Large Scale Mapping of Fractures and Groundwater Pathways in Crystalline Hardrock By AEM

In hardrocks that cover about 20% of the Earth’s surface, it is difficult to locate steady sources for groundwater due to inadequate understanding of the fracture networks. A comprehensive knowledge of fracture distribution at the regional scale is necessary to delineate sustainable aquifers and man...

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Bibliographic Details
Published in:Scientific reports 2019-01, Vol.9 (1), p.398-398, Article 398
Main Authors: Chandra, Subash, Auken, Esben, Maurya, Pradip K., Ahmed, Shakeel, Verma, Saurabh K.
Format: Article
Language:English
Subjects:
704/2151/241
704/2151/2809
Aquifers
Drilling
Fractures
Geological structures
Geology
Groundwater
Groundwater data
Groundwater potential
Humanities and Social Sciences
Hydrogeology
multidisciplinary
Science
Science (multidisciplinary)
Watersheds
Well data
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Summary:In hardrocks that cover about 20% of the Earth’s surface, it is difficult to locate steady sources for groundwater due to inadequate understanding of the fracture networks. A comprehensive knowledge of fracture distribution at the regional scale is necessary to delineate sustainable aquifers and manage them efficiently. The resistivity maps derived from the airborne electromagnetic (AEM) survey over the Ankasandra watershed in Karnataka, India, 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’. As groundwater occurrence is generally associated with lineaments, we analyzed the drilling and geophysical logs from 21 wells within a 380 sq.km area to study the relationships of various lineaments with ‘Hydrolins’, particularly in respect of their groundwater potential. AEM results, though calibrated and correlated with a limited number of well data, revealed a threshold groundwater horizon (TGWH), found to be at 80 m depth for Ankasandra watershed, beyond which a strong correlation exists between the depth of a well and its yield. While the TGWH may differ for different watersheds, the approach presented here can be readily adopted to map sustainable groundwater sources in hardrocks worldwide.
ISSN:2045-2322
2045-2322
DOI:10.1038/s41598-018-36153-1