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Renard, Philippe
Nom
Renard, Philippe
Affiliation principale
Fonction
Directeur de Recherche
Email
Philippe.Renard@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 8 sur 8
- PublicationAccès libreIntegrating aerial geophysical data in multiple-point statistics simulations to assist groundwater flow models(2015-10)
; ; - PublicationAccès libreComparison of three geostatistical methods for hydrofacies simulation: a test on alluvial sediments(2012-1-10)
- PublicationAccès libreThree-dimensional high resolution fluvio-glacial aquifer analog - Part 2: Geostatistical modeling(2011-7-21)
; ; Bayer, PeterThe heterogeneity of sedimentary structures at the decimeter scale is crucial to the understanding of groundwater flow and transport. In a series of two papers, we provide a detailed analysis of a fluvio-glacial aquifer analog: the Herten site. The geological data along a series of 2D sections in a quarry, the corresponding GPR measurements, and their sedimentological interpretation are described in the companion paper. In this paper, we focus on the three-dimensional reconstruction of the heterogeneity. The resulting numerical model is provided as an electronic supplementary material for further studies. Furthermore, the geostatistical parameters derived from this analysis and the methodology described in the paper could be used in the future for the simulation of similar deposits where less data would be available. To build the 3D model, we propose a hierarchical simulation method which integrates various geostatistical techniques. First, we model the subdivision of the domain into regions corresponding to main sedimentological structures (e.g. a sedimentation event). Within these volumes, we use multiple-point statistics to describe the internal heterogeneity. What is unusual here is that we do not try to use a complex training image for the multiple-point algorithm accounting for all the non-stationarity and complexity, but instead use a simple conceptual model of heterogeneity (ellipsoidal shapes as a training image) and constrain the multiple point simulations within the regions by a detailed interpolation of orientation data derived from the 2D sections. This method produces realistic geological structures. The analysis of the flow and transport properties (hydraulic conductivity and tracer breakthrough curves) of the resulting model shows that it is closer to the properties estimated directly from the 2D geological observations rather than those estimated from a model of heterogeneity based on probability of transitions and not including the modeling of the large-scale structures. - PublicationAccès libreThree-dimensional high resolution fluvio-glacial aquifer analog - Part 1: Field study(2011)
; Comunian, AlessandroDescribing the complex structures that exist in many sedimentary aquifers is crucial for reliable groundwater flow and transport simulation. However, hardly any aquifer can be inspected in such detail that all decimeter to meter heterogeneity is resolved. Aquifer analogs serve as surrogates to construct models of equivalent heterogeneity, and thus imitate those features relevant for flow or transport processes. Gravel pits found in excavation show excellent sections of the sedimentary sequence and thus offer direct insight into the structural and textural composition of the subsoil. This paper describes an approach to also inspect the third dimension: by mapping during the ongoing excavation it is possible to obtain a three-dimensional representation of the subsurface within a short period of time. A detailed description of a case study is presented and the findings from sedimentological, hydrogeological and geophysical analyses are compared. The gravel pit is located near the town of Herten in southwest Germany, where relatively young unconsolidated fluvio-glacial and fluvial sediments in the Rhine basin are mined. The excavated gravel body is built up by architectural elements typical for braided river deposits. The study generated a high-resolution data set of lithofacies, hydrofacies and ground penetrating radar (GPR) profiles. It represents the basis for a full three-dimensional geostatistical reconstruction presented in the second part. - PublicationAccès libreA numerical analysis of dimensionality and heterogeneity effects on advective dispersive seawater intrusion processes(2010)
; Two-dimensional (2D) and 3D numerical simulations of the dispersive Henry problem show that heterogeneity affects seawater intrusion differently in 2D and 3D. When the variance of a multi-Gaussian isotropic hydraulic conductivity field increases, the penetration of the saltwater wedge decreases in 2D while it increases in 3D. This is due to the combined influence of advective and dispersive processes which are affected differently by heterogeneity and problem dimensionality. First, the equivalent hydraulic conductivity controls the mean head gradient and therefore the position of the wedge. For an isotropic medium, increasing the variance increases the equivalent conductivity in 3D but not in 2D. Second, the macrodispersion controls the rotation of the saltwater wedge by affecting the magnitude of the density contrasts along the saltwater wedge. An increased dispersion due to heterogeneity leads to a decreasing density contrast and therefore a smaller penetration of the wedge. The relative magnitude of these two opposite effects depends on the degree of heterogeneity, anisotropy of the medium, and dimension. Investigating these effects in 3D is very heavy numerically; as an alternative, one can simulate 2D heterogeneous media that approximate the behaviour of the 3D ones, provided that their statistical distribution is rescaled. - PublicationAccès libreIntroducing wwhypda : a world-wide collaborative hydrogeological parameters database(2009)
- PublicationAccès libreDeterministic and probabilistic numerical modelling towards sustainable groundwater management: application to seawater intrusion in the Korba aquifer (Tunisia)(2008)
; This PhD endeavours numerical groundwater modelling considering heterogeneous and uncertain hydraulic parameters. It is made of three parts. First, we investigated the effects of dimensionality and heterogeneity of the hydraulic conductivity on dispersive seawater intrusion (SWI) processes. Multiple 2D and 3D unconditional simulations of hydraulic conductivity fields sharing the same statistics were generated then used to solve density-dependent flow and solute transport equations with a finite element code. Monte Carlo simulations were analysed in terms of dimensionless criteria including the penetration length and width of the saltwater wedge. Results showed that the 2D heterogeneity is affecting more strongly the SWI processes than the 3D heterogeneity. The saltwater wedge length in the 2D models is smaller than in the 3D ones while there is more mixing in 2D models. Most important, results showed that there is a critical ratio between advection and dispersion processes which is controlling the behaviour of SWI in heterogeneous porous medium. The second part of the thesis dealt with deterministic and probabilistic modelling and long term forecasts of SWI in the Korba aquifer (Tunisia). The study started by the development of a 3D density-dependent flow and solute transport model of the regional Korba aquifer. Then, two geostatistical models of the exploitation rates and of the hydraulic conductivities within the aquifer were built by combining incomplete direct data and secondary information including aquifer physical parameters. The effects of the uncertainty on the spatial distribution of the pumping rates and the uncertainty on the hydraulic conductivity field on the 3D density-dependent model were analysed separately and then jointly. To circumvent the large computing time required to run hundreds of 44-years transient models, the simulations were made in a parallel fashion on the EGEE Grid infrastructure as well as on a local Linux cluster. The deterministic numerical model allowed to estimate the current over-exploitation of the Korba aquifer to 135%. It also allowed to estimate the time lapse needed to turn back the initial head and slat distributions (before exploitation start) to about 150 years. The results of the stochastic simulations showed that both uncertainties led to a zone representing 12% of the aquifer area, where the groundwater heads and salt concentrations are not known with accuracy. Most important, results showed that reducing the pumping rates progressively by 50% until 2048 will not result in a recession of the saltwater wedge ; instead an additional 9.5% of the surface of the aquifer will be contaminated in 2048. In the third part of the thesis, the performances of kriging, stochastic simulations and sequential self-calibration inversion are assessed when characterizing a non-multi-Gaussian synthetic 2D braided channel aquifer. In a first step, the performance of the three methods was compared in terms of reproducing the original reference transmissivity or head fields. In a second step, the methods were compared in terms of accuracy of flow and transport (capture zone) forecasts. Results showed that the errors remain large even for a dense data network. In addition, some unexpected behaviours are observed when large transmissivity datasets are used. We also observed an increase of the bias with the number of transmissivity data and an increasing uncertainty with the number of head data. This was interpreted as a consequence of the use of an inadequate multi-Gaussian stochastic model.