ESTIMATION OF HYDRAULIC CONDUCTIVITY USING GEOELECTRICAL DATA FOR ASSESSING OF SCALE EFFECT IN A KARST AQUIFER

The Salman Farsi Dam was constructed on the Ghareh-Aghaj river in the catchment of the Asmari limestone aquifer, Chan gal Anticline, Zagros region, Iran. In order to estimate the hydraulic conductivity of the aquifer, combination of geoelectrical (i.e., bulk resistivity of the aquifer) and hydrophysical (i.e., electrical conductivity of groundwater) data are used as an alternative approach. Porosity of the aquifer is estimated based on the modified form of Archie's empirical law assuming well cemented carbonate rocks. Formation resistivity factor and critical pore size of the Asmari limestone aquifer are used for estimating the hydraulic conductivity on the small scale based on the Thompson Equation. The results suggest an average porosity and hydraulic conductivity of 14.4 % and 0.016 m/day, respectively. The estimated value for hydraulic conductivity is smaller than values previously determined for the aquifer, based on tracer, pumping and Lugeon tests. Comparison of the hydraulic conductivity obtained by different methods revealed scale effect of hydraulic conductivity measurements in the As marl limestone aquifer. As a result, application of the geoelectrical and hydrophysical data can provide a cost-effective and efficient alternative to estimate hydraulic conductivity in karst aquifers on the small scale.