References of "Dassargues, Alain"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailMeasured and computed solute transport behaviour in the saturated zone of a fractured and slightly karstified chalk aquifer
Dassargues, Alain ULg; Goderniaux, Pascal ULg; Daoudi, Moubarak et al

in Bertrand, C.; Carry, N.; Mudry, J. (Eds.) et al Proc. H2Karst, 9th Conference on Limestone Hydrogeology (2011, September)

Solute transport in the saturated zone of a micro-fissured, fractured and even locally slightly karstified aquifer has been studied by multi-tracer tests in groundwater convergent flow conditions to ... [more ▼]

Solute transport in the saturated zone of a micro-fissured, fractured and even locally slightly karstified aquifer has been studied by multi-tracer tests in groundwater convergent flow conditions to pumping wells or towards a collecting gallery. Different behaviour has been detected that can be described by three kinds of typical breakthrough curves: (a) transport with a dominant advective component, producing narrow and symmetrical observed breakthrough curves, characteristic of solute transport in open fractures or conduits; (b) transport with significant advective and dispersive components exhibiting more spread-out breakthrough curves, with also non-symmetrical trends caused by retardation effects; (c) transport with a dominant dispersive component, showing mostly a flat breakthrough curve where dispersion and possible immobile water effects are difficult to be separated. These results were synthesized from thirty-five injections of tracers, distributed between 11 sites. Groundwater flow and solute transport are simulated and illustrated here for one example, employing the finite element code HYDROGEOSPHERE, and using two ways for representing the fracture zones: highly contrasting hydraulic conductivity zones with a classical REV approach and discrete fractures combined with a porous medium by the use of a dual approach. Results are particularly illustrative to show that detailed parameterization and calibration of such a local situation remain difficult even on the basis of an extensive data sets from many tracer tests. [less ▲]

Detailed reference viewed: 58 (12 ULg)
See detailRegional scale groundwater flow and transport modelling: from conceptual challenges to pragmatic numerical solutions
Wildemeersch, Samuel ULg; Goderniaux, Pascal ULg; Leroy, Mathieu et al

Conference (2011, July 05)

National and international regulations require the management of groundwater resources at the regional scale, considering the physical limits of hydrogeological systems. Physically-based, spatially ... [more ▼]

National and international regulations require the management of groundwater resources at the regional scale, considering the physical limits of hydrogeological systems. Physically-based, spatially-distributed groundwater flow and transport models allow representing in a realistic and reliable way the dynamics of regional groundwater systems and processes and accounting for negative or positive feedbacks induced by a changed stress factors or particular measures set up in the basin such as increase in pumping, use of fertilizers or artificial recharge. Such models are complex and their development and implementation are challenging for several reasons related to numerical difficulties but also to data acquisition and management, conceptualization, calibration and validation. Variably-saturated, regional flow and transport models have been developed using two finite element simulators SUFT3D and HydroGeoSphere specifically suited to regional-scale applications. A complex synthetic case has been used as a reference model to test the impact on predictions made and computing times of various conceptual and technical choices such as spatial and time discretization, simplified unsaturated laws or boundary conditions. Real cases have been developed for regional groundwater bodies (from 500 to 1700 km²) to deliver relevant information such as the estimation and evolution with time of groundwater reserves, under different stress conditions such as climate changes and for the evaluation of regional groundwater quality status and nitrate trend assessment under alternative management scenarios and mitigation measures. Results provide guidelines for the conceptualisation, the calibration and the use of regional-scale groundwater flow and transport models for decision making. [less ▲]

Detailed reference viewed: 39 (14 ULg)
Full Text
Peer Reviewed
See detailUncertainty of climate change impact on groundwater resources considering various uncertainty sources
Goderniaux, Pascal ULg; Brouyère, Serge ULg; Orban, Philippe ULg et al

in Abesser, C.; Nutzmann, G.; Hill, M. (Eds.) et al Conceptual and Modelling Studies of Integrated Groundwater, Surface Water, and Ecological Systems (2011, July)

Many studies have highlighted that climate change will have a negative impact on groundwater. However, in previous studies, the estimation of uncertainty around projections was very limited. In this study ... [more ▼]

Many studies have highlighted that climate change will have a negative impact on groundwater. However, in previous studies, the estimation of uncertainty around projections was very limited. In this study, the impact of climate change on groundwater resources is estimated for the Geer basin using a surface–subsurface integrated model. The uncertainties around impact projections are evaluated from three different sources. The uncertainty linked to the climate model is assessed with six contrasted RCMs and two GCMs. The uncertainty linked to the natural variability of the weather is evaluated thanks to a weather generator which enables production of a large number of equiprobable climatic scenarios. The uncertainty linked to the calibration of the hydrological model is assessed by a coupling with UCODE_2005 and by performing a complete linear uncertainty analysis on predictions. A linear analysis is approximate for this nonlinear system, but provides some measure of uncertainty for this computationally demanding model. Results for this study show that the uncertainty linked to the hydrological model is the most important. [less ▲]

Detailed reference viewed: 74 (19 ULg)
Full Text
Peer Reviewed
See detailDirect multiple-point geostatistical simulation of edge properties for modeling thin irregularly-shaped surfaces
Huysmans, Marijke; Dassargues, Alain ULg

in Mathematical Geosciences (2011), 43

Thin irregularly-shaped surfaces such as clay drapes often have a major control on flow and transport in heterogeneous porous media. Clay drapes are often complex curvilinear 3-dimensional surfaces and ... [more ▼]

Thin irregularly-shaped surfaces such as clay drapes often have a major control on flow and transport in heterogeneous porous media. Clay drapes are often complex curvilinear 3-dimensional surfaces and display a very complex spatial distribution. Variogram-based stochastic approaches are often also not able to describe the spatial distribution of clay drapes since complex, curvilinear, continuous and interconnected structures cannot be characterized using only two-point statistics. Multiple-point geostatistics aims to overcome the limitations of the variogram. The premise of multiple-point geostatistics is to move beyond two-point correlations between variables and to obtain (cross) correlation moments at three or more locations at a time using "training images" to characterize the patterns of geological heterogeneity. Multiple-point geostatistics can reproduce thin irregularly-shaped surfaces such as clay drapes but is often computationally very intensive. This paper describes and applies a methodology to simulate thin irregularly-shaped surfaces with a smaller CPU and RAM demand than the conventional multiple-point statistical methods. The proposed method uses edge properties for indicating the presence of thin irregularly-shaped surfaces. This method allows directly simulating edge properties instead of pixel properties to make it possible to perform multiple-point geostatistical simulations with a larger cell size and thus a smaller computation time and memory demand. [less ▲]

Detailed reference viewed: 37 (7 ULg)
Full Text
See detailSite-specific soil classification from cone penetration tests and borehole data: a multivariate statistical analysis
Rogiers, Bart; Mallants, Dirk; Batelaan, Okke et al

in NovCare 2011 edition:2 (2011, May 11)

Groundwater flow and contaminant transport models are influenced by different kinds of uncertainty, including spatial variability in aquifer and aquitard properties. Appropriate models are developed to ... [more ▼]

Groundwater flow and contaminant transport models are influenced by different kinds of uncertainty, including spatial variability in aquifer and aquitard properties. Appropriate models are developed to support decision making related to environmental impact assessment for waste disposal sites or to develop cost-effective groundwater remediation. These modelling tools are required to incorporate spatial variability as observed at different scales. Several studies have investigated correlations between geotechnical data, e.g. cone penetration tests (CPT) results, and hydrogeological parameters such as hydraulic conductivity (K). However, very few studies have used geotechnical data in groundwater flow models, although gathering of such information is usually much easier and cheaper compared to expensive drilling and pumping test campaigns. It is however generally known that CPT soil behaviour type (SBT) classifications are only indicative, and parameters attributed to these SBTs should therefore be treated with caution. Moreover, since most parameters of interest in groundwater flow modeling do not share a one-to-one relationship with the standard CPT parameters, the assessment of the uncertainty related to this relationship is of great importance in stochastic modeling. Since a unique data set is available for the nuclear zone of Mol/Dessel (Belgium) different approaches to describe the spatial variability in flow and transport parameters can be tested. A detailed hydrogeological characterization reaching depths of 40 to 50 m (including Quaternary and Neogene formations) has been carried out in 2008-2009 coordinated by ONDRAF/NIRAS (Belgian Agency for Radioactive Waste and Enriched Fissile Materials) in the frame of a surface disposal project for low and intermediate short-lived radioactive waste. A large amount of quantitative and semi-quantitative information has been collected in an area of 60 km², including borehole logs, more than 200 CPTs, and roughly 340 K measurements on undisturbed cores. This study uses exploratory cluster analysis to classify this multivariate dataset into different groups. This is achieved with k-means clustering, minimizing the within-group variance. The resulting classes are then interpreted with respect to the site-specific lithotypes using factor analysis. Next, a simplified classification is derived, as it is not possible to distinguish between some groups solely based on CPT data. The resulting classification is compared with literature SBT classifications in relation to the mean and variance of groundwater flow and physical/chemical parameters within each class. Both classifications are also compared in their ability to identify the local litho- and hydro-stratigraphy. Hydraulic conductivity values derived from pore pressure dissipation tests are compared with estimations obtained from SBT classifications. A final discussion is devoted to the integral scales of the corresponding indicator fields of soil classes and how these differ between the different classification schemes. [less ▲]

Detailed reference viewed: 12 (1 ULg)
Full Text
See detailRegional scale flow and transport modelling for the management of groundwater and surface water bodies in the framework of the EU Water Directive
Leroy, Mathieu; Orban, Philippe ULg; Brouyère, Serge ULg et al

Conference (2011, May 02)

The Water Framework Directive requires from EU member states to manage water resources at the scale of surface water and groundwater bodies in a sustainable way, without altering the different functions ... [more ▼]

The Water Framework Directive requires from EU member states to manage water resources at the scale of surface water and groundwater bodies in a sustainable way, without altering the different functions provided by the system in natural conditions. Efficient management also requires qualitative tools to assess the evolution of water quality regarding the activities performed in the area of interest. In this context, the objective is to discuss the needs in terms of groundwater flow and transport modelling as a support to the Water Framework Directive and to present a methodological and numerical approach that fits with these requirements. Different variably-saturated models have been implemented for selected case studies ranging between 500 and 1700 km² in the Walloon Region of Belgium. The implementation of such models is challenging because of the scale and the processes that have to be simulated. However, when calibrated and used adequately, they are able to deliver most information required, such as the estimation and evolution with time of groundwater reserves, the calculation of different indicators on groundwater replenishment and exploitation, the base flow to rivers and surface water bodies, under different stress conditions such as pumping, rainfall and climate change. They are also used for the evaluation of regional groundwater quality status and for contaminant trend assessment (e.g. nitrate) under different alternative management scenarios and mitigation measures that could be implemented in the future. This study illustrates perfectly the efficiency and usefulness of regional scale groundwater flow and transport modelling as a tool for the management of groundwater bodies. [less ▲]

Detailed reference viewed: 81 (39 ULg)
Full Text
See detailUse of environmental isotopes to infer flow in the highly exploited aquifer system of the Diass region (Senegal)
Madioune, Diakher Hélène; Faye, Serigne; Dassargues, Alain ULg et al

Poster (2011, March 14)

The Diass horst multilayered aquifer constitutes a complex hydrogeological system. But stable isotopes are illustrated to be powerful tools for clarifying the origin of recharge water, and the groundwater ... [more ▼]

The Diass horst multilayered aquifer constitutes a complex hydrogeological system. But stable isotopes are illustrated to be powerful tools for clarifying the origin of recharge water, and the groundwater dynamics due to high exploitation of the system. Used with 3H and 14C, data confirms that most of the investigated groundwater are palaeowaters. Pumping has an impact on groundwater flow evidenced by the different water isotope compositions that illustrates the transient conditions of the system. Mixing of old waters and recently recharged (tritiated) waters occurs in some exploited boreholes, indicates lateral flow to the pumping field through the main groundwater flow directions. [less ▲]

Detailed reference viewed: 17 (1 ULg)
See detailCarte hydrogéologique de Wallonie, Huy - Nandrin 48/3-4, 1/25.000 : [notice explicative]
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Book published by Service Public de Wallonie, DGARNE - Actualisation partielle : mars 2011 - Première édition : août 2005 (2011)

Detailed reference viewed: 22 (4 ULg)
Full Text
Peer Reviewed
See detailA regional flux-based risk assessment approach of contaminated sites on groundwater bodies
Brouyère, Serge ULg; Jamin, Pierre ULg; Dollé, Fabien ULg et al

in Schirmer, Mario; Hoehn, Eduard; Vogt, Tobias (Eds.) Groundwater Quality 2010 : Groundwater Quality Management in a Rapidly Changing World (2011)

In the context of the Water Framework Directive, management plans have to be set up about water quality issues in surface and ground water bodies in the EU. In heavily industrialised and urbanised areas ... [more ▼]

In the context of the Water Framework Directive, management plans have to be set up about water quality issues in surface and ground water bodies in the EU. In heavily industrialised and urbanised areas, the cumulative effect of multiple contaminant sources is likely to present a risk which has to be evaluated. In order to propose adequate measures, the calculated risk should be based on criteria reflecting the risk of water quality deterioration, in a cumulative way and at the scale of the whole surface water or groundwater body. An integrated GIS- and flux-based risk assessment approach for groundwater and surface water bodies is described with a regional scale indicator for the evaluation of the quality status of the groundwater body. It is based on the SEQ-ESO currently used in the Walloon Region of Belgium which defines, for different water uses and for a detailed list of groundwater contaminants, a set of threshold values reflecting the levels of water quality and degradation with respect to each contaminant. The methodology is illustrated with a first real scale application on a groundwater body corresponding to a contaminated alluvial aquifer which has been classified at risk of not reaching a good quality status by 2015. [less ▲]

Detailed reference viewed: 136 (33 ULg)
Full Text
See detailChapter 4.8 Hydrogeological study of Somes-Szamos transboundary alluvial aquifer
Drobot, Radu; Szucs, Peter; Brouyère, Serge ULg et al

in Ganoulis, Jacques; Aureli, Alice; Fried, Jean (Eds.) Transboundary Water Resources Management: A Multidisciplinary Approach (2011)

Detailed reference viewed: 14 (2 ULg)
Full Text
See detailHydrogéologie du bassin du Samson
Gesels, Julie ULg; Goderniaux, Pascal ULg; Jamin, Pierre ULg et al

in Michel, Georges; Thys, Georges; De Broyer, Claude (Eds.) Atlas du Karst Wallon. Bassins du Bocq et du Samson (2011)

Ce chapitre décrit l'hydrogéologie du bassin du Samsonvdans la partie "articles thématiques" de l'Atlas du karst consacré aux bassins du Bocq et du Samson. Après une description générale, la nature et les ... [more ▼]

Ce chapitre décrit l'hydrogéologie du bassin du Samsonvdans la partie "articles thématiques" de l'Atlas du karst consacré aux bassins du Bocq et du Samson. Après une description générale, la nature et les potentialités aquifères du bassin du Samson sont abordées : les unités hydrogéologiques sont décrites, des aspects quantitatifs et des bilans hydrogéologiques sont détaillés et des aspects qualitatifs sont développés. [less ▲]

Detailed reference viewed: 47 (19 ULg)
Full Text
Peer Reviewed
See detailNumerical simulation of heat transfer associated with low enthalpy geothermal pumping in an alluvial aquifer
Fossoul, Frédérique ULg; Orban, Philippe ULg; Dassargues, Alain ULg

in Geologica Belgica (2011), 14(1-2),

In a context favourable to renewable energies, various aquifers are studied to supply heating and/or cooling systems. The groundwater flow and heat transport are modelled in the alluvial aquifer of the ... [more ▼]

In a context favourable to renewable energies, various aquifers are studied to supply heating and/or cooling systems. The groundwater flow and heat transport are modelled in the alluvial aquifer of the river Meuse in providing an integrated tool for assessing the feasibility of a low energy air cooling/heating system for a large office building by pumping groundwater and discharging it in the river after being heated/cooled by using heat pumps. First, a comparative sensitivity analysis is performed using different codes for assessing the influence of coupling and non linearities on the main parameters due to the temperature evolution in function of time. Then, assuming that the aquifer temperature variation is weak enough to neglect its influence on hydrodynamics and thermal parameters, the MT3DMS and HydroGeoSphere codes are used for modelling the actual case-study. In practice, the worst case scenario considered by the project manager is the cooling of the office building during the hottest summer conditions. So, the influence of the warm water from the river Meuse is computed as it constitutes the major limiting factor. An optimisation of the pumping schema is computed to maximise the efficiency of the system. [less ▲]

Detailed reference viewed: 136 (24 ULg)
See detailCarte hydrogéologique de Wallonie, Jehay-Bodegnée - Saint-Georges 41/7-8, 1/25.000 : [notice explicative]
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Book published by Service Public de Wallonie, DGARNE - Actualisation partielle : décembre 2010 - Première édition : mai 2003 (2010)

Detailed reference viewed: 16 (0 ULg)
Full Text
Peer Reviewed
See detailApplication of a multi-model approach to account for conceptual model and scenario uncertainties in groundwater modelling
Rojas, Rodriguo; Kahunde, Samalie; Peeters, Luk et al

in Journal of Hydrology (2010), 394(3-4), 416-435

Groundwater models are often used to predict the future behaviour of groundwater systems. These models may vary in complexity from simplified system conceptualizations to more intricate versions. It has ... [more ▼]

Groundwater models are often used to predict the future behaviour of groundwater systems. These models may vary in complexity from simplified system conceptualizations to more intricate versions. It has been recently suggested that uncertainties in model predictions are largely dominated by uncertainties arising from the definition of alternative conceptual models. Different external factors such as climatic conditions or groundwater abstraction policies, on the other hand, may also play an important role. Rojas et al. (2008) proposed a multimodel approach to account for predictive uncertainty arising from forcing data (inputs), parameters and alternative conceptualizations. In this work we extend upon this approach to include uncertainties arising from the definition of alternative future scenarios and we apply the extended methodology to a real aquifer system underlying the Walenbos Nature Reserve area in Belgium. Three alternative conceptual models comprising different levels of geological knowledge are considered. Additionally, three recharge settings (scenarios) are proposed to evaluate recharge uncertainties. A joint estimation of the predictive uncertainty including parameter, conceptual model and scenario uncertainties is estimated for groundwater budget terms. Finally, results obtained using the improved approach are compared with the results obtained from methodologies that include a calibration step and which use a model selection criterion to discriminate between alternative conceptualizations. Results showed that conceptual model and scenario uncertainties significantly contribute to the predictive variance for some budget terms. Besides, conceptual model uncertainties played an important role even for the case when a model was preferred over the others. Predictive distributions showed to be considerably different in shape, central moment and spread among alternative conceptualizations and scenarios analysed. This reaffirms the idea that relying on a single conceptual model driven by a particular scenario, will likely produce bias and under-dispersive estimations of the predictive uncertainty. Multimodel methodologies based on the use of model selection criteria produced ambiguous results. In the frame of a multimodel approach, these inconsistencies are critical and can not be neglected. These results strongly advocate the idea of addressing conceptual model uncertainty in groundwater modelling practice. Additionally, considering alternative future recharge uncertainties will permit to obtain more realistic and, possibly, more reliable estimations of the predictive uncertainty. [less ▲]

Detailed reference viewed: 56 (9 ULg)