Groundwater exploration, management strategies and sustainability: Geophysical approaches

Groundwater is a hidden yet vital for life sustainable resource for billions across the world. However, it is often overlooked despite accounting for over one-third of global freshwater supplies. Geophysics plays a critical role in exploring, developing, and sustaining groundwater resources. This review article provides an in-depth analysis of the various roles of geophysics in groundwater development and sustainability, highlighting the importance of geophysical methods in mapping subsurface structures, characterizing aquifer properties, monitoring groundwater levels, detecting contamination, optimizing well siting, and assessing groundwater recharge processes. It also examines the transformative power of geophysical techniques, highlighting their effectiveness in mapping aquifer properties such as thickness, depth, volume, hydraulic conductivity, flow pathway, faults, and fractures to monitor groundwater levels and assess aquifer potential and vulnerability. Case studies demonstrate the efficacy of geophysical methods in groundwater studies across the globe. For instance, electrical resistivity (ER) surveys have been employed to identify promising aquifer zones with relative resistivity values ranging from 10 Ωm to 500 Ωm and transmissivity values ranging from 0.79 to 1203 m²/day, occurring with depths of $\ge 5m$. Seismic surveys have accurately delineated aquifer depths from 24 to 150 m Furthermore, geophysical techniques have been instrumental in detecting and delineating groundwater contamination plumes, with studies revealing low resistivity zones (<15 Ωm) associated with contaminant plumes. The limitations and strengths of geophysical methods were also discussed alongside the other methods, such as geological observation, hydrogeological survey, test drilling, remote sensing (RS), and tracing its evolution from the era of blind exploration. While challenges exist, the future of groundwater management hinges on the continued development and application of geophysical methods. By integrating these techniques with the insights from hydrogeological and other methods, we can optimize well-siting, enhance aquifer recharge, and ensure long-term sustainable groundwater resource management (GWRM). This study underscores the vital role of geophysical methods in bridging the gap between knowledge and action, paving the way for a water-secure future.