ANALYSIS OF WATER, HEAT, AND SOLUTE TRANSFERS IN UNSATURATED POROUS MEDIA

The study of soil moisture movement, soil temperature, and solute transport in porous media is of great importance to the disciplines of hydrology, agriculture, and environmental engineering.; A comprehensive one-dimensional mathematical model is developed to simulate the flow of water, heat, and solute through an unsaturated zone subject to various initial and boundary conditions. The governing equations that represent the water flow in porous media under isothermal and non-isothermal conditions are formulated for both bare and vegetated soils. Included in the vegetated soil model is a simple sink function that represents the water uptake by plant root. The influence of soil temperature on the soil hydraulic parameters (soil hydraulic conductivity and soil pressure) are taken into consideration. In solute transport modeling, the system of equations that represents the movements of solute in a porous media under both isothermal and non-isothermal water flow conditions are formulated for a bare soil. The soil system is modeled one-dimensionally from the surface to a stationary water table as a homogenous porous domain. A number of mathematical expressions of boundary conditions over the porous medium domain are used to describe the details of this domain. A finite-element technique is used for the solution of the comprehensive flow model. The numerical solution of isothermal water flow equation, simultaneous equations of water and heat flow, solute transport equation, isothermal water flow and solute transport equations, and isothermal water flow equation with a sink term representing water uptake by plant root, were all simulated and tested with experimental data and analytical solutions. For all the above cases, excellent comparison was obtained between the model results and the test data. The comprehensive model is applied to a number of simulated unsaturated flow problems (leaching, evaporation, etc.) and the numerical results demonstrate the usefulness of the model as a tool for studying water, heat, and solute flow phenomena in the unsaturated zone.