Geophysical and hydrochemical study of the seawater intrusion in Mediterranean semi arid zones. Case of the Korba coastal aquifer (Cap-Bon, Tunisia)

Journal of African Earth Sciences 58 (2010) 242–254

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Geophysical and hydrochemical study of the seawater intrusion in Mediterranean semi arid zones. Case of the Korba coastal aquifer (Cap-Bon, Tunisia) Lamia Kouzana a,*, Ramdhane Benassi b, Abdallah Ben mammou a, Mennoubi Sfar felfoul c a

Faculté des Sciences de Tunis, Laboratoire des Ressources Minérales et Environnement, Département de Géologie, Université de Tunis, El Manar 2092, Tunisia Faculté des Sciences de Tunis, U.R. Dynamique des bassins sédimentaires, Paléoenvironnement et structures géologiques, Département de Géologie, Université de Tunis, El Manar, 2092 Tunis, Tunisia c Institut National Agronomique de Tunis 43 Av. Charles Nicolle, 1082 Tunis, Tunisia b

a r t i c l e

i n f o

Article history: Received 9 January 2009 Received in revised form 1 February 2010 Accepted 12 March 2010 Available online 19 March 2010 Keywords: Korba coastal aquifer Electric prospecting method Seawater intrusion Geo-electric sections Hydrochemical analyses Tunisia

a b s t r a c t Coastal aquifers serve as major sources for freshwater supply in many countries around the world, especially in arid and semi arid zones. The fact that coastal zones contain some of the densely populated areas in the world makes the need for freshwater even more acute. The intensive extraction of groundwater from coastal aquifers reduces freshwater outflow to the sea and creates local water aquifer depression, causing seawater migration inland and rising toward the wells. This phenomenon, called seawater intrusion, has become one of the major constraints imposed on groundwater utilization. As seawater intrusion progresses, existing pumping wells become saline and have to be abandoned. In this paper, we have the results of the seawater intrusion study of the Korba aquifer by the geophysical and hydrochemical methods. In order to locate the zones affected by saltwater intrusion, 38 Vertical electrical sounding (VES) were distributed over the coastal area between Korba and Oued Lebna. The interpretation of these electric soundings using Winsev software, based on mechanical boreholes, carry out iso-resistivity and iso-depth maps of seawater intrusion. The maps of apparent iso-resistivity having different lengths of line and the pseudosections differentiate dry grounds, grounds saturated with fresh water and those saturated with brackish water and saltwater. Mapping of the boundaries between freshwater and saltwater is an ideal application for resistivity surveys because of the high electrical conductivity of the saltwater and its contrast with that of fresh water. The correlation of the different electric surveys allowed realizing geo-electric sections showing the vertical configuration of seawater intrusion. It comes out from this study that saltwater intrusion reached approximately a distance of 3 km inland. The high groundwater salinity anomaly observed in Diar El Hajjej, Garaet Sassi and Takelsa-Korba zones was explained by the presence of seawater intrusion in these areas. This hypothesis is based on high chloride concentrations, the inverse cationic exchange reactions, and the lower piezometric level compared to sea level. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Saline water intrusion into aquifers of many coastal areas has resulted in acute environmental problems. Excessive withdrawal of groundwater, as well as significant decrease in recharge of the aquifer due to less rainfall, has largely aggravated the hazard. The extent of saline water intrusion in any coastal area is influenced by the nature of geological formations present, hydraulic gradient, rate of withdrawal of groundwater and its recharge (Freeze and Cherry, 1979). Previous studies were interested in the seawater intrusion problem (Demirel, 2004; Duque et al., 2008; Frohlich et al., 2008; Gaaloul et al., 2003).

* Corresponding author. Tel.: +216 99186975. E-mail address: [email protected] (L. Kouzana). 1464-343X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2010.03.005

Surface geophysics is important for the investigation of the hydrogeology at depth, as well as for providing critical data on the geometry and characteristics of a source aquifer (Boughriba et al., 2006; Guasmia, 2008; Mhamdi et al., 2006). A geophysical study, based on 38 electrical resistivity measurements, was carried out in the coastal parts of the Korba aquifer. The purpose of this study is primarily to improve the knowledge of the aquifers at shallow levels and also to obtain a new geological, hydrological, hydrochemical and electrical model for the Korba aquifer.

1.1. Geographic situation The study area, covering 430 km2 (Paniconi et al., 2001), is located in northeastern Tunisia, within the eastern coastal Plain of Cap-Bon (Fig. 1). This aquifer is bounded to the South by Oued

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Fig. 1. Geology and samples and VES location in the Korba aquifer and 3D view of the studied area.

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Boulidine, to the North by Oued Lebna, to the West by Jebel Abderrahmane and to the East by the Mediterranean Sea. 1.2. Geology The outcropping formations of the study area are represented by Mio-Plio-Quaternary sediments (Ben Salem, 1998). The lower part of The Middle Miocene corresponds to detrital deposits. The upper part is composed of lenticular sandstones and marls with lignite levels called the Saouaf Formation. In the study area, the Upper Miocene is absent. This is believed to have been caused by the widespread of erosion during the Miocene orogeny (Ennabli, 1980). The transgressional marine Pliocene sediments were unconformably deposited on these folded and eroded formations. These deposits are mainly composed of sandstone–sand–marl alterna-

tions topped by sandstones and sand (Damak Derbel et al., 1991). This facies changes laterally to argillaceous sands or to consolidated sandstones more or less argillaceous. The Pliocene formations largely outcrop in the North of Oued Chiba. The Pliocene is completely masked by Quaternary deposits in the Tafelloune and Diar El Hajjej areas (Ennabli, 1980). These deposits are usually composed of two units: the lower unit of marine facies is corresponding to sandy limestone with mollusks indicating the MFS (maximum flooding surface) of the Tyrrhenian transgression. The Upper unit is mainly composed of a continental facies (Ozer et al., 1980) with the occurrence of oolitic limestone and coprolites or pelloïdes. These deposits form nowadays coastal consolidated dunes built by wind following marine regression (Chakroun et al., 2005; Ozer et al., 1980). The old consolidated dunes cover the Tyrrhenian deposits (Ozer et al., 1980). It forms an essential feature of the littoral topography of the Cap-Bon

Fig. 2. Geological cross section B–B0 .

Fig. 3. Piezometric map of Korba aquifer (June 2006).

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(Ben Salem, 1998). The encrusted limestone extends over significant distances. They are very rich in calcite, silica, sometimes in gypsum and alumina and frequently colored by iron salts. Finally, The Holocene deposits are formed by recent alluvia of Oued Chiba, by sebkhas deposits and current dunes and beaches. 1.3. Hydrogeology The hydrogeological study of the Korba area shows that the Plio-Quaternary detrital deposits constitute a potential shallow aquifer. The marls of the Middle Miocene form the impermeable substratum of this aquifer (Ennabli, 1980) (Fig. 2). The aquifer recharge is primarily made in the carved glacis rivers having a very porous lithology. The intercommunication be-

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tween the Pliocene formations and recent alluvia is absent. The Quaternary recharge is raised partly by Pliocene sediments infiltration. Part of the underground flow occurs within the Tyrrhenian limestone before reaching the sea. Indeed, the Tyrrhenian deposits constitute a good reservoir and a key point of coastal aquifer recharge. Meteoric water recharge of the aquifer system is thought to occur through the coastal consolidated barriers which characterize the Tyrrhenian beach. This contribution is shown through its great infiltration capacity and its role as topographic obstacle against the surface run off. This helps water infiltration downstream in case it escapes infiltration upstream (Ennabli, 1980). The recent 2006 piezometric map (Fig. 3) shows the appearance of piezometric depressions related to overexploitation of the aquifer with negative piezometric levels locally posting values of around 12 m. This map (Fig. 3) shows a multidirectional flow mainly oriented to the piezometric depressions located at Diar El Hajjej-Garaet Sassi and to the east of Tafelloune (Kouzana et al., 2007). 1.4. Methods

Fig. 4. Wenner array (Chouteau and Gloaguen, 2003).

In recent times, one shallow well in the Korba coastal aquifer has yielded ground water having abnormally high total dissolved solids TDS of 5166 ppm and chloride content of 2844 ppm. The presence of high TDS has prompted geophysical investigations to be taken up in the Korba coastal aquifer to delineate the saline water contaminated regions, the saline–fresh water interface as well as to ascertain the nature of subsurface geological formations. Another important objective was to demarcate areas for groundwater development without the risk of further saline water intrusion in the inland aquifer system. The large resistivity contrast between the saltwater-saturated formation and the freshwatersaturated ones have been used by many investigators for studying the saltwater intrusion in coastal areas (De Moor and De Breuck,

Fig. 5. SEV and pseudosections location map.

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Fig. 6. Apparent iso-resistivities map in line length AB = 30 m.

Fig. 7. Apparent iso-resistivities map in line length AB = 150 m.

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Fig. 8. Apparent iso-resistivities map in line length AB = 300 m.

Fig. 9. Pseudosection P3.

Fig. 10. Pseudosection P5.

1969; Gasmi, 2001; Gemail et al., 2004; Choudhury et al., 2001; Lebbe et al., 1989; Margiotta and Negri, 2005; Wilson et al., 2006) using the resistivity method. Their interpreted resistivities were closely related to the analytically measured salinity of groundwater. Wenner sounding resistivity method is a powerful tool for delineating seawater–freshwater interface in the geological setting of the Korba aquifer and the approach was to determine the geoelectrical characteristics, the electrical resistivity in relation with the salinity and their lateral and vertical variations within Korba aquifer and to map the seawater intrusion zone in the area. Investigations of underground water-bearing formations in semi arid zones are rapidly becoming a worldwide priority with the need for additional water resources to satisfy economic development and demographic growth. The presence of freshwater in sedimentary rocks such as sandstone or limestone is characterized by an average or even high electric resistivity, whereas brackish water corresponds to conductors with a low resistivity. It is extre-

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mely difficult to distinguish freshwater from brackish water with any other physical property that can be measured from the surface. It is therefore logical to use vertical electric soundings (Tabbagh, 2006). The general principle of the electric prospecting by VES puts back on the injection of an electrical current I between two current electrodes A and B and the measurement of a potential difference DV between two other potential electrodes M and N. The under ground apparent resistivity is deduced from equation:

This article presents the analytical results of 28 samples, which were collected in June 2006. Twenty-six samples were collected from shallow wells and two were taken from the deep aquifer. The cations (Na+, K+, Ca2+ and Mg2+) were analyzed at ‘Laboratoire des Resources Minérales et Environnement’ of the Faculty of Sciences of Tunis using Atomic Absorption Spectrometry. Bicarbonates were determined by the volumetric method, Cl was determined using the Mohr method and finally SO2 was, 4 spectrophotometrically, analyzed.

qa ¼ KðDV=IÞ ðin X mÞ; Electrical sounding Wenner - T93K43.WS3

with K the geometrical coefficient of the device, which is function only of the distances between electrodes. The standard SE Wenner, used in this work, requires that the electrodes are aligned and MN = AB/3 and K = 2Pa (Fig. 4). So:

10000 [ohm

qa ¼ ðDV=IÞ  2Pa ðin X mÞ;

m]

1000

The interpretation of the results was conducted in two ways:  A qualitative way: This interpretation is based on the realization of the iso-resistivity maps and the pseudosections. The isoresistivity maps are established for AB of 30–300 m.  A quantitative way: The VES interpretation must be based on local databases that include information of the lithological and hydrogeological nature of the investigated area available from boreholes. Therefore, two VES (K43 and WL3) were located near boreholes (8626/2 and 11637/2). The results of such interpretation helped in the construction of geoelectrical cross sections for the investigated subsurface sequences. The geoelectric cross sections were established for two main directions, N–S and W–E. Previous studies (El Achheb et al., 2003; El Mansouri et al., 2003; Polido-Le bœuf, 2004; Psychoyou, 2007; Trabelsi et al., 2005; Zouhri et al., 2008) through analytical and hydrochemical methods have approached the problem and attempted to position the freshwater–seawater interface. They defined the chemical processes and reactions, which characterize mineralization and would thus, be responsible for groundwater chemical elements enrichment or impoverishment. This paper presents the geochemical analytical results of 28 samples, which were collected in June 2006 in order to characterize salinisation and different factors monitoring its space–time evolution.

100

10

1

.1

1

Location X = 585120

10

100

1000

a [m]

.1 10000

Y = 367500

Model Resistivity Thickness [ohm m] [m] 200 2 90 27 25 25 3.5

Depth [m] 2 29 54

W-GeoSoft / WinSev 6.1

Fig. 12. VES K43 Calibration based on the 8626/2 borehole of the Korba area.

Fig. 11. Pseudosection P12.

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Seawater contribution (fsea) based on the chloride contents in the sample (CCl,sample), the freshwater Cl concentration (CCl,f) and the seawater Cl concentration (CCl,sea):

F sea ¼

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ðC Cl;sample  C Cl;f Þ ; ðC Cl;sea  C Cl;f Þ

This allows calculation of seawater contents (%) in each sample.

Fig. 13. Geo-electrical model Calibration with the borehole data and the hydrogeological interpretation based on the two descriptions.

Fig. 14. Iso-resistivities map of the salinized zone.

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2.1.1. Qualitative interpretation This interpretation is based on the establishment of apparent iso-resistivity maps for lengths of different line AB and pseudosections (Fig. 5). For the realization of the pseudosections, we used the software IPI2Win (MT) v.2.0 (IPI2Win (MT) v.2.0 User’s guide (IPI2Win, 2002)). All the maps are traced for lengths of lines ranging between AB = 30 m and AB = 300 m.

and the Tafelloune South-east (up to 105 X m). The values lower than 10 X m correspond to the deposits saturated with salty to brackish water of the aquifer. Whereas, the highest values, correspond to the aquifer grounds saturated with more or less freshwater. The apparent iso-resistivity map in length of line AB = 300 m (Fig. 8) interests a ground section of depth approximately from 100 m. It reveals resistivities reaching 28 X m. The values lower than 10 X m are situated along the coast and in the Diar El Hajjej North. The low values correspond to the deposits saturated with salty to brackish water. The values higher than 10 X m correspond to the silt -sands saturated with more or less freshwater.

2.1.1.1. Apparent iso-resistivity maps. They were established from the apparent resistivities of the vertical electric soundings. Apparent resistivity maps were compiled for AB = 30 m, 150 m and 300 m. The map for AB = 30 m (Fig. 6) indicates the apparent iso-resistivity to a depth of approximately 10 m. It shows resistivities varying between 10 and 800 X m. The low values of resistivity (10 and 40 X m) appear in the North-East at the coast and in the extreme South of Diar El Hajjej. The high apparent resistivity values were found in the South-East at the coast and in the Wadi Chiba South (800 X m). This strong resistivity corresponds to the dry limestone Tyrrhenian deposits. The apparent iso-resistivity maps in length of line AB = 150 m (Fig. 7) corresponds to a depth approximately from 50 m. It shows resistivities varying between 5 and 105 X m. The low resistivities values are detected along the study zone coast and in the Diar El Hajjej North. These values increase in the continent direction. The strong resistivities values appear in the Diar El Hajjej South

2.1.1.2. Pseudosections. The pseudosection according to the profile P3 (Fig. 9) is of W–E direction. It shows the presence of the surface resistant anomalies (>100 X m) throughout this profile. This indicates the presence of dry Tyrrhenian limestone levels. In the west of this profile, the resistant anomaly does not outcrop on the surface. In the top of this zone, we note the presence of more conducting levels indicating the contribution of the coastal consolidated dunes to the aquifer recharge. The resistant anomalies are continued in-depth, then they disappear and are replaced by increasingly conducting levels (<100 X m). These layers correspond to the sandy Pliocene. In the Pliocene, we note the succession of levels saturated with freshwater and levels saturated with brackish water and finally layers saturated with more or less salty water. In fact, the resistivity continues to drop according to the depth until reaching conductive strata characterized by resistivities lower than 5 X m. These layers can correspond to the impermeable Miocene substratum or to levels saturated with salty water.

2. Results and discussion 2.1. Vertical electric sounding

Fig. 15. Iso-depth map of the salinized zone.

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Fig. 16. Geo-electrical cross section E1.

Fig. 17. Geo-electrical cross section E3.

Fig. 18. Geo-elctric cross section A–A0 .

The pseudosection along the profile P5 (Fig. 10) is of W–E direction. On the surface, this section shows the same surface resistant anomalies with a discontinuity in the electric sounding K41

(Fig. 10). These anomalies correspond to the dry Tyrrhenian limestone. The interruption of these resistant levels by a conducting level shows that this place corresponds to an aquifer recharge zone.

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2.2.1.4. Geo-electric sections. The inversion of the data of the vertical electric soundings along a profile, by using mechanical boreholes for the calibration, permits the construction of geo-electric sections showing the distribution of the resistivity of the aquifer along a vertical section. The E1 section, carried out parallel to the coast (Fig. 5), follows the same profile of the pseudosection P12. It shows that the salinized zone corresponds to a resistivity lower than 3 X m. Locally, some levels having a resistivity about 6–15 X m are located on the top of the salinized zone (Fig. 16). These layers correspond to argillaceous lenses. We notice the rise almost to the surface of the seawater intrusion in WL6 and WL8. The E3 section was carried out perpendicularly to the coast (Fig. 5). It shows a surface horizon made of dry Tyrrhenian

100

Internal area Coastal area Diar El Hajjej Garaet Sassi Deep aquifer Seawater Freshwater

Freshwater Seawater

0

0

+H CO 3 CO 3

Mg

4

0

0

100

0

100

Ca

SO

+K Na

100

100

100

0

0

2.2.1.3. Iso-resistivity and iso-depth maps of the salinized zone. The iso-resistivity map of the salinized zone (Fig. 14) shows in the North-East area two marine intrusion lobes measuring a distance at least 1 km. Whereas in the area located between Korba and Oued Chiba, we notice the presence of two great extension lobes. The first is located just at the Chiba Wadi South indicating the inland extend of seawater intrusion, which reach a distance approximately from 3 km from the coast. The second is located at the Diar El Hajjej South, reaching a distance about 2 km of the current coast.

g +M Ca

2.2.1.2. Geo-electric model. The borehole No. 8626/2, being in the internal area of the study zone, shows the resistant quaternary strata in discordance with conductive middle Miocene substratum (Fig. 12 and 13). The borehole 11637/2, located in the coastal zone, shows the resistant quaternary with the Tyrrhenian (resistant) in the top (Fig. 2). These groundwater strata surmount the conductive middle Miocene substratum. Therefore, in these strata, we note the succession of a resistant ground, layers less resistant and finally a conductive level.

100

2.2.1. Quantitative interpretation 2.2.1.1. Vertical electrical sounding calibration on Korba area boreholes. Fig. 12 shows the calibration of the VES K43 using borehole (IRH 8626/2). The lithological borehole section is represented for reasons of convenience on the bilogarithmic diagram of the VES. In fact, the true depths axis of the borehole is coinciding with the axis AB3 of the VES; it should be noted that it is only a representation convention.

Some small zones with relatively high resistivities located along the coast are the consequence of the direct rainwater infiltration through the sandy coastal recent dunes or with the rise of the substratum. This map shows the extent of the marine invasion of the Diar El Hajjej area compared to that of Tefelloune. The iso-depth map of the seawater intrusion (Fig. 15) shows a rise almost on the surface of the salinized zone in the North of the coast, which occupies a surface relatively limited, whereas in the Diar El Hajjej East, the surface occupied by the rise of seawater intrusion is relatively more significant.

O3

More in-depth, the Pliocene is saturated with more or less freshwater then it is saturated with brackish water. Lastly, we attend the presence of conductive strata. These layers correspond either to the substratum or to the Pliocene saturated with salty water. The distinction between these two assumptions will be made by quantitative interpretation. The pseudosection according to the profile P12 (Fig. 11) is of S– N direction and is parallel to the coast. This pseudosection shows the presence of two surface resistant anomalies. These anomalies correspond to dry Tyrrhenian limestone outcropping in this level. Between these two anomalies, more conductive strata are present (between 100 and 30 X m). These zones correspond to the limestone more or less saturated with freshwater. These levels are recharged by the Chiba Wadi. In this level, the resistivity decreases with the depth. We note the rise of the substratum at this place. This discontinuity can be explained by the presence of a fault that ruptured the Tyrrhenian limestone and raised the substratum rise. Moreover, as in the profiles P3 and P5, the aquifer levels are saturated with water that is more or less fresh. Under these levels, the strata are saturated with brackish water.

SO 4+ Cl+ N

252

0

Cl+NO3

100

Fig. 20. Water sampling analytical results plotted in the piper diagram (June 2006 survey).

Fig. 19. Geo-elctric cross section C–C0 .

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limestone grounds characterized by high resistivities (Fig. 17). More inland of the continent, under this horizon, we find strata saturated with more or less freshwater. Laterally and towards the coast, this horizon saturated with more or less freshwater passes to sandy deposits saturated with brackish to salty water. The geo-electric section B–B0 , of West-east direction, was built by combining the data from the Vertical electric soundings and the mechanical boreholes existing in the area. This section shows that the substratum of this aquifer is in a maximum depth of a 100 m. This substratum is surmounted in discordance by the quaternary. At the coast, the Tyrrhenian is situated at the top (Fig. 2). The geo-electric section A–A0 (Fig. 18), of WNW–ESE direction, and the geo-electric section C–C0 (Fig. 19), of NE–SW direction, shows towards the extreme West the presence of the Plio-quaternary deposed on middle Miocene. While towards the coast, the Tyrrhenian rests on the quaternary. The geo-electric section C–C0 illustrates always the appearance of an argillaceous layer in the coast of the Korba aquifer. This layer plays the barrier role against the seawater intrusion.

2.3. Hydrochemical study The determination of the groundwater salinity origin was based on a spatial evolution of the total dissolved salt (TDS) and the major elements contents. The piper diagram illustrates three chemical

253

facies (Fig. 20): Na–Cl facies, Ca–Mg–Cl facies and SO4-mixed facies. The calculation of seawater contents (%) presents values lower than 14% of seawater (Fig. 21). The aquifer of Korba shows especially high values of TDS in the coastal zones, the Diar El Hajjej, Garaet Sassi and Tazerka-Korba. These high TDS values are due to contamination by seawater. This assumption is justified by negative piezometric values, strong chloride concentrations and weak electric resistivity. The hydrochemical study shows a tendency between sample composition and marine water composition, which gives an additional argument in favour of the presence of a marine intrusion in the coastal zone, areas of Diar El Hajjej, Garaet Sassi and Tazerka-Korba (Kouzana et al., 2009). This seawater intrusion is accompanied by other processes, which modify the hydrochemistry of the coastal aquifer. The most remarkable process is that of the inverse cation exchange, characteristic of the changes of the theoretical mixture of seawater–freshwater, which is carried out between clays and the aquifer water. This exchange consists in the release of Ca2+ and/or Mg2+ and the adsorption of Na+. This process characterizes Diar El Hajjej-Garaet Sassi and the internal areas. The coastal zone is characterized by a low salinity and weak concentrations chloride (Kouzana et al., 2009). These low (Cl) values are due to the infiltration of meteoric water in the Tyrrhenian consolidated dunes (Ennabli, 1980) and to the presence of clay layers playing as a barrier against seawater intrusion (Fig. 2). Moreover, the direct cation exchange between Na+ and Ca2+ and/or

Fig. 21. Seawater percentage (%) distribution map.

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Mg2+ (Na+ release and adsorption of Ca2+ and/or Mg2+) indicating a local flushing of water of the aquifer is detected in this zone (Kouzana et al., 2009). 3. Conclusion Vertical electric soundings were used to map the Korba coastal aquifer. High apparent resistivities were measured near to the surface, the highest values corresponding to dry sandy–limestone Tyrrhenian deposits. The resistivities decreased with depth. Inland, the deeper strata are saturated with fresh water. The water becomes more brackish towards the coast. The invasion of seawater is detected near the coast, penetrating 1 km inland at Sebkhet Lebna, 1.5 km in the Chiba Wadi South, and 3 km in the Diar El Hajjej South. An horizon saturated with salty water approaches the surface near Sebkhet Lebna and in the Lebna Wadi South. It is believed that the area of saltwater intrusion will eventually spread due to the increased demand for freshwater for agriculture; particularly during dry periods. Consequently, both groundwater monitoring and management and groundwater conservation are essential for efficient surveillance of the saltwater intrusion. References Ben Salem, H., 1998. Notice explicative de la carte géologique de la Tunisie à 1/ 50.000 Menzel Bou Zelfa Feuille n 22. Boughriba, M., Melloul, A., Zarhloule, Y., Ouardi, A., 2006. Extension spatiale de la salinisation des ressources en eau et modèle conceptuel des sources salées dans la plaine des Triffa (Maroc nord-oriental). CR Acad. Sci. Paris 338, 768–774. Chakroun, A., Zaghbib-Turki, D., Moigne, A.M., De Lumley, H., 2005. Découverte d’une faune de mammifère du Pléisticène supérieur dans la grotte d’El Geffel (Cap-Bon, Tunisie). CR Palevol 4, 317–325. Chouteau, M., Gloaguen, E., 2003. Tomographie Électrique en génie et en environnement. Cours tomographie éléctrique. Ecole Polytech. Montréal, 11– 12. Damak Derbel, F., Zaghbib-Turki, D., Yaich, C., 1991. Le Pliocène marin du Cap-Bon (Tunisie): Exemple de dépôts gravitaires. Géologie Méditerranéenne, tome XVIII (4), pp. 189–198. Choudhury, K., Saha, D.K., Chakraborty, P., 2001. Geophysical study for saline water intrusion in a coastal alluvial terrain. J. Appl. Geophys. 46, 189–200. De Moor, G et., De Breuck, W., 1969. De freatische waters in het Oostelijke Kustgebied en in de Vlaamse Vallei. Natuurwet. Tijdsch. 51, 3–68. Demirel, Z., 2004. The history and evaluation of saltwater intrusion into a coastal aquifer in Mersin, Turkey. J. Environ. Manage. 70, 275–282. Duque, C., Calvache, M.L., Pedrera, A., Martin-Rosales, W.M., López-Chicano, M., 2008. Combined time domain electromagnetic soundings and gravimetry to determine marine intrusion in a detrital coastal aquifer (Southern Spain). J. Hydrol. 349, 536–547. El Achheb, A., Mania, J., Mudry, J., 2003. Mécanismes d’acquisition de la minéralisation des eaux souterraines dans le bassin Sahel-Doukkala (Maroc Occidental). Approche par des traceurs hydro-géochimiques. IGME, Madrid. ISBN: 84-7840-470-8. El Mansouri, B., Loukili, Y., Esselaoui, D., 2003. Mise en évidence et étude du phénomène de l’upconing dans la nappe côtière du Rharb (NW du Maroc). IGME, Madrid. ISBN: 84-7840-470-8.

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