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See detailThe Hybrid Finite-Element Mixing-Cell method: a new flexible method for large scale groundwater modelling
Orban, Philippe ULg; Brouyère, Serge ULg; Wildemeersch, Samuel ULg et al

Conference (2008)

Interest of end-users and policy makers for understanding and managing water systems at the regional scale has increased for years. At this scale, groundwater models of different complexity ranging from ... [more ▼]

Interest of end-users and policy makers for understanding and managing water systems at the regional scale has increased for years. At this scale, groundwater models of different complexity ranging from black-box models to physically based distributed models have been used in various hydrogeological conditions. Black-box models, such as transfer functions, have been applied for example to model groundwater in large scale hydrological models, to model karstic systems, in particular for the interpretation of isotopic data. Their concepts are simple and attractive because they require relatively few data. The main drawbacks are however that modelling results are not spatially distributed and their predictive capability is questionable due to the semi-empirical nature of process descriptions. On the contrary, due to a more advanced description of ongoing processes, physically-based distributed models are expected to have better predictive capabilities than black-box models. However, because such models require more data, they are generally applied for case studies that are better characterized from a hydrogeological point of view, for which the distribution of water levels or solute concentrations in the groundwater systems are needed. For large-scale modelling purposes, black-box models and physically-based distributed models have both proved their utilities and have their own justifications, advantages and disadvantages. However, few attempts have been made to combine the advantages of these two categories of approaches in a unified modelling application. 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 integrated way, different mathematical approaches of various complexities for groundwater modelling in complex and large scale environments. This method has been implemented in the groundwater flow and solute transport numerical code SUFT3D. The approach has been first tested and illustrated using basic and advanced “synthetic” examples that allow validating and discussing its advantages over existing modelling concepts. The HFEMC approach is now applied for the development of a large scale groundwater flow and solute transport model in different groundwater basins in Belgium. [less ▲]

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See detailThe Hybrid Finite-Element Mixing-Cell method: a new flexible method for modelling mine water problems
Brouyère, Serge ULg; Orban, Philippe ULg; Wildemeersch, Samuel ULg et al

in Rapantova, N.; Hrkal, Z. (Eds.) Mine Water and the Environment Proceedings of IWMA 2008 (2008)

Mine closure is often accompanied by a stop in dewatering operations. This generally induces groundwater rebound in the mined rock system with short and long term consequences that may be disastrous: soil ... [more ▼]

Mine closure is often accompanied by a stop in dewatering operations. This generally induces groundwater rebound in the mined rock system with short and long term consequences that may be disastrous: soil instabilities such as landslides and subsidence reactivation, flooding, flooded basement and acid mine drainage. Modelling tools can be very advantageous and efficient in helping understanding and managing such problems, however, classical modelling approaches have proved to be relatively unsuited to such contexts. Because of the former mining operations, the underground geological system is strongly disturbed (excavated, fractured and collapsed zones, galleries, large shafts, etc.). Using complex spatially distributed modelling approaches such as 3D finite elements usually lead to strong difficulties related to the lack of data, the complexity of geological and hydrogeological conditions (complex geometry, non Darcian fluxes…). On the other hand, using a simplified approach such as black-box models often leads to oversimplification of the reality: particularly when interactions between the mined system and its surrounding geological and hydrogeological environment are very important. A new modelling approach is developed for simulation of the groundwater flow in such complex environments. It combines, in a single fully integrated simulator, a representation of the unmined area by a classical finite element modelling technique, together with conceptualisation of the worked areas and galleries by a group of mixing cells connected by pipes. The whole assembled groundwater flow model allows an accurate estimation and representation of (a) water infiltration (precipitations, river losses …) through the unsaturated zone reaching the exploited area (recharge of boxes) and (b) water exchanges with adjacent aquifers. The model can estimate the flow of groundwater in and around the minefield and the mean water level in the boxes. It is also capable of considering water exchanges between different mined zones, through connection pathways such as old roadways galleries and shafts. Modelling concepts and equations are described and illustrated using basic and advances validation examples. A real case application corresponding to an abandoned coalfield in the region of Liège (Belgium) is used to illustrate the suitability and efficiency of the approach. [less ▲]

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See detailGroundwater vulnerability assessment using physically based modelling: from challenges to pragmatic solutions
Popescu, Ileana Cristina; Gardin, Nicolas; Brouyère, Serge ULg et al

in Refsgaard, J. C.; Kovar, K.; Haarder, E. (Eds.) et al Calibration and Reliability in Groundwater Modelling: Credibility in Modelling (2008)

Numerous groundwater vulnerability and risk mapping techniques have been developed taking into consideration a variable number of factors. The most common techniques are based on calculation of an index ... [more ▼]

Numerous groundwater vulnerability and risk mapping techniques have been developed taking into consideration a variable number of factors. The most common techniques are based on calculation of an index expressing the protective effect of underground formations overlying the groundwater resource. The limitation of most of these methods is related to their use of a qualitative definition of groundwater vulnerability, as opposed to a definition based on a quantitative description of contaminant migration. A physically-based point of view and definition of the vulnerability is proposed and based on three factors describing a pollution event, which are the contaminant transfer time from the hazard location to the 'target', the contamination duration at the 'target' and the level of contaminant concentration reached at the 'target'. This concept allows a clear distinction between conventional aspects and physically-based results in the building of a final vulnerability indicator. This methodology has the further advantage to consider the possible impact of runoff conditions occurring at the land surface and possibly leading to lateral contamination of groundwater through downstream preferential infiltration features. Practically, this method needs to describe and simulate the pollutant migration in the unsaturated zone and possibly in the saturated zone in order to assess the breakthrough curve at the 'target'. Preliminary application is illustrated on a case-study located in a limestone basin in Belgium. Perspectives are proposed towards a generalisation of the vulnerability concept for risk assessment within a pressure - state - impact framework. [less ▲]

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See detailConceptual model uncertainty in groundwater modeling: Combining generalized likelihood uncertainty estimation and Bayesian model averaging
Rojas, Rodrigo; Feyen, Luc; Dassargues, Alain ULg

in Water Resources Research (2008), 44

Uncertainty assessments in groundwater modeling applications typically attribute all sources of uncertainty to errors in parameters and inputs, neglecting what may be the primary source of uncertainty ... [more ▼]

Uncertainty assessments in groundwater modeling applications typically attribute all sources of uncertainty to errors in parameters and inputs, neglecting what may be the primary source of uncertainty, namely, errors in the conceptualization of the system.Confining the set of plausible system representations to a single model leads to underdispersive and prone-to-bias predictions. In this work, we present a general and flexible approach that combines generalized likelihood uncertainty estimation (GLUE) and Bayesian model averaging (BMA) to assess uncertainty in model predictions that arise from errors in model structure, inputs, and parameters. In a prior analysis, a set of plausible models is selected, and the joint prior input and parameter space is sampled to form potential simulators of the system. For each model, the likelihood measures of acceptable simulators, assigned to thembased on their ability to reproduce observed systembehavior, are integrated over the joint input and parameter space to obtain the integrated model likelihood. The latter is used to weight the predictions of the respective model in the BMA ensemble predictions. For illustrative purposes, we applied the methodology to a three-dimensional hypothetical setup. Results showed that predictions of groundwater budget terms varied considerably among competing models; despite this, a set of 16 head observations used for conditioning did not allow differentiating between the models. BMA provided average predictions that were more conservative than individual predictions obtained for individual models. Conceptual model uncertainty contributed up to 30% of the total uncertainty. The results clearly indicate the need to consider alternative conceptualizations to account for model uncertainty. [less ▲]

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See detailSmall-scale sedimentary structures and permeability in a cross-bedded aquifer
Huysmans, Marijke; Peeters, Luk; Moermans, Gert et al

in Journal of Hydrology (2008), (361), 41-51

The objective of this study is to investigate the relation between small-scale sedimentary structures and permeability in the Brussels Sands formation, an early Middle-Eocene shallow marine sand deposit ... [more ▼]

The objective of this study is to investigate the relation between small-scale sedimentary structures and permeability in the Brussels Sands formation, an early Middle-Eocene shallow marine sand deposit in Central Belgium that constitutes a major groundwater source in the region. A field campaign was carried out consisting of field observations of the sedimentary structures and in situ measurements of air permeability. The sedimentary structures were interpreted, sketched, digitally photographed and measured in a representative outcrop. Additionally, a total of 2750 cm-scale air permeability measurements were carried out in situ. Analysis of the spatial distribution of sedimentary structures and permeability shows that clay-rich sedimentary features such as bottomsets and distinct mud drapes exhibit a different statistical and geostatistical permeability distribution compared to the other lithofacies in the cross-bedded sands. Spatial analysis of the air permeability data shows that permeability anisotropy in the cross-bedded lithofacies is dominated by the foreset lamination orientation. These results show that smallscale sedimentary heterogeneity strongly influences the local spatial distribution of the hydraulic properties and results in permeability heterogeneity and stratification that would produce anisotropy in upscaled permeability values. [less ▲]

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See detailHydrogeological study of Somes-Szamos transboundary alluvial aquifer
Dassargues, Alain ULg; Drobot, Radu; Lenart, Laszlo et al

in Technical/Scientific Issues of Transboudary Water Management: Experience from around the world (2008)

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See detailBayesian data fusion applied to water table spatial mapping
Fasbender, D.; Peeters, Luk; Bogaert, P. et al

in Water Resources Research (2008), 44

Water table elevations are usually sampled in space using piezometric measurements that are unfortunately expensive to obtain and are thus scarce over space. Most of the time, piezometric data are ... [more ▼]

Water table elevations are usually sampled in space using piezometric measurements that are unfortunately expensive to obtain and are thus scarce over space. Most of the time, piezometric data are sparsely distributed over large areas, thus providing limited direct information about the level of the corresponding water table. As a consequence, there is a real need for approaches that are able at the same time to (1) provide spatial predictions at unsampled locations and (2) enable the user to account for all potentially available secondary information sources that are in some way related to water table elevations. In this paper, a recently developed Bayesian data fusion (BDF) framework is applied to the problem of water table spatial mapping. After a brief presentation of the underlying theory, specific assumptions are made and discussed to account for a digital elevation model and for the geometry of a corresponding river network. On the basis of a data set for the Dijle basin in the north part of Belgium, the suggested model is then implemented and results are compared to those of standard techniques such as ordinary kriging and cokriging. Respective accuracies and precisions of these estimators are finally evaluated using a ‘‘leave-one-out’’ cross-validation procedure. Although the BDF methodology was illustrated here for the integration of only two secondary information sources (namely, a digital elevation model and the geometry of a river network), the method can be applied for incorporating an arbitrary number of secondary information sources, thus opening new avenues for the important topic of data integration in a spatial mapping context. [less ▲]

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See detailMethodology for the integration of process studies and development of a decision support tool (FRAC-WECO Project Deliverable D1.2)
Brouyère, Serge ULg; Hérivaux, Cécile; Haberman, Michaël et al

Report (2007)

This deliverable allows one to clarify the objectives of the different partners involved in the FRAC-WECO project and how they are going to interact, to exchange data, research results and knowledge in ... [more ▼]

This deliverable allows one to clarify the objectives of the different partners involved in the FRAC-WECO project and how they are going to interact, to exchange data, research results and knowledge in order to meet the ambitious objectives of the project. Particularly, the complex interactions between researches dealing with physical processes and with socio-economic aspects have been described in details. The modelling applications will constitute the key interacting tools as they are going to integrate all the information on water and contaminant mass fluxes and on biogeochemical processes affecting the fate of contaminant in the field and they are also going to be used to produce all data required for risk assessment and for the socio-economic analysis which are two of the most important expected outcomes of the project. The deliverable also clarifies the use of flux-based concepts through the definition of risk assessment indicators in the form of contaminant mass fluxes and discharge at the various considered receptors. Finally, this document has also allowed one to clarify the scope and the limits of the researches foreseen in the FRAC-WECO project that will focus on the risk of contaminant leaching to groundwater, of contaminant dispersion through groundwater and on the impact of contaminant on groundwater and surface water as affected by groundwater discharge and on the impact on aquatic ecosystems. [less ▲]

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See detailCarte hydrogéologique de Harzé - La Gleize 49/7-8, 1/25.000 : [notice explicative]
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Book published by Ministère de la Région wallonne, DGRNE - Edition provisoire : septembre 2007 (2007)

Detailed reference viewed: 57 (8 ULg)
See detailCarte hydrogéologique de Wallonie, Harzé - La Gleize 49/7-8
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Cartographic material (2007)

Detailed reference viewed: 82 (11 ULg)
See detailCarte hydrogéologique de Wallonie, Durbuy - Mormont 55/1-2
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Cartographic material (2007)

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See detailCarte hydrogéologique de Wallonie, Bra - Lierneux 55/3-4
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Cartographic material (2007)

Detailed reference viewed: 34 (1 ULg)
See detailCarte hydrogéologique, Bra - Lierneux 55/3-4, 1/25.000 : [notice explicative]
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Book published by Ministère de la Région wallonne, Direction générale des ressources naturelles et de l'environnement - Edition provisoire : août 2007 (2007)

Detailed reference viewed: 22 (3 ULg)
See detailCarte hydrogéologique, Durbuy - Mormont 55/1-2, 1/25.000 : [notice explicative]
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Book published by Ministère de la Région wallonne, DGRNE - Edition provisoire : août 2007 (2007)

Detailed reference viewed: 47 (9 ULg)
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See detailThe effect of heterogeneity on the agreement between analytical and numerical solutions describing the recession flow in unconfined hillslope aquifers
Rocha, David; Feyen, Jan; Dassargues, Alain ULg

in Proceedings of the Int. Congress on Development, Environment and Natural Resources: Multi-level and multi-scale Sustainability (2007, July)

Analytical approximations or linearized versions of the Boussinesq equation, describing recession flow in unconfined hillslope aquifers have been applied extensively in the past. One of the major ... [more ▼]

Analytical approximations or linearized versions of the Boussinesq equation, describing recession flow in unconfined hillslope aquifers have been applied extensively in the past. One of the major assumptions in the conceptual formulation is isotropic homogeneity of the aquifer. Notwithstanding the effect of aquifer heterogeneity on recession flow has been pointed out [1], only recent studies are increasingly focusing on the quantification of this effect [2,3]. In the present research, the relevance of heterogeneity is being studied by analyzing the agreement between analytical approximations and the numerical solution of the receding flow in a layered unconfined aquifer with different domain configurations (horizontal, inclined and concave impervious bedrock). For the application of the analytical approximations use is made of the equivalent hydraulic conductivity concept. [less ▲]

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See detailGroundwater flow modelling of the regional aquifer of the Pampa del Tamarugal, northern Chile
Rojas, Rodrigo; Dassargues, Alain ULg

in Hydrogeology Journal (2007), 15(3), 537-551

The Pampa del Tamarugal Aquifer (PTA) is an important source of groundwater in northern Chile. In this study, a groundwater flow model of this aquifer is developed and calibrated for the period 1983-2004 ... [more ▼]

The Pampa del Tamarugal Aquifer (PTA) is an important source of groundwater in northern Chile. In this study, a groundwater flow model of this aquifer is developed and calibrated for the period 1983-2004. The model reproduces the observed flow-field and the water balance components reasonably well. Five scenarios are defined to evaluate the response to different pumping situations. These scenarios show that groundwater heads will continue to decrease with the present pumping discharge rates. To account for variations in the model results due to uncertainties in average recharge rates, randomly generated recharge realizations with different levels of uncertainty are simulated. Evaporation flow rates and groundwater flowing out of the modelled area seem unaffected by the recharge uncertainty, whereas the storage terms can vary considerably. For the most intensive pumping scenario under the generated random recharge rates, it is unlikely that the cumulative discharged volume from the aquifer, at the end of the simulation period, will be larger than 12% of the estimated groundwater reserve. Fluctuations in simulated groundwater heads due to uncertainties in the average recharge values are more noticeable in certain areas. These fluctuations could explain unusual behaviour in the observed groundwater heads in these areas. [less ▲]

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