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A Thesis Entitled Applicability of Soil Moisture Sensors in Determination A Thesis entitled Applicability of Soil Moisture Sensors in Determination of Infiltration Rate by Milan K C Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master of Science Degree in Civil Engineering _________________________________________ Dr. Cyndee L. Gruden, Committee Chair _________________________________________ Dr. Ashok Kumar, Committee Member _________________________________________ Dr. Liangbo Hu, Committee Member _________________________________________ Dr. Amanda Bryant-Friedrich, Dean College of Graduate Studies The University of Toledo December 2017 Copyright 2017, Milan K C This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author. An Abstract of Applicability of Soil Moisture Sensors in Determination of Infiltration Rate by Milan K C Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master of Science Degree in Civil Engineering The University of Toledo December 2017 The need for stormwater management has been heightened in urban areas due to the increase in impermeable surfaces, causing flooding, erosion and pollution of water and soil. This problem can be mitigated with a scientifically designed stormwater management system, which requires field data including soil infiltration rate. Conventional approaches to measuring infiltration are tedious, time-consuming, and do not address the need for extensive, real-time data. The main objective of this research is to develop a technique that incorporates readily available real-time soil sensor data into the Green and Ampt Infiltration Model. Initial laboratory experiments confirmed that estimates of infiltration using Green and Ampt Infiltration Model with parameters found in the literature compared well to actual laboratory measurements of infiltration. A sensitivity analysis was then performed on the Green and Ampt Infiltration Model parameters of which saturated hydraulic conductivity (K) showed largest influence and porosity (η) showed negligible influence on the calculated soil infiltration rate while average capillary suction at the wetting front (ψ) showed high influence only on initial iii values of calculated soil infiltration rate. The method was then validated to measure infiltration rate and cumulative infiltration of sand (with varying initial moisture content) and samples including sand and an equal volume of organic matter. Oven dried sand had average initial infiltration rate of 4.37 cm/min, 18.11% higher than that of sand, which was 3.7 cm/min. It also showed that sand mixed with equal volume of organic matter had average initial infiltration rate of 6.2 cm/min, 41.88% higher than that of oven dried sand. Saturated hydraulic conductivity (K) of oven dried sand and sand were 0.30 cm/min and 0.22 cm/min respectively, within normal range (0.19 cm/min to 0.40 cm/min). The value of saturated hydraulic conductivity (K) after mixing sand with organic matter was 0.51 cm/min, 27.5% more than that of oven dried sand. Future research will involve testing this approach in field studies. The resulting method would provide a more economical and useful approach for measuring soil infiltration rate in stormwater applications. iv Dedicated to my lovely wife, mom and dad. Acknowledgements I am especially thankful to my advisor Dr. Cyndee L. Gruden for all her support and guidance. I am thankful to my wife, family and friends for their constant support. I would also like to thank Dr. Ashok Kumar and Liangbo Hu for taking the time to be a part of my thesis committee. vi Table of Contents Abstract .............................................................................................................................. iii Acknowledgements ..............................................................................................................v Table of Contents ............................................................................................................... vi List of Tables ................................................................................................................. viii List of Figures .................................................................................................................... ix 1 Literature Review.....................................................................................................1 1.1 Background .......................................................................................................1 1.2 Soil and its phases .............................................................................................3 1.3 Soil Moisture .....................................................................................................5 1.3.1 Measurement of Soil Moisture............................................................6 1.3.2 Soil Moisture Sensor Applications .....................................................9 1.4 Hydraulic Conductivity ...................................................................................11 1.5 Soil Infiltration ................................................................................................15 1.5.1 Infiltration Process in Soil ................................................................16 1.5.2 Factors Affecting Infiltration Rate of Soil ........................................17 1.5.3 Soil Infiltration Measurements .........................................................18 1.5.4 Soil Infiltration Models .....................................................................19 1.6 Summary .......................................................................................................24 vii 2 Objective .......................................................................................................27 2.1 Study Objective ...............................................................................................27 3 Methodology .......................................................................................................29 3.1 Overview .......................................................................................................29 3.2 Soil Moisture Sensor .......................................................................................30 3.3 Soil Moisture Installation ................................................................................31 3.4 Comparison of Directly Measured Infiltration Rate with Green and Ampt Infiltration Rate ..............................................................................................33 3.5 Sensitivity Analysis of Green and Ampt Equation Parameters ......................36 3.6 Determination of Soil Infiltration Rate Using Two Soil Moisture Sensors ....38 4 Results .......................................................................................................42 4.1 Comparison of Directly Measured Infiltration Rate with Green and Ampt Infiltration Rate ..............................................................................................42 4.2 Sensitivity Analysis of Green and Ampt Equation Parameters ......................44 4.3 Determination of Soil Infiltration Rate Using Two Soil Moisture Sensors ....47 5 Discussion .......................................................................................................61 6 Conclusion ......................................................................................................65 References ..........................................................................................................................67 viii List of Tables 1.1 Comparison of different soil moisture sensors ........................................................9 3.1 Green and Ampt infiltration parameters for various soil classes ...........................35 3.2 Values of Green and Ampt infiltration parameters for sand ..................................36 3.3 Values of Green and Ampt infiltration parameters used for sensitivity analysis ...................................................................................................................37 4.1 Data points for directly measured infiltration rate and infiltration rate obtained using Green and Ampt infiltration model ..............................................................44 4.2 Saturated hydraulic conductivity and initial infiltration rate for sand and its organic matter mixture samples .............................................................................60 ix List of Figures 1-1 United States Department of Agriculture (USDA) soil classification textural triangle .....................................................................................................................4 1-2 Procedure, equation and sample calculation for gravimetric method ......................7 1-3 Simplified figure for Darcy’s law ..........................................................................12 1-4 Hydraulic conductivity versus water content graph for loam, clay and loamy sand ........................................................................................................................13 1-5 Infiltration rate versus time ....................................................................................17 1-6 Water infiltration process showing saturated, transmission and oven dried soil zones ......................................................................................................21 1-7 Layers of soils showing uniform water
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