Journal of Water Resource and Protection, 2013, 5, 502-510 http://dx.doi.org/10.4236/jwarp.2013.55050 Published Online May 2013 (http://www.scirp.org/journal/jwarp) Hydrogeological Study of the Aquifer System in Central Tunisia: New System Structuring of Horchane Aquifers Soumaya Chaibi, Wanissa Aydi, Moncef Chalbaoui Laboratory Water, Energy and Environment, National School of Engineers of Sfax, Sfax City, Tunisia Email: [email protected] Received January 18, 2013; revised February 19, 2013; accepted March 17, 2013 Copyright © 2013 Soumaya Chaibi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Hydrogeological investigations, tectonics and seismic reflection show the complexity of the Horchane groundwater and drainage possibilities with neighboring groundwater in central Tunisia. Seismic reflection lines intersecting the region show the role of halokinetic movements, by the intrusion along preexisting faults, in the restructuring of the hydro- geological basin. The salt domes associated with a chaotic facies at the base of outcrops, that limit the Horchane basin, puch to outcrops the areas of recharge area. Geoelectric section shows the anisotropy and the importance of Mio- Plio-Quaternary (MPQ) sediment along the gutters, between the outcrops of El Hafay and Kebar on the one hand, and outcrops of Kebar and Majoura on the other. These gutters are communicated with channels that facilitate drainage of the Horchane complex groundwater by that Gammouda in North-East and Braga in East. The results of this study clearly indicate the important role of the geology in the restructuring of groundwater basins, through early halokinetic movements. (i.e. halokinetic movements). The aquifer geometry is controlled by the ascent of Triassic salt material, from the Middle Jurassic, in central Tunisia. Keywords: Groundwater; Hydrogeological Basin; Halokinetic Movement; Aquifer Geometry; Water Recharge; Drainage; Filling; Triassic Salt Material 1. Introduction geological basins. Seismic data have been traditionally thought of as re- The Horchane Basin is situated in the Sidi Bouzid region gional screening tools capable of providing basin defini- in the central Tunisia (Figure 1), and it is characterized tions and basement mapping. However, in recent years, by a Mediterranean semi-arid to arid climate with irregu- the application of potential field data has been greatly lar annual rainfall not exceeding 350 mm/year and long expanded to include global in this study, we used data dry periods. Use of groundwater is increasing in order to from seismic reflection correlated with tectonic and hy- meet the demand for domestic, agricultural, and Indus- drogeological data to track architecture of the groundwa- trial needs. Therefore deep aquifer exploration and ex- ter as well as opportunities Horchane drainage with neigh- ploitation become a necessity in this area. boring aquifers. In central Tunisia, water tables are facing problems of The seismic reflection method was selected as the geo- overdrafts due to poor estimation of their architecture physical method that would give a regional picture of the [1-3], their preferred areas of recharge and their outlets. subsurface geology and geometry of hydrogeological ba- The Horchane basin has undergone a complex and poly- sin. phase structural history since middle Mesozoic time [4-7] The characterization of the Horchane complex aquifer that is marked by North-Sud and NE-SW faults [5,8-11]. was developed and applied to deeper aquifers with com- Recent studies [4,12-16] have indicated that the anticline bining all data, especially the geophysical, tectonic and structures of the central Atlas of Tunisia as a Triassic salt hydrodynamic ones. diaper at different evolutionary stages, such as El Hafay, Majoura and Souinia outcrops, where as the present plain 2. Study Area Setting structures should relate to corresponding compensation depocentre gutters. Triassic intrusions induced by strike- The study area called Horchane Basin is located west of slip movements contributed to restructure the hydro- central Tunisia, it is a basin bounded by the NE-SW ori- Copyright © 2013 SciRes. JWARP S. CHAIBI ET AL. 503 1 Gammouda 2 - 2 8 plain 04 K 2 T B U S El Hafay L1 G Zitoun Med.sea Kebar El Hafay L3 Tunisia 20008/5 A B 20007/5 19544/5 Libya A S Horchane 19841/5 Algeria 100 Km SABA plain 34. 50 Braga plain îch L2 i A Sid Sidi Aîch Majoura Sidi Aîch plain SOI 2 Km Souinia El Fej Mio-Plio-Quaternary 20008/5 Seismic line Hydrogeological well KAR I Upper Cretaceous Faults Lower Cretaceous Petroleum well Hydrogeological Urbain zone cross 9. 20 Figure 1. Geologic, seismic profile and location of the study area. ented anticlines (Figure 1). Lower cretaceous sediments geometry of this complex aquifer depends on the early outcrop as anticline cores of Sidi Aîch, Sidi Ali Ben halokinetic movements that characterize the Horchane Aoun (SABA), Bir El Hafay, Zitoun, Kebar and Ma- basin from the Middle Jurassic [4,9,23]. joura-Meloussi mountains. North-south, NE-SW and NW- SE faults (Figure 1) that have been reactivated since the 3. Materials and Methods upper Triassic-lower Jurassic rifting [5,9,11,15] bound The hydrogeological study requires not only the use of different tectonic blocks of Horchane area and are often conventional methods (rainfall, piezometric, lithology, associated with Triassic salt-pillow and domes that re- hydrodynamics...), but also methods of investigation us- sponsible for hydrogeological basin structuring. ing modern geophysics. The area is characterized by a semi-arid climate; it is by annual rainfall about 236 mm/year over the period The objective of the hydrogeological study is to un- 1974-2011, those are significant between December and derstand the functioning of an aquifer and to estimate the April. The temperature varies seasonally with a winter different characteristics that make each of the tools in- minimum of 15˚C and a summer maximum of 30˚C [17, formation and are implemented through a procedure adopt- 18]. The drainage system is dominated by the Oued El ed. Maksem which the flow appears only during the highest The seismic reflection survey method was selected as flood [19]. the geophysical method that would give a regional pic- The syncline Horchane lodges levels aquifers that ex- ture of the subsurface geology and groundwater geome- tend from the Jurassic to the Mio-Plio-Quaternary (MPQ), try before making extensive surveys by the geoelectrical those operated by citizens (drinking water, agriculture method. and domestic activities) are the upper Turonian carbonate The seismic reflection is a method of exploration geo- layers and Neogene sandy clay layers. The semi-perme- physics which the properties of the earth’s subsurface able levels between the Miocene and Cretaceous [1,20- from reflected seismic waves [11,24]. These will be re- 22] allow considering aquifers as they lodged a single flected when they encounter a boundary between two complex multilayer aquifer groundwater (Figure 2). The different materials with different acoustic impedances. Copyright © 2013 SciRes. JWARP 504 S. CHAIBI ET AL. lithology chronostratigraphy log Well Series/ System/ aquifer/ Formation Epoch period clayey sand Pleistocene sandy clay clayey sand Piacensian Segui Messinian Neogene coarse sand Tortonien Well:Ouled Brahim2 (19544/5) Serravallian Saouaf grayish clay pink calcareous Turonian calcareous marls marly calacreous blue marl marly calcareous with some gypsum crystals blue marl marly calcareous Upper Zebbag gray marl marly calcareous Upper blue plastic marl marly limestone Cretaceous blue marl marly calcareous 100 m calcaire Cenomanian limestone marly greyish with Well: Rabta (19885/5) a few crystals of gypsum greyish marly imestone calacire gray dolomitic Albian Lower gray marl Lower Zebbag Cretaceous blue marl Figure 2. Litho-hydro-stratigraphic column of Horchane basin and surrounding area. They are detected, on land, using geophone [25]. The used in hydrogeology for several objectives: the delinea- recorded signals are plotted on a seismic section after tion of lithological units; the investigation of thickness significant amounts of processing [26,27]: demultiplex- and nature of covering layer; the estimation of depth ex- ing, filtring, deconvolution, velocity analysis, stacking, tension and thickness of the aquifers; and the mapping of migration… discontinuation zones like fractures and faults. We propose to use the seismic reflection profiles to Whereas, the geophysical electrical measurements (geo- study the lateral location and geometry of the Upper electrical) are largely applied in the study of diverse un- Cretaceous units (Figure 2). Recent studies [15,20,21, derground irregularities. The rocks and geological for- 29-31], have shown that seismic refection profiling is mations may be distinguished by the way they conduct Copyright © 2013 SciRes. JWARP S. CHAIBI ET AL. 505 electricity, specifically by their physical property called electrical sounding were used to determinate the MPQ electrical resistivity. The electrical current consists of the levels lithology. movement of electrical charge, which is represented by The groundwater flow is determined by piezometric electrons or ions. Ions move within the fluids in the rock measurements consisting 42 hydrogeological pumped pores. The experimental results show that