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[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of the Republic of the Congo
 
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of the Republic of the Congo
  
  '''Lire cette page en français: [[Hydrogéologie de le République du Congo | Hydrogéologie de le République du Congo]]''' [[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]]]
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'''Most of the textual information on this page was taken from the chapter on the Congo in the report [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060005 ‘Groundwater in Eastern, Central and Southern Africa’] (UN 1989).  This information is outdated. If you have more recent information on the hydrogeology of the Republic of the Congo, please get in touch.'''  
 
 
'''Most of the textual information on this page was taken from the chapter on the Congo in the report [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060005 ‘Groundwater in Eastern, Central and Southern Africa’] (UN 1989).  If you have more recent information on the hydrogeology of the Republic of the Congo, please get in touch.'''  
 
  
  
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The geology map shows a simplified overview of the geology at a national scale (see [[Geology | the Geology resources page]] for more details).
 
The geology map shows a simplified overview of the geology at a national scale (see [[Geology | the Geology resources page]] for more details).
  
[https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html '''Download a GIS shapefile of the Republic of the Congo geology and hydrogeology map'''].
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[[File:RepublicOfCongo_Geology2.png | center | thumb| 500px | Geology of the Republic of the Congo 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]].]]
 
 
[[File:RepublicOfCongo_Geology3.png | center | thumb| 500px | Geology of the Republic of the Congo 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 Republic of the Congo geology and hydrogeology map].]]
 
  
 
{| class = "wikitable"
 
{| class = "wikitable"
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|
 
|
 
||Cenozoic
 
||Cenozoic
||Found in the coastal plain and the central Bateké plateau.  
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||Found in the coastal plain and the central Bateké plateaus.  
  
 
In the coastal plain, a series of sedimentary rocks rests on Lower Precambrian Mayombe series. From youngest to oldest, they include sandy to sandy-argillaceous rocks (50 to 200 m); sandy clays and argillaceous sands (up to 150 m); coarge grained ferruginous sands (up to 100 m); dolomitic sandstones and clays; and dolomitic limestones (60 to 400 m).  
 
In the coastal plain, a series of sedimentary rocks rests on Lower Precambrian Mayombe series. From youngest to oldest, they include sandy to sandy-argillaceous rocks (50 to 200 m); sandy clays and argillaceous sands (up to 150 m); coarge grained ferruginous sands (up to 100 m); dolomitic sandstones and clays; and dolomitic limestones (60 to 400 m).  
  
The Bateké plateau series comprises around 300 m of sandstones overlain by 40 to 90 m of sandy silts.  
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The Bateké plateaus series comprises around 300 m of sandstones overlain by 40 to 90 m of sandy silts.  
 
|-
 
|-
 
!colspan="4"| Mesozoic sedimentary
 
!colspan="4"| Mesozoic sedimentary
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This section provides a summary of the hydrogeology of the main aquifers in the Republic of the Congo. More information is available in the report [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060005 Groundwater in Eastern, Central and Southern Africa: Congo] (1989) (see References section, below).
 
This section provides a summary of the hydrogeology of the main aquifers in the Republic of the Congo. More information is available in the report [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060005 Groundwater in Eastern, Central and Southern Africa: Congo] (1989) (see References section, below).
  
The hydrogeology map shows a simplified overview of the type and productivity of the main aquifers at a national scale (see the [[Africa Groundwater Atlas Hydrogeology Maps | hydrogeology map]] resource page for more details).
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The hydrogeology map 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 Republic of the Congo geology and hydrogeology map'''].
 
  
 
Another map of water resources in the Republic of Congo and Gabon at 1:1,000,000 scale was published by [http://www.bgr.de/app/fishy/whymis/index.php?&type=country&id=COG BRGM/CIEH] (1982), with an [http://www.ircwash.org/node/31654 accompanying report].
 
Another map of water resources in the Republic of Congo and Gabon at 1:1,000,000 scale was published by [http://www.bgr.de/app/fishy/whymis/index.php?&type=country&id=COG BRGM/CIEH] (1982), with an [http://www.ircwash.org/node/31654 accompanying report].
  
[[File:RepublicOfCongo_Hydrogeology3.png | center | thumb| 500px | Hydrogeology of the Republic of the Congo at 1:5 million scale. For more information on how the map was developed see the [[Africa Groundwater Atlas Hydrogeology Maps | Hydrogeology map]] resource page. [https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html Download a GIS shapefile of the Republic of the Congo geology and hydrogeology map].]].
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[[File:RepublicOfCongo_Hydrogeology2.png | center | thumb| 500px | Hydrogeology of the Republic of the Congo at 1:5 million scale. For more information on how the map was developed see the [[Hydrogeology Map | Hydrogeology map]] resource page]].
  
  
 
====Unconsolidated====
 
====Unconsolidated====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality  
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|Named Aquifers||Period||General Description||Water quality  
 
|-
 
|-
 
|Congo Basin Alluvium
 
|Congo Basin Alluvium
||Moderate to High
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||Quaternary
 
||These deposits cover an immense area and are thought to be up to 400 m thick. They are likely to be relatively highly permeable and to store a large volume of groundwater.  
 
||These deposits cover an immense area and are thought to be up to 400 m thick. They are likely to be relatively highly permeable and to store a large volume of groundwater.  
 
||Thought to generally have a low mineral content and a pH of less than 6.5.
 
||Thought to generally have a low mineral content and a pH of less than 6.5.
 
|}
 
|}
  
==== Sedimentary - Intergranular/Fracture Flow====
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==== Sedimentary - Intergranular Flow====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality  
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|Named Aquifers||Period||General Description||Water quality  
 
|-
 
|-
 
|Coastal basin
 
|Coastal basin
||Moderate to High
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||Cenozoic
 
||A series of sands (variously clay-rich or argillaceous), clays, dolomitic sandstones and dolomitic limestones. Many potash, oil and water exploration boreholes have been drilled to depths of between 250 and 400 m. Recorded yields from borehole tests were generally between 10 and 20 m³/hour.  
 
||A series of sands (variously clay-rich or argillaceous), clays, dolomitic sandstones and dolomitic limestones. Many potash, oil and water exploration boreholes have been drilled to depths of between 250 and 400 m. Recorded yields from borehole tests were generally between 10 and 20 m³/hour.  
 
||Overall the groundwater has a low mineral content, below 250 mg/l, with a relatively low hardness and a pH of close to 7. However, chloride and sulphate can be high, varying between 2 and 80 mg/l, and there is relatively high salinity in tested boreholes at depths of 250 to 400 m, generally between 0.6 and 3.5 g/l (NaCl equivalent).  
 
||Overall the groundwater has a low mineral content, below 250 mg/l, with a relatively low hardness and a pH of close to 7. However, chloride and sulphate can be high, varying between 2 and 80 mg/l, and there is relatively high salinity in tested boreholes at depths of 250 to 400 m, generally between 0.6 and 3.5 g/l (NaCl equivalent).  
 
|-
 
|-
 
|Stanley Pool series
 
|Stanley Pool series
||
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||Cenozoic
 
||Located at Brazzaville, this is a dominantly sandstone series, sometimes marly or kaolinitic.
 
||Located at Brazzaville, this is a dominantly sandstone series, sometimes marly or kaolinitic.
 
||Thought to generally a low mineral content and a pH of less than 6.
 
||Thought to generally a low mineral content and a pH of less than 6.
 
|-
 
|-
 
|Bateké plateau series
 
|Bateké plateau series
||Moderate (occasionally Low)
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||Cenozoic
||A few shallow (e.g. 20 to 30 m) boreholes are used for water supply in some areas. One deep (300 m) borehole drilled in 1960 provided a yield of about 6 m³/hour for 20 to 25 m of drawdown (a specific capacity of about 6 to 7 m³/day/m). The highest permeabilities are thought to be in sandy series, with values of between about 5 and 60 m²/day.  
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||A few shallow (e.g. 20 to 30 m) boreholes are used for water supply in some areas. One deep (300 m) borehole drilled in 1960 provided a yield of abotu 6 m³/hour for 20 to 25 m of drawdown (a specific capacity of about 6 to 7 m³/day/m). The highest permeabilities are thought to be in sandy series, with values of between about 5 and 60 m²/day.  
  
 
Low productivity perched aquifers are known, from 3 to 70 m depth, which sometimes show small spring flows.
 
Low productivity perched aquifers are known, from 3 to 70 m depth, which sometimes show small spring flows.
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==== Sedimentary - Fracture Flow====
 
==== Sedimentary - Fracture Flow====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality  
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|Named Aquifers||Period||General Description||Water quality  
 
|-
 
|-
 
|Precambrian metasedimentary series: Inkisi; Mpioka; schist-limestone in Djoué valley; Bouenza and Louila  
 
|Precambrian metasedimentary series: Inkisi; Mpioka; schist-limestone in Djoué valley; Bouenza and Louila  
||Moderate to High
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||Upper Precambrian
 
||Drilling tests indicated moderate to high permeability. Borehole yields in similar formations in Gabon are between 0.5 and 24 m³/hour. A borehole at Loudima yielded 16 m³/hour with hardly any drawdown. Other boreholes between 20 and 70 m deep had rest water levels of between 6 and 35 m below ground level, and specific capacity values of 0.2 to 432 m³/day/m.
 
||Drilling tests indicated moderate to high permeability. Borehole yields in similar formations in Gabon are between 0.5 and 24 m³/hour. A borehole at Loudima yielded 16 m³/hour with hardly any drawdown. Other boreholes between 20 and 70 m deep had rest water levels of between 6 and 35 m below ground level, and specific capacity values of 0.2 to 432 m³/day/m.
 
||Groundwater in the schist-limestone formations has an average mineral content of 350 to 500 mg/l, and is of average hardness, with a pH of 7 or higher. Other formations, where tested, generally have a low mineral content and a pH of 6 to 6.5.
 
||Groundwater in the schist-limestone formations has an average mineral content of 350 to 500 mg/l, and is of average hardness, with a pH of 7 or higher. Other formations, where tested, generally have a low mineral content and a pH of 6 to 6.5.
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====Basement====
 
====Basement====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality  
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|Named Aquifers||Period||General Description||Water quality  
 
|-
 
|-
 
|Granite and gneiss, schists, quartzites
 
|Granite and gneiss, schists, quartzites
||Low
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||Middle and Lower Precambrian
 
||Generally low permeability and groundwater potential.  
 
||Generally low permeability and groundwater potential.  
 
||Typically low mineral content, with a pH of around 6.
 
||Typically low mineral content, with a pH of around 6.
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==References==
 
==References==
  
The following references provide more information on the geology and hydrogeology of the Republic of the Congo. They can also be accessed through the [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=listResults&title_search=&author_search=&category_search=&country_search=CG&placeboolean=AND&singlecountry=1 Africa Groundwater Literature Archive].
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The following references provide more information on the geology and hydrogeology of the Republic of the Congo. They can also be accessed through the [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=listResults&title_search=&author_search=&category_search=&country_search=CG&placeboolean=AND&singlecountry=1 Africa Groundwater Literature Archive]
  
 
CIEH/BRGM. 1982. [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA300018 Carte de Planification des Ressources en Eau du Gabon et du Congo; scale: 1 : 1 000 000]. Comité Interafricain d'Etudes Hydrauliques, Ouagadougou & Bureau de Recherches Géologiques et Minières (BRGM), Orléans
 
CIEH/BRGM. 1982. [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA300018 Carte de Planification des Ressources en Eau du Gabon et du Congo; scale: 1 : 1 000 000]. Comité Interafricain d'Etudes Hydrauliques, Ouagadougou & Bureau de Recherches Géologiques et Minières (BRGM), Orléans
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United Nations. 1989. [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060005  Groundwater in Eastern, Central and Southern Africa: Congo]. United Nations Department of Technical Cooperation for Development, Natural Resources/Water Series No.19
 
United Nations. 1989. [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060005  Groundwater in Eastern, Central and Southern Africa: Congo]. United Nations Department of Technical Cooperation for Development, Natural Resources/Water Series No.19
  
The reference list in the UN report (1989) provides other sources of information, although none are more recent than 1982.  
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The reference list in the UN report provides other sources of information, although none are more recent than 1982.  
  
  
Return to the index pages:
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==Return to the index pages==
[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]]  
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[[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of the Republic of the Congo
  
  

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