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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2018-519
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2018-519
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Dec 2018

Research article | 07 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

Large-scale ERT surveys for investigating shallow regolith properties and architecture

Laurent Gourdol1, Rémi Clément2, Jérôme Juilleret1, Laurent Pfister1, and Christophe Hissler1 Laurent Gourdol et al.
  • 1Catchment and Eco-hydrology Research Group (CAT), Luxembourg Institute of Science and Technology (LIST), Belvaux, L-4422, Luxembourg
  • 2REVERSAAL Research Unit, National Research Institute of Science and Technology for Environment and Agriculture (IRSTEA), Villeurbanne, F-69626, France

Abstract. Within the Critical Zone, regolith plays a key role in the fundamental hydrological function of water collection, storage, mixing and release. Electrical Resistivity Tomography (ERT) is recognized as a remarkable tool for characterizing the geometry and properties of the regolith, overcoming limitations inherent to conventional borehole-based investigations. However, ERT measurements with a high vertical resolution remain restricted to shallow depths, essentially due to the requirement of small electrode spacing increments (ESI). Under these circumstances, the use of ERT measurements for large horizontal surveys remains cumbersome and time-consuming. Here we focus on the need to optimize the ESI parameter in order to adequately characterize the subsurface fabric. We use a set of synthetic three-layered soil–saprock/saprolite–bedrock models in combination with a field dataset. We demonstrate that oversized ESI can significantly affect our perception of shallow subsurface structures by missing important layers and increasing the ill-posed inverse problem effects. More precisely, we document how a thin surficial layer can influence inverted ERT results and cause a resistivity bias, both at the surface and at deeper horizons. To overcome this limitation, we propose adding interpolated levels of surficial apparent resistivity based on a limited number of ERT profiles with small ESI. We demonstrate that our protocol significantly improves the accuracy of ERT profiles based on large ESI. Our protocol is time and cost efficient – especially in the case of large-scale ERT surveys.

Laurent Gourdol et al.
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Laurent Gourdol et al.
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Short summary
Electrical Resistivity Tomography (ERT) is a remarkable tool for characterizing the geometry and properties of the regolith. However, its use for large horizontal surveys remains cumbersome to characterize shallow subsurface structures due to the requirement of small electrode spacing increments. Here we propose a new approach to overcome this limitation. We demonstrate that our protocol significantly improves the accuracy of ERT profiles when using large electrode spacing increments.
Electrical Resistivity Tomography (ERT) is a remarkable tool for characterizing the geometry and...
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