Delineation of Aquifer Zones in the Interfluves of the Rivers Brahmaputra and Kolong, Assam

Abstract

The present study aims at the delineation of the aquifer zones in the interfluves of the rivers Brahmaputra and Kolong, Assam by studying the hydrogeological settings in the area, nature and areal extent of aquifers, subsurface disposition of aquifers through panel diagram, well inventory data, behaviour and direction of movement of groundwater with the help of water table contour mapping etc. The area is underlain by unconsolidated alluvial sediments deposited on a granite basement which outcrops as inselbergs within the alluvial terrain. Hydrogeological data such as depth to water level, seasonal fluctuations of groundwater level were collected from 61 key well locations from the study area in both pre- as well as post-monsoon seasons. The spatial and temporal variability of groundwater levels in the area were studied with depth to water level maps and the water level fluctuation maps of both pre- and post-monsoon seasons. Maps were prepared by using the 3D Analyst Extension of ArcGIS. Panel diagram was prepared using the litho-log data of 15 exploratory boreholes to delineate the extent and nature of disposition of aquifers. In major part of the study area groundwater fluctuations remain within 1.5 m to 2 m. There are much lateral variations in the aquifer zones with lateral and vertical intercalations; however, the subsurface geology of the study area indicates the presence of very good aquifer zones. The water table conforms to the general topography of the area. The general direction of groundwater flow in the study area is towards the river Brahmaputra.