Estimating Microscale Spatial Distribution of Conductivity and Pore Continuity using Computed Tomography

Despite the importance of information on the spatial distribution of unsaturated hydraulic conductivity (K us ) at microscale in soil, experimental determination of this property is difficult. The objectives of this study were to: (i) seek a simple, but reliable, procedure for the estimation of K us at microscale and (ii) determine the sensitivity of the estimates to wetting-induced changes in selected structural parameters (porosity, e, surface fractal dimension, D, and pore continuity, PC). Using computer-assisted tomography (CAT), spatial distributions of soil water content (θ) and changes in e that occurred during wetting were monitored at 2 by 2 mm resolution at 1-cm depth Increments in water-stable (WSA) and unstable aggregate (USA) columns. The Fuentes theoretical equation, which requires data on saturated hydraulic conductivity (K e ), θ, e, and D, was used for the estimation of the spatial distribution of K us . The spatial distribution of θ in WSA columns ranged from 0.113 to 0.327 cm 3 cm -3 and from 0.175 to 0.567 cm 3 cm -3 in the USA columns. The spatial distribution of e us ranged from 0.46 to 0.74 and was nsed in the computation of D and PC. Values of K e ranged from 0.006 to 0.745 cm h -1 . The spatial distribution of K us ranged from 6.87 × 10 -4 to 1.49 × 10 -2 cm h -1 in WSA compared with 7.3 × 10 -4 to All × 10 -2 cm h -1 in USA. Pore continuity, θ, D, and initial aggregate diameter (x) accounted for 94 to 95% of the variability in K us distributions. The results indicate that reliable estimates of K us distributions at microscale can be computed from single-source CAT-derived data on θ and e.