Stochastic Analysis of Unsaturated Flow in Heterogeneous Soils: 3. Observations and Applications

Results of stochastic theory for flow in heterogeneous soils are analyzed by comparisons with laboratory experiments and field observations, and through applications examples. The two key theoretical results are (1) the variability of capillary pressure or moisture content increases when mean capillary pressure increases and (2) the anisotropy ratio (horizontal/vertical) of effective (mean) unsaturated hydraulic conductivity increases when mean capillary pressure increases or mean moisture content decreases. Comparisons with the field data on moisture content and capillary pressure variability show trends similar to those predicted by the theory. Calculations of hydraulic conductivity anisotropy based on two actual soils show that the variations in soil texture produce large changes in anisotropy as the mean capillary pressure changes. Several previously reported field observations and laboratory experiments support the theoretical finding of a capillary pressure dependent hydraulic anisotropy for unsaturated flow. The importance of this anisotropy effect in applications involving groundwater recharge, irrigation, surface runoff generation, and waste isolation is discussed.