Heterogeneity of hydrodynamic properties and groundwater circulation of a coastal andesitic volcanic aquifer controlled by tectonic induced faults and rock fracturing – Martinique island (Lesser Antilles – FWI)

Benoit Vittecoq 1 Pierre-Alexandre Reninger 1 Sophie Violette 2 Guillaume Martelet 1 Benoît Dewandel 1 Jean-Christophe Audru 1
1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 SISYPHE - Structure et fonctionnement des systèmes hydriques continentaux
Abstract : We conducted a multidisciplinary study to analyze the structure and the hydrogeological functioning of an andesitic coastal aquifer and to highlight the importance of faults and associated rock fracturing on groundwater flow. A helicopter-borne geophysical survey with an unprecedented resolution (SkyTEM) was flown over this aquifer in 2013. TDEM resistivity, total magnetic intensity, geological and hydrogeological data from 30 boreholes and two pumping tests were correlated, including one which lasted an exceptional 15 months. We demonstrate that heterogeneous hydrodynamic properties and channelized flows result from tectonically-controlled aquifer compartmentalization along the structural directions of successive tectonic phases. Significant fracturing of the central compartment results in enhanced hydrodynamic properties of the aquifer and an inverse relationship between electrical resistivity and transmissivity. Basalts within the fractured compartment have lower resistivity and higher permeability than basalts outside the compartment. Pumping tests demonstrate that the key factor is the hydraulic conductivity contrast between compartments rather than the hydrodynamic properties of the fault structure. In addition, compartmentalization and associated transmissivity contrasts protect the aquifer from seawater intrusion. Finally, unlike basaltic volcanic islands, the age of the volcanic formations is not the key factor that determines hydrodynamic properties of andesitic islands. Basalts that are several million years old (15 Ma here) have favorable hydrodynamic properties that are generated or maintained by earthquakes/faulting that result from active subduction beneath these islands, which is superimposed on their primary permeability.
Keywords : Volcanic island hydrogeology Helicopter-borne time domain electromagnetism and magnetic survey Pumping test Compartmentalized aquifer Log-derivative diagnostic Seawater intrusion
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https://hal-brgm.archives-ouvertes.fr/hal-01357867
Contributeur : Anne-Marie Pouget <>
Soumis le : mardi 30 août 2016 - 15:25:35
Dernière modification le : samedi 20 avril 2019 - 01:54:44

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BRGM | EPHE | INSTITUT-TELECOM | UPMC | METIS_UMR7619 | ENSMP | PARISTECH | PSL | SORBONNE-UNIVERSITE | SU-SCIENCES

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Benoit Vittecoq, Pierre-Alexandre Reninger, Sophie Violette, Guillaume Martelet, Benoît Dewandel, et al.. Heterogeneity of hydrodynamic properties and groundwater circulation of a coastal andesitic volcanic aquifer controlled by tectonic induced faults and rock fracturing – Martinique island (Lesser Antilles – FWI). Journal of Environmental Hydrology, International Association for Environmental Hydrology, 2015, 529, pp.1041-1059. ⟨10.1016/j.jhydrol.2015.09.022⟩. ⟨hal-01357867⟩

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