Gravity and electrical resistivity investigations to mark concealed seepage sources from Kanjoor Dam, Pakistan

This study has been carried out to investigate the probable reasons of water seepage from Kanjoor Dam, lying at North Western end of Khairi Murat Fault (KMF), one of the splays of Kala Chitta Ranges in Northern Potowar Deformed Zone (NPDZ), Pakistan. Resistivity and gravity variations along and across the target zone have been studied to mark the probable causative subsurface structures responsible for water loss from the dam. Most of the structures located in the study zone are resultant of the northward movement being accommodated at Himalayas. In order to have a firsthand approximation about the subsurface structure, 2D resistivity survey was carried out along two profiles. Results from two profiles suggested the existence of weak zone in the subsurface as resistivity has varied from 0.7 to 990 Ωm. These variations were strong enough to believe about the structural variation. Resistivity survey was lately followed by relative gravity variations for validation of results. Gravity measurements were taken with approximately 50 m station spacing, so that maximum of the anomalous zones were studied. The gravity anomalies were analyzed using Oasis Montaj GM software, where built-in Gaussian filter was applied for regional to residual separations, and the vertical and horizontal derivatives were applied to sharpen the edges of anomalous zones. The outcome of the gravity survey was consistent with the resistivity measurements as the variation was from − 45 to 35 mGal, and therefore suggested the existence of weak zone too. The anomalous residuals are indicative of near-surface feature and give a clear difference of some continuous subsurface disturbance along which water percolation is taking place. Conclusively, it can be perceived that these two nondestructive and less laborious techniques can work in composite usefully to mark the approximate existence of the unsighted structures.