References of "Dassargues, Alain"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailA regional flux-based risk assessment approach for multiple contaminated sites on groundwater bodies
Jamin, Pierre ULg; Dollé, Fabien ULg; Chisala, Brenda et al

in Journal of Contaminant Hydrology (2012), 127(1-4), 65-75

In the context of the Water Framework Directive (EP and CEU, 2000), management plans have to be set up to monitor and to maintain water quality in groundwater bodies in the EU. In heavily industrialized ... [more ▼]

In the context of the Water Framework Directive (EP and CEU, 2000), management plans have to be set up to monitor and to maintain water quality in groundwater bodies in the EU. In heavily industrialized and urbanized areas, the cumulative effect of multiple contaminant sources is likely and has to be evaluated. In order to propose adequate measures, the calculated risk should be based on criteria reflecting the risk of groundwater quality deterioration, in a cumulative manner and at the scale of the entire groundwater body. An integrated GIS- and flux-based risk assessment approach for groundwater bodies is described, with a regional scale indicator for evaluating 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 first results at a regional scale on a groundwater body-scale application to a contaminated alluvial aquifer which has been classified to be at risk of not reaching a good quality status by 2015. These first results show that contaminants resulting from old industrial activities in that area are likely to contribute significantly to the degradation of groundwater quality. However, further investigations are required on the evaluation of the actual polluting pressures before any definitive conclusion be established. [less ▲]

Detailed reference viewed: 88 (34 ULg)
Full Text
See detailFlux-based Risk Assessement of the impact of Contaminants on Water resources and ECOsystems
Jamin, Pierre ULg; Dujardin, Juliette; Crèvecoeur, Sophie et al

Report (2012)

Detailed reference viewed: 36 (7 ULg)
See detailFlux-based risk assessment of the impact of contamnants on water ressources and ecosystems - FRAC-WECO.
Jamin, Pierre ULg; Dujardin, J.; Crévecoeur, Sophie et al

Report (2012)

Detailed reference viewed: 41 (5 ULg)
Full Text
Peer Reviewed
See detailModeling climate change impacts on groundwater resources using transient stochastic climatic scenarios
Goderniaux, Pascal ULg; Brouyère, Serge ULg; Blenkinsop, Stephen et al

in Water Resources Research (2011), 47

Several studies have highlighted the potential negative impact of climate change on groundwater reserves but additional work is required to help water managers to plan for future changes. In particular ... [more ▼]

Several studies have highlighted the potential negative impact of climate change on groundwater reserves but additional work is required to help water managers to plan for future changes. In particular, existing studies provide projections for a stationary climate representative of the end of the century, although information is demanded for the near-future. Such time-slice experiments fail to account for the transient nature of climatic changes over the century. Moreover, uncertainty linked to natural climate variability is not explicitly considered in previous studies. In this study, we substantially improve upon the state-of-the-art by using a sophisticated transient weather generator (WG) in combination with an integrated surface-subsurface hydrological model (Geer basin, Belgium) developed with the finite element modelling software 'HydroGeoSphere'. This version of the WG enables the stochastic generation of large numbers of equiprobable climatic time series, representing transient climate change, and used to assess impacts in a probabilistic way. For the Geer basin, 30 equiprobable climate change scenarios from 2010 to 2085 have been generated for each of 6 different RCMs. Results show that although the 95% confidence intervals calculated around projected groundwater levels remain large, the climate change signal becomes stronger than that of natural climate variability by 2085. Additionally, the WG ability to simulate transient climate change enabled the assessment of the likely timescale and associated uncertainty of a specific impact, providing managers with additional information when planning further investment. This methodology constitutes a real improvement in the field of groundwater projections under climate change conditions. [less ▲]

Detailed reference viewed: 74 (20 ULg)
Full Text
Peer Reviewed
See detailThe Hybrid Finite-Element Mixing-Cell method: a candidate for modelling groundwater flow and transport in karst systems
Brouyère, Serge ULg; Wildemeersch, Samuel ULg; Orban, Philippe ULg et al

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

Groundwater flow and contaminant transport modelling in karst systems remains a challenge because of the complexity of the geology made of caves, voids, conduits of various sizes and forms and interacting ... [more ▼]

Groundwater flow and contaminant transport modelling in karst systems remains a challenge because of the complexity of the geology made of caves, voids, conduits of various sizes and forms and interacting matrix. Such heterogeneous structures cause complex hydraulic conditions for groundwater flow and transport processes. Despite the progresses in field investigation techniques and experiments, detailed knowledge and characterization of the karst system geometry and connectivity remains inaccessible and pragmatic modelling approaches have to be used. Groundwater models of different complexities have been developed for karst systems, ranging from transfer functions and linear reservoir models to spatially distributed models. Here, a new flexible modelling approach, the Hybrid Finite-Element Mixing-Cell method (HFEMC), has been developed that allows combining in a single model, and in a fully interacting way, different mathematical approaches of various complexities for groundwater modelling in complex environments. This includes linear reservoirs, distributed reservoirs, groundwater flow in variably saturated equivalent porous media, with possibilities to consider by-pass flows along preferential flow paths, internal boundary conditions between the karstic features and the surrounding rock mass matrix background and drainage by surface waters. This method has been implemented in the groundwater flow and solute transport numerical code SUFT3D. The objective of this communication is to present the modelling concepts and to discuss the potentials and advantages of the HFEMC method for modelling groundwater flow in karst systems over existing more classical modelling approaches. The discussion is supported by illustrative “synthetic” examples representative of karst systems and a real modelling application to the case of groundwater rebound and water inrush in a closed underground coal mine which presents a very similar geometrical and hydrological context to a karst, with cavities, drains and interacting rock mass. [less ▲]

Detailed reference viewed: 47 (13 ULg)
See detailAssessing the impacts of technical uncertainty on coupled surface/subsurface flow model predictions using a complex synthetic case
Wildemeersch, Samuel ULg; Goderniaux, Pascal ULg; Orban, Philippe ULg et al

Poster (2011, September)

According to the EU Water Framework Directive, Member States have to manage surface water and groundwater at the water body scale and in an integrated way. Flow and transport models constitute useful ... [more ▼]

According to the EU Water Framework Directive, Member States have to manage surface water and groundwater at the water body scale and in an integrated way. Flow and transport models constitute useful management tools in this context since they can predict system responses to future stresses. However, numerical modelling at such a scale faces specific issues linked to (1) the representation of the geological and hydrogeological complexity, (2) the uneven level of characterisation knowledge, (3) the representativity of measured parameters and variables in the field, and (4) the CPU time needed for solving the numerical problem. Assumptions and simplifications made for dealing with these issues can lead to a series of models differing by their complexity and by the reliability of their predictions. Consequently, modellers have to find a compromise between complexity and reliability. The main objective of this research is to estimate the impacts of technical uncertainty, which is the uncertainty related to the numerical implementation, on groundwater flow model predictions. To reach that objective, the methodology consists in comparing reference predictions (hydraulic heads and flow rates) of a complex and close to reality synthetic case with the predictions provided by a series of simplified models (coarse spatial discretisation, coarse time discretisation, simplified law in the unsaturated zone). The synthetic case reflects the main characteristics found in groundwater bodies of South Belgium (Condroz region of Wallonia), characterised by a succession of limestone synclines and sandstone anticlines. The numerical model is developed with the fully-integrated surface/subsurface flow and transport code HydroGeoSphere using a mesh refined along the surface water network (153027 nodes and 269872 elements). A 5-year reference transient simulation, with daily stress factors is performed. The simulated hydraulic heads and flow rates constitute the reference observations and predictions for the comparison with the simplified models. The simplified models tested differ by their horizontal (500 m vs. 1000 m element size) and vertical (8 layers vs. 3 layers) spatial discretisations, their time discretisation (daily vs. monthly stress factors), and the type of constitutive law used for simulating the unsaturated flow (linear vs. van Genuchten). The models are run with the same parameter values than those used in the reference model to evaluate the deterioration in model predictions due to technical uncertainty. Additionally, some of the models are calibrated with the inverse modelling code PEST to distinguish how far a model calibration can possibly compensate for technical uncertainty. Then, predictions from each simplified model are compared with the reference predictions of the synthetic case. Then, the simplified models are ranked using several model performance criteria. Results of this research provide guidelines for the numerical implementation of groundwater flow models at the water body scale with respect to specific groundwater management objectives. [less ▲]

Detailed reference viewed: 39 (14 ULg)
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: 61 (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: 41 (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: 78 (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: 39 (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: 16 (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: 83 (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: 21 (1 ULg)