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Structure des écoulements et propriétés de transport des aquifères cristallins fracturés et altérés : Application au site de Choutuppal (Inde du Sud)

Abstract : The fractured and weathered crystalline aquifers are often the only viable water resource in arid and semi-arid regions. Nevertheless, these highly heterogeneous media are still poorly understood, especially the major structures that control groundwater ows and contaminant transport. To improve knowledge of those media, we have conducted a detailed analysis of the hydrological properties of the Choutuppal experimental site (Andhra Pradesh, Southern India) which has a dense network of observation boreholes. The study focus on 1) the identi cation of relevant structures and the spatial variability of hydraulic properties and 2) the dominant solute transport processes in these fractured media. First, the evolution of properties with depth highlights the most permeable structures. The properties were then studied in highly contrasted hydrological conditions. In high water level conditions, the saprolite { granite interface controls groundwater ows at watershed scale. By contrast, when groundwater level is lower than this interface, hydrological compartmentalization appears due to the decrease of the number of permeable fractures with depth which in turns decreases considerably connectivity with depth. A conceptual model of groundwater ow is proposed at the watershed scale to illustrate these contrasting behaviors. To identify the respective role of advective and di usive processes a ecting both solute transport, two kind of tracer experiments were conducted under di erent ows con gurations. Combination of tracer experiments between boreholes and single borehole tests (push-pull) permit to highlight the predominant role of heterogeneous advection. Matrix di usion can be neglected at least for the time scales considered. The push-pull experiments have also allowed identifying the impact of investigation scale on anomalous solute transport. All results give a better understanding of the properties and the vulnerability of those media subject to strong anthropogenic pressure.
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https://hal-insu.archives-ouvertes.fr/tel-01137304
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Submitted on : Tuesday, March 31, 2015 - 8:31:01 AM
Last modification on : Friday, April 5, 2019 - 8:17:38 PM
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  • HAL Id : tel-01137304, version 1

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Nicolas Guihéneuf. Structure des écoulements et propriétés de transport des aquifères cristallins fracturés et altérés : Application au site de Choutuppal (Inde du Sud). Sciences de la Terre. Universite Rennes 1, 2014. Français. ⟨tel-01137304⟩

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