EFFECTIVE HYDRAULIC PROPERTIES FOR LARGE SCALE TRANSIENT INFILTRATION IN HETEROGENEOUS FORMATIONS

Water flow in the unsaturated zone is often simulated using closed-form expressions for the soil hydraulic properties involving the soil water retention and the unsaturated hydraulic conductivity functions. Soil hydraulic properties at relatively large scales (e.g., large scale hydro-climate and groundwater flow model grids) are necessary for large-scale hydrologic applications. In this study, we investigate the effective soil hydraulic parameters from the field-measured local scale hydraulic properties. We interpret the effective hydraulic parameters as deriving “equivalent” homogeneous soil hydraulic properties to account for the spatially variable hydraulic parameters. Effective/average hydraulic properties are those that can be used for an entire field (or a larger-scale model grid) based on measurements at point scales, or using estimates obtained in some other ways. It is required that the effective hydraulic properties predict the ensemble vertical water flux. The large scale vertical flux is important because it is key input for water balance calculations in terms of partitioning upward and downward water fluxes at the land surface and for land-atmosphere feedback schemes in soil-vegetation-atmosphere transfer (SVAT) models. The local-scale transient hydrologic processes are simulated by using the HYDRUS-1D numerical model based on measured hydraulic parameter values. The ensemble behavior of the hydrologic processes is then aggregated from the multiple realizations of the local scale results. Inverse procedures along with the numerical approximations for solving Richards equation are used to find the effective hydraulic parameters.