Vadose Zone Hydrology: CONCEPTS AND TECHNIQUES TT 584/13 Vadose Zone Hydrology: Concepts and Techniques TT 584/13 Vadose MA Dippenaar, JL van Rooy, N Breedt, A Huisamen, SE Muravha, S Mahlangu & JA Mulders TT 584/13 Vadose Zone Hydrology: Concepts and Techniques MA Dippenaar, JL van Rooy, N Breedt, A Huisamen, SE Muravha, S Mahlangu & JA Mulders, Report to the Water Research Commission by Engineering Geology and Hydrology, Department of Geology, Faculty of Natural and Agricultural Sciences, University of Pretoria WRC Report No. TT 584/13 February 2014 Vadose Zone Hydrology: Concepts and Techniques Obtainable from Water Research Commission Private Bag X03 GEZINA, 0031 [email protected] or download from www.wrc.org.za The publication of this report emanates from a project entitled Vadose Zone Hydrology: Spatial and Temporal Influences, Assessment Techniques and Aquifer Susceptibility (WRC Project No. K5/2052). DISCLAIMER This report has been reviewed by the Water Research Commission (WRC) and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC nor does mention of trade names or commercial products constitute endorsement or recommendation for use. ISBN 978-1-4312-0507-3 © Water Research Commission ii Vadose Zone Hydrology: Concepts and Techniques Acknowledgements Gratitude is expressed to the Water Research Commission (WRC) for funding and management of this project on vadose zone hydrology. The following members of the steering committee are thanked for their significant guidance during the project and their peer-review of the final product being this document: • Dr S Adams Water Research Commission: Chairperson • Prof S Lorentz University of KwaZulu-Natal • Dr N Jovanovic CSIR • Dr J Nel University of Western Cape / GCS • Mr K Majola Department of Water Affairs Additional gratitude is expressed to the following: • City of Tshwane, for access to cemeteries and parks in the municipality • Department of Public Works, for access to the Randjesfontein site • The undisclosed mine and its personnel for authorising access to the tailings storage facility • UIS Analytical Services, Waterlab, Soillab and the University of Pretoria’s Analytical Facility, for reduced rates for laboratory analyses • Management of the University of Pretoria’s Experimental Farm, where many field methods were validated prior to field work of the individual case studies • University of Pretoria, for contribution of facilities, time and postgraduate students. iii Vadose Zone Hydrology: Concepts and Techniques iv Vadose Zone Hydrology: Concepts and Techniques CONTENTS 1. INTRODUCTION .......................................................................................................................... 1 1.1. Project Rationale ............................................................................................................. 1 1.2. How to use this Manual ................................................................................................... 2 2. THE VADOSE ZONE AND VADOSE ZONE HYDROLOGY ..................................................................... 6 2.1. Distribution of Water in the Crust ................................................................................. 6 2.2. The Movement of Water in the Subsurface ................................................................... 8 2.3. Vadose Zone Hydrology per Discipline ........................................................................ 10 2.3.1. Environmental science and ecology ......................................................................... 12 2.3.2. Hydrogeology and geohydrology ............................................................................. 13 2.3.3. Engineering geology and geotechnical engineering ................................................ 13 2.3.4. Soil science, pedology and hydrology ...................................................................... 14 2.4. Considerations in Vadose Zone Hydrology ................................................................. 15 3. THE MEDIA .............................................................................................................................. 17 3.1. Basic Phase Relationships ............................................................................................ 17 3.2. Voids and Porosity ........................................................................................................ 18 3.2.1. Type and scale of porosity ....................................................................................... 19 3.2.2. Effective porosity, specific yield and storativity ...................................................... 20 3.2.3. Pore space geometry ............................................................................................... 22 3.3. Earth Materials .............................................................................................................. 24 3.3.1. Soil material, type or texture ................................................................................... 28 3.3.2. Rock material ........................................................................................................... 32 3.4. Soil and Rock Mass (Structure) .................................................................................... 32 3.4.1. Soil mass or structure .............................................................................................. 32 3.4.2. Rock mass or structure ............................................................................................ 33 3.5. Tertiary Porosity ........................................................................................................... 34 3.6. Fluid Phase ..................................................................................................................... 34 4. PARTIAL AND VARIABLE SATURATION ....................................................................................... 36 4.1. Moisture below Saturation ........................................................................................... 36 4.2. Interaction between Solid and Fluid Phases ............................................................... 39 4.2.1. Surface tension and wettability ............................................................................... 39 4.2.2. Capillarity ................................................................................................................. 41 5. MOVEMENT OF WATER IN THE SUBSURFACE .............................................................................. 44 5.1. Mechanisms of Fluid Flow ............................................................................................ 44 5.2. Bernoulli’s Law and Hydraulic Head ........................................................................... 45 v Vadose Zone Hydrology: Concepts and Techniques 5.3. Darcy’s Law and Associated Parameters ..................................................................... 47 5.4. Unsaturated Flow .......................................................................................................... 49 5.5. Subsurface Translocation Processes ............................................................................ 51 5.5.1. Water and Clay Minerals .......................................................................................... 51 5.5.2. Water and Pedogenesis ........................................................................................... 54 6. METHODOLOGIES TO QUANTIFY RELEVANT PARAMETERS ........................................................... 58 6.1. Profile Description ........................................................................................................ 58 6.1.1. Soil profile description ............................................................................................. 58 6.1.2. Rock description ...................................................................................................... 60 6.1.3. Improved earth scientific profile description ........................................................... 60 6.2. Porosity .......................................................................................................................... 63 6.2.1. Quantifying porosity ................................................................................................ 63 6.2.2. Changing porosity of problem and pedogenic soils ................................................. 66 6.2.3. Considerations with respect to porosity .................................................................. 69 6.2.4. Bias in the quantification of porosity ....................................................................... 70 6.2.5. Advances in the quantification of porosity .............................................................. 70 6.3. Grading-based Empirical Hydraulic Conductivity Estimation ................................... 71 6.3.1. Development of empirical approaches .................................................................... 71 6.3.2. Standardisation to dimensionally homogenous form .............................................. 73 6.4. Efficacy of Empirical Porosity and Hydraulic Conductivity Estimates ...................... 75 6.5. Laboratory Permeability Methods ............................................................................... 79 6.6. Geotechnical/ Civil Engineering Centrifuge Modelling .............................................. 81 6.7. In-situ Methods ............................................................................................................