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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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See detailModelling groundwater pumping and coupled heat transport in a alluvial aquifer: tests using different codes an optimisation
Fossoul, Frédérique ULg; Orban, Philippe ULg; Dassargues, Alain ULg

in Carrera, Jesus (Ed.) XVIII International Conference on Computational Methods in Water Resources, CMWR 2010 (2010, June 24)

Various aquifers are studied in terms of low temperature geothermal potential. The feasibility and impact studies of these systems imply very often a numerical simulation of groundwater flow and heat ... [more ▼]

Various aquifers are studied in terms of low temperature geothermal potential. The feasibility and impact studies of these systems imply very often a numerical simulation of groundwater flow and heat transport. Nowadays, some finite element or finite difference codes are able to deal with such non linear simulations. On a synthetic case study and then on a real case study, a detailed comparative sensitivity analysis is performed using three different codes (MT3DMS, SHEMAT and HYDROGEOSHERE). For low temperatures and relatively small temperature changes, it appears rapidly that the uncertainty affecting values of the main hydrodynamic parameters (i.e. hydraulic conductivity) influences more the results than taking into account any coupling or non linearity. For a case study, the pumping and associated groundwater flow and heat transport are modeled in an alluvial aquifer interacting with a main river in order to assess feasibility of a low energy air cooling /heating system for a large office building. The worst case scenario corresponds to hot summer conditions simultaneously with river maximum temperature and the model leads to an optimization with intermittent pumping in minimum 6 wells. Numerical codes are ready to simulate complex groundwater flow, solute transport and heat transport situations in aquifers, however efforts must be realized to obtain reliable experimental in-situ measured values for the hydro-thermal properties. [less ▲]

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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

Poster (2010, April 22)

In the context of the water framework directive, management plans have to be set up about water quality in surface and groundwater bodies in the EU. One of the first steps is to evaluate the risk of ... [more ▼]

In the context of the water framework directive, management plans have to be set up about water quality in surface and groundwater bodies in the EU. One of the first steps is to evaluate the risk of contamination of these water resources, and particularly the risk posed by contaminated industrial sites. From the perspective of water resource management, each of these sites taken individually does not necessary constitute a major threat. However, in heavily industrialised and urbanised areas, the cumulative effect of multiple contaminant sources is likely to present a risk. In order to propose adequate but still economically reliable measures, the calculated risk should be based on a so-called megasite approaches using criteria reflecting the water quality deterioration, in a cumulative way, at the scale of the whole surface water or groundwater body. A GIS-based regional risk assessment approach is developed here for groundwater bodies using the SEQ-ESO currently used within the Walloon Region as indicator to reflect the quality status of the groundwater body. The approach is applied on the groundwater body RWM073 “Gravels and alluvial deposits of the Meuse river between Engis and Herstal”, identified at risk of not reaching a good quality status by 2015. The different steps of this methodology consist of an inventory of proved or potential contaminating industrial sites, a numerical modelling of pollutants behaviour at the scale of the groundwater body and the application of the SEQ-ESO that finally gives a global quality status of the whole groundwater body. This analysis also serves as basis for a socio-economic approach intending to provide indications on costs and benefits generated by total or partial remediation of the contaminated groundwater bodies according to the different management scenarios. [less ▲]

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See detailRegional transport modelling for nitrate trend assessment and forecasting in a chalk aquifer
Orban, Philippe ULg; Brouyère, Serge ULg; Batlle-Aguilar, Jordi et al

in Journal of Contaminant Hydrology (2010), 118

Regional degradation of groundwater resources by nitrate has become one of the main challenges for water managers worldwide. Regulations have been defined to reverse observed nitrate trends in groundwater ... [more ▼]

Regional degradation of groundwater resources by nitrate has become one of the main challenges for water managers worldwide. Regulations have been defined to reverse observed nitrate trends in groundwater bodies, such as the Water Framework Directive and the Groundwater Daughter Directive in the European Union. In such a context, one of the main challenges remains to develop efficient approaches for groundwater quality assessment at regional scale, including quantitative numerical modelling, as a decision support for groundwater management. A new approach combining the use of environmental tracers and the innovative ‘Hybrid Finite Element Mixing Cell’ (HFEMC) modelling technique is developed to study and forecast the groundwater quality at the regional scale, with an application to a regional chalk aquifer in the Geer basin in Belgium. Tritium data and nitrate time series are used to produce a conceptual model for regional groundwater flow and contaminant transport in the combined unsaturated and saturated zones of the chalk aquifer. This shows that the spatial distribution of the contamination in the Geer basin is essentially linked to the hydrodynamic conditions prevailing in the basin, more precisely to groundwater age and mixing and not to the spatial patterns of land use or local hydrodispersive processes. A three-dimensional regional scale groundwater flow and solute transport model is developed. It is able to reproduce the spatial patterns of tritium and nitrate and the observed nitrate trends in the chalk aquifer and it is used to predict the evolution of nitrate concentrations in the basin. The modelling application shows that the global inertia of groundwater quality is strong in the basin and trend reversal is not expected to occur before the 2015 deadline fixed by the European Water Framework Directive. The expected time required for trend reversal ranges between 5 and more than 50 years, depending on the location in the basin and the expected reduction in nitrate application. To reach a good chemical status, nitrate concentrations in the infiltrating water should be reduced as soon as possible below 50mg/l; however, even in that case, more than 50 years is needed to fully reverse upward trends. [less ▲]

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See detailTowards a better understanding of the Oulmes hydrogeological system (Mid-Atlas, Morocco)
Wildemeersch, Samuel ULg; Orban, Philippe ULg; Ruthy, Ingrid ULg et al

in Environmental Earth Sciences (2010), 60(8), 1753-1769

Located in the Mid-Atlas (Morocco), the Oulmes plateau is famous for its mineral water springs “Sidi Ali” and “Lalla Haya” commercialised by the company “Les Eaux minérales d’Oulmès S.A”. Additionally ... [more ▼]

Located in the Mid-Atlas (Morocco), the Oulmes plateau is famous for its mineral water springs “Sidi Ali” and “Lalla Haya” commercialised by the company “Les Eaux minérales d’Oulmès S.A”. Additionally, groundwater of the Oulmes plateau is intensively exploited for irrigation. The objective of this study, essentially performed from data collected during isotopic (summer 2004) and piezometric and hydrogeochemical field campaigns (spring 2007), is to improve the understanding of the Oulmes hydrogeological system. Analyses and interpretation of these data lead to the statement that this system is constituted by a main deep aquifer of large extension and by minor aquifers in a perched position. However, these aquifers interact enough to be in total equilibrium during the cold and wet period. As highlighted by isotopes, the origin of groundwater is mainly infiltration water except a small part of old groundwater with dissolved gas rising up from the granite through the schists. [less ▲]

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See detailApplication of the Hybrid Finite Element Mixing Cell method to an abandoned coalfield in Belgium
Wildemeersch, Samuel ULg; Brouyère, Serge ULg; Orban, Philippe ULg et al

in Journal of Hydrology (2010), 392(3-4), 188-200

The Hybrid Finite Element Mixing Cell (HFEMC) method is a flexible modelling technique particularly suited to mining problems. The principle of this method is to subdivide the modelled zone into several ... [more ▼]

The Hybrid Finite Element Mixing Cell (HFEMC) method is a flexible modelling technique particularly suited to mining problems. The principle of this method is to subdivide the modelled zone into several subdomains and to select a specific equation, ranging from the simple linear reservoir equation to the groundwater flow in porous media equation, to model groundwater flow in each subdomain. The model can be run in transient conditions, which makes it a useful tool for managing mine closure post-issues such as groundwater rebound and water inrushes. The application of the HFEMC method to an abandoned underground coal mine near the city of Liege (Belgium) is presented. The case study zone has been discretized taking advantage of the flexibility of the method. Then, the model has been calibrated in transient conditions based on both hydraulic head and water discharge rate observation and an uncertainty analysis has been performed. Finally, the calibrated model has been used to run several scenarios in order to assess the impacts of possible future phenomena on the hydraulic heads and the water discharge rates. Among others, the simulation of an intense rainfall event shows a quick and strong increase in hydraulic heads in some zones coupled with an increase in associated water discharge rates. This could lead to stability problems in local hill slopes. These predictions will help managing and predicting mine water problems in this complex mining system. [less ▲]

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See detailForeseeing nitrate concentration in groundwater: A review of available modelling approaches
Orban, Philippe ULg; Brouyère, Serge ULg

Conference (2009, December 10)

In the scientific community, increasing concerns on groundwater quality and quantity have motivated the development of numerical models for groundwater management since the 1970’s. Mathematical and ... [more ▼]

In the scientific community, increasing concerns on groundwater quality and quantity have motivated the development of numerical models for groundwater management since the 1970’s. Mathematical and numerical models are, for example, promising tools for prediction of concentration and they can be used to make the dynamic link between nitrogen manure and the resulting evolution of nitrate concentration in groundwater. However, from a practical and managerial perspective, there have been very few real attempts of developing efficient calibrated and validated transport models in particular at the scale of the groundwater body, which is the management unit of groundwater resource in the European Union. Actually two main challenges remains, (1) performing numerical tools are not really available and (2) parametrisation of such transport models at the regional scale is difficult due to the large amount of data required. Generally speaking models can be grouped in different categories ranging from black box models to physically based distributed models. The black box models such as transfer function are simple but attractive because they require relatively less data but with the drawback that modelling result are not spatially distributed while the predictive capability of these models is questionable due to the semi-analytical nature of the process descriptions. On the contrary, physically based distributed model require more data but, due to a more advanced description of ongoing processes, such models are expected to have better predictive capabilities than the black box models. Black box model and physically based distributed model approaches have all proved their utilities and have all their justifications, advantages and disadvantages regarding the development of regional scale groundwater model. A new flexible methodology (the Hybrid Finite Element Mixing Cell method) has been developed that allows combining in a single model, and in a fully integrated way, different mathematical approaches of various complexities for groundwater in complex environment. This method has been implemented in the SUFTD, a finite element groundwater flow and solute transport numerical model. Combining on the one hand the use of a spatially distributed groundwater flow and solute transport model taking advantages of this Hybrid Finite Element Mixing Cell Approach method and on the other hand spatial datasets of tritium and nitrate contents, an illustration on the problem of nitrate trend assessment and forecasting for an important groundwater resource located in the Geer groundwater body (480 km²) in the Walloon Region of Belgium will be proposed. [less ▲]

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