Editing Hydrogeology of Niger

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||A heterogeneous aquifer of unconsolidated or loosely consolidated, interbedded sandy and clayey layers. Groundwater storage and flow occur preferentially in sandy layers. Individual sandy layers can be confined by overlying clayey layers, forming a multilayered aquifer that can be artesian in some cases.   
 
||A heterogeneous aquifer of unconsolidated or loosely consolidated, interbedded sandy and clayey layers. Groundwater storage and flow occur preferentially in sandy layers. Individual sandy layers can be confined by overlying clayey layers, forming a multilayered aquifer that can be artesian in some cases.   
  
A study in the Komadugu Yobe aquifer estimated the porosity of the Chad Formation, to between 50 and 100 m depth, at between 20 and 28%, and estimated a range of transmissivity values from 160 to 575 m<sup>2</sup>/day, with a mean transmissivity of 260 m<sup>2</sup>/day (Descloitres et al. 2013). Other transmissivity values obtained from test pumping in the Chad Formation are 3 m<sup>2</sup>/day, 100 m<sup>2</sup>/day and 250 m<sup>2</sup>/day (Descloitres et al. 2013), varying depending on whether the tested part of the aquifer was dominated by aeolian sand or by alluvial, often clayey sand.
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A study in the Komadugu Yobe aquifer estimated the porosity of the Chad Formation, to between 50 and 100 m depth, at between 20 and 28%, and estimated a range of transmissivity values from 160 to 575 m<sup>2</sup>/day, with a mean transmissivity of 260 m<sup>2</sup>/day (Descloitres et al. 2013). Other transmissivity values obtained from test pumping in the Chad Formation are 3, 100 and 250 m<sup>2</sup>/day (Descloitres et al. 2013), varying depending on whether the tested part of the aquifer was dominated by aeolian sand or by alluvial, often clayey sand.
  
 
Recharge is low, estimated as only a few millimetres per year (e.g. Leduc et al. 2000). Residence times for groundwater in the aquifer have been calculated at 1000 to 2000 years (Leduc et al 2000). Recharge occurs both directly from intermittent rains, and indirectly via leakage from rivers and, close to Lake Chad, sometimes also from the lake. Where the upper layers are dominated by sands, recharge is largely unrestricted, and so these layers are vulnerable to pollution. Recharge to deeper sandy layers can be restricted by overlying clayey layers, which also provide some protection from pollution.  
 
Recharge is low, estimated as only a few millimetres per year (e.g. Leduc et al. 2000). Residence times for groundwater in the aquifer have been calculated at 1000 to 2000 years (Leduc et al 2000). Recharge occurs both directly from intermittent rains, and indirectly via leakage from rivers and, close to Lake Chad, sometimes also from the lake. Where the upper layers are dominated by sands, recharge is largely unrestricted, and so these layers are vulnerable to pollution. Recharge to deeper sandy layers can be restricted by overlying clayey layers, which also provide some protection from pollution.  
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====Sedimentary - Intergranular Flow====
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====Consolidated Sedimentary - Intergranular Flow====
 
{| class = "wikitable"
 
{| class = "wikitable"
 
|Named Aquifers||Aquifer Productivity||Description||Water quality  
 
|Named Aquifers||Aquifer Productivity||Description||Water quality  
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|Named Aquifers||Aquifer Productivity||Description||Water quality  
 
|Named Aquifers||Aquifer Productivity||Description||Water quality  
 
|-
 
|-
|Precambrian Basement
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|Basement
 
||Low
 
||Low
 
||Discontinuous, low productivity aquifers controlled by the thickness and nature of weathering (regolith) and the presence of deeper fractures. Where weathered products are dominated by argillaceous material, yields are particularly low. Weathered Precambrian basement aquifers play an important role in the supply of water to some rural centres, particularly in Liptako and Damagaram-Mounio.
 
||Discontinuous, low productivity aquifers controlled by the thickness and nature of weathering (regolith) and the presence of deeper fractures. Where weathered products are dominated by argillaceous material, yields are particularly low. Weathered Precambrian basement aquifers play an important role in the supply of water to some rural centres, particularly in Liptako and Damagaram-Mounio.

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