DESIGN AND CONSTRUCTION OF A RAINFALL SIMULATOR FOR LARGE-SCALE TESTING OF EROSION CONTROL PRACTICES AND PRODUCTS by Matthew Allen Horne A thesis submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Master of Science Auburn, Alabama May 6, 2017 Keywords: erosion, erosion control, rainfall, rainfall simulation, stormwater Copyright 2017 by Matthew Allen Horne Approved by Wesley C. Zech, Chair, Professor of Civil Engineering Xing Fang, Professor of Civil Engineering Jose G. Vasconcelos, Associate Professor of Civil Engineering ABSTRACT Soil erosion and the resulting sediment deposition constitutes one of the greatest pollutants in our nation’s waterways. Construction projects often generate large areas of exposed soil that remain disturbed throughout the duration of the project. Exposed soil, resulting from clearing, grubbing, and land grading activities, is more susceptible to erosion during a rain event due to lack of vegetative cover. Erosion control practices and products (i.e., vegetative cover, erosion control blankets, hydromulches, etc.) are an important aspect of any construction project due to their ability to limit the process of erosion. This study developed a testing apparatus capable of accurately and repeatedly simulating a 2-yr, 24-hr storm event in Auburn, Alabama with the goal of determining the performance and effectiveness of erosion control practices and products. The test protocols consisted of calibrating the rainfall simulator and validating the results through bare soil control tests. Data collection procedures consisted of recording rainfall depth in rain gauges, collecting and analyzing flour pellets for drop sizes, and suspended sediment concentration (SSC). The optimum location for each sprinkler riser as well as the most accurate nozzle configurations were determined through the test procedures developed for this study. Through calibration testing, the simulator was found to produce rainfall intensities of 1.10, 1.78, and 3.76 in./hr. Uniformity of rainfall distribution ranged from 79-81%. The rainfall simulator’s performance was also validated through three, 60 minute bare soil control tests. Results from these tests (i.e., erosion patterns, SSC) showed that consistent erosion patterns were achieved with maximum sediment concentrations ranging from approximately 55,000 – 82,000 mg/L. ii ACKNOWLEDGEMENTS The author would first like to thank Dr. Wesley C. Zech for his supervision and mentorship during the course of this research project and for encouraging a spirit of continued education throughout one’s professional life. The author would also like to thank Dr. Wesley N. Donald, Dr. Michael A. Perez, Dr. Xing Fang, and Dr. Jose G. Vasconcelos for their support and assistance throughout this research project. The author would also like to thank the Alabama Department of Transportation (ALDOT) and the Highway Research Center (HRC) for their financial support; Mr. Guy Savage for assisting in the oversight of the construction and testing of the rainfall simulator test apparatus; and all undergraduate research assistants who assisted the author in construction and testing efforts for this project. Finally, the author would like to thank his parents, Ken and Donna Horne, for providing love, advice, and encouragement that helped the author accomplish his goals. iii TABLE OF CONTENTS ABSTRACT .................................................................................................................................... ii ACKNOWLEDGEMENTS ........................................................................................................... iii LIST OF TABLES ......................................................................................................................... vi LIST OF FIGURES ..................................................................................................................... viii CHAPTER ONE: INTRODUCTION ............................................................................................. 1 1.1 BACKGROUND .............................................................................................................. 1 1.2 RAINFALL SIMULATORS ........................................................................................... 2 1.3 RESEARCH OBJECTIVES ............................................................................................ 3 1.4 ORGANIZATION OF THESIS ....................................................................................... 5 CHAPTER TWO: LITERATURE REVIEW ................................................................................. 7 2.1 BACKGROUND .............................................................................................................. 7 2.2 RAINFALL SIMULATORS CHARACTERISTICS ...................................................... 9 2.3 DROP SIZE DISTRIBUTION ....................................................................................... 11 2.4 TERMINAL VELOCITY .............................................................................................. 16 2.5 RAINFALL INTENSITY .............................................................................................. 17 2.6 KINETIC ENERGY of NATURAL RAINFALL ......................................................... 20 2.7 UNIFORM RAINFALL DROP DISTRIBUTION ........................................................ 21 2.8 CHARACTERISTICS OF VARIOUS PRESSURIZED RAINFALL SIMULATORS 22 2.9 CURRENT STANDARD TEST METHODOLOGIES ................................................. 30 2.10 SUMMARY ................................................................................................................... 34 CHAPTER THREE: RAINFALL SIMULATOR DESIGN AND CONSTRUCTION ............... 36 3.1 INTRODUCTION .......................................................................................................... 36 3.2 RAINFALL EVENT DESIGN AND CALCULATION OF FLOW RATES ............... 36 3.3 RAINFALL SIMULATOR DESIGN ............................................................................ 40 3.4 TEST PLOT CONSTRUCTION ................................................................................... 49 3.5 POWER SUPPLY AND AUTOMATION .................................................................... 59 3.6 COST ANALYSIS ......................................................................................................... 61 3.7 SUMMARY ................................................................................................................... 62 iv CHAPTER FOUR: METHODS AND PROCEDURES............................................................... 64 4.1 INTRODUCTION .......................................................................................................... 64 4.2 PRELIMINARY TESTING OF THE RAINFALL SIMULATOR ............................... 65 4.3 TESTING FACILITY .................................................................................................... 66 4.4 CALIBRATION PROCEDURES .................................................................................. 68 4.5 VALIDATION PROCEDURES .................................................................................... 74 4.6 STATISTICAL ANALYSES ......................................................................................... 82 4.7 SUMMARY ................................................................................................................... 84 CHAPTER FIVE: RESULTS AND DISCUSSION ..................................................................... 86 5.1 INTRODUCTION .......................................................................................................... 86 5.2 CALIBRATION RESULTS .......................................................................................... 86 5.3 VALIDATION RESULTS ............................................................................................. 98 5.4 SUMMARY ................................................................................................................. 109 CHAPTER SIX: CONCLUSIONS ............................................................................................. 112 6.1 INTRODUCTION ........................................................................................................ 112 6.2 CONSTRUCTION OF LARGE-SCALE RAINFALL SIMULATOR ....................... 113 6.3 CALIBRATION AND VALIDATION PROCEDURES ............................................ 114 6.4 RECOMMENDED FUTURE RESEARCH ................................................................ 115 REFERENCES ........................................................................................................................... 117 APPENDICES ............................................................................................................................ 122 v LIST OF TABLES Table 2.1 Precipitation Estimates for Alabama (NOAA 2014) ................................................... 19 Table 2.2 Summary of Pressurized Rainfall Simulator Designs.................................................. 23 Table 2.3 Summary of Previous Research Studies ...................................................................... 30 Table 2.4 Test Plot Soil Characteristics (ASTM 2015) ............................................................... 32 Table 2.5 Comparison of Rainfall Simulators ............................................................................. 35 Table 3.1 Rainfall Data for a