Water and solute transfer in porous media

Abstract

John Philip's classical approach to environmental problems was based on a flux equation whose elements permit measurement, and material continuity. This approach identifies a small set of material properties that are necessary and sufficient for analysis and can be measured at the scale of application. Philip warned, on a number of occasions, against quantitative prediction of material properties at one scale using insights developed at another. At the same time he encouraged simplifications where observation permitted them and he strongly objected to unnecessary complication when these insights are applied to practical problems. He was disappointed when simplifications and insights, revealed in some of his quasi-analytical solutions to flow equations, were not incorporated in computer models. This paper illustrates some of these issues in relation to 1-dimensional flow of liquid in swelling systems and, specifically, to approximations that simplify analysis of some chemical engineering unit processes. It also illustrates approaches to hydrodynamic dispersion that derive from early insights of Philip. In particular, it draws attention to benefits of solid- and water-based space-like coordinates in analysing hydrodynamic dispersion and reaction during unsteady flow in unsaturated soils and some benefits in field management.