Ground Water Exploration in Karst Terrains using Geoelectrical Tomography, Southwest Izeh

To determine the ground water potential of the karst aquifers، in the southwest of Izeh، three profiles and 62 vertical electrical sounding (VES) conducted by Schlumberger array، eight profiles were performed using dipole-dipole configuration، and 3-D configuration applied in two sites. However، Schlumberger tomography with high investigation depth (about 180 m) may be shows the different zone of karst aquifer but because of 50-100 m of VES spacing has not the detectability of cavities with lower than 50 m diameter. The results show that Ilam-Sarvak limestone is similar to hard rocks while Asmari formation has been identified as developed karst with high matrix porosity. The results in the 2-D geoelectrical tomography using a dipole-dipole configuration، shows that، compared to an electrode spacing of 5 m، an electrode spacing of 1 or 2 m has a higher ability to delineate karst voids. Because of the higher depth of the investigation، however، the longer electrode spacing allowed obtaining a comprehensive insight of different parts of karst regions. The high resolution 3-D electrical tomography has a good ability to detection of geological features and karst voids. The geoelectric results and interpretation of tomograms have been asserted by drilling success of four wells with high yield at Asmari formation and two wells with moderate yield at Ilam-Sarvak formation.