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.

The scale distribution is obtained from soil-water pressure head and water content measurements for soil sampling locations 30, 60, 120, 180, 240, and 300 cm below the surface in 12 plots planted to corn. Scale factors are found to have an approximate log-normal distribution.

Methods of computing scale factors directly from soil-water pressure head and hydraulic conductivity measurements and indirectly from soil-water content profiles for a drainage experiment are derived. Improved methods for estimating unsaturated hydraulic conductivity are also presented. Stochastic behavior of flux and cumulative seepage as random functions of the scale factors for a similar soil is described for a simple drainage experiment.