References of "Caterina, David"
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See detailCase studies of incorporation of prior information in electrical resistivity tomography: comparison of different approaches
Hermans, Thomas ULg; Caterina, David ULg; Nguyen, Frédéric ULg

in Near Surface Geophysics (in press)

Many geophysical inverse problems are ill-posed and their solution non-unique. It is thus important to reduce the amount of mathematical solutions to more geologically plausible models by regularizing the ... [more ▼]

Many geophysical inverse problems are ill-posed and their solution non-unique. It is thus important to reduce the amount of mathematical solutions to more geologically plausible models by regularizing the inverse problem and incorporating all available prior information in the inversion process. We compare three different ways to incorporate prior information for electrical resistivity tomography (ERT): using a simple reference model or adding structural constraints to Occam's inversion and using geostatistical constraints. We made the comparison on four real cases representing different field applications in terms of scales of investigation and level of heterogeneities. In those cases, when electromagnetic logging data are available in boreholes to control the solution, it appears that incorporating prior information clearly improves the correspondence with logging data compared to the standard smoothness constrain. However, the way to incorporate it may have a major impact on the solution. A reference model can often be used to constrain the inversion; however, it can lead to misinterpretation if its weight is too strong or the resistivity values inappropriate. When the computation of the vertical and/or horizontal correlation length is possible, the geostatistical inversion gives reliable results everywhere in the section. However, adding geostatistical constraints can be difficult when there is not enough data to compute correlation lengths. When a known limit between two layers exists, the use of structural constrain seems to be more indicated particularly when the limit is located in zones of low sensitivity for ERT. This work should help interpreters to include their prior information directly into the inversion process through an appropriate way. [less ▲]

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See detailTowards a better understanding of time-lapse electrical resistivity properties associated to organic contaminants and bioremediation processes in the subsurface
Caterina, David ULg

Doctoral thesis (2014)

Management of contaminated sites represents a major problem for our society. Geophysical methods arise progressively as non-conventional techniques that should allow decreasing the uncertainty linked to ... [more ▼]

Management of contaminated sites represents a major problem for our society. Geophysical methods arise progressively as non-conventional techniques that should allow decreasing the uncertainty linked to the local nature of punctual drilling/sampling measurements classically used to identify, characterize and monitor such sites. However, the use of geophysics for this purpose is relatively recent and still requires an improvement of geophysical imaging and a better understanding of the impact of contaminants and remediation processes on measured properties to be fully effective. The main objective of this thesis was thus to improve our knowledge on these two aspects. In order to assess the reliability of geophysical imaging, and electrical resistivity tomography (ERT) in particular, we first compare quantitatively different image appraisal indicators. The latter are developed to detect artefacts, estimate depth of investigation, address parameters resolution and appraise ERT-derived geometry. Numerical benchmarks are created representing different geological situations in terms of heterogeneity and scale. On the basis of this comparison, we propose a methodology and guidelines to appraise both qualitatively and quantitatively field ERT images. We show the successful applications on real data coming from the contaminated sites we investigated. It notably allows us to exclude from our interpretation zones of the electrical images that are not considered as sufficiently reliable. To enhance electrical imaging, we investigate three different approaches to incorporate prior information into the ERT inverse problem, namely reference model, structural constraint and regularized geostatistical inversion that we notably apply on real data coming from two contaminated sites. The results are benchmarked against the standard smoothness constraint inversion. Results with real data show that adding prior information in the inversion process always lead to a modification of the solution at least in zones of low sensitivity (allowing notably to better image contaminant plumes at depth). However, the choice of the constraint to apply is highly dependent on the type and amount of information available. Therefore, we provide guidelines that should help the practitioner to include their prior information directly into the inversion process through an appropriate way. To understand the temporal geoelectrical signature of organic contaminants and bioremediation processes, we monitor a site contaminated with hydrocarbons and subjected to stimulated bioremediation. We first show that the most contaminated areas above the groundwater table level are associated to very low resistivities. We then show that during biostimulation (promoting aerobic degradation) and natural attenuation, observed resistivity variations (up to 140%) are mostly located in the saturated zone of the contaminated area. They follow a seasonal trend suggesting a temperature dependence not observed in an uncontaminated zone of the site. However, in the contaminated area, changes largely exceed the expected variations due only to the temperature. We therefore investigate systematically different hypotheses that may explain such changes. Among those hypotheses, we show that microbial activity is a factor that may potentially influence the electrical signature of a contaminated soil and may contribute to the observed resistivity changes. In order to further study the electrical response associated to bacterial activity during bioremediation processes, we monitor a tank experiment that contains soils contaminated with hydrocarbons subjected first to biostimulation and then to bioaugmentation (with an inoculum of Rhodococcus erythropolis T902.1). Whereas no particular electrical signature is observed during the biostimulation phase, we observe a correlation between the evolution of bulk resistivity changes and the specific oil-degrading flora after bioaugmentation that cannot be attributed to fluid resistivity changes. This suggests a direct impact of microbial growth/activity on electrical properties through the modification of surface and/or local electrolytic conduction mechanisms. These latter results open up new perspectives for future experiments that should involve spectral induced polarization measurements allowing a better discrimination between the two conduction mechanisms. [less ▲]

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See detailA comparison study of image appraisal tools for electrical resistivity tomography
Caterina, David ULg; Beaujean, Jean ULg; Robert, Tanguy ULg et al

in Near Surface Geophysics (2013)

To date, few studies offer a quantitative comparison of the performance of image appraisal tools. Moreover, there is no commonly accepted methodology to handle them even though it is a crucial aspect for ... [more ▼]

To date, few studies offer a quantitative comparison of the performance of image appraisal tools. Moreover, there is no commonly accepted methodology to handle them even though it is a crucial aspect for reliable interpretation of geophysical images. In this study, we compare quantitatively different image appraisal indicators to detect artefacts, estimate depth of investigation, address parameters resolution and appraise ERT-derived geometry. Among existing image appraisal tools, we focus on the model resolution matrix (R), the cumulative sensitivity matrix (S) and the depth of investigation index (DOI) that are regularly used in the literature. They are first compared with numerical models representing different geological situations in terms of heterogeneity and scale and then used on field data sets. The numerical benchmark shows that indicators based on R and S are the most appropriate to appraise ERT images in terms of the exactitude of inverted parameters, DOI providing mainly qualitative information. In parallel, we test two different edge detection algorithms – Watershed’s and Canny’s algorithms – on the numerical models to identify the geom-etry of electrical structures in ERT images. From the results obtained, Canny’s algorithm seems to be the most reliable to help practitioners in the interpretation of buried structures. On this basis, we propose a methodology to appraise field ERT images. First, numerical bench¬mark models representing simplified cases of field ERT images are built using available a priori information. Then, ERT images are produced for these benchmark models (all simulated acquisition and inversion parameters being the same). The comparison between the numerical benchmark mod¬els and their corresponding ERT images gives the errors on inverted parameters. These discrepan¬cies are then evaluated against the appraisal indicators (R and S) allowing the definition of threshold values. The final step consists in applying the threshold values on the field ERT images and to validate the results with a posteriori knowledge. The developed approach is tested successfully on two field data sets providing important information on the reliability of the location of a contamina¬tion source and on the geometry of a fractured zone. However, quantitative use of these indicators remains a difficult task depending mainly on the confidence level desired by the user. Further research is thus needed to develop new appraisal indicators more suited for a quantitative use and to improve the quality of inversion itself. [less ▲]

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See detailA salt tracer test monitored with surface ERT to detect preferential flow and transport paths in fractured/karstified limestones
Robert, Tanguy ULg; Caterina, David ULg; Deceuster, John et al

in Berichte der Geologischen Bundesanstalt (2012, September), 93

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See detailComparison of temperature estimates from heat transport model and electrical resistivity tomography during a shallow heat injection and storage experiment
Hermans, Thomas ULg; Daoudi, Moubarak ULg; Vandenbohede, Alexander et al

in Berichte der Geologischen Bundesanstalt (2012, September), 93

Groundwater resources are increasingly used around the world as geothermal systems. Understanding physical processes and quantification of parameters determining heat transport in porous media is ... [more ▼]

Groundwater resources are increasingly used around the world as geothermal systems. Understanding physical processes and quantification of parameters determining heat transport in porous media is therefore important. Geophysical methods may be useful in order to yield additional information with greater coverage than conventional wells. We report a heat transport study during a shallow heat injection and storage field test. Heated water (about 50°C) was injected for 6 days at the rate of 80 l/h in a 10.5°C aquifer. Since bulk electric resistivity variations can bring important information on temperature changes in aquifers (water electric conductivity increases about 2%/°C around 25°C), we monitored the test with surface electric resistivity tomography and demonstrate its ability to monitor spatially temperature variations. Time-lapse electric images clearly show the decrease and then the increase in bulk electric resistivity of the plume of heated water, during respectively the injection and the storage phase. This information enabled to calibrate the conceptual flow and heat model used to simulate the test. Inverted resistivity values are validated with borehole electromagnetic measurements (EM39) and are in agreement with the temperature logs used to calibrate the parameters of the thermo-hydrogeological model for the injection phase. This field work demonstrates that surface electric resistivity tomography can monitor heat and storage experiments in shallow aquifers. These results could potentially lead to a number of practical applications, such as the monitoring or the design of shallow geothermal systems or the use of heated water to replace salt water in tracer tests. [less ▲]

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See detailInversion of multi-temporal geoelectrical field data sets: insights on noise characterization and regularization
Nguyen, Frédéric ULg; Kemna, Andreas; Robert, Tanguy ULg et al

Poster (2012, July 11)

Inversion of geoelectrical time-lapse data sets is increasingly growing as monitoring systems are being used in more applications such as seawater intrusion, landslides, remediation of contaminated sites ... [more ▼]

Inversion of geoelectrical time-lapse data sets is increasingly growing as monitoring systems are being used in more applications such as seawater intrusion, landslides, remediation of contaminated sites, landfill operation, shallow geothermal systems, or management of water resources. To date, several inversion strategies exist for taking into account the temporal dimension of the data. The most used nowadays are the independent inversion of multi-temporal data sets, the difference inversion, the temporally-constrained inversion, and the more recent process-based inversion. However, difference inversion schemes generally assume that part of the noise contained in the data cancels out when working with temporal data differences. Temporally-constrained inversion on the other hand assumes that the changes are localized and minor. Process-based inversion requires a more advanced knowledge of the system prior the inversion. In this study we demonstrate that the resolution of the time-lapse inversion scheme is mostly dependent on the quantification of the temporal behavior of the data error, on the resolution of the model-dependent pattern of the survey, and not on the regularization strategy. Our study is based on the imaging results of different data sets with different time and spatial scales, and with different degrees of geological complexity and resistivity contrast, The considered sites are a shallow sandy aquifer and a fractured hard rock aquifer where tracer experiments were performed and monitored using surface arrays. The two studied transport processes are advection, with velocities on the order of 10 m/hour and slower advection/diffusion processes. The strongest improvements were brought by using the data difference and a quantitative estimation of the data error. We found in particular a dependence of the time-lapse data error to the measured resistance (i.e., signal-to-noise-ratio), permitting to formulate an error model to describe the data error present in time-lapse data sets. We used minimum gradient support regularization to invert for model changes with enhanced contrast and found this technique more suited to time-lapse studies than for static images. Noise characterization and error models appear therefore as essential and the most impacting for a successful inversion both for static and time-lapse data whereas different spatio-temporal regularization techniques allowed to decrease artefacts but needs to be coherent with the process. [less ▲]

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See detailIncorporation of prior information in the regularized inversion of ERT data with CRTomo
Hermans, Thomas ULg; Caterina, David ULg; Martin, Roland et al

Conference (2012, February 03)

The electrical resistivity tomography (ERT) inverse problem is ill-posed leading to non-uniqueness of its solution. A possible way to reduce the amount of mathematical solutions to more geologically ... [more ▼]

The electrical resistivity tomography (ERT) inverse problem is ill-posed leading to non-uniqueness of its solution. A possible way to reduce the amount of mathematical solutions to more geologically plausible models is to incorporate priori information in the inversion process. In this presentation, we describe the implementation of three different techniques ways to go beyond standard Occam’s inversion for ERT with the code CRTomo : a simple reference model weighted by a user-defined parameter, a structural constraint defined by modifying the construction of the roughness matrix compared to standard Occam’s inversion and a geostatistical constraint based on a vertical correlation length deduced from borehole data to build the model covariance matrix and use it to regularize the inversion. With several examples, we show that the traditional smoothness constraint yield small contrasts of resistivity, far from the reality revealed by borehole measurements. Incorporating prior information from boreholes clearly or from another geophysical technique (like GPR or seismic refraction) improves the misfit with logging data. The choice of the prior information incorporation technique highly depends on which king of information is available and further developments are needed to extend the techniques to more complex cases. [less ▲]

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See detailGeoelectrical investigations (DC) on a contaminated site during biostimulation: monitoring results and resolution analysis
Caterina, David ULg; Nguyen, Frédéric ULg

Conference (2012, January 12)

In Belgium, as in many other countries, relatively anarchic economical and industrial development of the past century has resulted in a significant number of contaminated sites. When one of these sites ... [more ▼]

In Belgium, as in many other countries, relatively anarchic economical and industrial development of the past century has resulted in a significant number of contaminated sites. When one of these sites poses a risk to human or ecosystem, measures need to be taken to clean it up. Among these measures, methods using in situ bioremediation are beginning to become more important because of their ease of implementation and their relatively low cost. However, it is often difficult to ensure their effectiveness except by carrying out extensive drilling and sampling, which can be long and expensive while offering only punctual information. Thus, it becomes necessary to use other techniques to overcome these shortcomings. Recently, an increasing interest is being born to use geophysical methods as tools for remediation monitoring. As part of our work, we conducted several electrical resistivity tomography campaigns on a bus station located in Bassenge (Belgium) which has undergone a contamination of hydrocarbons (gasoline) for several years and on which a biostimulation remediation device was set up in order to clean it up. The aim of our investigations was to study the electrical response of the contaminated area during the remediation phase and whether electrical resistivity tomography allowed to monitor its effectiveness. After a year of monitoring, the time lapse images obtained show a significant decrease of electrical resistivities (up to -40%) during biostimulation at the location of the main contaminant plume and an increase again of resistivities from the time the biostimulation was stopped. The electrical response during the biostimulation is in agreement with the models presented by several authors in the literature. The increase again of resistivities after the stimulation is however more surprising and can be explained by several physico-chemical (sorption-desorption processes) or biological (decrease of conductive biofilms) assumptions. The results obtained tend to suggest that it is possible to use electrical resistivity tomography as a tool for qualitative control during the remediation of a contaminated site. However, for a more quantitative use of resistivity models, it is important to assess their reliability through the use of resolution indicators. We therefore developed a methodology to address this issue based on the creation of synthetic models representing simplified cases of field resistivities and we applied it on our case study. The results obtained provided us important information about the reliable parts of the resistivity models. These findings may lead in the future to the development of mathematical models that can link quantitatively geophysical properties to the level of (de)contamination of a site. [less ▲]

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See detailGeoelectrical monitoring on a contaminated site during biostimulation
Caterina, David ULg; Nguyen, Frédéric ULg

Poster (2011, December 01)

In Belgium, as in many other countries, relatively anarchic economical and industrial development of the past century has resulted in a significant number of contaminated sites. When one of these sites ... [more ▼]

In Belgium, as in many other countries, relatively anarchic economical and industrial development of the past century has resulted in a significant number of contaminated sites. When one of these sites poses a risk to human or ecosystem, measures need to be taken to clean it up. Among these measures, methods using in situ bioremediation are beginning to become more important because of their ease of implementation and their relatively low cost. However, it is often difficult to ensure their effectiveness except by carrying out extensive drilling and sampling, which can be long and expensive while offering only punctual information. Thus it becomes necessary to use other techniques to overcome these shortcomings. Recently, an increasing interest is being born to use geophysical methods as tools for remediation monitoring. As part of our work, we conducted several electrical resistivity tomography campaigns on a site contaminated by LNAPLs (gasoline) on which a biostimulation remediation device was set up. The aim of our investigations was to study the electrical response of the contaminated area during the remediation phase and whether electrical resistivity tomography allowed to monitor its effectiveness. After a year of monitoring, the time lapse images obtained show a significant decrease of the electrical resistivity (up to -50%) at the location of the main contaminant plume. This particular response during the biostimulation, in agreement with the models presented by several authors in the literature, tends to suggest that it is possible to use electrical resistivity tomography as a tool for qualitative control during the remediation. These findings may also lead in the future to the development of models to estimate more quantitatively the level of (de)contamination of a site. [less ▲]

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See detailInversion of multi-temporal geoelectrical data sets: insights from several case studies
Nguyen, Frédéric ULg; Kemna, Andreas; Robert, Tanguy ULg et al

Conference (2011, December)

Time-lapse inversion of geoelectrical data is increasingly growing as remote monitoring systems are being used in more applications such as seawater intrusions, landslides, bioremediation of contaminated ... [more ▼]

Time-lapse inversion of geoelectrical data is increasingly growing as remote monitoring systems are being used in more applications such as seawater intrusions, landslides, bioremediation of contaminated sites, landfill operations, shallow geothermal systems, or water resources. To date, several inversion strategies exist for taking into account the temporal dimension of the data. Among the most used ones are the independent inversion of multi-temporal data sets, the difference inversion, the temporally-constrained inversion, and the more recent process-based inversion. The success of a particular time-lapse inversion scheme depends on the validity of several assumptions made by these inversion schemes. Difference inversion schemes generally assume that part of the noise contained in the data cancels out when working with temporal data differences. Process-based inversion requires a more advanced knowledge of the system prior the inversion. Temporally-constrained inversion on the other hand assumes that the changes are localized and minor. We show in this paper using data sets with different time and spatial scales, and with different degrees of geological complexity and resistivity contrasts, that the particular success of a time-lapse inversion scheme is highly dependent on the temporal behaviour of the noise estimation in the time-lapse data set and of the model-dependent resolution pattern of the survey. We attempt to provide guidelines for successful quantitative interpretation of time-lapse data sets whenever possible. [less ▲]

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See detailHow to incorporate prior information in geophysical inverse problems: deterministic and geostatistical approaches.
Hermans, Thomas ULg; Caterina, David ULg; Martin, Roland et al

in EarthDoc - Near Surface 2011 - 17th European Meeting of Environmental and Engineering Geophysics (2011, September 13)

Many geophysical inverse problems are ill-posed leading to non-uniqueness of the solution. It is thus important to reduce the amount of mathematical solutions to more geologically plausible models by ... [more ▼]

Many geophysical inverse problems are ill-posed leading to non-uniqueness of the solution. It is thus important to reduce the amount of mathematical solutions to more geologically plausible models by regularizing the inverse problem and incorporating all available prior information in the inversion process. We compare three different ways to go beyond standard Occam’s inversion for electrical resistivity tomography (ERT) using electromagnetic logging data in the context of salt water infiltration: a simple reference model, a structural constraint and a geostatistical constraint based on a vertical correlation length. Results with the traditional smoothness constraint yield small contrasts of resistivity, far from the reality revealed by borehole measurements. Incorporating prior information from boreholes clearly improves the misfit with logging data. If a good reference model can always be used, it can lead to misinterpretation if its weight is too strong. When the computation of the correlation length is possible, the geostatistical inversion gives satisfactory results everywhere in the section. In this specific case, the geostatistical approach seems to be a more robust way to incorporate prior information. The structural constraint seems to be more indicated when integrating information from other geophysical methods such as GPR or seismic. [less ▲]

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See detailImage appraisal tools for electrical resistivity tomography
Caterina, David ULg; Beaujean, Jean ULg; Robert, Tanguy ULg et al

in Proceedings of SAGEEP (2011), 24

Image appraisal is a problem frequently encountered in electrical resistivity tomography (ERT), and more generally in non-linear geophysical inversion. It may include several aspects such as the ... [more ▼]

Image appraisal is a problem frequently encountered in electrical resistivity tomography (ERT), and more generally in non-linear geophysical inversion. It may include several aspects such as the identification of the geometry of buried structures, the detection of numerical artefacts, the estimation of the depth of investigation or the exactitude of inverted parameters. Geophysicists can rely on several tools published in the literature to address these issues. However, few studies offer a quantitative comparison on the performance of these tools concerning the different mentioned aspects. Moreover, to our knowledge, there is no commonly accepted methodology to handle image appraisal. In this contribution, we compared quantitatively the ability of different image appraisal indicators to reach different objectives (geometry, artefacts, depth of investigation, parameter resolution). Among possible image appraisal tools, the model resolution matrix (MRM), the cumulative sensitivity matrix (CSM) and the depth of investigation index (DOI) are the most cited ones and were studied here. We compared them first on numerical models representing different geological situations. This numerical benchmark showed that indicators based on the MRM and CSM were the more appropriate to appraise ERT images in terms of the geometry of structures and the exactitude of inverted parameters, DOI providing mainly qualitative information. On this basis, we propose a methodology to appraise field ERT images focusing on the resolution and geometric aspects (others being implicitly studied). First, True Synthetic Models (TSM), representing simplified cases of field ERT images, are built using available information. Then, through forward modelling, synthetic ERT data are computed and inverted to provide the Inverted Synthetic Models (ISM). Afterwards, a comparison between TSM and ISM (or their gradients for geometry) is made in order to define the errors on inverted parameters. This discrepancy is then plotted with respect to resolution indicator values and points out in every tested cases a resolution range over which the errors abruptly increase allowing the definition of threshold values. The final step consists in applying the threshold values on the field ERT images and to validate the results with a posteriori knowledge. [less ▲]

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See detailA Saline Tracer Test Monitored with ERT to Detect Preferential Flow/Transport Paths in Limestones
Robert, Tanguy ULg; Caterina, David ULg; Deceuster, John et al

in EarthDoc - Near Surface 2010 – 16th European Meeting of Environmental and Engineering Geophysics (2010, September 07)

The success of a tracer test highly depends on the number and the localisation of the sampling wells. When preferential solute transport paths are expected, one needs to set up carefully the tracer test ... [more ▼]

The success of a tracer test highly depends on the number and the localisation of the sampling wells. When preferential solute transport paths are expected, one needs to set up carefully the tracer test to recover information such as the local groundwater flow direction and an estimate of the transport velocities. In this work, we used electrical resistivity tomography (ERT) to monitor a saline tracer test. This experiment was performed in fractured limestones where high transport velocities and strong dilution effects were expected. This required a continuous injection and fast ERT acquisition. Two different salt concentrations (40 and 160 g/l) were injected to deal with dilution effects. We also tested the resolution and the depth of investigation of our dipole-dipole sequence by changing the electrode spacing. Two transversal (and a longitudinal) profiles were placed every 20 m from the injection well. During the first (second) test, a maximum of -8 % (-16 %) change of electrical resistivity was observed in the nearest ERT profile while no change occurred in the other ones. We were then able to estimate the transport velocities in addition to the local groundwater flow direction even if the dilution effects were important. [less ▲]

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See detailUse of image appraisal tools and covariance matrix
Caterina, David ULg; Beaujean, Jean ULg; Nguyen, Frédéric ULg

Conference (2010, July)

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See detailImage Appraisal Tools for Electrical Resistivity Tomography
Caterina, David ULg; Beaujean, Jean ULg; Robert, Tanguy ULg et al

Poster (2010, January 12)

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See detailCaractérisation hydrogéologique du bassin de la Haze
Caterina, David ULg

Master's dissertation (2007)

Le travail de fin d'études réalisé porte sur la caractérisation hydrogéologique du bassin du ruisseau de la Haze, situé dans la région d'Esneux-Sprimont (province de Liège, Belgique). Il s'inscrit dans le ... [more ▼]

Le travail de fin d'études réalisé porte sur la caractérisation hydrogéologique du bassin du ruisseau de la Haze, situé dans la région d'Esneux-Sprimont (province de Liège, Belgique). Il s'inscrit dans le cadre du Projet Synclin'eau résultant d'une convention signée entre l'Aquapôle-ULg d'une part, et la RW-DGRNE et la SPGE d'autre part. Ce projet vise à caractériser d'un point de vue hydrogéologique les aquifères du Synclinorium de Dinant dont la zone étudiée fait partie. Ce petit bassin (superficie d'environ 10 km²) a pour particularité d'être entièrement compris dans un synclinal de grès du Famennien, ce qui est relativement rare dans le cas des aquifères gréseux du Synclinorium de Dinant. Les propriétés de cet aquifère ont été estimées à l'aide des différents outils à la disposition de l'hydrogéologue. Ainsi, la collecte de données de températures et de précipitations provenant des stations IRM proches du bassin, la mise en place d'une sonde limnimétrique à son exutoire et la réalisation de jaugeages réguliers à cet endroit ont permis le calcul de bilans hydrologiques. De même, la réalisation de plusieurs essais de pompage et d'un essai de traçage (site SWDE de Dolembreux) combinée avec des mesures régulières des niveaux piézométriques ont permis d'estimer les propriétés hydrogéologiques des grès du Famennien. Pour finir, la prise d'échantillons d'eau à chaque piézomètre, chaque puits de captage et chaque source et leur analyse chimique a permis de déterminer les propriétés hydrochimiques du bassin. [less ▲]

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