Aspects quantitatifs et qualitatifs des eaux transitant par la grotte karstique de Hammamet Algérie

International audienceLes travaux portant sur la connaissance et le fonctionnement sont rares, en effet les derniers travaux effectués sur cette grotte sont très anciens. Cette situation freine les travaux actuels. Pour réaliser notre travail, nous nous sommes intéressés à la morphologie externe de la grotte. Le constat réalisé montre une morphologie gondolée traduisant la présence de petites dolines, ces dernières permettent l'infiltration des eaux dans les cavités. L'étude réalisée montre également la présence de sources sur la partie droite de la grotte en dessous de l'épikarst. Ce constat nous a permis de déduire une dissymétrie de la fissuration. En effet le coté gauche de la grotte est étanche, aucun écoulement ne se fait par contre le coté droit est très fissuré, ce qui favorise l'infiltration et la circulation des eaux. Les apports en eau sont soit directs, par infiltration des eaux de pluies soit indirects à partir des Djebels entourant la grotte, tel que le Djebel Tazbent, situé à plus haute altitude. Les débits jaugés à la sortie de la grotte varient en fonction des saisons et leur pluviosité. De ce fait à la sortie de la grotte les débits sont importants et peuvent atteindre 1 913L/s, par contre au niveau de l'oued Bouakous caractérisant la zone aval, le débit n'excède pas 10L/s. Les jaugeages différentiels effectués montrent une infiltration de 541L/s. Ces eaux vont modifier la composition chimique des eaux souterraines, ce dernier est bicarbonaté en période pluvieuse et devient chloruré en période sèche. Ce changement est accentué par la mise en solution des minéraux

HYDROGEOLOGIE D’UN SYSTEME AQUIFERE EN ZONE SEMI-ARIDE.CAS DE LA REGION DE KHENCHELA (ALGERIE)

L'hydrogéologie des zones arides et semi-aride de l'Algérie, est un thème complexe. La région de Khenchela, qui se trouve touchée par une sècheresse chronique et un bilan climatique toujours négatif ne permet pas de justifier ou de préciser l'existence d’une recharge des nappes aquifères. Or cette recharge, même si elle est limitée, existe souvent dans ces régions arides où l'irrégularité du climat peut provoquer certaines années quelques événements pluvieux exceptionnels [1, 2, 3, 4]. Trois systèmes aquifères sont distingués dans la wilaya de Khenchela : le Quaternaire, le Crétacé et le Miocène. On dénombre quatre nappes aquifères, l’une est superficielle, il s’agit de nappes phréatiques hétérogènes et le reste sont des nappes profondes représentées par la nappe des plaines d’effondrement, la nappe des calcaires fissurés et la nappe des formations continentales. La profondeur de ces formations aquifères varie de 5 à 600 m. Le volume total prélevé à partir de l’ensemble des aquifère est de 34 millions de m3/an [1]. L’objectif essentiel est d'identifier les aquifères de la région afin de constituer une base de données sur les possibilités hydriques des formations de la région de Khenchela.  The hydrology of arid and semi-arid Algeria is a complex subject. Khenchela region, which is affected by chronic drought and climate always negative balance does not justify or clarify the existence of a groundwater recharge. Now this charge, even if limited, often exists in these arid regions where the climate can cause irregularity in some years a few exceptional rainfall events [1, 2, 3, 4]. Three aquifer systems are distinguished in the wilaya of Khenchela: Quaternary, Cretaceous and Miocene. There are four aquifers, one is superficial, it is heterogeneous aquifers and the rest are represented by the deep groundwater aquifer plains of collapse, the web of cracked limestone formations and the water inland. The depth of these aquifers ranges from 5 to 600 m. The total collected from all aquifer is 34 million m3/year [1]. The main objective is to identify the aquifers in the region to establish a database on water training possibilities in the region of Khenchela

Hydrochemical and isotopic characterization of a complex aquifer system

A methodology was developed and applied to the Tindouf basin (south-western Algeria) to understand the hydrogeology of a complex aquifer system with a limited number of data, to identify the favorable areas for the design and building of new wells, and to know whether there is still current recharge of these aquifers. The principal components analysis (PCA), diagram of deuterium versus oxygen-18, and equilibrium diagrams Mg/Na and Ca/Na were the techniques used to combine different datasets in order to identify chemical and isotopic groups, which were in turn used to define the groundwater flow paths. In addition, on the basis of thermodynamic equilibrium, it is possible to define the chemical evolution of the Tindouf basin aquifer. The results of this study are consistent with the generally accepted hydrogeological conceptual model. The combination of the different methods made possible to define and and to characterise the main groundwater flow paths from their sources to the discharge zones. These flow paths are defined by water categories, which are represented by salinity and groundwater origin. This approach can be used to analyze aquifers characterized by a lack of data and can also be useful for studying other complex groundwater basins

Management and protection of Mediterranean groundwater-related coastal wetlands and their service

In the framework of the GEF/UNEP-MAP Strategic Partnership for the Mediterranean Sea Large Marine Ecosystem, UNESCO-IHP executed a component on “Management of coastal aquifers and groundwater”, which included an activity on “Implementation of eco-hydrogeology applications for management and protection of coastal wetlands”. The aim of the activity was to reverse degradation trends in coastal aquifers and groundwater-related coastal wetlands and enhance human wellbeing, namely by providing appropriate capacities for the integration of an ecosystem services approach into groundwater and wetlands assessment and management. To this end, UNESCO-IHP sought the cooperation of experts in order to design and carry out actions aiming to generate a new conceptual framework integrating hydrogeological, ecosystem, and management considerations in the management of Mediterranean groundwater-related coastal wetlands. Among key actions, a background document was prepared, detailing the basic aspects to be considered for an improved management of Mediterranean groundwater-related coastal wetlands through the assessment of the interlinkages between groundwater ows, wetlands services, and human wellbeing. This book sets forth the conceptual and empirical aspects that must be examined and followed to better understand the relationships between groundwater-associated wetlands, geology, hydrology, and services to human well-being. It also presents methods for inventorying the basic information needed to characterize wetlands and aquifer functioning and to assess wetlands’ contribution to human well-being. Finally, it proposes guidelines and recommendations for the evaluation and integrated management of Mediterranean groundwater-related coastal wetlands in order to preserve the sustaining role of groundwater in relation the many environmental services that wetlands provide.Global Environmental Facility (GEF) United Nations Environmental Programme/Mediterranean Action Plan (UNEP/MAP

Contribution a l'etude hydrogeologique de la nappe alluviale de la plaine d'effondrement de Tebessa : essai de modelisation

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Caractéristiques chimiques des eaux de la nappe du synclinal de Taoura, Souk Ahras (Nord-Est de L’Algérie)

La nappe karstique de Taoura est alimentée à partir des eaux de précipitations ou par les eaux en provenance des différentes zones drainant le bassin versant transfrontalier Medjerda-Mellegue dans la partie Sud-est de la ville de Souk Ahras. Les études géologiques réalisées ont montré que les formations à l’affleurement forment un synclinal, ce dernier contient un niveau aquifère, qui recèle une nappe captive, exploitée par plusieurs forges (T1, T3, T7, D3, D5). L’observation des logs stratigraphiques montre une hétérogénéité lithologique. Les prélèvements et les analyses réalisés, ont montrés que les eaux de la zone d’étude sont en grandes partie riches en bicarbonates et en calcium. Cependant quelques points se caractérisent par la domination des chlorures et des sulfates. Ces anions s’accompagnent de sodium ou de calcium, confirmant ainsi l’impact des formations traversées sur la qualité des eaux. Les eaux prélevées sont utilisées pour l’irrigation et l’AEP. De ce fait les risques de pollutions sont quasi inévitables, confirmée par les concentrations élevées des nitrates (> 50 mg/l).Mots Clés : Nappe karstique- Medjerda-Mellegue- Géologique-Pollution- Qualité des eaux. Chemical characteristics of waters aquifer of the syncline of Taoura, , Souk Ahras (North-east of Algeria)The karst aquifer of Taoura is fed from waters of rainfall or by waters from the different draining zones the basin pouring cross-border Medjerda-Mellegue in bet it south of the East of the city of Souk Ahras. Accomplished geological studies showed that trainings in outcrop form a syclinoriums, this last contains a water-bearing level, which conceals a captive tablecloth. This last is exploited by several smithy (T1, T3, T7, D3, D5). The observation of logs stratigraphic shows lithological heterogeneity, what is going to confer on water a variation of its chemical composition. Sample and analyses accomplished, showed that waters of the zone of study are in big left rich in and in calcium, bicarbonate however some points are characterized by the domination of chlorides, sulphates, these anions are accompanied by sodium or by calcium. Confirming so the impact of trainings crossed on the quality of waters. Taken a sample waters are used for irrigation and AEP. Of this fact risks of pollutions are quasi unavoidable, are confirmed by concentration of nitrates (> 50 mg / l).Keywords: Karst aquifer- Medjerda-Mellegue- Geological- pollution-Quality of waters

Biochemical Approach to Assess Groundwater Pollution by Petroleum Hydrocarbons (Case Skikda Algeria)

Due to the accelerated population growth and development in all sectors especially industry, more water has been pumped and more effluents have been rejected to the natural system. In the coastal Skikda Valley; Petrochemical indus-try is practiced along the year and almost groundwater are threatened. This work is referred to the characterization of the environmental hydrobiochemistry in the coastal petrochemical industrial area. The study has investigated the groundwater pollution by hydrocarbons using biochemical approach and assessing the nature and extent of contamina-tion of groundwater in relation to petroleum industrial activities surrounding tank, channel and pipe. At site of this in-dustrial zone, groundwater circulates on slight deep in the mio-pliocene alluviums (sand and gravel) which is character-ized by an important permeability. Groundwater quality analysis proved that groundwater quality is largely polluted with respect to BOD5, COD, TPH and TSS. So, a narrow relationship between BOD and TPH and important qualitative degradation of the groundwater is shown, especially in the parts situated in the down gradient area and in direct prox-imity of tank, channel and pipe. The extent of groundwater contamination is influencing by the depth of the water table, permeability of the soil and therefore infiltration rate. In order to prevent further pollution of groundwater, oil must be stored and transported via impervious tank, pipe and channel. So, effluents must be treated prior to discharge

Fuzzy analytical hierarchy process for groundwater potential mapping in a Mediterranean catchment: the case of the Medjerda catchment in northeast Algeria

In this study, groundwater potential was mapped for a Mediterranean catchment using remote sensing techniques, geographical information systems (GIS), and the fuzzy analytical hierarchy (FAHP) process. Seven environmental factors were considered to influence groundwater potential, including soil type, lithology, precipitation, land use/cover, slope, lineament density, and drainage density. A FAHP method was implemented to calculate the weight of each factor and each class in the groundwater potential. The FAHP confusion matrix was established by eliciting opinions of local experts on factors that drive groundwater potential in this area. A weighted overlay was made in Arc-GIS™ for producing the final groundwater potential map. Three groundwater potential classes were considered (low, moderate, strong). Areas of very high potential represent 107.09 km2 (8%) of the total surface of the basin and are located in alluvial and calcareous formations of a high density of lineament and in areas with a low slope which promotes rapid infiltration. About 1022.124 km2 (71%) of the surface of the sub-catchment is characterized by a moderate to strong potential, while the remainder 305.945 km2 (21%) is characterized by a low potential. The results of the classification are validated by establishing the receiver operating characteristic (ROC) curve using 61 data from the wells located in the study area. The area under curve (AUC) yields 75.5% demonstrating the effectiveness of the method in identifying groundwater potential areas

Hydrochemical study of Drean–Annaba aquifer system (NE Algeria)

Water quality is subject to frequent changes in the Drean-Annaba alluvium aquifer. Water-rock interaction can not be the only process that produces the observed modification, but dryness that the country knew during the last two decades has highly contributed to the water quality changes. During this period, irregularities in the distribution of rainfalls, in time and space, have been observed. As a result, a periodicity in hydrochemical changes in water of wells and rivers is noticed. Statistical, the principals components analysis (PCA) tools and Tickel diagram have been used to show, through chemical presentation, these effects. The results show, indeed, seasonal changes of water quality for the period 1999-2000. From a cationic point of view, a competition between alkaline and alkaline earths is shown. On the other hand, from an anionic point of view, there is a transition from chlorides to sulphates and may be to bicarbonates. The present work was carried out in a relatively small area and this was useful to show the relationship that existed between dryness and water quality of both the aquifer system and surface water