Evaluation of van Genuchten-Mualem relationships to estimate unsaturated hydraulic conductivity at low water contents
- Westinghouse Hanford Co., Richland, WA (United States)
- Washington State Univ. Tri-Cities, Richland, WA (United States)
Predicting contaminant migration within the vadose zone, for performance or risk assessment, requires estimates of unsaturated hydraulic conductivity for field soils. Hydraulic conductivities, K, were experimentally determined as a function of volumetric moisture content, {theta}, for Hanford sediments. The steady state head control method and an ultracentrifuge method were used to measure K{theta} in the laboratory for 22 soil samples. The van Genuchten model was used to fit mathematical functions to the laboratory-measured moisture retention data. Unsaturated conductivities estimated by the van Genuchten-Mualem predictive model, using the fitted moisture retention curve and measured saturated hydraulic conductivity, K{sub 2}, were compared to those obtained by a scaled-predictive method that uses a single K{theta} measurement as a match point near the dry regime. In general, the measured K values and those predicted form van Genuchten-Mualem relationships showed considerable disagreement. This suggests that the use of laboratory-measured K{sub s} results in an inadequate characterization of K{theta} for the desired range of moisture content. Deviations between the measured and predicted K were particularly severe at relatively low moisture contents; for some samples, there were differences in excess of 2 orders of magnitude at low {theta}. However, use of the same moisture retention curve-fitting parameters and a single steady state head control-based K{theta} measurement near the dry regime resulted in considerable improvement. In fact, for the coarse-textured soils considered in this study, results indicate that a K{theta} measurement near the dry regime must be used to obtain reliable estimates of unsaturated K at low {theta}. The study provided important insight on application of two different experimental techniques of measuring unsaturated conductivities. 27 refs., 11 figs., 3 tabs.
- DOE Contract Number:
- AC06-87RL10930
- OSTI ID:
- 181825
- Journal Information:
- Water Resources Research, Vol. 31, Issue 11; Other Information: PBD: Nov 1995
- Country of Publication:
- United States
- Language:
- English
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