Comparative studies of electromagnetic and geoelectrical methods to estimate the porosity and specific yield of karst aquifer, West of Iran

Knowledge of aquifer parameters is essential for the management of groundwater resources. Parameters such as porosity and specific yield are among the basic features used to describe the hydrogeological conditions of a region. This study compares the electromagnetic method with geoelectric sounding. The data collection was carried out through a field survey and is used to study and estimate the values of porosity and specific yield of the karst aquifer that feeds five springs: Famaseb (Sp1), Faresban (Sp2), Giyan (Sp3), Ghale Baroodab (Sp4), and Gonbad kabood (Sp5). All these springs are located in the Nahavand Plain, Hamadan Province, west of Iran. Fifteen (15) soundings were obtained upstream of each spring and were used to analyze the results, quantitative and qualitative interpretation of geoelectrical data, logs of subsurface layers, and ranges of true resistivities and their electromagnetic frequencies were determined. The value of the true resistivity was calculated for the saturated and unsaturated layer of each spring, the results were compared with the electromagnetic frequencies, which showed that the results of the two methods used were almost similar. Porosity and specific yield were calculated using Archie's law. It is found that the Faresban spring (Sp2) has maximum porosity of 55% and a specific yield of 0.48 and in contrast to the lowest value of parameters mentioned in the Ghale Baroodab spring (Sp3, porosity 26% and specific yield 0.18). All the estimated values are compatible with the discharge of springs measured in the field and consistent with the geological conditions of the study area.