Debasish Chutia, Satyajit Kataki, Ambrose Kumar Bora, Suraj Mahanta and Aditya Shankar Kataki
Abstract
The Lower-Digaru drainage basin, situated within the southern Brahmaputra Valley of Assam, NE India, exhibits complex hydrogeological conditions controlled by heterogeneous Quaternary alluvium and adjoining Precambrian crystalline formations. This study characterizes the hydrogeological framework and aquifer disposition of the basin through integrated field investigations, lithological interpretation of 11 exploratory boreholes, well-inventory surveys of 53 dug wells, and GIS-based spatial analysis. Lithological logs reveal multi-layered aquifer systems dominated by sand, gravel, and mixed alluvial units in the eastern and northern sectors, whereas shallow hard-rock formations limit groundwater occurrence in the western and southern hill zones. Depth-to-water levels range from 0.08-11.5 m (pre-monsoon) and 0.9-8.7 m (postmonsoon), with maximum depths along the Kolong/Kopili riverbank. Seasonal groundwater fluctuations vary between-1.9 and 4.3 m, with 83% of the area exhibiting <1 m fluctuation, indicating moderate rechargedischarge conditions. Water-table contour mapping reveals variable hydraulic gradients and groundwater flow from the elevated southwestern highlands toward the northern alluvial plains. Aquifer potential is highest in Jagiroad, Sonapur, and Dimoria, where thick granular zones provide favourable groundwater storage, while negligible potential is observed in Byrnihut, Bomfor, and Hastinapur due to massive crystalline bedrock at shallow depths. The findings enhance the understanding of spatial variability in aquifer geometry, groundwater availability, and flow dynamics in a rapidly urbanizing region adjacent to Guwahati. This study provides a scientific basis for sustainable groundwater planning and management in accordance with SDG-6, emphasizing the necessity of protecting both groundwater quantity and quality in a geologically sensitive basin.