One-parameter models for unsaturated hydraulic conductivity

Simple one-parameter models for predicting changes in unsaturated soil hydraulic properties with changing soil-water content are useful, considering the great uncertainty and variability in the hydraulic parameters, and the models are often used for stochastic simulations of water and solute transport under field conditions. Two general one-parameter models for predicting relative hydraulic conductivity between water saturation and -350 cm H2O of soil-water potential are presented. The two new hydraulic conductivity models were labeled the Double Log Conductivity (DLC) and the Single Log Conductivity (SLC) models and represent modifications of the Campbell and the Libardi et al. conductivity models, respectively. The DLC and SLC model constants were optimized based on conductivity and retention data from a broad texture group of 40 sieved soils, but they can be calibrated easily to specific series of soils. The main parameter in both models (the Campbell soil-water retention parameter, b) can be estimated readily from soil texture or water retention data. Both models gave improved predictions of relative hydraulic conductivity in sieved soils compared with traditionally used one-parameter models. DLC and SLC model predictions were further compared with conductivity data from 10 undisturbed soils. The results suggested that the new models are also useful for predicting both relative and absolute hydraulic conductivity in undisturbed soil, but in this case, a calibration of the model constants based on a larger undisturbed soil data set is recommended.