Hydrogeology of Tunisia

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Africa Groundwater Atlas >> Hydrogeology by country >> Hydrogeology of Tunisia

Authors

Amira Mekni, INAT, Tunisia

Safouan Ben Ammar, ISTEUB, Tunisia

Kirsty Upton & Brighid Ó Dochartaigh, British Geological Survey, UK


Geographical Setting

Map of Tunisia (For more information on the datasets used in the map see the geography resources section)

General

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%
Capital City Tunis
Region Northern Africa
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


Climate

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.

Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the Tunisia Climate Page.


Average monthly precipitation for Tunisia showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for Tunisia showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature Quarterly precipitation over the period 1950-2012 Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)

For further detail on the climate datasets used see the climate resources section.

Surface water

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).




Surface Water Map of Tunisia (For more information on the datasets used in the map see the surface water resources section)

Soil

Soil Map of Tunisia (For map key and more information on the datasets used in the map see the soil resources section)

Land cover

Land Cover Map of Tunisia (For map key and more information on the datasets used in the map see the land cover resources section)


Geology

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). The map is available to download as a shapefile (.shp) for use in GIS packages.

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).

Geological Environments
Key Formations Period Lithology Structure
Geological Environment 1
Name of formation1 Time period Description Structure
Geological Environment 2
Geological Environment 3

Hydrogeology

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 Aquifer properties resource page for more details). The map is available to download as a shapefile (.shp) for use in GIS packages.

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).

File:Tunisia Hydrogeology.png 


Unconsolidated

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Continental Intercalaire (CI) (Lower Cretaceous) The Continental Intercalaire (CI) aquifer 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 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 (Pliocene)-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 (Pliocene)-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.


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.

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:

[www.oss-online.org OSS]

Kamel et al (2005)


Sedimentary - Fracture Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge

Basement

Named Aquifers General Description Water quantity issues Water quality issues Recharge


Groundwater Status

Groundwater quantity

Groundwater quality

Groundwater use and management

Groundwater use

Groundwater management

Groundwater monitoring

Transboundary aquifers

For further information about transboundary aquifers, please see the Transboundary aquifers resources page


References

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:

National Office of Mines (ONM) https://www.onm.nat.tn/fr/ . 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:

DGRE (Direction Generale des Ressources en Eau) - the national department for water resources management and mobilization. https://www.semide.tn/DGRE.htm

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)


SEMIDE (Systeme Euro Méditerranéen de l'Information sur les savoir-faire dans le Domaine de l'Eau / Euro Mediterranean Information System on the Know-how in the water sector). https://www.semide.tn/index.htm

OSS (Observatoire du Sahara et du Sahel). www.oss-online.org


Key published references are:

DGRE (Direction Generale des Ressources en Eau). 2004. Annuaire Hydrologique de Tunisie 2003-2004.

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

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. https://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.


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