Hydrogeology of Chad
Africa Groundwater Atlas >> Hydrogeology by country >> Hydrogeology of Chad
Most of the textual information on this page was taken from the chapter on Chad in the report ‘Groundwater in North and West Africa’ (UN 1988). This information is outdated. If you have more recent information on the hydrogeology of Chad, please get in touch.
Compilers
Dr Kirsty Upton and Brighid Ó Dochartaigh, British Geological Survey, UK
Geographical Setting
The low lying Lake Chad Basin covers much of Chad, with an elevation of about 250 m. There is also low lying land in the dry north of the country. To the north, east and south of the Lake Chad Basin, the land rises gradually to plateaus and mountains. The highest elevations are in the Tibesti massif in the north, at over 3000 m. In the east are plateaus lying at more than 900 m.
General
Estimated Population in 2013* | 12,825,314 |
Rural Population (% of total) (2013)* | 77.8% |
Total Surface Area* | 1,259,200 sq km |
Agricultural Land (% of total area) (2012)* | 39.7% |
Capital City | N'Djamena |
Region | Central Africa |
Border Countries | Niger, Libya, Egypt, Sudan, Central African Republic, Cameroon, Nigeria |
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% |
* Source: World Bank
Climate
Chad has a varied climate. In the south, rainfall is high - an annual average of 1000 to 1400 mm. In the central zone, average annual rainfall is between 700 and 1000 mm. In the north, the climate is semi-arid, with average annual rainfall between 200 and 700 mm. The far north is arid, with total annual rainfall below 500 mm. The dry northern zones have high evaporation of around 2200 to 2300 mm.
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Koppen Geiger Climate Zones
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Average Annual Precipitation
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Average Temperature
For further detail on the climate datasets used see the climate resources section.
Surface water
Southern Chad is drained by two main perennial rivers: the Chari and its largest tributuary the Logone, both of which receive flow mainly from tributaries from outside the country. The Chari river drains into Lake Chad, which is the largest surface water resource in the country. The Lake Chad basin is one of the best studied in Africa, and is shared by a number of countries, including Chad, Niger, Nigeria and Cameroon. As well as the Chari river, it is fed by two other smaller rivers flowing from Nigeria and Cameroon.
In the central and northern parts of the country, all the rivers are ephemeral, generally flowing only for a few hours after heavy rain, or at most for a few months each year. |
Soil
Land cover
Land cover in Chad is largely controlled by climate. In the wetter southern zone, arable crops are and forest are widespread. In the central zone, arable crops and forest become rarer and land cover becomes dominated by grassland and savanna. In the dry north, vegetation is scarce. |
Geology
This section provides a summary of the geology of Chad. More information is available in the report ‘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 the Geology resources page for more details). A higher resolution map at 1:500,000 scale was published in 1969 by BRGM and a copy can be viewed on the WHYMAP site.
Key Formations | Period | Lithology | |
Quaternary | |||
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Quaternary | Quaternary formations occur across most of the Chad basin and are dominated by lacustrine deposits. However, 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. | ||
Tertiary | |||
Continental Terminal; also small area of Eocene marine deposits in northern Tibesti | Tertiary | The Continental Terminal includes a middle series of red sands and an upper series | |
Palaeozoic sedimentary | |||
Cambro-Ordovician, Devonian and Carboniferous | Occur only in the north of the country in Borkou and Ennedi, where they form large sandstone tables. | ||
Precambrian Basement | |||
Granitic and crystalline rocks of the Tibesti and Ouaddai in the north; and the Lam mountains in the south | Precambrian |
Hydrogeology
This section provides a summary of the hydrogeology of the main aquifers in Chad. More information is available in the report ‘Groundwater in North and West Africa: Chad’ (1988) (see References section, below).
The hydrogeology map shows a simplified version of the type and productivity of the main aquifers at a national scale (see the Aquifer properties resource page for more details).
Quaternary Unconsolidated
Named Aquifers | Period | General Description | Water quality |
Koros aquifers (south Chad); 'sanies' aquifer (northern Bastra); Chari-Baguirmi aquifer; shallow 'Oudian' aquifer (Kanem) | Quaternary | The Koros aquifer comprises permeable sands that receive recharge partly from infiltration of river flows in the alluvial valleys, but largely from direct rainfall infiltration.
The Chari-Baguirmi aquifer comprises a succession of clay-sand formations dotted with small higher area of |
Sedimentary - Intergranular Flow
Named Aquifers | Period | General Description | Water quality |
Sedimentary - Intergranular & Fracture Flow
Named Aquifers | Period | General Description | Water quality |
Sedimentary - Fracture Flow
Named Aquifers | Period | General Description | Water quality |
Basement
Named Aquifers | Period | General Description | Water quality |
Groundwater Status
Groundwater quantity
Groundwater quality
Groundwater use and management
Groundwater use
Groundwater management
Groundwater monitoring
Transboundary aquifers
For further information about transboundary aquifers, please see the Transboundary aquifers resources page
References
The following references provide more information on the geology and hydrogeology of Chad.
These, and others, can be accessed through the Africa Groundwater Literature Archive
Scheider JL and Wolff JP. 1969. Carte Hydrogeologique de la Republique du Tchad; Scale 1:500 000. Bureau de Recherches Geologiques et Minieres (BRGM), Orleans.
United Nations. 1988. 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.
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