Unsaturated hydraulic properties from upward flow into soil cores.
Hudson D.B. | Wierenga P.J. | Hills R.G.
Common methods for determining unsaturated hydraulic properties of soils are time consuming and measurements are restricted to relatively moist soil conditions. This study developed a transient upward infiltration procedure for estimating soil hydraulic properties. The procedure involves pumping a carefully controlled water flux into the bottom of an initially dry soil core. As the unsaturated core slowly absorbs water, soil water potentials are measured with tensiometers, and, optionally, soil water contents are measured with time domain reflectometry. No porous plates are required for this unsaturated flow procedure because a flux boundary is used. Applied fluxes of approximately 0.76 cm d-1 for 60 h to 7.6 cm diam. by 7.6 cm high cores increased the water content from an initial dry state (approximately -7500 kPa) to almost saturation. A Levenberg-Marquardt inverse parameter estimation procedure was combined with a one-dimensional numerical model of the experimental flow system to estimate the soil hydraulic properties from the collected water potential data using five different methods. Parameters in the van Genuchten water retention relationship and the van Genuchten-Mualem or the Campbell hydraulic conductivity relationships were simultaneously estimated. The optional water content data was combined with the water potential data to provide initial estimates of water retention parameters. The best method (lowest RMSE) that estimated all parameters in the water retention relationship and the hydraulic conductivity relationship produced similar hydraulic property relationships for four identically packed cores of a loamy fine sand.
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