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Increasing mineralization in the Complex Terminal aquifer in Kebili region (south Tunisia)

IWRA World Water Congress 2008 Montpellier France
2. Towards the Future: Water Resources and Global Changes
Author(s): Marouan Ben Hammadi
Claude Drogue
Hervé Jourde
Hamed Ben Dhia
Moncef Zairi
M. Ben Hammadi, C. Drogue , H. Jourde (université Montpellier 2, 300 avenue Emilie Jeanbrau , 34095 Montpellier ) H. Ben Dhia, M. Zairi (école nationale des ingénieurs de Sfax Tunisie) ENIS, BP W 3038, route de Soukra Sfax (Tunisie)

Keyword(s): Complex Terminal, Mixing process, salinity, arid region
Article: Poster:

AbstractThe northen Sahara sedimentary aquifer contains two important aquifer systems: the Continental Intercalary (CI) overlain by the Complex Terminal (CT). The groundwater reservoir CT describes a multi layer aquifer which consists of the most recent formations in the Sahara basins: Turonian dolomites, Senonian, Eocene and Mio-Pliocene formations. The Complex Terminal exists in Tunisian and Algerian Sahara and covers an area of around 350.000 km2. It has an average depth between 65 and 270 m. The groundwater reservoir of CI is contained in the continental formations of the lower Cretaceous between 1200 and 1800m depth. The Kébili region is charaterised by an arid climate with a highly variable pluviometry in time and space (80 mm/yr). The evapotranspiration is also high and reaches 2500 mm/yr. This situation increases pressure in groundwater ressources. Actually, CT provides 80 % of the domestic and agricultural water supply. The total exploitation of the both aquifers is 12 m3/s. The piezometric heads were around 100 m above sea level in 1950. The exploitation of CT aquifer for agricultural pratices has contributed to the loss of the artisian conditions and the decline of groundwater level. Actually, a negative piezometric level is observed in the presqu’ile of Kébili région. Since 1980, an increase of salinity of the CT water is observed. The hydrochemical study investigates the origin of the water pumping from the CT. We consider two possible causes of increasing salinity: 1- The decline of the CT piezometric level increases the seepage from the shallow plio-quaternary aquifer (salinity is about 13 g/l). The excess of irrigation water concentrates at different rates in the irrigation channels. Then, it can return to CT aquifer and mix with groundwater. 2- The upwelling from CI aquifer which is still artisian: the water of CI is more saline than CT. Interactions between the two aquifers exist in the vicinity of the presqu’ile of Kébili where the fault system Kébili-Tozeur establishes contacts between these two aquifers.
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