Integration of Borehole Electrical Resistivity and Lithological Logs for Hydrostratigraphic Classification of the Kathmandu Valley Aquifer System, Central Nepal

Abstract

Electrical resistivity logging and borehole lithological data provide important constraints for evaluating the hydrostratigraphic framework and groundwater potential of Kathmandu Valley. The Kathmandu Valley is an oval, fault-bounded intermontane basin in Bagmati Province, central Nepal, centred near 27.7°N, 85.3°E. The Kathmandu Valley population has grown roughly five-fold since the early 1970s to approximately four million residents today. This study integrates borehole lithologs, electrical resistivity logs, aquifer thickness, and spatial interpolation to characterize the subsurface distribution of aquifers from the southern to northern parts of the valley. A total of 22 borehole records were studied, with resistivity logging performed to identify variations in subsurface materials and their hydrogeological significance. The lithological logs of study area indicate spatial variation in hydro stratigraphy across Kathmandu Valley. Sand and gravel intervals form the principal aquifer materials, whereas clay and silty clay units constitute the major aquitard horizons. The central part of the valley contains substantial clay-dominated sequences, although discrete higher-resistivity intervals indicate the presence of permeable sand and gravel layers at several depths. The generated hydrostratigraphic map delineate study area into aquifer, leaky aquitard, and aquitard zones. These findings have significant implications for the management of water resources in the region as they provide valuable information of groundwater resources for future use.