Hydrogeology of Somalia

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


Authors

Hussein Gadain, Food and Agriculture Organisation of the United Nations, Kenya

Zoran Stevanovic, University of Belgrade, Serbia

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


Geographical Setting

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

General

Estimated Population in 2013* 10,495,583
Rural Population (% of total) (2013)* 61.4%
Total Surface Area* 627,340 sq km
Agricultural Land (% of total area) (2012)* 70.3%
Capital City Mogadishu
Region Eastern Africa
Border Countries Ethiopia, Djibouti, Kenya
Annual Freshwater Withdrawal (2013)* 3,298 Million cubic metres
Annual Freshwater Withdrawal for Agriculture (2013)* 99.48%
Annual Freshwater Withdrawal for Domestic Use (2013)* 0.45%
Annual Freshwater Withdrawal for Industry (2013)* 0.06%

* Source: World Bank


Climate

Much of the north and centre of Somalia have an arid climate; and much of the rest of the north and south of the country are semi arid. Only small areas in the south have a humid climate. Annual rainfall in the north and northeast is less than 100 mm, rising to 200 mm to 300 mm in the central plateaus, and between 500 mm and 600 mm in the northwest and southwest.

The little seasonal variation in climate is largely related to changes in wind patterns. There is a main monsoonal wet season in April and May, and a smaller wet season in October and November.


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


Average monthly precipitation for Somalia showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for COUNTRY 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

Somalia has two permanent rivers, the Jubba and the Shabele, both of which begin in the Ethiopian Highlands and flow southwards.











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

Soil

Most of the soils in Somalia have low nutrient and moisture availability, including calcisols, gypsisols, arenosols and solonchak and solonetz type soils that cover much of the country.

The adjacent map shows data from the Soil Map of Africa, available from the European Soil Portal; other soil data are available from the FAO Soils Portal









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

Land cover

The far north of Somalia is desert or semi-desert, with semi-arid land showing sparse vegetation through much of the north and centre, and grassland and sparse forest throughout much of the south.









Land Cover Map of Somalia (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 Somalia. 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. A more detailed geological map at 1:1,500,000 is also published (see Geology: key references, below).


Geological Environments
Key Formations Period Lithology Structure
Quaternary
Alluvium Pleistocene to Holocene/Recent Older Pleistocene alluvial terrace sediments and Holocene/Recent alluvium, including sandy clay with lenses of sand and fine gravel to coarse gravels and boulders.

In some areas fine sands, forming dunes, occur; as do red soils; and calcretes.

Thickness ranges from several metres to a few tens of metres
Volcanic basaltic rocks Pleistocene These basaltic lavas were deposited in different periods. They followed existing topographical depressions and uneven basin floors. Several lava flows have tuff intercalations in some places.

form a cover

Thickness ranges from a few metres to over 50 m
Tertiary sedimentary
Iskushuban Formation; Mudug Formation; Daban Formation; Hafun Series Tertiary (Oligocene to Miocene) Thick, extensive, complex series of sedimentary rocks.

The Miocene Iskushuban Formation comprises marl, sandstone, gypsum, coal, limestone and fine grained conglomerate.

The Oligocene/Miocene Mudug Formation comprises marly and biogenic limestones, calcarenites and sandstones

The Oligocene Daban Formation comprises siltstones, sandstones, conglomerates, gypsum and limestones.

500 m to over 2000 m thick
Auradu Formation; Taleex Formation; Karkar Formation Tertiary (Eocene) Limestone and evaporitic rocks. The Auradu and Karkar formations are limestone; the Taleex Formation was formed in typical arid climate conditions, and includes evaporitic gypsum and anhydrite as well as limestones and dolostones. The limestones are karstic. Average thicknesses of the formations are: Karkar - 300 m; Taalex - 250 m; and Auradu - 200-400 m
Mesozoic sedimentary
Upper Cretaceous Yessoma Formation - Nubian-type sandstones with thin limestones. From 100 m to over 1000 m thick
Cretaceous undifferentiated Sandstones, conglomerates, limestones and evaporitic rocks. These rocks occur in the northern part of southern Somalia, where they are dominated by calcareous and evaporitic rocks; and as scattered small outcrops in the north near the coast, where they are typically sandstones with conglomerates in the west, and limestones in the each.


Hamanlei Formation Jurassic Marine and clastic limestones, shales and sandstones. The limestones are karstic. Thickness varies, mainly due to lateral facies change, from 220 m (at Gowan) to 1000 m (at Bixinduule, between Sheekh and Berbera)
Basement Complex
Precambrian and Cambrian Includes metamorphic schists, orthogneisses, quartzites and paragneisses, Late Proterozoic migmatites and marble intercalations, migmatites of the Qabri Baxar Complex, and intruded by granites (some of Cambrian age), diorites and gabbros. Thousands of metres thick

Hydrogeology

This section provides a summary of the hydrogeology of the main aquifers in Somalia. 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.

File:Somalia Hydrogeology.png Hydrogeology Key.png

Summary

Groundwater is very important in Somalia, forming the sole water resource in most of the country's territories. A number of studies have laid down a good base for further hydrogeological works (see Hydrogeology: key references, below and other references in the Africa Groundwater Literature Archive). Numerous NGO’s have also worked in the region and supported urban centres and local rural and semi-urban communities by drilling water wells or conducting geophysical surveys. However, although many water projects have been implemented or supported in the region, water well drilling has commonly been conducted without adequate project feasibility studies, and to date, no systematic data collection has been carried on groundwate exploitation, capacity, and especially on groundwater level fluctuations. However, during the last few years, and mostly thanks to the FAO/SWALIM work, more accurate and adequate hydrogeological maps, whcih are essential for planning any groundwater exploration and exploitation, have been prepared and become available for northern Somalia (FAO/SWALIM 2012).

Unconsolidated

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Alluvial terrace deposits - Pleistocene to Holocene/Recent Terrace deposits in major wadis (ephemeral river beds - called toggas). Younger Holocene/Recent deposits often overlie and are in hydraulic continuity with older Pleistocene deposits, which can result in very thick aquifers of over 100 m.

Typically high productivity aquifers, with medium to high permeability and high infiltration capacity. Estimated transmissivity values are commonly in the range 10-2 to 10-3 m²/sec. In the Geed Deeble area (source for the Hargeysa water supply), only one in ten tested boreholes showed a transmissivity of less than 10-3 m²/sec; the others ranged from 2.86 to 5.18 x 10-3 m²/sec. Calculated equivalent hydraulic conductivities were in the range 1.4 x 10-4 m/sec to 7.7 x 10-5 m/sec. Test yields of the production boreholes ranged from 12 to 20 l/s, with drawdowns typically less than 20 m (data provided by Hargeysa Water Utility).

Generally unconfined, but where covered or associated with Quaternary volcanic basalts, they can be confined, sometimes with considerable artesian pressure (e.g. in the Xunboweyle area). In unconfined aquifers the water table is typically 2 to 3 m deep throughout the year, related to seasonal flows along riverbeds. In deeper confined, artesian aquifers in older deposits, the piezometric head does not fluctuate much throughout the year.

Vary from a few metres to over 100 m thick. At Geed Deeble (source for the Hargeysa water supply), the tapped aquifer depth is over 150 m. Boreholes are typically between 10 m and 50 m deep.

In Somaliland in the north of Somalia, dynamic (sustainable) groundwater reserves in the major alluvial aquifers are estimated at an average flow of ~30 m³/se. Generally low levels of mineralisation, with TDS below 1000 mg/l, and drinkable. High infiltration capacity
Alluvial sediments filling major valleys and plateaus - Pleistocene to Holocene/Recent Low to moderate productivity

Key references for this aquifer are Faillace and Faillace 1986, FAO/SWALIM 2012, Water Supply Survey Team of the PRC 1983, Petrucci, 2008 and German Agro-Action, 2005.


Volcanic

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Pleistocene basaltic lava flows These are a potential aquifer in some areas. They contain groundwater only where fractured and/or weathered, or in lenses of pyroclastic material between lava flows. They typically have low to moderate permeability, but are locally highly fractured, increasing permeability. However, they occur primarily as elevated plateaus, and are often unsaturated. In some areas, such as Agabar and Las Dhure, they are found in the lowlands and may be saturated, and in this case are likely to be unconfined. Boreholes drilled in these areas have intersected water-bearing zones composed of sand/pyroclastic lenses and weathered basalt. In some areas, vertical fractures resulting from cooling of the basalts may occur, and are likely to form primary recharge routes.

Key references for this aquifer are Faillace and Faillace 1986, FAO/SWALIM 2012 and German Agro-Action 2005.

Sedimentary - Fracture Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Tertiary: Iskushuban Formation (Miocene); Mudug Formation (Oligocene/Miocene); Daban Formation (Oligocene) These form moderate productivity aquifers. Fractures act as pathways for rapid groundwater flow, but permeability and groundwater storage are small.

A borehole drilled into the Miocene Iskushuban Formation in Timirishe in the Bari area yielded 5 l/s for a drawdown of some 50 m, with a calculated transmissivity of 4.5 x 10-4 m²/sec.

Boreholes in the Oligocene/Miocene Mudug Formation are drilled to 180 to 220 m deep, and provide yields of 3 to 5 l/s for drawdowns in the range 3 to 24 m. Transmissivity values of 3.1 x 10-3 to 2.9 x 10-4 m²/sec were calculated.

Recharge is estimated to be approximately in the range of 3 to 5% of annual rainfall (Van der Plac 2001).
Upper Cretaceous Yessoma Formation (Nubian sandstone) The Yessoma Formation is of Nubian sandstone type and forms a high productivity aquifer. The coarsest grained part of the formation occurs between 140 m and 180 m depth. Calculated aquifer transmissivity is around 2 x 10-3 m²/sec (220 m²/day), with an average specific capacity of 7.5 m³/hour/m. Most boreholes penetrating the formation can sustain a yield of more than 30 m³/hour. Recharge is estimated to be approximately in the range of 3 to 5% of annual rainfall (Van der Plac 2001).
Cretaceous undifferentiated: sandstones, conglomerates, limestones and evaporitic rocks Little is known about the aquifer properties of these rocks.
Karstic aquifers - Eocene Karkar, Taalex and Auradu limestones; Jurassic limestones Karstic aquifers of Tertiary (Eocene) and Jurassic age are the most significant aquifers in the north of Somalia, in the Somaliland and Puntland regions.

The Eocene limestone (Karkar and Auradu) and limestone/evaporite (Taalex) formations are often karstic.

The Karkar limestone represents the most promising fresh groundwater resource for further development in the Sool and Hawd plateaus in the north of Somalia. It typically forms a moderately productive aquifer.

The Auradu limestones can form a high productivity aquifer, with good quality groundwater, although more investigation is needed. If groundwater is present, the overlying Taalex aquifer should be sealed off to prevent inflow of lower quality water. Many boreholes abstract from the aquifer, particularly in the Puntland region, with an average transmissivity of 10-3m²/sec (860 m²/day). Other boreholes over 200 m deep are drilled in limestones in the Garoowe area. Where these limestones are overlain by the Karkar formation, they are often semi-confined, with low sub-artesian pressure.

The Jurassic limestones have the greatest potential for groundwater development in the country. There is usually pure limestone in the upper part of the formation, with marly levels and calcareous sandstones in the lower part. The upper parts in particular are usually characterised by a high degree of fracturing and probably karstic cavities, and groundwater circulation probably develops mainly in this zone. The limestones can be highly permeable, with a transmissivity value from one test borehols at Borama of 3.1 x 10-3 m²/sec (270 m²/day).

The depth to water table in unconfined parts of these aquifers is usually between 5 and 15 m throughout the year.

Fresh groundwater reserves in the Auradu aquifer in the Somaliland and Puntland regions are estimated as equivalent to an average flow of 63.4 m³/sec. The estimated fresh groundwater reserve in the Karkar aquifer is lower at approximately 10 m³/sec.

Groundwater reserves in the Jurassic limestone aquifer in the Awadal region are estimated as equivalent to an average flow fo 18.9 m³/sec.

Groundwater in the Karkar karst aquifer is slightly mineralised, with an SEC (conductivity) value typically between 1500 and 1800 micromhos/cm.

The Taalex aquifer usually yields moderately to highly mineralised groundwater, derived from geogenic evaporitic minerals. Ca or CaSO4 type groundwater is dominant, with TDS usually greater than 3800 mg/l. Many boreholes have been abandoned because of a high salinity content.

Groundwater from the Auradu limestones is typically of bicarbonate type with an SEC (conductivity) value generally lower than 1000 micromhos/cm.

Groundwater in the Jurassic aquifer is generally of bicarbonate type with low levels of mineralisation.

Approximate estimates of recharge are between 35% of annual rainfall for the Karkar aquifer to 50% of rainfall for the Jurassic limestone aquifer.

Key references for these aquifer are: Faillace and Faillace 1986, FAO/SWALIM 2012, Petrucci 2008, German Agro-Action 2005, GKW 1977 and Van der Plac 2001.


Basement

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Forms a low productivity aquifer or an aquitard, depending on the development of permeability by weathering/fracturing.


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 Somalia. These, and others, can be accessed through the Africa Groundwater Literature Archive

Geology: key references

Abbate E, Sagri M & Sassi FP (with the collaboration of Aden IH, Arush MA, Yusuf OS). 1994. The geological map of Somalia 1:1,500,000. University of Florence, SELCA, Florence


Hydrogeology: key references

Faillace C, Faillace ER. 1986. Water quality data book of Somalia. Hydrogeology and water quality of northern Somalia, Vol. 1, Text. GTZ & WDA, Rosdorf

FAO/SWALIM. 2011. Water sources inventory for northern Somalia, Technical Report No. W-12, January 2009, Nairobi

FAO-SWALIM (Balint Z, Stevanovic Z, Gadain H et al.). 2012. Hydrogeological Survey and Assessment of Selected Areas in Somaliland and Puntland. Technical Report No. W-20, FAO-SWALIM (GCP/SOM/049/EC) Project, Nairobi, Kenya. http://www.faoswalim.org/content/w-20-hydrogeological-survey-and-assessment-selected-areas-somaliland-and-puntland-report-no

German Agro-Action. 2005. Inception Report of the integrated water resource management plan - Community based natural resource management in the Dur-Dur watershed, Awdal Region, Somaliland, EC: 424-NGO-AG02-03; GAA: SOM 1003

GKW. 1977. Water resource development project in Somalia. New water supply system in Burco, Hydrogeological Report, Mannheim

Humphreys H & Sons. 1960. Hargeysa water supply investigation. Westminster and Nairobi.

Macfadyen WA. 1951. Water supply and geology of parts of British Somaliland. Hargeysa

Petrucci B. 2007. Rehabilitation and improvement of Hargeysa urban water supply system. Hydrogeological Monitoring. Final report, January 2007, Water & Land, Hargeysa

Petrucci B. 2008. Research of new water source for Borama town, Awdal – Somaliland. UNICEF - UNA – Africa 70, Hargeysa Popov AP, Kidwai AL and Karrani SA. 1973: Mineral and ground water survey (Phase II), ground water in the Somali Democratic Republic. Vol. III - Technical Report, UNDP, New York

SHAAC Co. 2006. 13 sites, Hydrogeological site investigation report, UNDP, New York SOGREAH, 1982/83: North-West region agricultural development project. Technical Report 16, Hydrogeology, Grenoble

UNICEF. 1983-1986. Rural water supply and sanitation programme in the Northern Regions", Internal Reports, Hargeysa

Van der Plac MC. 2001. Burao water supply project XB=SOM-00-X01, Hydrogeological Site Investigations, Togdheer Region (Somaliland), UNCHS (Habitat)

Water Supply Survey Team of the People's Republic of China. 1983. Survey report on the possibility of the second water source of Hargeysa City of Somali Democratic Republic, Beijing

Wilson G. 1958. Ground water geology in Somalia, Mogadishu


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