Effective Soil Water Characteristics and Ensemble Soil Water Profiles in Heterogeneous Soils

Abstract

One‐dimensional vertical flows through spatially heterogeneous areas are studied with numerical solutions for a variety of soil types, to ascertain the behavior of the ensemble. Soil heterogeneity is treated using the distributions of parameters describing the characteristic relations of conductivity, water content, and pressure head. Values of the critical parameters, taken from a modified Brooks‐Corey or van Genuchten model, have previously 7lsqb;Smith and Diekkrüger, 1992] been shown in two extensive data sets to exhibit little interdependence. The static ensemble characteristics, except for saturated and residual water content parameters, are shown to have regular bias compared to a soil with the mean characteristic parameters. The measured data also are shown not to support the popular similar media heterogeneity model. Using both analytic approximate flow models and an ensemble solution of Richards' equation, the effective dynamic ensemble characteristics in three example soils are studied. As suggested in previous studies, such effective characteristics are conditional to flow conditions and are here shown to be quite different from ensemble static characteristics. This indicates that irrespective of the sample size, effective soil dynamic characteristics are not measurable for samples possessing significant heterogeneity.