Concepts of similar soil and scaling are applied to investigate the spatial variability of the field-measured soil-water properties, soil-water pressure head, hydraulic conductivity, and soil-water diffusivity associated with unsaturated flow. The classical, analytical aspects of scale factors as regards the invariance of the flow equations expressed in terms of “reduced variables” are reviewed and extended by considering stochastic aspects of random variations in soil-water properties. It is demonstrated that scaling can best be achieved when soil-water properties are represented by a set of related model functions.
