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[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Additional resources | Resource pages ]] >> Overview of Groundwater in Africa


[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> Overview of Groundwater in Africa
Please cite page as: Africa Groundwater Atlas. 2019. Overview of Groundwater in Africa. British Geological Survey. Accessed [date you accessed the information]. ''Weblink''.




Groundwater is an invaluable resource in Africa. Groundwater provides safe and reliable source drinking water for hundreds of millions of people across the continent; and supports food production and economic development through irrigation and livestock watering.
==Groundwater in Africa==


Groundwater has many advantages as a source of safe, sustainable water in Africa. It is particularly suited to regions with large rural populations, where demand for water is dispersed across large areas. The main advantages and limitations of groundwater as a water resource are summarised below.


{|
====Advantages of groundwater as a water resource in Africa====
|-
|
*Groundwater can be found in most environments, at least enough to provide small domestic supplies. It is therefore usually available close to the point of demand.
|
*Groundwater usually has excellent natural water quality and is usually suitable for potable use with no prior treatment.
[[File:EthiopiaHandPump.png | left |300px]]
*Groundwater is naturally more protected from contamination than surface water/
*Groundwater provides large volumes of natural water storage. Seasonal variations in amount or quality aren't usually significant, so that groundwater is more drought resistant than surface waters.
*Groundwater lends itself well to principles of community management. It can be developed incrementally, often at relatively low cost/initial capital investment.


[[File:Irrigation.png | right |300px]]
====Limitations of groundwater as a water resource in Africa====


*In some hydrogeological environments, considerable investment is needed to locate and develop suitable sites for groundwater abstraction - dug wells, drilled boreholes or improved springs.
*In some hydrogeological environments, there can be natural groundwater quality problems - such as iron, fluoride or arsenic.
*As human development increases, the threat of groundwater pollution increases, and there is a greater need for awareness of, and action on, groundwater and aquifer protection.
*Groundwater can be vulnerable to over-abstraction, particularly in low productivity aquifers and/or as water demand and the ability to abstract large volumes of water both grow. Long term changes in rainfall patterns can also impact on groundwater recharge and renewal.
*As overall water supply coverage increases, more hydrogeologically difficult areas can remain unserved, and they become more costly to develop.


|}
===Hydrogeological environments in Africa===


How and where groundwater occurs depends primarily on '''geology''', '''geomorphology/weathering''', and '''rainfall''' (both current and historic). The interaction between these three factors gives rise to complex hydrogeological environments, with countless variations in the quantity, quality, ease of access to and renewability of groundwater resources. Because the hydrogeology - how groundwater exists and behaves - is different in each environment, different methods are needed to find, abstract and manage groundwater. Successfully developing groundwater resources depends on a good understanding of the hydrogeological environment.


Groundwater has excellent natural microbiological quality, and generally has adequate chemical quality for most uses. However problems can arise from the chemistry of groundwater in some circumstances: for example, high sulphate from some types of weathered basement and mudstones; or excessive hardness in limestone aquifers or sandstones cemented with carbonate material. Minor and trace constituents, which make up about 1% of the solute content of natural groundwaters, can also sometimes lead to health problems or make the water unacceptable for human and animal consumption. For example, high fluoride in some volcanic aquifers; elevated iron and manganese where groundwaters are anoxic; high arsenic in some unconsolidated sediments; and a lack of iodine in aquifers far from the sea (MacDonald and Davies, 2001).
Africa is hugely diverse in its geology, climate and hydrology. As a result, the hydrogeology of Africa is also hugely variable. But at a continental scale, there are only four main types of '''hydrogeological environment''' (or '''aquifer type''') - shown in the map, below:


Groundwater is generally more resilient to short-term climate variability and less vulnerable to pollution than surface water sources. However, sustainable groundwater development requires a good understanding of the groundwater resource, in order to avoid overabstraction and environmental degradation. This will become more and more important in future, as pressure increases on Africa's groundwater resources because of growing population and increasing demands on water supplies - for domestic, agricultural (especially growing demand for irrigation) and industrial use.
*'''basement''' aquifers;
*'''volcanic''' aquifers;
*'''consolidated sedimentary''' aquifers (which can be dominated by either fracture and/or intergranular flow); and
*'''unconsolidated sedimentary''' aquifers.  


How and where groundwater occurs depends on many interacting factors. The most important of these are '''geology'''; '''geomorphology''' (including '''weathering'''); and '''climate''' (mainly '''rainfall''' and '''evapotranspiration'''). Spatial and temporal variations in these factors across Africa mean that hydrogeological environments are complex and variable, with very different aquifer properties and recharge. Understanding these factors, and how they interact, is necessary in order to properly characterise the groundwater resources in any one area.
A detailed description of these environments is in [https://nora.nerc.ac.uk/501047/ MacDonald and Davies (2001)]; and a summary is below.  


For many parts of Africa, there is a lack of information on groundwater. This may be because data aren't being collected - or haven't been in the past; or because data aren't easily avaialble or accessible. This makes it very difficult to assess the groundwater resources. It can lead to inappropriate groundwater development - such as over-abstraction, or groundwater contamination - which can have long term implications for groundwater availability and quality.
[[File:Africa_Hgcl_Envs.png|thumb| 400px|center| The main hydrogeological environments in Africa]]


However, there is also much work that has been done to address some of the key issues relating to groundwater resources in Africa. This section of the Atlas brings together available information to provide a continental-scale overview of [[Hydrogeological environments of Africa | '''the main aquifer groups (or hydrogeological environments) of Africa''']], as well as [[Recharge | recharge]] and [[Groundwater quality in Africa | groundwater quality in Africa]], among other issues. These pages provide general background and context for the more detailed information available in each [[Hydrogeology by country | country profile]].
====Basement aquifers====


There is more information on specific groundwater issues in these [[Additional resources | Resource Pages]]:
Crystalline basement rocks of Precambrian age underlie much of Africa. They form low productivity aquifers that provide small rural water supplies for tens, if not hundreds, of millions of people. Groundwater occurs where the rocks have been significantly weathered and/or in fracture zones, most of which are usually shallower than a few tens of metres depth. Borehole and well yields are generally low, but usually sufficient for rural demand.


'''Supporting information'''
<center>


:- [[Geography| Topography]]
<div><ul>


:- [[Geology  | Geology]]
<li style="display: inline-block;"> [[File:weathered basement.png| 300 px| thumb |left | Groundwater occurrence in a weathered basement aquifer]] </li>


:- [[Climate | Climate]]
</ul></div>


:- [[Land cover | Land cover]]
</center>


:- [[Soil | Soil]]
====Volcanic aquifers====


:- [[Surface water | Surface water]]
Volcanic rocks underlie a small but significant proportion of Africa's land area, and are an important water source for tens of millions of people, many of whom live in the drought stricken areas of the Horn of Africa. Groundwater in volcanic aquifers is found within palaeosoils and fractures between lava flows. Yields can be high, and springs are important sources in highland areas.


'''Hydrogeology'''
<center>


:- [[Hydrogeology Map | Hydrogeology map]]
<div><ul>


:- [[Aquifer properties | Aquifer properties]]
<li style="display: inline-block;"> [[File:volcanic_aquifers.png| 300 px| thumb| right| Groundwater occurrence in a volcanic rock aquifer]] </li>


:- [[Recharge | Recharge]]
</ul></div>


:- [[Groundwater quality in Africa | Groundwater quality]]
</center>


:- [[Long term groundwater datasets | Long term groundwater datasets]]
====Consolidated sedimentary aquifers====


'''Groundwater development'''
Consolidated sedimentary rocks underlie around one third of Africa's land area, and can form thick, highly productive aquifers. The most significant aquifers are sandstones and limestones, which can be exploited for large urban as well as rural supplies. Mudstones however, which account for about 65% of all sedimentary rocks in Africa, contain little groundwater, and careful study is required to develop groundwater supplies from mudstones.


:- [[Groundwater development techniques | Groundwater development techniques]]
<center>


:- [[Groundwater development best practice | Groundwater development best practices]]
<div><ul>


'''Groundwater use and management'''
<li style="display: inline-block;"> [[File:sedimentary_aquifers.png| 300 px| thumb| left | Groundwater occurrence in a consolidated sedimentary aquifer]] </li>


:- [[Groundwater use | Groundwater use]]
</ul></div>


</center>


====Unconsolidated sedimentary aquifers====


;Citations and Llnks
Unconsolidated sediments directly underlie much of Africa, and are extremely important for both rural and urban water supplies. Unconsolidated sands and gravels occur in most river valleys throughout Africa, and in many coastal areas. These deposits are often highly permeable and can store large volumes of groundwater at shallow depths, which is easy to exploit by traditional shallow wells and boreholes.


[https://www.agw-net.org/ Africa Groundwater Network]
<center>


[http://www.bgs.ac.uk/research/groundwater/international/africanGroundwater/maps.html Quantitative Groundwater Maps for Africa]
<div><ul>
 
<li style="display: inline-block;"> [[File:riverside_alluvium.png| 300 px| thumb|  right| Groundwater occurence in unconsolidated valley alluvium]] </li>


</ul></div>


MacDonald, A M, and Davies, J. 2000. [http://nora.nerc.ac.uk/501047/ A brief review of groundwater for rural water supply in sub-Saharan Africa]. British Geological Survey Report, WC/00/033, 30pp.
</center>


MacDonald, A M, Bonsor, H C, Ó Dochartaigh B É, and Taylor, R G. 2012. [https://iopscience.iop.org/article/10.1088/1748-9326/7/2/024009;jsessionid=18D8D7F69C3ACBEED0D7494F46850BD6.c1 Quantitative maps of groundwater resources in Africa]. Environmental Research Letters, Vol. 7, No. 2.
===More Information===


More information on geology and aquifer characteristics across Africa can be found in these [[Additional resources | resource pages]]: [[Geology | geology]]; [[Hydrogeology Map | hydrogeology map]]; and [[Aquifer properties| aquifer properties]]. More detailed information on aquifers in each country can be found in the [[Hydrogeology by country | country pages]].


Maps summarising the hydrogeology of Africa:
[https://www.bgs.ac.uk/research/groundwater/international/africanGroundwater/maps.html Quantitative Groundwater Maps for Africa]


MacDonald, A.M. & Davies, J. 2000. [https://nora.nerc.ac.uk/501047/ A brief review of groundwater for rural water supply in sub-Saharan Africa]. British Geological Survey Report WC/00/033.


MacDonald, A.M., Bonsor, H.C., Ó Dochartaigh, B.É. & Taylor, R.G. 2012. [https://iopscience.iop.org/article/10.1088/1748-9326/7/2/024009;jsessionid=18D8D7F69C3ACBEED0D7494F46850BD6.c1 Quantitative maps of groundwater resources in Africa]. Environmental Research Letters 7(2).


MacDonald, A.M. & Calow, R.C. 2009. [https://nora.nerc.ac.uk/8460/ Developing groundwater for secure water supplies in Africa]. Desalination 248, 546-556. doi: 10.1016/j.desal.2008.05.100






[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> Overview of Groundwater in Africa
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Additional resources | Resource pages ]] >> Overview of Groundwater in Africa


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Revision as of 10:01, 2 July 2019

Africa Groundwater Atlas >> Resource pages >> Overview of Groundwater in Africa 

Please cite page as: Africa Groundwater Atlas. 2019. Overview of Groundwater in Africa. British Geological Survey. Accessed [date you accessed the information]. Weblink.


Groundwater in Africa

Groundwater has many advantages as a source of safe, sustainable water in Africa. It is particularly suited to regions with large rural populations, where demand for water is dispersed across large areas. The main advantages and limitations of groundwater as a water resource are summarised below.

Advantages of groundwater as a water resource in Africa

  • Groundwater can be found in most environments, at least enough to provide small domestic supplies. It is therefore usually available close to the point of demand.
  • Groundwater usually has excellent natural water quality and is usually suitable for potable use with no prior treatment.
  • Groundwater is naturally more protected from contamination than surface water/
  • Groundwater provides large volumes of natural water storage. Seasonal variations in amount or quality aren't usually significant, so that groundwater is more drought resistant than surface waters.
  • Groundwater lends itself well to principles of community management. It can be developed incrementally, often at relatively low cost/initial capital investment.

Limitations of groundwater as a water resource in Africa

  • In some hydrogeological environments, considerable investment is needed to locate and develop suitable sites for groundwater abstraction - dug wells, drilled boreholes or improved springs.
  • In some hydrogeological environments, there can be natural groundwater quality problems - such as iron, fluoride or arsenic.
  • As human development increases, the threat of groundwater pollution increases, and there is a greater need for awareness of, and action on, groundwater and aquifer protection.
  • Groundwater can be vulnerable to over-abstraction, particularly in low productivity aquifers and/or as water demand and the ability to abstract large volumes of water both grow. Long term changes in rainfall patterns can also impact on groundwater recharge and renewal.
  • As overall water supply coverage increases, more hydrogeologically difficult areas can remain unserved, and they become more costly to develop.

Hydrogeological environments in Africa

How and where groundwater occurs depends primarily on geology, geomorphology/weathering, and rainfall (both current and historic). The interaction between these three factors gives rise to complex hydrogeological environments, with countless variations in the quantity, quality, ease of access to and renewability of groundwater resources. Because the hydrogeology - how groundwater exists and behaves - is different in each environment, different methods are needed to find, abstract and manage groundwater. Successfully developing groundwater resources depends on a good understanding of the hydrogeological environment.

Africa is hugely diverse in its geology, climate and hydrology. As a result, the hydrogeology of Africa is also hugely variable. But at a continental scale, there are only four main types of hydrogeological environment (or aquifer type) - shown in the map, below:

  • basement aquifers;
  • volcanic aquifers;
  • consolidated sedimentary aquifers (which can be dominated by either fracture and/or intergranular flow); and
  • unconsolidated sedimentary aquifers.

A detailed description of these environments is in MacDonald and Davies (2001); and a summary is below.

The main hydrogeological environments in Africa

Basement aquifers

Crystalline basement rocks of Precambrian age underlie much of Africa. They form low productivity aquifers that provide small rural water supplies for tens, if not hundreds, of millions of people. Groundwater occurs where the rocks have been significantly weathered and/or in fracture zones, most of which are usually shallower than a few tens of metres depth. Borehole and well yields are generally low, but usually sufficient for rural demand.

  • Groundwater occurrence in a weathered basement aquifer

Volcanic aquifers

Volcanic rocks underlie a small but significant proportion of Africa's land area, and are an important water source for tens of millions of people, many of whom live in the drought stricken areas of the Horn of Africa. Groundwater in volcanic aquifers is found within palaeosoils and fractures between lava flows. Yields can be high, and springs are important sources in highland areas.

  • Groundwater occurrence in a volcanic rock aquifer

Consolidated sedimentary aquifers

Consolidated sedimentary rocks underlie around one third of Africa's land area, and can form thick, highly productive aquifers. The most significant aquifers are sandstones and limestones, which can be exploited for large urban as well as rural supplies. Mudstones however, which account for about 65% of all sedimentary rocks in Africa, contain little groundwater, and careful study is required to develop groundwater supplies from mudstones.

  • Groundwater occurrence in a consolidated sedimentary aquifer

Unconsolidated sedimentary aquifers

Unconsolidated sediments directly underlie much of Africa, and are extremely important for both rural and urban water supplies. Unconsolidated sands and gravels occur in most river valleys throughout Africa, and in many coastal areas. These deposits are often highly permeable and can store large volumes of groundwater at shallow depths, which is easy to exploit by traditional shallow wells and boreholes.

  • Groundwater occurence in unconsolidated valley alluvium

More Information

More information on geology and aquifer characteristics across Africa can be found in these resource pages: geology; hydrogeology map; and aquifer properties. More detailed information on aquifers in each country can be found in the country pages.

Maps summarising the hydrogeology of Africa: Quantitative Groundwater Maps for Africa

MacDonald, A.M. & Davies, J. 2000. A brief review of groundwater for rural water supply in sub-Saharan Africa. British Geological Survey Report WC/00/033.

MacDonald, A.M., Bonsor, H.C., Ó Dochartaigh, B.É. & Taylor, R.G. 2012. Quantitative maps of groundwater resources in Africa. Environmental Research Letters 7(2).

MacDonald, A.M. & Calow, R.C. 2009. Developing groundwater for secure water supplies in Africa. Desalination 248, 546-556. doi: 10.1016/j.desal.2008.05.100


Africa Groundwater Atlas >> Resource pages >> Overview of Groundwater in Africa

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