Predicting saturated hydraulic conductivity from air permeability: Application in stochastic water infiltration modeling

Several relationships exist for predicting unsaturated hydraulic conductivi ty K (psi) from saturated hydraulic conductivity K-s and the soil-water ret ention curve. These relationships are convenient for modeling of field scal e system sensitivity to spatial variability in K (psi). It is, however, fas ter and simpler to measure air permeability k(a) at psi = -100 cm H2O, than K-s. This study explores the existence of a general prediction relationshi p between k(a), measured at -100 cm H2O, and K-s. Comparative analyses betw een k(a)-K-s relationships for nine Danish and Norwegian soils, six differe nt soil treatments, and three horizons validated the establishment of a soi l type, soil treatment, and depth/horizon independent log-log linear k(a)-K -s relationship. The general k(a)-K-s relationship is based on data from a total of 1614 undisturbed, 100-cm(3) core samples and displays general pred iction accuracy better than +/-0.7 orders of magnitude. The accuracy and us efulness of the general relationship was evaluated through stochastic analy ses of held scale infiltration and pending during a rainstorm event. These analyses showed possible prediction bias associated with the general k(a)-K -s relationship, but also revealed that sampling uncertainty associated wit h estimation of field scale variability in K-s from a limited number of sam ples could easily be larger than the possible prediction bias.