Editing Hydrogeology of Chad

Jump to navigation Jump to search

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.

This page supports semantic in-text annotations (e.g. "[[Is specified as::World Heritage Site]]") to build structured and queryable content provided by Semantic MediaWiki. For a comprehensive description on how to use annotations or the #ask parser function, please have a look at the getting started, in-text annotation, or inline queries help pages.

Latest revision Your text
Line 1: Line 1:
 
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Chad
 
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Chad
  
[[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]]]
+
'''The textual information on this page was taken from a number of reports, which are referenced at the bottom of this page. Some of this information is outdated. If you have more recent information on the hydrogeology of Chad, please get in touch.'''
 
 
 
 
With a history of agriculture, fishing and trading dating back thousands of years, Chad became independent from French colonisation in 1960. Civil war and military unrest occurred sporadically from then until the current president took office in 1990. For at least two decades, Chad has been significantly affected by the arrival of refugees from neighbouring countries, including Darfur in Sudan and the Central African Republic, and by people internally displaced by unrest within Chad. Chad is also involved in international anti-terrorism efforts to tackle Boko Haram and Al Qaida in the Islamic Maghreb.
 
 
 
Most of Chad’s population depends on subsistence arable and livestock agriculture. Most of the population lives in the more humid south; the central and northern parts of the country are much drier and support only a sparse population. Cotton used to dominate industry and export earnings, and remains a primary export, but an oil industry has developed since 2000, with pipelines carrying oil exports to the Atlantic coast. GDP grew from 2003 to 2014, but global oil price falls led to recession in 2016. Chad also has gold and uranium deposits, but development of these is still very limited.
 
 
 
Rainfall is highly variable both spatially and temporally across the country. Lake Chad is the major surface water resource, shared with neighbouring nations. Droughts in the 1970s and 80, combined with anthropogenic activity, reduced the area of Lake Chad to record low levels, placed huge stress on water resources, and increased dependence on groundwater. Most rural areas of Chad depend on groundwater for potable water supplies and often for livestock, and in the north, for small-scale irrigation, and groundwater is also an important resource in many cities.  
 
  
  
Line 15: Line 8:
 
'''Dr Kirsty Upton''' and '''Brighid Ó Dochartaigh''', British Geological Survey, UK
 
'''Dr Kirsty Upton''' and '''Brighid Ó Dochartaigh''', British Geological Survey, UK
  
'''Dr Imogen Bellwood-Howard''', Institute of Development Studies, UK
+
Please cite this page as: Upton & Ó Dochartaigh, 2016.
  
Please cite this page as: Upton, Ó Dochartaigh & Bellwood-Howard, 2018.
+
Bibliographic reference: Upton, K. & Ó Dochartaigh, B.É. 2016. Africa Groundwater Atlas: Hydrogeology of Chad. British Geological Survey. Accessed [date you accessed the information]. http://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Chad
 
 
Bibliographic reference: Upton, K., Ó Dochartaigh, B.É & Bellwood-Howard, I. 2018. Africa Groundwater Atlas: Hydrogeology of Chad. British Geological Survey. Accessed [date you accessed the information]. http://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Chad
 
  
 
==Terms and conditions==
 
==Terms and conditions==
Line 35: Line 26:
 
{| class = "wikitable"
 
{| class = "wikitable"
 
|-
 
|-
|Capital city || N'Djamena
+
|Estimated Population in 2013* || 12,825,314
 
|-
 
|-
|Region || Central Africa
+
|Rural Population (% of total) (2013)* || 77.8%
 
|-
 
|-
|Border countries || Niger, Libya, Egypt, Sudan, Central African Republic, Cameroon, Nigeria
+
|Total Surface Area* || 1,259,200 sq km
 
|-
 
|-
|Total surface area* || 2km<sup>2</sup>  (128,400,000 ha)
+
|Agricultural Land (% of total area) (2012)* || 39.7%
 
|-
 
|-
|Total population (2015)* || 14,037,000
+
|Capital City || N'Djamena
 
|-
 
|-
|Rural population (2015)* || 10,980,000 (78%)
+
|Region || Central Africa
 
|-
 
|-
|Urban population (2015)* || 3,057,000 (22%)
+
|Border Countries || Niger, Libya, Egypt, Sudan, Central African Republic, Cameroon, Nigeria
 
|-
 
|-
|UN Human Development Index (HDI) [highest = 1] (2014)*|| 0.3919
+
|Annual Freshwater Withdrawal (2013)* || 879.6 Million cubic metres
 +
|-
 +
|Annual Freshwater Withdrawal for Agriculture (2013)* || 76.4%
 +
|-
 +
|Annual Freshwater Withdrawal for Domestic Use (2013)* || 11.8%
 +
|-
 +
|Annual Freshwater Withdrawal for Industry (2013)* || 11.8%
 +
|-
 +
|Rural Population with Access to Improved Water Source (2012)* || 44.8%
 +
|-
 +
|Urban Population with Access to Improved Water Source (2012)* || 71.8%
 
|}
 
|}
  
<nowiki>*</nowiki> Source: [http://www.fao.org/nr/water/aquastat/data/query/index.html?lang=en FAO Aquastat]
+
<nowiki>*</nowiki> Source: World Bank
  
  
Line 94: Line 95:
 
|}
 
|}
  
===Water statistics===
 
  
{| class = "wikitable"
 
| || 2002 ||2005||2014||2015
 
|-
 
|Rural population with access to safe drinking water (%) || || ||  || 44.8
 
|-
 
|Urban population with access to safe drinking water (%) || || ||  || 71.8
 
|-
 
|Population affected by water related disease ||No data||No data||No data||No data
 
|-
 
|Total internal renewable water resources (cubic metres/inhabitant/year) || || ||1069||
 
|-
 
|Total exploitable water resources (Million cubic metres/year) || || ||  ||
 
|-
 
|Freshwater withdrawal as % of total renewable water resources || ||1.925|| ||
 
|-
 
|Total renewable groundwater (Million cubic metres/year) ||  || ||11,500 ||
 
|-
 
|Exploitable: Regular renewable groundwater (Million cubic metres/year) ||  || || ||
 
|-
 
|Groundwater produced internally (Million cubic metres/year) || || ||11,500  ||
 
|-
 
|Fresh groundwater withdrawal (primary and secondary) (Million cubic metres/year) ||No data|| No data || No data || No data
 
|-
 
|Groundwater: entering the country (total) (Million cubic metres/year) || || ||  ||
 
|-
 
|Groundwater: leaving the country to other countries (total) (Million cubic metres/year) || || ||  ||
 
|-
 
|Industrial water withdrawal (all water sources) (Million cubic metres/year) || || 103.7|| ||
 
|-
 
| Municipal water withdrawal (all water sources) (Million cubic metres/year)  || ||103.7 || ||
 
|-
 
|Agricultural water withdrawal (all water sources) (Million cubic metres/year) || ||672.2 || ||
 
|-
 
|Irrigation water withdrawal (all water sources) (Million cubic metres/year) || ||672.2 ||  ||
 
|-
 
|Irrigation water requirement (all water sources) (Million cubic metres/year) ||206 || ||  ||
 
|-
 
|Area of permanent crops (ha) || || ||35,000  ||
 
|-
 
|Cultivated land (arable and permanent crops) (ha) || || ||4,935,000  ||
 
|-
 
|Total area of country cultivated (%) || || ||3.843  ||
 
|-
 
|Area equipped for irrigation by groundwater (ha) ||6,000  || || ||
 
|-
 
|Area equipped for irrigation by mixed surface water and groundwater (ha) || No data || No data ||No data  || No data
 
|}
 
 
Source and more statistics at: [http://www.fao.org/nr/water/aquastat/data/query/index.html?lang=en FAO Aquastat].
 
  
 
==Geology==
 
==Geology==
  
This section provides a summary of the geology of Chad. More information is available in the report [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060033 ‘Groundwater in North and West Africa: Chad’] (1988) (see References section, below).
+
This section provides a summary of the geology of Chad. More information is available in the report [http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA060033 ‘Groundwater in North and West Africa: Chad’] (1988) (see References section, below).
  
 
The geology map shows a simplified version of the geology at a national scale (see [[Geology | the Geology resources page]] for more details).
 
The geology map shows a simplified version 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 Chad geology and hydrogeology map'''].
+
  [[File:Chad_Geology2.png | center | thumb| 500px | Geology of Chad at 1:5 million scale. Developed from USGS map (Persits et al. 2002). For more information on the map development and datasets see the [[Geology | geology resource page]]]]
 
+
'''Summary'''
  [[File:Chad_Geology3.png | center | thumb| 500px | Geology of Chad at 1:5 million scale. Developed from USGS map (Persits et al. 2002). 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 Chad geology and hydrogeology map].]]
 
  
'''Summary'''
+
The geology of Chad is dominated by the Lake Chad Basin, a sedimentary basin formed in the Mesozoic era and infilled with older Tertiary Continental Terminal sandstones and argillaceous sands, and younger Pliocene-Quaternary sandy/clayey deltaic and lacustrine deposits (Ngatcha et al. 2008, UNICEF 2010).
  
The geology of Chad is dominated by the Lake Chad Basin, a sedimentary basin that started to form in the Mesozoic era. It is infilled with, at depth, Tertiary age sandstones and argillaceous sands of the Continental Terminal; and above these, Pliocene-Quaternary age sandy/clayey deltaic and lacustrine sediments (Ngatcha et al. 2008, UNICEF 2010).
+
Smaller outcrops of unconsolidated Quaternary deposits, largely alluvium in river valleys, also occur in other parts of the country overlying bedrock.
  
Other, smaller outcrops of unconsolidated Quaternary sediments - mostly alluvium in river valleys - occur in other parts of the country, overlying bedrock.
+
To the north and east of the Lake Chad Basin are older rocks. These include small outcrops of Cretaceous continental and marine sedimentary rocks; Cretaceous rocks are also present at depth below the Lake Chad Basin and other parts of the country.  
  
Across the northern part of the country, to the north and east of the Lake Chad Basin, are older rocks, mostly Palaeozoic sedimentary rocks, largely of continental origin and dating from the Cambrian to the Jurassic. There are also small outcrops of Cretaceous age continental and marine sedimentary rocks. These Cretaceous and Palaezoic rocks are also present at depth in parts of central Chad, buried beneath Quaternary and Tertiary sediments in the Lake Chad Basin.
+
Palaeozoic sedimentary rocks crop out over a large part of northern Chad, largely of continental origin and dating from the Cambrian to the Jurassic. They are also present at depth in parts of central Chad.  
  
There are some outcrops of volcanic rocks, particularly in the northwest, forming the Tibesti masasif.
+
There are some areas of volcanic rocks, particularly in the northwest
  
Precambrian metamorphic and crystalline basement rocks crop out in two main areas: one in eastern Chad and one in the northwest.  
+
Precambrian metamorphic and crystalline basement rocks crop out in eastern Chad and in the northwestern part.  
  
  
Line 173: Line 123:
 
|Key Formations||Period||Lithology
 
|Key Formations||Period||Lithology
 
|-
 
|-
!colspan="4"|Quaternary-Pliocene unconsolidated sedimentary
+
!colspan="4"|Quaternary
 
|-
 
|-
|Undifferentiated
+
|Chad Formation
 
||Quaternary
 
||Quaternary
||Relatively small outcrops of undifferentiated unconsolidated Quaternary sediments occur across Chad, including alluvium in river valleys, and areas of aeolian sand dunes in the arid north.
+
||Quaternary and Pliocene-Quaternary deposits, known as the Chad Formation, occur across most of the Chad basin. They consist of lake-margin, alluvial fan and deltaic deposits, with lacustrine clay layers, that are present at depths of up to 500 m. The clays are most extensive near to the present day lake shore (Goni 2008). Lithology was controlled by the climate during deposition, with wet periods favouring the deposition of clays and diatomites; periods of alternating wet and dry seasons tending to produce sandy deltaic deposits; and dry periods favouring the formation of aeolian sand dunes. The deposits therefore range from pure sand to clayey sand, and include some kaolinitic clays. Abrupt changes in clay and sand content are common, and the sediments usually occur as overlapping lenses.  
|-
 
|Chad Formation
 
||Quaternary-Pliocene
 
||Quaternary and Pliocene-Quaternary sediments, known as the Chad Formation, occur across most of the Chad basin. They consist of unconsolidated sediments of lake-margin, alluvial fan and deltaic origin, with some interbedded lacustrine clays. The Chad Formation is up to 500 m thick in Chad. Lacustrine clays are most extensive near to the present day lake shore (Goni 2008).  
 
  
The sediment lithology was controlled by the climate during deposition, with wet periods favouring the deposition of clays and diatomites; periods of alternating wet and dry seasons tending to produce sandy deltaic deposits; and dry periods favouring the formation of aeolian sand dunes. The deposits therefore range from pure sand to clayey sand, and include some kaolinitic clays. Abrupt changes in clay and sand content are common, and the sediments usually occur as overlapping lenses.  
+
Smaller outcrops of Quaternary deposits occur in other parts of the country, including alluvium in river valleys, and areas of aeolian sand dunes in the arid north.  
 
|-
 
|-
!colspan="4"|Upper Mesozoic sedimentary
+
!colspan="4"|Tertiary
 
|-
 
|-
 
|Continental Terminal; also a small area of Eocene marine deposits in northern Chad
 
|Continental Terminal; also a small area of Eocene marine deposits in northern Chad
||Tertiary: Eocene, Oligo-Miocene, Neogene  
+
||Eocene, Oligo-Miocene, Neogene  
||The Oligo-Miocene to Neogene Continental Terminal Formation occurs across large parts of southern Chad, in the Lake Chad Basin. It consists of alternating sandstone, argillaceous sand and clay layers. They are generally at depths of 400 to 700 m, below the Quaternary-Pliocene Chad Formation. In some parts of the south and southeast of the Lake Chad Basin, the Continental Terminal rocks crop out at the ground surface, shown on the geology map.  
+
||The Oligo-Miocene to Neogene Continental Terminal formation occurs across large parts of southern Chad, in the Lake Chad Basin, and consists of alternating sandstone, argillaceous sand and clay layers. They are generally at depths of 400 to 700 m, covered by Quaternary and Pliocene deposits. In some parts of the south and southeast of the Lake Chad Basin, they crop out at the ground surface. The upper part of the series is a lacustrine sequence of Neogene age called the Chad Formation.
 
|-
 
|-
 
|
 
|
||Cretaceous
+
||Mesozoic (Permo-Triassic to Cretaceous)
||There are few outcrops of Cretaceous rocks at the ground surface in Chad, but they occur at depth in the Lake Chad Basin.
+
||There are few outcrops of Cretaceous rocks in Chad, but they occur at depth in the Lake Chad Basin.
  
The Lower Cretaceous is characterised by continental fluviatile and lacustrine clastic rocks, part of the Permo-Triassic to Lower Cretaceous age Continental Intercalaire Formation.  
+
The Lower Cretaceous is characterised by continental fluviatile and lacustrine clastic rocks, part of the Permo-Triassic to Lower Cretaceous Continental Intercalaire formation. The Upper Cretaceous includes marine to continental clastic rocks, including fossiliferous shales.  
 
 
The Upper Cretaceous includes marine to continental clastic rocks, including fossiliferous shales.  
 
 
|-
 
|-
!colspan="4"|Igneous Volcanic
+
!colspan="4"|Palaeozoic sedimentary
|-
 
|Mesozoic to Quaternary
 
||
 
||There are a few isolated small outcrops of igneous rockos in the east and south of the country, of which little is known. The largest outcrop of igneous rocks is in the Tibesti massif, which are thought to be dominantly Tertiary to Quaternary volcanic rocks, mainly lavas but also including some tephra and other volcaniclastic rocks (Permenter and Oppenheimer 2007).
 
|-
 
!colspan="4"|Palaeozoic to Lower Mesozoic sedimentary
 
 
|-
 
|-
 
|
 
|
||Cambro-Ordovician - Jurassic
+
||Cambro-Ordovician, Silurian, Devonian, Carboniferous
||Palaeozoic and Lower Mesozoic continental sandstone sequences crop out over a large part of northern Chad, and are known to be present at depth below younger deposits in the Lake Chad Basin in the centre of the country.  
+
||Palaeozoic continental sandstone sequences crop out over a large part of northern Chad, and are known to be present at depth below younger deposits in the Lake Chad Basin in the centre of the country.  
 +
 
 +
In the north, this includes the Kufra basin, with largely Cambrian to Carboniferous rocks, which is shared with Libya. Thick continental sandstones within the Kurfa basin form the Nubian formations, which are at least 1000 m and possibly up to 4000 m thick.
 +
 
 +
  
In the north, this includes the Kufra basin, with largely Cambrian to Carboniferous rocks, which is shared with Libya and the Sudan. Thick continental sandstones within the Kufra basin form the Nubian formations, which are at least 1000 m and possibly up to 4000 m thick.
 
 
|-
 
|-
 
!colspan="4"|Precambrian Basement
 
!colspan="4"|Precambrian Basement
Line 220: Line 161:
 
|-
 
|-
 
|}
 
|}
 +
  
 
==Hydrogeology==
 
==Hydrogeology==
  
This section provides a summary of the hydrogeology of the main aquifers in Chad. More information at a country-scale is available in the report [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060033 ‘Groundwater in North and West Africa: Chad’] (1988) (see References section, below).  
+
This section provides a summary of the hydrogeology of the main aquifers in Chad. More information for the whole country is available in the report [http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA060033 ‘Groundwater in North and West Africa: Chad’] (1988) (see References section, below). For areas where the ResEau program has produced hydrogeological maps and descriptions, these provide the most detailed available information on groundwater and hydrogeology (see below).
 
 
For areas where the [http://www.unitar.org/pillars/2030-agenda-support/reseau-project '''ResEau'''] program has produced hydrogeological maps and descriptions, these provide the most detailed available information on groundwater and hydrogeology (see below).
 
 
 
The hydrogeology map shown on this page shows a simplified version 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).  
 
  
[https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html '''Download a GIS shapefile of the Chad geology and hydrogeology map'''].
+
The hydrogeology map shown on this page shows a simplified version of the type and productivity of the main aquifers at a national scale (see the [[Hydrogeology Map | hydrogeology Map]] resource page for more details).  
  
 
===Other hydrogeological maps ===
 
===Other hydrogeological maps ===
Line 237: Line 175:
 
* A hydrogeological map at 1:500,000 scale was published in 1969 by BRGM and a scanned copy can be viewed on the [http://www.bgr.de/app/fishy/whymis/index.php?&type=country&id=TCD WHYMAP] site.  
 
* A hydrogeological map at 1:500,000 scale was published in 1969 by BRGM and a scanned copy can be viewed on the [http://www.bgr.de/app/fishy/whymis/index.php?&type=country&id=TCD WHYMAP] site.  
  
* [http://geoportal.reseau-tchad.org '''ResEau''']
+
* '''ResEau'''
  
The ongoing [https://reseau-tchad.org/ ResEau] program is collecting detailed new hydrogeological information and producing new hydrogeological maps for Chad. Eventually, the whole country will be covered at 1:500,000 scale, and already these scale maps are available for the north and east of the country. More detailed hydrogeological maps at 1:200,000 scale are being produced for specific important areas.  
+
The ongoing [https://reseau-tchad.org/ ResEau] program is collecting extensive new hydrogeological information and producing new hydrogeological maps for Chad. Eventually, the whole country will be covered at 1:500,000 scale, and already these scale maps are available for the north and east of the country. More detailed hydrogeological maps at 1:200,000 scale are being produced for specific important areas. Digital versions of these maps can be viewed in the ResEau [https://reseau-tchad.org/index.php?pId=8 geoportal]. Pdf versions of the maps, with accompanying hydrogeological descriptions, can be freely downloaded from [https://reseau-tchad.org/index.php?pId=10 ResEau]. These maps and descriptions are the key source for detailed information on the hydrogeology of Chad.
  
Digital versions of these maps can be viewed in the [http://geoportal.reseau-tchad.org '''ResEau geoportal''']. Pdf versions of the maps, with accompanying hydrogeological descriptions, can be freely downloaded from [https://reseau-tchad.org ResEau].
 
  
A detailed [https://reseau-tchad.org/upload/Documents/Publication/ResEau1-Synthese-hydrogeologique-Nord&Est-Tchad.pdf synthesis of the hydrogeology of the north and east of Chad] is available as a report (in French).
+
[[File:Chad_Hydrogeology2.png| center | thumb| 500px | Hydrogeology of Chad at 1:5million scale. For more information on how the map was developed see the [[Hydrogeology Map | hydrogeology map]] resource page]]
  
These maps and descriptions are the key source for information on the hydrogeology of Chad.
 
  
 +
The information below provides a summary of the hydrogeology of Chad at a national scale.
  
[[File:Chad_Hydrogeology3.png| center | thumb| 500px | Hydrogeology of Chad at 1:5million 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 Chad geology and hydrogeology map].]]
+
The Lake Chad Basin in southern Chad is one of the largest sedimentary groundwater basins in Africa. It includes three main aquifers: an upper, unconsolidated Quaternary/Pliocene aquifer of lacustrine and deltaic deposits; the underlying Tertiary Continental Terminal sequence; and a lower aquifer of Cretaceous age, which is less well understood.  
  
 +
Other aquifers in Chad are less well studied. They include unconsolidated Quaternary valley alluvium and other deposits; Palaeozoic sedimentary rocks in the north, part of the Nubian Sandstone Aquifer System; Precambrian basement rocks; and smaller areas of volcanic rocks.
  
The information below provides a summary of the hydrogeology of Chad at a national scale.
 
 
The Lake Chad Basin in southern Chad is one of the largest sedimentary groundwater basins in Africa. It includes three main aquifers: an upper, unconsolidated Quaternary/Pliocene aquifer of lacustrine and deltaic deposits (the Chad Formation); a Tertiary sequence underlying this (the Continental Terminal formation); and a basal aquifer of Cretaceous age, which is less well understood.
 
 
Away from the Lake Chad Basin, other aquifers in Chad are not as well studied or understood. Other aquifers include Quaternary valley alluvium and other unconsolidated sediments; Palaeozoic sedimentary rocks in the north, part of the Nubian Sandstone Aquifer System; Precambrian basement rocks; and smaller areas of volcanic rocks.
 
  
 
====Unconsolidated====
 
====Unconsolidated====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality  
+
|Named Aquifers||Period||General Description||Water quality  
 
|-
 
|-
 
|Alluvium in river valleys; aeolian sand in the north
 
|Alluvium in river valleys; aeolian sand in the north
||Usually Moderate to High
+
||Quaternary
 
||Outcrops of Quaternary alluvium in major river valleys are likely to be permeable and to have high groundwater storage potential, and shallow water tables. Where they are hydraulic connection with groundwater in underlying bedrock, such as weathered Precambrian basement, they can contribute significantly to local groundwater potential.
 
||Outcrops of Quaternary alluvium in major river valleys are likely to be permeable and to have high groundwater storage potential, and shallow water tables. Where they are hydraulic connection with groundwater in underlying bedrock, such as weathered Precambrian basement, they can contribute significantly to local groundwater potential.
 
||
 
||
 +
|}
 +
 +
====Sedimentary - Intergranular Flow====
 +
{| class = "wikitable"
 +
|Named Aquifers||Period||General Description||Water quality
 
|-
 
|-
|Chad Formation: Quaternary (to Pliocene) - upper part of the '''Lake Chad Basin Aquifer'''
+
|Chad Formation of the Lake Chad Basin
||High
+
||Pliocene-Quaternary
||The Pliocene-Quaternary Chad Formation aquifer within the Lake Chad Basin is dominated by permeable sands that are present at depths of up to 500 m; the top surface of the aquifer varies from 250 to 350 m. Clays are most extensive near to the present day lake shore (Goni 2008). The upper part of the aquifer is often unconfined but in some places semi-confined to confined by clay layers (Goni 2008), and in its shallowest zones is in direct hydraulic contact with the Logone-Chari river system and with Lake Chad. Parts of the lower aquifer are confined by clay layers, and under artesian pressure. Sub-aquifers are identified within the overall basin, including the Kanem, Koros and Chari-Baguirmi areas. Borehole yields of 2.5 litres/second (l/s) have been recorded (United Nations 1988), but it is likely that much higher potential yields are possible.  
+
||The Pliocene-Quaternary Chad Formation aquifer within the Lake Chad Basin are dominated by permeable sands that are present at depths of up to 500 m; the top surface of the aquifer varies from 250 to 350 m. Clays are most extensive near to the present day lake shore (Goni 2008). The upper part of the aquifer is often unconfined but in some places semi-confined to confined by clay layers (Goni 2008), and in its shallowest zones is in direct hydraulic contact with the Logone-Chari river system and with Lake Chad. Parts of the lower aquifer are confined by clay layers, and under artesian pressure. Sub-aquifers are identified within the overall basin, including the Kanem, Koros and Chari-Baguirmi areas. Borehole yields of 2.5 litres/second (l/s) have been recorded (United Nations 1988), but it is likely that much higher potential yields are possible.  
  
 
Isotopic studies have highlighted recharge zones to the shallow aquifer in areas of higher elevation and in exposed sand dune areas; as well as infiltration from rivers Lake Chad and wetlands (GWP 2013). In the northern part, in Kanem region, studies have also show high recharge from the slopes of the mountain areas to the north.
 
Isotopic studies have highlighted recharge zones to the shallow aquifer in areas of higher elevation and in exposed sand dune areas; as well as infiltration from rivers Lake Chad and wetlands (GWP 2013). In the northern part, in Kanem region, studies have also show high recharge from the slopes of the mountain areas to the north.
 
   
 
   
In the centre of the basin, groundwater levels are typically deepest - often more than 25 m below ground level - although it is not clear whether these relate to the Chad Formation or to the deeper Continental Terminal aquifer (see below). They tend to shallow towards the west of the basin, to between 10 and 25 m deep; and even more towards the southern edge of the basin, often to less than 5 m deep (UNICEF 2010).
+
In the centre of the basin, groundwater levels are typically deepest - often more than 25 m below ground level - although it is not clear whether these relate to the Quaternary or to the deeper Continental Terminal aquifer (see below). They tend to shallow towards the west of the basin, to between 10 and 25 m deep; and even more towards the southern edge of the basin, often to less than 5 m deep (UNICEF 2010).
  
 
Groundwater is abstracted for domestic use and livestock watering through hand dug wells (in the shallow aquifer) and boreholes.  
 
Groundwater is abstracted for domestic use and livestock watering through hand dug wells (in the shallow aquifer) and boreholes.  
  
||In the Chad Formation aquifer there are areas of high nitrate concentrations linked to agriculture discharges and faecal contamination. High fluoride concentrations are also seen. Groundwater in parts of the northern Kanem region contains high concentrations of sodium carbonates and sodium sulphates.
+
||In the Lake Chad basin Quaternary aquifer there are high nitrate concentrations linked to agriculture discharges and faecal contamination. High fluoride concentrations are also seen. Groundwater in parts of the northern Kanem region contains high concentrations of sodium carbonates and sodium sulphates.
 
|}
 
|}
  
====Sedimentary - Intergranular Flow====
+
==== Sedimentary - Intergranular & Fracture Flow====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality  
+
|Named Aquifers||Period||General Description||Water quality  
 
|-
 
|-
|Continental Terminal: Tertiary - lower part of the '''Lake Chad Basin Aquifer'''
+
|Continental Terminal of the Lake Chad Basin
||Moderate to High
+
||Tertiary
||The alternating sandstones and clay rich bands of the Continental Terminal underlie the Pliocene-Quaternary Chad Formation; together they form the Lake Chad Basin Aquifer. The Continental Terminal lies at depths of between approximately 100 to 200 m up to 400 to 600 m. It is artesian, confined by overlying clay bands. Average borehole yields are high, given as 27.5 l/s (United Nations 1988).  
+
||The alternating sandstones and clay rich bands of the Continental Terminal underlie the Quaternary aquifer of the Lake Chad Basin, at depths of between approximately 100 to 200 m up to 400 to 600 m. It is artesian, confined by overlying clay bands. Average borehole yields are high, given as 27.5 l/s (United Nations 1988).  
  
 
Isotopic studies suggest that groundwater in the Continental Terminal aquifer in the Lake Chad Basin is at least 20,000 years old and is not replenished by modern recharge (GWP 2013).  
 
Isotopic studies suggest that groundwater in the Continental Terminal aquifer in the Lake Chad Basin is at least 20,000 years old and is not replenished by modern recharge (GWP 2013).  
Line 291: Line 229:
 
Groundwater is abstracted for drinking water in rural and urban areas, but extraction costs are considerable.  
 
Groundwater is abstracted for drinking water in rural and urban areas, but extraction costs are considerable.  
 
||High fluoride concentrations in groundwater are seen.
 
||High fluoride concentrations in groundwater are seen.
|}
 
 
==== Sedimentary - Intergranular & Fracture Flow====
 
{| class = "wikitable"
 
|Named Aquifers||Aquifer Productivity||General Description||Water quality
 
 
|-
 
|-
|Continental Intercalaire: Cretaceous
+
|Continental Intercalaire
||Unknown
+
||Permo-Triassic to lower Cretaceous
 
||This aquifer occurs at depth in the Lake Chad Basin in southern and central Chad. Relatively little is known of its properties in Chad.  
 
||This aquifer occurs at depth in the Lake Chad Basin in southern and central Chad. Relatively little is known of its properties in Chad.  
 
||
 
||
 
|-
 
|-
|Nubian Sandstone: Palaeozoic to Mesozoic
+
|Nubian Sandstone  
||Moderate to High
+
||Mesozoic - Palaeozoic
 
||The Nubian Sandstone aquifer in the Kufra basin is at least 1000 m and possibly up to 4000 m thick, and is dominated by well-cemented sandstones, with intercalations of shales and clays. Groundwater flow is largely through fractures but also by intergranular flow. The Nubian Sandstone aquifer system as a whole, which extends across much of north Africa, forms a productive aquifer which contains huge volumes of largely fossil groundwater. Little specific investigation has been done on the aquifer in Chad.  
 
||The Nubian Sandstone aquifer in the Kufra basin is at least 1000 m and possibly up to 4000 m thick, and is dominated by well-cemented sandstones, with intercalations of shales and clays. Groundwater flow is largely through fractures but also by intergranular flow. The Nubian Sandstone aquifer system as a whole, which extends across much of north Africa, forms a productive aquifer which contains huge volumes of largely fossil groundwater. Little specific investigation has been done on the aquifer in Chad.  
 
||Groundwaters vary from fresh to slightly brackish, with salinity ranges from 240 to 1300 ppm. High concentrations of ions including sodium, chloride, and sulphate reflect the leaching and dissolution processes of gypsiferous shales and clay, in addition to long groundwater residence times.
 
||Groundwaters vary from fresh to slightly brackish, with salinity ranges from 240 to 1300 ppm. High concentrations of ions including sodium, chloride, and sulphate reflect the leaching and dissolution processes of gypsiferous shales and clay, in addition to long groundwater residence times.
 
|}
 
|}
  
====Igneous (mostly Volcanic)====
 
{| class = "wikitable"
 
|Named Aquifers||Aquifer Productivity||General Description||Water quality
 
|-
 
|
 
||Probably Low to Moderate
 
||Little is known about the aquifer properties of volcanic or other igneous rock aquifers in Chad.
 
||
 
|}
 
  
 
====Basement====
 
====Basement====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality  
+
|Named Aquifers||Period||General Description||Water quality  
 
|-
 
|-
 
|Weathered basement, often in hydraulic continuity with overlying Quaternary alluvial sands
 
|Weathered basement, often in hydraulic continuity with overlying Quaternary alluvial sands
||Low
+
||Precambrian
 
||In deep valleys in the granitic massifs, the upper parts of the Precambrian rocks can be heavily weathered. These weathered basins form low to moderate productivity aquifers, especially where they are in hydraulic continuity with overlying permeable Quaternary sands, which supply additional groundwater storage.  
 
||In deep valleys in the granitic massifs, the upper parts of the Precambrian rocks can be heavily weathered. These weathered basins form low to moderate productivity aquifers, especially where they are in hydraulic continuity with overlying permeable Quaternary sands, which supply additional groundwater storage.  
 
||  
 
||  
Line 331: Line 255:
  
 
The Lake Chad Basin aquifer has been widely studied and it is clear that it is highly sensitive to climatic changes (GWP 2013). Recharge to the aquifer has decreased in recent years, mainly due to drought, but also related to management decisions in upstream regions. Because recharge is derived from surface water (river and lake) infiltration as well as from direct rainfall infiltration, the decline in river flows and inflow to the lake (of nearly 50% since the 1960s) has had significant impact on groundwater recharge (GWP 2013).
 
The Lake Chad Basin aquifer has been widely studied and it is clear that it is highly sensitive to climatic changes (GWP 2013). Recharge to the aquifer has decreased in recent years, mainly due to drought, but also related to management decisions in upstream regions. Because recharge is derived from surface water (river and lake) infiltration as well as from direct rainfall infiltration, the decline in river flows and inflow to the lake (of nearly 50% since the 1960s) has had significant impact on groundwater recharge (GWP 2013).
 
A recent project by BGR found that point source nitrate pollution of groundwater was a concern around boreholes where livestock are watered in the Lake Chad area, with groundwater nitrate values up to 350 mg/l measured in some boreholes. This is thought to be caused by direct contamination of abstraction bucket ropes, and therefore of boreholes, by livestock faeces, rather than the infiltration  of nitrate into groundwater (Vassolo et al 2009).
 
  
 
==Groundwater use and management==
 
==Groundwater use and management==
Line 338: Line 260:
 
=== Groundwater use===
 
=== Groundwater use===
  
Recent information states that nearly 80% of groundwater abstracted in Chad is used for agriculture, and around 20% for domestic use (Global Water Partnership, 2013).  
+
Many rural areas, particularly in the drier north, depend on groundwater from shallow hand dug wells and boreholes for domestic and in some cases, also for livestock use in dry seasons. Groundwater is also used for small scale irrigation in the north.
  
Many rural areas, particularly in the drier north, depend on groundwater from shallow hand dug wells and boreholes for domestic use, and in some cases also for livestock use in dry seasons.  Groundwater is also used for small scale irrigation in the north.  
+
Groundwater also provides a large proportion of water supply in many urban centres, including N'Djamena (United Nations 1988).
  
Groundwater also provides a large proportion of water supply in many urban centres, including N'Djamena (United Nations 1988).
+
A small number of industrial users abstract groundwater, including for textile manufacture, sugar refining, cotton milling and brewing.  
 
 
A small number of industrial users also abstract groundwater, including for textile manufacture, sugar refining, cotton milling and brewing.
 
  
 
=== Groundwater management and monitoring===
 
=== Groundwater management and monitoring===
Line 370: Line 290:
 
The following references provide more information on the geology and hydrogeology of Chad.
 
The following references provide more information on the geology and hydrogeology of Chad.
  
Many of these, and others, can be accessed through the [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=listResults&title_search=&author_search=&category_search=&country_search=TD&placeboolean=AND&singlecountry=1 Africa Groundwater Literature Archive]
+
These, and others, can be accessed through the [http://www.bgs.ac.uk/africagroundwateratlas/searchResults.cfm?title_search=&author_search=&category_search=&country_search=TD&placeboolean=AND&singlecountry=1 Africa Groundwater Literature Archive]
 +
 
  
  
 
Alker M. 2008. The Lake Chad Basin Aquifer System: a case study for the research project 'Transboundary groundwater management in Africa'. German Development Institute
 
Alker M. 2008. The Lake Chad Basin Aquifer System: a case study for the research project 'Transboundary groundwater management in Africa'. German Development Institute
 
BGR (Federal Institute of Geosciences and Natural Resources). 2017. [https://www.bgr.bund.de/EN/Themen/Zusammenarbeit/TechnZusammenarb/Projekte/Laufend/Afrika/1073_2010-2274-8_Tschad_Grundwasserberatung_Tschadseebeckenkommission_en.html Supraregional Africa: Groundwater Management of Lake Chad Basin]. Project website, 11 April 2017.
 
 
BGR (Federal Institute of Geosciences and Natural Resources). Undated. [https://www.bgr.bund.de/EN/Themen/Wasser/Projekte/laufend/TZ/Tschad/tschad-II_fb_en.html  Supraregional Africa: Groundwater Management of Lake Chad Basin]. N.D. Project website: BGR: TC Lake Chad Basin: Groundwater Management
 
 
Danert K. 2015. [http://www.rural-water-supply.net/_ressources/documents/default/1-656-34-1425638967.pdf Professionalising Manual Drilling: Chad’s Growing Manual Drilling Industry]. RWSN, UNICEF, Skat Foundation.
 
  
 
GWP (Global Water Partnership). 2013. [http://www.gwp.org/Global/ToolBox/References/Lake_Chad_fact_sheet.pdf The Lake Chad Basin Aquifer System]. Global Water Partnership Transboundary Groundwater Fact Sheet, compiled by F Bontemps.
 
GWP (Global Water Partnership). 2013. [http://www.gwp.org/Global/ToolBox/References/Lake_Chad_fact_sheet.pdf The Lake Chad Basin Aquifer System]. Global Water Partnership Transboundary Groundwater Fact Sheet, compiled by F Bontemps.
  
Ngatcha BN, Mudry J and Leduc C. 2008. [http://www.inweb.gr/twm4/abs/NGOUNOU%20Ngatcha%20Benjamin.pdf The state of understanding on groundwater recharge for the sustainable management of transboundary aquifer in the Lake Chad Basin]. Presentation at 4th International Symposium on Transboundary Water Management, Thessaloniki, Greece, 15-18 October 2008.
+
Ngatcha BN, Mudry J and Leduc C. 2008. [http://www.inweb.gr/twm4/abs/NGOUNOU%20Ngatcha%20Benjamin.pdf The state of understanding on groundwater recharge for the sustainable management of transboundary aquifer in the Lake Chad Basin]. Presentation at 4th International Symposium on Transboundary Water Management, Thessaloniki, Greece, 15-18 October 2008
 
 
Permenter JL and Oppenheimer C. 2007. [http://pages.mtu.edu/~raman/papers2/Parmeter&OppChadBV.pdf Volcanoes of the Tibesti massif (Chad, northern Africa). Bull. Volcanol. 69, 609-626 . Doi: 10.1007/s00445-006-0098-x.
 
 
 
Practica Foundation, UNICEF and Enterprise Works/VITA. 2009. [https://www.unicef.org/wash/files/CHAD_Case_Study_Aug14_lowRes.pdf The impact of manual drilling for the construction of sustainable water-points in Chad].
 
 
 
Practica Foundation, UNICEF and Enterprise Works/VITA. 2010. [http://www.unicef.org/wash/files/Chad_manual_drilling_final_report_(FINAL).pdf Republic of Chad: feasibility study for manual drilling: mapping of favourable zones]. Ministere de l'Environnement, de l'Eau et des Ressources Halieutiques. Practica/Enterprise Works/VITA/UNICEF
 
 
 
Practica Foundation, UNICEF and Enterprise Works/VITA. 2014. [https://www.practica.org/wp-content/uploads/2014/10/Identification_des_Zones_Favorables_Pour_les_Forages_Manuels_FINAL.pdf Identification des zones favorables pour les forages manuels: rapport final sur la methodologie utilise et les resultas obtenus]. Practica/Enterprise Works/VITA/UNICEF
 
  
Scheider JL and Wolff JP. 1969. [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA300006 Carte Hydrogeologique de la Republique du Tchad; Scale 1:500 000]. Bureau de Recherches Geologiques et Minieres (BRGM), Orleans.  
+
Scheider JL and Wolff JP. 1969. [http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA300006 Carte Hydrogeologique de la Republique du Tchad; Scale 1:500 000]. Bureau de Recherches Geologiques et Minieres (BRGM), Orleans.  
  
 
Thorweihe U and Heinl M. 2002. [http://web.archive.org/web/20030723113049/http://geosys.bg.tu-berlin.de/archiv/downloads/NAS_syn.pdf Groundwater resources of the Nubian Aquifer System NE Africa]. Technical University of Berlin: Modified synthesis submitted to Observatoire du Sahara et du Sahel (OSS, Paris) 1998: Aquifers of major basins - non renewable Water Resource Groundwater Resources of the Nubian Aquifer System.
 
Thorweihe U and Heinl M. 2002. [http://web.archive.org/web/20030723113049/http://geosys.bg.tu-berlin.de/archiv/downloads/NAS_syn.pdf Groundwater resources of the Nubian Aquifer System NE Africa]. Technical University of Berlin: Modified synthesis submitted to Observatoire du Sahara et du Sahel (OSS, Paris) 1998: Aquifers of major basins - non renewable Water Resource Groundwater Resources of the Nubian Aquifer System.
  
United Nations. 1988. [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060033 Chad: in Groundwater in North and West Africa]. United Nations Department of Technical Cooperation for Development and Economic Commission for Africa, Natural Resources/Water Series No. 18, ST/TCD/5.
+
United Nations. 1988. [http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA060033 Groundwater in North and West Africa: Chad]. United Nations Department of Technical Cooperation for Development and Economic Commission for Africa, Natural Resources/Water Series No. 18, ST/TCD/5.
  
Vassolo S, Bila M, Hamit A. 2009. [http://www.cblt.org/sites/default/files/download_documents/bgr_report_2_engl.pdf A review of the groundwater situation in the Lake Chad Basin. Lake Chad Sustainable Water Management Project Activities - Report N° 2]. Federal Institute of Geosciences and Natural Resources (BGR), Hanover.  
+
UNICEF. 2010. [http://www.unicef.org/wash/files/Chad_manual_drilling_final_report_(FINAL).pdf Republic of Chad: feasibility study for manual drilling: mapping of favourable zones]. Ministere de l'Environnement, de l'Eau et des Ressources Halieutiques. Practica/Enterprise Works/VITA/UNICEF
  
  

Please note that all contributions to Earthwise may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Earthwise:Copyrights for details). Do not submit copyrighted work without permission!

Cancel Editing help (opens in new window)

  [] · [[]] · [[|]] · {{}} · · “” ‘’ «» ‹› „“ ‚‘ · ~ | ° &nbsp; · ± × ÷ ² ³ ½ · §
[[Category:]] · [[:File:]] · <code></code> · <syntaxhighlight></syntaxhighlight> · <includeonly></includeonly> · <noinclude></noinclude> · #REDIRECT[[]] · <translate></translate> · <languages/> · ==References== · {{reflist}} · ==Footnote== · {{reflist|group=note}} · <ref group=note> · __notoc__ · {{DEFAULTSORT:}} <div class="someclass noprint"></div> {{clear}} <br>