GIS and geophysics: an integrative and inter-evaluating approach towards groundwater assessment

Abstract

Efforts have been made to explore groundwater assessment possibilities employing geospatial and geophysical techniques as well as statistically authenticate the connection between these two techniques. The study was carried out at Chotanagpur Granite-Gneiss Complex (CGGC), Ranchi, Jharkhand, India. The analytical hierarchy process (AHP) was used for Multi-Criteria Decision Making (MCDM) for various thematic factors such as land use land cover, drainage density, lineament density, lithology, rainfall, soil texture, and slope based on their interaction with atmospheric water and contribution towards groundwater replenishment. These remotely-sensed raw datasets were enriched and overlaid in the Geographic Information System (GIS) atmosphere using the weighted overlay analysis tool, which yielded the groundwater potential index (GWPI) map. Based on the estimated GWPI, the watershed area has been demarcated into five distinct groundwater potential classes in terms of poor, low, moderate, good, and very good. The inverted resistivity tomography models revealed exploitable groundwater zone lies at five sites at depth ranges between 60–70, 70–100, and 140–170 m underlie in the saturated weathered/fractured rocks where characteristic resistivities range between 80 and 800 Ω.m. In the target area, i.e. the IIAB campus, five different zones have been demarcated for groundwater exploitation in terms of low, moderate, and good considering groundwater exploitable depth and their connectivity to the near-surface recharge source. Geophysical findings were also corroborated with the existing borehole datasets for their authenticity and helped to generate conceptual geological models. The accuracy assessment combining geospatial and geophysical results validated their inter-relationship as per the generated error matrix with the overall accuracy of 87.5%.