University of Southern Queensland Faculty of Health, Engineering and Sciences Improving infiltration modelling for crusting soils A dissertation submitted by Cameron Leckie In fulfilment of the requirements for ENG4111 and 4112 Research Project Towards the degree of Bachelor of Engineering (Honours) (Agricultural) Submitted October, 2019 2 Abstract Infiltration and surface runoff modelling is important in many disciplines including environmental engineering, mine site rehabilitation, ecology and agronomy. Major errors in modelling can occur when the throttling effect of soil surface crusts, which reduce infiltration and subsequently increase surface runoff, are not considered. The aim of this project was to improve the modelling of infiltration on crusting soils by measuring the density of the soil surface crust. A rainfall simulator was used to create a surface crust on soils (Sodosol and Chromosol) susceptible to surface crusting. The surface crusts resulted in greater than 90 per cent of applied rainfall becoming runoff. Several methods of measuring the crust density were trialled, with X-ray micro Computed Tomography (X-ray CT), when combined with the traditional soil core method, found to be the most accurate and reliable. The HYDRUS-1D software application was used to model infiltration. Measured soil parameters, including crust density, and applied rainfall rates were used as model inputs. The inclusion of crust density into HYDRUS-1D resulted in insignificant improvements to modelling accuracy. Inverse modelling identified that this was as a result of HYDRUS-1D predicted saturated hydraulic conductivity values being three to four orders of magnitude larger than obtained from the inverse solution. The application of average crust hydraulic parameters, obtained from the set of inverse solutions, was found to provide a close approximation of infiltration rates— once surface runoff had commenced — and cumulative infiltration. The findings of this project indicate that the use of average surface crust hydraulic parameters could provide major improvements in infiltration modelling accuracy using HYDRUS-1D without the requirement for additional sampling and analysis during field surveys. Further experimentation on a broader range of soils under differing vegetation regimes is required to validate the conclusions of this project. Cameron Leckie ( ENG4112 Research Project 3 University of Southern Queensland Faculty of Health, Engineering and Sciences ENG4111/ENG4112 Research Project Limitations of Use The Council of the University of Southern Queensland, its Faculty of Health, Engineering & Sciences, and the staff of the University of Southern Queensland, do not accept any responsibility for the truth, accuracy or completeness of material contained within or associated with this dissertation. Persons using all or any part of this material do so at their own risk, and not at the risk of the Council of the University of Southern Queensland, its Faculty of Health, Engineering & Sciences or the staff of the University of Southern Queensland. This dissertation reports an educational exercise and has no purpose or validity beyond this exercise. The sole purpose of the course pair entitled “Research Project” is to contribute to the overall education within the student’s chosen degree program. This document, the associated hardware, software, drawings, and other material set out in the associated appendices should not be used for any other purpose: if they are so used, it is entirely at the risk of the user. Cameron Leckie ( ENG4112 Research Project 4 University of Southern Queensland Faculty of Health, Engineering and Sciences ENG4111/ENG4112 Research Project Certification of Dissertation I certify that the ideas, designs and experimental work, results, analyses and conclusions set out in this dissertation are entirely my own effort, except where otherwise indicated and acknowledged. I further certify that the work is original and has not been previously submitted for assessment in any other course or institution, except where specifically stated. Cameron Leckie Student Number: Cameron Leckie ( ENG4112 Research Project 5 Acknowledgements Completing this project could not have been completed without the assistance of many people. Firstly I would like to thank my supervisor, Professor John McLean Bennett. His encouragement resulted in me joining Soil Science Australia and provided a much needed focus on the direction of my studies. Without that encouragement, and his subsequent support and guidance, this project may never have been initiated let alone completed. Another pivotal supporter of this project was Dr Rob Loch from Landloch Pty Ltd. It was as a result of a presentation delivered by Dr Loch at a Soil Science Australia meeting that the idea for this project was conceived. Dr Loch was extremely generous in allowing me to use his premises and facilities for the conduct of the rainfall simulator experiments. The support of Landloch staff including Tim, Rikki, Locky and Geoff is also greatly appreciated. Dr Richard Flavel from the University of New England facilitated access to the X-ray CT apparatus. His generous support, including taking time out of his busy schedule, to provide advice and assistance with X-ray CT and image processing was pivotal. Thank you Richard. The staff and students at the Centre for Sustainable Agricultural Systems also provided significant practical support throughout the project. Dr Afshin Ghahramani provided a great deal of assistance with the modelling aspects of the project whilst Stirling, David, Aram, Yingcan and Alla provided support and advice related to the various laboratory activities. Thanks team! Finally I would like to thank my wife Beverley and family for their love and support. I will make soil scientists out of you yet! Cameron Leckie ( ENG4112 Research Project 6 Table of Contents LIST OF FIGURES .............................................................................................................................. 11 LIST OF TABLES ................................................................................................................................ 14 SYMBOLS AND ABBREVIATIONS ................................................................................................. 16 1. CHAPTER ONE – INTRODUCTION ......................................................................................... 17 1.1. Project aim ............................................................................................................................ 17 1.2. Project objectives .................................................................................................................. 18 1.3. Dissertation overview ........................................................................................................... 18 1.3.1. Literature review ........................................................................................................... 18 1.3.2. Modelling ...................................................................................................................... 18 1.3.3. Methods and materials .................................................................................................. 18 1.3.4. Results ........................................................................................................................... 18 1.3.5. Discussion ..................................................................................................................... 18 1.3.6. Conclusion .................................................................................................................... 18 2. CHAPTER TWO – LITERATURE REVIEW ............................................................................. 19 2.1. Introduction ........................................................................................................................... 19 2.2. Section One - Infiltration and Surface Runoff ...................................................................... 19 2.2.1. Infiltration Overview..................................................................................................... 19 2.2.2. Surface runoff overview ................................................................................................ 20 2.2.3. Measurement of infiltration - infiltrometers ................................................................. 20 2.2.4. Measurement of infiltration – rainfall simulators ......................................................... 21 2.2.5. Measurement and modelling of surface runoff – catchment scale ................................ 21 2.3. Section Two - Surface Crusts ................................................................................................ 22 2.3.1. Description .................................................................................................................... 22 2.3.2. Types ............................................................................................................................. 22 2.3.3. Crust formation ............................................................................................................. 23 2.3.4. Crust thickness .............................................................................................................. 23 2.3.5. Soils prone to crusting................................................................................................... 24 2.3.6. Rainfall characteristics .................................................................................................