Pierre Fischer

Université de Poitiers | UP · Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP)

Le Site Expérimental Hydrogéologique de Poitiers (SEH) a été le lieu d’implantation de deux profils de résistivité électrique, l’un de 47m et l’autre de 23m. Six acquisitions de résistivités apparentes ont été réalisées entre le 18 juillet 2023 et le 17 novembre 2023 afin de calculer les différences de résistivités avec un profil sec et d’obtenir l...

This article presents a multiphysics-based approach for a large-scale spatial reconstitution of head and tracer tests responses measured in a regional scale karst aquifer in Southern France. The main dataset consists in hydraulic heads measured in 11 wells during 6 weeks and 4 tracer tests. A pump station withdraws groundwater from this aquifer at...

In the unsaturated zone of fractured and karstified media, although the fractures and incipient karst conduits generally account for a minor volume in the bulk geologic formations, they contribute significantly to the flow and transport properties. The reason is due to the significant difference (i.e., several orders of magnitude) of permeability i...

Study region A 1 km² mountainous karst watershed on the Larzac Plateau in Southern France. Study focus The village of La Vacquerie, located at the outlet of the watershed, is punctually affected by flash floods during storm events. On the contrary, no runoff is observed in the village during other rainfalls. A sinkhole, draining surface flows at t...

The freshwater supply and protection constitute a major challenge in the context of global change. Among other freshwater stocks, karst aquifers constitute heterogeneous hydro-systems with non-linear hydrogeological behavior. The high level of heterogeneity in such aquifers and the lack of knowledge of their internal structure lead to strong diffic...

In this manuscript, we discuss the capabilities of a deep learning algorithm implemented with the Conventional Neural Network concept to characterize the hydraulic properties of aquifers. The algorithm called CNN-HT is designed to predict the inverse operator of hydraulic tomography using a synthetic training dataset in which the hydraulic head dat...

The accurate characterization of the underground depositional structure and hydraulic property distribution is essential to understand flow and solute transport in heterogeneous rocks or soils. Hydraulic tomography was shown to be an efficient technique to infer the spatial distribution of hydraulic properties. Due to the fact that information abou...

We present a synthetic hydraulic analysis of the propagation of oscillatory perturbations in a two-dimensional saturated zone bounded above by a capillary fringe. Unsaturated flows are simulated in a physical model using a hysteretic form of Richards' equation parameterized using the van Genuchten water retention curve and the Mualem hydraulic cond...

Imaging characterization of a heterogeneous alluvial aquifer at a decametric scale is presented. The characterization relies on responses to oscillatory pumping tests led in two different wells and at two different periods of oscillation (5 and 10 min). These specific oscillatory responses are extracted from the hydraulic pressure values, measured...

The hydraulic characterization of a highly anthropized coastal aquifer in France is presented. The current industrial operations of the study site prevent the use of standard ‘active’ hydrogeological investigation methods (pumping, slug tests). However, the studied field is bordered on its north-western side by a channel directly connected to the s...

Hydraulic characterization of a contaminated aquifer is an important step in depollution processes because its hydraulic parameters control the choice and efficiency of the depollution protocol to be adopted. The characterization presented in this article uses a 3D electrical resistivity imagery to identify the spatial heterogeneities of a contamin...

We present the results of a hydraulic tomography led on a 60 × 40 m² fractured and karstic field in Southern France in order to image, in a model, its transmissivity field. The dataset employed for the tomography consists in drawdown responses to cross-boreholes pumping tests reaching pseudo steady-state, with 8 different pumping wells and 22 measu...

This works aims to study how unconfined aquifers hydraulic properties (K, Ss and the Van Genuchten coefficients α and n) influence the spatial responses to periodic signals in groundwater. Therefore we have built a numerical model in order to simulate flows associated to oscillating perturbations in a silty soil and a sandy soil. Then we have used...

Clogging due to transport and accumulation of the colloids in the pore space has been recognized as one of the most significant challenges in water management research and environmental engineering. This paper proposes an inversion algorithm in time-lapse mode to track that complex process through the assessment of alteration in the transmissivity...

The localization of the network of conduits in karstic fields and the characterization of their equivalent hydraulic properties represents a complex scientific problematic. Hydraulic tomography represents an efficient way to image the distribution of the field properties, but, in order to produce realistic results regarding the particularities of k...

In this paper, we introduce a pore-scale model to study the interaction between biofilm growth and non-aqueous-phase-liquid (NAPL) dissolution. Liquid flow and dissolved NAPL transport are coupled with a biofilm growth model to correctly describe the complex dynamics of the processes including fluid flow, NAPL dissolution/biodegradation and biofilm...

This thesis manuscript presents a novel approach to characterize qualitatively and quantitatively the structures localization and properties in a fractured and karstic aquifer at a decametric scale. This approach relies on a hydraulic tomography led from responses to a pumping investigation and interpreted with inversion methods adapted to the comp...

In this work, we present a novel method to interpret, at a field scale, the preferential flows generated by harmonic pumping tests, in which the pumped flowrate varies according to a sinusoidal function with a given period. The experimental protocol relies on the application of harmonic pumping tests in a karstic field located near to Mont- pellier...

We present a qualitative and quantitative study to understand and interpret the information carried by the responses to harmonic pumping tests performed with different frequencies in a karstic aquifer. This study is first led theoretically on a synthetic case, then on an application case on a karstic field at a decametric scale.

In a karstic field, the flow paths are very complex as they globally follow the conduit network. The responses generated from an investigation in this type of aquifer can be spatially highly variable. Therefore, the aim of the investigation in this case is to define a degree of connectivity between points of the field, in order to understand these...

In this paper, we present a novel inverse modeling method called Discrete Network Deterministic Inversion (DNDI) for mapping the geometry and property of the discrete network of conduits and fractures in the karstified aquifers. The DNDI algorithm is based on a coupled discrete–continuum concept to simulate numerically water flows in a model and a...

Imaging in a Model the Flow Networks Generated by Harmonic Pumping Tests in a Karstic Field (Lez Aquifer, France)

The distributed modeling of flow paths within karstic and fractured fields remains a complex task because of the high dependence of the hydraulic responses to the relative locations between observational boreholes and interconnected fractures and karstic conduits that control the main flow of the hydrosystem. The inverse problem in a distributed mo...

Inverse problem permits to map the subsurface properties from a few observed data. The inverse problem can be physically constrained by a priori information on the property distribution in order to limit the non-uniqueness of the solution. The geostatistical information are often chosen as a priori information, however when the field properties pre...

Large-scale inversion methods have been recently developed and permitted now to considerably reduce the computation time and memory needed for inversions of models with a large amount of parameters and data. In this work, we have applied a deterministic geostatistical inversion algorithm to a hydraulic tomography investigation conducted in an exper...

Cellular Automata-based Deterministic Inversion (CADI) method is developped to model heterogeneous fields and this model is applied on a karstic site in Southern France.