Integrated approach for assessing climate change impacts on a regional chalky aquifer in Belgium

in Changes in water resource systems: methodologies to maintain water security and ensure integrated management (2007)

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 ... [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 ground¬water 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). [less ▲]

Identification of groundwater quality trends in a chalk aquifer threatened by intensive agriculture in Belgium

in Hydrogeology Journal (2007), 15(8), 1615-1627

The European Union (EU) has adopted directives requiring that Member States take measures to reach a "good" chemical status of water resources by the year 2015 (Water Framework Directive: WFD). In order ... [more ▼]

The European Union (EU) has adopted directives requiring that Member States take measures to reach a "good" chemical status of water resources by the year 2015 (Water Framework Directive: WFD). In order to achieve the environmental objectives for groundwater, the identification and reversal of significant upward trends in pollutant concentrations are required. A very detailed dataset available for the Hesbaye chalk aquifer in Belgium is used to evaluate tools and to propose efficient methodologies for identifying and quantifying nitrate trends in groundwater. Results indicate that the parametric linear regression and the non-parametric Mann-Kendall tests are robust; however, the latter test seems more adequate as it does not require verification of the normality of the dataset and it provides calculated nitrate trends very comparable to those obtained using linear regression. From a hydrogeological point of view, results highlight a general upward trend in the whole groundwater basin. The extrapolation of the trend analysis results indicates that measures have to be taken urgently in order to avoid further major degradation of groundwater quality within the next 10-70 years. However, a good groundwater quality status cannot be expected in the Hesbaye aquifer for the 2015 EU WFD deadline. [less ▲]

Identification and quantification of sources of major solutes in a sandy, phreatic aquifer in Central Belgium through ionic ratios and geochemical mass-balance modelling

in Groundwater and Ecosystems, Proc. of the XXXV IAH Congress (2007)

In this study the processes affecting groundwater chemistry in the Eocene Brussels sands aquifer in Central Belgium are identified based on evaluation of ionic ratios of major solutes. Based on these ... [more ▼]

In this study the processes affecting groundwater chemistry in the Eocene Brussels sands aquifer in Central Belgium are identified based on evaluation of ionic ratios of major solutes. Based on these results, in combination with mineralogical and hydrogeological information of the aquifer, a geochemical mass-balance model is created to quantify the contribution of each of the processes to the observed composition of groundwater. After a rigorous validation process, a dataset of 99 groundwater samples is obtained from observation and pumping wells in the Eocene Brussels sands aquifer, which is one of the main aquifers for drinking water production in Belgium. The aquifer consists of heterogeneous alteration of calcified and silicified coarse sands, with local presence of clay drapes and glauconite-rich zones (Laga et al. 2001). The entire aquifer is overlain by Quaternary eolian deposits, mainly consisting of loam with the exception of the north east, where the Quaternary deposits are sandy loam. The groundwater in this aquifer is of Ca-Mg-HCO3-type with locally elevated nitrate concentrations. Based on the evaluation of ionic ratios and the mineralogy of the aquifer, a conceptual geochemical model is developed for mass-balance modeling, including (1) concentration of precipitation by a factor 1 to 5 due to evaporation, (2) dissolution of a pure calcite phase and a calcite phase containing 25 % magnesium by both carbonic acid and sulfuric acid, (3) anthropogenic inputs for all major cations and anions except bicarbonate, (4) dissolution of glauconite, (5) cation exchange of sodium and potassium for calcium and magnesium. The two calcite phases can be thought of as end-members of a solid solution of magnesium in calcite. The mass-balance modeling consists of a mole-balance equation for each considered element according to: [Obs] = p[Prec] + p1[Phase 1] + ... + pi[Phase i] + a [Anthropogenic] +/- c[Cation Exchange] This set of linear equations is additionally constrained by (1) defining a range for concentration factors p based on measured and calculated evaporation rates, (2) charge balance for the anthropogenic sources and (3) pi being positive or negative according to whether the phase dissolves or precipitates. The set of linear equations with the given constraints is solved using a least squares optimization. Based on the possible processes and reactions several geochemical models are tested for each sample and a model is considered adequate if the root mean squared error (RMSE) between observed and calculated concentrations is less than 10-10 mol/L and the charge balance of the calculated composition is less than 5 %. If several models are able to explain the observed concentrations, the RMSE provides an objective measure to compare the quality of the models. The best model for each sample is selected and the spatial distribution of these models is compared to the spatial variations in lithology and land-use to asses the feasibility of the proposed models. [less ▲]

Etude exploratoire relative à la datation des eaux souterraines en Région wallonne à l’aide du Tritium. Application aux nappes de Hesbaye, du Pays de Herve, Hoyoux-Néblon et du Tournaisis

Report (2006)

Carte hydrogéologique, Aye - Marche-en-Famenne 54/7-8, 1/25.000 : [notice explicative]

Book published by Ministère de la Région wallonne, Direction générale des ressources naturelles et de l'environnement - Edition provisoire : juillet 2006 (2006)

Simulations MOHICAN pour la statistique des débits maxima (projet STATHY) : bassins de la Warchenne, la Wamme et la Gueule

Report (2006)

Le modèle MOHICAN (« Modèle hydrologique intégré pour le calcul des crues et l’amplitude des niveaux d’eau ») a été développé conjointement par l’Université de Liège (Laboratoire d’hydrodynamique ... [more ▼]

Le modèle MOHICAN (« Modèle hydrologique intégré pour le calcul des crues et l’amplitude des niveaux d’eau ») a été développé conjointement par l’Université de Liège (Laboratoire d’hydrodynamique appliquée, Laboratoire de Géologie de l’Ingénieur et d’Hydrogéologie, Centre d’Etude et de Modélisation de l’environnement) et la Faculté Universitaire des Sciences Agronomiques de Gembloux (Unité d’Hydraulique agricole) pour le compte et avec le support du Ministère de l’Equipement et des Transports, Service d’Etudes Hydrologiques (MET/SETHY) de la Région wallonne. Dans le cadre du projet STATHY visant à établir la cartographie des zones d’inondation en région Wallonne, il était nécessaire de disposer de séries étendues de débits horaires pour chaque sous-bassin versant. Le modèle MOHICAN a été utilisé à la demande du SETHY pour générer ces données sur 14 années (1991 à 2004) pour 3 sous-bassins pour lesquels la Région Wallonne ne disposait pas de données horaires suffisantes : • La Warchenne à Malmédy (+/- 29 km²), • La Wamme à Hargimont (+/- 81 km²), • La Gueule à Sippenaeken (+/- 120 km²). [less ▲]

Complément d'étude hydrogéologique sur les incidences potentielles d'un extension de la carrière de la Warchennee

Report (2006)

Description of hydrogeological conditions in the Geer sub-catchment and synthesis of available data for groundwater modelling

Report (2006)

In the framework of Workpackage R3 Meuse, the Hydrogeology Group of the University of Liège (HGULg) will develop a groundwater flow and transport model for the Geer sub-catchment (tributary of the Meuse ... [more ▼]

In the framework of Workpackage R3 Meuse, the Hydrogeology Group of the University of Liège (HGULg) will develop a groundwater flow and transport model for the Geer sub-catchment (tributary of the Meuse). This model will be used for collaborations HYDRO H1 and TREND T2. The deliverable describes the hydrogeological conditions prevailing in the sub-catchment and provides a synthesis of available data for groundwater and transport modelling. [less ▲]

A framework for an optimised groundwater monitoring network and aggregated indicators

in Environmental Geology (2006), 50(2), 194-201

The implementation of the Water Framework Directive (EU 2000) requires a groundwater quality monitoring. It is used for characterisation of the 'good' chemical status of each groundwater body and for the ... [more ▼]

The implementation of the Water Framework Directive (EU 2000) requires a groundwater quality monitoring. It is used for characterisation of the 'good' chemical status of each groundwater body and for the restoration or protection purposes of those bodies already at 'good' status. Interpretative aspects are lying in the design of monitoring network and in the way of building global indicators. Attention is given here to the global chemical status of the groundwater bodies and to the role of diffuse pollution, much of which is brought via groundwater to surface water. Monitoring 'local' pollution associated with individual sites is not addressed. Groundwater bodies with different contrasted hydrogeology conditions, land use and topography have been considered to establish an approach for choosing an optimised monitoring network. Then, a quality assessment system has been developed and applied for qualifying the general status of each groundwater body. The use of non-dimensional indexes allows us to process with all kinds of chemical parameters in a normalised way and, by means of adequate aggregation rules, to qualify the general quality status of a groundwater body. The obtained diagnostic, even if not fully validated, is closely linked to the pragmatic objectives contained in the EU Water Directive. [less ▲]

Hydrogeological modeling of radionuclide transport in heterogeneous low-permeability media: a comparison between Boom Clay and Ieper Clay

in Soares, A.; Pereira, M. J.; Dimitrakopoulos, R. (Eds.) GeoENV VI: Geostatistics for Environmental Applications (2006)

Deep low-permeability clay layers are considered as possible suitable environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is the reference host formation and the Ieper ... [more ▼]

Deep low-permeability clay layers are considered as possible suitable environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is the reference host formation and the Ieper Clay an alternative host formation for research and safety and feasibility assessment of deep disposal of nuclear waste. In this study, two hydrogeological models are built to calculate the radionuclide fluxes that would migrate from a potential repository through these two clay formations. Transport parameters heterogeneity is incorporated in the models using stochastic sequential simulation of hydraulic conductivity, diffusion coefficient and diffusion accessible porosity, using primary information and several types of secondary information, i.e. resistivity, gamma ray and grain size. The calculated radionuclide fluxes in the two clay formations are compared. Results show that in the Ieper Clay larger differences between the fluxes through the lower and the upper clay boundary occur, larger total output radionuclide amounts are calculated, and a larger effect of parameter heterogeneity on the calculated fluxes is observed, compared to the Boom Clay. [less ▲]