Application of EM38 and ERT methods in estimation of saturated hydraulic conductivity in unsaturated soil

• Soil moisture content evaluation was accomplished using ERT and EM38 methods.
• ERT and EM38 images were converted to moisture content distribution maps.
• Unsaturated flow model was built using HYDRUS 2D.
• Hydraulic conductivity was estimated based on ERT/EM38 and flow model comparison.

Soil apparent electrical conductivity is being considerably used as a surrogate measure for soil properties and hydraulic parameters. In this study, measurements of electrical conductivity were accomplished with electrical resistivity tomography (ERT) and EM38 to develop multiple datasets for defining spatiotemporal moisture content variations and estimating saturated hydraulic conductivity under natural conditions in an experimental site located in Lisbon, Portugal. In addition, EM38 capability in monitoring electrical conductivity variations in comparison with ERT method was examined. In order to achieve these objectives, appropriate relationships were derived based on determination of experimental curve resistivity vs. degree of saturation by in-situ investigation to convert electrical resistivity maps inferred from ERT and EM38 data to moisture content distribution maps. In addition, the surface temperature variations during the experiment were measured and the effects of the temperature variations were removed by assuming 2% change in electrical resistivity per °C change in temperature. The conducted experiment proves that the soil is fairly homogenous and semi-pervious sediment and the spatiotemporal moisture content variations during the experiment barely exceed 10%. Our calculations constrain the range of saturated hydraulic conductivity to be 3–9 (cm/day) range.