HS8.1.8 | Hydrogeophysics: a tool for hydro(geo)logy, contaminant transport, ecology, and beyond
Hydrogeophysics: a tool for hydro(geo)logy, contaminant transport, ecology, and beyond
Convener: Damien Jougnot | Co-conveners: Ulrike Werban, Philippe Leroy, Marc Dumont, Remi Clement
Orals
| Thu, 27 Apr, 16:15–18:00 (CEST)
 
Room 2.31
Posters on site
| Attendance Thu, 27 Apr, 10:45–12:30 (CEST)
 
Hall A
Orals |
Thu, 16:15
Thu, 10:45
This session deals with the use of geophysical methods for the characterization of subsurface properties, states, and processes in contexts such as hydrology, ecohydrology, contaminant transport, reactive media, etc. Geophysical methods potentially provide subsurface data with an unprecedented high spatial and temporal resolution in a non-invasive manner. However, the interpretation of these measurements is far from straightforward in many contexts and various challenges remain. Among these are the need for improved quantitative use of geophysical measurements in model conceptualization and parameterization, and the need to move quantitative hydrogeophysical investigations beyond the laboratory and field scale towards the catchment scale. Therefore, we welcome submissions addressing advances in the acquisition, processing, analysis and interpretation of data obtained from geophysical and other minimally invasive methods applied to a (contaminant) hydrological context. In particular, we encourage contributions on innovations in experimental and numerical methods in support of model-data fusion, including new concepts for coupled and joint inversion, and improving our petrophysical understanding on the link between hydrological and geophysical properties.

Orals: Thu, 27 Apr | Room 2.31

Chairpersons: Damien Jougnot, Marc Dumont
16:15–16:20
Linking groundwater processes to geoelectrical signals
16:20–16:40
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EGU23-9639
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ECS
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solicited
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On-site presentation
Flore Rembert, Arnaud Stolz, Sophie Roman, and Cyprien Soulaine

We miniaturize the low-frequency (<1kHz) geoelectrical acquisition using advanced micro-fabrication technologies to investigate coupled processes in the critical zone (CZ). With this innovation in the experimental acquisition, we focus on the development of the complex electrical conductivity monitoring with the spectral induced polarization (SIP) method. The interpretation of the SIP signal is based on the development of petrophysical models that relate the complex electrical conductivity to structural, hydrodynamical, and geochemical properties or distributions. State-of-the-art petrophysical models, however, suffer from a limited range of validity and presume too many microscopic mechanisms to define macroscale parameters. Thus, direct observations of the underlying processes coupled with geoelectrical monitoring are keys to deconvolute the signature of the biochemical-physical mechanisms and, then, developing more reliable models. Microfluidic experiments enable direct visualization of flows, reactions, and transport at the pore-scale thanks to transparent micromodels coupled with optical microscopy and high-resolution imaging techniques. Micromodels are a two-dimensional representation of the porous medium, ranging in complexity from single channels to replicas of natural rocks. Cutting-edge micromodels use reactive minerals to investigate the water-mineral interactions involved in the CZ. In this work, we propose a new kind of micromodels equipped with four aligned electrodes within the channel for SIP monitoring of calcite dissolution, a key multiphase process of the CZ involved in karstification. We highlight the strong correlation between SIP response and dissolution through electrical signal examination and image analysis. In particular, degassed CO2 bubbles generated by the dissolution play a major role.  Our technological advancement brings a deeper understanding of the physical interpretation of the complex electrical conductivity and will provide a further understanding of the CZ dynamic processes through SIP observation.

How to cite: Rembert, F., Stolz, A., Roman, S., and Soulaine, C.: Development of geoelectrical monitoring of the critical zone processes on microfluidic chips, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9639, https://doi.org/10.5194/egusphere-egu23-9639, 2023.

16:40–16:50
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EGU23-11013
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On-site presentation
Jan Vinogradov, Nacha Atiwurcha, David Vega-Maza, and Jos Derksen

Zeta potential is an important interfacial property that controls electrostatic interactions between mineral, water, and non-aqueous phase fluids. These interactions play an important role in defining the wetting state of reservoir rocks and transport of ionic species through porous media. The zeta potential is shown to be an efficient means for a broad range of applications including monitoring of single- and multi-phase flows in subsurface settings, characterization of fracture networks, efficiency of CO2 sequestration, hydrogen underground storage and enhanced oil recovery. It is widely agreed that the zeta potential in carbonate rocks is controlled by the concentration of potential determining ions (PDI), but the understanding of the underlying mechanisms is still limited as there are little experimental data on quantitative characterization of the dependence of the zeta potential on concentration of negative potential determining ions (PDI) such as SO42-, CO32-, HCO3-, especially when their concentration is high and exceeds that of the positive PDIs.

In this study, the streaming potential method is used to investigate the zeta potential of natural carbonate rock samples in contact with natural aqueous solutions of low-to-high ionic strength and with varying concentration of sulphate (SO42-) and carbon (C4) related (HCO3-, CO32-) ions. In each set of experiments the total ionic strength was kept constant to eliminate the impact of concentration on the zeta potential so that the increasing/decreasing concentration of negative PDI was adjusted by decreasing/increasing concentration of indifferent Cl- ions. The study probed the concentration of negative PDIs that has never been reported before, with their respective lowest concentration consistent with previously reported equilibrium values, and the highest concentration being equal to the maximum achievable through stripping the tested solutions of Cl-.

Our results demonstrate for the first time that magnitude of the negative zeta potential increases linearly with log10 of C4 concentration, however its dependence on the log10 of SO42- concentration is non-linear suggesting varying mechanisms of this PDI’s specific adsorption. Moreover, the results demonstrate that the zeta potential strongly depends on the total ionic strength, interpreted from slopes of the linear regressions for each negative PDI in different background solution. This observation suggests that equilibrium constants of negative PDI specific adsorption may be affected by the total ionic strength. Our findings improve the current understanding of the complex physicochemical processes that take place at calcite-water interface and provide important experimental data for surface complexation modelling of carbonate-brine systems.

How to cite: Vinogradov, J., Atiwurcha, N., Vega-Maza, D., and Derksen, J.: New Insights into the Effect of HCO3-, CO32- and SO42- Ions on the Zeta Potential of Intact Carbonate Rock Sample, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11013, https://doi.org/10.5194/egusphere-egu23-11013, 2023.

16:50–17:00
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EGU23-10845
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ECS
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On-site presentation
Kaiyan Hu, Qinghua Huang, Peng Han, Yihua Zhang, Chunyu Mo, and Damien Jougnot

Understanding the physical process of soil imbibition and water flow in the porous media in depth is significant in assessing the risk of forming landslides. Volumetric soil moisture sensors can be used to measure water content variations in situ. However, it has a spatial gap due to the limited number of installed sensors. On the other hand, geophysics can provide integrated measurements that can be spatially resolved. Among existing geophysical methods, Self-Potential (SP) is a method of choice to monitor water flow. Indeed, pore-water flows can generate the electrical streaming current based on the electrokinetic mechanism. This electrokinetic cross-coupling process is not only sensitive to the water flow but also depends on water content variations. This study relies on a soil-column experiment by artificially imposing rainfall to examine if the electrical SP could indicate the water infiltrating process. Combined with the observed data, our results indicate the water infiltrating stages can be characterized by the extracted SP signatures under a comprehensive numerical model. As a passive hydrogeophysical method, the capacity of SP to capture the characteristics of the spatio-temporal variations of water fluxes and soil-water conditions can offer early warning information of rainfall-induced landslides.

How to cite: Hu, K., Huang, Q., Han, P., Zhang, Y., Mo, C., and Jougnot, D.: Rainwater infiltrating process revealed from the self-potential signatures, insight for landslide monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10845, https://doi.org/10.5194/egusphere-egu23-10845, 2023.

17:00–17:10
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EGU23-956
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ECS
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On-site presentation
Ziv Moreno and Peleg Haruzi

Accurate modeling of water flow and solute transport in unsaturated soils are of significant importance for precision agriculture and environmental protection. Traditional modeling approaches are considerably challenging since they require well-defined boundaries and initial conditions. Harnessing machine-learning techniques, specifically deep neural networks (DNNs), to detect water flow and solute transport in porous media have recently gained considerable attention. In traditional DNNs, an artificial neural network with several hidden layers is trained solely using data to approximate parameter and state estimation, e.g., the spatiotemporal distribution of water content and pore-water salinity. However, data is extremely limited and sparsely available in subsurface applicationsPhysics-informed neural networks (PINNs) have recently been developed to learn and solve forward and inverse problems constrained to a set of partial differential equations (PDEs). Unlike traditional DNNs, PINNs are confined to physics and do not require" big" data for training. However, hydrological applications of PINNs only considered an in-silico environment with spatial measurements of hydraulic head, water content and/or solute concentrations well distributed in the subsurface. Such measurements are hard to obtain in real-world applications since they require drilling to extract soil samples or installing in-situ measurement devices at depth which also violets the soil's natural structure. As opposed to conventional subsurface characterization and monitoring techniques, non-invasive geoelectrical methods can provide continuous, extensive, and non-invasive information of the subsurface. Nevertheless, the sensitivity of the measured electrical signal to various soil parameters, mainly water content and pore-water salinity, as well as inversion errors, could result in biased hydrological interpretations. This work adopted the PINNs framework to simulate two-dimensional water flow and solute transport during a drip irrigation event and the following redistribution stage, using time-lapse geoelectrical measurements with unknown initial conditions. For that manner, a PINNs system containing two coupled feed-forward DNNs was constructed, describing the spatiotemporal distribution of both water content and pore-water salinity. The system was trained by minimizing the loss function, which incorporates physics-informed penalties, i.e., mismatch with the governing PDEs and boundary conditions, and measurement penalties, i.e., mismatch with the geoelectrical data. Two-dimensional flow and transport numerical simulations were used as benchmarks to examine the suitability of the described approach.  Results have shown that the trained PINNs system was able to reproduce the spatiotemporal distribution of both water content and pore-water salinity during both stages, i.e., irrigation and redistribution, with high accuracy, using five time-lapse geoelectrical measurements conducted with 59 electrodes placed at the surface. The trained PINNs system also reconstructed the initial conditions of both state parameters for both stages. It was also able to separate the "measured" electrical signal into its two components, i.e., water content and pore-water salinity. In addition, the subsurface geoelectrical tomograms were significantly improved compared to those obtained from a classical inversion of the raw geoelectrical data.    

How to cite: Moreno, Z. and Haruzi, P.: Simulating water flow and solute transport at unsaturated soils with unknown initial conditions using physics-informed neural networks trained with time-lapse geoelectrical measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-956, https://doi.org/10.5194/egusphere-egu23-956, 2023.

17:10–17:20
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EGU23-5444
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ECS
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Virtual presentation
Behshad Koohbor, Pierre Fischer, Marwan Fahs, Anis Younes, and Hervé Jourde

In the unsaturated zone of fractured and karstified media, although the fractures and incipient karst conduits generally account for a minor volume in the bulk geologic formations, they contribute significantly to the flow and transport properties. The reason is due to the significant difference (i.e., several orders of magnitude) of permeability in comparison with the surrounding porous matrix. Thus, the simulation of groundwater flow in such heterogeneous porous media requires knowledge of geometry and hydrodynamical characteristics of the fractures. However, identifying fractures and incipient karst conduits in the unsaturated zone has been a challenge in hydrogeology. Electrical resistivity tomography (ERT) as a non-invasive geophysical method has the potential to deliver vast information rapidly in a relatively economical way related to fractures and incipient karst conduits. However, the sole use of ERT for the interpretation of geological formation and hydrodynamic properties of fractured domains is not possible as it may lead to ambiguity of interpretations. The main goal of this work is to investigate the performance of coupling water flow and electrical current for fracture characterization. Thus, we develop a new numerical model for the simulation of coupled water flow and electrical current. In this model, the fractures or incipient karst conduits are simulated with the discrete fracture matrix approach which is known to be the most accurate approach for addressing flow in fractured domains as it considers fractures without any simplification. This approach is applied for both electrical current and water flow. The hybrid dimensional approach, which assumes 1D fractures in a 2D porous matrix is used to improve the computational efficiency of the developed model. The partial differential equations describing the flow and electrical current are solved using the mixed hybrid finite element method for space discretization and the method of lines for time integration. These numerical techniques have been selected to ensure an accurate solution to the nonlinear problem in a time-efficient and effective way. The newly developed model is validated for simplified test cases against the results obtained by an equi-dimensional approach based on the conforming finite element method (i.e., using COMSOL Multiphysics®). The effect of major fracture orientation and length on the temporal response of bulk resistivity during a percolation scenario has been studied numerically. In addition, the effect of injection of electrical dipole has been simulated and discussed for the same problem. The results show that the proper placement of the electrical dipole can significantly affect the resolution of the fracture signature response and the bulk resistivity measured on the surface of the domain through time.

 

How to cite: Koohbor, B., Fischer, P., Fahs, M., Younes, A., and Jourde, H.: An advanced hybrid-dimensional discrete fracture-matrix model for coupled simulation of water flow and electrical current in variably saturated fractured porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5444, https://doi.org/10.5194/egusphere-egu23-5444, 2023.

In-site aquifer and vadose zone hydrogeophysical characterization
17:20–17:30
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EGU23-9723
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ECS
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On-site presentation
Lukas Aigner, Nathalie Roser, Anna Hettegger, Daniel Höfelmaier, Arno Cimadom, Hadrien Michel, Thomas Hermans, and Adrián Flores Orozco

Reliable information about the aquifer geometry and its spatial variability from geophysical methods plays a critical role for various hydrological research questions. Such information can be obtained with the transient electromagnetic (TEM) method that reaches a larger depth of investigation with a smaller survey layout compared to electrical or seismic methods. However, the quantitative interpretation of the resistivity model obtained from TEM data in terms of groundwater level and aquifer geometry might be biased by the non-uniqueness of the deterministic inversion. To overcome such limitations, we propose here to use Bayesian evidential learning (BEL1D) to evaluate the uncertainty of the groundwater level and aquifer thickness interpreted from TEM results using a classical deterministic inversion approach. Additionally, we investigate the effect of different prior model spaces on the uncertainty obtained from BEL1D and use the distance-based global sensitivity analysis (DGSA) to determine whether model parameters with a large uncertainty are actually non-influential on the model response. To test the uncertainty quantification, TEM data were measured at three sites in Austria representative of different hydrogeological settings and groundwater levels, namely: 1) a shallow (1 m - 10 m) aquifer located in the soda lakes of the Neusiedl-Seewinkel Basin in Burgenland, 2) an aquifer in intermediate (5 m – 15 m) depth located in the hydrological open-air laboratory (HOAL) in lower Austria and 3) a deep (> 35 m) aquifer in a farm land located in Upper Austria. We obtain TEM data with the TEM-FAST 48 instrument with a 6 m, 12.5 m and a 25 m square single-loop configuration to achieve sensitivities corresponding to the three different aquifer depths. Additionally, we use electrical resistivity tomography (ERT) and multi-channel analysis of surface waves (MASW) data to assess the TEM inversion results. The interpretation of the TEM inversion results is evaluated with BEL1D to obtain the uncertainty of the groundwater level from the cumulative uncertainty of all layers above the layer representing the groundwater level as well as the thickness of the aquifer. Additionally, we achieve a quantitative evaluation of the solved TEM model uncertainties with the DGSA method as well as with the ERT and MASW inversion results. Our results show a lower uncertainty for the electrical resistivity than for the layer thickness, while the DGSA reveals a decrease of sensitivity with depth.

How to cite: Aigner, L., Roser, N., Hettegger, A., Höfelmaier, D., Cimadom, A., Michel, H., Hermans, T., and Flores Orozco, A.: Uncertainty quantification of aquifer geometry and groundwater level using electrical resistivity models obtained from transient electromagnetic data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9723, https://doi.org/10.5194/egusphere-egu23-9723, 2023.

17:30–17:40
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EGU23-5777
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On-site presentation
Susann Birnstengel, Uta Koedel, Marco Pohle, Götz Hornbruch, Johannes Nordbeck, Ulrike Werban, and Peter Dietrich

The use of near-surface geothermal energy implying geothermal infrastructure increases significantly in Germany [1]. Therefore it becomes an essential subject for impact analysis of our groundwater resource. Rock physical properties change through the alteration of the pore fluid properties such as temperature. Those alterations happen under the influence of heat in the subsurface. Variations in geophysical proxies can provide information about the subsurface changes. Laboratory measurements by Jaya et al. [2] show that P-wave velocities decrease with increasing temperature.

Within the BMBF funded follow-on project – TestUM II a “cyclic high temperature aquifer thermal energy storage (ATES) experiment” has been conducted in the north or Germany to verify these findings. With this field experiment at a shallow aquifer environment we are able to avoid difficulties in frequency dependent upscaling procedures [3]. We investigated the coherence between geophysical proxies and the temperature distribution in the near surface with a combined hydrogeological, microbiological and geophysical monitoring system covering an area of approximately 100 m². A cyclic heat injection at a depth between 7 – 14 m was monitored over 15 months with seismic cross-hole measurements in 16 different wells to cover heat propagation and direction-dependent heterogeneities across the field. The purpose was to investigate geophysical proxy responses on the alteration of the pore fluid that is likely to change rock physical properties in the near-surface. To predict the effect of temperature on P-wave velocity we took advantage of the Jaya’s [2] modification of the Gassmann equation which accounts for the related thermophysical characteristics of the pore fluid. Unlike the findings of Jaya et al. [2], that the P-wave velocity decreases, we see the opposite, an increase in P-wave velocity in our non-closed system assuming different thermophysical characteristics of the saturating fluid. We excluded a bubble-formation since we only cover temperatures below 80°C. However, a decrease in the amplitudes due to the P-wave attenuation can be observed. According to Jaya et al. [2] this can be attributed to the decrease in water viscosity.

[1] Blöcher, G., Reinsch, T., Regenspurg, S., Henninges, J., Brehme, M., Saadat, A., Kranz, S., Frick, M., Spalek, A., Huenges, E. (2019): Geothermie in urbanen Räumen: thermische Untergrundspeicherung und Tiefe Geothermie in Deutschland. - System Erde, 9, 1, 6-13.
https://doi.org/10.2312/GFZ.syserde.09.01.1

[2] Jaya, Makky S. / Shapiro, Serge A. / Kristinsdóttir, L\iney H. / Bruhn, David / Milsch, Harald / Spangenberg, Erik
Temperature dependence of seismic properties in geothermal rocks at reservoir conditions, 2010-03, Geothermics , Vol. 39, No. 1, Elsevier BV

[3] Müller, T. M. / Gurevich, Boris / Lebedev, Maxim 
Seismic wave attenuation and dispersion resulting from wave-induced flow in porous rocks - A review, 2010-09, Geophysics , Vol. 75, No. 5 ,Society of Exploration Geophysicists 

How to cite: Birnstengel, S., Koedel, U., Pohle, M., Hornbruch, G., Nordbeck, J., Werban, U., and Dietrich, P.: Monitoring of an aquifer thermal storage system on the field scale using cross-hole seismics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5777, https://doi.org/10.5194/egusphere-egu23-5777, 2023.

17:40–17:50
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EGU23-5954
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Virtual presentation
Benjamin Mary, Konstantinos Kaffas, Matteo Censini, Francesca Sofia Manca di Villahermosa, Andrea Dani, Matteo Verdone, Federico Preti, Paolo Trucchi, Daniele Penna, and Giorgio Cassiani

Subsurface flow at the hillslope scale is a critical process responsible for water redistribution and transport of nutrients to the stream. Despite its hydrological importance, understanding the mechanisms governing subsurface flow generation is still challenging. 

We investigated the case of a small forested catchment located in the Apennine mountains, Tuscany, central Italy, which experiences shallow lateral downslope water redistribution resulting in substantial differences in vadose zone water supply along the hillslope. We developed an integrated experimental and modelling approach in order to shed some light on the role of the subsurface structure on the generation of hillslope-scale subsurface flow in the study catchment.  

We used a combination of methods sensitive to different soil properties. Ground Penetrating Radar (GPR) surveys show a complex response reflecting the interplay of different factors such as the presence of rocks, banks and counterslope in the near-surface and thus highlighting the very heterogeneous soil that may control water flow patterns. Several Electromagnetic (EM) mappings were conducted and show top-down hillslope variations of soil electrical conductivity revealing that trees located at the footslope and that experience longer vegetative periods might benefit from larger soil moisture content compared to the smaller trees located on the hillslope top. Similar observations are made from the two parallel top-bottom hillslope Electrical Resistivity Tomography (ERT) transects. 

The geophysical results will be integrated into hydrogeological simulations using the CATHY model for different scenarios (e.g., initial soil moisture, preferential flow paths, drainable porosity, soil properties, bedrock topography or stratification of soils) to explore the main drivers for subsurface preferential flow. 

How to cite: Mary, B., Kaffas, K., Censini, M., Manca di Villahermosa, F. S., Dani, A., Verdone, M., Preti, F., Trucchi, P., Penna, D., and Cassiani, G.: Supporting subsurface preferential flow in a small forested catchment from geophysical data and hydrological modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5954, https://doi.org/10.5194/egusphere-egu23-5954, 2023.

17:50–18:00
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EGU23-9156
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ECS
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On-site presentation
Clémence Ryckebusch, Jean-Michel Baltassat, Anatoly Legchenko, Pauline Kessouri, Nadia Amraoui, Mohamad Abbas, and Mohamed Azaroual

In the current climate change context, the quality and availability of water resource are important society issues. Indeed, the consumption of water and fertilizers by farms and their discharge into the soil and aquifers leads to a critical environmental situation. To manage the effect and fate of these contaminations, it is necessary to have a relevant knowledge of the vadose zone dynamics and exchanges especially flow paths from the soil to the deep aquifers. Parts of the vadose zone are well studied such as the first meters with an adapted instrumentation, and the water table properties with piezometric measurements and pumping tests. The geophysics methods allow studying the deep vadose zone properties. The surface nuclear magnetic resonance (SNMR) is a direct geophysical method based on the protons magnetic resonance to measure water content in the subsurface. This method can be used to detect the water table level coupled with hydrogeological measurements (piezometric measurements and pumping tests) or to characterize aquifers properties and boundaries coupled with other geophysical methods (electrical, EM or gravimetric methods).

 

The current study is carried out in Villamblain (France) at the heart of the Beauce region; one of the most cultivated and highly nitrate-contaminated area in France. The vadose zone is a highly heterogeneous limestone with geochemical alteration, complex network of fractures and karstification. This field site was chosen to develop an observatory of transfers in the Vadose Zone named O-ZNS (https://plateformes-pivots.eu/o-zns/). This observatory consists of an exceptional well (20 m-deep and 4 m-diameter) equipped with multiple sensors and accessible for direct characterization of the heterogeneous vadose zone, surrounded by 8 boreholes used for water sampling, geophysical well-logging, piezometric level monitoring and vadose zone geochemical properties monitoring.   

 

In this study, the SNMR method is used (1) to characterize the spatial heterogeneities of the 3D aquifer and of the vadose zone limestone, in a 3D-model jointly interpreted with other geophysical measurements (3D-ERT, 3D-IP, gravimetric, GPR profiles) and soundings; (2) to characterize the vadose zone water content, in combination with GPR and NMR logging water content profiles. Both these works are ongoing.

   

This research aims to know more accurately the vadose zone water content measured by SNMR in the context of a heterogeneous limestone with the goal to monitor the vadose zone flow dynamics with time-lapse measurements coupled with hydrogeological measurements.   

How to cite: Ryckebusch, C., Baltassat, J.-M., Legchenko, A., Kessouri, P., Amraoui, N., Abbas, M., and Azaroual, M.: Vadose zone water content characterization of a heterogeneous limestone by 3D-SNMR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9156, https://doi.org/10.5194/egusphere-egu23-9156, 2023.

Posters on site: Thu, 27 Apr, 10:45–12:30 | Hall A

Chairpersons: Damien Jougnot, Marc Dumont
A.122
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EGU23-13763
Ludovic Bodet, Marine Dangeard, Ramon Sanchez Gonzalez, Alexandrine Gesret, and Agnès Rivière

Over the past decade, we have done our best to develop alternative methods to image the heterogeneities of the critical zone, describe the dynamics of its hydrosystems, and add seismic techniques to the hydrogeophysics toolbox. With the growth of long-term observation infrastructures in this field, the geophysical tools recently developed by the community tend to be viewed as state-of-the-art geophysical characterization methods mainly deployed to augment observatory and network databases. A major problem is that geophysical results are mostly just sets of parameters, in other words "models", deduced from sparse data sets and poorly posed problems. They certainly cannot be considered as data by observatories. In order to better transport information from the data into models that could be safely exploited by non-geophysicists, we need to: increase the extent and throughput of our surveys; optimize our acquisition configurations with respect to the target of interest; greatly increase our spatial and temporal sampling capabilities; automate our tedious processing workflows; and improve, if not completely revise, our inversion tools. We illustrate this last point with examples from the field. They show how a thorough interpretation of geophysical models can provide valuable prior information on the distribution of hydrofacies and calibrate the hydrogeological modeling domain. In addition, we raise the question of the propagation of uncertainty from the geophysical data to the hydrogeological model and suggest the use of alternative petrophysics to better interpret the data collected in the partially saturated zone.

How to cite: Bodet, L., Dangeard, M., Sanchez Gonzalez, R., Gesret, A., and Rivière, A.: About the use of near-surface seismic data to better constrain hydrogeological models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13763, https://doi.org/10.5194/egusphere-egu23-13763, 2023.

A.123
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EGU23-8922
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ECS
Clara Jodry, Kamal Bayramov, Gunel Alizada, and Nigar Karimova

Underground water resources face an increase stress due to human activities and global climate change. To ensure sustainable and effective management of water resources, it is important to identify and characterize hydrogeologic systems and associated processes. In Azerbaijan, the groundwater is unevenly distributed due to a wide variety of climate conditions and the lowland areas depend mainly on water supply from the mountain areas to subsist. Especially since the alluvial plain aquifers undergo over consumption and pollution due to industrial and agricultural activities.

Our study focusses on the Talysh Mountain area in the Lesser Caucasus basin, where aquifers are characterized by alluvial terrain over volcanic-sedimentary tuff. This implies a high flow rate and quick discharge to low land. Yet, this area is also characterized by higher precipitation than evaporation which makes it favorable to host consequent groundwater aquifer. Geophysics has proved many times that it can bring valuable information to hydrogeological issue in subsurface environment such as unconsolidated ground or weathered hard rock aquifers. Thus, this project aims to characterized the underground structure (lithology, weathering profiles, fault and fissures, etc.) of a mountain aquifer in the region with Electrical Resistivity Tomography (ERT). We realized three separate measurements along the Lenkaran river which should enable us to image the 2D heterogeneity at the catchment scale and identify preferential pathways which influence the hydrodynamic circulations.

All three tomographies display two main resistivity layers which seem to be linked to the location along the river. The first layer shows resistivities in between 100 Ω.m with 3 m thickness upstream to 600 Ω.m and 6 m thickness downstream. The second layer is less resistive as a whole and goes from 60 Ω.m upstream to 15 Ω.m downstream. The resistivity limit in-between these two layers is rather abrupt and appear more linear downstream whereas the two profiles up stream display a non-linear limit. We interpret the first layer as dry alluvial sediments over a sedimentary tuff with an irregular top limit. The difference of resistivity from upstream to downstream could be linked to small changes in the lithology as well as variations of water content.

To help interpret further the hydrodynamic circulations in the region, these geophysical images will need to be associated with two essential data: groundwater levels and rainfall. Hydrogeology and hydrogeophysics campaign are rarely applied in Azerbaijan, especially in mountain areas, and existing data are either not available or date back to the 1960’s. This study represents the first step in developing environmental geophysics research in Azerbaijan and help put light on key environmental issues in the country.

How to cite: Jodry, C., Bayramov, K., Alizada, G., and Karimova, N.: Hydrogeophysical imaging of an aquifer in the Talysh mountain area, Azerbaijan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8922, https://doi.org/10.5194/egusphere-egu23-8922, 2023.

A.124
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EGU23-9982
Titouan Harrouet, Pascal Sailhac, Henri Robain, Christian Camerlynck, Benjamin Baud, Julien Amelin, Laurent Ruiz, Sekhar Muddu, and Jean Riotte

Space and time variability of water content in aquifers are fundamental issues to understand complex interactions taking part in the critical zone, such as land use and irrigated agricultural production. Fundamental parameters on aquifer behavior are commonly monitored through hydrogeological methods, such as piezometric levels and pumping tests in boreholes. Precisions on the water quality and residence time are provided by geochemical analyses of samples collected in surface streams and boreholes. Several studies showed how additional data can be obtained from non-invasive hydrogeophysical methods, that reveal structural heterogeneities of hydrogeological parameters filling the gaps between boreholes.

We carried out a multimethod geophysical survey in the Berambadi experimental catchment (India) which is part of the M-TROPICS CZO (Multiscale TROPIcal CatchmentS Critical Zone Observatory). Two surveys including seismic, electrical, and electromagnetic methods have been repeated for contrasting piezometric levels (high in December 2019, low in May 2022) corresponding to contrasted water contents. We considered time-lapse imaging using electrical resistivity tomography (ERT) and audio-magneto-tellurics (AMT), which sensitivities apply at complementary scales. Changes in the electrical resistivity from ERT shallow cross-sections and deeper jointly inverted ERT-AMT vertical profiles are compared for the two seasons. Results are discussed in terms of water content and porosity of the regolith as well as uncertainties caused by inherent repeatability issues of time-lapse measurements. Final discussion concerns perspectives of combined time-lapse electrical and seismic velocity models to assess the impact of the spatial variability of regolith properties at the catchment scale.

How to cite: Harrouet, T., Sailhac, P., Robain, H., Camerlynck, C., Baud, B., Amelin, J., Ruiz, L., Muddu, S., and Riotte, J.: Spatial heterogeneity of regolith properties using time-lapse electrical imaging combining Electrical Resistivity Tomography and Audio-Magneto-Telluric in the Berambadi Critical Zone Observatory (India), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9982, https://doi.org/10.5194/egusphere-egu23-9982, 2023.

A.125
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EGU23-13675
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ECS
Arnaud Watlet, Rémi Clément, Guillaume Blanchy, Vivien Dubois, Yannick Fargier, Nicolas Forquet, Helène Guyard, and Olivier Kaufmann

Shallow geophysics is being increasingly applied to solve a broad range of problems in hydrology, ecology, and beyond. In the recent years, geophysical monitoring, and geoelectrical monitoring in particular, has also become more popular to track down physical processes. In this context, the accessibility of geophysical equipment is key to expanding the use of geophysical monitoring, and to developing novel, versatile strategies, especially in the environmental sector. Commercial equipments have participated to the development of applied geophysics and are usually robust and practical. However, their cost can be prohibitive in some contexts, such as for humanitarian, non-profit applications or simply to equip a large number of sites. Being designed for generic use, they can also come with a lack of versatility for dedicated monitoring applications. For these reasons, the OhmPi project (https://gitlab.irstea.fr/reversaal/OhmPi) was initiated to provide an open-source, open-hardware resistivity meter to the community, in a DIY fashion. It is designed to offer enhanced flexibility, especially for monitoring experiments, and can easily incorporate new functionalities. Relying on low-cost components and devices, OhmPi is specifically designed for laboratory or small-scale field experiments. Developed as an open-source project, new collaborations are warmly welcomed.

The OhmPi hardware is based on a Raspberry Pi board which pilots I2C multiplexer boards, and an acquisition board triggering the current injection and voltage readings. The software is written in Python and allows to interact with the OhmPi instrument via a web interface, IoT communication protocols (e.g. MQTT) and/or directly through the Python API. Here, we will introduce the latest and future developments, comprising voltage injection up to 80V, sensor-controlled acquisitions or multi-channel voltage readings. We will also present dedicated applications including a case study detailing the field deployment of a small-scale 3D panel for monitoring water infiltration.

How to cite: Watlet, A., Clément, R., Blanchy, G., Dubois, V., Fargier, Y., Forquet, N., Guyard, H., and Kaufmann, O.: Latest developments of OhmPi, an open-hardware resistivity meter for small scale monitoring applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13675, https://doi.org/10.5194/egusphere-egu23-13675, 2023.

A.126
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EGU23-2553
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ECS
Haoran Wang, Johan Alexander Huisman, Egon Zimmermann, and Harry Vereecken

Spectral electrical impedance tomography (sEIT) is a non-invasive geophysical method to image the complex resistivity distribution of subsurface materials in a broad frequency range. Laboratory studies of spectral induced polarization (SIP) have prompted the application of sEIT at the field scale in recent years. However, electromagnetic (EM) coupling effects including both inductive and capacitive coupling can affect the accuracy of sEIT measurements, especially at higher frequencies. With the development of advanced measurement equipment and the use of shielded cables, EM coupling effects can be reduced to a large extent and the remaining EM coupling is mainly due to the use of long cables. The aim of this work is to develop filters to remove sEIT measurements with large inductive and capacitive coupling effects and to conduct inversion without correction of the data. Inductive coupling is independent of soil properties and can be quantified by the mutual inductance determined from known cable positions. It is the most important source of EM coupling in conductive environments. Previous work proposed correction methods for inductive coupling in sEIT measurements. To achieve inversion without correction, we propose an index called inductive coupling strength (ICS) to evaluate the inductive coupling for a given measurement configuration. Capacitive coupling is more complicated to correct and avoid, and it is the dominant source of EM coupling in resistive environments. Previous studies showed promising correction results by integrating the capacitances in the forward modelling. However, the proposed correction method was not sufficiently accurate for high frequencies in resistive environments. To achieve inversion without correction, we propose an index called capacitive coupling strength (CCS) based on sEIT modelling with capacitances and leakage currents to quantify the influence of capacitive coupling on each measurement configuration. To evaluate the use of ICS and CCS for data filtering, we use two field sEIT datasets. The first dataset was acquired in a conductive environment and the second dataset was acquired in a resistive environment. We found that reliable inversion results over a broad frequency range up to kHz can be obtained without correction for EM coupling effects by using a 5% threshold value for ICS and CCS to filter out measurements with significant EM coupling effects. 

How to cite: Wang, H., Huisman, J. A., Zimmermann, E., and Vereecken, H.: Data filtering methods for broadband spectral electrical impedance tomography (sEIT) measurements to reduce electromagnetic coupling effects, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2553, https://doi.org/10.5194/egusphere-egu23-2553, 2023.

A.127
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EGU23-6805
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ECS
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Joost Hase, Grigory Gurin, Konstantin Titov, and Andreas Kemna

The time-domain (TD) induced polarization (IP) method is used as an extension to classical DC resistivity measurements to capture information on the ability of the subsurface to develop electrical polarization, which is closely coupled to petrophysical parameters of relevance in hydrogeophysical characterization. In a TD IP measurement, the transient voltage decay between two electrodes is measured after the termination of an injected current between two other electrodes. TD IP measurements are typically analyzed in terms of chargeabilities, while in the frequency domain (FD) polarization responses are measured as complex-valued impedances. The latter can be inverted into a subsurface model of complex electrical resistivity by means of existing tomographic inversion algorithms. In order to apply these FD inversion algorithms to TD IP measurements, the necessity of TD to FD data conversion arises. A suitable conversion approach must transform the measured decay curve into a FD impedance and, preferably, also propagate the corresponding measurement uncertainty from TD into FD. Here we present such an approach based on a Debye decomposition (DD) of the decay curve into a relaxation-time distribution (RTD). Since equivalent formulations of the DD exist in TD and FD, it is possible to compute the FD response from the RTD inverted from the TD response. The corresponding FD data error can be obtained by applying error propagation through all these steps, assuming that the errors on the underlying parameters are normally distributed. To accomplish the DD we implemented a non-linear Gauss-Newton inversion scheme which automatically tunes the regularization strength to achieve a stable FD estimate and FD uncertainty. We test the performance of the inversion scheme in a synthetic study and demonstrate its application to field data on a tomographic TD IP data set measured on the Maletoyvaemskoie field of altered rocks (Kamchatka, Russia), which features epithermal gold deposits of high sulfidation type. The converted tomographic TD IP data set is inverted into subsurface models of complex electrical resistivity at frequencies of 1 Hz and 20 Hz. The proposed conversion approach yields accurate impedance data for relaxation processes which are resolved by the TD measurements. The error propagation scheme provides a reasonable FD uncertainty estimate, as revealed by a Monte-Carlo analysis of the underlying parameter distributions. Propagated FD errors are in agreement with previously established FD error models. The presented methodology to convert TD to FD IP data allows to invert and analyze field data collected with widely used TD instruments in the frequency domain, where the diagnostic potential of electrical impedance spectroscopy can be fully exploited for an improved interpretation.

How to cite: Hase, J., Gurin, G., Titov, K., and Kemna, A.: Conversion of IP data and its uncertainty from time-domain to frequency-domain using Debye decomposition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6805, https://doi.org/10.5194/egusphere-egu23-6805, 2023.

A.128
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EGU23-9281
Jan Gunnink and Sjef Meekes

A novel way of collecting electromagnetic measurements makes use of an All Terrain Vehicle (ATV) that pulls a transmitter and receiver. This so-called towed Transient Electro Magnetics system (tTEM, described in detail by Auken et al, 2019)  provide a fast way to obtain 3-dimensional images of the electrical resistivity of the subsurface. The unprecedented and speedy spatial coverage that can be obtained by the technique is a clear advantage over other land-based EM techniques. The technique acquires data with a speed of 10-15km/h, resulting in large coverages per day in open terrain (meadows, agricultural fields). The depth of investigation varies from 60 – 100m, depending on the characteristics of the subsurface (resistive or conductive). We present results here that are taken from various projects in the Netherlands, ranging from mapping buried glacial valleys, continuity of clay layers for groundwater protection, trying to detect faults and to investigate the lateral extent of Holocene clay deposits for dike reinforcements studies. We find the application of the tTEM technique for characterizing typical Dutch subsurface very useful, providing excellent insight in the 3D distribution of clay layers.

Auken, Esben, Nikolaj Foged, Jakob Juul Larsen, Knud Valdemar Trøllund Lassen, Pradip Kumar Maurya, Søren Møller Dath, and Tore Tolstrup Eiskjær, (2019), "tTEM — A towed transient electromagnetic system for detailed 3D imaging of the top 70 m oaf the subsurface," GEOPHYSICS 84: E13-E22. https://doi.org/10.1190/geo2018-0355.1.

How to cite: Gunnink, J. and Meekes, S.: tTEM: experiences in the Netherlands of this novel Electro Magnetic data acquisition technique, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9281, https://doi.org/10.5194/egusphere-egu23-9281, 2023.

A.129
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EGU23-13283
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ECS
Arsalan Ahmed, Lukas Aigner, Hadrien Michel, Wouter Deleersnyder, David Dudal, Adrian Flores Orozco, and Thomas Hermans

Understanding the subsurface is of prime importance for many geological and hydrogeological applications. Geophysical methods offer an economical alternative for investigating the subsurface compared to costly boreholes investigation methods, but results are often obtained through an inversion problem whose solution is non-unique. There are two types of inversion approaches: deterministic and stochastic. Deterministic inversion provides a unique solution with no way to efficiently and accurately assess uncertainty  but is relatively fast to compute. Stochastic inversions investigate the full range of solutions which make them computationally very expensive. In this research, we assess the robustness of the recently introduced BEL1D method for the stochastic inversion of the time domain electromagnetic data (TDEM). We analyze the effect of the accuracy of the forward model (through the open-source SimPEG code) on the estimation of the posterior space using a synthetic case and discuss the importance of prior selection. We also apply the algorithm on field data collected in Vietnam to assess saltwater intrusions. We observed that the proper selection of timesteps and space discretization is essential to limit the computation cost while maintaining the accuracy of the posterior estimation. Secondly, the selection of the prior distribution has a direct impact on fitting the observed data and is crucial to a realistic uncertainty quantification. Furthermore, in contrast to previous studies, we suggest rejecting models not fitting the data at an early stage for reducing computational costs. Lastly, the application of BEL1D together with SimPEG for stochastic TDEM inversion is a very efficient approach as it allows us to estimate the uncertainty at a limited cost.

Keyword: Saltwater intrusion, uncertainty, TDEM, BEL1D, SimPEG

How to cite: Ahmed, A., Aigner, L., Michel, H., Deleersnyder, W., Dudal, D., Flores Orozco, A., and Hermans, T.: Analyzing the ability of BEL1D for inverting TEM data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13283, https://doi.org/10.5194/egusphere-egu23-13283, 2023.

A.130
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EGU23-17158
Insun Song

Analysis of the sensitivity of measurable physical variables (i.e., pressure and flow) to material properties is very useful to reduce uncertainty in estimation of the properties. The subsurface fluid flow through a porous rock is characterized by two hydraulic properties, hydraulic permeability k and specific storage Ss. The pore pressure diffusion is controlled by the hydraulic diffusivity implicating the ratio of the transmitting ability to the storage capacity. Both values of k and Ss can be determined only from a transient pore pressure curve. However, the hydraulic properties (k and Ss) are defined in the relation between pressure (gradient) and flow (rate). The permeability is a proportional parameter between volumetric flux of fluid and pressure gradient. The specific storage denotes the proportionality constant between the increment of fluid content and the pore pressure. Thus, the flow (rate) measurement is also beneficial to obtain the hydraulic properties. This paper presents the sensitivity analysis of pressure and flow data to the properties. One-dimensional pressure diffusion test was conducted on a cylindrical sample of shale subjected to a triaxial confining stress. No flow was allowed at the downstream for the boundary condition. A sudden increase in the upstream pressure followed by a constant pressure leads to the downstream pressure rising transiently until it reached an equilibration to the constant upstream pressure. During the transient period, the upstream fluid flows into the sample because of the time-dependent pressure gradient. Both the downstream pressure and the upstream flow were measured to estimate the hydraulic parameters using curve fittings. The downstream pressure curve fitting yields 4.1×10-20 m2 for the permeability and 1.2×10-11 Pa-1 for the specific storage. However, these values for the best fit of the pressure data yield a completely different flow curve from the flow measurements. The permeability and the specific storage obtained from the best fit of the flow curve are 2.6×10-19 m2 and 2.1×10-10 Pa-1, respectively. The theoretical pressure curve using these values fits well (not the best) the measured data. Conclusively, the flow data is more sensitive to the hydraulic properties than the pressure data. The flow analysis yields less uncertainty in the optimization of hydraulic properties than the pressure analysis.

How to cite: Song, I.: Sensitivity analysis for the optimization of hydraulic properties using transient pressure and flow data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17158, https://doi.org/10.5194/egusphere-egu23-17158, 2023.