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Water 2018, 10(9), 1117; https://doi.org/10.3390/w10091117

Characterizing Near-Surface Fractured-Rock Aquifers: Insights Provided by the Numerical Analysis of Electrical Resistivity Experiments

1
Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland
2
Geosciences Montpellier (CNRS), University of Montpellier, 34090 Montpellier, France
Authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Received: 16 July 2018 / Revised: 15 August 2018 / Accepted: 16 August 2018 / Published: 23 August 2018
(This article belongs to the Section Hydraulics)
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Abstract

Fractured-rock aquifers represent an important part of the groundwater that is used for domestic, agricultural, and industrial purposes. In these natural systems, the presence and properties of fractures control both the quantity and quality of water extracted, meaning that knowledge about the fractures is critical for effective water resource management. Here, we explore through numerical modeling whether electrical resistivity (ER) geophysical measurements, acquired from the Earth’s surface, may potentially be used to identify and provide information about shallow bedrock fractures. To this end, we conduct a systematic numerical modeling study whereby we evaluate the effect of a single buried fracture on ER-profiling data, examining how the corresponding anomaly changes as a function of the fracture and domain characteristics. Two standard electrode configurations, the Wenner-Schlumberger (WS) and dipole-dipole (DD) arrays, are considered in our analysis, with three different spacing factors. Depending on the considered electrode array, we find that the fracture dip angle and length will impact the resistivity anomaly curves differently, with the WS array being better adapted for distinguishing between sub-horizontal and sub-vertical fractures, but the DD array leading to larger overall anomaly magnitudes. We also find that, unsurprisingly, the magnitude of the resistivity anomaly, and thus fracture detectability, is strongly affected by the depth of overburden and its electrical resistivity, as well as the fracture aperture and contrast between the fracture and bedrock resistivities. Further research into the electrical properties of fractures, both above and below the water table, is deemed necessary. View Full-Text
Keywords: fractured rock; geophysics; electrical resistivity; numerical simulations; sensitivity fractured rock; geophysics; electrical resistivity; numerical simulations; sensitivity
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Supplementary materials

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  • Externally hosted supplementary file 1
    Link: https://drive.google.com/open?id=1zm_xTl0jmrDPGv5bjLJBn4ZaUM6DuaM4
    Description: Supplementary ER-profiling movies to help with the data interpretation in our manuscript. The movies are labeled by case number (1-6), followed by array type (WS = Wenner-Schlumberger; DD = dipole-dipole), followed by spacing factor (n = 1,2,3).
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Demirel, S.; Roubinet, D.; Irving, J.; Voytek, E. Characterizing Near-Surface Fractured-Rock Aquifers: Insights Provided by the Numerical Analysis of Electrical Resistivity Experiments. Water 2018, 10, 1117.

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