On the value of combining surface and cross‐borehole ERT measurements to study artificial tile drainage processes

Clément, Rémi; Moreau, Sandra; Henine, Hocine; Guérin, Alexis; Chaumont, Cédric; Tournebize, Julien

doi:10.3997/1873-0604.2014034

Cited by 17 publications

(10 citation statements)

References 45 publications

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“…The characterization of subsurface properties and the delineation of structural units within it should thus go hand in hand with a suitable resolution of ERT images. Otherwise, the results can be inaccurate (Chambers et al, , 2014Clément et al, 2009Clément et al, , 2014Ward et al, 2014). Chambers et al (2014) emphasize that using ERT to detect thin surficial layers remains challenging.…”

Section: Introductionmentioning

confidence: 99%

Exploring the regolith with electrical resistivity tomography in large-scale surveys: electrode spacing-related issues and possibility

Laurent

Clément²,

Juilleret

et al. 2021

Hydrol. Earth Syst. Sci.

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Abstract. Within the critical zone, regolith plays a key role in the fundamental hydrological functions 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. For exploring shallow layers, a small electrode spacing (ES) will provide a denser set of apparent resistivity measurements of the subsurface. As this option is cumbersome and time-consuming, larger ES – albeit offering poorer shallow apparent resistivity data – is often preferred for large horizontal ERT surveys. To investigate the negative trade-off between larger ES and reduced accuracy of the inverted ERT images for shallow layers, we use a set of synthetic “conductive–resistive–conductive” three-layered soil–saprock/saprolite–bedrock models in combination with a reference field dataset. Our results suggest that an increase in ES causes a deterioration of the accuracy of the inverted ERT images in terms of both resistivity distribution and interface delineation and, most importantly, that this degradation increases sharply when the ES exceeds the thickness of the top subsurface layer. This finding, which is obvious for the characterization of shallow layers, is also relevant even when solely aiming for the characterization of deeper layers. We show that an oversized ES leads to overestimations of depth to bedrock and that this overestimation is even more important for subsurface structures with high resistivity contrast. To overcome this limitation, we propose adding interpolated levels of surficial apparent resistivity relying on a limited number of ERT profiles with a smaller ES. We demonstrate that our protocol significantly improves the accuracy of ERT profiles when using large ES, provided that the top layer has a rather constant thickness and resistivity. For the specific case of large-scale ERT surveys the proposed upgrading procedure is cost-effective in comparison to protocols based on small ES.

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Section: Introductionmentioning

confidence: 99%

Exploring the regolith with electrical resistivity tomography in large-scale surveys: electrode spacing-related issues and possibility

Laurent

Clément²,

Juilleret

et al. 2021

Hydrol. Earth Syst. Sci.

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“…Various applications of the ERT method have been presented over the past two decades for: hydrogeological studies (Clément et al, 2014; Hübner et al, 2017, 2015; Nimmer et al, 2008), agricultural applications (Cassiani et al, 2012; Michot et al, 2003; Uhlemann et al, 2016b), ground water resources (Binley et al, 2002; Kuras et al, 2009), tracer and contaminant plume monitoring (Audebert et al, 2016a, 2016b; Koestel et al, 2009, 2008; Kuras et al, 2016, 2014; Power et al, 2014; Rucker et al, 2011; Wilkinson et al, 2010), geotechnical applications (Chambers et al, 2014, 2015; Uhlemann et al, 2016a, 2017) and mining environmental issues (Anterrieu et al, 2010; Dimech, 2018; Dimech et al, 2018, 2017; Intissar, 2009; Power et al, 2018).…”

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confidence: 99%

“…This issue has been addressed for laboratory studies where one (or several) physical parameters can be controlled and the medium is usually homogeneous (Bechtold et al, 2012; Binley et al, 1996; Garré et al, 2010; Koestel et al, 2008; Kremer et al, 2018; Slater et al, 2000). Large‐scale field studies usually assume that either solute conductivity or volumetric water content is constant over time to provide quantitative hydrogeological results by using empirical or laboratory petrophysical relationships (Clément et al, 2014; Dimech et al, 2018; Dumont et al, 2018; Hübner et al, 2017; Jayawickreme et al, 2008; Kuras et al, 2009; Uhlemann et al, 2017). However, these hypotheses may not be applicable for some media where both water content and quality change during hydrogeological processes, such as for landfills and WRPs.…”

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confidence: 99%

Three‐Dimensional Time‐Lapse Geoelectrical Monitoring of Water Infiltration in an Experimental Mine Waste Rock Pile

Dimech

Chouteau

Aubertin

et al. 2019

Vadose Zone Journal

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Core Ideas 3D time‐lapse ERT is used to monitor water infiltration for mining environmental issues. Geoelectrical images provide information where no hydrogeological data is available. Water resistivity must be taken into account to understand bulk resistivity variations. Electrical resistivity of water is used as a tracer to reconstruct water infiltration. Infiltration model integrating both hydrogeological and geophysical data is proposed. Open‐pit mines often generate large quantities of waste rocks that are usually stored in waste rock piles (WRPs). When the waste rocks contain reactive minerals (mainly sulfides), water and air circulation can lead to the generation of contaminated drainage. An experimental WRP was built at the Lac Tio mine (Canada) to validate a new disposal method that aims to limit water infiltration into reactive waste rocks. More specifically, a flow control layer was placed on top of the pile, which represents a typical bench level, to divert water toward the outer edge. Hydrogeological sensors and geophysical electrodes were installed for monitoring moisture distribution in the pile during infiltration events. A three‐dimensional (3D) time‐lapse hydrogeophysical monitoring program was conducted to assess water infiltration and movement. Readings from the 192 circular electrodes buried in the WRP were used to reconstruct the 3D bulk electrical resistivity (ER) variations over time. A significant effort was devoted to assessing the spatiotemporal evolution of water ER because the bulk ER is strongly affected by water quality (and content). The water ER was used as a tracer to monitor the infiltration and flow of resistive and conductive waters. The results indicate that the inclined surface layer efficiently diverts a large part of the added water away from the core of the pile. Local and global models of water infiltration explaining both bulk and water ER variations are proposed. The results shown here are consistent with hydrogeological data and provide additional insights to characterize the behavior of the pile.

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“…The characterization of subsurface properties and the delineation of layer boundaries should thus go hand in hand with a suitable resolution of ERT images. Otherwise, the results can be inaccurate (Chambers et al, 2013(Chambers et al, , 2014Clément et al, 2009Clément et al, , 2014Ward et al, 2014). Chambers et al (2014) emphasize that using ERT to detect thin surficial layers remains Hydrol.…”

mentioning

confidence: 99%

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

Laurent

Clément

Juilleret

et al. 2018

Preprint

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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.

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On the value of combining surface and cross‐borehole ERT measurements to study artificial tile drainage processes

Cited by 17 publications

References 45 publications

Exploring the regolith with electrical resistivity tomography in large-scale surveys: electrode spacing-related issues and possibility

Exploring the regolith with electrical resistivity tomography in large-scale surveys: electrode spacing-related issues and possibility

Three‐Dimensional Time‐Lapse Geoelectrical Monitoring of Water Infiltration in an Experimental Mine Waste Rock Pile

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

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