Difference between revisions of "Hydrogeology of Somalia"

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(Geology)
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!colspan="4"| Tertiary sedimentary
 
!colspan="4"| Tertiary sedimentary
 
|-
 
|-
|Daban Series; Hafun Series and Iskushuban Formation
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|Iskushuban Formation; Mudug Formation; Daban Formation; Hafun Series  
 
||Tertiary (Oligocene to Miocene)
 
||Tertiary (Oligocene to Miocene)
||Thick, extensive, complex series of sedimentary rocks: sandstone, conglomerate, gypsum and siltstone.  
+
||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
 
||500 m to over 2000 m thick
  
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|Auradu Formation; Taleex Formation; Karkar Formation
 
|Auradu Formation; Taleex Formation; Karkar Formation
 
||Tertiary (Eocene)
 
||Tertiary (Eocene)
||Limestone and evaporitic rocks. The Auradu Formation is limestone; the Taleex Formation has evaporitic rocks - gypsum and anhydrite; and the Karkar Formation is limestones. The limestones can be karstic.  
+
||Limestone and evaporitic rocks. The Auradu Formation is limestone; the Taleex Formation has evaporitic rocks - gypsum and anhydrite; and the Karkar Formation is limestones. The limestones are karstic.  
 
||Average thicknesses of the formations are: Karkar - 300 m; Taalex - 250 m; and Auradu - 200-400 m
 
||Average thicknesses of the formations are: Karkar - 300 m; Taalex - 250 m; and Auradu - 200-400 m
 
|-
 
|-
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|Hamanlei Formation
 
|Hamanlei Formation
 
||Jurassic
 
||Jurassic
||Marine and clastic limestones, shales and sandstones. Limestones are karstic.
+
||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)
 
||Thickness varies, mainly due to lateral facies change, from 220 m (at Gowan) to 1000 m (at Bixinduule, between Sheekh and Berbera)
  
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|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|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<sup>-2(/sup> to 10<sup>-3(/sup> 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<sup>-3(/sup> m²/sec; the others ranged from 2.86 to 5.18 x 10<sup>-3(/sup> m²/sec. Calculated equivalent hydraulic conductivities were in the range 1.4 x 10<sup>-4(/sup> m/sec to 7.7 x 10<sup>-5(/sup> 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
  
 
||
 
||
 
||
 
||
||  
+
||
 +
 
 
|}
 
|}
  
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|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
|
+
|Tertiary (Miocene Iskushuban Formation; Oligocene/Miocene Mudug Formation; Oligocene Daban Formation); Upper Cretaceous Yessoma Formation (Nubian sandstone); Jurassic Ahl Madow Group
 +
||These can 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<sup>-4</sup> 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<sup>-3</sup> to 2.9 x 10>sup>-4</sup> m²/sec were calculated.
 +
 
 +
 
 +
The Jurassic 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<sup>-3</sup> 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).
 +
 
 +
|-
 +
|Karstic aquifers - Jurassic limestones; Eocene Karkar, Taalex and Auradu limestones
 
||  
 
||  
 
||
 
||
 
||
 
||
 
||  
 
||  
 +
 
|}
 
|}
  
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UNICEF. 1983-1986. Rural water supply and sanitation  programme in the  Northern  Regions",  Internal  Reports,  Hargeysa
 
UNICEF. 1983-1986. Rural water supply and sanitation  programme in the  Northern  Regions",  Internal  Reports,  Hargeysa
 +
 +
Van der Plac. 2001
  
 
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
 
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

Revision as of 12:33, 9 July 2015

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 Formation is limestone; the Taleex Formation has evaporitic rocks - gypsum and anhydrite; and the Karkar Formation is limestones. The limestones are karstic. Average thicknesses of the formations are: Karkar - 300 m; Taalex - 250 m; and Auradu - 200-400 m
Mesozoic sedimentary
Cretaceous Nubian sandstones and thin limestones From 100 m to over 1000 m thick
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)
Precambrian Basement Complex
Precambrian Metamorphic schists, orthogneisses, quartzites and paragneisses, intruded by granites, 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


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(/sup> to 10-3(/sup> 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(/sup> m²/sec; the others ranged from 2.86 to 5.18 x 10-3(/sup> m²/sec. Calculated equivalent hydraulic conductivities were in the range 1.4 x 10-4(/sup> m/sec to 7.7 x 10-5(/sup> 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

Sedimentary - Intergranular Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge

Sedimentary - Intergranular & Fracture Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge

Sedimentary - Fracture Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Tertiary (Miocene Iskushuban Formation; Oligocene/Miocene Mudug Formation; Oligocene Daban Formation); Upper Cretaceous Yessoma Formation (Nubian sandstone); Jurassic Ahl Madow Group These can 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>sup>-4 m²/sec were calculated.


The Jurassic 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).
Karstic aquifers - Jurassic limestones; Eocene Karkar, Taalex and Auradu limestones

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 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

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

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. 2001

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