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Bouzelboudjen, Mahmoud

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Bouzelboudjen, Mahmoud
Affiliation principale
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https://libra.unine.ch/handle/123456789/1079

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  • Publication
    Accès libre
    3-D groundwater modeling at regional scale
    (2001)
    Kimmeier, Francesco
    ;
    Bouzelboudjen, Mahmoud 
    ;
    Király, László
    Large hydrogeological basins are constituted of several superimposed aquifers, separated by geological formations of relatively low permeabilities. The delimitation of the different flow systems is far more difficult to realize for a heterogeneous system. Flux vectors provide valuable indications about groundwater flow paths and hydraulic exchanges between the different geological formations. Hydraulic relationships between two superimposed aquifers can vary locally: an aquifer can «feed» the underlying one at some point and conversely elsewhere. These relationships, which constitute in fact the flow field, will be determined by the structure of the basin as defined by the spatial distribution of the rock permeabilities, and by the boundary conditions, as defined by the locations of the recharge and discharge areas. The aim of this study is to show schematically the deep groundwater flow patterns between the massives of the Aar and the Black Forest. The hydrogeological profiles illustrate three-dimensional flow fields inside a large volume of terrain and represent but one of the numerous solutions of the mathematical modelling realized. Computations have been performed for a steady state flow regime, which means that the boundary conditions do not vary with time.
    On the basis of modelling results, it was possible to illustrate schematically the deep flow systems of the most important aquifers between the Aar massives and the Black Forest (Malm, Muschelkalk and upper Cristallin). An approximate but plausible representation of the groundwater circulation in deep aquifers was obtained thanks to the model. We are able to distinguish between the hydraulic relationships of two superimposed aquifers in various regions. The three-dimensional representation shows the outcrop zones of the different geological formations as well as the situation of recharge areas, which are characterised by high potentials, and discharge zones, which are characterised by low potentials in valleys represented by the hydrographic network.
    Modelling results are then compared to available measurements in an attempt to validate the results. It is interesting to notice that it was possible, to a certain extent, to verify the modelling results by deep drillings. Most particularly, measurements of the hydraulic potentials at various depths in these boreholes have revealed upwellings close to the regional discharge areas.
  • Publication
    Accès libre
    Numerical simulation as a tool for checking the interpretation of karst spring hydrographs
    Eisenlohr, Laurent
    ;
    Király, László
    ;
    Bouzelboudjen, Mahmoud 
    ;
    Rossier, Yvan
    A schematic representation of karst aquifers may be that of a high hydraulic conductivity channel network with kilometre-wide intervals, surrounded by a low hydraulic conductivity fractured limestone volume and connected to a local discharge area, the karst spring. The behaviour of the karst spring (hydrographs, chemical or isotopic composition, etc.) represents the global response of the karst aquifer to input events.
    The available data on karst aquifer hydraulic parameters are limited. Global response is therefore more easily obtained and is commonly used to make inferences on the recharge and groundwater flow processes, as well as on the hydraulic parameter fields. Direct verification of these interpretations is, obviously, very difficult.
    We have used an indirect method of verification, consisting of introducing well-defined theoretical karst structures into a finite element model and then analysing the simulated global response according to presently accepted interpretation schemes. As we know what we put into the numerical model, the validity of any interpretation may be checked.
    The first results indicate that some of the generally accepted interpretations are not necessarily true. In particular: (i) separation of simulated recession hydrographs into several components shows that different exponential components do not necessarily correspond to aquifer volumes with different hydraulic conductivities; (ii) non-exponential parts of recession hydrographs do not always give information about the infiltration process; and (iii) the recession coefficient of the baseflow (i.e. the last, nearly exponential part of the recession hydrograph) depends on the global configuration of the whole karst aquifer, not just on the hydraulic properties of the low hydraulic conductivity volumes.
  • Publication
    Accès libre
    Numerical versus statistical modelling of natural response of a karst hydrogeological system
    Eisenlohr, Laurent
    ;
    Bouzelboudjen, Mahmoud 
    ;
    Király, László
    ;
    Rossier, Yvan
    Structural and hydrodynamic characteristics of karst aquifers are mostly deduced from studies of global responses of karst springs (hydrographs, chemical or isotopic composition). In this case, global response is often used to make inferences with respect to infiltration and ground water flow processes as well as on the hydrodynamic parameters. Obviously, the direct verification of these inferences is very difficult. We have used an indirect method of verification, introducing well defined theoretical karst structures into a finite element model and then analysing the simulated global response according to the currently accepted interpretation schemes. As we know what we are introducing into the numeric model, the consistency of the interpretation may be checked immediately. The results obtained in the hydrogeological study of two karst basins in the Swiss Jura and from 2-D and 3-D numerical simulations show the difficulty of finding structural parameters and hydrodynamic behaviour from statistical methods alone, i.e. correlation analyses discharge-discharge and precipitation-discharge. In effect, our first results show that the form of the correlograms depends on several factors besides the structure of the karst aquifer: (i) on the form of the floods, in other words the contrast between quick flow and base flow, (ii) on the frequency of hydrological events during the period analysed and (iii) on the type of infiltration processes, in other words the ratio of diffuse infiltration to concentrated infiltration. Obviously, the variability of a karst hydrograph is a result of a combination of these factors. Distinction between them is not always possible on hydrographs, and therefore on correlations (discharge-discharge and precipitation-discharge).