Quantitative Application of AEM for Regional Groundwater Productivity in Fractured Basement Rocks
Thursday, 13 June 2019: 11:40
Davie West Building, DW103 (Florida Atlantic University)
Subash Chandra1, Joy Choudhury1, Erugu Nagaiah2, Esben Auken3 and Saurabh K Verma4, (1)CSIR-National Geophysical Research Institute, Electrical Geophysics-Groundwater, Hyderabad, India, (2)CSIR-National Geophysical Research Institute, Electrical Geophysics-Groundwater, Hyderabad, Denmark, (3)University of Aarhus, Aarhus, Denmark, (4)CSIR-National Geophysical Research Institute, Groundwater, Hyderabad, India
Abstract:
The past few decades have seen increasing use of ground-based electromagnetic (EM) surveys for various applications such as minerals and groundwater exploration, archeological and geotechnical investigations, etc. Recent developments, particularly in the last couple of decades, have further led to the development of airborne electromagnetic (AEM) systems such as SkyTEM, V-TEM, AeroTEM, GeoTEM, etc., that are now established as the most popular exploration tool for regional surveys. The AEM methods have been traditionally applied for mapping the conductive bodies in the resistive host medium and interpreted more qualitatively than quantitatively. This paper presents a quantitative application of AEM methods applied in the fractured-basement hard rocks for groundwater in India. An effective and sustainable management of the groundwater resources in such terrain requires a comprehensive knowledge of fracture distribution at the regional scale.
An AEM survey was carried out in parts of Tumkur district, Karnataka under AQUIM pilot project in the year 2013. The resistivity maps derived from the airborne electromagnetic (AEM) survey reveal sharp and deep zones of low formation resistivity, which indicate groundwater-bearing zones. It is found that some of these zones are hydrogeologically connected through fracture networks resulting in augmented yield. AEM results in combination with an in-depth understanding of the geological structures successfully map these groundwater-saturated fracture networks (or hydrogeological lineaments) that we term as 'Hydrolins'. Besides the fracture network, we have established a threshold groundwater horizon (Fig.1) beyond which a strong correlation exists between the depth of a well and its yield. A novel approach is developed to map major fracture networks that contain significant amount of water. The concept of threshold groundwater horizon helps in improving the success rate in terms of high yielding potential borewells. The study also helps in the identification of suitable zones to construct artificial recharge structures
