ESTIMATING HYDRAULIC CONDUCTIVITY IN THE VADOSE ZONE USING GPR TECHNIQUES

This project uses recent advances in Ground Penetrating Radar (GPR) methodology to estimate the unsaturated and saturated hydraulic conductivity in the very shallow subsurface at the field scale. GPR data were acquired at a seven-acre, agricultural field site in northern Wisconsin before and after irrigation. These data were used to estimate the soil water content over a known depth. Using these water content values with the assumption of steady state flux during irrigation, the unsaturated hydraulic conductivity (K_unsat) was estimated. The water content values were then used in conjunction with van Genuchten parameters appropriate for the main soil texture observed at the site to estimate the saturated hydraulic conductivity (K_sat). To assess the accuracy of the GPR estimates of hydraulic conductivity, conventional point-measurement values of saturated hydraulic conductivity were obtained using a double-ring infiltrometer at 15 locations throughout the field. The infiltrometer locations were chosen to cover a range of soil textures, based on the previously acquired GPR data at this site. A comparison of the K_sat distributions derived from the GPR data and from the double-ring infiltrometer data showed that the GPR-derived distribution matches the pattern of the distribution from infiltrometer data well, although some discrepancies occur in the magnitudes of the values. The correlation between K_sat estimates from GPR and from conventional measurement techniques indicates that GPR methods have significant potential for high resolution, field-scale estimation of K_sat.