References of "Dassargues, Alain"
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See detailCarte hydrogéologique du plateau d’Oulmès (Maroc)
Elbatloussi, Dounia; Cheddadi, Meriem; Dadi, Sliman et al

Report (2005)

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See detailL’eau dans tous ses état : enjeux et difficultés de la gestion des eaux souterraines
Dassargues, Alain ULg

Scientific conference (2005, January 20)

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See detailInfluence of injection conditions on field tracer experiments
Brouyère, Serge ULg; Carabin, Guy; Dassargues, Alain ULg

in Ground Water (2005), 43(3), 389-400

Calibration of ground water transport models is often performed using results of field tracer experiments. However, little attention is usually paid to the influence, on resulting breakthrough curves, of ... [more ▼]

Calibration of ground water transport models is often performed using results of field tracer experiments. However, little attention is usually paid to the influence, on resulting breakthrough curves, of injection conditions and well-aquifer interactions, more particularly of the influence of the possible trapping of the tracer in the injection wellbore. Recently, a new mathematical and numerical approach has been developed to model injection conditions and well-aquifer interactions in a very accurate way. Using an analytical solution derived from this model, a detailed analysis is made of the evolution of the tracer input function in the aquifer. By varying injection conditions from one simulation to another, synthetic breakthrough curves are generated with the SUFT3D ground water flow and transport finite-element simulator. These tests show clearly that the shape of the breakthrough curves can be dramatically affected by injection conditions. Using generated breakthrough curves as "actual" field results, a calibration of hydrodispersive parameters is performed, neglecting the influence of injection conditions. This shows that neglecting the influence of actual injection conditions can lead to (1) errors on fitted parameters and (2) misleading identification of the active transport processes. Conclusions and guidelines are drawn in terms of proposed methodologies for better controlling the tracer injection in the field, in order to minimize risk of misinterpretation of results. [less ▲]

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See detailIntegrated modelling of the hydrological cycle in relation to global climate change
Deliège, Jean-François ULg; Bourouag, Mohamed ULg; Dzisiak, J. P. et al

Report (2005)

The main objectives of the project “INTEGRATED MODELLING OF THE HYDROLOGICAL CYCLE IN RELATION TO GLOBAL CLIMATE CHANGE” (CG/DD/08), are : - to gain knowledge in the understanding of the hydrological ... [more ▼]

The main objectives of the project “INTEGRATED MODELLING OF THE HYDROLOGICAL CYCLE IN RELATION TO GLOBAL CLIMATE CHANGE” (CG/DD/08), are : - to gain knowledge in the understanding of the hydrological system at different time and space scales; - to develop and test an integrated holistic approach that can be able to assess the effects of climate change on the terrestrial hydrologic cycle and on water resources systems. The project is focused on two main aspects : 1) The comparison of models : 3 different types of models are used and compared : - the IRM/KMI uses a spatially non-discretized model (the IRMB model) and develops a spatially semi-discretized model (the SCHEME model); - the ILWM-KUL uses an existing spatially discretized integrated model, the MIKE-SHE model; - the HA-FUSAG, HG-KUL, LGIH-ULG and CE-ULG teams develop and use a spatially-discretized integrated model, composed of existing sub-models of land surface (soils), groundwater and surface water (the MOHISE model). These models have been tested and compared using the same data set, to assess their capabilities to represent the different phases of the terrestrial hydrological cycle (soil, groundwater, surface water). 2) The simulation of the impacts of climate changes on the terrestrial hydrological cycle : climate change scenarios (monthly changes of meteorological variables) were elaborated on the basis of the results of three GCM (Global Climate Models) experiments provided by the IPCC (International Panel on Climate Change) and tested on the test-basins. During the 4 years-project period (1997-2000), the scientific work has been devoted to the construction, integration and implementation of the models and related data bases. The models were tested, calibrated and validated on a few representative Belgian basins. The selected test-basins are the Gette basin (at Budingen : 600 km²), the Geer basin (at Kanne : 465 km²) and the Ourthe Orientale basin (at Mabompré : 319 km²). The results of this research demonstrate the ability of the models to simulate the functioning of the terrestrial hydrological cycle under the present climate and to take into account the major processes that occur in the soils, groundwater and surface water compartments. The models have been used to assess the effects of potential climate changes on the terrestrial hydrological cycle. [less ▲]

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See detailStochastic analysis of the effect of heterogeneity and fractures on radionuclide transport in a low-permeability clay layer
Huysmans, Marijke; Dassargues, Alain ULg

in Environmental Geology (2005), 48(7), 920-930

Deep low-permeability clay layers are considered as safe environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is a candidate host rock for deep geological disposal. In this ... [more ▼]

Deep low-permeability clay layers are considered as safe environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is a candidate host rock for deep geological disposal. In this study, we analyze the effects of fractures and spatially variable hydraulic conductivity on radionuclide migration through the clay. Fracture geometry and properties are simulated with Monte Carlo simulation. The heterogeneity of hydraulic conductivity is simulated by direct sequential co-simulation using measurements of hydraulic conductivity and four types of secondary variables. The hydraulic conductivity and fracture simulations are used as input for a transport model. Radionuclide fluxes computed with this heterogeneous model are compared with fluxes obtained with a homogeneous model. The output fluxes of the heterogeneous model differ at most 8% from the homogeneous model. The main safety function of the Boom Clay is thus not affected by the fractures and the spatial variability of hydraulic conductivity. [less ▲]

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See detailStudy of cavernous underground conduits in Nam La (Northwest Vietnam) by an integrative approach
Tam, V. T.; De Smedt, F.; Batelaan, Okke et al

in Hydrogeology Journal (2005), 13(5-6), 675-689

This paper presents the result of an investigation of underground conduits, which connect the swallow holes and the resurgence of a blind river in the tropical, highly karstified limestone Nam La ... [more ▼]

This paper presents the result of an investigation of underground conduits, which connect the swallow holes and the resurgence of a blind river in the tropical, highly karstified limestone Nam La catchment in the NW of Vietnam. The Nam La River disappears underground in several swallow holes near the outlet of the catchment. In the rainy season this results in flooding upstream of the sinkholes. A hypothesis is that the Nam La River resurges at a large cavern spring 4.5 km east of the catchment outlet. A multi-thematic study of the possible connections between the swallow holes and the resurgence was carried out to investigate the geological structure, tectonics, cave structure analysis and discharge time series. The existence of the underground conduits was also tested and proven by tracer experiments. On the basis of a lineament analysis the location of the underground conduits were predicted. A remote sensing derived lineament-length density map was used to track routes from the swallow holes to the resurgence, having the shortest length but highest lineament density. This resulted in a plan-view prediction of underground conduits that matches with the cave and fault development. The functioning of the conduits was further explained by analysing flooding records of a nearby doline, which turns out to act as a temporary storage reservoir mitigating flooding of the catchment outlet area. [less ▲]

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See detailSimulation of radionuclide mass fluxes in a heterogeneous clay formation locally disturbed by excavation
Huysmans, Marijke; Berckmans, Arne; Dassargues, Alain ULg

in Renard, Philippe; Demougeot-Renard, H.; Froidevaux, R. (Eds.) Geostatistics for Environmental Applications (Proc. of GEOENV’2004) (2005)

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See detailTravel time simulation of radionuclides in a 200 m deep heterogeneous clay formation locally disturbed by excavation
Huysmans, Marijke; Berckmans, Arne; Dassargues, Alain ULg

in Seventh International Geostatistics Congress (2005)

In the North of Belgium the Boom Clay Formation, at a depth of 200m below surface, is being evaluated as a potential host formation for the disposal of vitrified nuclear waste. The aim of this study is to ... [more ▼]

In the North of Belgium the Boom Clay Formation, at a depth of 200m below surface, is being evaluated as a potential host formation for the disposal of vitrified nuclear waste. The aim of this study is to model the transport of radionuclides through the clay, taking into account the geological heterogeneity and the excavation induced fractures around the galleries in which the waste will be stored. This is achieved by combining a transport model with geostatistical techniques used to simulate the geological heterogeneity and fractures of the host rock formation. In a first phase, 100 simulations of the hydraulic conductivity of the clay are generated by conditional stochastic simulation, using measurements of hydraulic conductivity and 4 types of secondary variables: resistivity logs, gamma ray logs, grain size measurements and descriptions of the lithology. Thereafter, 100 simulations of the fractures around the excavation are generated based on information about the extent, orientation, spacing and aperture of excavation induced fractures, measured around similar galleries. Subsequently, the hydraulic conductivity simulations and the fracture simulations are randomly combined and used as input for a transport model that calculates the transport by advection, diffusion, dispersion, adsorption and decay through the heterogeneous and fractured medium. The effect of “self healing” of the clay formation as a function of time after excavation is taken into account. Finally, this results in 100 breakthrough curves of radionuclides in the aquifers surrounding the Boom Clay, reflecting the uncertainty of travel time through the clay resulting from the uncertainty of the hydraulic conductivity and the fracture distribution. The breakthrough curves can serve as a risk management tool in the evaluation of the suitability of the Boom Clay Formation as a host rock for vitrified nuclear waste storage. [less ▲]

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See detailLarge-scale groundwater flow and transport modeling: Methodology and application to the Meuse Basin – Belgium
Orban, Philippe ULg; Brouyère, Serge ULg; Corbeanu, Horatiu et al

in Bringing Groundwater Quality Research to the Watershed Scale - Proceedings of GQ2004 (2005)

To meet the requirements of the EU Water Framework Directive, an integrated water management project named PIRENE was initiated by the Walloon Region of Belgium. A partner of this project, the ... [more ▼]

To meet the requirements of the EU Water Framework Directive, an integrated water management project named PIRENE was initiated by the Walloon Region of Belgium. A partner of this project, the Hydrogeology Group of the University of Liège, is in charge of the development of a physically based transient groundwater flow and transport model for the Walloon part of the Meuse Basin (approximately 17 000 km2). To face the problems associated with this large-scale model, a general approach has been developed that combines a hydrogeological database and GIS systems to manage data. Techniques of spatial discretization have been applied that optimize the number of unknowns. For modelling groundwater flow and transport on a large scale, a new numerical approach called the Hybrid Finite Element Mixing Cell (HFEMC) has been implemented in the 3-D simulator SUFT3D. [less ▲]

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See detailMarché de services en vue de simuler l’impact, sur le régime hydrologique de l’Ourthe, de l’implantation de bassins écrêteurs dans les vallées de l’Ourthe et de l’Amblève (MOHICAN)
Deliège, Jean-François ULg; Bourouag, Mohamed ULg; Dautrebande, Sylvia et al

Report (2004)

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. En 2004, le SETHY a demandé aux développeurs du projet de simuler l’impact sur le régime hydrologique de l’Ourthe, de bassins écrêteurs dans les vallées de l’Ourthe et de l’Amblève. Plus spécifiquement, les objectifs de l’étude étaient d’estimer l’efficacité réelle de ces bassins écrêteurs (Les Combes, 16.3 Mm³, Ourthe ; Gran Han, 15.0 Mm³, Ourthe ; Stoumont, 5.7 Mm³, Amblève) pour la diminution des débits de pointe et des hauteurs d’eau, en particulier lors de très grandes crues. Dans le cas des grandes crues testée, les simulations montrent clairement la grande sensibilité des résultats aux différentes combinaisons possibles des bassins écrêteurs et surtout aux lois de gestion à utiliser pour ces bassins : il n’existe pas une loi générale qui donne un résultat maximal pour tous les types de grandes crues, et la gestion combinée des bassins est délicate. [less ▲]

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See detailStudy on the relationship between lineaments and borehole specific capacity in a fractured and karstified limestone area in Vietnam
Tam, V. T.; De Smedt, F.; Batelaan, Okke et al

in Hydrogeology Journal (2004), 12(6), 662-673

For a karstified limestone area in NW Vietnam, the relationship between the distribution of lineaments and borehole specific capacity is determined, resulting in the conclusion that not only the borehole ... [more ▼]

For a karstified limestone area in NW Vietnam, the relationship between the distribution of lineaments and borehole specific capacity is determined, resulting in the conclusion that not only the borehole geomorphological-hydrogeological position but also the lineament distribution influences the specific capacity. No significant spatial well yield patterns are evident in this highly fractured-karstified region. The supposition is that lineaments caused by geotectonic activities affect the local variability in borehole specific capacity. Sixteen pumping tests in conjunction with a comprehensive lineament analysis are used to prove this relationship. The boreholes and lineaments are classified into two groups according to their similarity in geomorphological-hydrogeological features. Lineaments tend to be less detectable in discharge areas (lowland, wide and flat valleys) in contrast to the high density in recharge areas (highland narrow-mountainous ravines). In addition, the presence of a stream network in the former can act as a recharge source to the underlain karstic groundwater system. Consequently, boreholes that are in the discharge areas with a lower density of lineaments often produce high yield. For recharge areas with a high density of lineaments, a good correlation is found between lineament density and borehole specific capacity. [less ▲]

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See detailModelling seasonal variations in nitrate and sulphate concentrations in a vulnerable alluvial aquifer
Peeters, Luk; Haerens, Bruno; Van der Sluys, Jan et al

in Environmental Geology (2004), 46(6-7), 951-961

The Eisden-Meeswijk region in Belgium has been affected by mining subsidence due to the deep coal mining activities. Groundwater levels in the alluvial plain of the Meuse River are maintained below the ... [more ▼]

The Eisden-Meeswijk region in Belgium has been affected by mining subsidence due to the deep coal mining activities. Groundwater levels in the alluvial plain of the Meuse River are maintained below the ground surface by drainage installations and municipal well fields. A correlation between the water level in the Meuse River and the variation in nitrate and sulphate concentrations in the aquifer has been observed. A transient groundwater model is developed for the period May 1998-May 2002 and advective transport simulations have been carried out using this model. During dry periods, the major groundwater flow is directed towards the Meuse River, thereby feeding the river. During wet periods, however, groundwater flows in the opposite direction. Due to these variations in groundwater flow direction and to the extraction of groundwater, zones of higher solute concentration exist of which the position and extension vary both spatially and temporally. [less ▲]

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See detailCharacterization of a cavern conduit system in Vietnam by time series correlation, cross-spectrum and wavelet analyses
Tam, V. T.; De Smedt, F.; Batelaan, Okke et al

in Hydrological Sciences Journal = Journal des Sciences Hydrologiques (2004), 49(5), 879-900

Time series analyses are applied to characterize the transient flow regimes of the Nam La cavern conduit, northwest Vietnam. The conduit transforms the input signal to an output signal, and the degree of ... [more ▼]

Time series analyses are applied to characterize the transient flow regimes of the Nam La cavern conduit, northwest Vietnam. The conduit transforms the input signal to an output signal, and the degree of transformation provides information on the nature of the flow system. The input for the analysis is net precipitation and the flow hydrograph at the cave entrance, while the output series is the flow hydrograph at the resurgence. Cross-correlation and cross-spectrum analysis are used to investigate the stationarity and linearity of the input-output transformation of the system, resulting in hydrodynamic properties such as system memory, response time, and mean delay between input and output. It is shown that during high flow periods, the flow in the conduit is pressurized. Consequently, the linear input-output assumption holds only for low flows. To highlight the hydrodynamics of the cavern conduit for the high flow periods, wavelet spectrum and wavelet cross-spectrum analyses are applied. [less ▲]

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See detailModelling groundwater flow and solute transport in karstic systems: from dreams to the reality – how can models help for groundwater vulnerability assessment ?
Dassargues, Alain ULg

in Proceedings of Trans-Karst 2004, International Transdisciplinary Conference on Development and Conservation of Karst Regions (2004, September)

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See detailMigration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation
Brouyère, Serge ULg; Dassargues, Alain ULg; Hallet, Vincent

in Journal of Contaminant Hydrology (2004), 72(1-4), 135-164

This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone ... [more ▼]

This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone overlying a chalk aquifer in Belgium. Various laboratory measurements were performed on core samples collected during the drilling of boreholes in the experimental site. In the field, experiments consisted of well logging, infiltration tests in the unsaturated zone, pumping tests in the saturated zone and tracer tests in both the saturated and unsaturated zones. Results show that gravitational flows govern groundwater recharge and solute migration mechanisms in the unsaturated zone. In the variably saturated chalk, the migration and retardation of solutes is strongly influenced by recharge conditions. Under intense injection conditions, solutes migrate at high speed along the partially saturated fissures, downward to the saturated zone. At the same time, they are temporarily retarded in the almost immobile water located in the chalk matrix. Under normal recharge conditions, fissures are inactive and solutes migrate slowly through the chalk matrix. Results also show that concentration dynamics in the saturated zone are related to fluctuations of groundwater levels in the aquifer. A conceptual model is proposed to explain the hydrodispersive behaviour of the variably saturated chalk. Finally, the vulnerability of the chalk to contamination issues occurring at the land surface is discussed. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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