A convenient method to estimate soil hydraulic conductivity using electrical conductivity and soil compaction degree

Soil hydraulic conductivity (K) significantly affects subsurface flow and solute transport, but convenient measurement of K remains a challenge. Electrical conductivity (EC), which can be measured conveniently and accurately, can be quantitatively related to K because of the similarity between current movement and groundwater flow, motivating us to estimate K using EC. A soil column apparatus was built to explore the relation between EC and K. Fifty-four experiments were conducted under various degrees of soil compaction and grain diameters, including six different particle sizes, three compaction levels, and six solution concentrations. The overall (negative) correlation between K and EC can be fitted reasonably well by an exponential function with a large determination coefficient (> 0.81) for each solute concentration, while a power-law function better fits the correlation when K is larger than 10 m/d. These experiments led to several empirical models (for specific solution concentrations) and one comprehensive model (with variable parameters) to estimate K given EC. In the field, if the EC of pore water can be measured, the empirical models under the specific solution concentrations can be applied to greatly improve the K estimation. Comparison showed that the proposed models, which provides a quick estimate of K using easily available EC, performed better than most of the classical grain size-based formulas. Although there is uncertainty in the K estimation likely due to the limited control factors considered in this study, the new method proposed above can provide a convenient estimate for K for the field site with strong spatial heterogeneity.