2013 Volume 125 Pages 3-15
Parameters of the bimodal van Genuchten (VG) hydraulic functions for two aggregated Andisols were in-versely determined using the evaporation method. Initial estimates of the water retention parameters were deter-mined from separate retention measurements, which fa-cilitated rapid convergence of the parameter optimization process regardless of the number of optimized parame-ters. When the bimodal water retention parameters were fixed according to the independently measured retention data from near saturation to very low pressure heads down to −105 cm, it was possible to estimate the unsaturated hydraulic conductivity, K(h), by optimizing only two con-ductivity parameters (Ks, ℓ). Since the flat region of the bi-modal retention curve at intermediate pressures is difficult to measure precisely, however, we still recommend opti-mizing all bimodal VG parameters to yield the best overall results. Including water retention data at very low pressure heads in the dry range extended the applicable range of the model predictions, at least down to pressure heads of ap-proximately −104 cm.