Hydrogeology of Tunisia
- 1 Authors
- 2 Geographical Setting
- 3 Geology
- 4 Hydrogeology
- 5 Groundwater Status
- 6 Groundwater use and management
- 7 References
- 8 Return to the index pages
Safouan Ben Ammar, ISTEUB, Tunisia
Amira Mekni, INAT, Tunisia
Kirsty Upton & Brighid Ó Dochartaigh, British Geological Survey, UK
Tunisia has a long coastline onto the Mediterranean Sea. In the north of the country is the Tunisian Dorsale mountain chain, which rises to 1,554 m. In the centre of the country are a series of east-west trending depressions, called chotts. The south of Tunisia is dominated by the Sahara.
|Estimated Population in 2013*||10,886,500|
|Rural Population (% of total) (2013)*||33.5%|
|Total Surface Area*||155,360 sq km|
|Agricultural Land (% of total area) (2012)*||64.9%|
|Border Countries||Algeria, Libya|
|Annual Freshwater Withdrawal (2013)*||2850 Million cubic metres|
|Annual Freshwater Withdrawal for Agriculture (2013)*||76.0%|
|Annual Freshwater Withdrawal for Domestic Use (2013)*||12.8%|
|Annual Freshwater Withdrawal for Industry (2013)*||3.9%|
|Rural Population with Access to Improved Water Source (2012)*||90.5%|
|Urban Population with Access to Improved Water Source (2012)*||100%|
* Source: World Bank
Tunisia has a semi-arid Mediterranean climate in the north; arid in the centre, and desert (Saharan) in the south. Rainfall distribution is determined by the direction of the prevailing winter winds (north-west) and the presence of high ground, and is heaviest in the north (over 400 mm/year and up to 1,500 mm/year in the far northwest), declining towards the centre (150 to 300 mm/year) and becoming very light in the south (less than 150 mm/year and less than 50 mm/year in the far south), with some years of no rain.
For further detail on the climate datasets used see the climate resources section.
The main permanent surface watercourses which drain to the sea are in the north, mostly rising in the northwest and flowing eastwards. In the arid central reason, surface watercourses are ephemeral, flowing only for a few days or weeks a year. In the south, surface flows are rare and small. None of these central and southern ephemeral flows reach the sea; instead, surface water infiltrates over plains or in inland depressions (sabhkas).
The Direction Generale des Ressources en Eau (DGRE) and the General Direction of Dams and Hydraulic Works (DGBGTH) operate 75 surface water gauging stations and 164 gauging points. The frequency of observation and length of record varies from one station to another. There are most stations in the Mejerda River basin, the largest in Tunisia. The collected data for 2003-2004 are available in the report DGRE (2004) (see References, below).
|The north of Tunisia is dominated by calcisols with some fluvisols and, along the coast, luvisols.
The centre of the country includes cambisols and gypsisols, with smaller areas of solonchaks and leptosols.
The south is dominated by leptosols, cambisols and arenosols, with smaller areas of gypsisols.
|In the north of Tunisia is a belt of rain-fed cropland with natural grassland, shrubland and forest.
The centre of the country has sparse vegetation; and the south has very little or no vegetation.
This section provides a summary of the geology of Tunisia. More detail can be found in the references listed at the bottom of this page. Many of these references can be accessed through the Africa Groundwater Literature Archive.
The geology map on this page shows a simplified version of the geology at a national scale (see the Geology resources page for more details).
More detailed geological maps are published by the Service Geologique de Tunisie (at 1:500,000 scale) and the National Office of Mines (ONM) (at 1:50,000 and 1:100,000 scale) (see Geology: Key References, below).
The north of Tunisia has been extensively affected by tectonic movements, with anticlines and synclines generally trending southwest - northeast, and a series of faults.
The central part of the country includes two big sedimentary basins of Miocene and Pliocene-Quaternary age, which have been less heavily tectonized.
In the south of the country, the Saharan platform is a largely undeformed basin which saw sedimentation from Triassic to Quaternary.
|Alluvial plains, including Ghardimou,Kalaa Khasba, Oued Guinniche basin (northern Tunisia) and Kairouan and Sfax basins (central Tunisia)||Tertiary to Quaternary||Detrital formations that vary considerably in thickness from less than 20 m to more than 700 m.|
|Cretaceous and Tertiary sedimentary|
|Series of marine and continental formations||Cretaceous - Tertiary||Cretaceous and Tertiary sedimentary formations occur across most of Tunisia. In the south, the two largest formations are the Complex Terminal and Continental Intercalaire (see below). Across the centre and north of the country are many othe rsmaller marine and continental sedimentary formations.
Continental sandstones occur in major sedimentary basins across much of central Tunisia, sometimes directly underlying Quaternary unconsolidated alluvium, such as in the Sfax basin and the Pliocene-Quaternary Kairouan basin. Small outcrops of limestone formations, sometimes with marls, dolostones, gypsum and other evaporates, are scattered across northern and central Tunisia, often interbedded with sand formation.
|Complex Terminal (CT)||Upper Cretaceous - Tertiary||Upper Cretaceous (Senonian and Turonian) carbonate rocks; and Tertiary (Mio-Pliocene) detrital sand formations.|
|Continental Intercalaire (CI)||Lower Cretaceous||A continental facies of sands, limestones and clays.|
|Triassic - Jurassic||Limited; occurs at the base of the southern CT and CI series, and in small outcrops in the north. In the south, includes Triassic sandstones, dolomites and gypsum; overlain by Jurassic marls, limestones and dolomites.|
This section provides a summary of the hydrogeology of the main aquifers in Tunisia. More information is available in the references listed at the bottom of this page. Many of these references can be accessed through the Africa Groundwater Literature Archive.
The hydrogeology map on this page shows a simplified version of the type and productivity of the main aquifers at a national scale (see the Hydrogeology Map resource page for more details).
A more detailed hydrogeological map at 1:500,000 scale is published by the DGRE (Zebidi 1991), and a different simplified map is published by SEMIDE (see Hydrogeology: Key References, below).
Aquifers in Tunisia are classified according to whether they are:
Phreatic aquifers - not exceeding 50 m deep
Deep aquifers - more than 50 m deep.
In the following summary and in the hydrogeology map above, the aquifers are classified by their hydrogeological environment and the way that groundwater flow and storage occur: either unconsolidated, in which groundwater flow and storage is entirely intergranular; or, in consolidated aquifers, a mixture of intergranular and fracture flow.
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge|
|Continental Intercalaire (CI) (Lower Cretaceous)||The Continental Intercalaire (CI) aquifer in southern Tunisia is of Lower Cretaceous age (Neocomian, Barremian, Aptian and Albian). It comprises detrital and continental formations, between 125 and 150 m thick, which are buried at depths of 1500 to at least 2400 m. The aquifer is confined, and piezometric water levels range from 500 to 3500 m depth.
Aquifer transmissivity values range from 0.8 to 170 x 10-3. Storativity values range from 0.2 to 1.4 x 10-4.
|Annual abstraction from the CI aquifer in 2000 was 83.1 million cubic metres (Mm³).||Total dissolved solids in groundwater in the CI aquifer aquifer are between 1.5 and 4 g/l.||Recharge to the aquifer comes from the Algerian Atlas mountains.|
|Sfax basin (Tertiary)||The Sfax basin in the east of the country is a sand sequence and forms an important coastal aquifer system, of Tertiary (Upper Miocene) age. The aquifer sequence is between 50 and 90 m thick, and it is buried at depths of between 200 to 600 m. The aquifer is confined. Piezometric water levels are 200 to 600 m deep. Boreholes abstracting from the aquifer are typically between 190 and 600 m deep.
Transmissivity values for the aquifer range from 0.1 to 7.3 x 10-2. Storativity values range from 0.7 to 1.8 x 10-4.
|Annual abstraction from the Sfax basin aquifer in 2000 was 19.16 million cubic metres (Mm³), from a total of 41 boreholes. Of this, abstraction for industrial use was 13.25 Mm³; for agriculture was 4.57 Mm³; and for domestic use was 1.34 Mm³.||Total dissolved solids in groundwater in the Sfax basin aquifer range from 2.5 to 10.5 g/l.||There is recent recharge to the aquifer in the upstream region. In the downstream region, stable isotope and radiocarbon data have shown that there is no active recharge.|
|Kairouan plain (Tertiary - Quaternary)||This is the most important aquifer system in central Tunisia, formed of detrital alluvial sediments of Plio-Quaternary age, which can be more than 700 m thick. The aquifer is unconfined and the water table depth ranges from 1 to 700 m. The aquifer is exploited both by large diameter dug wells only a few metres deep, and by boreholes that can be more than 700 m deep; the mean borehole depth is between 100 and 250 m.
Transmissivity values for the aquifer range from 4.8 x 10-4 to 2.3 x 10-2. Storativity values range from 1.5 x 10-4 to 1 x 10-3.
|Annual abstraction from the aquifer in 2000 was 53.5 million cubic metres (Mm³). Of this, 26 Mm³ was from a total of 118 boreholes, and 27.5 Mm³ was from a total of 4000 wells.||Total dissolved solids in groundwater from the aquifer range from 1 to 3 g/l.||Active recharge comes from direct infiltration of precipitation on the plain, and from water released from the Sidi Saad (Zeroud) and El Haouereb (Merguellil) dams. Before the dams were constructed, recharge occurred during flood events in the Oued Zeour and Merguellil areas.|
|Oued Guinniche Basin (Tertiary - Quaternary)||This is one of the most important aquifers in northeastern Tunisia. It is a multi-layered aquifer system, formed of heterogeneous alluvial deposits of Plio-Quaternary age. The aquifer is typically 100 to 200 m thick in total. There is an upper aquifer layer, which is unconfined, with a water table depth of less than 50 m; and a deeper layer, with a piezometric water level of 200 to 300 m depth. Boreholes abstracting from the aquifer are between 50 and 300 m deep.
Transmissivity values range from 3.1 to 130 x 10-5. The mean storativity value is 5.5.
|Annual abstraction from a total of 233 boreholes is on the order of 8 million cubic metres (Mm³) (data from 2012) and from a total of 1540 wells is 11 million cubic metres (Mm³) (data from 2008).||Total dissolved solids in groundwater from the aquifer range from 0.3 to 4 g/l.||There is active and rapid recent recharge by direct infiltration of precipitation.|
|Local Cretaceous - Tertiary sedimentary aquifers||A series of more local scale sedimentary aquifers is scattered across northern and central Tunisia, often composed of an interbedded sequence of marine sandstones and limestones and continental sandstone formations. Some of the limestone formations are karstic. In the sandstone formations, groundwater flow can be by both intergranular and fracture flow. One example is the Korba aquifer in the Cap Bon peninsula, where Tertiary continental sandstones pass upwards into marine limestones, which are overlain by Quaternary deposits.||
Key references for these unconsolidated aquifers are (see Hydrogeology: Key References, below, for more details):
Maliki MA (2000); Maliki et al. (2000); Nazoumou (2002); Ben Ammar (2007); Ben Ammar et al. (2009); Leduc et al. (2007); Ben Ammar et al. (2006); Jeribi (2004).
Sedimentary - Intergranular & Fracture Flow
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge|
|Complex Terminal (CT) (Upper Cretaceous - Tertiary)||The Complex Terminal (CT) aquifer is formed by Upper Cretaceous (Senonian and Turonian) carbonate rocks, which occur in Tunisia between the Dahar mountains and the eastern part of Chott Jerid; and by Tertiary (Mio-Pliocene) detrital sand formations in the west and south of Chott Jerid. The aquifer outcrops at the ground surface in the Dahar mountains in the southeast, and is present between about 300 to 700 m depth in the Jerid region. The aquifer thickness varies from 30 to 200 m. The aquifer is typically confined. Boreholes abstracting from the aquifer in the Jerid and Nefzaoua regions are between 225 and 400 m deep. Parts of the carbonate formations are karstic.
The carbonate formations of the CT aquifer have a typical range in transmissivity of 50 x 10-3 to 300 x 10-3 m²/sec. The sand formations have a typical transmissivity range of 1 x 10-3 to 5 x 10-3. Storativity values for the CT aquifer range from 1 to 8 x 10-5.
|Annual abstraction from the CT aquifer in 2000 was 451.6 million cubic metres (Mm³).||Total dissolved solids in groundwater from the CT aquifer are between 0.7 and 7 g/l.||Recharge to the aquifer comes from the Algerian Atlas mountains; from the Dahar uplands in southeast Tunisia; and from mountains in the northern part of the Chott.|
Key references for the Complex Terminal aquifer are (see Hydrogeology: Key References, below, for more details):
Kamel et al (2005).
The total water resources in Tunisia are estimated (by DGRE) at 4825 million cubic metres (Mm³), of which 2125 Mm³ are groundwater. Of this volume, there is an estimated 745 Mm³ of groundwater stored in phreatic (unconfined) aquifers (55% in the north of the country; 30% in the centre; and 15% in the south). Some 1380 Mm³ of groundwater is stored in deep (confined) aquifers, of which only some 650 Mm³ is renewable (18% in the north; 24% in the centre; and 58% in the south).
Abstraction from phreatic aquifers in 2000 was estimated at 780 Mm³, from 90000 wells. This is equivalent to 105% of the estimated total storage in phreatic aquifers. Abstraction from deep aquifers in 2000 was estimated at 1100 Mm³, from 3500 boreholes. This is equivalent to 80% of the estimated total storage in deep aquifers.
The DGRE publishes an annual report on the exploitation of deep aquifers; and a report every 5 years on the exploitation of phreatic aquifers.
Salinisation of groundwater is widespread in Tunisia, linked to intensive exploitation; to the geochemical nature of geological deposits; and sometimes to leaching of irrigation water. Salinity generally increases towards the south and in older (fossil) groundwater: much of the groundwater in the south and parts of the centre of the country has total dissolved solids (TDS) of more than 3 g/l; and in much of the centre and north groundwater TDS is typically between 1.5 and 3 g/l.
Groundwater use and management
Abstraction from phreatic aquifers is from around 90000 wells, equipped with motorised/electric pumps. Abstraction from deep aquifers is from around 3500 boreholes and springs, of which 60.5% are pumped boreholes; 35% are artesian boreholes; and 4.5% are springs (data from DGRE).
Groundwater use by sector in Tunisia in 2000 was as follows (data from DGRE):
Domestic 16.2 %
Irrigation in Tunisia uses 2.14 billion m³/year (data from 2012), of which 74% comes from groundwater. Much irrigation is based on a system of family farms using thousands of shallow wells, many of which are uncontrolled by the Ministry of Agriculture. This is leading to aquifer over-exploitation, especially as wells and boreholes are increasingly converted to use electric pumps.
Tunisia has invested heavily in monitoring, mobilizing and managing groundwater resources. The key institutions involved in groundwater management are:
The Direction Générale des Ressources en Eau (DGRE)/General Direction of Water Resources. This institution has a representation in all 24 departments in the country.
The Société National d’Exploitation et de Distribution des Eaux (SONEDE)/ National Water Distribution Utility (www.sonede.com.tn). This institution has resposibility for exploiting and distributing domestic water supplies.
The legal framework for groundwater management falls under the Law No. 16-75 of 31 March 1975 on the promulgation of the Water Code. A new revised version of the Law is under preparation (http://www.semide.tn/CDE072014.pd).
A permit from the DGRE is required for drilling any borehole or well exceeding 50 m in depth.
Some river basins suffering from overexploitation or/and pollution are protected, and no drilling permit is allowed in these basins.
There is strict regulation of waste disposal or polluted water discharge, but in some cases overruns can occur.
Domestic water is treated by the ONAS (Office National d’Assanissement/National Sanitation Utility) (http://www.onas.nat.tn).
A number of experiments into artificial recharge using treated waste water were carried out between 1992 and 2006 in the Cap Bon aquifer.
Enhanced recharge of flood waters is carried out at at least 35 sites, and is expanding, using engineered structures in wadis (both above and below ground) and other areas prone to flooding, in order to dam up flood water and allow it to infiltrate to underlying aquifers. Depending on the availability of surface water from year to year, there is between 30 and 70 million m³/year of artificial recharge in Tunisia. The north of the country, where surface water flooding occurs most often, is most suited to this practice. It is also useful in the centre of the country, where floods are still relatively common (10-15 per year); here, artificial recharge of flood waters is combined with soil conservation practices to ensure maximum underground storage of water (Louati & Bucknell 2010).
Groundwater level monitoring
Groundwater level monitoring is done twice a year by different departments of the DGRE (there are 24 departments covering the country). DGRE publish an annual report on the piezometric monitoring of deep aquifers, and a 5-yearly report on the piezometric monitoring of the phreatic aquifers. See also Horriche & Besbes (2006).
Groundwater quality monitoring
Groundwater quality is monitored twice a year (in September-October and March-April) by the DGRE, at more than 1214 points: 736 wells in phreatic aquifers and 478 boreholes in deep aquifers. The main parameters monitored are total dissolved solids (TDS) and nitrate (NO3). The DGRE publishes the monitoring results in regular (annual or 5-yearly) reports. The SEMIDE programme also publishes monitoring results online at www.semide.tn .
Boreholes from which groundwater is abstracted for domestic use by SONEDE are monitored monthly. SONEDE analysed 55,886 water sampels in 2013. These results are published online at https://www.sonede.com.tn/index.php?id=43 .
Groundwater in the Djeffara coastal basin aquifer is shared between Libya and Tunisia.
Fossil groundwater in the Continental Intercalaire (CI) and Complex Terminal (CT) Northwest Saharan Aquifer System in the south of the country is shared between Tunisia, Algeria and Libya. This aquifer system has more than 1 million km³ of stored groundwater, of which some 80,000 km³ are in Tunisia. Tunisia, Algeria and Libya have established a commission to monitor the aquifer and have agreed to cooperate on its management to mimimise cross-border impacts - this is one of only two such agreements in the world. Many studies of the aquifer are carried out by the Observatoire du Sahara et du Sahel (OSS - www.oss-online.org).
For further information about transboundary aquifers, please see the Transboundary aquifers resources page
The following references provide more information on the geology and hydrogeology of Tunisia. These, and others, can be accessed through the Africa Groundwater Literature Archive
Geology: key references
Key sources of geological information for Tunisia are:
The ONM publish geological maps at various scales, e.g. 1:50,000 for the north and central parts of the country and 1:100,000 for the south.
Other key published references are:
Service Geologique de Tunisie. 1985. Carte geologique de Tunisie; 1:500,000.
Castany G. 1951. Etude géologique de l'Atlas Tunisien oriental.
Hydrogeology: key references
Key sources of hydrogeological information for Tunisia are:
The national department for water resources management and mobilization.
The DGRE publish a number of periodical reports, including:
Annuaire de réalisation des forages (annually since 1994)
Annuaire de l’exploitation des nappes profondes de Tunisie (annually since 1973)
Situation de l’exploitation des nappes phréatiques (annually)
Annuaire piezometrique de Tunisie (annually since 1990, with groundwater level/piezometric data from nearly 2500 monitoring points).
Annuaire de la qualité des EST
Situation de l’exploitation des nappes phréatiques (every 5 years)
Euro Mediterranean Information System on the Know-how in the water sector.
Key published references are:
Ben Ammar S, Zouari K, Leduc C et M'barek J. 2006. Caractérisation isotopique de la relation barrage-nappe dans le bassin du Merguellil (plaine de Kairouan, Tunisie centrale). Hydrological Sciences Journal, 51, 2, 272- 284.
Ben Ammar S. 2007. Contribution à l’étude hydrogéologique, géochimique et isotopique des aquifères de Ain el Beidha et du bassin de Merguellil (plaine de Kairoun) : implications pour l’étude de la relation barrage-nappe PhD Thesis, Université Sfax
Ben Ammar S, Favreau G, Zouari K, Leduc C, Beji R et M’barek J. 2009. Approche géochimique de la vulnérabilité des eaux souterraines de la nappe phréatique de la plaine de Kairouan (Tunisie). Sécheresse, 20, 1, 87-95.
Cary L, Casanova J, Mekni A, Gaaloul N, Guerrot C et Petelet-Giraud E. 2013. Effect of artificial recharge by treated wastewater on the quality of the Korba coastal aquifer (Cape Bon, Tunisia): insights from Boron isotopes. https://hal.archives-ouvertes.fr/hal-00772743/document
DGRE (Direction Generale des Ressources en Eau). 2004. Annuaire Hydrologique de Tunisie 2003-2004.
Horriche F et Besbes M. 2006. Analyse du réseau piézométrique national tunisien. Journal of Water Science, 19 (4), 347-363.
Jeribi L. 2004. Caractérisation hydrochimique et isotopique des eaux du système aquifère du bassin de Zeroud (plaine de Kairouan, Tunisie centrale. PhD Thesis, Universitie Sfax
Kamel S, Dassi L, Zouari K and Abidi B. 2005. Geochemical and isotopic investigation of the aquifer system in the Djerid-Nefzaoua basin, southern Tunisia. Environmental Geology 49, 159–170
Kerrou J, Renard P and Tarhouni J. 2010. Status of the Korba groundwater resources (Tunisia): observations and three-dimensional modelling of seawater intrusion. Hydrogeology Journal, Volume 18, Issue 5, pp 1173-1190
Leduc C, Ben Ammar S, Favreau G, Béji R, Virrion R, Lacombe G, Tarhouni J, Aouadi C, Zenati Chelli B, Jebnoun N, Oï M, Michelot JL et Zouari K. 2007. Impacts of hydrological changes in the Mediterranean zone: env ironmental modifications and rural development in the Merguellil catchment, central Tunisia. Hydrological Sciences Journal, 52 (6), 1162-1178.
Louati ME and Bucknell J. 2010. Tunisia's experience in water resource mobilization and management. Development and Climate Change WDR2010 Background Note.
Maliki MA. 2000. Etude hydrogeologique, hydrochimique et isotopique de système aquifère de Sfax, Tunisie. PhD Thesis, University of Tunis I, Tunis
Maliki MA, Krimissa M, Michelot J-L, Zouari K. 2000. Relation entre nappes superﬁcielles et aquifère profond dans le bassin de Sfax (Tunisie). C. R. Acad. Sci. Paris, Sciences de la Terre et des planètes / Earth and Planetary Sciences 331, 1–6
Mekni A, Cary L, Abderrazek S et Noureddine G. 2012. Evolution spatio‐temporelle de la nappe phréatique de Korba‐El Mida, Cap‐Bon (Tunisie) et impact de sa recharge artificielle par les eaux usées traitées. Presenté a Dix‐huitièmes journées techniques du Comité Français d’Hydrogéologie de l’Association Internationale des Hydrogéologues: Ressources et gestion des aquifères littoraux, Cassis 2012. http://www.cfh-aih.fr/cassis_2012/documents/doc/articles/4.MEKNI-et-al.pdf
Nazoumou Y. 2002. Impact des barrages sur la recharge des nappes en zone aricde. Etude par modélisation numérique sur le cas de Kairouan (Tunisie cenyrale). PhD Thesis, Université Tunis el Manar
OSS (Observatoire du Sahara et du Sahel). 2003. Systeme Aquifere du Sahara Septentrional: gestion commune d’un bassin transfrontière. Rapport de synthese, 1ere edition, Janvier 2003.
SEMIDE (Systeme Euro Méditerranéen de l'Information sur les savoir-faire dans le Domaine de l'Eau). Carte des Ressources en Eau en Tunisie. http://www.semide.tn/loupe.htm
Tunisian Institute for Strategic Studies. 2014. Système Hydraulique de la Tunisie à l’horizon 2030.
Zebidi H. 1991. Carte des Ressources en Eau de la Tunisie; echelle 1:500,000. Direction Generale des Ressources en Eau.