Purposes and methodology

1. Modeling of the chaotic behavior of Sidi El Hani discharge playa, Tunisian Sahel: which exogenous factor commands this saline environment? The subsurface flow or the climatic variability? Elhoucine Essefia,b,f, JamelTouira,b, Mohamed Ali Tagortic, Salem Bouria,b, HendaEssefid, JamelOualia,e and Hayet Ben Jmaaf a Laboratoire Eau Énergie Environnement (L3E); Ecole Nationale des ingénieurs de Sfax B.b.w. 3038 Sfax Tunisie. b Facultés des Sciences de Sfax (FSS) c Institut Supérieur de Biotechnologie de Monastir (ISBM) d Faculté des Sciences Economiques et de Gestion de Sfax (FSEGS) e Ecole Nationale des Ingénieurs de Sfax (ENIS) f Faculté des Lettres et Sciences Humaines de Sfax (FLSHS)

2. OUTLINE Presentation of the study area and the problematic Purposes and methodology Results Convergence of the surrounding aquifers toward Sidi El Hani discharge playa Response of the hydrogeological balance to the climatic physical forcing Numerical model on the basis of salt budget technique and the chaos theory Geochemistry of the convergent aquifers Hydrogeological model of Sidi El Hani discharge playa-Kairouan aquifer Conclusion

3. Presentation of the study area and the problematic ? Problematic??? Sidi El Hani (stricto sensu) Endorheic system ? Salt crust Ever flooded surface ? Souassi ? ? Dkhila ? Oued Chrita Localisation and topography (Ben Jmaa, 2008)

4. Purposes This study is meant to provide an insight into how discharge playas, which are strongly influenced by a regional salty groundwater flow regime, such as Sidi El Hani discharge playa, would respond to the climatic variability on the one hand and to the salty materials coming from the subsurface of the Sahel area on the other Methodology To achieve this purpose, two lines of attack were followed: a hydrological-hydrogeological approach and a geochemical approach.

5. The hydrological-hydrogeological approach Relation between the surrounding aquifers and the discharge playa -The hydrogeological map Confrontation between the physical forcing imposed by the climate and the groundwater contribution -Evolution of the fluid density -Evolution of the actual evaporation with fluid density -Modeling of the fluid density on the basis of the chaos theory and the salt budget technique The geochemical approach -Piper diagram: geochemical facies of the convergent aquifers

6. Convergence of the surrounding aquifers towards Sidi El Hani discharge playa

7. Hypotheticalmeteorological station Correlation D4.D9.D22.D39.D52.D62.D67.D69.D75.D90. Location of some drills Convergence of the surrounding aquifers (Castany, 1952; modified)

8. Response of the hydrogeological balance to the climatic physical forcing

9. Evolution of the fluid density in the discharge playa of Sidi El Hani during the water year 2006/2007

10. Relationship between the actual evaporation and the fluid density in Sidi El Hani discharge playa during July 2008

11. Numerical model on the basis of the salt budget and the chaos theory

12. FDn -1 – FDn = H xAEn +H2 xPn + H4 x GWn FD: Fluid Density AEn: Actual Evaporation during this month Pn: Precipitation during this month GWn: Groundwater contribution during this month H, H2 and H3 are constants of respectively AE, P and GW AE= K x PE x FD Differential equation Solution (Maple) Initial conditions

13. Simulation of salt budget in the Sidi El Hani discharge playa from November 2006 to November 2026

14. Simulation of water budget in the GSL in the USA from 1900 to 2005 (Khalil et al., 2006)

15. Geochemistry of the convergent aquifers

16. Chlorinated and/or Sodic Sulphated and/or Potassic Chlorinated and/or SulfatedSodic and/or Magnesian D4 Calcic Bicarbonate and/or Magnesian D67 Sodic/Potassic Sulphated D9 No dominant cations Carbonate /Bicarbonate Chlorinatedd D9 D4 D67 D9 D67 D4 Piper diagram if some drills in the vicinities of Sidi El Hani discharge palya

17. Model of Sidi El Hani discharge playa

18. E-W correlation between two drills in the vicinity of Sidi El Hani discharge playa (Crude data from the Ministry of Agriculture of Tunisia, 1995)

19. Precipitation The climate as minor component Evaporation Dams effect Sidi El Hani dischargeplaya Kairouan aquifer The hydrogeology as major component Levels of Kairoan aquifer Somewhere domes of salt and/or salty water Hydrogeological model: the hydrogeology as major component in Sidi El Hani saline environment (Besbes, 1975; modified and reinterpreted)

20. Conclusion The whole previous analyses show the primary role of the hydrogeological framework at the expense of the climatic factor An ever present high fluid density is the result of the convergence of the surrounding aquifers and the leaching of somewhere domes of salt or the transporting of huge quantities of salty water. The actual evaporation does not response linearly to the physical forcing imposed by the climate; because it is limited by the groundwater contribution Mathematically also, in spite of the chaotic behavior, it may be proved that the hydrogeological balance will be in the near future stable, regardless of the climatic change Geochemically, the leached domes or the transported water is basically dominated by chlorinated anions and Sodic/Potassic cations

21. THANK YOU