References of "Dassargues, Alain"
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See detailDevelopment trajectory of an integrated framework for the mitigation of future flood risk: results from the FloodLand project
Saadi, Ismaïl ULg; Bruwier, Martin ULg; El Saeid Mustafa, Ahmed Mohamed ULg et al

in Transportation Letters: The International Journal of Transportation Research (in press)

In this paper, the development trajectory of an integrated framework for the mitigation of future flood risk of the Ourthe river basin in Belgium is discussed. The paper contributes to the state-of-the ... [more ▼]

In this paper, the development trajectory of an integrated framework for the mitigation of future flood risk of the Ourthe river basin in Belgium is discussed. The paper contributes to the state-of-the-art by presenting an integrated multidisciplinary framework capable of making long-term projections (time horizon 2050 and 2100) with the objective of mitigating future flood risk by proposing alternative land-use scenarios. It bridges numerous different fields, including urban planning, transport engineering, hydrology, geology, environmental engineering, and economics. The overall design and validation results of the different sub-modules of the framework are presented, and ongoing and future enhancements are highlighted. [less ▲]

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See detailMONitOring des flux de POLluants dans les Eaux Souterraines
Jamin, Pierre ULg; Dassargues, Alain ULg; Brouyère, Serge ULg

Poster (2017, May 05)

Contaminated aquifers management is currently based on the evaluation of pollutant concentration in the groundwater. This approach is necessary but totally insufficient to evaluate the risk posed by the ... [more ▼]

Contaminated aquifers management is currently based on the evaluation of pollutant concentration in the groundwater. This approach is necessary but totally insufficient to evaluate the risk posed by the contamination to potential receptors. Since the risk is due to the pollutant that are actually moving, and might reach a receptor, this concentration measurement should be combined to a measurement of the groundwater flow velocity (i.e. the driving force of contaminant migration in aquifers), to quantify the contaminant mass flux at which the receptor is exposed. We propose a new point dilution technique able to measure accurately the groundwater flux and to monitor continuously its changes with time. [less ▲]

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See detailModel-based classification of CPT data and automated lithostratigraphic mapping for high-resolution characterization of a heterogeneous sedimentary aquifer
Rogiers, Bart; Mallants, Dirk; Batelaan, Okke et al

in PLoS ONE (2017), 12(5), 0176656

Cone penetration testing (CPT) is one of the most efficient and versatile methods currently available for geotechnical, lithostratigraphic and hydrogeological site characterization. Currently available ... [more ▼]

Cone penetration testing (CPT) is one of the most efficient and versatile methods currently available for geotechnical, lithostratigraphic and hydrogeological site characterization. Currently available methods for soil behaviour type classification (SBT) of CPT data however have severe limitations, often restricting their application to a local scale. For parameterization of regional groundwater flow or geotechnical models, and delineation of regional hydro- or lithostratigraphy, regional SBT classification would be very useful. This paper investigates the use of model-based clustering for SBT classification, and the influence of different clustering approaches on the properties and spatial distribution of the obtained soil classes. We additionally propose a methodology for automated lithostratigraphic mapping of regionally occurring sedimentary units using SBT classification. The methodology is applied to a large CPT dataset, covering a groundwater basin of ~60 km2 with predominantly unconsolidated sandy sediments in northern Belgium. Results show that the model-based approach is superior in detecting the true lithological classes when compared to more frequently applied unsupervised classification approaches or literature classification diagrams. We demonstrate that automated mapping of lithostratigraphic units using advanced SBT classification techniques can provide a large gain in efficiency, compared to more time-consuming manual approaches and yields at least equally accurate results. [less ▲]

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See detailThe Prediction-Focused Approach: An opportunity for hydrogeophysical data integration and interpretation
Hermans, Thomas ULg; Nguyen, Frédéric ULg; Klepikova, Maria et al

Conference (2017, April 28)

Hydrogeophysics is an interdisciplinary field of sciences aiming at a better understanding of subsurface hydrological processes. If geophysical surveys have been successfully used to qualitatively ... [more ▼]

Hydrogeophysics is an interdisciplinary field of sciences aiming at a better understanding of subsurface hydrological processes. If geophysical surveys have been successfully used to qualitatively characterize the subsurface, two important challenges remain for a better quantification of hydrological processes: (1) the inversion of geophysical data and (2) their integration in hydrological subsurface models. The classical inversion approach using regularization suffers from spatially and temporally varying resolution and yields geologically unrealistic solutions without uncertainty quantification, making their utilization for hydrogeological calibration less consistent. More advanced techniques such as coupled inversion allow for a direct use of geophysical data for conditioning groundwater and solute transport model calibration. However, the technique is difficult to apply in complex cases and remains computationally demanding to estimate uncertainty. In a recent study, we investigate a prediction-focused approach (PFA) to directly estimate subsurface physical properties from geophysical data, circumventing the need for classic inversions. In PFA, we seek a direct relationship between the data and the subsurface variables we want to predict (the forecast). This relationship is obtained through a prior set of subsurface models for which both data and forecast are computed. A direct relationship can often be derived through dimension reduction techniques. PFA offers a framework for both hydrogeophysical “inversion” and hydrogeophysical data integration. For hydrogeophysical “inversion”, the considered forecast variable is the subsurface variable, such as the salinity. An ensemble of possible solutions is generated, allowing uncertainty quantification. For hydrogeophysical data integration, the forecast variable becomes the prediction we want to make with our subsurface models, such as the concentration of contaminant in a drinking water production well. Geophysical and hydrological data are combined to derive a direct relationship between data and forecast. We illustrate the process for the design of an aquifer thermal energy storage (ATES) system. An ATES system can theoretically recover in winter the heat stored in the aquifer during summer. In practice, the energy efficiency is often lower than expected due to spatial heterogeneity of hydraulic properties combined to a non-favorable hydrogeological gradient. A proper design of ATES systems should consider the uncertainty of the prediction related to those parameters. With a global sensitivity analysis, we identify sensitive parameters for heat storage prediction and validate the use of a short term heat tracing experiment monitored with geophysics to generate informative data. First, we illustrate how PFA can be used to successfully derive the distribution of temperature in the aquifer from ERT during the heat tracing experiment. Then, we successfully integrate the geophysical data to predict medium-term heat storage in the aquifer using PFA. The result is a full quantification of the posterior distribution of the prediction conditioned to observed data in a relatively limited time budget. [less ▲]

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See detailWater chemical evolution in Underground Pumped Storage Hydropower plants and induced consequences.
Pujades, Estanislao ULg; Orban, Philippe ULg; Jurado Elices, Anna ULg et al

Conference (2017, April 27)

Underground Pumped Storage Hydropower (UPSH) using abandoned mines is an alternative to manage the elec- tricity production in flat regions. UPSH plants consist of two reservoirs; the upper reservoir is ... [more ▼]

Underground Pumped Storage Hydropower (UPSH) using abandoned mines is an alternative to manage the elec- tricity production in flat regions. UPSH plants consist of two reservoirs; the upper reservoir is located at the surface or at shallow depth, while the lower reservoir is underground. These plants have potentially less constraints that the classical Pumped Storage Hydropower plants because more sites are available and impacts on landscape, land use, environment and society seem lower. Still, it is needed to consider the consequences of the groundwater exchanges occurring between the underground reservoir and surrounding porous media. Previous studies have been focused on the influence of these groundwater exchanges on the efficiency and on groundwater flow impacts. However, hydrochemical variations induced by the surface exposure of pumped water and their consequences have not been yet addressed. The objective of this work is to evaluate the hydrochemical evolution of the water in UPSH plants and its effects on the environment and on the UPSH efficiency. The problem is studied numerically by means of reactive transport modelling. Different scenarios are considered varying the chemical properties of the surrounding porous medium and groundwater. Results show that the dissolution and/or precipitation of some compounds may affect (1) the groundwater quality, and (2) the efficiency and the useful life of the used pumps and turbines of the UPSH system. [less ▲]

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See detailUnderground pumped storage hydropower plants using open pit mines: How do groundwater exchanges influence the efficiency?
Pujades, Estanislao ULg; Orban, Philippe ULg; Bodeux, Sarah ULg et al

in Applied Energy (2017), 190

Underground Pumped Storage Hydropower (UPSH) is a potential alternative to manage electricity production in flat regions. UPSH plants will interact with the surrounding porous medium through exchanges of ... [more ▼]

Underground Pumped Storage Hydropower (UPSH) is a potential alternative to manage electricity production in flat regions. UPSH plants will interact with the surrounding porous medium through exchanges of groundwater. These exchanges may impact the surrounding aquifers, but they may also influence the efficiency of the pumps and turbines because affecting the head difference between the reservoirs. Despite the relevance for an accurate efficiency assessment, the influence of the groundwater exchanges has not been previously addressed. A numerical study of a synthetic case is presented to highlight the importance of considering the groundwater exchanges with the surrounding porous medium. The general methodology is designed in order to be further applied in the decision making of future UPSH plants introducing each case specific complexity. The underground reservoir of a hypothetical UPSH plant, which consists in an open pit mine, is considered and modelled together with the surrounding porous medium. Several scenarios with different characteristics are simulated and their results are compared in terms of (1) head difference between the upper and lower reservoirs and (2) efficiency by considering the theoretical performance curves of a pump and a turbine. The results show that the efficiency is improved when the groundwater exchanges increase. Thus, the highest efficiencies will be reached when (1) the underground reservoir is located in a transmissive porous medium and (2) the walls of the open pit mine do not constrain the groundwater exchanges (they are not waterproofed). However, a compromise must be found because the characteristics that increase the efficiency also increase the environmental impacts. Meaningful and reliable results are computed in relation to the characteristics of the intermittent and expected stops of UPSH plants. The frequency of pumping and injection must be considered to properly configure the pumps and turbines of future UPSH plants. If not, pumps and turbines could operate far from their best efficiency conditions. [less ▲]

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See detailFactors controlling the evolution of groundwater dynamics and chemistry in the Senegal River Delta
Gning, Abdoul Aziz; Orban, Philippe ULg; Gesels, Julie ULg et al

in Journal of Hydrology: Regional Studies (2017), 10

tStudy region: Senegal River Delta. Study focus: The Senegal River Delta is a strategic region for the development of irri-gated agriculture. Despite a Sahelian climatic context, the management of the ... [more ▼]

tStudy region: Senegal River Delta. Study focus: The Senegal River Delta is a strategic region for the development of irri-gated agriculture. Despite a Sahelian climatic context, the management of the river withdams ensures water availability throughout the year. With the intensification of agri-culture, degradation of cultivated soils is observed, mostly linked to the existence of ashallow salty aquifer. In this context, regional surveys were performed to characterizegroundwater–surface water interactions and to identify the impact of artificial river man-agement and agricultural intensification on the evolution of groundwater dynamics andchemistry.New hydrological insights for the region: Results show that groundwater far away from riversand outside irrigated plots has evolved from marine water to brines under the influenceof evapotranspiration. Near rivers, salinity of groundwater is lower than seawater andgroundwater mineralization seems to evolve in the direction of softening through cationicexchanges related to permanent contact with fresh water. Despite large volumes of waterused for rice cultivation, groundwater does not show any real softening trend in the culti-vated parcels. Results show that the mechanisms that contribute to repel salt water fromthe sediments correspond to a lateral flush near permanent surface water streams and notto vertical drainage and dilution with rainfall or irrigation water. It is however difficultto estimate the time required to come back to more favorable conditions of groundwatersalinity. [less ▲]

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See detailTemporal changes in groundwater quality of the Saloum coastal aquifer
Dieng, Ndeye Maguette ULg; Orban, Philippe ULg; Otten, Joël ULg et al

in Journal of Hydrology: Regional Studies (2017), 9

Abstract Study region: Groundwater in the southern part of the Saloum Basin in Senegal. Study focus: The Saloum estuary is a hypersaline and ‘inverse’ estuary where the salinity of river water increases ... [more ▼]

Abstract Study region: Groundwater in the southern part of the Saloum Basin in Senegal. Study focus: The Saloum estuary is a hypersaline and ‘inverse’ estuary where the salinity of river water increases in the upstream direction. This region is problematic in that due to the underlain superficial Continental Terminal aquifer bordered by the hypersaline estuary constitutes the unique fresh groundwater reservoir for water supply for its estimated 466,000 residents living in 18 rural districts (belonging to the regions of Fatick, Kaolack and Kaffrine). This is of high value given that the deep Maastrichtian aquifer (200-300m depth) is saline. This study aims to describe and understand temporal changes in the chemical and isotopic compositions of groundwater, the geochemical processes and especially the groundwater salinization. New hydrological insights for the region: The analytical data were discriminated into 3 groups on the basis of the water types. Na-Cl, Ca-Cl and Ca-SO4 rich waters derived from saline water intrusion at the vicinity of the Saloum River accompanied by ion exchange reactions and pollution dominate the first group. The second group located mainly in the centre and eastern parts of the region is featured fresh groundwater of Ca-HCO3 derived from calcite dissolution reactions. The third group of Na-HCO3 type and less mineralized indicates freshening processes by recently infiltrating rainwaters. Slight seasonal chemical variations are observed due to new infiltrating water reaching the water table. High variation in rainfall between the 2 reference years (2003 and 2012) also changes chemical patterns in the groundwater. Chemical evolution of the groundwater is geographically observed and is due to a combination of dilution by recharge, anthropic contamination and seawater intrusion. The results of environmental isotopes (δ18O, δ2H) compared with the local meteoric line indicate that the groundwater has been affected by evaporation processes before and during infiltration. The results also clearly indicate mixing with saltwater and an evolution towards relative freshening between 2003 and 2012 in some wells near the Saloum River. [less ▲]

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See detailInteractions between groundwater and the cavity of an old slate mine used as lower reservoir of an UPSH (Underground Pumped Storage Hydroelectricity): A modelling approach
Bodeux, Sarah ULg; Pujades, Estanislao ULg; Orban, Philippe ULg et al

in Engineering Geology (2017), 217

In the actual evolving energy context, characterized by an increasing part of intermittent renewable sources, the development of energy storage technologies are required, such as pumped storage ... [more ▼]

In the actual evolving energy context, characterized by an increasing part of intermittent renewable sources, the development of energy storage technologies are required, such as pumped storage hydroelectricity (PSH). While new sites for conventional PSH plants are getting scarce, it is proposed to use abandoned underground mines as lower reservoirs for Underground Pumped Storage Hydroelectricity (UPSH). However, the hydrogeological consequences produced by the cyclic solicitations (continuous pumpings and injections) have been poorly investigated. Therefore, in this work, groundwater interactions with the cyclically fill and empty cavity were numerically studied considering a simplified description of a slate mine. Two pumping/injection scenarios were considered, both for a reference slate rock case and for a sensitivity analysis of variations of aquifer hydraulic conductivity value. Groundwater impacts were assessed in terms of oscillations of piezometric heads and mean drawdown around the cavity. The value of the hydraulic conductivity clearly influences the magnitude of the aquifer response. Studying interactions with the cavity highlighted that seepage into the cavity occurs over time. The volume of seeped water varies depending on the hydraulic conductivity and it could become non-negligible in the UPSH operations. These preliminary results allow finally considering first geological feasibility aspects, which could vary conversely according to the hydraulic conductivity value and to the considered groundwater impacts. [less ▲]

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See detailFactors controlling spatial and temporal patterns of multiple pesticide compounds in groundwater (Hesbaye chalk aquifer, Belgium)
Hakoun, Vivien; Orban, Philippe ULg; Dassargues, Alain ULg et al

in Environmental Pollution (2017)

Factors governing spatial and temporal patterns of pesticide compounds (pesticides and metabolites) concentrations in chalk aquifers remain unclear due to complex flow processes and multiple sources. To ... [more ▼]

Factors governing spatial and temporal patterns of pesticide compounds (pesticides and metabolites) concentrations in chalk aquifers remain unclear due to complex flow processes and multiple sources. To uncover which factors govern pesticide compound concentrations in a chalk aquifer, we develop a methodology based on time series analyses, uni- and multivariate statistics accounting for concentrations below detection limits. The methodology is applied to long records (1996–2013) of a restricted compound (bentazone), three banned compounds (atrazine, diuron and simazine) and two metabolites (deethylatrazine (DEA) and 2,6–dichlorobenzamide (BAM)) sampled in the Hesbaye chalk aquifer in Belgium. In the confined area, all compounds had non-detects fractions >80%. By contrast, maximum concentrations exceeded EU’s drinking-water standard (100 ngL-1) in the unconfined area. This contrast confirms that recent recharge and polluted water did not reach the confined area, yet. Multivariate analyses based on variables representative of the hydrogeological setting revealed higher diuron and simazine concentrations in the southeast of the unconfined area, where urban activities dominate land use and where the aquifer lacks protection from a less permeable layer of hardened chalk. At individual sites, positive correlations (up to τ =0,48 for bentazone) between pesticide compound concentrations and multi-annual groundwater level fluctuations confirm occurrences of remobilization. A downward temporal trend of atrazine concentrations likely reflects decreasing use of this compound over the last 28 years. However, the lack of a break in concentrations time series and maximum concentrations of atrazine, simazine, DEA and BAM exceeding EU’s standard post-ban years provide evidence of persistence. Contrasting upward trends in bentazone concentrations show that a time lag is required for restriction measures to be efficient. These results shed light on factors governing pesticide compound concentrations in chalk aquifers. The developed methodology is not restricted to chalk aquifers, it could be transposed to study other pollutants with concentrations below detection limits. Several factors govern pesticide compounds concentrations in the chalk: hydrogeological setting, land use, groundwater level fluctuations and persistence. [less ▲]

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See detailGroundwater flow and saltwater intrusion modelling in the Continental Terminal (CT) aquifer near the Saloum inverse estuary in Senegal
Dieng, Ndeye Maguette ULg; Orban, Philippe ULg; Dassargues, Alain ULg et al

Conference (2016, September 27)

The Saloum River hypersaline estuary (Senegal) is an ‘inverse estuary’ showing a salinity increasing from the river mouth towards inland. This salinization process is mainly driven by a net loss of ... [more ▼]

The Saloum River hypersaline estuary (Senegal) is an ‘inverse estuary’ showing a salinity increasing from the river mouth towards inland. This salinization process is mainly driven by a net loss of freshwater due to intense evaporation. In this context, interactions between the river and the surrounding aquifer of the Continental Terminal (CT) may lead to local and progressive salinization of this groundwater main resource for water supply. Our study, based on available data and new measured data in 2012 and 2013, is focused on the southern part of the Saloum basin. It confirms that the groundwater resource is threatened by local saltwater intrusions in the vicinity of the Saloum River and along the western coastal part of the aquifer. For a long term water resources management, it is thus essential to predict the future evolution of this process in a context of increasing groundwater pumping rate together with climate variability and changes. A groundwater flow model is developed using MODFLOW. Starting from a conceptual steady-state situation corresponding to the CT aquifer state in 1973 before development of pumping, a transient calibration of the groundwater flow model is performed on data from 1974 to 2012. Despite the low number of measured data, the model can be considered as the current best assessment tool for future predictions. Using the particle tracking technique (MODPATH), a first assessment of the saltwater intrusions in the aquifer is simulated (neglecting the density effect on the hydraulic conductivity) confirming the measured data. Results, for an increased pumping of 20% in 2050 combined with different climatic scenarios, are useful to assess how the saltwater intrusions will evolve in the next years. [less ▲]

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See detailAn old slate mine as lower reservoir for UPSH (Underground Pumping Storage Hydroelectricity)- groundwater interactions and limitations
Bodeux, Sarah ULg; Pujades, Estanislao ULg; Orban, Philippe ULg et al

Conference (2016, September 27)

Renewable energy sources have an increasing role to play in the future energy framework but their intermittence cannot afford a stable production according to the demand. Pumped Storage Hydroelectricity ... [more ▼]

Renewable energy sources have an increasing role to play in the future energy framework but their intermittence cannot afford a stable production according to the demand. Pumped Storage Hydroelectricity (PSH) is an efficient technology to store and release electricity. However, the development of new PSH plants is limited by environmental and topographic constraints. An innovative alternative consists in using old underground mines as lower reservoirs of Underground Pumped Storage Hydroelectricity (UPSH) plants. In this configuration, large amount of water is pumped and injected in underground cavities and these cyclic stresses impact the groundwater system. A hybrid 3D finite element mixing cell method is used to numerically simulate the use of an UPSH facility, in the case of an abandoned slate mine. Different scenarios are computed with varying pumping injection time-sequences. In order to assess the impact on the surrounding groundwater conditions, the resulting head evolution in the cavity and at different distances is analyzed in terms of groundwater oscillation magnitude, drawdown, and seepage into the cavity. Results show clearly the influence of the pumping injection time-sequence (rates, regularity, timing and duration of no-activity periods) on the actual head evolution in the surrounding medium and consequently on the magnitude of interactions with the cavity. For a given hydraulic conductivity of the surrounding medium (i.e. slates in this case study), the main conclusion is that the resulting interaction seepage flows (in and out of the cavity) are highly dependent on the chosen pumping injection sequences. The future impact of UPSH operation must be assessed taking this fact into account. [less ▲]

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See detailInfluence of groundwater exchanges on the efficiency of Underground Pumped Storage Hydroelectricity plants using open pit mines
Pujades, Estanislao ULg; Bodeux, Sarah ULg; Orban, Philippe ULg et al

Poster (2016, September 27)

Underground Pumped Storage Hydropower (UPSH) plants can be used to manage the production of electrical energy according to the demand. These plants consist in two reservoirs, the upper one is located at ... [more ▼]

Underground Pumped Storage Hydropower (UPSH) plants can be used to manage the production of electrical energy according to the demand. These plants consist in two reservoirs, the upper one is located at the surface while the lower one is underground. The energy is stored by pumping water from the lower to the upper reservoir and produced by releasing water from the upper to the lower one. As a result, the hydraulic head in the lower reservoir varies continuously. UPSH plants interact with the surrounding aquifers exchanging groundwater. These groundwater exchanges, which play an important role in the evolution of the hydraulic head inside the underground reservoir, are a fact of concern in the selection of pumps and turbines because their efficiency varies with respect to the head difference between the two reservoirs. Therefore, the aquifer parameters should be considered in the selection of pumps and turbines. In this context, with an UPSH plant made up by an open pit mine, we study numerically (1) the influence of groundwater exchanges on the efficiency and (2) how the hydraulic head evolution varies depending on the aquifer properties. The relation among the groundwater exchanges, the efficiency of pumps and turbines and the aquifer parameters is considered by comparing the numerical results of several simulations. It is shown that groundwater exchanges are not negligible when optimizing the efficiency of UPSH plants. A priori, low hydraulic conductivity geological media were preferred to decrease interactions with the open-pit or the cavity used as lower reservoir. Taking into account the pump/turbine performance curves, it appears that, on the contrary, the global efficiency would be increased if the surrounding medium facilitates large groundwater exchanges because hydraulic head variations are softened. [less ▲]

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See detailComparison of temperature from DTS and ERT with direct measurements during heat tracer experiments in heterogeneous aquifers
Nguyen, Frédéric ULg; Hermans, Thomas ULg; Jamin, Pierre ULg et al

Conference (2016, September 27)

Geothermal field characterization and heat tracer experiments often rely on scarce temperature data collected in boreholes. Electrical resistivity tomography (ERT) and distributed temperature sensing (DTS ... [more ▼]

Geothermal field characterization and heat tracer experiments often rely on scarce temperature data collected in boreholes. Electrical resistivity tomography (ERT) and distributed temperature sensing (DTS) have the potential to provide spatial information on temperature changes in the subsurface. In this contribution, we show how DTS and ERT have been used to investigate the heterogeneity of a heterogeneous aquifer during a heat tracing experiment under forced gradient conditions. Optic fibers were installed in the heat injection well and in two piezometers intersecting the main flow directions at 8 m from the injection well. These piezometers were also equipped with ERT. The DTS measurement in the injection well clearly shows the two-layer nature of the aquifer. After the end of injection, the temperature in the bottom part of the well decreases faster than in the upper part due to the higher water fluxes. Those results are confirmed by DTS measurements in natural flow conditions during a heating wire test. DTS and ERT in the cross-panel both show the vertical and lateral heterogeneity of the aquifer. Temperatures only increase significantly in the bottom part of the aquifer where advection is predominant. However, strong differences are observed laterally. ERT additionally shows that the hot plume is divided in two main flow paths, which is confirmed by direct temperature measurements. The comparison of DTS and ERT shows that one of the well is suffering from water mixing. Indeed, temperature from DTS are homogeneous over the whole tichkness of the aquifer, whereas ERT temperature, less affected by local variations, are varying. Our study demonstrate the value of spatially distributed measurements for the monitoring of heat tracer experiment and highligths the issue of multilevel sampling. The detailed temperature measurements can be subsequently used in hydrogeological model to better estimates heat flow and transport parameters. [less ▲]

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See detailGroundwater flow and saltwater intrusion modelling in the Continental Terminal (CT) aquifer near the Saloum inverse estuary in Senegal
Faye, Serigne; Ndeye, Maguette Dieng; Orban, Philippe ULg et al

Conference (2016, September 26)

The Saloum River hypersaline estuary (Senegal) is an ‘inverse estuary’ showing a salinity increasing from the river mouth towards inland. This salinization process is mainly driven by a net loss of ... [more ▼]

The Saloum River hypersaline estuary (Senegal) is an ‘inverse estuary’ showing a salinity increasing from the river mouth towards inland. This salinization process is mainly driven by a net loss of freshwater due to intense evaporation. In this context, interactions between the river and the surrounding aquifer of the Continental Terminal (CT) may lead to local and progressive salinization of this groundwater main resource for water supply. Our study, based on available data and new measured data in 2012 and 2013, is focused on the southern part of the Saloum basin. It confirms that the groundwater resource is threatened by local saltwater intrusions in the vicinity of the Saloum River and along the western coastal part of the aquifer. For a long term water resources management, it is thus essential to predict the future evolution of this process in a context of increasing groundwater pumping rate together with climate variability and changes. A groundwater flow model is developed using MODFLOW. Starting from a conceptual steady-state situation corresponding to the CT aquifer state in 1973 before development of pumping, a transient calibration of the groundwater flow model is performed on data from 1974 to 2012. Despite the low number of measured data, the model can be considered as the current best assessment tool for future predictions. Using the particle tracking technique (MODPATH), a first assessment of the saltwater intrusions in the aquifer is simulated (neglecting the density effect on the hydraulic conductivity) confirming the measured data. Results, for an increased pumping of 20% in 2050 combined with different climatic scenarios, are useful to assess how the saltwater intrusions will evolve in the next years. [less ▲]

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See detailDirect measurement of evapotranspiration from a forest using a superconducting gravimeter
Van Camp, Michel; de Viron, Olivier; Pajot-Métivier, Gwendoline et al

in Geophysical Research Letters (2016), 43

Evapotranspiration (ET) controls the flux between the land surface and the atmosphere. Assessing the ET ecosystems remains a key challenge in hydrology. We have found that the ET water mass loss can be ... [more ▼]

Evapotranspiration (ET) controls the flux between the land surface and the atmosphere. Assessing the ET ecosystems remains a key challenge in hydrology. We have found that the ET water mass loss can be directly inferred from continuous gravity measurements: as water evaporates and transpires from terrestrial ecosystems, the mass distribution of water decreases, changing the gravity field. Using continuous superconducting gravity measurements, we were able to identify daily gravity changes at the level of, or smaller than, 10-9 nms-2 (or 10-10 g) per day. This corresponds to 1.7mmof water over an area of 50 ha. The strength of this method is its ability to enable a direct, traceable and continuous monitoring of actual ET for years at the mesoscale with a high accuracy. [less ▲]

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See detailHow groundwater interactions can influence UPSH (Underground Pumping Storage Hydroelectricity) operations
Bodeux, Sarah ULg; Pujades, Estanislao ULg; Orban, Philippe ULg et al

Conference (2016, July 28)

In the current energy grid, renewable energy has an increasing role to play. However, their intermittence cannot afford to regulate the produced electricity according to the irregular demand (Evans et al ... [more ▼]

In the current energy grid, renewable energy has an increasing role to play. However, their intermittence cannot afford to regulate the produced electricity according to the irregular demand (Evans et al., 2012). Pumped Storage Hydroelectricity (PSH) is a well-known efficient technology to store and release electricity according to the demand needs but appropriate potential new sites are getting scarce (Steffen, 2012). An innovative alternative consists in using abandoned mines as lower reservoir of an Underground Pumping Storage Hydroelectricity (UPSH) plant. In such configuration, large amount of water will be pumped or injected in underground cavities, creating subsequently head oscillations in the surrounding aquifers. Consequently, this seepage occurring between the considered cavity and the varying groundwater heads in the surrounding geological medium may influence the efficiency of the UPSH plant but also the magnitude of the potential impacts on the groundwater resources. A hybrid 3D finite element mixing cell method (Brouyère et al., 2009) is used to simulate numerically the use of a representative UPSH cavity and calculate the induced changes in groundwater heads in the surrounding geological medium. Different scenarios are computed varying parameter values (hydrogeological and lower reservoir characteristics), boundary conditions, and pumping/injection time-sequences. By analyzing the computed piezometric heads at different distances from the underground reservoir, the magnitude of the aquifer response to pumping storage operations is assessed. The most expected and noticeable effect is the oscillation of groundwater levels. The existence a mean pseudo/ dynamic steady-state and the required time to reach it are also determined. The head difference and its time evolution between the cavity and the surrounding medium is triggering the leakage of groundwater into the cavity or the contrary. The resulting effects on the UPSH plant efficiency can be estimated. Combining these outcomes, some feasibility criteria of this type of projects are identified. Going into practice, further models should include more in de-tails local and specific geometrical and hydrogeolog-ical data of the considered old mine cavities used as lower reservoir. This kind of modelling approach can be used as a first approach for determining how the aquifer will response to short and long term changes in UPSH pumping/injection schemes. [less ▲]

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