References of "Lemieux, Jean-Michel"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailDevelopping a physically based groundwater vulnerability concept in a DPSIR framework
Beaujean, Jean ULg; Brouyère, Serge ULg; Lemieux, Jean-Michel et al

Conference (2014, September 15)

A general physically based method is presented to assess vulnerability of groundwater to external pressures with respect to quality and/or quantity issues. In the vulnerability assessments, many ... [more ▼]

A general physically based method is presented to assess vulnerability of groundwater to external pressures with respect to quality and/or quantity issues. In the vulnerability assessments, many scientific authors agree nowadays that ‘physically based’ methods must be preferred to traditional approaches based on empirical overlay and index methods where physical attributes are often mixed with implicitly embedded conventional priorities. Results from one or another of these last methods can consequently be very dissimilar for a given case study and decision makers are losing confidence in these tools. A methodology is proposed to reframe the groundwater vulnerability assessment in a Pressure-State-Impact causal chain that is familiar to decision makers. The DPSIR framework, for describing interactions between society and the environment, defines a chain of Drivers that exert Pressures on the State of a given resource, such as water, which then generates an Impact that will require an appropriate Response (Kristensen, 2004). The concept of groundwater vulnerability assessment considered here is based on the calculation of sensitivity coefficients for a user-defined groundwater state for which several physically-based indicators are proposed. These sensitivity coefficients reflect the easiness with which the groundwater state transmits pressures into impacts. They are grouped into a vulnerability matrix of pressures and impacts that quantify vulnerability for every combination of causal links identified in the DPSIR chain. For that reason, the sensitivity coefficients are converted to vulnerability, using the concept of ‘falling below a given threshold’, which is commonly used in socioeconomic sciences (Luers et al. 2003). Outside the careful selection of the sensitivity analysis method that can significantly influence the computational effort (Beaujean et al., 2013), emphasis will be given to the illustration of the general methodology on a simple case (of an alluvial aquifer with concerns related to water supply) demonstrating the potential use of this general and physically based vulnerability assessment method. While the methodology is general, 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. This choice is arbitrary such that the vulnerability is sensitive to the choice of the threshold. The framework is general and, when applied to water, can include states that are not limited to quality such as, for example, water quantity and availability. [less ▲]

Detailed reference viewed: 27 (4 ULg)
Full Text
Peer Reviewed
See detailPhysically Based Groundwater Vulnerability Assessment Using Sensitivity Analysis Methods
Beaujean, Jean ULg; Lemieux, Jean-Michel; Dassargues, Alain ULg et al

in Ground Water (2013), 52(6), 864-874

A general physically based method is presented to assess the vulnerability of groundwater to external pressures by numerical simulation of groundwater flow. The concept of groundwater vulnerability ... [more ▼]

A general physically based method is presented to assess the vulnerability of groundwater to external pressures by numerical simulation of groundwater flow. The concept of groundwater vulnerability assessment considered here is based on the calculation of sensitivity coefficients for a user-defined groundwater state for which we propose several physically based indicators. Two sensitivity analysis methods are presented: the sensitivity equation method and the adjoint operator method. We show how careful selection of a method can significantly minimize the computational effort. An illustration of the general methodology is presented for the Herten aquifer analog (Germany). This application to a simple, yet insightful, case demonstrates the potential use of this general and physically based vulnerability assessment method to complex aquifers. [less ▲]

Detailed reference viewed: 45 (17 ULg)
Peer Reviewed
See detailImproving groundwater flow model conceptualisation and calibration with electrical resistivity tomography and self-potential methods
Robert, Tanguy ULg; Therrien, René; Lemieux, Jean-Michel et al

Conference (2011, September 19)

Developing a conceptual model for groundwater flow requires knowledge on the distribution of geological materials, which generally comes from geological observations on outcrops and boreholes, from the ... [more ▼]

Developing a conceptual model for groundwater flow requires knowledge on the distribution of geological materials, which generally comes from geological observations on outcrops and boreholes, from the interpretation of hydraulic tests or from geophysical surveys. The identification of spatial structures in the subsurface, such as preferential flow paths created by fractured zones, is also critical in developing a reliable conceptual model but it is difficult to achieve. Geophysical methods have been widely used to map the subsurface distribution of geological materials. Recent developments in geophysics, such as the increased use of joint inversion of geophysical and hydrogeological data, have further allowed to quantify the hydraulic conductivity of geological materials. The objective of our work is to demonstrate that the electrical resistivity tomography (ERT) and the self-potential (SP) methods can improve both the conceptual model developed for groundwater flow systems and the calibration of the corresponding groundwater flow model. The use of the two geophysical methods, combined with a groundwater flow model, is presented for a fractured limestone aquifer. The self-potential method relies on passive measurements of the ambient electrical potential at ground surface or in boreholes. One of the mechanisms responsible for the measured signal measured is the transport of dissolved ions with groundwater flow. When this electrokinetic effect is the dominant contribution, the resulting signal is called the streaming potential and it contains information about groundwater fluxes that can be useful to calibrate groundwater flow models. The solution to the SP forward problem was added to the HydroGeoSphere model, which simulates 3D groundwater flow and solute transport in porous media, including fractured geological formations. With this addition, the model can calculate the self-potential signal associated with groundwater flow, given the distribution of Darcy fluxes resulting from the forward flow solution and the electrical resistivity that is, for example, outputted by ERT data inversion. Darcy fluxes are transformed into sources of electrical current by using the streaming potential coupling coefficient. This parameter can be measured either in the laboratory or in-situ from the self-potential signal between two locations where the depth of the water table is known, such as observation wells. We used here both ERT and SP to develop a conceptual model for groundwater flow in a typical carboniferous limestone syncline in South Belgium. The rolling topography in the investigated area results from a succession of calcareous valleys (synclines) and sandstone crests (anticlines). The calcareous synclines form aquifers that are very complex since they are highly fractured and even karstified. A typical calcareous syncline has a width of about 800 m and, using ERT, we could subdivide the syncline into zones of different hydraulic conductivity, based on the degree of fracturation. The zones are oriented along the axis of the syncline and their width ranges between 10 and 40 m. The ERT profiles showed that there is a highly conductive zone, in terms of electrical conductivity, near the syncline fold axis. That zone is interpreted as being highly fractured. Other conductive zones are located symmetrically along both flanks of the calcareous syncline, with respect to the syncline fold axis. The main flow direction is along the axis of the syncline, towards a nearby river. The SP raw signals also showed that, locally, there is a second flow component perpendicular to the axis of the syncline, with groundwater flowing from the flanks of the syncline towards the axis. The conceptual groundwater flow model developed here includes the zones identified with ERT, which were then incorporated into the numerical model. The SP signals were inverted with PEST to calibrate the hydraulic conductivity value of the different zones. HydroGeoSphere was therefore used to simulate first groundwater flow and then the associated self-potential signals in an iterative process. At the start of an iteration, HydroGeoSphere solves the groundwater flow equation given one particular set of hydraulic conductivities and calculates the resulting Darcy fluxes. These fluxes are transformed into sources of electrical current assuming that the electrokinetic effect is the dominant contribution of the SP signals. HydroGeoSphere then calculates the distribution of self-potential given the sources of electrical current and the distribution of electrical resistivity. The hydraulic conductivity values of the zones are then modified and the iteration continues until the model reproduces the measured self-potential signal. [less ▲]

Detailed reference viewed: 87 (9 ULg)
Full Text
Peer Reviewed
See detailImproving Groundwater Flow Model Conceptualisation and Calibration with ERT and Self-potential Methods
Robert, Tanguy ULg; Therrien, René; Lemieux, Jean-Michel et al

in EarthDoc - Near Surface 2011 – 17th European Meeting of Environmental and Engineering Geophysics (2011, September 14)

The self-potential (SP) method relies on passive measurements of the ambient electrical potential at the ground surface or in boreholes. When the electrokinetic effect is the dominant contribution, the ... [more ▼]

The self-potential (SP) method relies on passive measurements of the ambient electrical potential at the ground surface or in boreholes. When the electrokinetic effect is the dominant contribution, the resulting signal is called the streaming potential and contains information about groundwater fluxes that can be useful for calibration of groundwater flow models. The streaming potential forward equation was implemented in the HydroGeoSphere model, which simulates 3D groundwater flow and solute transport in porous media, including fractured geological formations. HydroGeoSphere is able to calculate the streaming potential given a distribution of Darcy velocity and electrical resistivity. Since groundwater flow modelling relies on a conceptual model, prior information on the distribution of the geological units and hydraulic conductivity at the site is mandatory. However, this information is often scarce or missing. In this work, we use the electrical resistivity tomography (ERT) and the SP methods as an additional source of information for building the groundwater flow model. ERT is used to identify the location of fractured zones in a fractured and karstified calcareous aquifer of South Belgium. The SP signal is used with PEST in order to calibrate the groundwater flow model and better constrain the hydraulic conductivity of the fractured zones. [less ▲]

Detailed reference viewed: 50 (9 ULg)
Full Text
See detailImproved automatic calibration of groundwater flow models using self-potential measurements
Robert, Tanguy ULg; Therrien, René; Lemieux, Jean-Michel et al

Conference (2011, April 11)

Detailed reference viewed: 21 (3 ULg)
Full Text
See detailMethodology and setup of the adopted groundwater vulnerability assessment method
Beaujean, Jean ULg; Lemieux, Jean-Michel; Brouyère, Serge ULg

Scientific conference (2010, February 04)

Detailed reference viewed: 45 (10 ULg)
Full Text
Peer Reviewed
See detailReframing groundwater vulnerability assessment for a better understanding between decision makers and hydrogeologists
Dassargues, Alain ULg; Popescu, Ileana Cristina; Beaujean, Jean ULg et al

in Liebscher, Hans-Jurgen; Clarke, Robin; Rodda, John (Eds.) et al The Role of Hydrology in Water Resources Management (2009, June)

Management of water resource systems includes adequate decisions about groundwater resource protection. Groundwater vulnerability maps can greatly help for these decisions. In the vulnerability assessment ... [more ▼]

Management of water resource systems includes adequate decisions about groundwater resource protection. Groundwater vulnerability maps can greatly help for these decisions. In the vulnerability assessment, physical attributes are often mixed with conventional priorities implicitly embedded in the applied methods. Results from one or another method can consequently be very dissimilar and decision makers are losing confidence in these tools. A methodology is proposed to reframe the groundwater vulnerability assessment in a Pressure-State-Impact causal chain that is familiar to decision makers. The physically-based analysis is clearly separated from the agreement aspects induced by local societal, environmental or political priorities. An example is given and perspectives of generalisation are evoked. [less ▲]

Detailed reference viewed: 141 (40 ULg)
Full Text
See detailDL 45 : Application and validation of the general methodology and concept of groundwater vulnerability assessment at regional scale on the Israeli coastal aquifer
Beaujean, Jean ULg; Lemieux, Jean-Michel; Brouyère, Serge ULg

Report (2008)

This deliverable consists in applying the concepts and methodologies developed in Deliverable D43 and D44 to synthetic and real case studies. Our researches have focused on the generalized groundwater ... [more ▼]

This deliverable consists in applying the concepts and methodologies developed in Deliverable D43 and D44 to synthetic and real case studies. Our researches have focused on the generalized groundwater vulnerability assessment methodology, and more precisely on evaluating, under the framework of physically-based indicators, the groundwater sensitivity/vulnerability to stress factor considering artificial recharge as a potential response to the degradation of the groundwater resource. In the context, different approaches have been identified in the literature and implemented in appropriate modelling tools (i.e. HydroGeoSphere) for calculating the various sensitivity/vulnerability coefficients. These approaches are the influence coefficient method, the sensitivity equation method and the adjoint operator method. The two first methods show relevant results on both the considered synthetic case studies that relate groundwater vulnerability to (1) quantity issues and (2) to sea water intrusion. They illustrate the way of applying the methodology to “real case studies”.These first applications should be the object of more complex but strongly related case studies. [less ▲]

Detailed reference viewed: 27 (3 ULg)