An Introduction into Applied Soil Hydrology

Transcription

1 Klaus Bohne An Introduction into Applied Soil Hydrology

2 Preface Contents 1 Introduction: The soil as a reactor between the earth's atmosphere and the subsurface 1 2 Mechanical composition of mineral soils Soil texture Mechanical analysis Grain size distribution Textural classes Soil structure 8 3 Basic parameters of bulk soil Macroscopic approach Soil as a three-phase system Standard values of bulk density 14 4 Soil water balance in the field Water balance equation Precipitation Surface runoff Evapotranspiration A first approximation to real evapotranspiration and groundwater recharge Simplified approach to drainage and capillary rise The soil water storage term Measurement of soil water content in the field Simulation of water storage in soil Spreadsheet model of soil water storage (see Appendix, files "Simulations.xls" or "Simulations.sxc") Simple multi-layer soil water balance simulation model (see Appendix, files "Swb") 31 5 Energy status of water in soil Total potential of soil water Gravitational potential Solute potential Tensiometer pressure potential Air pressure potential Overburden potential Hydrostatic pressure potential Wetness and matrix potential Soil water potential related to flow phenomena Soil water potential and vapor pressure Measurement of soil water potential 43 6 Water retention in soil Capillary tubes Soil water retention curve 48

3 6.2.1 Fundamentals Differential water capacity, air entry point, and residual water content Pore size distribution Effect of temperature on pressure head Hysteresis Mathematical functions representing the water retention curve Introduction The Brooks and Corey model The van Genuchten model Multi-porosity models Obtaining soil water retention data Field measurements Laboratory methods Estimation of soil water retention from non-hydraulic soil properties " 7 Flow of water through saturated soil ^f 7.0 Introduction J 7.1 Flow through capillary tubes "4 7.2 Darcy's law Steady-state flow of water in saturated soil «7.4 Saturated soil hydraulic conductivity Specific permeability /,, Estimation of saturated hydraulic conductivity Laboratory measurements ' n \ Field methods "\ Statistical data processing Criticism and conclusions 'SL 1A2.S Prediction of saturated soil hydraulic conductivity J Flow of water through saturated layered soil ' b 8 Groundwater flow f Jj 8.1 Comment ^ 8.2 Some basic terms of groundwater hydrology ^ 8.3 Groundwater flow net i 8.4 Aquifer Hydraulic properties Confined aquifer Groundwater recharge and groundwater balance Steady-state groundwater flow ' One-dimensional flow ' Introduction ' Groundwater flow equation Steady-state groundwater flow toward wells *Z oo Groundwater flow: The general case 11 o.8 Closing remarks " > 9 Flow through unsaturatd rigid soil 'J? 9.1 Fundamentals Steady-state flow 97 n 9.3 Transient flow " 48 K. Bohne, An Introduction into Applied Soil Hydrology

4 9.4 Solutions to flow equations Unsatu rated soil hydraulic conductivity Introduction Models of unsaturated soil hydraulic conductivity Gardner's equations The Burdine and Brooks and Corey theory The Mualem and van Genuchten theories Measurement of unsaturated hydraulic conductivity Overall view Steady-state evaporation or seepage Steady-state infiltration field methods: The disc infiltrometer Non-steady laboratory methods Non-steady field methods Prediction of unsaturatd hydraulic conductivity Predictions based on soil water retention Pedotransfer functions Databases Elementary soil hydrologic processes Introduction Steady-state vertical flow: Capillary rise and constant flux infiltration Infiltration Introduction Vertical infiltration under pressure head boundary condition Philip's infiltration formula Haverkamp's equation The Green"and Ampt method Vertical infiltration under flux boundary condition Complicating phenomena occurring in field situations Crust-topped and layered soils Fingering and preferential flow Redistribution Infiltration-based methods to estimate soil hydraulic properties Two-dimensional, flux boundary condition infiltration from line and point sources Internal drainage Introduction Internal drainage of groundwater-affected soils Unit gradient drainage The concept of field capacity Drying of bare soil by evaporation Soil hydrologic processes and Burgers' equation Coupled heat and water flow in soil Thermal properties of soil Heat transport in soil Non-isothermal flow of water through soil Soil temperature changes in the field 164

5 13 Solute transport in soil Introduction J Basic processes J Convection { Hydrodynamic dispersion Diffusion Total solute flux Chemical reactions Classification Fast reactions (Classes I through III) Slow reactions (Classes IV through VI) Simplified approach to solute transport prediction Convection-Dispersion Equation (CDE) General problem The simplified CDE and solutions Breakthrough curves and solutions to the CDE Experimental procedure and results Analytical solutions to the CDE Solute transport by groundwater flow Non-equilibrium and the mobile-immobile concept Parameter estimation Stochastic descriptions of solute transport Solute management: Soil salinization Overview Leaching requirement Salt distribution in soil Irrigation balances root water uptake Irrigation on slowly permeable soils The ultimate sink for soil salinity - the ocean Soil water and crops Soil moisture requirements Optimal levels of plant available soil water Deficit irrigation Aeration Soil mechanical properties Closing remarks Some general remarks on simulation models Important issues not included in this book 206 References 208 Abbreviations 216 Glossary 218 Index 227 K. Bohne, An Introduction into Applied Soil Hydrology