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Cornaton, Fabien

Nom
Cornaton, Fabien
Affiliation principale
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https://libra.unine.ch/handle/123456789/806

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31
2011
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  • Publication
    Métadonnées seulement
  • Publication
    Accès libre
    Bacteriophage transport through a fining-upwards sedimentary sequence : laboratory experiments and simulation
    (Elsevier, 2004)
    Flynn, Raymond
    ;
    Cornaton, Fabien 
    ;
    Hunkeler, Daniel 
    ;
    Pierre Rossi
    A column containing four concentric layers of progressively finer-grained glass beads (graded column) was used to study the transport of the bacteriophage T7 in water flowing parallel to layering through a fining-upwards (FU) sedimentary structure. By passing a pulse of T7, and a conservative solute tracer upwards through a column packed with a single bead size (uniform column), the capacity of each bead type to attenuate the bacteriophage was determined. Solute and bacteriophage responses were modelled using an analytical solution to the advection–dispersion equation, with first-order kinetic deposition simulating bacteriophage attenuation. Resulting deposition constants for different flow velocities indicated that filtration theory-determined values differed from experimentally determined values by less than 10%. In contrast, the responses of solute and bacteriophage tracers passing upwards through graded columns could not be reproduced with a single analytical solution. However, a flux-weighted summation of four one-dimensional advective–dispersive analytical terms approximated solute breakthrough curves. The prolonged tailing observed in the resulting curve resembled that typically generated from field-based tracer test data, reflecting the potential importance of textural heterogeneity in the transport of dissolved substances in groundwater. Moreover, bacteriophage deposition terms, determined from filtration theory, reproduced the T7 breakthrough curve once desorption and inactivation on grain surfaces were incorporated. To evaluate the effect of FU sequences on mass transport processes in more detail, bacteriophage passage through sequences resembling those sampled from a FU bed in a fluvioglacial gravel pit were carried out using an analogous approach to that employed in the laboratory. Both solute and bacteriophage breakthrough responses resembled those generated from field-based test data and in the graded column experiments. Comparisons with the results of simulations using averaged hydraulic conductivities show that simulations employing averaged parameters overestimate bacteriophage travel times and underestimate masses recovered and peak concentrations.
  • Publication
    Accès libre
    Analytical 1D dual-porosity equivalent solutions to 3D discrete single-continuum models. Application to karstic spring hydrograph modelling
    (Elsevier, 2002)
    Cornaton, Fabien 
    ;
    Perrochet, Pierre 
    One-dimensional analytical porosity-weighted solutions of the dual-porosity model are derived, providing insights on how to relate exchange and storage coefficients to the volumetric density of the high-permeability medium. It is shown that porosity-weighted storage and exchange coefficients are needed when handling highly heterogeneous systems—such as karstic aquifers—using equivalent dual-porosity models. The sensitivity of these coefficients is illustrated by means of numerical experiments with theoretical karst systems. The presented 1D dual-porosity analytical model is used to reproduce the hydraulic responses of reference 3D karst aquifers, modelled by a discrete single-continuum approach. Under various stress conditions, simulation results show the relations between the dual-porosity model coefficients and the structural features of the discrete single-continuum model. The calibration of the equivalent 1D analytical dual-porosity model on reference hydraulic responses confirms the dependence of the exchange coefficient with the karstic network density. The use of the analytical model could also point out some fundamental structural properties of the karstic network that rule the shape of the hydraulic responses, such as density and connectivity.
  • Publication
    Accès libre
    Deterministic models of groundwater age, life expectancy and transit time distributions in advective-dispersive systems
    Cornaton, Fabien 
    ;
    Perrochet, Pierre 
    The main objective of this dissertation consisted in the elaboration of a methodology to determine reservoir groundwater age, life expectancy, and transit time probability distributions in a deterministic manner, considering advective-dispersive transport in steady velocity fields. In the first section, it is shown that by modelling the statistical distribution of groundwater age at aquifer scale by means of the classical advection-dispersion equation (ADE) for a conservative and non-reactive tracer, associated to proper boundary conditions, the obtained function corresponds to the density of probability of the random variable age, defined as the time elapsed since the water particles entered the aquifer. In a second step, the evaluation of the life expectancy, being the time remaining before a water particle leaves the aquifer was derived from an adjoint backward model, yielding the life expectancy distribution. The convolution of these two distributions (age and life expectancy) is then shown to correspond to the groundwater total transit time distribution, from inlet to outlet, and is fully defined for the entire aquifer domain. From the ADEs simulating the full distributions of age and life expectancy, moment averaged equations are defined, like e.g. the well-known mean age equation. The mathematical models developed in the first section are illustrated by two-dimensional numerical experiments based on a scaled groundwater simulator model. In the second section, the focus is directed towards the reservoir theory (RT). An accurate and efficient method is presented to simulate the transit time distribution at discharge zones. It was shown that for systems with a known internal age probability distribution, the application of the RT to advective-dispersive aquifer systems allows full definition of the discharge zone transit time distribution. The RT can also be applied to internal life expectancy probabilities, yielding the recharge zone life expectancy distribution. One-, two-, and three-dimensional theoretical examples are presented to illustrate the application of the RT in advective-dispersive systems, and make inferences on the effect of boundary conditions, aquifer structure, and macro-dispersion on age, life expectancy and transit time distributions. Also, the particular case of vertically averaged forward and backward ADEs is developed. In the last section, the RT is extended to arbitrary aquifer configurations by subdividing the entire flow system into subsystems, treating each of them as a compartment. Transfer of water fluxes within these compartments from recharge zones to a particular discharge zone could then be considered isolated from any other subsystem. Nevertheless, the effects of mixing and interaction with other compartments and dispersion processes are considered in this approach. In this way, the RT was made applicable to any sub-drainage basin of an aquifer of arbitrary complexity. It was then found that the backward transport of the life expectancy to a specific outlet could predict the forward transport of a contaminant introduced anywhere in space. In other words, the concentration breakthrough curve at any particular outlet, which would result from the transport of a unit mass release at any point can be predicted with only one single realization of the life expectancy field. The usefulness of the elaborated method to deal with environmental settings such as the well-head vulnerability and protection problem, or also the problem of underground storage of high-level nuclear waste, is illustrated on twodimensional synthetic examples. Finally the work is concluded with a brief summary and with a critical view on the obtained results, as well as possible directions for future investigations