Vertical Electrical Soundings to Decipher Aquifer Conditions in Midlands and Plains of Bhima Basin

The occurrence, storage and movement of groundwater in Deccan trap basalt are determined by several factors such as geology, geomorphology and hydrogeology. Improper irrigation practices and excessive use of groundwater for industrial requirements have led to overstressed condition on groundwater. In addition, recurring drought conditions in upper Bhima region of Maharashtra resulted in over exploitation of water resources in general and groundwater in particular. Groundwater is available in this region mainly in weathered zones and fractures in bedrock. Various geophysical methods can be applied to map groundwater potential zones at various stages and scales. Electrical Resistivity method is popular due to its cost effectiveness, simplicity in use and its success rate in all stages. Under purpose driven study (National Hydrology Project), midlands and plains of the Bhima basin which include Ghod, Kukdi and Mina rivers and the command area of the Ghod reservoir was selected to decipher the subsurface geometry of the aquifer. At present, six major watersheds i.e BM-17, BM-18, BM-26, BM-27, BM-35, BM-34 were considered. 14 Vertical Electrical Soundings (VES) were carried out based on geological and hydrogeological reconnaissance. The inventory of dug wells and the results of soundings showed the presence of two to three distinct lithological layers those overlay the impermeable bed rock. The top most unit contains the soil cover having thickness of 1.0 to 4.0 meters with resistivity range of 12 ω-m to 95ω-m, with resistivity ranging up to 270 ω-m where dry weathered rock was encountered on the surface in some locations. The second unit belongs to weathered saturated/semi-saturated basalts thickness ranging from 2 to 70 meters with resistivity range of 14 ω-m to 200 ω-m. In some places, very high resistivity (up to 300–700 ω-m) was observed where the layer was moderately weathered with dry conditions. Below this bed rock was encountered. In some locations presence of redbole was observed having very low resistivity in third layer. Aquifer geometry was mapped at preliminary stage in the area under study by conducting VES surveys. The results corroborate with well inventory. The result will be useful for further investigations for Purpose Driven Study in the study area.