Programme  Poster session 4  abstract 336

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

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: abs336_article.pdf
Poster: abs336_poster.ppt
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Session: Poster session 4

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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