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Bouzelboudjen, Mahmoud

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

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  • Publication
    Accès libre
    A statistical time series analysis of hydro-climatic stress on karst aquifer system (Switzerland)
    Kimmeier, Francesco
    ;
    Bouzelboudjen, Mahmoud 
    ;
    Eisenlohr, Laurent
    ;
    Rossier, Yvan
    ;
    Zwahlen, François 
    In order to determine the impact of climatic variations on several spring discharge, five karst aquifer systems were chosen in the Neuchâtel Jura (three basins over an area of 359 km2) and in the Prealps (2 basins of 4 and 10 km2 respectively). The records of air temperature, precipitation and groundwater discharge vary between 13 and 91 years. Statistical trend analyses (Kendall and Spearman tests) and correlation and spectral analyses have been used to analyze these records. The aim of this paper is not to generalize the results to all karstic aquifers in Switzerland but to answer the three following questions : (i) is there a trend at a given station for given parameters ?, (ii) are the trends the same for the different stations ?, (iii) and finally can we detect the impact of possible climatic changes on the natural responses of five karst springs in the Jura and Prealps ? For the Neuchâtel Jura, a regional trend of rising air temperature has been demonstrated. This is marked by two successive increases in 1945 and 1980. In the Prealps of Vaud, this trend is less well defined. Only the increase in the 1980's has been locally detected. The statistical study of precipitation shows its random character at the regional scale of the Neuchâtel Jura and Prealps. The trend of a reduction in groundwater discharge at Champs-du-Moulin in the Areuse basin is visible since 1945. It is part of a regional trend towards lower discharge, no trend has been observed at the La Doux and Noiraigue Springs. In the Prealps, a rising trend has been observed at Les Avants Spring since 1976 and a falling trend in discharge can be identified at Grandchamp Spring since 1988. Despite the fact that in certain cases, there has been a coincidence between the beginning of temperature increase and of falling discharge, the trends shown do not allow us to state that the only cause is that of climatic changes.
  • Publication
    Accès libre
    Drought risk analysis applied to porous Swiss aquifers
    Kimmeier, Francesco
    ;
    Bouzelboudjen, Mahmoud 
    ;
    Eisenlohr, Laurent
    ;
    Rossier, Yvan
    The impact of hydrogeological drought on groundwater has been studied in the context of natural flow systems. The aim of this article is to find the relative resistance of 18 unconfined aquifer systems in porous media to a prolonged shortfall in recharge. A synthetic relative drought resistance indicator has been calculated for each of the aquifer systems based on 4 variables which are the half-recession time, the specific regulatory capacity, the drainage density and the aquifer system area.
    The analysis shows that 33% of the chosen aquifer systems are weakly resistant. By contrast, 22% have a high drought resistance. The other aquifer systems are of moderate resistance (22%) or of good resistance (22%).
  • 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).
  • 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.