Papers by Pascal Goderniaux
Restricted to a group specified by the consortium (including the Commission Services) CO Confiden... more Restricted to a group specified by the consortium (including the Commission Services) CO Confidential, only for members of the consortium (including the Commission Services) SUMMARY Tracer experiments were performed in the Brévilles test site in order to highlight vertical variations in groundwater fluxes related to vertical variations hydraulic conductivity, to estimate contaminant travel time from several locations in the catchment to the springs and to identify transport processes affecting the fate of solutes in the saturated part of the aquifer. Following a first tracer experiment with uranine and sulforhodamine G in 2003, four tracer injections were performed in November 2005 in different piezometers, using uranine, sulforhodamine B, iodide and lithium. Tracer concentrations were monitored in the injection wells and at the basin outlet (spring and gauging station). Using the FVPDM method, concentration evolutions monitored in the injection wells allowed one to estimate local Darcy fluxes. At the basin outlet, only two tracers were recovered. Analyses of breakthrough curves confirm the stratification of the aquifer with more permeable levels in the lower part. They also suggest the probable occurrence of vertical interactions within the aquifer. MILESTONES REACHED (from DOW II p. 81 to 86) The present DL benefits from the system description presented in previous HYDRO2 DL (DL H2.1; H2.1bis) as well as COMPUTE (DL C2.1). It uses climatic and hydrometric data from the database presented in the work package BASIN (DL R1.8) and described in HYDRO2 (DL H2.2). It is an important element for the understanding of the groundwater behaviour in the Brévilles catchment (future HYDRO2 DL H2.4). It gives some useful parameters (and data) for the models to be implemented in the WP COMPUTE and TRENDS. The present DL is not linked to a specific milestone. dual-porosity Characterises a medium with two different kinds of porosity. E.g. : interconnected red of fractures (macro-porosity)-porous matrix (microporosity)
An overview is proposed of the recent groundwater modelling works, at the groundwater body scale,... more An overview is proposed of the recent groundwater modelling works, at the groundwater body scale, performed by the Hydrogeology & Environmental Geology team of the University of Liège. The developed modelling tools are built in the general objective of improving our understanding and management, at short, middle and long terms, of the groundwater bodies. The general strategy to be followed implies that conceptualization, parameterization and calibration must be adapted to the actual objectives of each model (Wildemeersch et al., 2014). 3 specific applications are illustrated involving two main groundwater bodies: application of the HFEMC method (Wildemeersch et al., 2010) within the SUFT3D code for groundwater flow modelling of the ‘Synclinorium of Dinant’ (Orban et al., 2010 and Brouyère et al., 2011); application of the HFEMC method and the SUFT3D code for the nitrate trends (Batlle-Aguilar et al., 2007) simulations in the Geer basin (Orban et al., 2010) for different scenarios of...
Water Practice and Technology, 2007
Several local groundwater studies within the EU project AquaTerra in the Basins of the Meuse, Elb... more Several local groundwater studies within the EU project AquaTerra in the Basins of the Meuse, Elbe point at significant influences of groundwater on surface water, while the Brévilles Catchment shows a distinct problematic of pesticide loading to groundwater. Further modeling studies are currently being developed. In the Danube Basin no specific groundwater studies were carried out in the framework of AquaTerra. However on larger scales geochemical proxies such as strontium isotope ratios can give an insight into groundwater contributions to the river that reflects an integral signal of the environmental status of the Basin. Future local groundwater studies should be further correlated to the environmental status of rivers nearby.
Journal of Hydrology, 2015
Recent studies have evaluated the impact of climate change on groundwater resources for different... more Recent studies have evaluated the impact of climate change on groundwater resources for different geographical and climatic contexts. However, most studies have either not estimated the uncertainty around projected impacts or have limited the analysis to the uncertainty related to climate models. In this study, the uncertainties around impact projections from several sources (climate models, natural variability of the weather, hydrological model calibration) are calculated and compared for the Geer catchment (465 km 2) in Belgium. We use a surface-subsurface integrated model implemented using the finite element code HydroGeoSphere, coupled with climate change scenarios (2010-2085) and the UCODE_2005 inverse model, to assess the uncertainty related to the calibration of the hydrological model. This integrated model provides a more realistic representation of the water exchanges between surface and subsurface domains and constrains more the calibration with the use of both surface and subsurface observed data. Sensitivity and uncertainty analyses were performed on predictions. The linear uncertainty analysis is approximate for this nonlinear system, but it provides some measure of uncertainty for computationally demanding models. Results show that, for the Geer catchment, the most important uncertainty is related to calibration of the hydrological model. The total uncertainty associated with the prediction of groundwater levels remains large. By the end of the century, however, the uncertainty becomes smaller than the predicted decline in groundwater levels.
Water Resources Research, 2011
Several studies have highlighted the potential negative impact of climate change on groundwater r... more Several studies have highlighted the potential negative impact of climate change on groundwater reserves, but additional work is required to help water managers 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 in combination with an integrated surface-subsurface hydrological model (Geer basin, Belgium) developed with the finite element modeling software ''HydroGeoSphere.'' This version of the weather generator 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 six different regional climate models (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 weather generator's ability to simulate transient climate change enabled the assessment of the likely time scale 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.
Journal of Hydrology, 2014
Large-scale physically-based and spatially-distributed models (>100 km 2) constitute useful tools... more Large-scale physically-based and spatially-distributed models (>100 km 2) constitute useful tools for water management since they take explicitly into account the heterogeneity and the physical processes occurring in the subsurface for predicting the evolution of discharge and hydraulic heads for several predictive scenarios. However, such models are characterized by lengthy execution times. Therefore, modelers often coarsen spatial discretization of large-scale physically-based and spatially-distributed models for reducing the number of unknowns and the execution times. This study investigates the influence of such a coarsening of model grid on model performance and prediction uncertainty. The improvement of model performance obtained with an automatic calibration process is also investigated. The results obtained show that coarsening spatial discretization mainly influences the simulation of discharge due to a poor representation of surface water network and a smoothing of surface slopes that *Manuscript Click here to download Manuscript: revised_manuscript.doc Click here to view linked References prevents from simulating properly surface water-groundwater interactions and runoff processes. Parameter sensitivities are not significantly influenced by grid coarsening and calibration can compensate, to some extent, for model errors induced by grid coarsening. The results also show that coarsening spatial discretization mainly influences the uncertainty on discharge predictions. However, model prediction uncertainties on discharge only increase significantly for very coarse spatial discretizations.
Journal of Environmental Monitoring, 2009
Land use changes and the intensification of agriculture since the 1950s have resulted in a deteri... more Land use changes and the intensification of agriculture since the 1950s have resulted in a deterioration of groundwater quality in many European countries. For the protection of groundwater quality, it is necessary to (1) assess the current groundwater quality status, (2) detect changes or trends in groundwater quality, (3) assess the threat of deterioration and (4) predict future changes in groundwater quality. A variety of approaches and tools can be used to detect and extrapolate trends in groundwater quality, ranging from simple linear statistics to distributed 3D groundwater contaminant transport models. In this paper we report on a comparison of four methods for the detection and extrapolation of trends in groundwater quality: (1) statistical methods, (2) groundwater dating, (3) transfer functions, and (4) deterministic modeling. Our work shows that the selection of the method should firstly be made on the basis of the specific goals of the study (only trend detection or also extrapolation), the system under study, and the available resources. For trend detection in groundwater quality in relation to diffuse agricultural contamination, a very important aspect is whether the nature of the monitoring network and groundwater body allows the collection of samples with a distinct age or produces samples with a mixture of young and old groundwater. We conclude that there is no single optimal method to detect trends in groundwater quality across widely differing catchments.
Journal of Contaminant Hydrology, 2008
Quantification of pollutant mass fluxes is essential for assessing the impact of contaminated sit... more Quantification of pollutant mass fluxes is essential for assessing the impact of contaminated sites on their surrounding environment, particularly on adjacent surface water bodies. In this context, it is essential to quantify but also to be able to monitor the variations with time of Darcy fluxes in relation with changes in hydrogeological conditions and groundwater - surface water interactions. A new tracer technique is proposed that generalizes the single-well point dilution method to the case of finite volumes of tracer fluid and water flush. It is called the Finite Volume Point Dilution Method (FVPDM). It is based on an analytical solution derived from a mathematical model proposed recently to accurately model tracer injection into a well. Using a non-dimensional formulation of the analytical solution, a sensitivity analysis is performed on the concentration evolution in the injection well, according to tracer injection conditions and well-aquifer interactions. Based on this analysis, optimised field techniques and interpretation methods are proposed. The new tracer technique is easier to implement in the field than the classical point dilution method while it further allows monitoring temporal changes of the magnitude of estimated Darcy fluxes, which is not the case for the former technique. The new technique was applied to two experimental sites with contrasting objectives, geological and hydrogeological conditions, and field equipment facilities. In both cases, field tracer concentrations monitored in the injection wells were used to fit the calculated modelled concentrations by adjusting the apparent Darcy flux crossing the well screens. Modelling results are very satisfactory and indicate that the methodology is efficient and accurate, with a wide range of potential applications in different environments and experimental conditions, including the monitoring with time of changes in Darcy fluxes.
Journal of Contaminant Hydrology, 2010
Regional degradation of groundwater resources by nitrate has become one of the main challenges fo... 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 50 mg/l; however, even in that case, more than 50 years is needed to fully reverse upward trends.
Hydrogeology Journal, 2010
For good management of groundwater resources, and to comply with European and national regulation... 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 (27months) 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.
An integrated hydrological model was developed in order to study the potential effects of climate... more An integrated hydrological model was developed in order to study the potential effects of climate change on groundwater resources. This model considers most hydrological processes in a physically consistent way. More particularly, groundwater flows are modelled using a spatially distributed finite element approach. The river-aquifer interactions are explicitly taken into account in the model, as well as the spatial heterogeneity of the chalk geology characteristics. After a detailed calibration on the last 30 years and validation on recent periods, quantitative interpretations can be drawn from the groundwater model results. Considering IPCC climate change scenarios, it appears that, on a multi-annual basis, most tested scenarios predict a decreasing trend in groundwater levels in the Geer basin. These first results indicate that groundwater deficits may be expected in the future in Belgium. Moreover, at this stage of the study, this trend is computed for a very "optimistic" scenario, neglecting all other pressure changes on the groundwater resources (i.e. no change in land use and in pumping conditions).
Quantification of pollutant mass fluxes is essential for assessing the impact of contaminated sit... more Quantification of pollutant mass fluxes is essential for assessing the impact of contaminated sites on their surrounding environment, particularly on adjacent surface water bodies. In this context, it is essential to quantify but also to be able to monitor the variations with time of Darcy fluxes in relation with changes in hydrogeological conditions and groundwater – surface water interactions. The Finite Volume Point Dilution Method (FVPDM) is a new tracer technique that generalizes the single-well point dilution method to the case of finite volumes of tracer fluid and water flush. It is based on an analytical solution derived from a mathematical model proposed recently to accurately model tracer injection into a well. After a brief description of the underlying concepts and mathematical model, an analytical solution is derived for calculating straightforwardly the evolution of concentration of the tracer in the injection well during and after injection operations. Based on sensitivity analysis performed on the concentration evolution in the injection well, the technique is described and interpretation methods are proposed. It is shown that this new tracer technique is easier to implement in the field than the classical point dilution method while it allows going further by monitoring changes with time of the magnitude of estimated Darcy fluxes, which is not the case for the former technique. The FVPDM was performed and validated in two experimental sites characterized by contrasted objectives, geological and hydrogeological conditions, and field equipment facilities. In site A, the objective was to estimate contaminant travel times in groundwater to a spring while assessing vertical variations in groundwater fluxes, using a combined FVPDM – classical tracer test, with “non-ideal” experimental conditions. In site B, the purpose was to estimate the groundwater fluxes flowing out from a contaminated site to a neighbouring river, in very well controlled experimental conditions. In both cases, field tracer concentrations monitored in the injection wells are used to fit the calculated modelled concentrations by playing on the ‘apparent’ Darcy flux crossing the well screens. Modelling results are very satisfactory and indicate that the methodology is efficient and accurate, with a wide range of potential applications in different environments and experimental conditions.
Integrated Modelling of the river-sediment-soil-groundwater system; advanced tools for the manage... more Integrated Modelling of the river-sediment-soil-groundwater system; advanced tools for the management of catchment areas and river basins in the context of global change Integrated Project Thematic Priority: Sustainable development, global change and ecosystems Deliverable No.: BASIN R3.21 (Meuse) Title: Intermediate report on the development of the Geer hydrological model (surface and subsurface water) for climatic change scenario on that subcatchment
For large-scale groundwater modeling purposes, black-box models and physically-based distributed ... more For large-scale groundwater modeling 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 modeling application. An Hybrid Finite-Element Mixing-Cell method (HFEMC), has been developed that allows combining in a single
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Papers by Pascal Goderniaux