Joshua Heitman, Dr. William Hunt III, Dr. Erin Rivers, Dr. Adam Howard, Dr. Rachel Cook, Sarah Slover, Dr. Louie Rivers III, Dr. Stacy Supak, Dr. Helena Mitasova, Neil Bain Community Members: Christy Perrin, Amin Davis, Leann Walker, Sean Gough, Aaron Schettler, Wayne Miles All the participants who took the survey, sent the survey out, or gave permission for infiltration sampling on their property. Thank you especially to the greater Walnut Creek watershed community, including the residents of some of Raleigh’s oldest historically black communities. I acknowledge that my research took place on the ancestral lands of the Skaruhreh/ Tuscarora and Lumbee people who are still a vital part of North Carolina’s community today. iv TABLE OF CONTENTS LIST OF TABLES ....................................................................................................................... vii LIST OF FIGURES .................................................................................................................... viii 1. INTRODUCTION ..................................................................................................................... 1 1.1 Background and Rationale .................................................................................................. 1 1.2 Infiltration Modeling ........................................................................................................... 4 1.3 Participatory Mapping ......................................................................................................... 7 2. MATERIALS AND METHODS ............................................................................................. 11 2.1 Study Area ......................................................................................................................... 11 2.2 Data Collection .................................................................................................................. 12 2.2.1 Site Selection .......................................................................................................... 12 2.2.2 Infiltration Measurements ....................................................................................... 13 2.2.3 Soil Texture/ Hydrologic Soil Group ...................................................................... 15 2.2.4 Land Use ................................................................................................................. 16 2.2.5 Ground Cover/Vegetation Cover ............................................................................ 17 2.2.6 Time Since Development ........................................................................................ 18 2.2.7 Soil Compaction...................................................................................................... 18 2.2.8 Antecedent Soil Moisture ....................................................................................... 19 2.2.9 Saturated Hydraulic Conductivity..........................................................................