Textural averages of saturated soil hydraulic conductivity predicted from water retention data

Abstract

Modeling of transport processes in soils relies on predicted values of saturated hydraulic conductivity, K s. The objective of this work was to derive the parameters of a K s power-law model from water retention (WR) properties defined at the inflection point of s-shaped WR functions. The proposed model uses water content, θ inf, pressure potential, ψ inf, and the slope, S, at the inflection point to derive an effective porosity, Φ inf, (air filled porosity at θ inf) and a pore distribution index, λ⁎, (estimated from WR data between pressure potential at air-entry and ψ inf or as S/ θ inf). The Φ inf is raised to 3 − λ⁎ or 3 − S/ θ inf and multiplied by C inf D inf where C inf is a constant and pore diameter is defined as D inf ∝ ψ inf − 1 . The model was developed from: A) a dataset containing 374 measurements of K s together with detailed WR and particle size distribution information, B) a subset of the HYPRES dataset containing 1827 values of K s and their corresponding sand, silt and clay percentages and parameter values from an s-shaped WR model; and tested for consistency with C) a published dataset containing textural averages of parameters of an s-shape WR model and K s values developed from 2134 and 1036 samples, respectively. Linear regression between 16 (A), 10 (B) and 12 (C) textural averages of log K s and their predicted values with C inf = 20 resulted in R 2 values of 0.95, 0.82 and 0.82, respectively. The proposed model is physically sound and except for C inf all its parameters are derived from one point in the WR curve.