PREDICTING SATURATED AND UNSATURATED HYDRAULIC CONDUCTIVITY IN UNDISTURBED SOILS FROM SOIL WATER CHARACTERISTICS

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Abstract
Hydraulic conductivity is likely the most important soil property controlling water and solute movement in soils. It is also one of the most variable and uncertain soil properties. Models for predicting soil hydraulic conductivity from other soil characteristics are, therefore, useful in both deterministic and stochastic transport studies. A new model for predicting saturated hydraulic conductivity (KS) in undisturbed soils from macroporosity (∊100), defined as the air-filled porosity at a soil-water potential of Ψ = −100 cm H2O, was developed using data for 23 undisturbed soils (90 horizons). The new KS model compared well with measurements when tested against independent data sets for 73 undisturbed soils (191 horizons) from the UNSODA database and gave improved predictions (accuracy within one order of magnitude) compared with existing KS models. Two new models for predicting relative hydraulic conductivity (K/KS) in relatively moist, (Ψ > −350 cm H2O) undisturbed soils from soil-water content (θ) and the Campbell soil-water retention parameter, b, were developed using conductivity and water retention data for the 73 soils from UNSODA. The new K/KS models represent modifications of the recently presented DLC and SLC models (Poulsen et al. 1998. Soil Science 163:425-435 ) for predicting K/KS in sieved, repacked soils. The modified DLC and SLC models were combined with the new KS model, yielding new two-parameter (∊100, b) models for unsaturated hydraulic conductivity (K(θ)) in undisturbed soil. The two new K(θ) models were successfully tested against independent K(θ) data. Also, the classical Campbell (Campbell. 1974. Soil Science 117:311-314 ) K/KS model, combined with the new, more accurate KS model, gave K(θ) prediction accuracy almost as good as the modified DLC and SLC K(θ) models. The suggested two-parameter K(θ) models require knowledge of only the soil-water retention curve, including a measurement at Ψ = −100 cm H2O, and seem promising for use in deterministic and stochastic models for water transport in natural, undisturbed soils.