References of "Dassargues, Alain"
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See detailStudy of historical groundwater level changes in two Belgian chalk aquifers in the context of climate change impacts
Goderniaux, Pascal; Orban, Philippe ULiege; Rorive, Alain et al

in Farrell, R.P.; Massei, N.; Foley, A.E. (Eds.) et al The Chalk Aquifers of Northern Europe (2021)

In southern Belgium, 23% of abstracted groundwater volumes are from chalk aquifers, representing strategic resources for the region. Due to their specific nature, these chalk aquifers often exhibit ... [more ▼]

In southern Belgium, 23% of abstracted groundwater volumes are from chalk aquifers, representing strategic resources for the region. Due to their specific nature, these chalk aquifers often exhibit singular behaviour and require specific analysis. The quantitative evolution of these groundwater resources is analysed for the Mons Basin and Hesbaye chalk aquifers as a function of past evolution, in the short and long term. Groundwater level time series exhibit decreases when analysed over different periods. This is particularly visible for the Hesbaye chalk aquifer when comparing the 1960–90 and 1990–2020 periods. Such decreases are associated with observed temperature increases and precipitation decreases, inducing a decrease of aquifer recharge, and a probable increase of groundwater abstraction in the adjacent catchment. Past evolution is also discussed considering recent winter and summer drought events. The aquifers exhibit long delays in response to recharge events, particularly where the thickness of the partially saturated zone plays a crucial role in observed delays. Regarding future evolution, simulations of the impact of climate changes using medium–high emission scenarios indicate a probable decrease of the groundwater levels over the Hesbaye chalk aquifer. [less ▲]

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See detailDifferentiated influence of the double porosity of the chalk on solute and heat transport
Hoffmann, Richard ULiege; Goderniaux, Pascal; Jamin, Pierre ULiege et al

in Farrell, R.P.; Massei, N.; Foley, A.E. (Eds.) et al The Chalk Aquifers of Northern Europe (2021)

Chalk porosity plays a decisive role in the transport of solutes and heat in saturated chalk. From a geological point of view, there are at least two types of porosity: the porosity of pores corresponding ... [more ▼]

Chalk porosity plays a decisive role in the transport of solutes and heat in saturated chalk. From a geological point of view, there are at least two types of porosity: the porosity of pores corresponding to the micro-spaces between the fossil coccoliths that form the chalk matrix and the porosity owing to the micro and macro-fractures (i.e. secondary porosity). For groundwater flow, the fracture porosity is a determining factor at the macroscopic scale. The multiscale heterogeneity of the porous/fractured chalk induces different effects on solute and heat transport. For solute transport considered at the macroscopic scale, tracer tests have shown that the ‘effective transport porosity’ is substantially lower than the ‘effective drainable porosity’. Moreover, breakthrough curves of tracer tests show an important influence of diffusion in a large portion of the ‘immobile water’ (‘matrix diffusion’) together with rapid preferential advection through the fractures. For heat transport, the matrix diffusion in the ‘immobile water’ of the chalk is hard to distinguish from conduction within the saturated chalk. [less ▲]

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See detailGroundwater flow modeling: a case study of the Lower Rusizi alluvial plain aquifer, North-Western Burundi
Ngenzebuhoro, Pierre Claver; Dassargues, Alain ULiege; Bahaj, Tarik et al

in Water (2021), 13

The study area, in northwestern Burundi, is an alluvial plain consisting of fine clayey sands and coarse sands with mixed lithology. The aquifer of the lower Rusizi plain could be considered as confined ... [more ▼]

The study area, in northwestern Burundi, is an alluvial plain consisting of fine clayey sands and coarse sands with mixed lithology. The aquifer of the lower Rusizi plain could be considered as confined under a clay layer. A 2D horizontal groundwater flow model was developed under steady-state conditions using the Modflow software. The study aims to determine the most productive areas of this confined alluvial aquifer and the main aquifer inflow and outflow values together with the recharge and river–aquifer interactions. The groundwater potential is dependent on the spatial distribution of hydraulic conductivity and aquifer thickness values providing the local transmissivity values. The calibrated model made it possible to assess the spatial distribution of the hydraulic conductivity values at the regional scale, which ranged from 6 x 10-6 (contact between alluvial plain and Precambrian basement) to 7.5 x 10-3 m/s (coastal barriers). The results also provided the computed groundwater flow directions and an estimation of the groundwater levels in areas not yet investigated by drilling. The results of the computed groundwater flow budget allowed us to deduce that recharge and river–aquifer interaction constitute the main inflow while the downwards boundaries (where piezometric heads could be prescribed) are the main zones where outflows occur. The results of this model can be used in the planning of pumping test programs, locating areas with high groundwater potential to plan water supply for different private and public users. This predictive tool will contribute to the resolution of problems related to the use and integrated management of the groundwater resource in this part of Burundi. [less ▲]

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See detailHeat Tracing in a Fractured Aquifer with Injection of Hot and Cold Water
Hoffmann, Richard ULiege; Maréchal, Jean-Christophe; Selles, Adrien et al

in Ground Water (2021)

Heat as a tracer in fractured porous aquifers is more sensitive to fracture-matrix processes than a solute tracer. Temperature evolution as a function of time can be used to differentiate fracture and ... [more ▼]

Heat as a tracer in fractured porous aquifers is more sensitive to fracture-matrix processes than a solute tracer. Temperature evolution as a function of time can be used to differentiate fracture and matrix characteristics. Experimental hot (50 ◦C) and cold (10 ◦C) water injections were performed in a weathered and fractured granite aquifer where the natural background temperature is 30 ◦C. The tailing of the hot and cold breakthrough curves, observed under different hydraulic conditions, was characterized in a log–log plot of time vs. normalized temperature difference, also converted to a residence time distribution (normalized). Dimensionless tail slopes close to 1.5 were observed for hot and cold breakthrough curves, compared to solute tracer tests showing slopes between 2 and 3. This stronger thermal diffusive behavior is explained by heat conduction. Using a process-based numerical model, the impact of heat conduction toward and from the porous rock matrix on groundwater heat transport was explored. Fracture aperture was adjusted depending on the actual hydraulic conditions. Water density and viscosity were considered temperature dependent. The model simulated the increase or reduction of the energy level in the fracture-matrix system and satisfactorily reproduced breakthrough curves tail slopes. This study shows the feasibility and utility of cold water tracer tests in hot fractured aquifers to boost and characterize the thermal matrix diffusion from the matrix toward the flowing groundwater in the fractures. This can be used as complementary information to solute tracer tests that are largely influenced by strong advection in the fractures [less ▲]

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See detailNumerical modeling of the interference of thermally unbalanced Aquifer Thermal Energy Storage systems in Brussels (Belgium)
Bulté, Manon; Duren, Thierry; Bouhon, Olivier et al

in Energies (2021), 14

A numerical model was built using FEFLOW® to simulate groundwater flow and heat transport in a confined aquifer in Brussels where two Aquifer Thermal Energy Storage (ATES) systems were installed. These ... [more ▼]

A numerical model was built using FEFLOW® to simulate groundwater flow and heat transport in a confined aquifer in Brussels where two Aquifer Thermal Energy Storage (ATES) systems were installed. These systems are operating in adjacent buildings and exploit the same aquifer made up of mixed sandy and silty sublayers. The model was calibrated for groundwater flow and partially for heat transport. Several scenarios were considered to determine if the two ATES systems were interfering. The results showed that a significant imbalance between the injection of warm and cold water in the first installed ATES system led to the occurrence of a heat plume spreading more and more over the years. This plume eventually reached the cold wells of the same installation. The temperature, therefore, increased in warm and cold wells and the efficiency of the building’s cooling system decreased. When the second ATES system began to be operational, the simulated results showed that, even if the heat plumes of the two systems had come into contact, the influence of the second system on the first one was negligible during the first two years of joint operation. For a longer modeled period, simulated results pointed out that the joint operation of the two ATES systems was not adapted to balance, in the long term, the quantity of warm and cold water injected in the aquifer. The groundwater temperature would rise inexorably in the warm and cold wells of both systems. The heat plumes would spread more and more over the years at the expense of the efficiency of both systems, especially concerning building’s cooling with stored cold groundwater. [less ▲]

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See detailThe LASUGEO project: monitoring LAnd SUbsidence caused by Groundwater exploitation through gEOdetic measurements
Devleeschouwer, Xavier; Choopani, Atefe; Moreau, Aline ULiege et al

Poster (2021, September 15)

In the last decades, rapid urbanization, global climate change and uncontrolled anthropogenic transformations of the territory caused a relevant increase in geo-hazards events with huge economic and ... [more ▼]

In the last decades, rapid urbanization, global climate change and uncontrolled anthropogenic transformations of the territory caused a relevant increase in geo-hazards events with huge economic and social consequences. The dramatic increase of these events with environmental degradation highlights the importance of improving ground monitoring and natural resources management with a continuous exchange of knowledge between the scientific community and authorities in charge of environmental risk management. Since the late 1990s, SAR (Synthetic Aperture Radar) data allow measuring slow-moving ground deformations. In the last decades, the use of spaceborne InSAR (Interferometric SAR) has increased significantly thanks to the availability of large-area coverage, millimetre precision, high spatial/temporal data resolution and good cost-benefit. For the last 3 decades, the development of Multi-Temporal Interferometric SAR techniques (MT-InSAR), commonly grouped into PSI-like (Persistent Scatterers Interferometry) and SBAS-like (Small BAseline Subset) algorithms, has changed the way radar images can be exploited for geohazard monitoring (natural gas extraction, mining activities, groundwater overexploitation, karst or landslides processes, etc.). Most of the subsidence bowls mapped by the PSI technique in Belgium have been related to strong fluctuations of an aquifer implying at the surface ground deformations (Declercq et al., 2017; 2021). Besides, the recent dry years are related to ground stability problems in large areas of Flanders. Land subsidence poses significant problems. The most affected regions lie on compressible loose sediments. Any change in the piezometric heads modifies the pore pressure, which may induce consolidation if the geological formations are compressible. Geomechanical aspects are fully coupled to groundwater flow equations. If groundwater levels and pressures are restored, a partial rebound (uplift) corresponding to the elastic part of the geological formations is observed. Consolidation and elastic rebound processes occur in confined and unconfined conditions. The most sensitive parts of the concerned aquifers contain clay, loam or peat lenses but consolidation may occur mostly in the underlying and overlying layers that are often less permeable and more compressible than the aquifer itself. In this case, it is largely a delayed process occurring as far as the pore pressure variation slowly propagates in the low permeability (aquitard) layers. We propose to confront the results of the PSinSAR technique data with hydrogeological groundwater models and two other geodetic techniques: GNSS and gravimetry. LASUGEO focusses on ground deformations in different areas in Belgium: the deep aquifer system of western Flanders, the Tertiary aquifer system in Central Flanders, the Antwerp area, the Leuven area and the Brussels Region. The possible groundwater overexploitation needs to be established through a transient hydrogeological model considering all the stress factors applied to the aquifers. The estimated compaction in the subsiding bowls will be compared with 1D geomechanical model results. The latter will be performed using geotechnical effective stresses as deduced from the pore pressure distribution from the hydrogeological model (Dassargues et al., 1989). These different steps will be done by the partners of the LASUGEO project that are involved in the different case study areas. [less ▲]

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See detailModeling hot and cold water injections in a fractured aquifer: Influence of the thermal gradient direction on measured breakthrough curves
Hoffmann, Richard ULiege; Goderniaux, Pascal; Dassargues, Alain ULiege

Conference (2021, September 10)

Heat tracer tests have shown a high potential to estimate hydraulic and thermal conductivities and heat capacity at the field scale. Most often, such tracer tests are performed in moderately warm aquifers ... [more ▼]

Heat tracer tests have shown a high potential to estimate hydraulic and thermal conductivities and heat capacity at the field scale. Most often, such tracer tests are performed in moderately warm aquifers by injecting hot water, compared to the natural background. For aquifers with a high natural background temperature, such as in tropical regions, it is interesting to inject cold water. Several tracer tests with injection of hot and cold water were conducted in a weathered/fractured aquifer in southern India. The natural background temperature was about 30 °C. In the injection well, a sub-horizontal fracture was isolated by use of a packer system for injection of 1000 L of hot (50 °C) and cold (10 °C) water, respectively. Tracers were recovered by pumping in a well at a distance of 5.4 m and connected by the isolated fracture. The observed temperature breakthrough curves were characterized by their thermal recovery rate and cumulative energy recovery. A plot of logarithmic time against the logarithmic observations translated in residence time distributions allowed to estimate the breakthrough curve tailing slope values close to 1.5 for all temperature tracers, representing a diffusive behavior. For simulating the observations numerically using HydroGeoSphere, a low-porosity and low-hydraulic conductivity porous medium, intersected by highly transmissive discrete fractures, is defined. The fracture aperture, the effective transport porosity, the hydraulic conductivity and the specific storage coefficient of the porous medium were manually calibrated minimizing the differences between observations and simulations of the drawdown and temperature breakthrough curves. The estimated tailing slope values are well reproduced. The observed and simulated thermal recovery rate and the cumulative energy recovery tend to be lower for a cold water injection. Small differences remain between the simulated hot and cold water tests even when no density-viscosity effect is considered and all calibrated parameters are similar. These results confirm that heating and cooling the porous medium from an injected highly permeable fracture is influenced by conduction. However, the conduction direction (from the fracture towards the matrix or vice-versa) influences the thermal recovery rate. For the first time, it is evidenced that the difference in results from similar hot and cold water tracer tests is not only due to water density-viscosity changes but induced also by the inversed direction of the thermal gradient between the fracture and the matrix. [less ▲]

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See detailSimulation of a geothermal aquifer storage in Brussels showing the need for a better balanced system with regards to the local hydrogeological conditions
Bulté, Manon; Duren, Thierry; Bouhon, Olivier et al

Conference (2021, September 09)

An Aquifer Thermal Energy Storage (ATES) system was started in 2014 in the center of Brussels using the Landenian confined aquifer for heat and cold needs of an administrative building. Unfortunately, the ... [more ▼]

An Aquifer Thermal Energy Storage (ATES) system was started in 2014 in the center of Brussels using the Landenian confined aquifer for heat and cold needs of an administrative building. Unfortunately, the imbalance between the injection of warm and cold water combined with the local hydrogeological conditions, has led rapidly to thermal interferences between the heat plume and the cold wells. A second ATES system located nearby started to operate around August 2017 for the heat and cold needs of another large administrative building. In the scope of the MUSE project (GeoERA/ERA-NET program), a numerical model was built using FEFLOW® to simulate groundwater flow and heat transport in the confined aquifer. After calibration on the available piezometric and temperature data, realistic scenarios were simulated to determine possible interferences and to image the year after year persisting and growing heat plume in the aquifer. Results show that even if the heat plumes of the two systems had come into contact, the influence of the second system on the first one was negligible during the first two years of joint operation. Indeed, for a longer period, simulated results pointed out that due to the thermal imbalance and the limited advection in the aquifer, the groundwater temperature would rise inexorably in the warm and cold wells of both systems. A business as usual scenario will lead to a decrease in efficiency for both systems. This case-study is showing how it could be difficult to find an optimum with regards to the local hydrogeological conditions. If advection is very important, thermal energy cannot actually be stored locally as heat and cold plumes are transported far away from the wells. On the contrary, if advection is limited, a global thermal balance is required for hot and cold injections. If advection is moderate (as in this case study), a detailed simulation of the groundwater flow and heat transport in the aquifer is required to find out if the annual imbalance can be managed in relation to the specific local hydrogeological conditions. [less ▲]

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See detailModeling the diffusive behavior of helium and uranine in a porous/fractured chalk aquifer
Hoffmann, Richard ULiege; Goderniaux, Pascal; Le Borgne, Tanguy et al

Conference (2021, September 09)

Informative data is needed to understand transport processes in the heterogeneous subsurface. For example, realistic modeling of transport processes in fractured rocks requires information about the ... [more ▼]

Informative data is needed to understand transport processes in the heterogeneous subsurface. For example, realistic modeling of transport processes in fractured rocks requires information about the fracture network and possible fracture-matrix exchanges. Field experiments involving the use of tracers with different values for the molecular diffusion coefficient are promising for imaging possible fracture-matrix exchanges more accurately and on different time and spatial scales. This can bring complementary data for modeling and support the reconstruction of the porous/fractured medium. In this context, dissolved gases (helium, argon, and xenon) and uranine were jointly injected into a saturated and porous/fractured chalk aquifer and recovered at a distance of 7.55 m (convergent test) or in the injection well after a specific ‘resting time’ (push-pull). For both tests, a sub-horizontal orientated fracture was isolated for injection using an inflatable double packer system. Uranine was measured with a field fluorimeter, and concentrations of the recovered dissolved gases were accurately measured on site with a mobile mass spectrometer. The diffusion coefficient of the tested tracers varies by one order of magnitude, resulting in significantly different breakthrough curves of uranine and helium during the convergent test. Analytical solutions involving multi-fracture and multi-channel conceptualization were used to simulate the experimental observations and to account for diffusion in the rock matrix. Dispersivity, fractures aperture and number, channels radius and number were manually adjusted using the experimental uranine and helium breakthrough curves in residence time distribution (RTD). The difference between observations and simulations was minimized by giving equal weight to the peak value, peak time, and slope in the RTD. For the convergent test, the uranine behavior was realistically simulated with the multi-fracture model, while for helium the multi-channel model was required. In contrast, all push-pull results could be simulated with a multi-fracture model as a smaller volume of porous medium was investigated. In addition, the experimental uranine and helium breakthrough curves of the convergent test were numerically simulated using a 3-dimensional model developed with HydroGeoSphere. Multiple discrete fractures are conceptualized, 3-dimensional diffusion is considered, and parameters are manually calibrated. The experimental data are simulated realistically by considering the contrasted diffusion coefficients of the tracers. The study demonstrates the potential of higher diffusive tracers and that such informative field data clearly support further modeling of dual media, including the application of innovative predictive approaches with the goal of more robust simulations and predictions. [less ▲]

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See detailSelf-organizing maps for groundwater quality assessment of a Belgian chalk aquifer in the presence of 1,1,1-Trichloroethane abiotic degradation
Boudjana, Youcef ULiege; Brouyère, Serge ULiege; Gasparella, Davide et al

Conference (2021, September 09)

In a Belgian chalky aquifer, groundwater quality has been locally affected by a mixture of Chlorinated Aliphatic Hydrocarbons (CAHs) dominated by 1,1,1-trichloroethene (1,1,1-TCA). The first results ... [more ▼]

In a Belgian chalky aquifer, groundwater quality has been locally affected by a mixture of Chlorinated Aliphatic Hydrocarbons (CAHs) dominated by 1,1,1-trichloroethene (1,1,1-TCA). The first results showed that the latter undergoes abiotic degradation by hydrolysis and dehydrohalogenation in the saturated zone. The released acids (hydrochloric and acetic acid) from these reactions influence calcite buffer action in the aquifer and change locally the water hydrochemistry. In addition, the leaching of soluble inorganic compounds from a backfill layer has also influenced the groundwater composition in the same area. Calcium sulfate has migrated to the saturated zone with recharge water. To confirm the first findings and elucidate the effect of each pollution source on the groundwater quality, 3 datasets from 3 annual sampling campaigns were used for Kohonen's Self-Organizing Map (SOM) analysis. The groundwater chemistry dataset used comprised: pH, electrical conductivity, Ca2+, Cl-, SO42-, HCO3-, (Ca2+-HCO3- ), TCE, 1,1,1-TCA, 1,1-DCE and the molar ratio 1,1-DCE/(1,1,1-TCA + 1,1-DCE). For each dataset, 3 clusters were identified within the groundwater plume. The first cluster is characterized by a chemical composition that reflects the presence of 1,1,1-TCA degradation reaction products, an increased calcite dissolution, and migration of Ca2+ and SO42- from backfill soil to the groundwater. The second cluster is characterized mainly by the effect of Ca2+ and SO42- migration to groundwater. The third cluster reflects the less contaminated groundwater with a composition approaching the groundwater background composition (before pollution) in the studied aquifer. The cluster's spatial distribution and their chemical specifications were quite similar between the 3 datasets. In this study, the application of SOM’s is a useful tool to improve the understanding of groundwater quality changes in a contaminated site. Based on this multivariate statistical method, detection of zones influenced by two different groundwater pollution sources was possible within the studied plume. The combination of SOM’s results with the results from: backfill soil characterization, sulfate isotopic signature in groundwater, compared to the one in backfill eluates, has led to a better understanding of the ongoing mechanisms influencing hydrochemistry in this study site. [less ▲]

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See detailModelling land subsidence caused by groundwater exploitation and revealed by geodetic InSAR measurements in the Leuven area
Moreau, Aline ULiege; Declercq, Pierre-Yves ULiege; Orban, Philippe ULiege et al

Conference (2021, September 09)

Synthetic Aperture Radar (SAR) is used since the late 1990s to measure slow-moving ground deformations. The SAR Interferometry (InSAR) technique provides high-density measurements of changes in land ... [more ▼]

Synthetic Aperture Radar (SAR) is used since the late 1990s to measure slow-moving ground deformations. The SAR Interferometry (InSAR) technique provides high-density measurements of changes in land surface altitude over large-scale areas. In Belgium, most of the identified subsidence areas have been related to piezometric fluctuations in aquifers1. Using data acquired by satellite ERS and ENVISAT, from 1992 to 2001 and from 2003 to 2010 respectively, two areas of significant subsidence have been detected in the north of Leuven. In these specific locations, there are also many historical and currently active pumping wells. The problem of land subsidence induced by changes in the groundwater conditions is significant locally and a link between pumping or drainage and subsidence had been clearly shown in many locations2. For the area north of Leuven, data collection showed that the most important pumping wells are screened in the Brussels Formation and the Hannut Formation. Then, a 3D regional groundwater flow model of 5 layers have been developed. Transient simulations are performed starting in the 1990s for the next 30 years. This numerical groundwater flow simulation is coupled to a 1D geomechanical model for consolidation and rebound calculation. Even if the aquifer drawdowns are generally well reproduced by the model, it is less easy to obtain simulated subsidence in agreement with InSAR measurements during the corresponding periods. The subsidence observed by the InSAR measurements is the result of a delayed consolidation process as the pore pressure variations propagate slowly in the compressible low permeability aquitards of the Ieperian. Results comparison to the InSAR measurements can also be used to constrain (calibrate) better the geomechanical model. The coupled models could probably then be used as predictive tools for future groundwater management in relation with local land subsidence risks. This research work is performed in the framework of the BESLSPO BRAIN project: "monitoring LAnd SUbsidence caused by Groundwater exploitation through gEOdetic measurements (LASUGEO)". [less ▲]

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See detailRecent advances in the use of process-based groundwater vulnerability for risk mapping
Brouyère, Serge ULiege; Micelle, Ilaria; Thomas, Caroline ULiege et al

Scientific conference (2021, September 09)

Groundwater vulnerability and hazard maps are often combined to produce GIS-based cartographic representations of the risk of groundwater pollution in studied aquifers. Results remain however often quite ... [more ▼]

Groundwater vulnerability and hazard maps are often combined to produce GIS-based cartographic representations of the risk of groundwater pollution in studied aquifers. Results remain however often quite subjective for two main reasons. First, identification, in the investigated catchment, of anthropogenic activities often requires a combination of heterogeneous sources of information. Their classification in terms of the potential hazard they induce for groundwater quality remains subjective. Second, most of the time, groundwater vulnerability maps that are used for this combination are often based on relatively empirical approaches, with the combination of different factors using rating and weighting methods. These factors are also often implicitly interdependent which is not so consistent for evaluation methods based on multi-factor indicators. Here, we take advantage of the process-based groundwater vulnerability Apsû method (Popescu et al. 2019) to develop a more rigorous methodological framework for the integration of groundwater vulnerability and hazard maps into sound risk assessment maps. We show with examples that the different process-based criteria that are the basis of the Apsû method for intrinsic vulnerability mapping (travel time to groundwater) and specific vulnerability mapping (relative quantity of pollutant reaching the saturated zone or water table) can be used to elaborate efficient decision support maps for land use planning and groundwater protection. We also propose a new concept of “aquifer scale protection zone” and a screening approach that allows restricting the use of targeted hazardous substances in specific areas of the groundwater catchment zone where they show elevated risks of groundwater pollution. The proposed concepts and methodology are illustrated using a mixed urban – agricultural catchment in the Walloon region of Belgium. Ref : Popescu, C., Brouyère, S. and A. Dassargues, 2019. The APSÛ method for process-based groundwater vulnerability assessment. Hydrogeology Journal 27(7): 2563-2579. [less ▲]

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See detailThe first known piezometric map in the world was published in 1856 in Belgium
Dassargues, Alain ULiege; Batelaan, Okke; Anceau, Annick ULiege

Conference (2021, September 07)

To our current knowledge, the first piezometric map ever published in the world is the map of Gustave Dumont in February 1856. Gustave Dumont (1821-1891) was a cousin of the well-known geologist André ... [more ▼]

To our current knowledge, the first piezometric map ever published in the world is the map of Gustave Dumont in February 1856. Gustave Dumont (1821-1891) was a cousin of the well-known geologist André Dumont (1809-1857). This oldest known piezometric map is showing piezometric levels (heads) in the chalk Hesbaye aquifer of the Geer basin near the city of Liège in Belgium. The map is included in a comprehensive report ordered by the city in 1855 to increase drinking water production with a large extension of drainage galleries in this aquifer. A long tradition of underground coal mining activities in Southern Belgium did lead in the 19th century to new advances in practical hydrogeology. For example, drainage techniques linked to mining activities were developed actively as the mines were going deeper and deeper. This period corresponds also to a first complementary collaboration between engineers and geologists, leading to the early steps of geological engineering. André Dumont was a Professor at the University of Liège in Geology and Mineralogy and was the most famous Belgian geologist of that period. He is known for his many detailed and rigorous geological maps. In 1851, he published a note about the application of geological regional knowledge for groundwater exploration in Hesbaye. Gustave Dumont was a mining engineer with experience in hydraulic problems. A water commission of the city of Liège provided Gustave Dumont in 1855 with the task to study the feasibility and impact of an optimized network of drainage galleries in this chalk aquifer. The official report is delivered and published in February 1856 (Dumont 1856) including the first piezometric map entitled: ‘Carte hydrographique de la Hesbaye aux environs de Liége’ (in French). This map shows the piezometric contours every meter from 57 m until 106 m. These contours were described as ‘the intersection between the underground water surface with horizontal planes’ (literal translation from French). This study was particularly innovative, as it was not only driven by the required feasibility and efficiency of the project but also by an estimation of the potential impacts of groundwater levels on private wells of farmers. [less ▲]

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See detailThe potential of a Monte Carlo based sensitivity analysis for transport using a heat-solute tracer test in alluvial sediments
Hoffmann, Richard ULiege; Goderniaux, Pascal; Dassargues, Alain ULiege et al

Conference (2021, September 06)

For numerical aquifer modeling with uncertainty quantification, a sensitivity analysis is a mandatory process. One-factor-at-a-time procedures, i.e., changing one, calibrated input parameter and keeping ... [more ▼]

For numerical aquifer modeling with uncertainty quantification, a sensitivity analysis is a mandatory process. One-factor-at-a-time procedures, i.e., changing one, calibrated input parameter and keeping the other fixed, are still very popular for hydrogeologists. This show immediately which input parameters have the most influence on the results, but the simultaneous variation of multiple input parameters cannot be taken into consideration. This avoids the detection of interactions between input parameters and makes this procedure uncertain. A sensitivity analysis must quantify the relationship between input and model response uncertainty. Thus, a Monte Carlo based sensitivity analysis as a distance-based global sensitivity analysis (DGSA), is here performed. This new kind of sensitivity analysis can reveal key information about parameters most influencing the model outcomes. In this study, the basis for DGSA are 250 Monte Carlo realizations, sampled from a prior distribution that was not previously rejected (i.e., falsified) considering a joint heat-solute tracer experiment in alluvial sediments. In other words, several sets of randomly chosen model parameters were tested for their consistency with the observed data (i.e., prior falsification). In DGSA, the distance between model outcomes is calculated and projected in a low dimensional space. Simulations with a comparable distance to the reference data are a cluster. The parameter cumulative distribution function within k clusters is compared to the reference distribution to deduce the sensitivity. DGSA analyzes both, global parameters (Mean hydraulic conductivity, porosity, etc.) and local high dimensional parameters characterizing the spatial heterogeneity like the complex hydraulic conductivity field generated with sequential Gaussian simulation in the prior. The latter are considered through their principal components replacing multiple statistical parameters with a limited, smaller, and approximated amount of linear combinations. The results show that the heat tracer seems to be less sensitive to global advective parameters like porosity, indicating the complementary tracer behavior. The principal components describing local spatial heterogeneity are sensitive for the heat and the solute tracer, but heat tends to remain more dominated by conduction. Thus, for robust transport decisions using any stochastic Bayesian inversion, an adequate prior description in conjunction with a global sensitivity analysis considering uncertainty is a prerequisite. [less ▲]

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See detailLand subsidence as revealed by PS-InSAR observations in the Antwerp area (Belgium): first steps towards the understanding and modelling
Choopani, Atefe; Declercq, Pierre-Yves; Orban, Philippe ULiege et al

Poster (2021, September 06)

PS-InSAR observations using multi-sensor radar data acquired by ERS 1-2, ENVISAT ASAR, and Sentinel-1A satellite sensors operating in C-band, have shown various land subsidence rates in different zones of ... [more ▼]

PS-InSAR observations using multi-sensor radar data acquired by ERS 1-2, ENVISAT ASAR, and Sentinel-1A satellite sensors operating in C-band, have shown various land subsidence rates in different zones of the Antwerp area along the Scheldt River and in the harbor zone during the 1992 to 2021 period1. The LOS velocity values calculated from different radar datasets collected over Antwerp City Centre are ranged between -0.96 - +1.14 mm/year (ERS 1-2), -2.21 - +1.11 mm/year (ENVISAT), and -3.31 - +3.87 mm/year (Sentinel-1A). Moreover, the LOS velocity values for Antwerp Harbor are -4.38 - +1.02, -4.06 - +1.65, and -9.46 - +3.86 which are more significant than their corresponding ranges in the Antwerp City Centre. Groundwater is intensively pumped from the sandy Vlaanderen Formation (Holocene), Lillo and Poederlee Formations (Pliocene), and Berchem Formation (Miocene). However, in this area, land subsidence can be attributed to four potentially complementary consolidation processes: - natural consolidation of the Holocene estuarine sediments, - additional consolidation in the saturated Holocene estuarine sediments due to the backfill overload (8 m thick embankments) along the harbor docks, - saturated-unsaturated consolidation of the backfill materials, - consolidation of the most compressible layers, probably in the Boom Formation (Paleocene) and in the Asse clay of the Maldegem Formation (Eocene) due to pore pressure decrease induced by groundwater pumping in the different Cenozoic aquifers. Indeed, several of these processes could be added to produce the actual observed land subsidence. Geomechanical and hydrogeological data were being collected in the frame of the BESLSPO BRAIN project: "monitoring LAnd SUbsidence caused by Groundwater exploitation through gEOdetic measurements (LASUGEO)". For consolidation of estuarine sediments induced by the backfill overload, the rapid increase of total stress should be equilibrated by an increase of both water pore pressure and effective stress. This later, inducing land subsidence, will progressively increase as the water overpressure can be dissipated mostly laterally through groundwater flow. A coupled approach including a 3D groundwater flow model and 1D geomechanical models will be needed for a detailed analysis2,3,4. First, local models will probably be needed in specific zones to understand in detail the ongoing consolidation processes. Then a large 3D groundwater flow model will be considered over the Antwerp area including all the complex boundary conditions with the Scheldt River and the harbor docks to provide realistic transient water pressure conditions to numerous 1D geomechanical models in the area. [less ▲]

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See detailThe first potentiometric map
Dassargues, Alain ULiege; Batelaan, Okke; Anceau, Annick ULiege

in Ground Water (2021), 59(5), 772-779

To our current knowledge, the first piezometric map ever published in the world is the map of Gustave Dumont in February 1856. Gustave Dumont (1821-1891) was a cousin of André Dumont (1809-1857) that had ... [more ▼]

To our current knowledge, the first piezometric map ever published in the world is the map of Gustave Dumont in February 1856. Gustave Dumont (1821-1891) was a cousin of André Dumont (1809-1857) that had published five years before (1851) an excellent note about the application of the geological regional knowledge for groundwater exploration in the chalk Hesbaye aquifer of the Geer basin near the city of Liège in Belgium. This piezometric map is included in a comprehensive report ordered by the city of Liège in 1855 to increase drinking water production with a large extension of drainage galleries in this aquifer. At that time, a long tradition of underground coal mining activities in Southern Belgium has led to new advances in practical hydrogeology. Dewatering techniques were developed actively as the mines were going deeper and deeper. This is also a perfect illustration of the early fruitful collaboration between engineers and geologists. André Dumont (1809-1857) was the most famous Belgian geologist of that period. Gustave Dumont was a mining engineer with experience in hydraulic problems. He received the task in 1855 to study the feasibility and impact of a new network of drainage galleries to improve the water supply of Liège. The official report is delivered and published in February 1856 (Dumont 1856) including the first piezometric map entitled: ‘carte hydrographique de la Hesbaye aux environs de Liége’ (in French). This map shows piezometric contours for every meter described as ‘the intersection between the underground water surface with horizontal planes’ (literal translation from French). This work could be considered as a start for the 'Liege School of Hydrogeology'. [less ▲]

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See detailLand subsidence observed in the Merchtem area (Flanders) – 30 years of SAR data associated to groundwater withdrawal?
Choopani, Atefe; Declercq, Pierre-Yves; Dassargues, Alain ULiege et al

in IGARSS2021 Proceedings (2021, July 12)

A land subsidence affecting several towns at the joining limits of the Belgian Provinces of East Flanders, Antwerp and Flemish Brabant is followed during the last three decades. ERS 1-2, ENVISAT, TerraSAR ... [more ▼]

A land subsidence affecting several towns at the joining limits of the Belgian Provinces of East Flanders, Antwerp and Flemish Brabant is followed during the last three decades. ERS 1-2, ENVISAT, TerraSAR-X and Sentinel 1A satellites SAR scenes were processed from 1992 till October 2020 to map the land subsidence evolution. The subsidence corresponds to a surface area of 220 km² during the ERS1/2 time interval distributed over three distinct subsidence bowls. During the ENVISAT and TerraSAR-X time interval, only one residual subsidence bowl was mapped affecting a surface area of about 70 km². Several towns (Londerzeel and Steenhuffel) remained in the center of the subsidence bowl. The annual average negative velocity values range between -5.99 and -0.5 mm/year. More recently, during the Sentinel 1A period, the subsidence bowl has lost half of its surface reaching 36 km². The velocity values have also decreased during the period 2016-2020. [less ▲]

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See detailAreas prone to land subsidence and their evolutions in Belgium during the last 30 years
Declercq, Pierre-Yves; Choopani, Atefe; Dassargues, Alain ULiege et al

in IGARSS2021 Proceedings (2021, July 12)

PSInSAR analyses across Belgium using ERS 1-2, ENVISAT, TerraSAR-X, and Sentinel 1 allowed to follow several ground movements areas during the last three decades. Several areas of regional importance are ... [more ▼]

PSInSAR analyses across Belgium using ERS 1-2, ENVISAT, TerraSAR-X, and Sentinel 1 allowed to follow several ground movements areas during the last three decades. Several areas of regional importance are affected by land subsidence processes that have been observed during this period (i.e. the alluvial plain of the Schelde estuary in Antwerpen, a large area in the West Flanders province, and one around Merchtem area). Other land subsidence areas associated with old coal mining both in Flanders (Campine basin) and Wallonia (Hainaut and Liège province) are affected by progressive uplifting conditions linked to the mining aquifer piezometric rebound. It is extremely important to follow the spatio-temporal behavior of these phenomena to forecast their influences and their effects on the urban developments. [less ▲]

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