References of "Dassargues, Alain"
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See detailHeat tracer test in an alluvial aquifer: field experiment and inverse modelling
Klepikova, Maria; Wildemeersch, Samuel; Jamin, Pierre ULg et al

Poster (2016, April 20)

Using heat as an active tracer for aquifer characterization is a topic of increasing interest. In this study, we investigate the potential of using heat tracer tests for characterization of a shallow ... [more ▼]

Using heat as an active tracer for aquifer characterization is a topic of increasing interest. In this study, we investigate the potential of using heat tracer tests for characterization of a shallow alluvial aquifer. A thermal tracer test was conducted in the alluvial aquifer of the Meuse River, Belgium. The tracing experiment consisted in simultaneously injecting heated water and a dye tracer in a piezometer and monitoring the evolution of groundwater temperature and tracer concentration in the recovery well and in monitoring wells. To get insights in the 3D characteristics of the heat transport mechanisms, temperature data from a large number of observation wells distributed throughout the field site (space-filling arrangement) were used. Temperature breakthrough curves in observation wells are contrasted with what would be expected in an ideal layered aquifer. They reveal strongly unequal lateral and vertical components of the transport mechanisms. The observed complex behavior of the heat plume was explained by the groundwater flow gradient on the site and heterogeneity of hydraulic conductivity field. Moreover, due to high injection temperatures during the field experiment a temperature-induced fluid density effect on heat transport occurred. By using a flow and heat transport numerical model with variable density coupled with the pilot point inverse approach, main preferential flow paths were delineated. [less ▲]

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See detailHow heterogeneity of the K-field influences a heat plume in a shallow alluvial aquifer: responses from a heat tracer test
Klepikova, Maria; Jamin, Pierre ULg; Orban, Philippe ULg et al

in Abstract book (2016, January 26)

Simultaneous solute and heat tracer test provides essential information for a reliable assessment of low temperature geothermal systems. The actual efficiency of ‘open systems’, including heat storage ... [more ▼]

Simultaneous solute and heat tracer test provides essential information for a reliable assessment of low temperature geothermal systems. The actual efficiency of ‘open systems’, including heat storage projects, is strongly affected by the heterogeneity of the hydraulic conductivity field (K-field). It could be also useful for assessing the cumulative impacts of numerous projects in urban areas on the groundwater resources. Using field data from a solute and heat tracer test conducted in the alluvial aquifer of the Meuse River (Belgium), an inverse problem of parameter estimation is solved. The tracing experiment consisted in simultaneously injecting heated water and a dye tracer in a piezometer and monitoring the evolution of groundwater temperature and tracer concentration in the recovery well and in monitoring wells. To get insights in the 3D characteristics of the heat plume, an arrangement of three transects of observation wells was used. The breakthrough curves measured in the recovery well showed that heat transfer in the alluvial aquifer is slower and more dispersive than solute transport. Recovery is very low for heat while in the same time it is measured as relatively high for the solute tracer. This is due to the fact that heat transport is a thermal diffusion dominated process. For conditions corresponding to high Peclet numbers, the hydraulic conductivity is the primary calibration parameter for predicting heat plume distribution. Heat diffusion is larger than molecular diffusion, implying that exchange between groundwater and the porous medium matrix is far more significant for heat than for solute tracers. [less ▲]

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See detailHydrogeological conditions required for Underground Pumping Storage Hydroelectricity (UPSH) in old mines
Bodeux, Sarah ULg; Pujades, Estanislao ULg; Orban, Philippe ULg et al

in Abstract book (2016, January 26)

Renewable energy sources, because of their intermittence, could not afford a stable production and an adequate variability according to the energy demand. Underground Pumped Storage Hydroelectricity (UPSH ... [more ▼]

Renewable energy sources, because of their intermittence, could not afford a stable production and an adequate variability according to the energy demand. Underground Pumped Storage Hydroelectricity (UPSH) using abandoned mine works is an interesting alternative, in flat regions, to store energy during low demand periods by pumping water from an underground mine to an upper reservoir. From the hydrogeological point of view, two considerations can arise for studying the feasibility before constructing an UPSH plant: 1) the alteration of the natural conditions of surrounding aquifers, and (2) the efficiency of the plant depending on possible leakage in the cavities from the hydrogeological environment. A potential old slate mine was selected through a multi-criterion method and its geometrical and hydrogeological characteristics are used to build a simple but typical model. With the help of the HFEMC approach implemented in the code SUFT3D (HEG-ULg), the groundwater flows are modelled for a representative cavity. Simulations of groundwater flow induced by a UPSH system are performed and the main variables are identified. Piezometric heads around the reservoir oscillate, the magnitude of the oscillations and the time to achieve a pseudo-steady state (magnitude and head reached during oscillations not varying anymore with time) depend on the boundaries, the parameters of the aquifer and the characteristics of the underground reservoir. The required hydrogeological conditions are deduced and a screening methodology can be proposed to assess the main impacts caused in aquifers by UPSH plants. Their efficiency regarding the water level evolution inside the reservoir is also considered accommodating the cyclic pumped storage schemes. [less ▲]

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See detailHeat tracer and solute tests in an alluvial aquifer: field experiment and inverse modelling
Dassargues, Alain ULg; Klepikova, Maria; Jamin, Pierre ULg et al

Poster (2015, December 18)

Using heat as an active tracer in different types of aquifers is a topic of increasing interest. In this study, we investigate the potential interest of using heat tracer tests for characterization of a ... [more ▼]

Using heat as an active tracer in different types of aquifers is a topic of increasing interest. In this study, we investigate the potential interest of using heat tracer tests for characterization of a shallow alluvial aquifer. A thermal tracer test was conducted in the alluvial aquifer of the Meuse River, Belgium. The tracing experiment consisted in simultaneously injecting heated water and a dye tracer in a piezometer and monitoring the evolution of groundwater temperature and tracer concentration in the recovery well and in monitoring wells. To get insights in the 3D characteristics of the heat transport mechanisms the space-filling arrangement of observation wells was used. The breakthrough curves measured in the recovery well showed that heat transfer in the alluvial aquifer is slower and more dispersive than solute transport. Recovery is very low for heat while in the same time it is measured as relatively high for the solute tracer. This is due to the fact that heat diffusion is larger than molecular diffusion, implying that exchange between groundwater and the porous medium matrix is far more significant for heat than for solute tracers. Temperature breakthrough curves in other piezometers are contrasted with what would be expected in an ideal layered aquifer. They reveal strongly unequal lateral and vertical components of the transport mechanisms. The observed complex behavior of the heat plume was explained by the groundwater flow gradient on the site and heterogeneities of hydraulic conductivity field. By using numerical model of heat and flow coupled with pilot points inverse approach main preferential paths were characterized. [less ▲]

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See detailUnderground Pumped Storage Hydroelectricity using abandoned works (open pits and deep mines)
Pujades, Estanislao ULg; Willems, Thibault ULg; Bodeux, Sarah ULg et al

Conference (2015, December 15)

Pumped Storage Hydroelectricity (PSH) is a good alternative to increase the efficiency of power plants, which cannot regulate the amount of electricity generated according to the demand (wind, solar or ... [more ▼]

Pumped Storage Hydroelectricity (PSH) is a good alternative to increase the efficiency of power plants, which cannot regulate the amount of electricity generated according to the demand (wind, solar or even nuclear power plants). PSH plants, which consist in two reservoirs located at different heights (upper and lower), can store energy during low demand periods (pumping water from the lower to the upper reservoir) and generate electricity during the high demand peaks (falling water from the upper to the lower reservoir). Given that the two reservoirs must be located at different heights, PSH plants cannot be constructed in flat regions. Nevertheless, in these regions, an alternative could be to use abandoned underground works (open pits or deep mines) as lower reservoirs to construct Underground Pumped Storage Hydroelectricity (UPSH) plants. To select the best place to construct a plant, two considerations must be taken into account regarding the interaction between UPSH plants and groundwater: 1) the alteration of the natural conditions of aquifers and 2), the efficiency of the plant since the electricity generated depends on the hydraulic head inside the underground reservoir. Obviously, a detailed numerical model must be necessary before to select a location. However, a screening methodology to reject the most disadvantageous sites in a short period of time would be useful. Groundwater flow impacts caused by UPSH plants are analyzed numerically and the main variables involved in the groundwater evolution are identified. The most noticeable effect consists in an oscillation of the groundwater. The hydraulic head around which groundwater oscillates, the magnitude of the oscillations and the time to achieve a “dynamic steady state” depend on the boundaries, the parameters of the aquifer and the characteristics of the underground reservoir. A screening methodology is proposed to assess the main impacts caused in aquifers by UPSH plants. Finally, the efficiency regarding the groundwater evolution inside the reservoir is determined. [less ▲]

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See detailGroundwater and sinking coastal zones: how pumping and drainage create more trouble than climatic changes
Dassargues, Alain ULg

Conference (2015, December 10)

Much attention is paid to sea-level rise due to climate change. However, the problem of land subsidence because of human-induced changes of (fluid) groundwater conditions in the underground can be by far ... [more ▼]

Much attention is paid to sea-level rise due to climate change. However, the problem of land subsidence because of human-induced changes of (fluid) groundwater conditions in the underground can be by far more significant locally (Showstack, 2014). The ‘sinking’ regions correspond most often to densely populated coastal areas located in regions where compressible and under-consolidated loose sediments are found. This is the case in late Quaternary coastal settings consisting of estuarine, deltaic and lagoonal sediments. Venice, Mexico, Bangkok, Shanghai, Changzhou, Jakarta, Manila, New Orleans, Houston, Tokyo, Ho Chi Minh City, Hanoi, … are only a few examples among the numerous ‘sinking cities’ (Gambolati & Teatini, 2015). Late Quaternary, and more particularly Holocene unconsolidated or semi-consolidated deposits form often a succession of layers that can be considered, from a hydrogeological point of view, as semi-confined or confined aquifer systems (Poland, 1984). In confined aquifers but also in unconfined aquifers, the lowering of the piezometric head due to pumping or drainage induces additional effective stresses directly in the concerned aquifer and then, with a delay depending on their characteristics, in the compressible confining layers or in the compressible lenses of silt, clay, and peat included in the aquifer. Coupling the transient groundwater flow equation with geomechanical aspects, allows understanding of the considered transient processes induced by the artificial lowering of the water pressure in the porous medium. For accurate calculations, used for understanding the observed subsidence and predicting the future subsidence, it is important to take into account the strongly non-linear effects such as the variation of the specific storage coefficient and of the permeability during the consolidation process (Dassargues, 1995, 1997, 1998). Typical and emblematic examples involving regional as well as very local land subsidence will be presented showing the general approach. Land subsidence is an important issue linked to global change and groundwater management challenges (Gorelick & Zheng, 2015). [less ▲]

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See detailGroundwater pumping and sinking cities: back to the forefront due to global change
Dassargues, Alain ULg

Scientific conference (2015, November 12)

Much attention is paid to sea level rise but the problem of land subsidence, induced by man-changed (fluid) groundwater conditions in the underground, can be by far more significant locally (Showstack ... [more ▼]

Much attention is paid to sea level rise but the problem of land subsidence, induced by man-changed (fluid) groundwater conditions in the underground, can be by far more significant locally (Showstack, 2014). The ‘sinking’ regions correspond most often to coastal densely populated areas located in regions where compressible loose sediments are found. As they are usually under-consolidated and compressible, geological settings made of recent coastal and especially estuarine, deltaic and lacustrine sediments are particularly concerned. Venice, Mexico, Bangkok, Shanghai, Changzhou, Jakarta, Manila, New Orleans, Houston, Tokyo, Ho Chi Minh City, Hanoi, … are only a few examples among the numerous ‘sinking cities’ (Gambolati & Teatini, 2015). Recent unconsolidated or semi-consolidated deposits form often a succession of layers that can be considered, from a hydrogeological point of view, as semi-confined or confined aquifer systems (Poland, 1984). In confined aquifers but also in unconfined aquifers, it is well known that the lowering of the piezometric head due to pumping or drainage induces additional effective stresses directly in the concerned aquifer and then, with a delay depending on their characteristics, in the compressible confining layers or in the compressible lenses of loam, clay, and peat included in the aquifer. This effective stress increase induces a drained consolidation process in the compressible layers. Coupling the transient groundwater flow equation with geomechanical aspects, allows understanding the considered transient processes induced by the artificial lowering of the water pressure in the porous medium. For accurate calculations, used for understanding the observed subsidence and predicting the future subsidence, it is important to take into account the strongly non-linear effects as the variation of the specific storage coefficient and of the permeability during the consolidation process (Dassargues, 1995, 1997, 1998). Recently this issue was back to the forefront of the scientific actuality as land subsidence plays an important role linked to global change and groundwater management challenges (Gorelick & Zheng, 2015). [less ▲]

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See detailHydrology and gravimetry (Assessing groundwater mass balance: Keynote lecture: Hydrogeodesy in Membach and Rochefort)
Van Camp, Michel; Vanclooster, Marnik; Watlet, A. et al

Conference (2015, October 23)

For the 10 last years, terrestrial and satellite (GRACE) gravity measurements have reached such a precision that they can be of interest to better monitor underground water masses. First, we show that ... [more ▼]

For the 10 last years, terrestrial and satellite (GRACE) gravity measurements have reached such a precision that they can be of interest to better monitor underground water masses. First, we show that terrestrial measurements provide high-precision information about the time evolution of mass changes in the few kilometres square around the gravimeter. Then, examples of the possibilities and limitations of terrestrial measurements are given in Membach, close to Eupen, and in the Rochefort karst system. In Membach, we show that the evapotranspiration can be directly inferred from continuous gravity measurements: as water evaporates and transpires from terrestrial ecosystems, the mass distribution varies through the system, changing its gravity field at the level of, or smaller than 10-10 g per day. This corresponds to 2.0 mm of water over an area of 50 ha. The strength of this method is its ability to ensure a direct, traceable and continuous monitoring of actual ET for years at the mesoscale (~50 ha) with a precision of a few tenths of mm of water. In Rochefort, gravity measurements at the surface and in the cave allows separating the water contained in the unsaturated zone from the saturated one and therefore monitoring groundwater content changes that occur in the unsaturated zone only. [less ▲]

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See detailHydrogeological assessment of diaphragm walls used to excavate deep shafts associated to tunnels construction
Pujades, Estanislao ULg; Jurado, Anna; Carrera, Jesus et al

Poster (2015, September 17)

Deep shafts are usually required during tunnels construction (for maintenance tasks when tunnel boring machines –TBM- are used) and/or the operation stage of tunnels (emergency exits). Generally, these ... [more ▼]

Deep shafts are usually required during tunnels construction (for maintenance tasks when tunnel boring machines –TBM- are used) and/or the operation stage of tunnels (emergency exits). Generally, these shafts are constructed below the water table and by the cut and cover method. Therefore, impervious diaphragm walls are desired for two main reasons: (1) to reduce risks (stability, inflows, flooding, etc.) and outside impacts (loose of groundwater resource, holes and sinkholes, etc.) during the excavation stage of a shaft and, (2) to avoid leaks and inflows of groundwater during the operation stage once the shaft is finished. Given that defects in diaphragm walls are frequent and can relatively easy be repaired before starting the excavation stage, a useful and new methodology to assess the state of enclosures before excavation is proposed. Its use would allow to reduce impacts on groundwater (construction and operation stages) and costs in case of defects as well as to increase the safety during the construction. The groundwater response regarding different scenarios of diaphragm walls is studied numerically in order to propose a successful procedure to evaluate underground enclosures imperviousness by internal pumping tests. The scenarios consist in circular and square enclosures where the diaphragm walls are assumed as homogeneous (with numerous defects) or heterogeneous (one discrete defect). The homogeneous cases are modeled by considering different effective hydraulic conductivities, while the size and position of the single defect is varied in the simulations of heterogeneous walls. An analysis of diagnostic plots and the comparison between the expected and measured groundwater evolutions inside the enclosure, is proposed to ascertain: (1) if the diaphragm walls can be considered as homogeneous or heterogeneous, (2) the effective hydraulic conductivity of the walls (if they are homogeneous) and, (3) the position of a defect (if they are heterogeneous). [less ▲]

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See detailUnderground Pumped Storage Hydroelectricity (UPSH) using abandoned works
Pujades, Estanislao ULg; Willems, Thibault ULg; Orban, Philippe ULg et al

Poster (2015, September 17)

Underground Pumped Storage Hydroelectricity (UPSH) using abandoned works is an interesting alternative to increase the efficiency of some power plants, which cannot regulate the amount of electricity ... [more ▼]

Underground Pumped Storage Hydroelectricity (UPSH) using abandoned works is an interesting alternative to increase the efficiency of some power plants, which cannot regulate the amount of electricity generated according to the demand. UPSH plants can store (pumping water from an underground to an upper reservoir) or produce energy (releasing water from an upper to an underground reservoir) during the low or high demand periods. Two considerations must be taken into account in order to construct an UPSH plant: 1) the alteration of the natural conditions of aquifers and 2), the efficiency of the plant, which depends on the hydraulic head inside the underground reservoir. Obviously, a detailed numerical model must be necessary to design a plant. However, a screening methodology to apply during the early stages of the design of a UPSH plant in order to reject the most disadvantageous sites in a short period of time would be useful. Groundwater flow impacts caused by UPSH plants are analyzed numerically and the main variables involved in the groundwater evolution are identified. The most noticeable effect consists in an oscillation of the groundwater. The hydraulic head around which groundwater oscillates, the magnitude of the oscillations and the time to achieve a pseudo-steady state (magnitude and head reached during oscillations do not vary anymore with time) depend on the boundaries, the parameters of the aquifer and the characteristics of the underground reservoir. From the numerical study, a screening methodology, which is based on existing analytical procedures (solutions for large diameter wells, methodologies for cyclic pumpings and the image well theory), is proposed to assess the main impacts caused in aquifers by UPSH plants and their efficiency regarding the groundwater evolution inside the reservoir. The procedure can be applied in a relatively short period of time and is useful to select those appropriate sites to construct a UPSH plant. [less ▲]

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See detailTowards processes-based groundwater vulnerability assessments
Dassargues, Alain ULg; Popescu, Cristina; Brouyère, Serge ULg

Conference (2015, September 15)

Various groundwater vulnerability methods have recently been developed. Considering groundwater quality issues, the most common techniques are based on calculation of an index expressing the protective ... [more ▼]

Various groundwater vulnerability methods have recently been developed. Considering groundwater quality issues, the most common techniques are based on calculation of an index expressing the protective effect (i.e. in terms of solute contaminant transport) of underground formations overlying the groundwater resource (Gogu & Dassargues, 2000, Gogu et al., 2003)). However, there is a strong need for new methods giving more emphasis on the processes-based calculation of vulnerability indicators. As a first alternative, a method is proposed based on three factors describing a pollution event (Brouyère et al., 2001): (1) the transit time from the source to the target, (2) the duration of the contamination breakthrough at the target, (3) the ratio between the maximum concentration at the target to the released concentration at the contamination source. The method can feature the impact of surface runoff to preferential infiltration points. Practically, the assessment can then be based on the simulated breakthrough curves at the ‘target’ corresponding to Dirac-type solicitations (Popescu et al., 2008). Different vulnerability maps can be built according to the relative importance conventionally given to each of the three factors. This concept allows a clear distinction between conventional aspects and processes-based results in the building of a final vulnerability indicator. A second proposal consists in reframing the groundwater vulnerability assessment in a Pressure-State-Impact causal chain that is familiar to decision makers (Beaujean et al., 2013). The method is here based on the calculation of sensitivity coefficients for a user-defined groundwater state for which several physically-based indicators are proposed. The sensitivity coefficients reflect the easiness with which the groundwater state transmits pressures into impacts. They are converted to vulnerability, using the concept of ‘transgressing a given threshold’ (Luers et al., 2003). While the methodology is general and can be applied in quantity as quality issues, the choice of causal chains has to be made prior to the calculation. The vulnerability is also related to a damaged state and is related to the ‘distance’ between the current state and a given threshold. Here also, the method allows a clear distinction between conventional choices (threshold) and scientific work (Dassargues et al., 2009). [less ▲]

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See detailA new hybrid approach for modelling groundwater flow in karst aquifers
Willems, Thibault ULg; Hakoun, Vivien ULg; Renard, Philippe et al

Conference (2015, September)

Groundwater flow modelling in karst aquifers represents a real challenge that requires adapted methods. The applicability of an innovative hybrid approach for modelling groundwater flow in karst aquifers ... [more ▼]

Groundwater flow modelling in karst aquifers represents a real challenge that requires adapted methods. The applicability of an innovative hybrid approach for modelling groundwater flow in karst aquifers, namely the Hybrid Finite Element Mixing Cell (HFEMC) method, is evaluated. The hybrid approach consists in combining a classical finite element (FE) model, to model slow flow in the rock matrix, with spatially distributed lumped reservoirs, to model fast flow in the karst conduits network. Water exchanges between the rock matrix and the conduits network are accounted for by means of an internal Fourier boundary conditions (BC). This BC (1st order exchange relation) allows to control the magnitude of water transfers between fast and slow flow domains. We tested the applicability of the HFEMC method on a schematic synthetic domain and on a real karst system. In the synthetic case analysis, we discussed dynamic processes of groundwater storage occurring in the karst system during a recharge pulse. The study focuses on the influence of selected parameters on representative variables such as the discharge curve of the karst system or pressure and mass transfers between conduits and rock matrix sub-domains. In this way, an inversion of the hydraulic gradient between karst conduits and the surrounding rock matrix is shown to occur during the recharge pulse. This phenomenon results in a temporary storage of water from conduits to the rock matrix, which impacts the modelled discharge curve. The first test performed on a real study site, the Noiraigue spring karst system (Jura mountains, Switzerland), exemplify the use of two separated lumped reservoirs for describing the conduits network, which allows to consider two base levels in the karst system. It also points out the challenges to face when modelling a complex natural karst system with the HFEMC approach. The results obtained show that the HFEMC approach is a good candidate to model groundwater flow in karst aquifers. [less ▲]

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See detailThe use of the Vadose Zone Experimental Setup as an innovative in situ characterization method for the vadose zone: a case study at an industrial contaminated site in Belgium
Fernandez de Vera, Natalia ULg; Beaujean, Jean ULg; Jamin, Pierre ULg et al

Conference (2015, September)

The development of protection and remediation plans for contaminated soil and groundwater require a detailed understanding of the transport of pollutants in the subsurface. However, such understanding is ... [more ▼]

The development of protection and remediation plans for contaminated soil and groundwater require a detailed understanding of the transport of pollutants in the subsurface. However, such understanding is affected by the lack of spatial and temporal coverage provided by the current in situ characterization technologies. A new system has been developed in order to overcome such limitations. The vadose zone experimental setup is a new development combining cross-hole geophysics and the Vadose Zone Monitoring System (VMS). In cross-hole geophysics, an injection of an electrical current using electrodes installed in vertical boreholes is triggered. From measured potential differences, spatial patterns related with subsurface heterogeneities, water content and solute concentrations are inferred. The VMS allows continuous measurements of water content at different depths of the vadose zone, as well as water sampling. The system is formed by a flexible sleeve containing monitoring units along its depth which is installed in a slanted borehole. The system was installed at a former industrial site in Belgium, where soil and groundwater are contaminated with BTEX, PAH, and heavy metals. Two VMS were installed in two slanted boreholes on site, together with four vertical boreholes containing electrodes for geophysical measurements. The site was initially monitored under natural recharge conditions. Water content sensors located along the VMS registered fast wetting and draining reactions to rainfall events followed by the activation of water transport through fractures. Results from soil water samples show continuous evolution of water chemistry with depth, due to disequilibrium between infiltrated water and the hydrochemical conditions in the unsaturated zone. Subsequently, a saline tracer was injected in the surface. The transport of the tracer in the subsurface was monitored via cross-hole and surface geophysics. Results from imaging reflect the evolution of a plume through vertical and lateral transport and dilution. [less ▲]

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See detailRegional occurence of greenhouses gases in groundwater: Initial results in shallow Belgian aquifers.
Hakoun, Vivien ULg; Gesels, Julie ULg; Tseng, Jean Hsiao-Chun et al

Poster (2015, September)

Currently, the lack of robust, context-distributed subsurface greenhouses gases (GHG) concentrations data is a key bottleneck to reduce the uncertainty range of GHG groundwater input to continental ... [more ▼]

Currently, the lack of robust, context-distributed subsurface greenhouses gases (GHG) concentrations data is a key bottleneck to reduce the uncertainty range of GHG groundwater input to continental surface water bodies such as rivers or lakes estimates. Carbon dioxyde (CO2), methane (CH4) and nitrous oxyde (N2O) are likely to be indirectly transferred to the atmosphere through groundwater discharge into continental surface water bodies. We aim to extend regional-scale estimates of indirect GHG emissions by screening, in numerous hydrogeological (such as alluvial, sandstone, chalk and limestone aquifers) and land use contexts (such as industrial and agricultural), the occurence of these gases. Here, we report and discuss CO2, CH4 and N2O concentrations from an initial survey conducted over selected sites (n= 40) within shallow (0-100 m depth) aquifers in Wallonia (Belgium) for the first time. The preliminary results obtained in this study show that the range of GHG concentrations varies between 5160 and 47544 ppm, 0 and 1064 nmol.L-1, as well as 1 and 5637 nmol.L-1 for the partial pressure of CO2, CH4 and N2O respectively. This new and unique regional dataset provides a first step in developping a refined understanding of favorable contexts for GHG occurence in groundwater which may be used to reduce the uncertainties related to indirect emissions of GHG through groundwater-surface water transfers. [less ▲]

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See detailOpen pits or deep mines used for Underground Pumped Storage Hydroelectricity (UPSH): impacts on groundwater exchanges
Pujades, Estanislao ULg; Willems, Thibault ULg; Orban, Philippe ULg et al

Poster (2015, July 08)

UPSH using abandoned works is an attractive alternative to improve the efficiency of power plants, which cannot regulate the amount of electricity generated according to the demand (wind, solar or nuclear ... [more ▼]

UPSH using abandoned works is an attractive alternative to improve the efficiency of power plants, which cannot regulate the amount of electricity generated according to the demand (wind, solar or nuclear). UPSH plants can store (pumping water from an underground to an upper reservoir) or produce energy (releasing water from an upper to an underground reservoir) during the low or high demand periods. However, it is mandatory to determine 1) the impacts caused on aquifers and 2) the role played by the aquifer characteristics in order to assess the suitability of UPSH plants. Numerical simulations are developed in order to ascertain the groundwater flow impacts and the variables involved in the process. Given the earlier stages of our study, results are obtained considering regular pumping-injection cycles and simplifying the shape of the mine/open pit. The most noticeable effect consists in an oscillation of the groundwater. The hydraulic head around which groundwater oscillates, the magnitude of the oscillations and the time to achieve a pseudo-steady state (magnitude and head reached during oscillations do not vary anymore with time) depend on the boundaries, the parameters of the aquifer and the characteristics of the underground reservoir. [less ▲]

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See detailAssessment of climate change effects on groundwater resource in transient conditions
Goderniaux, Pascal; Wildemeersch, Samuel; Brouyère, Serge ULg et al

Conference (2015, June 27)

A sophisticated transient weather generator (WG) in combination with an integrated surface-subsurface hydrological model (HydroGeoSphere) are used for producing a stochastic generation of large numbers of ... [more ▼]

A sophisticated transient weather generator (WG) in combination with an integrated surface-subsurface hydrological model (HydroGeoSphere) are used for producing a stochastic generation of large numbers of equiprobable climatic time series, representing transient climate change, and assess impacts on groundwater resources in a probabilistic way. The modelling approach, involving the catchment-scale fully integrated surface-subsurface model, is described in Goderniaux et al. [2009]. Biased-corrected climate change scenarios are applied as input of the hydrological model to quantify their impact on groundwater resources. In Goderniaux et al. [2011], the integrated model is used in combination with a stochastic daily weather generator (WG). This WG allowed generating a large number of equiprobable climate change scenarios representative of a full transient climate between 2010 and 2085. These scenarios enabled to account for the transient nature of the future climate change, and to assess the uncertainty related to the weather natural variability. The downscaling method considers changes in the climatic means, but also in the distribution of wet and dry days. This new methodology is applied for the unconfined chalky aquifer of the Geer catchment in Belgium. A general decrease of the mean groundwater piezometric heads, has been calculated. The approach allowed also to assess different uncertainty sources: (1) the uncertainty linked to the calibration of the hydrological model, using 'UCODE_2005'; (2) the uncertainty linked to the global and regional climatic models (GCMs and RCMs), by using a multi-model ensemble; (3) the uncertainty linked to the natural variability of the weather, by using stochastic climate change scenarios. 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. The WG ability to simulate transient climate change enabled the assessment of the likely timescale and associated uncertainty of a specific impact. This methodology constitutes a real improvement in the field of groundwater projections under transient climate change conditions as it enables water managers to analyse risks and take decisions with full knowledge of projected impact and their degree of confidence. [less ▲]

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See detailUncertainty of climate change impact on groundwater reserves - Application to a chalk aquifer
Goderniaux, Pascal; Brouyère, Serge ULg; Wildemeersch, Samuel et al

in Journal of Hydrology (2015), 528

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 ... [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 km2) 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. [less ▲]

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