• Subash Chandra

      Articles written in Journal of Earth System Science

    • Exploring deep potential aquifer in water scarce crystalline rocks

      Subash Chandra E Nagaiah D V Reddy V Ananda Rao Shakeel Ahmed

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      Characterization of the shear zone with pole–pole electrical resistivity tomography (ERT) was carried out to explore deep groundwater potential zone in a water scarce granitic area. As existing field conditions does not always allow to plant the remote electrodes at sufficiently far of distance, the effect of insufficient distance of remote electrodes on apparent resistivity measurement was studied and shown that the transverse pole–pole array affects less compared to the collinear pole–pole array. Correction factor have been computed for transverse pole–pole array for various positions of the remote electrodes. The above results helped in exploring deep aquifer site, where a 270 m deep well was drilled. Temporal hydro-chemical samples collected during the pumping indicated the hydraulic connectivity between the demarcated groundwater potential fractures. Incorporating all the information derived from different investigations, a subsurface model was synthetically simulated and generated 2D electrical resistivity response for different arrays and compared with the field responses to further validate the geoelectrical response of deep aquifer set-up associated with lineament.

    • Multiparametric coupling and constrained interpolation to improve natural recharge estimation

      SUBASH CHANDRA BO HOLM JACOBSEN NIELS B CHRISTENSEN SHAKEEL AHMED SAURABH K VERMA

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      The inverse modelling technique seeks to improve the existing estimates of natural recharge in hard rocks by coupling multiple hydrogeophysical parameters that jointly affect natural hydrogeological processes. This approach involves coupling of an initial set of multiple hydrogeophysical (soil resistivity, bedrockdepth and rainfall) parameters in the form of exponents assigned to each parameter and a multiplication coefficient to obtain natural recharge. These model parameters (i.e., exponents and coefficients) are then quantified using linear least squares inversion against the known recharge values. To reduce the effect of geomorphic heterogeneity, viz., hills on natural recharge, laterally constrained inversion has been employed to integrate data sets (e.g., recharge measured at various points and logical expectation over exposed hills in an area) and constrained interpolation is then carried out along the grid lines for increaseddata density. Finally, Kriging interpolation over dense data obtained through data integration and constrained interpolation is used to significantly minimise the risks of overshooting the observations. Thus, the present approach provides a realistic spatial distribution of natural recharge values in a highly heterogeneous hard rock terrain.

    • Hydrogeological simulation for groundwater management strategies in crystalline aquifers, southern India

      ABHILASH KUMAR PASWAN SYED ADIL MIZAN SUBASH CHANDRA VIRENDRA M TIWARI

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      Crystalline hard-rock aquifers, one of the most complex groundwater systems, are facing serious groundwater management issues due to their limited storage capacity and understanding of their complex hydrogeological characteristics. In this study, we have employed an operational decision support tool to calculate the groundwater budget under variable agro-climatic conditions for groundwater management in the crystalline hard rock aquifers of the Ankasandra watershed (${\sim}$380 km$^2$), southern India. The nature of fractures and the aquifer geometry are categorized based on a borehole camera logging and resistivity model derived from the airborne electromagnetic (AEM) survey. The water level and groundwater recharge, simulated at the seasonal time step for the three hydrological years from June 2015–May 2018, show a negative trend for all years with groundwater depletion of ${\sim}$19 m, indicating the status of the aquifer is overexploited. The futuristic simulations further predict that the depletion in water level would result in an increasing number of drying up of borewells and perhaps zero water days in coming years if no appropriate measure is taken. The model also suggests that changes in land use with a significant increase in artificial recharge in the coming years could rapidly transform the groundwater scenario and lead to a long-term sustainable management solution.

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