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Watershed-Scale Distributed Hydrologic Modeling and Assessment of Low Impact Development Features in White Oak Bayou, Houston, TX by Christina M

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Watershed-Scale Distributed Hydrologic Modeling and Assessment of Low Impact Development Features in White Oak Bayou, Houston, TX by Christina M ABSTRACT Watershed-scale Distributed Hydrologic Modeling and Assessment of Low Impact Development Features in White Oak Bayou, Houston, TX by Christina M. Hughes This thesis proposes a method for modeling site-scale Low Impact Development (LID) features at the watershed scale to evaluate the as-yet unknown performance of LID in a high intensity rainfall region. Increased impervious cover from urban development causes increased peak flows at the watershed outlet during rainfall events, often leading to flooding. Although LID features have been constructed across the U.S. to address this issue, their performance has not been evaluated in a high intensity rainfall region or cumulatively in a large watershed. Using the fully-distributed Vflo® hydrologic model of the White Oak Bayou watershed in Houston, TX, two common urban retrofit LID features were modeled (rain gardens and green roofs) using a simple parameter-averaging method for various frequency storms. Findings indicate that although unable to significantly control the 100-year storm event, LID features can effectively reduce outlet discharges during smaller storms when fully implemented across a large urban watershed. Acknowledgments Special thanks to Dr. Philip B. Bedient for your support, guidance, and freedom of direction on this project, and for providing me with the invaluable opportunity to connect with community partners through research. Thank you to Dr. Baxter Vieux for providing access to the Vflo® model and for your prompt feedback, valuable insight, and enthusiastic assistance on developing the modeling methodology for this project. Thanks also to Dr. Qilin Li for agreeing to serve on my committee and for providing me with excellent background and guidance from which to shape my analysis. Special thanks to Dr. Jeffrey Nittrouer for your mentorship, patience, for broadening my perspective, and for encouraging my enthusiasm for scientific research. I would not have had the courage or endurance to finish this project without the continuous support of my research colleagues Toni Sebastian, Tatyana Luttenschlager, Ben Bass, Nick Irza, Courtney Hale, Jessie Gill, Katherine Anarde, Mikaela Mahoney, Larry Dunbar, Nick Fang, and the Sed Sisters. Special thanks to Jacob Torres and Andrew Juan for allowing me to interrupt you constantly for guidance and feedback. Thank you to members of the White Oak Bayou Association and TIRZ 5 for background information on the project and support for this research. Finally, I would like to express thanks to my family and friends for their unconditional love and support, and to the countless others who have leant me their time, resources, opinions, and expertise during this process. Contents Acknowledgments ............................................................................................................ iii Contents ............................................................................................................................ iv List of Figures ................................................................................................................... vi List of Tables .................................................................................................................. viii List of Equations .............................................................................................................. ix Nomenclature .................................................................................................................... x Introduction ..................................................................................................................... 11 1.1. Low Impact Development ...................................................................................... 12 1.2. Hydrologic Modeling ............................................................................................. 19 1.2.1. Lumped Hydrologic Models ............................................................................ 19 1.2.2. Distributed Hydrologic Models ....................................................................... 20 1.3. Summary of Objectives .......................................................................................... 22 Model Background and Application ............................................................................. 24 2.1. General Description of the Vflo® Model ............................................................... 24 2.2. White Oak Bayou Study Area ................................................................................ 29 2.2.1. Flood Control in White Oak Bayou ................................................................. 34 2.3. Base Model Development ...................................................................................... 37 2.3.1. Model Application ........................................................................................... 37 2.3.2. Sensitivity Analysis ......................................................................................... 40 2.3.3. Model Calibration ............................................................................................ 44 2.3.3.1. Hurricane Ike (11.2 in/48 hrs) ................................................................... 46 2.3.3.2. July 2012 Storm (5.3 in/72 hr) .................................................................. 50 2.3.3.3. September 2013 Storm (4 in/24 hr) ........................................................... 52 LID Modeling Methodology ........................................................................................... 56 3.1. LID Model Development ....................................................................................... 56 3.1.1. LID Feature Modeling Assumptions ............................................................... 57 3.1.2. Modeling Rain Gardens as Residential LID Features ..................................... 59 3.1.3. Modeling Green Roofs as Commercial and Public LID Features ................... 65 Results and Discussion .................................................................................................... 70 4.1. LID Performance for Design Storms ..................................................................... 72 v 4.2. LID Feature Parameter Analysis ............................................................................ 77 4.3. The Effects of Spatial Rainfall Distribution ........................................................... 82 4.4. Distribution Analysis of Subcatchment Response ................................................. 86 Conclusions ...................................................................................................................... 92 5.1. Major Findings ....................................................................................................... 93 5.2. Future Work ........................................................................................................... 95 References ...................................................................................................................... 100 Appendix ........................................................................................................................ 107 List of Figures Figure 2.1.1- Vflo® Geospatial Data Inputs. ................................................................ 25 Figure 2.1.2: Vflo® Grid-cell System and Cell Components. ...................................... 28 Figure 2.2.1: Relative Location of the White Oak Bayou Watershed, Houston, Texas................................................................................................................................. 30 Figure 2.2.2 – White Oak Bayou Watershed and Elevation Map. ............................. 31 Figure 2.2.3 – White Oak Bayou 10-year Floodplain Showing Inundated Structures Generated from HCFCD 2010 HEC-RAS Model E100-00-00. ................................... 35 Figure 2.3.1 – Base Model Sensitivity Analysis Results. .............................................. 42 Figure 2.3.2 - Rain and Stream Gauge Networks and Subcatchment areas in and around White Oak Bayou Watershed in Houston, TX. .............................................. 46 Figure 2.3.3 - Spatially-distributed Rainfall Totals (inches) over White Oak Bayou during Hurricane Ike. ..................................................................................................... 47 Figure 2.3.4 – Calibration Results for Hurricane Ike at Lower White Oak Bayou (8074500) and the Outlet (8074598) Gauges. ................................................................ 49 Figure 2.3.5 – Calibration Results for July 2012 Storm at Lower White Oak Bayou (8074500) and the Outlet (8074598) Gauges. ................................................................ 51 Figure 2.3.6 – Calibration Results for September 2013 Storm at Lower White Oak Bayou (8074500) and the Outlet (8074598) Gauges. .................................................... 53 Figure 3.1.1 - Cottage Grove Rain Gardens Post-construction.. ................................ 59 Figure 3.1.2 – Visual Representation of Rain Garden Infiltration Modeling Technique......................................................................................................................... 63 Figure 3.1.3 – Extensive Green Roofs on the NASA Johnson Space Center and Rice University Campuses. ..................................................................................................... 66 Figure 4.1.1 – Cumulative Hydrologic Performance of LID Scenarios
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