Abstract:
The inhabitants of Rawalakot and its surrounding are faced with shortage of water due to population increase, modernization of living style and shortage of rainfall/precipitation. Surface water supply through springs and streams is insufficient. Inspired by the success of Geological Survey of Pakistan (GSP) in exploration of hard-rock aquifer in Quetta valley, the AJK Government requested GSP to undertake such a study for groundwater in Rawalakot area. In consequence, earth resistivity investigations were made in Rawalakot and its surrounding area. Vertical Electrical Soundings (VES) were carried out at 33 sites using Schlumberger configuration with maximum current electrode separation of 300 m (≈ 150 meter depth) during the first quarter of 2002. Bison Resistivity Meter, model 2350 was used for field measurements. Layer parameters i.e. true resistivity and thickness of different resistivity layers were determined using computer software "Resist 87". From the shapes of VES curves, three resistivity zones can generally be recognized, a thin top soil zone of resistivity 30-80 ohmm and thickness 1-5 m, a shallow low resistivity zone of resistivity 10-40 ohmm and thickness 5-45 m, and a deeper zone having resistivity 40-315 ohmm. Low resistivity zone below the topsoil layer may represent alluvial clays and sub-alluvial shales with thin layers of sandstone. This zone may contain a good quantity of water but due to low permeability of clays and shales sufficient water cannot be extracted for a water supply scheme. Had it been not so there would have not been any groundwater problem. The high resistivity zone of 80-120-ohmm below the low resistivity zone may represent porous and soft sandstone, and/or sandstone and shale intercalations. This zone may comparatively prove a better aquifer, at least for local domestic supplies, due to comparatively better permeability. However, test drilling and pumping tests may only determine the real potential of this zone. Recharge and extent of the aquifer at a certain location will remain the main consideration even if the water potential is proved. The subsurface zone with resistivity value above 120 ohmm may represent hard and massive sandstone with least potential of groundwater. Drilling at proposed site of VES No. 4 to a depth of 328 feet has shown that the low resistivity zone represents a zone of dominating argillaceous material and the high resistivity zone represents a zone of dominating arenaceous material. Water at small quantity has been encountered at various depths, especially from 98-112 ft, and 230-245 ft. So far poor groundwater potential of Rawalakot area is obvious.
Page(s):
225-239
DOI:
DOI not available
Published:
Journal: Proceedings of 5th Pakistan Geological Congress , Volume: 0, Issue: 0, Year: 2007