Prabhat Jain

By Prabhat Jain, Abhay Soni and Rahul Shende

In the Maharashtra State of India, Deccan Trap basaltic lava flows are spread over around 82% of the area and form the most prominent aquifer in the entire state. Nasik district occurring in the northern part of Maharashtra also known as Khandesh represents a typical area of Deccan Trap basalt. The storage and transmission capabilities of the basaltic lava flow aquifer are very limited due to the inherent absence of primary pore spaces. These basaltic rocks act as aquifers only when they are weathered, jointed or fractured, thus giving rise to secondary porosity and permeability. Due to wide variations in secondary openings, the potential areas for groundwater are generally localized. In this way, Deccan Trap basalt possesses a unique challenge to aquifer mapping, both spatially and vertically due to its hydrogeological heterogeneity. In the current study, this challenge of aquifer mapping and management in basalt was tackled through a multidisciplinary, multipronged approach involving data integration of various thematic layers viz., geomorphology, soil, drainage, land use-land cover, hydrometeorology, and geophysical techniques etc., as indirect tools and combining it with direct tools such as drilling, well inventory, water level monitoring, groundwater quality checks, and aquifer pumping tests for obtaining reliable results. By following the above methodology, the 3-D aquifer geometry, lithological sections, fence diagrams, aquifer characteristics, yield potentials, and aquifer-wise resources were deciphered. The results showed that the area has two aquifer systems comprising of Aquifer-I, that is. shallow aquifer, which is generally tapped by the dug wells of 8 to 32 m depth with water levels of 1.2 to 15 meters below ground level (m bgl) and yield varies from 10 to 100 m3/day. Whereas, the Aquifer-II, that is, deeper aquifer is being tapped by bore wells with a depth ranging from 30 to 200 m bgl and a water level from 8 to 55 m bgl. However, their pumping sustainability was limited to 0.5 to 3 hours due to low storage potential resulting in overexploitation. The given aquifer maps indicate that major parts of the area have limited yield (Aquifer-I: between the depth of 10 m - 15 m bgl and Aquifer-II: between the depth of 80 m −140 m bgl). In hard rock areas, especially basaltic aquifers due to their low storage potential, groundwater development is always a challenging task unless it is combined with the management of the resources. Considering the issues plaguing the area, the aquifer management plan encompassing supply and demand-side interventions, and groundwater development has been devised. It is concluded that 139.30 MCM of groundwater resources can be augmented by artificial recharge under supply-side interventions. Whereas the groundwater demand for irrigation can also be reduced by 272 MCM by adopting drip irrigation in 117 sq. km. of sugarcane and 790 sq. km. of onion cultivated areas under the demand-side interventions. The implementation of these measures will minimize the stress on groundwater by bringing down the stage of groundwater development from 88–55% (safe category) in six water-stressed blocks/taluka, whereas the overall stage of groundwater development will be reduced from 58.45% to 40.70%. Thus, the adoption of both supply-side and demand-side interventions interlinked with water budgeting through community participation will provide long-term solutions to combat the overexploitation, water level decline, low storage potential, recurring droughts and other issues of the area and also help in improving socioeconomic conditions of the area.

Part of the book: Sedimentary Rocks and Aquifers