A geoelectrical resistivity survey using vertical electrical sounding (VES) was conducted at Chaj Doab (land between rivers Jhelum and Chenab, Pakistan) and Rachna Doab (land between rivers Chenab and Ravi, Pakistan), with the objective of investigating groundwater conditions. A total of 90 sites were selected with 43 sites in Chaj and 47 sites in Rachna Doabs. The resistivity meter (ABEM Terrameter SAS 4000, Sweden) was used to collect the VES data by employing a Schlumberger electrode configuration, with half current electrode spacings (AB/2) ranging from 2 to 180 m and the potential electrode (MN) from 1 to 40 m. The field data were interpreted using the Interpex IX1D computer software and the resistivity versus depth models for each location was estimated. The outputs of subsurface layers with resistivities and thickness presented in contour maps and 3-D views by using SURFER software were created. A total of 102 groundwater samples from nearby hydrowells at different depths were collected to develop a correlation between the aquifer resistivity of VES and the electrical conductivity (EC) of the groundwater and to confirm the resulted geophysical resistivity models. From the correlation developed, it was observed that the groundwater salinity in the aquifer may be considered low and so safe for irrigation if resistivity [45 X m, and marginally fit for irrigation having resistivity between 25 and 45 X m. The study area has resistivities from 3.9 to 2,222 X m at the top of the unsaturated layer, between 1.21 and 171 X m, in the shallow aquifers, and 0.14-152 X m in the deep aquifers of the study area.The results indicate that the quality of groundwater is better near the rivers and in the shallow layers compared to the deep layers.
Electrical resistivity surveys (1-D) were carried out at selected sites in the region between the confluent rivers (Ravi and Jhelum) of Punjab, Pakistan, to audit tubewell placement and depth in order to minimize the amount of salt applied to the soil through irrigation. The Schlumberger electrode configuration was employed to collect the resistivity data and the resultant resistivity vs depth models for each site were estimated. From the interpretation of vertical electrical sounding (VES) data, the sites had one to three aquifer layers of different salinity levels and fitness for irrigation (FFI) classes ranging from good groundwater quality (FFI1) to highly saline up to 6.4 dS m À1 (FFI3). Twenty-one tubewells were investigated and it was found that not only were most wells theoretically suboptimally placed (57%) with respect to the best water quality available but also 33% were sunk at too deep a level, bypassing aquifer layers of better water quality [FFI1]. From the cost-benefit analysis, it was estimated that a total of 64 000 Pakistan rupees could have been saved on five wells through installation costs due to suboptimal depths. It is concluded that VES is an effective method for the evaluation of existing wells and aquifer systems. RÉSUMÉDes études de résistivité électrique (1-D) ont été réalisées au droit de sites sélectionnés dans une région située entre deux rivières confluentes du Punjab (Ravi and Jhelum, Pakistan), afin d'évaluer l'emplacement et la profondeur des forages dans le but de minimiser la quantité de sel dissous injectés dans le sol via l'irrigation.La résistivité a été mesurée par des électrodes configurées selon la méthode Schlumberger. Des modèles de résistivité en fonction de la profondeur ont été établis pour chaque site. A partir de l'interprétation des sondages électriques verticaux (SEV), un à trois aquifères de salinités différentes ont été identifiés à chaque site, avec des niveaux d'aptitude à l'irrigation (FFI) [fitness for irrigation] variant entre « bonne qualité des eaux souterraines » (FFI1) et « haut niveau de salinité » (6.4 dS m À1 ; FFI3). Vingt et un forages ont été ainsi étudiés et il a été démontré que non seulement la plupart (57%) des puits étaient théoriquement mal positionnés pour produire de l'eau à la meilleure qualité d'eau disponible, mais aussi que 33% étaient trop profonds, parce qu'ils transperçaient des aquifères de meilleure qualité (FFI1). L'analyse coût-bénéfice a montré qu'un total de 64 000 roupies aurait pu être économisé sur les couts d'installation de 5 puits en raison de profondeurs inadéquates. Il a été conclu que le SEV est une méthode efficace pour l'évaluation des forages existants et des systèmes aquifères.
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