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Prof. Shakeel Ahmed
Academy of Scientific and Innovative Research (AcSIR), India
Heliborne Dual Moment Transient Electromagnetic Investigation in Geologically Divergent Terrenes for Groundwater Mapping
India is now facing serious water challenges and issues due to global climate change, the green revolution, environmental and human influences which have exacerbated the pressure and compromised the sustainability of India`s water resources, particularly the groundwater. Although the country is beset with variable water problems simply as the distribution of water resources are highly uneven, the biggest issue is of the groundwater management. Comprehensive knowledge of aquifer system is an important requisite for its affective management. Given the fact that geological formations where aquifers exist are highly variable and complex, punctual and scarce information are not enough to understand, asses and manage them. Thus continuous data acquisition and their interpretation as well as integration is the solution. 

Heliborne Dual moment Transient Electromagnetic (HTEM) along with Magnetic measurement (HMAG) have been carried out in the divergent geological terrenes comprising of Gangetic alluvium, Tertiary sediments underlying the desert, Deccan basalts and Gondwana sediments, weathered and fractured granite gneisses and schists and the coastal alluvium and Tertiary sediments. The survey was carried out using state of the art equipment SkyTEM.

The paper presents a synopsis of the results of HeliTEM and HeliMAG surveys that have helped in obtaining the continuous data acquisition scanning the sub-surface in representative geological formations in India. These HeliTEM data were supported by a number of Ground Geophysical surveys viz., Ground TEM, Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT). The result has provided the 3D subsurface structures controlling the groundwater conditions, the regional continuity of probable aquifers, the variations in lithological character of aquifers and the quality of water in terms of salinity. The results have been used to generate database using convenient grid size, as small as 50m x 50m to the proposed National Aquifer Grid (NAG) of 2 km x 2 km for the desired aquifer based groundwater management plan. 

The specialized features pertaining to hydrogeological characteristics obtained from this study are as follows: 

§  A very clear delineation clay beds and their spatial distribution providing the multi-layered aquifer setup in the Gnagetic plains.

§  Delineation of low resistivity zones in the quartzite underlain by an over exploited aquifers providing the possibility of new aquifers.

§  Presence of comparatively freshwater zones underneath the saline water aquifers in the thick and dry sands in deserts.

§  Clear demarcation of different lava flow, mapping the structural controls as well as highly porous zones in the contact of basalt and gondwanas.

§  A complete and continuous mapping of weathered portions in the crystalline hard rock areas providing information on the recharge zones.

§  The setting of multi-layered aquifer and different zones of salt water intrusion in the coastal sedimentary formations.

Thus the study has established an appropriate cost-effective methodology for deploying specific geophysical investigation on one hand and carried out the aquifer mapping with continuous aquifer information for performing aquifer modeling on the other hand.
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