Use of material coordinates in porous media solute and water flow

Material coordinates relating to water flow in saturated swelling systems and to solute movement during non-steady water flow in unsaturated porous materials often simplify descriptions of these processes. Furthermore, they may be formulated similarly and result in similar mathematical forms for the flow equations. The analysis may be extended to solute transport during non-steady flow of water in a deforming system. These space-like coordinates are simply defined and measured. Their use ensures material balance for all entities of concern and, for some important situations, results in a non-linear diffusion equation that may be solved for many practically important initial and boundary conditions.