Impact of sub-horizontal discontinuities and vertical heterogeneities on recharge processes in a weathered crystalline aquifer in southern India

Abstract : In the face of increasing demands for irrigated agriculture, many states in India are facing water scarcity issues, leading to severe groundwater depletion. Because perennial water resources in southern India consist mainly of crystalline aquifers, understanding how recharge takes place and the role of preferential flow zones in such het- erogeneous media is of prime importance for successful and sustainable aquifer management. Here we investigate how vertical heterogeneities and highly transmissive sub-horizontal discontinuities may control groundwater flows and recharge dynamics. Recharge processes in the vadose zone were examined by analysing the propagation of an infiltration front and mass transfers resulting from the implementation of a managed aquifer recharge (MAR) structure. Said structure was set up in the Experimental Hydrogeological Park in Telangana (Southern India), a well-equipped and continuously monitored site, which is periodically supplied with surface water deviated from the nearby Musi river, downstream of Hyderabad. An initial volume balance equation was applied to quantify the overall inputs from the MAR structure into the groundwater system, which was confirmed using a chloride mass balance approach. To understand how this incoming mass is then distributed within the aquifer, we monitored the evolution of water volumes in the tank, and the resulting lateral propagation front observed in the surrounding borehole network. Borehole logs of temperature and conductivity were regularly performed to identify preferential flow paths. As a result we observed that mass transfers take place in the way of preferential lateral flow through the most transmissive zones of the profile. These include the interface between the lower portion of the upper weathered horizon (the saprolite) and the upper part of the underlying fissured granite, as well as the first flowing fractures. This leads to a rapid lateral transfer of recharge, which allows quick replenishment of aquifers but may have severe implications regarding groundwater quality, whether contaminants originate from diffuse sources (such as fertilizers), or a localized injection of polluted surface water. These findings confirm previous studies about the non-linear behaviour of hard rock aquifers (Guihéneuf et al., 2014) and recharge processes (Boisson et al., 2015; Alazard et al., 2015). Depending on water level conditions, the aquifer shifts from a regional flow system (when superficial more connected and weathered levels are saturated), to independent local flow systems (when only the lower lesser fractured portion is saturated). Thus recharge seems to be controlled by the existence of (i) vertical heterogeneities within the unsaturated zone and (ii) highly transmissive sub-horizontal discontinuities, both of which controlling groundwater flows and recharge dynamics.
Type de document :
Poster
European Geosciences Union General Assembly 2017, Apr 2017, Vienne, Austria. Geophysical Research Abstracts, 19, pp.EGU2017-11738, 2017
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Contributeur : Isabelle Dubigeon <>
Soumis le : mercredi 7 juin 2017 - 11:35:53
Dernière modification le : jeudi 11 janvier 2018 - 06:24:06

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  • HAL Id : insu-01534119, version 1

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Madeleine Nicolas, Adrien Selles, Olivier Bour, Jean-Christophe Maréchal, Marion Crenner, et al.. Impact of sub-horizontal discontinuities and vertical heterogeneities on recharge processes in a weathered crystalline aquifer in southern India. European Geosciences Union General Assembly 2017, Apr 2017, Vienne, Austria. Geophysical Research Abstracts, 19, pp.EGU2017-11738, 2017. 〈insu-01534119〉

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