EFFECTIVE SOIL-WATER CHARACTERISTICS AND ENSEMBLE SOIL-WATER PROFILESIN HETEROGENEOUS SOILS

One-dimensional vertical flows through spatially heterogeneous areas a re studied with numerical solutions for a variety of soil types, to as certain the behavior of the ensemble. Soil heterogeneity is treated us ing the distributions of parameters describing the characteristic rela tions of conductivity, water content, and pressure head. Values of the critical parameters, taken from a modified Brooks-Corey or van Genuch ten model, have previously [Smith and Diekkruger, 1992] been shown in two extensive data sets to exhibit little interdependence. The static ensemble characteristics, except for saturated and residual water cont ent 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 bo th analytic approximate flow models and an ensemble solution of Richar ds' equation, the effective dynamic ensemble characteristics in three example soils are studied. As suggested in previous studies, such effe ctive 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 dynami c characteristics are not measurable for-samples possessing significan t heterogeneity.