Saturday, 15 July 2006
137-8

Linking the Gardner and Campbell Models for Predicting Unsaturated Hydraulic Conductivity in Near-Saturated Soil.

Ken Kawamoto, Dept of Civil and Environmental Engineering, Saitama Univ, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan, Per Moldrup, Environmental Engineering Section, Dept of Life Sciences, Aalborg Univ, Sohngaardsholmsvej 57, Aalborg, DK-9000, Denmark, Ty P.A. Ferré, Dept of Hydrology and Water Resources, Univ of Arizona, Tucson, AZ 85721-0011, Markus Tuller, Soil and Land Resources Division, Ag. Sci. 113, Univ of Idaho, Moscow, ID 83844-2339, Ole H. Jacobsen, Dept of Agroecology, Institute of Agricultural Research Centre Foulum, P.O. Box 50, Tjele, DK-8830, Denmark, and Toshiko Komatsu, Graduate School of Science and Engineering, Saitama Univ, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.

Linking the classical Gardner and Campbell models for soil hydraulic properties yields a combined Gardner-Campbell (GC) relationship for predicting unsaturated hydraulic conductivity (K) from soil-water retention. The new GC water retention and hydraulic conductivity relationships are described by simple linearized expressions based on Campbell-b-scaled values of volumetric water content (θ). The GC hydraulic properties models include four parameters, the pore-connectivity parameter x (typically between 1 and 2), the Campbell pore-size distribution parameter b, the Gardner macroscopic capillary length λ, and the air-entry soil-water matric potential ψe. In the GC model for K(θ), all four parameters are merged into a single dimensionless parameter, A. The GC models are applied to seven different undisturbed soils within a soil-water matric potential (ψ) range of 0 to –60 cm H2O. Results show that the simple GC ψ(θ) model adequately describes water retention data close to saturation, and that the GC K(θ) model performs well for predicting near-saturated hydraulic conductivity. The GC water retention and hydraulic conductivity parameters were incorporated into Wooding's equation for steady state infiltration rate to examine effects of variability in physical characteristics on infiltration. The steady state infiltration rate was less sensitivity to the GC water retention and hydraulic conductivity parameters than the saturated hydraulic conductivity. The GC models, which combine advantages of the Gardner model for linearization of Richards' equation and the simple Campbell model for soil-water retention, seem useful for evaluating water transport at near-saturated water conditions in undisturbed soil systems and spatial variability in water transport properties at the field scale.

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