Orals: Mon, 4 May, 16:15–18:00 | Room 2.17
Hydrological disturbances, including intense precipitation and sea level rise along coastal interfaces, lead to freshwater flooding and saline water overwash that changes the soil saturation and salinity and, in turn, alters subsurface biogeochemical reactions and soil-plant-atmosphere exchanges. The extents of these state changes are not well known, limiting their accurate representation in earth system models. In this study, we combined the spatial-temporal parameter measurements advantage of geophysical imaging with discrete in-situ and laboratory measurements and petrophysical relationships to quantify changes in soil moisture and salinity at an improved spatial scale.
We simulated a concurrent freshwater and estuarine water flooding at two adjacent 2,000 m2 forested plots by inundating them with 265 m3 of freshwater and estuarine water with salinities of 0.06 and 8.1 practical salinity units (PSUs), respectively. The flooding experiment was conducted over a single 10-hour cycle for year 1 and for two and three flooding cycles for years 2 and 3, respectively, with a 14-hour pause between each cycle. During each flooding experiment, repeated electrical resistivity and induced polarization measurements were used to image the water and solute infiltration fronts along two 100 m and 42 m transects while soil moisture, temperature, and electrical conductivity were monitored every 15 minutes with soil sensors installed at 5, 15 and 30 cm depths and co-located with the geophysical transects. Petrophysical models derived from laboratory multi-salinity electrical measurements were used to estimate changes in soil moisture and fluid salinity from field measurements of real and imaginary conductivity during the flooding experiment.
During flooding, the real electrical conductivity increased by ~100% in the freshwater plot and ~570% in the estuarine water plot. The change in imaginary conductivity in the freshwater plot was < 1 mS/m, whereas that of the estuarine water plot was ~5 mS/m. The real conductivity shows a dependence on soil moisture content with a coefficient of determination (R2) >0.7, while the imaginary conductivity shows a dependence on soil salinity with R2 >0.6. Repeated monitoring over 3 years shows >60% change in ambient soil electrical conductivity at the estuarine water plot, indicating an increase in soil salinity over time.
These results validate the use of electrical resistivity for estimating changes in coastal soils' moisture content in response to flooding. Combining the electrical resistivity with induced polarization measurements provides the possibility to account for changes in pore fluid conductivity. The intermittent geophysical monitoring limits the comparison of geophysical data with in-situ soil parameters measurement to develop a more robust petrophysical model. This study would benefit from the use of continuous automatic electrical resistivity and induced polarization monitoring, which is becoming increasingly popular for ecohydrological studies.
How to cite: Doro, K. O., Emmanuel, E. D., Chen, X., Kenton, R. A., Megonigal, J. P., Regier, P., Ward, N. D., and Bailey, V. L.: Geophysical monitoring for quantifying changes in soil saturation and salinity along coastal interfaces during flooding, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20792, https://doi.org/10.5194/egusphere-egu26-20792, 2026.
River regulation has contributed to increased soil and groundwater salinity across many floodplains in semi-arid Australia. Floodplain inundation has the potential to flush salt from the soil profile and reduce groundwater salinity in shallow aquifers. However, the effectiveness of flood events in removing accumulated floodplain salt remains poorly constrained. This uncertainty reflects the long-term legacy of salt accumulation, spatial variability in groundwater depth, and changes in the capillary transport zone. Salt movement within floodplains is influenced by multiple interacting factors, including river geomorphology, shallow aquifer properties, remnant paleochannels, and hydraulic gradients between surface water and groundwater. To assess the impact of flooding on salt redistribution at the river–floodplain aquifer interface, instream hydrogeophysics surveys (transient electromagnetic-TEM) were conducted along Katarapko Creek and the River Murray at Bookpurnong, South Australia, following the major 2022–2023 River Murray flood event. These surveys mapped spatial variations in riverbed electrical conductivity and identified potential zones of saline groundwater inflow. Comparisons with surveys undertaken in 2015 and 2019 reveal substantial post-flood changes in riverbed conductivity, including an overall reduction in conductivity. A follow-up survey in 2024 confirmed that the spatial distribution of conductivity features remained consistent across all survey periods. Despite the general decrease in riverbed conductivity following the flood, several discrete zones continue to act as preferential pathways for saline groundwater discharge from the floodplain to the river. The persistence of these salinity hotspots indicates that considerable salt stores remain within the floodplain system. These findings suggest that while large flood events can reduce near-surface salinity, targeted adjustments to river regulation may be required to restore key hydrological processes and support long-term ecological recovery of the river system.
How to cite: Banks, E. W., Hatch, M., Noorduijn, S., and Wallace, T.: Flood‑Induced Changes in Riverbed Salinity Observed Using Instream Hydrogeophysics in a Semi‑Arid River System, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4223, https://doi.org/10.5194/egusphere-egu26-4223, 2026.
Floodplains in low-energy depositional environments often feature fine-grained facies with relatively low hydraulic conductivities (< 1 × 10⁻⁵ m s⁻¹). In such systems, the most hydraulically conductive zones are often associated with calcareous-rich deposits, which consist of freshwater unlithified tufa, but also include organic-rich layers. This study examines the spatial distribution and hydrogeological significance of calcareous-rich units under fully-saturated conditions at two contrasting floodplain sites in Southwestern Germany. Site 1 is located within a relatively wide floodplain (~800 m wide), where these calcareous units can reach a thickness of up to 7 m. In contrast, site 2 is located within a narrower floodplain (~100 m wide), where these units reach a thickness of up to 3 m.
At site 1, we acquired 2-D geoelectrical and borehole nuclear magnetic resonance data, which were used within a rock-physics framework combining Archie’s law and the Kozeny-Carman model to estimate the hydraulic properties of calcareous-rich units. Collocated pumping test, which indicate hydraulic conductivities of 1 × 10⁻⁶ to 1 × 10⁻⁵ m s⁻¹, were used as ground truth to calibrate the site-specific parameters of the rock-physics models. Such calibrated models may subsequently be applied at other field sites with similar characteristics where only resistivity data are available.
At field site 2, we collected geoelectrical and seismic data (P- and S-waves) to identify the spatial distribution of the calcareous-rich units. The resulting resistivity and S-wave velocity models delineated these units in agreement with collocated borehole data. In contrast, the P-wave velocity model did not clearly resolve them but provided useful constraints on the depth to bedrock. At this site, rock-physics approaches similar to those applied at field site 1 will be used to support planned hydrogeological modeling and enable direct comparison between the two sites.
Our preliminary results demonstrate the potential of integrated geophysical and rock-physics approaches to identify and characterize hydraulically relevant units within fine-grained–dominated aquifer systems.
How to cite: Arboleda-Zapata, M., Drach, K., Leven, C., Dietrich, P., and Cirpka, O. A.: Hydrogeological Characterization of Fine-Grained Floodplain Aquifers Using Integrated Geophysical and Rock-Physics Approaches, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7101, https://doi.org/10.5194/egusphere-egu26-7101, 2026.
In arid regions such as the Eastern Bahira Basin (Morocco), groundwater represents the primary resource for drinking water supply and irrigation. The sustainable management of these resources requires a detailed understanding of aquifer geometry, deep structural controls, and the identification of the most favorable zones for groundwater exploitation. However, this remains a major challenge in the Eastern Bahira Basin, directly affecting the effectiveness of regional water supply and irrigation programs.
This study adopts an integrated geophysical approach combining newly acquired Electrical Resistivity Tomography (ERT) data with the compilation and reinterpretation of legacy gravity, seismic reflection, and vertical electrical sounding (VES) datasets. Gravity data were reprocessed using advanced techniques, including residual anomaly analysis and horizontal gradient maxima, to delineate major subsurface structural lineaments. Seismic reflection data were reinterpreted to improve the characterization of the basin’s deep structure, incorporating recent borehole information. The interpretations derived from gravity and seismic analyses were further constrained and validated by VES and ERT results acquired across key sectors of the basin.
The integrated interpretation reveals the dominant structural framework controlling aquifer geometry and groundwater distribution in the Eastern Bahira Basin and identifies the most promising hydrogeological targets. These results provide new insights into the deep structural organization of the basin and contribute to improving groundwater exploration strategies and the sustainability of ongoing drinking water supply and irrigation projects in this arid region.
How to cite: Charbaoui, A., Kchikach, A., and Jaffal, M.: Deep Structural Control on Groundwater Systems in the Eastern Bahira Basin (Morocco) Revealed by Integrated Gravity, Seismic, and Electrical Resistivity Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1644, https://doi.org/10.5194/egusphere-egu26-1644, 2026.
Understanding recharge processes in heterogeneous hard-rock terrains is essential for sustainable groundwater management. This study examines the spatiotemporal recharge dynamics of a 2 km² experimental micro-catchment in Rajasthan, India, using integrated hydrometeorological observations, Direct Current resistivity and Induced Polarization (DC–IP) imaging, Normalized Difference Vegetation Index (NDVI) time series, and aquifer tests. NDVI provided seasonal moisture variability, while ten DC–IP profiles delineated subsurface architecture and structural controls on flow.
Geophysical sections reveal a highly heterogeneous system dominated by massive high-resistivity sandstone blocks (>200 Ω·m) intersected by vertical to sub-vertical low-resistivity fracture zones (<50 Ω·m). Low to moderate chargeability (<10 mV/V) within these conductive features indicates groundwater-bearing fractures rather than shale layers. The fracture networks near Wells S1 and S2 are structurally isolated, despite being separated by only ~30 m. Slug tests indicate low hydraulic conductivities in both wells (Ks₁ = 2.42×10⁻⁸ m/s; Ks₂ = 1.06×10⁻⁸ m/s), with S1 being slightly more conductive.
Event-based analysis of 25 monsoon rainfall–recharge events shows contrasting well responses due to their structural positions. Well S1, located 5 m from an intermittent stream bank, exhibits a flashy early-season bank-storage response with high Specific Water Level Rise (SWLR), later transitioning to rapid recession and reduced efficiency as water levels exceed the streambed. In contrast, Well S2 (35 m from the stream bank) shows delayed but consistent responses, with stable SWLR and recession rates, characteristic of a structurally confined storage zone. Cross-correlation analysis confirms strong coupling in peak responses but moderate similarity in lag and recession behaviour.
These findings show that rapid water-level rises in hard-rock terrains often reflect transient drainage pathways rather than sustainable storage. Managed Aquifer Recharge strategies should therefore target structurally controlled, high-retention fractured zones (e.g., S2) instead of stream-connected fracture corridors (e.g., S1).
How to cite: Khalique, A., Singh, A., Singh, V., and Gaurav, K.: Event-Based Analysis of Recharge Dynamics in a Heterogeneous Hard-Rock Catchment using Hydrogeophysical Techniques, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-763, https://doi.org/10.5194/egusphere-egu26-763, 2026.
Electrical resistivity tomography (ERT) is a non-destructive geophysical method that provides images of the soil electrical resistivity. In particular, this study focuses on small-scale soil subsurface areas (up to 1 m deep). Soil resistivity depends on several factors, particularly soil water content. Consequently, ERT has proven to be effective in detecting water flow pathways during infiltration tests. ERT has already been used for hydroecological and hydrogeological applications, but its use still requires further investigation and new developments, particularly for specific processes such as preferential flows. Indeed, water infiltration into the soil is all but homogeneous with the occurrence of preferential flows due to several factors (lithological heterogeneity, macropores, cracks, macrofauna galleries, and root channels). The presence of these preferential flows promotes the downward movement of water and solutes to deeper soil horizons. Thus, the detection of these flows using geophysical methods, such as ERT, should provide a better understanding of the dynamics of preferential flows. However, conventional ERT inversion methods have proven unable to provide insight into the processes at adequate scales (e.g., the macropore scale) and have shown difficulties in detecting sharp variations because of smoothing constraints. Information from apparent resistivity may be lost because of these constraints.
To overcome these limitations, an inversion method based on Convolutional Neural Networks (CNNs) is proposed to detect small-scale resistivity heterogeneities. For the training step, we designed a specific generator to produce synthetic resistivity data for various 2D random electrical resistivity distributions mimicking different types of soil heterogeneity (earthworm and root induced macropore, layering, etc.) and for typical protocols for ERT acquisition. For each case, our database associates the true resistivity field with the apparent resistivity. This database contains a large number of training pairs that allow machine learning.
The preliminary results show that while some predictions were able to predict properly the soil heterogeneities (shape and size), the values of the estimated true resistivity were far from the target values. To avoid unrealistic estimates, we added physical constraints during the training process. An additional forward calculation was performed based on the true resistivities predicted by the neural network, then the apparent resistivities corresponding to the predicted resistivities were compared to the apparent resistivities corresponding to the targeted true resistivities and a supplementary loss function was added to the initial loss function. At this stage, the neural networks were trained on heterogeneous resistivity distributions in the soil with neither time evolution nor link to hydrological processes. In the future, the resistivity generator will be coupled with hydrological models to simulate water infiltration dynamics and changes in soil water content over time. This perspective is essential for applying the proposed method to detect flow pathways during infiltration tests.
How to cite: Florent, G., Rémi, C., and Laurent, L.: Detection of macropore-sacle soil heterogeneities related to water preferential flows at meter depth by using Electrical Resistivity Tomography (ERT) and machine learning 2D inversion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9402, https://doi.org/10.5194/egusphere-egu26-9402, 2026.
Understanding water dynamics in the root zone is crucial for improving eco-hydrological modelling and sustainable agricultural practices. However, soil processes in agricultural environments are strongly affected by spatial heterogeneity, and observations often depend on the measurement scale and on the sampled support volume. Here we present a multi-scale hydrogeophysical investigation carried out in a vineyard in the Chianti area (Tuscany, Italy), designed to connect field-scale characterization with high-resolution imaging at the plant scale. The study combines electromagnetic induction (EMI) surveys using a multi-coil CMD Mini Explorer to map near-surface variability across the vineyard, and electrical resistivity tomography (ERT) profiles acquired with different electrode spacings (1 m, 0.5 m and 0.25 m) to progressively increase spatial resolution in the first meters of the subsurface, with a specific focus on the first meter. To further explore root-zone dynamics at the finest scale, we performed a high-resolution 3D time-lapse ERT experiment around a single grapevine. A dense micro-ERT array was installed around the plant and repeated measurements were acquired every two hours. The experiment was repeated in two contrasting periods (October and July), and each monitoring campaign included two controlled irrigation phases to trigger transient hydrological responses. In parallel, the vineyard hosts additional monitoring activities (e.g. Cosmic Ray Neutron Sensing), which provide broader hydrological context. Overall, this dataset illustrates how combining EMI, multi-resolution ERT and plant-scale 3D time-lapse imaging can help quantify soil heterogeneity across scales and improve the interpretation of near-surface processes relevant to infiltration and root-zone dynamics in precision viticulture.
How to cite: Censini, M., Peruzzo, L., Pavoni, M., Cioffi, V., Manca Di Villahermosa, F. S., and Cassiani, G.: Exploring soil heterogeneity across scales in a Chianti vineyard (Italy) using EMI, multi-resolution ERT and plant-scale time-lapse imaging, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7679, https://doi.org/10.5194/egusphere-egu26-7679, 2026.
The investigation of preferential flow paths in the subsurface is necessary e.g., for the prediction of contaminant transport. Usually, hydraulic methods are applied for that, however, the geophysical method Spectral Induced Polarization (SIP) offers a different approach. As it can be applied from the earth’s surface, the groundwater state does not get disturbed and it is capable of continuous imaging. As hydraulic heterogeneity is a key factor that causes preferential flow paths, it was our aim to describe hydraulic anisotropy and heterogeneity in a series of laboratory experiments electrically and hydraulically.
The experimental set up consists of a sample holder that can contain samples of 18 cubic decimeters in size. Electric and hydraulic measurements can be carried out without disturbing the sample. In two measurement series we investigated a combination of two different sands and a combination of sand and sandstone. The samples were investigated under pressurized groundwater conditions. In the measurement series we varied the volume share of the two components of the sample and the orientation of the layer boundaries relative to the direction of flow.
The results indicate that the electrical parameters like imaginary part of conductivity, phase shift and chargeability are dependent on the sample orientation, but only if there is a significant contrast in the conductivity amplitude of the two components. Otherwise, only the volume share of both components can be determined. The results can be useful for an improved interpretation of field measurements. Future work could be aimed at validating these findings in further measurement series with different material and field measurements.
How to cite: Herold, R. and Börner, F.: Laboratory experiments to determine the hydraulic heterogeneity of sediments with SIP, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8159, https://doi.org/10.5194/egusphere-egu26-8159, 2026.
Electrical Resistivity Tomography (ERT) is a widely used method for characterizing subsurface structures and monitoring time‑lapse processes. Its versatility across scales has enabled laboratory investigations of solute and gas dynamics in rocks and sediments. ERT has also been applied to assess landfill interiors, where electrical conductivity variations reflect differences in moisture content and waste chemistry. Landfill gas, mainly consisting of CO₂ and CH₄ produced during the degradation of organic waste may influence these electrical signatures. However, monitoring landfill gas release with ERT remains challenging due to the complex and dynamic nature of landfills. To examine how ERT responds to gas presence and movement under controlled landfill‑relevant conditions, we constructed a laboratory‑scale cylindrical ERT column system. Here, we present the first stage of the experiment, focusing on the design, optimization, and validation of the ERT column. By combining forward modeling and preliminary laboratory tests, we identified the limitations of the laboratory column in terms of spatial resolution, measurement sensitivity patterns, and errors related to measurement and both forward and inverse modeling. Beyond demonstrating the importance of pre-optimizing an ERT system before implementation, this study provides guidelines for designing laboratory columns for similar research. Most previous studies have only provided a brief documentation of this process.
How to cite: Adebunmi, S. O., French, H. K., Bloem, E., and Clement, R.: Optimising the Design of a Laboratory Column for Evaluating ERT Detectability of Changes in Landfill Gas Production, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19766, https://doi.org/10.5194/egusphere-egu26-19766, 2026.
Geophysical methods offer substantial potential to support the characterization, monitoring, and remediation of contaminated soil and groundwater systems. Their ability to provide spatially continuous information through non- or minimally invasive techniques has motivated a wide range of applications in heterogeneous subsurface environments. Over the past decades, this has resulted in numerous case studies and several review papers. Nevertheless, insights reported in the literature remain difficult to relate across contamination types, subsurface conditions, spatial scales, and the timing of geophysical use.
This contribution presents a work-in-progress synthesis of recent peer-reviewed literature (approximately the last five years) on geophysical methods in soil and groundwater contamination studies. The synthesis covers studies ranging from controlled experimental settings to pilot-scale setups and full-scale field investigations. It provides an overview of the contaminants addressed, the geophysical techniques applied – individually and in combination – and their associated spatial scale, coverage, and resolution.
A specific point of attention is how geophysical data are interpreted, calibrated, or validated in relation to contaminant distribution, fate, and transport, as reported in the literature. For field-based studies, the synthesis also considers contextual aspects such as historic and present land use, the timing of geophysical application relative to investigation and remediation activities, and the level of detail and transparency in data reporting.
By structuring recent applications reported in the literature, this synthesis provides an updated overview of current practices and recurring challenges. By relating reported studies to different stages of the contaminated site investigation and remediation value chain, it aims to be relevant to both the scientific community and users in professional practice.
How to cite: Van De Vijver, E. and Orta, D.: Geophysical methods in soil and groundwater contamination studies: recent applications and developments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20687, https://doi.org/10.5194/egusphere-egu26-20687, 2026.
Abstract. Dynamic changes in soil water content (SWC) are a crucial controlling factor for ecosystem function, agricultural productivity, and geotechnical stability against settlement and seepage failures. Real-time and accurate monitoring is essential for understanding hydrological processes and their response to climate change. Estimates of relative velocity variations (dv/v) from ambient seismic noise measurements have emerged as a highly sensitive and non-invasive geophysical tool for long-term surveillance of near-surface property changes. However, during non-frozen periods, dv/v signals are jointly affected by changes in both subsurface temperature and SWC. Inadequate corrections of temperature effects are indeed emerging as a key limitation for the quantitative interpretation of dv/v measurements for changes in SWC. To date, most temperature correction schemes approximate the subsurface thermal state using surface temperature, thus, overlooking the depth-dependent attenuation of thermal diffusion, which, in turn, biases the estimations of soil water content changes (SWCC). We propose a frequency-depth thermal correction framework that links the depth sensitivity of dv/v at different frequencies with the subsurface temperature profile. By establishing a quantitative relationship between frequency and depth, the temperature profile is transformed into frequency-dependent equivalent temperatures. This allows to correct dv/v estimates in each frequency band using the corresponding equivalent temperature rather than the surface temperature, thereby capturing the true depth-dependent thermal state governed by heat diffusion. Using temperature-corrected dv/v estimates and rock physics models combining Hertz–Mindlin contact theory and Gassmann’s fluid substitution, we retrieve dynamic changes in surficial SWC. Tests on both synthetic and field data ground-trothed by time-domain reflectivity (TDR) measurements demonstrate that the proposed FDTC method effectively suppresses temperature-induced artifacts in relating dv/v estimates to changes in SWC. The proposed method thus provides a robust temperature correction for ambient-noise-based SWC monitoring during non-frozen periods.
Acknowledgements. This project was funded by the National Key Laboratory of Jilin Province (Discipline Category) Major Project (Research and Development of Geophysical Imaging and Equipment for Freeze-Thaw Hydrological Processes in Black Soil in High-Latitude Regions, No. SKL202502020JC).
How to cite: Hu, R., Li, J., and Liu, H.: A depth-sensitive thermal correction method allowing for quantitative monitoring of changes in soil water content from ambient noise measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9397, https://doi.org/10.5194/egusphere-egu26-9397, 2026.
By 2050, climate changed-induced extreme heat waves and urban heat island phenomenon will lead to severe soil drought, which can affect trees health and sustainability of green spaces. By-product of the pyrolysis of biomass, biochar incorporation can favor soil water retention and can be seen as a potential tool to mitigate future soil drought. In order to test the ability of biochar incorporation into soil to improve water retention, experimentations are necessary to evaluate its efficiency. To do so, experimental tests involving monitoring would require destructive, costly and sparse spot measurements that are not representative of the heterogeneous nature of studied technosols. This work explores how geophysics can overcome such limitations, by enabling spatialized, non-invasive monitoring of soils at the scale of experimental plots. Control and biochar-amended plots (n > 3) were monitored over time with spectral induced polarization (SIP) and active seismic methods. Initial results suggest that SIP can distinguish the presence of biochar through marked contrasts in resistivity and phase, which evolve with time suggesting a potential monitoring of biochar aging (e.g. fragmentation, migration and oxidation). At the same time, seismic surface-wave velocity measurements show sensitivity to seasonal variations, as well as a quasi-systematic decrease in velocities in amended soils, which could reflect changes in porosity and/or water content. This approach serves as a proof of concept for highlighting the potential of geophysics as an in situ diagnostic tool, capable of monitoring the effect of biochar by providing reliable and integrative indicators of water content in heterogenous urban soils.
How to cite: Delarue, F., Pasquet, S., Thiesson, J., Laden, A., Dubois, N., Burzawa, A., Aubry, E., Prothery, E., and Bodet, L.: Contribution of Geophysics to the Study of Urban Soils Amended with Biochar, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12558, https://doi.org/10.5194/egusphere-egu26-12558, 2026.
Hydrological models, which simulate natural processes, are prone to uncertainty due to shortcomings such as data being insufficient or incomplete, limited to point scale or the equifinality of the model itself. Using varying data sources to constrain the model can help to overcome these issues and to create more reliable models. As variations in subsurface water storage are equivalent to mass redistributions that are proven to be measurable using modern gravimetry equipment, gravity measurements can advance hydrological modelling. Magnetic resonance soundings (MRS) probe the 1H spin magnetization of subsurface water molecules and provide vertical water content distributions covering both the saturated and unsaturated zone. The use of gravity and MRS data to improve hydrological modelling is explored in this project. An integrated hydrological model is built, which simulates surface and subsurface flows, and its output is converted into the corresponding changes in gravity on the one hand, and in the MRS response on the other. These numerical results are then compared with real measurements of a high-precision quantum absolute gravimeter as well as of an MRS device with reduced instrumental dead time optimized to provide water content information from the unsaturated zone with increased accuracy. Whereas MRS measurements are point information similar to borehole data, yet non-invasive and thus cheaper than hydrogeological drillings, gravity measurements are beneficial, as they provide integrated information over extended areas. However, they also capture other processes causing mass redistributions, which is why they can produce significant noise. Thus, it is expected that processes in the unsaturated zone, although contributing to the signal, might be difficult to detect by the quantum gravimeter despite of its improved resolution properties. This is why we expect the combination with the additional MRS data might be superior to the usage of hydrogravimetry alone.
How to cite: Schmidt, I., Freier, C., Leykauf, B., Schkolnik, V., Willkommen, G., and Stephan, C.: Constraining hydrological models by combining ground-based gravimetry and magnetic resonance sounding, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12656, https://doi.org/10.5194/egusphere-egu26-12656, 2026.
Geophysical methods provide a cost-effective way to characterize the subsurface for hydrogeological projects, but they rely on solving an inverse problem. Traditionally, deterministic approaches are used, which face challenges related to non-uniqueness of the solution. In contrast, stochastic methods offer uncertainty quantification but generally require higher computational resources. Bayesian Evidential Learning (BEL) has been proven as a reliable alternative to solve the inverse problem stochastically. BEL bypasses full stochastic inversion by learning a direct relationship between data and model parameters, allowing to approximate the posterior distribution at a lower computational cost. However, as with most Monte Carlo techniques, BEL efficiency depends on the number of inversion parameters.
In this contribution, we show that incorporating prior physical knowledge about the imaged processes into the parameterization of model parameters efficiently reduces the number of unknowns, and subsequently the computational burden of BEL. Using time-domain electromagnetic data (TEM), we characterize the fresh - saltwater transition zone in the Flemish coastal aquifer. This transition can be sharp, gradual or very smooth depending on the local hydrogeological context. Conventional blocky or smooth deterministic inversions then often misrepresent this transition zone as too sharp or too gradual. To address this, we explicitly incorporate the transition zone in the parameterization, with two variables: its depth and its thickness, assuming a linear increase of conductivity within this thickness. The transition zone is underlying a freshwater zone with constant conductivity and overlying a saline zone, also with constant conductivity. This retains the compactness of blocky or layered inversion while allowing sharp or gradual interfaces like voxel-based methods.
To assess the reliability and robustness of the method, we invert these parameters stochastically using BEL with Thresholding (BEL1D-T). Results indicate this approach effectively captures uncertainty for synthetic and field data. The transition zone remains largely uncertain due to the limited sensitivity of the TEM set-up to the relatively shallow transition observed in the Belgian coastal area. Yet, our probabilistic method achieves this without the heavy computational cost of traditional stochastic approaches. The result also shows that the uncertainty can be efficiently reduced when prior information on the presence of confining layer (e.g., clay layer) is further introduced in the parameterization.
Keywords: time-domain electromagnetics, inverse problem, uncertainty quantification, fresh-saltwater interface (FSI)
How to cite: Ahmed, A., Hermans, T., Dudal, D., and Deleersnyder, W.: Uncertainty Quantification of the Fresh-Saltwater Interface from Time-Domain Electromagnetic Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19740, https://doi.org/10.5194/egusphere-egu26-19740, 2026.
Urban development in central Saudi Arabia is frequently challenged by subsurface cavities formed through dissolution and weathering of limestone formations. These hidden features pose significant geotechnical risks, including differential settlement and structural instability. This research presents the results of a high-resolution three-dimensional Electrical Resistivity Tomography (ERT) investigation conducted at a construction site in Riyadh to detect and delineate subsurface cavities and weak zones prior to foundation construction.
The survey covered a 30 m × 40 m site excavated to basement level and was performed using an AGI SuperSting R8 system with a total of 111 electrodes deployed at 1 m spacing along three sides of the plot. A mixed dipole-gradient array configuration was adopted to optimize lateral resolution and depth penetration. Approximately 7,600 data points were acquired and processed using AGI EarthImager 3D software, with rigorous quality control applied prior to inversion. The resulting 3D resistivity model imaged subsurface conditions down to 10 m depth.
The inversion results reveal a heterogeneous limestone subsurface characterized by high-resistivity zones corresponding to competent, massive limestone and distinct low-resistivity anomalies interpreted as cavities, fractured zones, or weathered limestone. Three major weak zones were identified at the southwestern, southeastern, and northeastern portions of the site, extending to depths of 5-7 m. Borehole data confirmed the presence of cavities in two of these zones, validating the ERT interpretation. This research demonstrates the effectiveness of 3D ERT as a non-invasive tool for detecting subsurface cavities in karst-prone limestone environments and highlights its value in guiding targeted ground improvement and foundation design in urban construction projects.
How to cite: Jadoon, K. Z. and Shahzad, S.: Detection of Subsurface Cavities in Limestone Terrain Using 3D Electrical Resistivity Tomography (ERT): A Case Study from Riyadh, Saudi Arabia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15729, https://doi.org/10.5194/egusphere-egu26-15729, 2026.
The Republic of Djibouti faces a steadily increasing demand for drinking water due to rapid urbanization and population growth, from 273,974 inhabitants in 1983 to more than 1 million in 2023, with 73% of the population living in the capital. Water supply relies mainly on groundwater abstracted from the coastal hosted in basaltic formations interbedded with paleosols layers, which constitute the geological framework of the study area. Surface water resources are extremely limited, apart from a few reservoirs, and groundwater recharge mainly occurs during episodic flooding of wadis.
Limited recharge, intensive groundwater pumping, and the proximity of the aquifer to the coastline have led to a progressive degradation of groundwater quality over recent decades, particularly through salinization. The Djibouti plain is characterized by heterogeneous relief, intense fracturing, and a complex volcanic geology. Basaltic formations of different ages and origins overlap discordantly and are locally associated with rhyolitic units, while Quaternary marine sedimentary deposits are present in the coastal zone. Despite the strategic importance of this aquifer, the internal structure of the fractured basalt system remains poorly constrained, limiting the understanding of groundwater flow and freshwater-saltwater interactions. In this study we present the results of more than 30electrical resistivity tomography (ERT) profiles, ranging from 600 to 1200 m in length, acquired in the Djibouti plain. These profiles are used to investigate the lateral and vertical variability of subsurface resistivity and to identify structural and lithological heterogeneities within the basaltic formations. The ERT results are interpreted in combination with available hydrogeological data in order to improve the characterization of the aquifer structure and to provide new constraints on groundwater circulation and recharge processes.
How to cite: Elmi Ragueh, B., Albaric, J., Celle, H., Robleh Ragueh, R., Osman Awaleh, M., and Mohamed, J.: Hydrogeophysical characterization of the basaltic aquifer of Djibouti., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21623, https://doi.org/10.5194/egusphere-egu26-21623, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot A
EGU26-3766 | ECS | Posters virtual | VPS8
Integration of electrical resistivity tomography, permeability and infiltrometer tests for modelling hydraulic conductivity and infiltration rates in the fieldTue, 05 May, 14:18–14:21 (CEST) vPoster spot A
Accurate or exact estimations of hydraulic conductivity (K) and infiltration rate are crucial for understanding soil-water interactions, optimising irrigation practices, evaluating groundwater recharge potential, and designing drainage systems. Conventionally laboratory permeability tests and in-situ infiltrometer tests, provide direct estimates of soil hydraulic behaviour. However, these methods have limitations of their point-specific nature and are unable to capture subsurface heterogeneity across larger spatial scales. In contrast, the electrical resistivity tomography (ERT) technique offers a non-invasive geophysical approach that is capable of detecting subsurface variations in soil electrical resistivity properties. The electrical resistivity estimates can further be interpreted to analyse soil types, soil layer structures, moisture and mineral contents, and pore connectivity. These are ultimately related to soil hydraulic properties, such as hydraulic conductivity and soil-water interaction behaviour, such as vertical infiltration rates. One of the accurate methods of estimating K is a pumping test, which is expensive and time-consuming. Other methods include laboratory permeameter tests, which require the collection of soil samples from the field, which often are disturbed ones and thus may produce K values with considerable uncertainties. The primary goal of this study is to establish the relationship between hydraulic conductivity (K) and electrical resistivity (ER) to replace the tests mentioned above. The second objective of this study is to establish an ER-infiltration rate relationship to convert point-based infiltration measurements into area-wide infiltration maps using resistivity data, minimizing the number of infiltrometer tests needed, saving time, manpower, and resources. Field investigations executed here involve ERT surveys using different electrode configuration arrays, such as the Wenner, Schlumberger, and dipole-dipole, across selected test sites that represent various soil textures and moisture conditions. The resistivity profiles are inverted to generate 2D subsurface sections, enabling identification of moisture zones and shallow saturation patterns. Parallelly, laboratory permeability tests are carried out on undisturbed soil samples to determine hydraulic conductivity, while infiltrometer tests are performed to obtain field-scale infiltration characteristics and steady-state infiltration rates. The combined dataset provided a comparative evaluation of resistivity variations in relation to measured soil-hydraulic parameters. Once these relationships are established, ERT can move beyond the simple imaging and serve as a fast and cost-effective way to estimate how water moves through the soil over a wider area. This will significantly reduce the need for frequent point-based tests and help capture natural variations in soil conditions that are often required in hydrological studies. Site evaluations can thus become faster and efficient, while areas with higher infiltration potential can be identified with greater confidence, and the overall planning of irrigation, drainage, and groundwater recharge strategies becomes more informed and robust.
Keywords: Electrical Resistivity Tomography (ERT); Hydro-geophysical characterization; Hydraulic Conductivity; Infiltration Rate; Groundwater recharge; Soil Heterogeneity.
How to cite: Jaiswal, M., Ganguly, S., and Prashanth, T.: Integration of electrical resistivity tomography, permeability and infiltrometer tests for modelling hydraulic conductivity and infiltration rates in the field, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3766, https://doi.org/10.5194/egusphere-egu26-3766, 2026.
EGU26-16051 | ECS | Posters virtual | VPS8
Characterization of Paleochannel and Floodplain Aquifers Using Vertical Electrical Sounding: A Case Study from the Western Part of Bengal BasinTue, 05 May, 15:09–15:12 (CEST) vPoster spot A
The subsurface architecture of paleochannel and floodplain deposits, as well as their hydrogeological significance, remains insufficiently characterized in the Ganges upper delta region. The present study evaluates the hydrogeological implications for groundwater resource assessment and aquifer vulnerability in Chakla, North 24 Parganas, West Bengal. Descriptions and discrimination of different subsurface regimes are provided based on electrical resistivity. Vertical Electrical Sounding (VES) surveys are conducted at 51 sites, distributed across paleochannel (np = 31) and floodplain (nf = 20) geomorphic settings. Six-layer resistivity models are developed for each site through inversion analysis. Regime-specific hydrogeological properties are quantified through non-parametric statistical testing (Wilcoxon rank-sum and Kruskal-Wallis) on the modeled VES data. Furthermore, longitudinal conductance and transverse resistance, as obtained from the Dar-Zarrouk parameter analysis, are explored. VES inferences are found to be in well accordance with the borehole lithology from six cores. Paleochannel aquifers and floodplain aquitards exhibit significantly different resistivity distributions due to different grain sizes and saturation. Paleochannel sites reveal higher median resistivity (49.5 Ω·m) and coarser grain sizes, indicating high-capacity aquifers with enhanced investigation depth. On the other hand, floodplain sites are characterized by lower resistivity (19.2 Ω·m), finer grain sizes, and low-permeability confining layers. The findings of the present study support targeted groundwater exploration in paleochannel zones and aquifer protection in floodplain areas, providing key insights for water supply assessment and contaminant vulnerability.
Keywords: Vertical Electrical Sounding (VES), Paleochannel aquifer, Electrical resistivity, Dar-Zarrouk parameters, Hypothesis testing, Non-parametric statistics
How to cite: Dutta, A. D., Yadav, A. K., Mukherjee, A., and Sengupta, P.: Characterization of Paleochannel and Floodplain Aquifers Using Vertical Electrical Sounding: A Case Study from the Western Part of Bengal Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16051, https://doi.org/10.5194/egusphere-egu26-16051, 2026.
