Editing Hydrogeology of Guinea

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  Do you have more information on the hydrogeology of Guinea? Please get in touch.
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'''Do you have more information on the hydrogeology of Guinea? Please get in touch.'''
  
 
[[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]]]
 
  
 
Present-day Guinea was historically on the periphery of the ancient Ghana, Mali, Songhai and Fulani empires between the 7th and 19th centuries, and its coastal zone was subject to the slave trade from the 16th century. It became a French colony in the 1890s, and the present-day national boundaries date from negotiations between France, Britain, Portugal and Liberia in the late 19th and early 20th centuries. Since independence in 1958 as the Republic of Guinea, the country has experienced periodic armed conflict, attempted and actual coups, civil and political unrest and contested elections. From the late 1980s, Guinea received a large influx of refugees as a result of wars in neighbouring Sierra Leone and Liberia, exacerbating internal tensions. The 2014 Ebola outbreak also affected Guinea significantly.
 
Present-day Guinea was historically on the periphery of the ancient Ghana, Mali, Songhai and Fulani empires between the 7th and 19th centuries, and its coastal zone was subject to the slave trade from the 16th century. It became a French colony in the 1890s, and the present-day national boundaries date from negotiations between France, Britain, Portugal and Liberia in the late 19th and early 20th centuries. Since independence in 1958 as the Republic of Guinea, the country has experienced periodic armed conflict, attempted and actual coups, civil and political unrest and contested elections. From the late 1980s, Guinea received a large influx of refugees as a result of wars in neighbouring Sierra Leone and Liberia, exacerbating internal tensions. The 2014 Ebola outbreak also affected Guinea significantly.
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====Unconsolidated====
 
====Unconsolidated====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Aquifer||Aquifer Productivity||Description
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|Aquifer||Description
 
|-
 
|-
|Dominantly Quaternary (minor Tertiary-Upper Cretaceous)
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|Dominantly Quaternary (minor Tertiary-Upper Cretaceous) - Low to High (Variable) Productivity
||Low to High (Variable) Productivity
 
 
||Aquifer properties are likely to be very variable, depending on the sediment lithology and thickness, Thick sands and gravels will have higher permeability and groundwater storage potential, but thin silts and fine-grained sands will have lower permeability and storage. Borehole yields can also vary seasonally in relation to rainfall.  
 
||Aquifer properties are likely to be very variable, depending on the sediment lithology and thickness, Thick sands and gravels will have higher permeability and groundwater storage potential, but thin silts and fine-grained sands will have lower permeability and storage. Borehole yields can also vary seasonally in relation to rainfall.  
  
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|}
 
|}
  
====Igneous====
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====Igneous - Unknown aquifer potential====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Aquifer||Aquifer Productivity||Description
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|Aquifer||Description
 
|-
 
|-
 
|Mesozoic Igneous Intrusive rocks  
 
|Mesozoic Igneous Intrusive rocks  
||Largely unknown
 
 
||Very little is known of the aquifer characteristics of these rocks. They are likely to be crystalline with very low intergranular porosity and permeability, so that groundwater potential will depend largely on the degree and type of  weathering and/or fracturing in the rocks. Groundwater is likely to be present mainly in the uppermost few tens of metres. Overall aquifer productivity is likely to be low.
 
||Very little is known of the aquifer characteristics of these rocks. They are likely to be crystalline with very low intergranular porosity and permeability, so that groundwater potential will depend largely on the degree and type of  weathering and/or fracturing in the rocks. Groundwater is likely to be present mainly in the uppermost few tens of metres. Overall aquifer productivity is likely to be low.
 
|}
 
|}
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====Sedimentary - Fracture flow====
 
====Sedimentary - Fracture flow====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Aquifer||Aquifer Productivity||Description
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|Aquifer||Description
 
|-
 
|-
|Silurian-Devonian
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|Silurian-Devonian - probably Low to Moderate Productivity
||probably Low to Moderate Productivity
 
 
||Silurian and Devonian rocks are dominated by fine-grained mudstones and siltstones, and are likely to form relatively low productivity aquifers, occasionally moderate productivity. Intergranular porosity and permeability are likely to be very low, and groundwater storage and flow are therefore expected to occur largely in fractures, probably in the uppermost few tens of metres of rock. A transmissivity value of 7 m<sup>2</sup>/day was quoted for Devonian rocks in United Nations (1988).
 
||Silurian and Devonian rocks are dominated by fine-grained mudstones and siltstones, and are likely to form relatively low productivity aquifers, occasionally moderate productivity. Intergranular porosity and permeability are likely to be very low, and groundwater storage and flow are therefore expected to occur largely in fractures, probably in the uppermost few tens of metres of rock. A transmissivity value of 7 m<sup>2</sup>/day was quoted for Devonian rocks in United Nations (1988).
 
|-
 
|-
|Cambrian-Ordovician
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|Cambrian-Ordovician - probably Moderate to High Productivity
||probably Moderate to High Productivity
 
 
||Cambrian and Ordovician rocks are dominated by sandstones, with some conglomerates in the Cambrian sequence. These are likely to be strongly indurated, so that intergranular porosity and permeability are likely to be low. Groundwater storage and flow are therefore expected to occur largely in fractures. A transmissivity value of 20 m<sup>2</sup>/day was quoted for Ordovician sandstones in United Nations (1988), but higher values may be more common.
 
||Cambrian and Ordovician rocks are dominated by sandstones, with some conglomerates in the Cambrian sequence. These are likely to be strongly indurated, so that intergranular porosity and permeability are likely to be low. Groundwater storage and flow are therefore expected to occur largely in fractures. A transmissivity value of 20 m<sup>2</sup>/day was quoted for Ordovician sandstones in United Nations (1988), but higher values may be more common.
 
|-
 
|-
|Precambrian: Upper Proterozoic - metasedimentary  
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|Precambrian: Upper Proterozoic - metasedimentary - probably Low to Moderate Productivity
||probably Low to Moderate Productivity
 
 
||Upper Proterozoic rocks are likely to have similar groundwater potential to the Silurian and Devonian rocks, probably forming mostly low productivity aquifers, in which groundwater flow and storage occurs largely in fractures in the uppermost few tens of metres of the rock. If fractures are particularly well developed, the aquifers may have moderate productivity.  
 
||Upper Proterozoic rocks are likely to have similar groundwater potential to the Silurian and Devonian rocks, probably forming mostly low productivity aquifers, in which groundwater flow and storage occurs largely in fractures in the uppermost few tens of metres of the rock. If fractures are particularly well developed, the aquifers may have moderate productivity.  
 
|}
 
|}
  
====Basement====
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====Basement - Low to Moderate Productivity====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Aquifer||Aquifer Productivity||Description
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|Aquifer||Description
 
|-
 
|-
 
|Precambrian (Archaean and Lower Proterozoic)
 
|Precambrian (Archaean and Lower Proterozoic)
||Low to Moderate Productivity
 
 
||Crystalline basement rocks have virtually no intergranular porosity and permeability, and groundwater flow and storage is entirely dependent on the nature and degree of weathering and/or fracturing of the rock. A typical pattern in basement rocks is 'pockets' of weathering forming weathered basins, typically a few tens of metres deep and a few tens or hundreds metres across, in which there is enhanced permeability and groundwater storage potential. Typically, these kind of weathered basins have enough permeability and groundwater storage capacity to supply a borehole hand pump supply.
 
||Crystalline basement rocks have virtually no intergranular porosity and permeability, and groundwater flow and storage is entirely dependent on the nature and degree of weathering and/or fracturing of the rock. A typical pattern in basement rocks is 'pockets' of weathering forming weathered basins, typically a few tens of metres deep and a few tens or hundreds metres across, in which there is enhanced permeability and groundwater storage potential. Typically, these kind of weathered basins have enough permeability and groundwater storage capacity to supply a borehole hand pump supply.
 
|}
 
|}
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===Groundwater status===
 
===Groundwater status===

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