Predicting saturated and unsaturated hydraulic conductivity in undisturbedsoils from soil water characteristics

Hydraulic conductivity is likely the most important soil property controlli ng water and solute movement in soils. It is also one of the most variable and uncertain son properties. Models for predicting soil hydraulic conducti vity from other son characteristics ape, therefore, useful in both determin istic and stochastic transport studies. A new model for predicting saturate d hydraulic conductivity (K-s) in undisturbed sons from macroporosity (epsi lon(100)), defined as the air-filled porosity at a soil-water potential of Psi = -100 cm H2O, was developed using data for 23 undisturbed soils (90 ho rizons). The new K-s model compared well with measurements when tested agai nst 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 K-s models. Two new models for predictin g relative hydraulic conductivity (K/K-s) in relatively moist, (Psi > -350 cm H2O) undisturbed sons from soil-water content (theta) and the Campbell s oil-water retention parameter, b, were developed using conductivity and wat er retention data for the 73 soils from UNSODA. The new K/K-s models repres ent modifications of the recently presented DLC and SLC models (Poulsen et al. 1998. Soil Science 163:425-435) for predicting K/K-s in sieved, repacke d soils. The modified DLC and SLC models were combined with the new K-s mod el, yielding new two-parameter (epsilon(100), b) models for unsaturated hyd raulic conductivity (K(theta)) in undisturbed soil. The two new K(theta) mo dels were successfully tested against independent K(theta) data. Also, the classical Campbell (Campbell. 1974. Son Science 117:311-314) K/K-s model, c ombined with the new, more accurate K-s model, gave K(theta) prediction acc uracy almost as good as the modified DLC and SLC K(theta) models. The sugge sted two-parameter K(8) models require knowledge of only the soil-water ret ention curve, including a measurement at yr = -100 cm H2O, and seem promisi ng for use in deterministic and stochastic models for water transport in na tural, undisturbed soils.