Recharge Mode and Mineralization of Groundwater in a Semi-Arid Region: Sidi Bouzid Plain (Central Tunisia)
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Environ Earth Sci DOI 10.1007/s12665-010-0771-4 ORIGINAL ARTICLE Recharge mode and mineralization of groundwater in a semi-arid region: Sidi Bouzid plain (central Tunisia) Hichem Yangui • Kamel Zouari • Rim Trabelsi • Kazimierz Rozanski Received: 18 May 2010 / Accepted: 26 September 2010 Ó Springer-Verlag 2010 Abstract Groundwater is the most important source of Introduction water supply in Sidi Bouzid plain located in central Tuni- sia. Proper understanding of the geochemical evolution of In arid and semi-arid countries, issues related to water groundwater is important for sustainable development of resources are of growing concern due to different envi- water resources in this region. A hydrogeochemical survey ronmental, economic and social factors. Continuously was conducted on the Mio–Plio–Quaternary aquifer system increasing abstraction of groundwater resources to meet using stable isotopes, radiocarbon, tritium and major ele- rising industrial, agricultural and domestic needs, coupled ments, in order to evaluate the groundwater chemistry with severe drought periods during the past decades leads patterns and the main mineralization processes occurring in to growing deficit of water. The drawdown of piezometric this system. The chemical data indicate that dissolution of levels and progressing degradation of water quality are the evaporate minerals and evaporation are the main processes main consequences of such intensive exploitation. controlling groundwater mineralization. The isotopic data The plain of Sidi Bouzid (SBZ) which was the subject show that groundwater in the study area is a mixture of of this study is located in central Tunisia (Fig. 1). SBZ is recent shallow waters located upstream and along Wadi Al a typical example of a semi-arid climate region where Fakka bed and paleowaters located towards plain limits and groundwater resources are intensively exploited for human discharge areas. Low 3H and 14C contents are observed in needs as a result of agricultural and demographic devel- major part of the plain indicating that recharge of the opment. In 2005, the renewable water resources in the aquifer occurs mainly through direct infiltration at Wadi Al region were estimated to 19.5 Mm3/year with annual Fakka while there is no evidence of significant recharge in exploitation in the order of 27.1 Mm3 (DGRE 2005). major part of the plain and mountains piedmonts. Rainfall occurs on an irregular basis in brief, high-intensity events causing strong floods mainly in Wadi Al Fakka. Keywords Semi-arid region Á Geochemistry Á Stable Thus, significant part of precipitation and the resulting isotopes Á 3H Á 14C Á Groundwater recharge Á Plain of Sidi surface runoff are lost via evaporation and cannot con- Bouzid Á Central Tunisia tribute to groundwater recharge. Therefore, there is a need to explore possibilities to store those surface waters and utilize them for artificial recharge schemes of the aquifer system. Different structures to control surface water flows H. Yangui (&) Á K. Zouari Á R. Trabelsi were constructed between 1983 and 1994 in the upstream Laboratoire de Radio-Analyses et Environnement, bed of the main watercourse on SBZ plain. The objective Ecole Nationale d’Inge´nieurs de Sfax, BP 1173, 3038 Sfax, Tunisia of these structures was to apply an artificial spreading of e-mail: [email protected] Wadi Al Fakka floods for irrigation and then for an artifi- cial recharge of the aquifer. K. Rozanski Although several modelling studies focussing on artifi- Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, cial groundwater recharge on SBZ plain have been con- al. Mickiewicza 30, 30059 Krakow, Poland ducted in 1980s and 1990s (Bouzaiane and Lafforgue 1981; 123 Environ Earth Sci Fig. 1 Geographic location, simplified geology and piezometric map (status as of 2005) of Mio–Plio–Quaternary aquifer system located in the plain of Sidi Bouzid, central Tunisia. AA’ cross-section as shown in Fig. 2 Bouraoui 1984; Amouri 1994; Simonot 1996), the effi- plain from west to east, to discharge then into a large ciency of these management schemes remains largely evaporation area in the north-east (Naggada). The baseflow unknown because of the climate aridity and the lack of of Wadi Al Fakka is in the order of 8.8 Mm3/year (Laf- quantitative data with regard to effective infiltration rates forgue 1981). The major part of this flow infiltrates before and exploitation of the system. As it will be demonstrated reaching SBZ plain. Annualy, there are 12–15 floods into below, the use of hydrochemical and particularly isotopic Wadi Al Fakka bed totalling to approximately 36.3 Mm3 tools for characterization of groundwater resources in the (Bouzaiane and Lafforgue 1981; Lafforgue 1981). study area resulted in a better understanding of the recharge mode and mineralization processes occurring in the system. Geological and hydrogeological setting This in turn can guide future groundwater management schemes in the area. The plain of SBZ is located in the oriental part of central Atlas of Tunisia. The latter is characterized by northeast- southwest fold belts bordered by fault corridor systems and Study area separated by basins filled with Mio–Plio–Quaternary deposits (Burollet 1956; Khessibi 1978; Ben Ayed 1986; The SBZ plain is located in central Tunisia, on the eleva- Boukadi 1994;Be´dir 1995; Chekhma 1996; Ben youssef tion of ca. 350 m.a.s.l (meters above sea level). It is bor- 1999; Zouaghi 2008). On SBZ plain, the sedimentary series dered by mountains (Dj) of Hamra to the west and the consist of deposits going from Lower Cretaceous to Qua- north-west, Al Hfay to the south-west, Kebar to the south ternary, affected by important tectonic features occasion- and Lessouda to the north (Fig. 1). The plain is charac- ally associated with salt Triassic activities (Figs. 1, 2). The terized by a semi-arid climate with low and irregular deposits are characterized by several hiatuses and uncon- rainfall of about 250 mm/year and an intense potential formities; the most important are represented by the middle evaporation rate estimated to ca. 1,600 mm/year (Amouri Turonian–Maastrichtian and Paleogene series (Fig. 2). 1994). Indeed, since middle Turonian, a large part of central The Wadi Al Fakka and its tributary constitute the Tunisia (including the study area) corresponds to an principal watercourse in the study area. It crosses the SBZ emerged area known as ‘‘Kasserine islets’’ (Burollet 1956) 123 Environ Earth Sci Fig. 2 Hydrogeological cross- section of Mio–Plio–Quaternary aquifer located in the plain of Sidi Bouzid, central Tunisia. For the position of the cross- section, see Fig. 1 and, as consequence, it was devoid of deposits character- heterogeneity of the aquifer formation (Amouri 1994). The istic of this period. exploitation of the aquifer is carried out through boreholes After a local transgressive phase (Lower Miocene) the with depths ranging from 100 to 400 m and by dug wells central Tunisia emerged in totality (Middle and upper for the shallow levels (40–100 m). Miocene) and was subject of extension–compression The piezometric map shows that groundwater flows regimes (Atlas phase) which led to the formation of fold mainly from SW to the NE, along the major axis of Wadi ranges oriented NE-SW and separated by many Mio–Plio– Al Fakka bed (Fig. 1). Two natural discharge areas of the Quaternary microbasins as a result of active erosion aquifer are shown on the map: the evaporation area of affecting uplifts (Mannaı¨-Tayech 2006; Zouaghi et al. Naggada at the north-east (outlet of surface waters), and 2008). In central Tunisia, these thick continental infilled the depression of Garet Al Akarisch to the east of the plain. basins represent important groundwater reserves held by multi-layer aquifer systems. The aquifer system of SBZ plain is located in 800 m Sampling and analytical procedures Mio–Plio–Quaternary sediment-filled basin bordered by fold belts (Fig. 1) whose main outcrops are formed by During this study, deep and shallow levels of the SBZ upper cretaceous deposits (Zebbag formation) (Fig. 2) The aquifer system were sampled at 38 locations in June 2005. aquifer is composed essentially of sand (with varying grain Water samples for chemical and isotope analyses were sizes), inter-bedded with layers of clay and sandy clay as collected from 14 boreholes and 24 dug wells (Fig. 3). The well as gravels, pebbles and gypsum. The deposits are chemical analyses (major ions) were conducted by liquid- characterized by significant vertical and lateral heteroge- ion chromatography (HPLC) in the laboratory of radio- neity. Thus, the SBZ plain aquifer system is identified as a analysis and environment (LRAE) at the National School single multi-layer aquifer, represented by three major of Engineering in Sfax (Tunisia). Stable isotope composi- lithologic sections (Fig. 2) (Koschel 1980; Bouraoui 1984; tion of water samples (d18O, d2H) was determined by Amouri 1994; Simonot 1996): (1) 0 to 100 m (clay and isotope ratio mass spectrometry at the laboratory of Inter- sand); (2) 100 to 400 m (sand and clayey sand), and (3) 400 national Atomic Energy Agency (IAEA) in Vienna. The to 800 m (clay and sandy clay). Transmissivity values results are expressed as relative deviations d (in per mil) obtained by pumping tests vary from 0.73 9 10-3 m2 s-1 from the Vienna standard mean ocean water (VSMOW). to 1.14 9 10-2 m2 s-1 reflecting substantial lithological The analytical precision of stable isotope analyses (one 123 Environ Earth Sci Fig. 3 Distribution map of TDS values (mg l-1) showing location of sampling sites sigma) was in the order of 0.1% for d18O and 1% for d2H. Fakka bed, especially in the Saddouguia area where the The tritium content was measured at the IAEA laboratory TDS values are the lowest (W.17, W.18, W.19 and W.21).