Multi-dimensional characterization of groundwater distribution in sub-Himalayan region of Pakistan

The groundwater scarcity, lack of scientific approaches, and increasing number of unsuccessful boreholes coupled with climate change are crucial issues faced in sub-Himalayan region. Integrated geophysical techniques of electrical resistivity and magnetotelluric survey in conjunction with hydrochemical analysis were utilized at Rawalakot city and adjoining areas of sub-Himalayan region to demarcate groundwater potential, identify water-bearing fractured lithologies, and aquifer vulnerability along with water quality. Due to structural complexity, subsurface lithological units demarcated by electrical resistivity survey included broad spectrum of lithologies consisting of topsoil, clay, boulder, sandstone, mudstone, siltstone, gravel, and sandy gravel that resemble closely to the available borehole data. Different aquifer zones were identified in the southern portion of the study area with most aquifers as unconfined in nature. The overall apparent resistivity fluctuates between 0.001 and 7118 Ω-meters with 40 to 60 Ω-meters in aquifer zone. The aquifer thickness ranges from 20 to 180 m in the subsurface, while 2D-AMT models also reveal the maximum depth of fractures up to 200 m. The 2D sections of electrical resistivity were compared with 2D magnetotelluric profiles to enhance the identification of subsurface lithology, structural elements as well as the aquifer potential in the study area. The pseudo-sections acquired from the electrical resistivity survey and magnetotelluric profiles were in accordance with each other. To validate the geophysical results with groundwater quality, 39 water samples were acquired from different localities in the study area, among which 16 samples were marked as unsafe for drinking, whereas 23 samples were marked as safe.