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[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Mali
 
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Mali
  
  '''Lire cette page en français: [[Hydrogéologie du Mali| Hydrogéologie du Mali]]''' [[File: flag_of_france.png  | 50px]]
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'''Lire cette page en français: [[Hydrogéologie du Mali| Hydrogéologie du Mali]]''' [[File: flag_of_france.png  | 50px]]
 
 
[[File:CC-BY-SA_logo_88x31.png | frame | This work is licensed under a [https://creativecommons.org/licenses/by-sa/3.0/ Creative Commons Attribution-ShareAlike 3.0 Unported License]]]
 
 
 
Mali is a landlocked country, formerly part of the three ancient Sahelian empires of Ghana, Mali and Songhai. A the height of the Mali empire in the 13th century, the town of Timbuktu was a centre of culture, learning and Islamic religion, and Djenne was an international trade centre. In the late 19th century, France seized control of the present day area of Mali, making it a part of French Sudan. Mali won independence in 1960 as the Mali Federation with Senegal, shortly afterwards becoming the Republic of Mali in its current borders. Under one-party rule until a coup in 1991, Mali transitioned to a multi-party state with the first elections in 1992. Mali was perceived internationally as a fairly stable democratic country during this time. In 2012 there were two military coups and armed conflict between the state, Tuareg Islamic militants, which was eventually resolved with a return to democratic elections in 2013.
 
 
 
The economy has traditionally relied on agriculture. Desert areas are only suited for pastoralism, but there is cultivation of many crops including rice, groundnut and cotton (the latter particularly important as an export crop) in the less arid south and around the Niger River. There are also areas of irrigated vegetable production, but these are less economically significant on a national scale. Post-independence, drought was one factor leading to economic decline. Remittances from migrants to Cote d’Ivoire have also been important, and the return of many of these people during periods of instability in Cote d’Ivoire in 2002 and 2010 had an impact on the livelihoods on many Malians. There are attempts to diversify the economy with development of the mining industry, including gold, phosphate and kaolin.
 
 
 
With a largely semi-arid to arid climate, Mali has limited surface water resources in the north, but two major river systems in the south of the country are a key resource. Mali also has huge stores of groundwater in major aquifer systems, with a mix of fossil and actively recharged groundwater.
 
  
  
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'''Aboubacar Sidibe''', Mali
 
'''Aboubacar Sidibe''', Mali
  
'''Dr Kirsty Upton''', '''Brighid Ó Dochartaigh''', British Geological Survey, UK
+
'''Kirsty Upton''', '''Brighid Ó Dochartaigh''', British Geological Survey, UK
  
'''Dr Imogen Bellwood-Howard''', Institute of Development Studies, UK
+
Please cite this page as: Traore, Bokar, Sidibe, Upton & Ó Dochartaigh, 2016.
  
Please cite this page as: Traore, Bokar, Sidibe, Upton, Ó Dochartaigh and Bellwood-Howard, 2018.
+
Bibliographic reference: Traore, A.Z., Bokar, H., Sidibe, A., Upton, K. & Ó Dochartaigh, B.É. 2016. Africa Groundwater Atlas: Hydrogeology of Mali. British Geological Survey. Accessed [date you accessed the information]. http://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Mali
 
 
Bibliographic reference: Traore AZ, Bokar H, Sidibe A, Upton K, Ó Dochartaigh BÉ and Bellwood-Howard, I. 2018. Africa Groundwater Atlas: Hydrogeology of Mali. British Geological Survey. Accessed [date you accessed the information]. http://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Mali
 
  
 
==Terms and conditions==
 
==Terms and conditions==
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{| class = "wikitable"
 
{| class = "wikitable"
 
|-
 
|-
|Capital city || Bamako
+
|Estimated Population in 2013* || 15,301,650
 
|-
 
|-
|Region || West Africa
+
|Rural Population (% of total)* || 62%
 
|-
 
|-
|Border countries || Algeria, Niger, Burkina Faso, Cote d’Ivoire, Guinea, Senegal, Mauritania
+
|Total Surface Area* || 1,220,190 sq km
 
|-
 
|-
|Total surface area* || 1,240,190 km<sup>2</sup>  (124,019,000  ha)
+
|Agricultural Land (% of total area)* || 34%
 
|-
 
|-
|Total population (2015)* || 17,600,000
+
|Capital City || Bamako
 
|-
 
|-
|Rural population (2015)* ||11,110,000 (63%)
+
|Region || Western Africa
 
|-
 
|-
|Urban population (2015)* || 6,490,000 (37%)
+
|Border Countries || Algeria, Niger, Burkina Faso, Cote d’Ivoire, Guinea, Senegal, Mauritania
 
|-
 
|-
|UN Human Development Index (HDI) [highest = 1] (2014)*|| 0.4193
+
|Annual Freshwater Withdrawal (2013)* || 5,186 Million cubic metres
 +
|-
 +
|Annual Freshwater Withdrawal for Agriculture* || 98%
 +
|-
 +
|Annual Freshwater Withdrawal for Domestic Use* || 2%
 +
|-
 +
|Annual Freshwater Withdrawal for Industry* || <0.1%
 +
|-
 +
|Rural Population with Access to Improved Water Source* || 54%
 +
|-
 +
|Urban Population with Access to Improved Water Source* || 91%
 
|}
 
|}
  
<nowiki>*</nowiki> Source: [http://www.fao.org/nr/water/aquastat/data/query/index.html?lang=en FAO Aquastat]
+
<nowiki>*</nowiki> Source: World Bank
 
 
  
  
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| [[File:Mali_LandCover.png | frame | Land Cover Map of Mali, from the European Space Agency GlobCover 2.3, 2009. For more information on the map see the [[Land cover | land cover resource page]].]]
 
| [[File:Mali_LandCover.png | frame | Land Cover Map of Mali, from the European Space Agency GlobCover 2.3, 2009. For more information on the map see the [[Land cover | land cover resource page]].]]
 
|}
 
|}
 
 
===Water statistics===
 
 
{| class = "wikitable"
 
| ||2000||2006||2014||2015
 
|-
 
|Rural population with access to safe drinking water (%) || || ||  || 64.1
 
|-
 
|Urban population with access to safe drinking water (%) || || ||  || 96.5
 
|-
 
|Population affected by water related disease || No data || No data || No data || No data
 
|-
 
|Total internal renewable water resources (cubic metres/inhabitant/year) || || ||3,409  ||
 
|-
 
|Total exploitable water resources (Million cubic metres/year) || No data || No data || No data || No data
 
|-
 
|Freshwater withdrawal as % of total renewable water resources || ||4.32 || ||
 
|-
 
|Total renewable groundwater (Million cubic metres/year) ||  || ||20,000 ||
 
|-
 
|Exploitable: Regular renewable groundwater (Million cubic metres/year) || No data || No data || No data || No data
 
|-
 
|Groundwater produced internally (Million cubic metres/year) || || ||20,000 ||
 
|-
 
|Fresh groundwater withdrawal (primary and secondary) (Million cubic metres/year) ||||61||  ||
 
|-
 
|Groundwater: entering the country (total) (Million cubic metres/year) disease || No data || No data || No data || No data
 
|-
 
|Groundwater: leaving the country to other countries (total) (Million cubic metres/year) || No data || No data || No data || No data
 
|-
 
|Industrial water withdrawal (all water sources) (Million cubic metres/year) || ||4 || ||
 
|-
 
| Municipal water withdrawal (all water sources) (Million cubic metres/year)  || ||107 || ||
 
|-
 
|Agricultural water withdrawal (all water sources) (Million cubic metres/year) || ||5,075 || ||
 
|-
 
|Irrigation water withdrawal (all water sources)<sup>1</sup> (Million cubic metres/year) || ||5,000 ||  ||
 
|-
 
|Irrigation water requirement (all water sources)<sup>1</sup> (Million cubic metres/year) ||1,469 || ||  ||
 
|-
 
|Area of permanent crops (ha) || || || 150,000 ||
 
|-
 
|Cultivated land (arable and permanent crops) (ha) || || || 6,561,000 ||
 
|-
 
|Total area of country cultivated (%) || || || 5.29 ||
 
|-
 
|Area equipped for irrigation by groundwater (ha) ||1,000 || ||  ||
 
|-
 
|Area equipped for irrigation by mixed surface water and groundwater (ha) || No data || No data || No data || No data
 
|}
 
 
These statistics are sourced from [http://www.fao.org/nr/water/aquastat/main/index.stm FAO Aquastat]. They are the most recent available information in the Aquastat database. More information on the derivation and interpretation of these statistics can be seen on the FAO Aquastat website.
 
 
Further water and related statistics can be accessed at the [http://www.fao.org/nr/water/aquastat/data/query/index.html?lang=en Aquastat Main Database].
 
 
<sup>1</sup> More information on [http://www.fao.org/nr/water/aquastat/water_use_agr/index.stm irrigation water use and requirement statistics]
 
  
 
==Geology==
 
==Geology==
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This section provides a summary of the geology of Mali. More detail can be found in the references listed at the bottom of this page. Many of these references can be accessed through the [http://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].
 
This section provides a summary of the geology of Mali. More detail can be found in the references listed at the bottom of this page. Many of these references can be accessed through the [http://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].
  
The geology map on this page shows a simplified version of the '''bedrock geology''' at a national scale (see [[Geology | the Geology resource page]] for more details.
+
The geology map on this page shows a simplified version of the geology at a national scale (see [[Geology | the Geology resource page]] for more details.
 
 
[https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html '''Download a GIS shapefile of the Mali geology and hydrogeology map'''].
 
  
[[File:Mali_Geology4.png | center | thumb| 500px | Geology of Mali at 1:5 million scale. Based on map described by Persits et al. 2002 / Furon and Lombard 1964. For more information on the map development and datasets see the [[Geology | geology resource page]]. [https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html Download a GIS shapefile of the Mali geology and hydrogeology map].]]
+
[[File:Mali_Geology2.png | center | thumb| 500px | Geology of Mali at 1:5 million scale. Developed from USGS map (Persits et al. 2002). For more information on the map development and datasets see the [[Geology | geology resource page]].]]
  
 
{| class = "wikitable"
 
{| class = "wikitable"
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|| Variable thickness from a few tens of metres (Nara ditch) to over 1000 m (Sudanese Strait).
 
|| Variable thickness from a few tens of metres (Nara ditch) to over 1000 m (Sudanese Strait).
 
|-
 
|-
!colspan="4"| Sedimentary: Upper Cretaceous-Tertiary
+
!colspan="4"| Sedimentary: Cretaceous
|-
 
|Marine Sediments
 
||Upper Cretaceous – Lower Eocene (Tertiary)
 
|| This unit comprises marine sediments, which were deposited primarily along the western margin of the Adrar des Iforas (Sudanese Strait). Limestone, containing varying amounts of marl, predominates at the base of the sequence. Sandstone and clay are dominant towards the top of the sequence.
 
||
 
|-
 
!colspan="4"| Sedimentary: Lower Cretaceous
 
 
|-
 
|-
|Continental Intercalaire
+
| Continental Intercalaire
 
||Lower Cretaceous
 
||Lower Cretaceous
 
||These rocks consist of sandstone, conglomerate and arkose, with varying amounts of clay. It is a continental infill sequence, which was deposited in the Azaouad Basin (north) and the Iullemeden Basin (east) prior to the mid-Cretaceous marine transgression.
 
||These rocks consist of sandstone, conglomerate and arkose, with varying amounts of clay. It is a continental infill sequence, which was deposited in the Azaouad Basin (north) and the Iullemeden Basin (east) prior to the mid-Cretaceous marine transgression.
 
||Thicknesses of 500  to 1000 m.   
 
||Thicknesses of 500  to 1000 m.   
 +
|-
 +
| Marine Sediments
 +
||Upper Cretaceous – Lower Eocene
 +
|| This unit comprises marine sediments, which were deposited primarily along the western margin of the Adrar des Iforas (Sudanese Strait). Limestone, containing varying amounts of marl, predominates at the base of the sequence. Sandstone and clay are dominant towards the top of the sequence.
 +
||
 
|-
 
|-
 
!colspan="4"|Igneous
 
!colspan="4"|Igneous
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The hydrogeology map on this page shows a simplified overview of the type and productivity of the main aquifers at a national scale (see the [[Hydrogeology Map | Hydrogeology map resource page]] for more details).  
 
The hydrogeology map on this page shows a simplified overview of the type and productivity of the main aquifers at a national scale (see the [[Hydrogeology Map | Hydrogeology map resource page]] for more details).  
 
[https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html '''Download a GIS shapefile of the Mali geology and hydrogeology map'''].
 
  
 
'''Summary'''
 
'''Summary'''
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Intrusive igneous rocks (dolerites) can either act as a barrier to flow, or can provide preferential pathways for groundwater flow. Under certain conditions they also form aquifers of local importance.
 
Intrusive igneous rocks (dolerites) can either act as a barrier to flow, or can provide preferential pathways for groundwater flow. Under certain conditions they also form aquifers of local importance.
  
[[File:Mali_Hydrogeology4.png | center | thumb| 500px | Hydrogeology of Mali at 1:5 million scale. For more information on how the map was developed see the [[Hydrogeology Map | Hydrogeology map]] resource page. [https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html Download a GIS shapefile of the Mali geology and hydrogeology map].]].
+
[[File:Mali_Hydrogeology2.png | center | thumb| 500px | Hydrogeology of Mali at 1:5 million scale. For more information on how the map was developed see the [[Hydrogeology Map | Hydrogeology map]] resource page]].
  
====Unconsolidated Aquifers====
+
====Unconsolidated====
 
{| class = "wikitable"
 
{| class = "wikitable"
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
|Continental Intercalaire (Lower Cretaceous)  
+
|Continental Intercalaire/Terminal Aquifer (Taoudeni Basin)
'''Unconsolidated Aquifer - High to Low Productivity'''
+
||The continental sedimentary deposits of the Taoudeni Basin can be separated into four main regions:
||The continental sedimentary deposits of the Continental Intercalaire in the Taoudeni Basin can be separated into four main regions:
 
 
*In the Khenachich Region the deposits primarily comprise coarse sandstones and conglomerates interbedded with thick clays. Aquifers are shallow and isolated.  
 
*In the Khenachich Region the deposits primarily comprise coarse sandstones and conglomerates interbedded with thick clays. Aquifers are shallow and isolated.  
*Along the southeastern flank of Adrar des Iforas, coarse sandstones are interbedded with shales, forming continuous, multi-layered aquifers. The Tegama sandstone forms the most significant aquifer in this region.  
+
*Along the southeastern flank of Adrar des Iforas (Iullemeden Basin), coarse sandstones are interbedded with shales, forming continuous, multi-layered aquifers. The Tegama sandstone forms the most significant aquifer in this region.  
 
*In the Azaouad region the deposits comprise locally coarse sands interbedded with sandy clays forming a multi-layered aquifer.
 
*In the Azaouad region the deposits comprise locally coarse sands interbedded with sandy clays forming a multi-layered aquifer.
 
*In the Nara ditch region an upper aquifer, comprising mainly sands, is separated from a lower conglomeratic sandstone aquifer by a clay layer. The upper aquifer is unconfined and exploited by many traditional wells.       
 
*In the Nara ditch region an upper aquifer, comprising mainly sands, is separated from a lower conglomeratic sandstone aquifer by a clay layer. The upper aquifer is unconfined and exploited by many traditional wells.       
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||Recharge is generally low.
 
||Recharge is generally low.
 
|-
 
|-
|Upper Cretaceous - Eocene (Tertiary)
+
|Upper Cretaceous/Eocene Aquifer
'''Unconsolidated Aquifer - Moderate to Low Productivity'''
 
 
||The Upper Cretaceous/Eocene aquifer occurs around the western fringes of the Adrar des Iforas region. The aquifer comprises marine sediments: shale and argillaceous sandstone interbedded with limestone; local phosphatic layers; and lignite layers. To the west and south the marine deposits sit unconformably over the Precambrian basement, while to the north and southeast they overlie Continental Intercalaire deposits.  
 
||The Upper Cretaceous/Eocene aquifer occurs around the western fringes of the Adrar des Iforas region. The aquifer comprises marine sediments: shale and argillaceous sandstone interbedded with limestone; local phosphatic layers; and lignite layers. To the west and south the marine deposits sit unconformably over the Precambrian basement, while to the north and southeast they overlie Continental Intercalaire deposits.  
  
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||
 
||
 
|-
 
|-
|Continental Terminal/Quaternary  
+
|Continental Terminal/Quaternary Aquifer
'''Unconsolidated Aquifer - High productivity'''
 
 
||The Continental Terminal formation and the overlying Quaternary deposits are in hydraulic continuity, and are generally considered a single, multi-layered aquifer. The aquifer consists of vast alluvial plains with permanent surface water and extensive flood zones.
 
||The Continental Terminal formation and the overlying Quaternary deposits are in hydraulic continuity, and are generally considered a single, multi-layered aquifer. The aquifer consists of vast alluvial plains with permanent surface water and extensive flood zones.
  
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|}
 
|}
  
====Consolidated Sedimentary Aquifers - Fracture Flow====
+
====Consolidated Sedimentary - Fracture Flow====
 
{| class = "wikitable"
 
{| class = "wikitable"
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
|Infracambrian metasedimentary  
+
|Infracambrian metasedimentary aquifer
'''Sedimentary Fractured Aquifer - Moderate to Low Productivity'''
 
 
||The Infracambrian metasediments contain varying amounts of low permeability shale, located in the Sahelian region where recharge from rainfall is relatively low. The Infracambrian aquifers are therefore discontinuous and associated with fractures in the more competent sandstone and limestone layers.  They are typically semi-confined.
 
||The Infracambrian metasediments contain varying amounts of low permeability shale, located in the Sahelian region where recharge from rainfall is relatively low. The Infracambrian aquifers are therefore discontinuous and associated with fractures in the more competent sandstone and limestone layers.  They are typically semi-confined.
  
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||Aquifers are recharged by surface water from the inland Niger River delta.
 
||Aquifers are recharged by surface water from the inland Niger River delta.
 
|-
 
|-
|Cambrian Sedimentary  
+
|Cambrian Sedimentary aquifer
'''Sedimentary Fractured Aquifer - High to Moderate Productivity'''
 
 
||The hydrogeological characteristics of this aquifer are determined by the presence of low permeability shale in the sedimentary sequence, and the frequency and character of the often massive dolerite intrusions. Groundwater flow occurs predominantly in fractures within the sandstone and limestone layers.  
 
||The hydrogeological characteristics of this aquifer are determined by the presence of low permeability shale in the sedimentary sequence, and the frequency and character of the often massive dolerite intrusions. Groundwater flow occurs predominantly in fractures within the sandstone and limestone layers.  
  
 
Average borehole yields are around 6 m³/hr, with a maximum reported value of 90 m³/hr.  
 
Average borehole yields are around 6 m³/hr, with a maximum reported value of 90 m³/hr.  
  
Transmissivity varies between <0.01 and 450 m²/day, with an average of around 20 m²/day. Storage is generally around 10<sup>-5</sup>.  
+
Transmissivity varies between <0.01 and 450 m²/day, with an average of around 20 m²/day. Storage is generally around 10-5.  
  
 
The Cambrian aquifers are typically semi-confined. The fractured horizons are around 40-45 m thick with major inflows generally occurring between 20 and 40 m depth. Rest water levels are typically deeper in the north and east. Boreholes are typically drilled to 50-80 m depth, with a maximum depth of 242 m recorded.  
 
The Cambrian aquifers are typically semi-confined. The fractured horizons are around 40-45 m thick with major inflows generally occurring between 20 and 40 m depth. Rest water levels are typically deeper in the north and east. Boreholes are typically drilled to 50-80 m depth, with a maximum depth of 242 m recorded.  
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||Preferential recharge occurs through fractures from overlying alluvial deposits.
 
||Preferential recharge occurs through fractures from overlying alluvial deposits.
 
|-
 
|-
|Cambrian Sedimentary (Taoudeni Basin)
+
|Cambrian Sedimentary aquifer (Taoudeni Basin)
'''Sedimentary Fractured Aquifer - probably Moderate to Low Productivity'''
 
 
||Little is known about the hydrogeology of the Cambrian aquifer in northern Mali. Groundwater is associated with karst features in limestone layers in the central part of the Taoudeni Basin.  
 
||Little is known about the hydrogeology of the Cambrian aquifer in northern Mali. Groundwater is associated with karst features in limestone layers in the central part of the Taoudeni Basin.  
 
||Exploitation is limited due to poor water quality.
 
||Exploitation is limited due to poor water quality.
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|}
 
|}
  
====Consolidated Sedimentary Aquifer - Intergranular & Fracture Flow====
+
====Consolidated Sedimentary - Intergranular & Fracture Flow====
 
{| class = "wikitable"
 
{| class = "wikitable"
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
|Infracambrian metasedimentary  
+
|Infracambrian metasedimentary aquifer
'''Sedimentary Intergranular/Fractured Aquifer - High Productivity'''
 
 
||In the south and southwest of Mali the Infracambrian metasediments form a multi-layered, and generally semi-confined, aquifer. Higher permeability layers are generally associated with fracturing and are often connected by a network of sub-vertical fractures. Dolerite intrusions may increase the density of fracturing in some areas. The metasediments are considered a dual permeability aquifer: low permeability layers provide greater storage, while more fractured layers have higher permeability and lower storage.   
 
||In the south and southwest of Mali the Infracambrian metasediments form a multi-layered, and generally semi-confined, aquifer. Higher permeability layers are generally associated with fracturing and are often connected by a network of sub-vertical fractures. Dolerite intrusions may increase the density of fracturing in some areas. The metasediments are considered a dual permeability aquifer: low permeability layers provide greater storage, while more fractured layers have higher permeability and lower storage.   
  
Average borehole yields are around 5-10 m³/hr; however, several boreholes have reported yields of more than 100 m³/hr. Transmissivity varies between <0.1 and 1750 m²/day, with an average of around 20 m²/day. Storage varies between 10<sup>-7</sup> and 10<sup>-1</sup>.  
+
Average borehole yields are around 5-10 m³/hr; however, several boreholes have reported yields of more than 100 m³/hr. Transmissivity varies between <0.1 and 1750 m²/day, with an average of around 20 m²/day. Storage varies between 10-7 and 10-1.  
  
 
The fractured horizons in the aquifer are around 30-50 m thick, although deeper fractures can increase aquifer thickness to 80-100 m. Rest water levels are shallower in the south (typically 10-17 m below ground level) and increase northwards to >50 m below ground level. Boreholes are typically drilled to depths of 55-75 m, but can reach 400 m depth in some areas
 
The fractured horizons in the aquifer are around 30-50 m thick, although deeper fractures can increase aquifer thickness to 80-100 m. Rest water levels are shallower in the south (typically 10-17 m below ground level) and increase northwards to >50 m below ground level. Boreholes are typically drilled to depths of 55-75 m, but can reach 400 m depth in some areas
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|}
 
|}
  
====Basement Aquifers====
+
====Basement====
 
{| class = "wikitable"
 
{| class = "wikitable"
 
|Named Aquifers||General Description||Water quality issues||Recharge
 
|Named Aquifers||General Description||Water quality issues||Recharge
 
|-
 
|-
|'''Basement Aquifers - Moderate to Very Low Productivity'''
+
|Basement aquifers
 
||The basement aquifers of Mali can be divided into three regions with different hydrogeological properties. All are generally semi-confined.
 
||The basement aquifers of Mali can be divided into three regions with different hydrogeological properties. All are generally semi-confined.
  
*The basement aquifers in the south and southwest are characterised by a thick weathered zone and high rainfall; these aquifers are generally drained by the Niger River system.
+
*The basement aquifers in the south and southwest are characterised by a thick weathered zone and high rainfall; these aquifers are generally drained by the Niger River system;
*In the west (Kayes region) the weathered zone is less well developed, and rainfall is lower
+
*In the west (Kayes region) the weathered zone is less well developed, and rainfall is lower;
*The eastern outcrop (Adrar des Iforas) is located in the Sahelian region where rainfall is low. Groundwater occurs mainly in fractures in the basement rock. Small perched aquifers are sometimes found in overlying alluvium.  
+
*The eastern outcrop (Adrar des Iforas) is located in the Sahelian region where rainfall is low. Groundwater occurs mainly in fractures in the basement rock. Small perched aquifers are sometimes found in overlying alluvium.
  
 
Average borehole yields range from 4 to 6 m³/hour, depending on the lithology.  
 
Average borehole yields range from 4 to 6 m³/hour, depending on the lithology.  
  
The average transmissivity of the basement rocks is 7 m²/day, with a maximum of 350 m²/day and a minimum of <0.1 m²/day. Storage is generally around 10<sup>-4</sup>.  
+
The average transmissivity of the basement rocks is 7 m²/day, with a maximum of 350 m²/day and a minimum of <0.1 m²/day. Storage is generally around 10-4.  
  
 
The thickness of the productive zone varies from 12 to 51 m. Rest water levels are generally between 8 and 20 m below ground level, but can be as deep as 70 m. Boreholes are typically drilled to depths of 40-80 m, but can exceed 200 m in some areas.  
 
The thickness of the productive zone varies from 12 to 51 m. Rest water levels are generally between 8 and 20 m below ground level, but can be as deep as 70 m. Boreholes are typically drilled to depths of 40-80 m, but can exceed 200 m in some areas.  
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==References==
 
==References==
Many of the references below, and others relating to the hydrogeology of Mali, can be found in the [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=listResults&title_search=&author_search=&category_search=&country_search=ML&placeboolean=AND&singlecountry=1 Africa Groundwater Literature Archive]
+
Many of the references below, and others relating to the hydrogeology of Mali, can be found in the [http://www.bgs.ac.uk/africagroundwateratlas/searchResults.cfm?title_search=&author_search=&category_search=&country_search=ML&placeboolean=AND&singlecountry=1 Africa Groundwater Literature Archive]
  
 
===Key Geology References===
 
===Key Geology References===

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