References of "Goderniaux, Pascal"
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See detailHow tracer tests simulations strongly constrain flow and solute transport models in fractured chalk aquifers
Goderniaux, Pascal ULg; Daoudi, Moubarak; Orban, Philippe ULg et al

Conference (2012, May)

Flow and solute transport in the saturated zone of a micro-fissured and fractured chalk aquifer (Geer basin, Belgium) has been studied by more than 35 tracer tests in 11 sites. The tracer tests campaign ... [more ▼]

Flow and solute transport in the saturated zone of a micro-fissured and fractured chalk aquifer (Geer basin, Belgium) has been studied by more than 35 tracer tests in 11 sites. The tracer tests campaign was preceded by a morphostructural study associated to a geophysical survey including electrical resistivity and refraction seismic measurements. Results provided information on the main expected fracturation axis where a series of injection and monitoring wells were drilled. In each of the 11 sites, multi-tracer tests have been performed in groundwater convergent flow conditions to pumping wells or draining galleries (used for drinking water production). The analysis of the detailed quantitative breakthrough curves allowed identifying various transport behaviours, from rapid advective to dominant dispersive processes with immobile water effects. Groundwater flow and solute transport in such a fractured chalk can be simulated using different conceptual approaches. Using HYDROGEOSPHERE (Therrien and Sudicky, 1996), a comparison is made between two ways for representing the fracture zones: (1) high contrasted hydraulic conductivity zones with a classical REV approach and (2) the explicit representation of discrete fractures interacting with a porous medium. Promising results are found using the discrete approach for representing the fractures. In this last case, an aperture of the order of the millimetre is enough for creating, where it is needed, a fast advective peak combined with a long highly dispersive component due to the chalk matrix. The discrete fracture approach prevents the modeller from introducing unrealistic parameters values in the fracture zones as it is generally the case in the classical REV-based method where the fractured zones are simply represented by elongated REV. However, it is shown that the availability of field data, as multi-tracers test results, creates very high constraints to be taken into account in the calibration processes (i.e calibration on the measured groundwater flow and transport conditions). The detailed calibration on the different breakthrough curves is not an easy task and automatic calibration is not easy to organize. Results are particularly illustrative to show that a detailed parameterization and calibration of such a local situation remain difficult. Perspectives will be discussed about the potential use of automatic calibration tools as UCODE_2005 or PEST for solving such local situation models and the needed further steps for ‘upscaling’ local situation models at the scale of the whole aquifer or groundwater body. [less ▲]

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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 ▲]

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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 ▲]

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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 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 ▲]

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See detailImpact of climate change on groundwater reserves
Goderniaux, Pascal ULg

Doctoral thesis (2010)

Estimating the impacts of climate change on groundwater represents one of the most difficult challenges faced by water resources specialists. One difficulty is that simplifying the representation of the ... [more ▼]

Estimating the impacts of climate change on groundwater represents one of the most difficult challenges faced by water resources specialists. One difficulty is that simplifying the representation of the hydrological system, or using too simple climate change scenarios often leads to discrepancies in projections. Additionally, these projections are affected by uncertainties from various sources, and these uncertainties are not evaluated in previous studies. In this context, the objective of this study is to provide an improved methodology for the estimation of climate change impact on groundwater reserves, including the evaluation of uncertainties. This methodology is applied to the case of the Geer basin catchment (480 km²) in Belgium. A physically-based surface-subsurface flow model has been developed for the Geer basin with the finite element model HydroGeoSphere. The simultaneous solution of surface and subsurface flow equations in HydroGeoSphere, as well as the internal calculation of the actual evapotranspiration as a function of the soil moisture at each node of the defined evaporative zone, improve the representation and calibration of interdependent processes like recharge, which is crucial in the context of climate change. Fully-integrated surface-subsurface flow models have recently gained attention, but have not been used in the context of climate change impact studies. This surface-subsurface flow model is combined with advanced climate change scenarios for the Geer basin. Climate change simulations were obtained from six regional climate model (RCM) scenarios assuming the SRES A2 greenhouse gases emission (medium-high) scenario. These RCM scenarios were statistically downscaled using two different methods: the 'Quantile Mapping Biased Correction' technique and a 'Weather Generator' technique. Both of them are part of the most advanced downscaling techniques. They are able to apply corrections not only to the mean of climatic variables, but also across the statistical distributions of these variables. This is important as these distributions are expected to change in the future, with more violent rainfall events, separated by longer dry periods. The 'quantile mapping bias-correction' technique generate climate change time series representative of a stationary climate for the periods 2011-2040, 2041-2070 and 2071-2100. The 'CRU' weather generator is used to generate a large number of equiprobable scenarios simulating full transient climate change between 2010 and 2085. All these scenarios are applied as input of the Geer basin model. The uncertainty is evaluated from different possible sources. Using a multi-model ensemble of RCMs and GCMs enables to evaluate the uncertainty linked to climatic models. The application of a large number of equiprobable climate change scenarios, generated with the 'weather generator', as input of the hydrological model allows assessing the uncertainty linked to the natural variability of the weather. Finally, the uncertainty linked to the calibration of the hydrological model is evaluated using the computer code 'UCODE_2005'. The climate change scenarios for the Geer basin model predict hotter and drier summers and warmer and wetter winters. Considering the results of this study, it is very likely that groundwater levels and surface flow rates in the Geer basin will decrease. This is of concern because it also means that groundwater quantities available for abstraction will also decrease. However, this study also shows that the uncertainty surrounding these projections is relatively large and that it remains difficult to state on the intensity of the decrease. [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 detailMulti-tracer tests to evaluate the hydraulic setting of a complex aquifer system (Brévilles spring catchment, France)
Goderniaux, Pascal ULg; Brouyère, Serge ULg; Gutierrez, Alexis et al

in Hydrogeology Journal (2010)

For good management of groundwater resources, and to comply with European and national regulations, a detailed understanding of an aquifer’s hydraulic setting is required. In order to better characterize ... [more ▼]

For good management of groundwater resources, and to comply with European and national regulations, a detailed understanding of an aquifer’s hydraulic setting is required. In order to better characterize a sandy aquifer that is affected by diffuse pollution (Brévilles spring catchment, Val d'Oise, France), and to quantify the transfer time in the saturated zone, a multi-tracer test involving a new technique, the ‘Finite Volume Point Dilution Method’, has been performed in natural flow conditions. In November 2005, injections of four different tracers took place in four piezometers involving different locations and depths in the aquifer. Recovery of the tracers was observed at two different places near the aquifer outlet. A particularly long and unusual monitoring exercise (27 months) demonstrated the existence of several different velocities within the sandy layer, which seems to be linked to the decrease of hydraulic conductivity with depth. The new insight and parameter quantification brought by interpretation of these tests contribute to a better characterization of the saturated zone. The particularly long-term monitoring exercise also gives new information to understand and forecast the trend and persistence of groundwater contamination by pesticides in the catchment. [less ▲]

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See detailHow can large scale integrated surface - subsurface hydrological model be used to evaluate long term climate change impact on groundwater reserves
Goderniaux, Pascal ULg; Brouyère, Serge ULg; Fowler, Hayley J. et al

in Proceeding of the 7th international conference on calibration and reliability in groundwater modeling (2009, September)

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See detailState-of-the-art climate change scenarios in AquaTerra
Fowler, Hayley J; Blenkinsop, Stephen; Burton, Aidan et al

in AquaTerra Final Conference. Programme & Proceedings (2009, March)

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See detailProducing transient climate change scenarios for AquaTerra catchments
Blenkinsop, Stephen; Burton, Aidan; Fowler, Hayley J et al

Poster (2009, March)

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See detailLarge-scale flow and transport modelling for the management of groundwater bodies: the Geer case-study
Orban, Philippe ULg; Goderniaux, Pascal ULg; Brouyère, Serge ULg

in AquaTerra Final Conference. Programme & Proceedings (2009, March)

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