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NSG2021 1st Conference on Hydrogeophysics
- Conference date: August 29, 2021 - September 2, 2021
- Location: Hybrid
- Published: 29 August 2021
1 - 20 of 53 results
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Integrated Inversion Algorithms to Analyse TDEM Data for Groundwater Resource Assessment in Volcanic Aquifers
Authors A. Vergnano, F. Pace and C. CominaSummaryAssessing groundwater resources in arid or semiarid environments often implies problems of previous data scarcity or logistical difficulties. In our work, we analyse one of such contexts, the volcanic island of Fogo, Cape Verde, to evaluate the presence of groundwater for solving drought problems of a local vineyard. We acquired a profile of Time Domain Electromagnetic (TDEM) soundings inside the target area, whereas we surveyed also external zones, near the few available wells, to correlate the acquisitions with stratigraphic information and water analyses. For the interpretation, we tailored three different inversion algorithms. First, we adopted a global search method, to obtain a 1D resistivity model without being trapped in possible local minima of the solution. We chose the stochastic Particle Swarm Optimization (PSO) algorithm, a computational-intelligence method based on the social dynamics of groups of animals. It was the starting point for the second inversion method, based on local search (1D inversion). In the end, a Spatially Constrained Inversion (SCI) interpretated the dataset with a pseudo-2D model. Our work provided a detailed characterization of the resistivity distribution in the subsurface of the vineyard, which outlined the presence of a probable thick suspended aquifer, which may contain exploitable groundwater resources.
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Measuring Soil Moisture Using Surface-NMR With Prepolarization
Authors T. Hiller, S. Costabel, R. Dlugosch, T. Radic and M. Müller-PetkeSummarySmall-scale investigations of the unsaturated zone has gained increasing interest in the hydro-geophysical research community. The technique of surface-NMR (SNMR), while providing valuable data on water content and permeability in the saturated zone, has difficulties to reliably detect and interpret signals from partly-saturated soils due to low signal amplitudes. Recently, SNMR using prepolarization (SNMR-PP) has gained interest to overcome this limitation. Here, a strong prepolarization field enhances the SNMR signal of coils with a footprint of below 1m up to a level that promises to enable soil moisture measurements in the upper two meters of the subsurface in the near future.
We present the first SNMR-PP measurements on a real soil and demonstrate the general feasibility of this technique to qualitatively and quantitatively detect soil moisture. Our soil moisture measurements are validated by independent time domain reflectometry (TDR) data.
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Electrical Signatures of Dual Domain Mass Transfer Observed in Rock Cores
Authors L. Slater, F. Day-Lewis, B. Parker and L. SlaterSummaryDual domain mass transfer (DDMT), or the transfer of solute between mobile and less-mobile porosity domains, can cause anomalous breakthrough behavior observed during pumping operations. One novel method for characterizing DDMT is through geoelectrical inference, whereby electrical geophysical measurements are combined with pore fluid specific conductance measurements during a tracer experiment. Studies have shown the effectiveness of this method for characterizing DDMT in unconsolidated materials. We describe first of a kind instrumentation and results aimed at investigating evidence for a geoelectrical signature of DDMT in a rock core. A flow through apparatus was designed with the capability to simultaneously acquire bulk conductivity and specific conductance measurements on fluids extracted from the center of the core. A tracer experiment was run in three phases: initial, tracer flush, and tracer injection. Both specific conductance and bulk conductivity time series exhibit characteristic breakthrough behavior, with a delayed breakthrough of bulk conductivity relative to specific conductance, indicative of DDMT in the core. A strong hysteresis loop in the plot of bulk conductivity versus specific conductance is observed, consistent with the electrical geophysical signature of DDMT. The occurrence of DDMT at the core-scale indicates that it is likely ubiquitous within porous media across multiple scales.
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Combining Multi-temporal Electric Resistivity Tomography and Predictive Algorithms for supporting aquifer monitoring and management
Authors V. Giampaolo, P. Dell’Aversana, L. Capozzoli, G. De Martino and E. RizzoSummaryThis work presents the results of geophysical data prediction by applying statistical and predictive algorithms to a multi-temporal Electric Resistivity Tomography dataset.
A cross-hole time-lapse resistivity survey was carried out during an experiment addressed to monitor a tracer diffusion in a real aquifer. In order to retrieve a number of “predicted” pseudo sections of apparent resistivity values, we applied the Vector Autoregressive (VAR) and Recurrent Neural Network (RNN) algorithms over a sequence of 18 ERT surveys. Real and predicted dataset allow to delineate plume evolution under 30 m depth, describing a complex transport pathway influenced by hydraulic properties of the studied aquifer.
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Predicting streaming potentials in partially saturated porous media, a review of capillary-based models
Authors D. Jougnot, L.D. Thanh, M. Soldi, F. Rembert, J. Vinogradov and L. GuarracinoSummaryIn the last two decades, geophysical methods are emerging to characterize and monitor hydrosystems in the critical zone. The vadose zone is the compartment of the near surface where the pore space is saturated both by water and air, this yields a very complex and non-linear behavior in terms of water distribution and dynamics. The combination of electrical resistivity imaging and streaming potential have shown their potential to study this compartment. The streaming potential is particularly interesting as it is directly linked to the water flow and therefore offers a way for in situ monitoring. Nevertheless, the use of appropriate petrophysical relationships is required to quantitatively relate the streaming potential signals to the water flow, i.e., to model the electrokinetic coupling phenomena. During the last decade, the development of capillary-based models opened large perspectives to model flow, transport, and coupling in partially saturated porous media. In this contribution, we propose a critical comparison of existing electrokinetic coupling models, from the up-scaling approach they are based on to the capillary size distribution they consider to explain the streaming potential signal, or the shape of the capillaries they consider to explain complex features such as hysteresis.
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Integrated analysis of the coastal aquifer system of Thorikos Valley, Attica, Greece
Authors G. Apostolopoulos, C. Pouliaris, S. Karizonis, M. Perdikaki and A. KalliorasSummaryAn integrated study is presented with the combination of a series of hydrogeological and geophysical investigations that took place in the coastal aquifer system of Thorikos valley (Attica Region, Greece). Both studies prove that seawater intrusion is an ongoing hydrologic process that takes place within both aquifer layers of the investigated area. The extent of the seawater intrusion front is limited within the coastal zone, while the piezometric conditions suggest that this is a passive type of intrusion.
A FEM map of the subtraction of conductivities for two effective depths (HCP mode) shows great similarity with the distribution of chloride ions in the alluvial aquifer.
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Valles Half-Graben (NE Spain), a Preliminary Regional Geothermal Model
Authors A. Llobet, L. Rivero, A. Sendrós, M. Himi, A. Urruela, R. García-Artiga, R. Lovera, C. Abancó and A. CasasSummaryThe Vallès basin is located in the NE area of the Iberian Peninsula. In this area, some sources of thermal water are known and used since ancient times. These upwellings indicate that there are hot waters at a certain depth, and maybe, that could be exploited. Not much depth geological information is avalaibe in this area but the hydraulic regime sems controlled by the tectonic configuration and the sedimentary material in the subsurface develops aquifers capable to redistribute fluids, solutes and heat. This preliminary study tries to deduce the possible origin of these waters and the comparison with other similar better known areas.
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Geophysical Characterization of Alluvial Aquifers in Plutonic and Volcanic Semi-Arid Andes Using Electromagnetic Methods.
Authors G. de Pasquale, R. Valois, E. Bresciani and P. AlvarezSummaryDrought periods are common events in the semi-arid zone of Chile and their length and frequency has increased with climate change. Within periods of water resource stresses, subsurface water exploitation increases with the use of deeper wells for irrigation and drinking water supplies. Moreover, in case of severe droughts, aquifers could contain a reserve to mitigate the drought. Within this study, we aim to test the feasibility of electromagnetic geophysical methods to map groundwater reserve in a mountainous watershed of the semi-arid Andes, characterized by narrow valleys alluvial fillings within plutonic and volcanic sequences. The area of study is part of the Limarí catchment, in the Coquimbo Region, where information about the amount of underground water available and its depth is scarce. Here we present the first results, interpretation and limitations of the application of transient electromagnetic (TEM) and magnetic resonance soundings (MRS) for the characterization of the Limarí catchment alluvial aquifers.
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Enhanced Geology of the Chalk Aquifer (Northern France) From Ert Imaging for Hydrogeological Purposes
Authors A. Portal, L. Cary, R. Sylvain, B. Maurice, A. Bonnière and A. Bouvet-SwialkowskiSummaryThis study is part of a large multidisciplinary project aiming at characterize the geometry of the Chalk aquifer and its structures (faults, fracturing…), in two well fields in the South of Lille metropolis (Northern France), for hydrogeology purposes, especially drinking water production. We focus on two main results obtained through Electrical Resistivity Tomography (ERT) imaging. First, we define a petrophysical-linked electrical signature of the Chalk that allows us to image the hydrogeological stratification of the aquifer. Then, we refine the geological settings of the largest and the most exploited (in terms of water resource) well field which is also the most affected by water quality problems. We identify a fracturing corridor inside the unaltered Chalk and we precise the geometry of the overlying Tertiary formations (Louvil Clays). The refinement of the geological structures enhances our understanding of the Chalk hydrosystem functioning that represents a key issue to guarantee the sustainable management of a water resource.
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Identifying Ice-Rich Layers in Rock Glaciers Using Geophysics: A Case Study in the Andes
Authors G. de Pasquale, R. Valois, S. MacDonell and N. SchaeferSummaryRock glaciers play an important hydrological role in the semi-arid Andes, by providing water to streamflow when water needs are the most. Identifying if a rock glacier contains more or less ice is not an easy task, because most of the time, the ice is buried below rock blocks. Surface based geophysics can be a way to assess ice content, even tough calibration or ground truth is necessary to properly give any quantitative figure. This study aims to identify ice rich layers using geophysics on two Rock Glaciers (RG): an active and inactive one. Electrical Resistivity Tomography (ERT), Seismic Refraction Tomography (SRT) and Ground Penetrating Radar (GPR) surveys were carried out on those two RG. Seismic velocities and resistivity are higher in the active RG, which is in agreement with a higher ice content. Whilst velocities are in still in the usual geological range, resistivities are really high, which is not abnormal in the absence of liquid water or clay minerals. Interpretating resistivities only could led to misunderstandings because high resistivities could be seen as ice. The two RGs show a distinct signature regarding seismic velocities and resistivities, which demonstrate the potential of those tools to characterize RG.
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Passive Seismic Monitoring of a Karst Aquifer During Flood Events.
Authors A. Abi Nader, J. Albaric, A. Marchand, M. Gros, M. Steinmann, B. Fores, V. Stefani, B. Pohl, H. Celle-Jeanton and C. SueSummaryKarst aquifers are considered challenging sites for monitoring. They endure various behaviors during floods due to their heterogeneous structure and complex recharge mechanisms. This shows that multiple parameters should interfere as well as multiple methods emerging from different disciplines should be used to investigate such environments. This work is held with the objective of identifying the dynamics of superficial and deep water flows in a karst environment. Taking Fourbanne’s aquifer as a case study, we show in the following the ability of seismic noise combined with hydrological data to detect water flows and bedload transport in the vicinity of the underground conduit. This study is a part of the SISMEAUCLIM project that aims to develop a new approach to temporal monitoring of karst aquifers, subject to floods by analyzing jointly seismological, hydrogeological, and atmospheric data.
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Mapping a Fluvial Aquifer in New Zealand Using Airborne Tem, Seismic, and Electrical Soundings
Authors R. Kellett, Z. Rawlinson, R. Westerhoff, R. Reeves, J. Smith, S. Harper, N. Foged, J. B. Pedersen and P. MauryaSummaryA SkyTEM airborne survey has been flown over 1820 km2 of an area of intense agriculture in Hawkes Bay region of New Zealand. The survey is designed to map the characteristics of a coastal fluvial aquifer and support the management of groundwater resources. Processing the data from a 590 km2 subset of the survey, adjacent three urban centres, has been helped by using ground-based geophysical data. These data include ground-TEM, DC resistivity soundings, and borehole geophysical logs. Seismic reflection data across the region provide constraints on the deeper sections of the aquifer system (200 – 500 m). One of the key aims of the study is to map the variability of the surface geological strata that in places are a recharge zone and in other places a confining layer for the aquifer. The SkyTEM data have a spatial coverage (170 m line spacing and 20–30 m station spacing) that enables these units to be mapped in more detail than is possible with the current boreholes and ground geophysical data. In places the ground-based data provide valuable support for constraining the shallow SkyTEM models where data can be missing and deep parts of the SkyTEM model where the resolution is low.
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Data-driven hydrogeophysical and redox modelling
Authors N. Claes, N. Foged, T. Norvin Vilhelmsen, R. Rumph Frederiksen, H. Kim and A. Vest ChristiansenSummaryDetailed 3D structural information of the subsurface is fundamental for development of both the hydrological and the geochemical models that can be used for analysis of nitrate reduction processes in the subsurface and targeted nitrate regulation. In some areas data, coverage might be sparse or suffering from bad data quality, which results in information gaps. We suggest therefore a workflow that merges tTEM resistivity data and borehole lithologies, and uses these datasets to generate an ensemble of equally plausible 3D models of hydrogeological units and redox conditions. In an initial step the input datasets are merged via accumulated clay thickness modeling. This dataset is in a second step transformed into a training image, that is to be used in multipoint statistical simulations. The application of Direct Sampling within this workflow allows for simultaneous simulation of these variables. This approach allows for retaining the complex geostatistical spatial relationships that can exist between the different datasets in the resulting generated 3D models.
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Ohmpi project: an open-source resistivity meter
Authors R. Clément, H. GUYARD, V. Dubois, N. Forquet, O. Kaufmann and Y. FarquierSummaryA major research effort in recent decades has led to the development of multi-electrodes, multi-channels, accurate, robust and versatile resistivity meters. This work has contributed to the emergence of the electrical resistivity tomography technique and has led to major advances in many fields such as geosciences or the environment or civil engineering. The main limitation of this equipment does not lie in its quality or robustness in the field. It concerns the cost of the equipment and its low adaptability for specific scientific problems. For these reasons, the method is underused for humanitarian applications, in developing countries and for non-profit applications (archaeology, environment). In the field of environment, civil engineering or geosciences, geophysical monitoring has become a key to assess natural systems and phenomena. For these problems, the immobilisation of one or more resistivity meters is not always technically and financially possible. Finally, many applications today require the ability to control the measurement with external information and thus optimise the measurement in the context of a “big data”. The OhmPi project aims at proposing an open source hardware and software resistivity meter to the community and the academic world.
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Validation of a newly developed surface NMR system
By D.J. OkholmSummaryThe surface NMR system, Apsu, is a newly developed system, focused on the shallow subsurface. The system shows promising results regarding resolution of the shallow subsurface as well as in relation to collection of field data in less remote areas. Additionally, field measurements are fast and efficient, thus increasing the value of the system even further.
The Apsu system’s capabilities of resolving the water table depth is tested through synthetic analysis. This analysis uses the standard deviation factor as a measure of the sensitivity of the system. Further, different loop configurations are tested for the system to examine their influence on the sensitivity.
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Airborne geophysical survey for water resources planning, a case history, Bromölla, Southern Sweden
Authors H. Jeppsson, B. Bergman, A. Edsen, J. Jager Jensen, A. Johnsson, C. Brolin and P. DahlqvistSummaryOne of the major groundwater resources in Sweden is found in the sedimentary bedrock of the Kristianstad plain in Southern Sweden. It is the main resource for water supply in several municipalities in the region. During 2020 WSP has, on behalf of the Bromölla Energy and Water Ltd, processed and interpreted the airborne geophysical survey data from the Bromölla area. The primary aim was to identify possible areas of groundwater extraction. By combining the interpretation of the thickness of the main aquifer, the thickness of interpreted fine material in the soil layers and the interpreted soil depth from the airborne geophysical survey data, a map has been produced that shows where the best interpreted conditions are for groundwater abstraction.
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Original experimental bench based on a large loop for environmental measurements at LSBB
Authors C. Dezord, G. Micolau, C. Abbas, A. Mesgouez and E. Pozzo Di BorgoSummaryIn this paper, we present the first step of an instrumental development of an original environmental sensor, based on a giant magnetic loop. It is a simple electrical cable existing and used for years at the LSBB (France). Its singular location in this specifically transdisciplinary laboratory is an asset for its future use by a large scientific community. We propose to take advantage of the unusual length and surface of the loop and its very specific environment to increase its functionalities. More specifically, we investigate two different approaches : an active method consisting in monitoring the time evolution of its electrical characteristic; and a passive method consisting in measuring the environmental induced electrical voltage. We present both the experimental setup, the experimental protocols and a proof-of-concept for these two methods with surprising first experimental results. We discuss the opportunity offered by sharing this work with different scientific communities.
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Geophysical characterization of near-surface formations in the La Villa River catchment (Los Santos, Panama)
SummaryThe central Pacific Region (Panama) is known to suffer from water scarcity during periods of extended drought. The groundwater/surface water interactions and dynamics, provided by conceptual or numerical models are crucial for water resource management. At the regional scale, such models generally lack of structural information concerning the internal variability of the near surface formations. The spatialization of the direct observations from sparse boreholes can only achieved by geophysical investigations. The aim of this work is to characterize, in the La Villa groundwater basin, the near surface aquifer located in the lateritic horizon using electrical resistivity imaging (ERI), vertical electrical soundings (VES) and time domain electromagnetic soundings (TDEM). This case study illustrates the relevance of the use coupled ERI, TDEM and VES to describe the near surface variability due to the leaching of the lateritic horizon as well as the level of the water table.
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Evaluating the cause of TDIP signals in woochips-filled infiltration trenches for treated wastewater
Authors L. Delgado-Gonzalez, V. Dubois, L. Lassabatère, J. Aubert, C. Boutin, M. Seger and R. ClémentSummarySoil infiltration is regularly practised downstream of wastewater treatment plants, particularly in areas without surface water systems. In France, stakeholders are considering the use of biodegradable and renewable material such as woodchips. This material has two main advantages: it has a high capillarity, thus a great capacity for water retention, and it amends the soil with carbon improving its structure. Moreover, woodchips have been told to promote biodiversity in particular for bioturbating species like earthworms, which play a major role regarding soil structure and organic matter transport into the soil. Such macrofaune is expected to promote water infiltration for poorly infiltrating capacity soils and to limit soil clogging caused by the infiltration of treated wastewater.
In this study, we evaluate the interaction between woodchips and loamy soils on woodchip-filled trenches operated for 2 to 6 years using a non-destructive geophysical approach: Electrical Resistivity Tomography (ERT) and Time Domain Induced Polarisation (TDIP). ERT provided information of the structure of the soil under the woodchip-filled trenches, but anything could be said about the impact of such system in the soil. By contrast, TDIP showed significant variations of the signal around the trenches which may result from the presence of organic matter.
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Groundwater Dynamics in Karst Hydrosystem Unsaturated Zone; Evidences from a 2-years SNMR Monitoring
Authors K. Chalikakis, N. Mazzilli, S.D. Carrière, G. Massonnat, C. Danquigny and A. LegchenkoSummaryThe unsaturated zone (UZ) of karst aquifers plays an important role in groundwater recharge processes. Comprehensive knowledge of UZ structure and hydrodynamic functioning is a key to better assess and manage groundwater resources in karst. In this extended abstract we present the results from a 2-year long Surface Nuclear Magnetic Resonance (SNMR) monitoring implemented in the Low-Noise Underground Laboratory (LSBB) site located within the Fontaine de Vaucluse karst hydrosystem in south-France. This exceptional 2-years SNMR monitoring demonstrated the efficiency of SNMR firstly to assess and validate the permanent presence of groundwater within karst hydrosystem UZ and secondly to monitor his temporal variations. Compared to boreholes, SNMR provides an integrated but accurate estimation of groundwater dynamics without disturbing the media.
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