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[[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_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].]].
  
====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)  
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|Continental Intercalaire (Lower Cretaceous)
'''Unconsolidated Aquifer - High to Low Productivity'''
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Unconsolidated Aquifer - High to Low Productivity
 
||The continental sedimentary deposits of the Continental Intercalaire in 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.  
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||Recharge is generally low.
 
||Recharge is generally low.
 
|-
 
|-
|Upper Cretaceous - Eocene (Tertiary)  
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|Upper Cretaceous - Eocene (Tertiary)
'''Unconsolidated Aquifer - Moderate to Low Productivity'''
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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  
'''Unconsolidated Aquifer - High productivity'''
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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====
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====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  
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|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)
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|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====
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====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====
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====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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