No abstract

Accurate estimates of the unsaturated hydraulic properties are needed for any quantitative description of multiphase flow in porous media. This paper presents a consistent set of parametric models for the isothermal, hysteretic unsaturated fluid phase content (retention) and hydraulic conductivity functions of typical two-phase systems like water and air, or water and hydrocarbons. The equations are obtained by combining expressions for the hysteretic fluid retention curves with the statistical pore size distribution model of Mualem (1976) which predicts the hydraulic conductivity from more easily measured fluid retention data. Hysteresis is described using the model of Scott et al. (1983). The existence of residual fluid saturations for both the wetting and nonwetting fluids is justified. Theoretical and experimental considerations indicate a need to match predicted and observed hydraulic conductivities at fluid phase contents less than full saturation. 1Visiting Professor, 44(5), 892--898, 1980. van Genuchten, M. Th., and D. R. Nielsen, On describing and predicting the hydraulic properties of unsaturated soils, Ann. Geophys., 3(5), 615-628, 1985.

No abstract

To develop simplified methods of hydraulic characterization of field soils and effects of management, frequency distribution of macroporosity (or effective porosity) in a soil is investigated as a measure of its saturated hydraulic conductivity distribution. The effective porosity (φe) of a soil is related to its saturated hydraulic conductivity (Ks) by a generalized Kozeny‐Carman equation. The exponent of this relationship is assumed to vary within a narrow range (value of 4 or 5). The equation is then combined with scaling theory to derive the frequency distribution of Ks scaling factors from the φe distribution. These concepts are tested on experimental data for two widely different soils, a mollisol and an oxisol. The φe is defined as total porosity minus soil water content at −33 kPa pressure head. The exponent of the Ks‐φe relationship is found to be nearly 4 for the soil‐core data of both soils, while for a smaller set of in‐situ field data for oxisol, which was within a narrow range of φe, the value of the exponent was smaller. There was a considerable scatter in the relationships. However, with the exponent set equal to 4 or 5 the distribution of Ks scaling factors derived from φe distribution closely matched the experimental Ks‐derived distribution. The approach has a promise for large‐scale applications.