Effect of Soil Properties on Unsaturated Hydraulic Conductivity Pore‐Interaction Factors

The variability of the pore‐interaction factor, ρ, for a microscopic model proposed for predicting unsaturated hydraulic conductivity, K (θ), from soil water‐retention, Ψ(θ), data was examined in relation to soil particle‐size data and indices, bulk density, organic C, parameters for the van Genuchten Ψ(θ) function, an index ( W ) of total energy of drainage and soil‐series, toposequential, and geographic groupings. The ρ exhibited no trend relationship to any of the soil properties tested. However, a change in the distribution of ρ was observed in relation to the geometric‐mean particle diameter ( G d ) and other soil textural variables. For G d < 0.08 mm, variability was much larger than for soils with G d ≥ 0.08 mm. The latter consisted entirely of soils in the sand and loamy sand textural groups. A similar distributional relationship also occurred for ρ vs. W. Examination of ρ on three sites of the Hecla soil series and on related toposequential soils indicated that classification of ρ on the basis of soil series or of soil‐association groupings is a feasible strategy for ρ parameter estimation on some soils. The exponential factor η for a macroscopic model was also investigated. The η was found to be related to W as an exponential function over the full data range. However, η vs. W was nearly identical to a linear function for W data extending from 0 to 400 cm‐γ (where γ is the density of water). The η was also strongly related to G d as a power function, and to other textural variables as exponential functions. The increasing slope of the power function for G d < 0.08 mm indicated a large potential error of prediction for K (θ) on fine‐textured soils.