Couplages de modèles en hydrodynamique environnementale et hydrologie (sols, nappes, rivières, zones côtières)

Cette conférence présente une revue générale des problèmes de couplages de modèles en hydrodynamique environnementale et en hydrologie. On considère les couplages ou les interactions des écoulements à travers les sols, les nappes souterraines, les zones côtières (oscillations de la mer dans les structures poreuses), et les interactions eaux de surface/souterraines en milieu fluvial (cours d’eau, plaines d’inondation)...

Stochastic PDE's for water flow, solute transport and wave propagation phenomena in heterogeneous geologic media.

This lecture will present stochastic PDE's (Partial Differential Equations) to model various "transport" phenomena like water flow, solute transport and wave propagation, in heterogeneous geologic porous media. The material properties are represented by random functions of space F(x) (random fields). The resulting transport PDE’s contain random field coefficients, and their solutions are stochastic (randomly heterogeneous)

Equivalent permeability tensor in fractured media : an algebraic approach.

This work is part of an extensive investigation on the equivalent permeability of heterogeneous and fractured media. We focus here on the problem of Darcian/Poiseuille flow in an irregular network of fracture segments (in 2D) or conduits (in 2D or 3D). An exact algebraic relation between the mean flux vector(Q) and the mean hydraulic gradient (J) is developed through a mathematical analyzis of the network flow problem, based on concepts from graph theory, leading to a discrete definition of DIV and GRAD operators. The resulting equivalent permeability is a 2nd rank tensor Kij, not necessarily symmetric and not necessarily positive-definite. Its properties are analyzed for given types of boundary conditions and averaging procedures

L'intégration socioprofessionnelle des personnes présentant une déficience intellectuelle : ses effets sur le co-travailleur intégrant

Nous sommes tous en mesure de reconnaître l'importance du rôle que joue l'intégration dans notre société et son impact sur nos vies. L'intégration est un instrument qui permet a priori, de rapprocher, d'inclure, d'interagir et qui favorise la pleine participation sociale. L'intégration est un droit qui rend légitime la différence et l'altérité.\ud Toutefois, il devient important de prendre conscience des effets de l'intégration, qu'ils soient positifs ou négatifs, autant sur l'intégrant que sur l'intégré et ce, afin de mieux la comprendre, la circonscrire et la déployer dans un contexte favorable et gagnant. Ne pas saisir et tenir compte des effets de l'intégration, c'est minimiser leur importance et les banaliser, pire encore, c'est idéaliser et idolâtrer l'intégration comme si elle est parfaite. Dans cette étude qualitative nous nous intéressons aux effets de l'intégration socioprofessionnelle des personnes présentant une déficience intellectuelle sur les co-travailleurs\ud intégrants dans un contexte de travail en stage et en emploi. Nous démontrons que l'intégration a certes des effets positifs en général sur les co-travailleurs mais qu'elle peut aussi générer des effets négatifs qui surgissent dans des situations très spécifiques. Nous avons vérifié dans quelle mesure le statut professionnel de la personne présentant une déficience intellectuelle peut moduler les effets de l'intégration sur le co-travailleur et comment il influence sa motivation à s'impliquer dans le projet d'intégration. Nous avons remarqué, en particulier, que les co-travailleurs dans le contexte de stage ont une perception mitigée et paradoxale de l'intégration lorsque l'on envisage une ascension de la personne du stage à l'emploi. Par ailleurs, nous remarquons que l'appropriation du projet d'intégration par le co-travailleur est une arme à double tranchant: si l'appropriation est bien circonscrite par le co-travailleur et le milieu, l'intégration a des effets positifs; mais si le co-travailleur s'approprie excessivement le projet, l'intégration peut avoir des retombées négatives sur lui. Nous faisons également ressortir le lien existant entre une sur-appropriation du projet par le co-travailleur et le sentiment de supériorité et de contrôle de sa part sur la personne intégrée. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Déficience intellectuelle, Intégration, Stage, Emploi

Effect and propagation of water level fluctuations in a sloping sandy beach -- Unsaturated porous media II: numerical simulation test of single harmonic wave (long run)

In coastal processes, the strong water movements due to short periodic waves (such as sea swell) can induce irregular water level fluctuations in the swash zone and within the sandy beach. The measured water level fluctuations with very complex entry water level fluctuations in a wave canal with a sloping sandy beach were analyzed by using 7 capacitive sensors. Numerical simulations have also been implemented in order to complement the experimental water level signal analyses. In this paper, a numerical test of single harmonic wave (long run) with same computational domain and porous media properties as the experiment is conducted to understand the effect and propagation of the water level fluctuations in the unsaturated porous media. The key coupling parameter of the macro (sea water) porous and micro (sloping sandy beach) porous media in the Richards equation model is further identified by this numerical test, which is the basis to simulate and explain the complex experimental results

Macro-permeability distribution and anisotropy in a 3D fissured and fractured clay rock: ‘Excavation Damaged Zone’ around a cylindrical drift in Callovo-Oxfordian Argilite (Bure)

The Underground Research Laboratory at Bure (CMHM), operated by ANDRA, the French National Radioactive Waste Management Agency, was developed for studying the disposal of radioactive waste in a deep clayey geologic repository. It comprises a network of underground galleries in a 130 m thick layer of Callovo Oxfordian clay rock (depths 400–600 m). This work focuses on hydraulic homogenization (permeability upscaling) of the Excavation Damaged Zone (EDZ) around a cylindrical drift, taking into account: (1) the permeability of the intact porous rock matrix; (2) the geometric structure of micro-fissures and small fractures synthesized as a statistical set of planar discs; (3) the curved shapes of large ‘chevron’ fractures induced by excavation (periodically distributed). The method used for hydraulic homogenization (upscaling) of the 3D porous and fractured rock is based on a ‘frozen gradient’ superposition of individual fluxes pertaining to each fracture/matrix block, or ‘unit block’. Each unit block comprises a prismatic block of permeable matrix (intact rock) obeying Darcy’s law, crossed by a single piece of planar fracture obeying either Darcy or Poiseuille law. Polygonal as well as disc shaped fractures are accommodated. The result of upscaling is a tensorial Darcy law, with macro-permeability Kij(x) distributed over a grid of upscaling sub-domains, or ‘voxels’. Alternatively, Kij(x) can be calculated point-wise using a moving window, e.g., for obtaining permeability profiles along ‘numerical’ boreholes. Because the permeable matrix is taken into account, the upscaling procedure can be implemented sequentially, as we do here: first, we embed the statistical fissures in the matrix, and secondly, we embed the large curved chevron fractures. The results of hydraulic upscaling are expressed first in terms of ‘equivalent’ macro-permeability tensors, Kij(x,y,z) distributed around the drift. The statistically isotropic fissures are considered, first, without chevron fractures. There are 10,000 randomly isotropic fissures distributed over a 20 m stretch of drift. The resulting spatially distributed K ij tensor is nearly isotropic (as expected). At the scale of the whole EDZ, the global K FISSURES is roughly 5000 times larger than permeability matrix KM. The detailed distribution of the equivalent K FISSURES (x, y, z) defined on a grid of voxels is radially inhomogeneous, like the statistics of the disc fissures. In addition, a moving window procedure is used to compute detailed radial profiles of K FISSURES versus distance (r) to drift wall, and the results compare favorably with in situ permeability profiles (numerical vs. experimental boreholes at Bure’s GMR drift). Finally, including the large curved chevron fractures in addition to the random fissures, the resulting K ij (x, y, z) appears strongly anisotropic locally. Its principal directions are spatially variable, and they tend to be aligned with the tangent planes of the chevron fracture surfaces. The global equivalent Kij of the whole EDZ is also obtained: it is only weakly anisotropic, much less so than the local Kij’s. However, because of the radially divergent structure of the ‘chevrons’ (although not quite cylindrical in geometry), it is recognized that the global Kij due to chevrons lacks physical meaning as a tensor. Considering only the magnitude, it is found that the permeability due to ‘chevrons’ (K CHEVRONS ) is about 4 orders of magnitude larger than that due to statistical fissures (K FISSURES ), assuming a hydraulic aperture a CHEVRON = 100 microns. By a simple argument, K CHEVRONS would be only one order of magnitude larger than K FISSURES with the choice a CHEVRON = 10 microns instead of 100 microns. This significant sensitivity is due to several factors: the large extent of chevron fractures, the assumption of constant hydraulic aperture, and the cubic law behavior based on the assumption of Poiseuille flow. The equivalent macro-permeabilities obtained in this work can be used for large scale flow modeling using any simulation code that accommodates Darcy’s law with a full, spatially variable permeability tensor Kij(x)

Flash flood modeling with the MARINE hydrological distributed model

International audienceFlash floods are characterized by their violence and the rapidity of their occurrence. Because these events are rare and unpredictable, but also fast and intense, their anticipation with sufficient lead time for warning and broadcasting is a primary subject of research. Because of the heterogeneities of the rain and of the behavior of the surface, spatially distributed hydrological models can lead to a better understanding of the processes and so on they can contribute to a better forecasting of flash flood. Our main goal here is to develop an operational and robust methodology for flash flood forecasting. This methodology should provide relevant data (information) about flood evolution on short time scales, and should be applicable even in locations where direct observations are sparse (e.g. absence of historical and modern rainfalls and streamflows in small mountainous watersheds). The flash flood forecast is obtained by the physically based, space-time distributed hydrological model "MARINE'' (Model of Anticipation of Runoff and INondations for Extreme events). This model is presented and tested in this paper for a real flash flood event. The model consists in two steps, or two components: the first component is a "basin'' flood module which generates flood runoff in the upstream part of the watershed, and the second component is the "stream network'' module, which propagates the flood in the main river and its subsidiaries. The basin flash flood generation model is a rainfall-runoff model that can integrate remotely sensed data. Surface hydraulics equations are solved with enough simplifying hypotheses to allow real time exploitation. The minimum data required by the model are: (i) the Digital Elevation Model, used to calculate slopes that generate runoff, it can be issued from satellite imagery (SPOT) or from French Geographical Institute (IGN); (ii) the rainfall data from meteorological radar, observed or anticipated by the French Meteorological Service (Météo France); and (iii) the spatially distributed soil and other surface properties viewed from space (land cover map from SPOT or LANDSAT, main rivers, ...). The stream flood propagation model simulates flood propagation in main rivers by solving 1-D Saint Venant equations. The data required for this part of the model are the river morphology, topography and roughness. The MARINE model has already been used previously for real time flash floods forecasting in the frame of the PACTES project on "forecasting and anticipation of floods with spatial techniques'' (funded by the CNES and the French Ministry of Research) concerning the catastrophic 1999 flash flood that occurred in the South of France. The main advantages of MARINE are its ability to run on insufficiently gauged basins (with the help of satellite information) and to run in an operational mode for real-time flood forecasting

Equivalent Upscaled Hydro Mechanical Properties of a Damaged and Fractured Claystone Around a Gallery (Meuse / Haute Marne Underground Research Laboratory).

In this work, we present calculations and analyses of equivalent continuum (upscaled) coefficients describing the damaged, fissured and fractured claystone around an underground gallery. We focus here on mechanical and coupled hydro-mechanical properties of the damaged claystone (the upscaled Darcy permeability of the same claystone was studied in a previous paper focused on hydraulics without mechanical deformations). Concerning the geometric structure of the damaged clay stone around the cylindrical excavation, we use a hybrid 3D geometric model of fissuring and fracturing, comprising (a) a set of 10 000 statistical fissures with radially inhomogeneous statistics (size, thickness and density increasing near the wall), and (b) a deterministic set of large curved ‘chevrons’ fractures, periodically spaced along the axis of the drift according to a 3D chevron pattern. The hydro-mechanical coefficients calculated here are second- and fourth-rank tensors, which are displayed using ellipsoids. For simplicity, we also calculate equivalent isotropic coefficients extracted from these tensors: Young’s modulus (E), bulk modulus (K), Lame' shear modulus (m), Poisson’s ratio (Nu), Biot coefficient (B, stress–pressure coupling) and Biot modulus (M, pressure–fluid production coupling). All of these coefficients are affected by the degree of damage and fracturing, which increases near the wall of the gallery. Both 3D and ‘2D transverse’ distributions are analysed, on grids of 3D cubic voxels and 2D pixels, respectively. Global coefficients upscaled over the entire damaged and fractured zone are also analysed. Other types of averages are presented, for example, upscaled values over a cylindrical annular shell at various radial distances from the gallery wall. The relation to the degree of fracturing is discussed, including for instance the effect of fracturing on bulk and shear stiffnesses, and on the hydro-mechanical coupling coefficients of the damaged claystone

Moving Multi-Front (MMF): A generalized Green-Ampt approach for vertical unsaturated flows

A Moving Multi-Front (MMF) method is developed and tested for solving the Richards equation governing unsaturated flow in vertical homogeneous porous columns. The MMF model is a gridless method. It can be viewed as a generalization of the Green-Ampt piston flow approach, which models flow as a single abrupt moving front separating saturated and dry regions during infiltration. The MMF model further generalizes this concept, using a parametrization of unsaturated water retention and conductivity-pressure curves. It reduces the Richards PDE to an ODE system governing “M” moving front positions. Different tests are developed to validate this approach for 1D transient downwards/upwards flows submitted to constant and time-varying pressure boundary conditions. They include: (i) infiltration to deep water tables; (ii) infiltration to shallow water tables; (iii) capillary rise from fixed water tables; (iv) gradual water table rise (partially saturated column with evolving pressure condition at bottom). The MMF results are compared favorably to finely discretized fixed grid solutions of Richards PDE. Analyses of error and accuracy show satisfactory results in terms of water content profiles and boundary fluxes (e.g. infiltration rate)

Random walks with negative particles for discontinuous diffusion and porosity

This study develops a new Lagrangian particle method for modeling flow and transport phenomena in complex porous media with discontinuities. For instance, diffusion processes can be modeled by Lagrangian Random Walk algorithms. However, discontinuities and heterogeneities are difficult to treat, particularly discontinuous diffusion or porosity. In the literature on particle Random Walks, previous methods used to handle this discontinuity problem can be characterized into two main classes as follows: “Interpolation techniques”, and “Partial reflection methods”. One of the main drawbacks of these methods is the small time step required in order to converge to the expected solution, particularly in the presence of many interfaces. These restrictions on the time step, lead to inefficient algorithms. The Random Walk Particle Tracking (RWPT) algorithm proposed here is, like others in the literature, discrete in time and continuous in space (gridless). We propose a novel approach to partial reflection schemes without restrictions on time step size. The new RWPT algorithm is based on an adaptive “Stop&Go” time-stepping, combined with partial reflection/refraction schemes, and extended with a new concept of negative mass particles. To test the new RWPT scheme, we develop analytical and semi-analytical solutions for diffusion in the presence of multiple interfaces (discontinuous multi-layered medium). The results show that the proposed Stop&Go RWPT scheme (with adaptive negative mass particles) fits extremely well the semi-analytical solutions, even for very high contrasts and in the neighborhood of interfaces. The scheme provides a correct diffusive solution in only a few macro-time steps, with a precision that does not depend on their size