Editing Hydrogeology of Togo

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There are three main hydrogeological environments in Togo:
 
There are three main hydrogeological environments in Togo:
  
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*Basement aquifers, including the West African Craton and Dahomeyides Chain
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*The Volta Basin aquifer
 
*Coastal Sedimentary aquifers
 
*Coastal Sedimentary aquifers
*The Volta Basin aquifer
 
*Basement aquifers, including the West African Craton and Dahomeyides Chain
 
  
 
The basement aquifers and Volta Basin aquifer represent 94% of the area of Togo. The basement is predominantly composed of low permeability granite, gneiss and migmatite and groundwater occurs in the weathered horizon or fractures. The Volta Basin comprises sandstone and quartzite while the Coastal Basin is a layered sedimentary sequence that dips gently from north to south.  
 
The basement aquifers and Volta Basin aquifer represent 94% of the area of Togo. The basement is predominantly composed of low permeability granite, gneiss and migmatite and groundwater occurs in the weathered horizon or fractures. The Volta Basin comprises sandstone and quartzite while the Coastal Basin is a layered sedimentary sequence that dips gently from north to south.  
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====Sedimentary Aquifers - Intergranular and Fracture Flow====
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====Sedimentary - Intergranular//Fracture ====
  
The coastal basin sedimentary aquifer (Keta Basin) is a multi-layered aquifer, which generally has high productivity and groundwater potential. Intergranular flow dominates in the shallower systems, but fracture flow is important at depth. The coastal basin contains the following aquifers in a layered system:
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The coastal basin sedimentary aquifer (Keta Basin) is a multi-layered aquifer. Intergranular flow dominates in the shallower systems, but fracture flow is important at depth. The coastal basin contains the following aquifers in a layered system:
  
 
*Quaternary Sand Aquifer
 
*Quaternary Sand Aquifer
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*Maestrichtian Aquifer
 
*Maestrichtian Aquifer
  
These aquifers are separated by thick, low permeability aquicludes.
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These aquifers are separated by thick aquicludes.
  
  
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| Quaternary Sand Aquifer
 
| Quaternary Sand Aquifer
 
||This forms a 2-3km wide aquifer along the coast and is typically exploited by wells for domestic use. Flow is predominantly intergranular and the aquifer is unconfined.  
 
||This forms a 2-3km wide aquifer along the coast and is typically exploited by wells for domestic use. Flow is predominantly intergranular and the aquifer is unconfined.  
The properties of this aquifer are largely unknown. The aquifer thickness varies from 10 - 30 m and the water table depth varies from 0.5 - 3 m.  
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The properties of this aquifer are largely unknown, however the aquifer thickness varies between 10 and 30 m and the water table depth varies between 0.5 and 3 m.  
 
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|-
 
|-
 
| Continental Terminal Aquifer
 
| Continental Terminal Aquifer
|| This is the most heavily exploited aquifer in the coastal basin, providing the drinking water supply for the city of Lome. Flow is predominantly intergranular and the aquifer is unconfined. Transmissivity is typically on the order of 10-³ – 10<sup>-2</sup> m²/s. Storage is typically 1-8%. Borehole yields generally vary between 10 and 200 m³/h.
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|| This is the most heavily exploited aquifer in the basin, providing the drinking water supply for the city of Lome. Flow is predominantly intergranular and the aquifer is unconfined. Transmissivity is typically on the order of 10-³ – 10-2 m²/s. Storage is typically 1-8%. Borehole yields generally vary between 10 and 200 m³/h.
  
 
The aquifer thickness varies between 20 and 80 m, the water table depth varies between 1.5 and 50 m, and boreholes are generally drilled to depths of 10-60 m.
 
The aquifer thickness varies between 20 and 80 m, the water table depth varies between 1.5 and 50 m, and boreholes are generally drilled to depths of 10-60 m.
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*pH values vary between 6.7 and 7.6
 
*pH values vary between 6.7 and 7.6
  
||Recharge occurs in the north of the basin by infiltration through the Continental Terminal aquifer.
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|| Recharge occurs in the north of the basin by infiltration through the Continental Terminal aquifer.
  
 
|-
 
|-
|Maestrichtian Aquifer
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| Maestrichtian Aquifer
||The Maestrichtian Aquifer comprises sandstone (and sometimes sandy limestone) and flow is predominantly intergranular. It is mainly exploited in the northern part of the basin where it is more easily accessible, although it remains confined across the basin. The lateral extent of this aquifer towards the south of the basin is currently unknown due to the significant depth of the sediments.  
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|| The Maestrichtian Aquifer comprises sandstone (and sometimes sandy limestone) and flow is predominantly intergranular. It is mainly exploited in the northern part of the basin where it is more easily accessible, although it remains confined across the basin. The lateral extent of this aquifer towards the south of the basin is currently unknown due to the significant depth of the sediments.  
  
Transmissivity is typically on the order of 10<sup>-3</sup> – 10<sup>-2</sup> m²/s. Storage is typically 1-3%. Borehole yields generally vary between 15 and 140 m³/h. The aquifer thickness varies between 5 and 25 m and boreholes are generally drilled to depths of 80-150 m (these would need to be significantly deeper in the southern part of the basin).
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Transmissivity is typically on the order of 10-3 – 10-2 m²/s. Storage is typically 1-3%. Borehole yields generally vary between 15 and 140 m³/h. The aquifer thickness varies between 5 and 25 m and boreholes are generally drilled to depths of 80-150 m (these would need to be significantly deeper in the southern part of the basin).
  
 
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|}
 
|}
  
====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
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====Basement Aquifers====
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====Basement====
 
{| 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
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|West African Craton and Dahomeyides Chain
 
|West African Craton and Dahomeyides Chain
  
||The West African Craton (north of Dapaong) and the Dahomeyides Chain are the principal groundwater-bearing formations of the basement. However, these are generally discontinuous aquifers, either related to fracturing or alteration/weathering of the bedrock.
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|| The West African Craton (north of Dapaong) and the Dahomeyides Chain are the principal groundwater-bearing formations of the basement. However, these are generally discontinuous aquifers, either related to fracturing or alteration/weathering of the bedrock.
  
 
The properties of the basement aquifers are controlled by the frequency of fracturing, which varies depending on the nature of the rock, bedding, structural position and tectonic history. Harder rocks are generally more fractured, while schistose rocks are more deformable and therefore less fractured.
 
The properties of the basement aquifers are controlled by the frequency of fracturing, which varies depending on the nature of the rock, bedding, structural position and tectonic history. Harder rocks are generally more fractured, while schistose rocks are more deformable and therefore less fractured.

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