Estimation of effective unsaturated hydraulic conductivity tensor using spatial moments of observed moisture plume

摘要

Knowledge of unsaturated zone hydraulic properties is critical for many environmental and engineering applications. Various stochastic methods have been developed during the past 2 decades to estimate the effective unsaturated hydraulic properties. Independent of these stochastic methods, we develop in this paper a practical approach to estimate the three-dimensional (3-D) effective unsaturated hydraulic conductivity tensor using spatial moments of 3-D snapshots of a moisture plume under transient flow conditions. An application of the new approach to data collected at the Hanford Site in southeastern Washington State yields an effective unsaturated hydraulic conductivity tensor that exhibits moisture-dependent anisotropy. The effective hydraulic conductivities compare well with laboratory-measured unsaturated hydraulic conductivity data from small core samples; they also reproduce the general behavior of the observed moisture plume at the site. We also define a moisture diffusivity length concept which we use in conjunction with estimated correlation scales of the geologic media at the field site to explain deviations between the observed and simulated plumes based on the derived effective hydraulic properties.