A computational investigation of the effects of heterogeneity on the behavior of soil moisture in the unsaturated zone

Proper prediction of water flow in the unsaturated zone is vital in the study of the migration of contaminants because water flow and contaminant transports are interdependent processes. Most hydraulic properties of soils vary significantly at different locations in the field. This heterogeneity of soil properties is often an important control on the migration and distribution of water. To completely characterize the movement of water in a heterogeneous soil at field-scale, we first need to identify local values of all relevant soil properties. But this approach is impractical because the data and computational requirements are unreasonable. An alternative to this approach is to estimate effective soil hydraulic parameters which, when used in a simulation, are able to capture the average effects of local soil heterogeneity. The ultimate objective of this research work is to investigate the feasibility of effective parameters to capture the effect of heterogeneity on the average flow of soil moisture through unsaturated heterogeneous soil.; Prediction of soil water movement in a given unsaturated soil requires knowledge of the pressure - moisture content relationship and pressure - relative permeability relationship. Since the unsaturated flow model uses the combined pressure-moisture content-relative permeability model proposed by van Genutchten (VG), VG model parameters α and n becomes the most important parameters in this research.; For this research work, average behavior of water movement will be quantified by transient first and second spatial moments of moisture content distribution. A series of heterogeneous simulations reveal that there are mainly three types of impact of heterogeneity on the average movement of the moisture plume. The features of Type I impact of heterogeneity are reduced average velocity, reduced vertical spreading and increased transverse spreading. The features of Type II impact of heterogeneity are reduced average velocity, increased transverse spreading and increased vertical spreading. The features of Type III impact of heterogeneity are reduced average velocity, reduced transverse and vertical spreading. Based on Type curves developed in this research, it can be concluded that impact of heterogeneity cannot be captured in a homogeneous medium by a single set of parameters using the current unsaturated flow model.