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− | [[Africa Groundwater Atlas | + | [[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Côte d'Ivoire |
− | + | '''Most of the textual information on this page was taken from the chapter on Côte d'Ivoire in the report[http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA060034 ‘Groundwater in North and West Africa’] (UN 1988). Some of this information is outdated. If you have more recent information on the hydrogeology of Cote d'Ivoire, please get in touch.''' | |
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'''Dr Kirsty Upton''' and '''Brighid Ó Dochartaigh''', British Geological Survey, UK | '''Dr Kirsty Upton''' and '''Brighid Ó Dochartaigh''', British Geological Survey, UK | ||
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==Geographical Setting== | ==Geographical Setting== | ||
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Côte d'Ivoire is in west Africa with a southern coast on the Gulf of Guinea. The country is largely flat, less than 500 m, with local relief. The west of the country is more hilly, with parts rising above 500 m, to a maximum of about 1200 m elevation. The south has many low lying areas and a few isolated or groups of low hills rising to around 650 m elevation. | Côte d'Ivoire is in west Africa with a southern coast on the Gulf of Guinea. The country is largely flat, less than 500 m, with local relief. The west of the country is more hilly, with parts rising above 500 m, to a maximum of about 1200 m elevation. The south has many low lying areas and a few isolated or groups of low hills rising to around 650 m elevation. | ||
− | [[File:Côte d'Ivoire_Political.png | right | frame | Côte d'Ivoire | + | [[File:Côte d'Ivoire_Political.png | right | frame | Map of Côte d'Ivoire (For more information on the datasets used in the map see the [[Geography | geography resources section]])]] |
===General=== | ===General=== | ||
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{| class = "wikitable" | {| class = "wikitable" | ||
|- | |- | ||
− | | | + | |Estimated Population in 2013* || 20,316,086 |
|- | |- | ||
− | | | + | |Rural Population (% of total) (2013)* || 47.2% |
|- | |- | ||
− | | | + | |Total Surface Area* || 318,000 sq km |
|- | |- | ||
− | | | + | |Agricultural Land (% of total area) (2012)* || 64.8% |
|- | |- | ||
− | | | + | |Capital City || Yamoussoukro |
|- | |- | ||
− | | | + | |Region || Western Africa |
|- | |- | ||
− | | | + | |Border Countries || Liberia, Guinea, Mali, Burkina Faso, Ghana |
|- | |- | ||
− | | | + | |Annual Freshwater Withdrawal (2013)* || 1549 Million cubic metres |
+ | |- | ||
+ | |Annual Freshwater Withdrawal for Agriculture (2013)* || 38.4% | ||
+ | |- | ||
+ | |Annual Freshwater Withdrawal for Domestic Use (2013)* || 41.1% | ||
+ | |- | ||
+ | |Annual Freshwater Withdrawal for Industry (2013)* || 20.5% | ||
+ | |- | ||
+ | |Rural Population with Access to Improved Water Source (2012)* || 67.8% | ||
+ | |- | ||
+ | |Urban Population with Access to Improved Water Source (2012)* || 91.5% | ||
|} | |} | ||
− | <nowiki>*</nowiki> Source: | + | <nowiki>*</nowiki> Source: World Bank |
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===Climate=== | ===Climate=== | ||
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The southern coastal zone has an equatorial climate with the highest rainfall, at around 2,400 mm/year, and rainfall is fairly evenly distributed throughout the year. The centre of the country has a tropical climate, with average annual rainfall of around 1,000 to 1,400 mm, and two wet seasons: the main one starting in December and the smaller one from August to October. The north is drier, with average annual rainfall betweewn 400 and 1,000 mm, concentrated in a short rainy season from July to September. | The southern coastal zone has an equatorial climate with the highest rainfall, at around 2,400 mm/year, and rainfall is fairly evenly distributed throughout the year. The centre of the country has a tropical climate, with average annual rainfall of around 1,000 to 1,400 mm, and two wet seasons: the main one starting in December and the smaller one from August to October. The north is drier, with average annual rainfall betweewn 400 and 1,000 mm, concentrated in a short rainy season from July to September. | ||
− | + | <gallery widths="375px" heights=365px mode=nolines> | |
− | + | File:Côte d'Ivoire_ClimateZones.png |Koppen Geiger Climate Zones | |
− | + | File:Côte d'Ivoire_ClimatePrecip.png |Average Annual Precipitation | |
− | + | File:Côte d'Ivoire_ClimateTemp.png |Average Temperature | |
− | + | </gallery> | |
− | + | [[File:Côte d'Ivoire_pre_Monthly.png| 255x124px| Average monthly precipitation for Côte d'Ivoire showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Côte d'Ivoire_tmp_Monthly.png| 255x124px| Average monthly temperature for Côte d'Ivoire showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Côte d'Ivoire_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Côte d'Ivoire_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]] | |
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+ | For further detail on the climate datasets used see the [[Climate | climate resources section]]. | ||
===Surface water=== | ===Surface water=== | ||
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− | | [[File:Côte d'Ivoire_Hydrology.png | frame | | + | | [[File:Côte d'Ivoire_Hydrology.png | frame | Surface Water Map of Côte d'Ivoire (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]] |
|} | |} | ||
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{| | {| | ||
|- | |- | ||
− | | [[File:Côte d'Ivoire_soil.png | frame | Soil Map of Côte d'Ivoire | + | | [[File:Côte d'Ivoire_soil.png | frame | Soil Map of Côte d'Ivoire (For map key and more information on the datasets used in the map see the [[Soil | soil resources section]])]] |
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The south of the country is equatorial with forest; the centre is dominated by tropical forest; and the north is dominated by savannah vegetation. | The south of the country is equatorial with forest; the centre is dominated by tropical forest; and the north is dominated by savannah vegetation. | ||
− | | [[File:Côte d'Ivoire_LandCover.png | frame | Land Cover Map of Côte d'Ivoire | + | | [[File:Côte d'Ivoire_LandCover.png | frame | Land Cover Map of Côte d'Ivoire (For map key and more information on the datasets used in the map see the [[Land cover | land cover resources section]])]] |
|} | |} | ||
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==Geology== | ==Geology== | ||
− | This section provides a summary of the geology of Côte d'Ivoire. More information is available in the report [ | + | This section provides a summary of the geology of Côte d'Ivoire. More information is available in the report [http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA060034 ‘Groundwater in North and West Africa: Côte d'Ivoire’] (UN 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). | ||
− | + | [[File:Côte d'Ivoire_Geology.png | center]] | |
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− | [[File: | ||
'''Summary''' | '''Summary''' | ||
− | + | A narrow strip along the southern coast forms the coastal basin. Here, sedimentary rocks of Cretaceous-Tertiary age and unconsolidated Quaternary sediments form a wedge which narrows towards the north, where it terminates at the edge of the basement rock, less than 35 km from the coast. The basin is crossed from west to east by a fault with a displacement of several thousand metres, which separates two distinct zones: | |
- to the north is a shallower basin where the sedimentary infill is not usually more than 300 m thick | - to the north is a shallower basin where the sedimentary infill is not usually more than 300 m thick | ||
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There is a series of lagoons, part of an ancient hydrographic system, which have very thick mud deposits and are now submerged. | There is a series of lagoons, part of an ancient hydrographic system, which have very thick mud deposits and are now submerged. | ||
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+ | Across the rest of the country are basement rocks. | ||
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|Continental Terminal | |Continental Terminal | ||
||Cretaceous-Tertiary | ||Cretaceous-Tertiary | ||
− | || | + | ||The lower part of the sedimentary infill in the coastal basin comprises detrital continental Tertiary (Miocene-Pliocene) formations - mostly coarse sands - and, in the deepest areas, Upper and Middle Cretaceous marine formations, mostly sandstone, including ferruginous sandstone, and clays. Together, these form the Continental Terminal formation (sometimes, the Cretaceous is treated as a separate aquifer). |
− | |- | + | |- |
− | !colspan="4"| | + | !colspan="4"|Basement (West African Shield) |
|- | |- | ||
|Birrimian | |Birrimian | ||
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||Metamorphic rocks, mainly of sedimentary origin. These are generally schists, with meta-sandstones and meta-conglomerates in places. In places there are granitic intrusions, accompanied by volcano-sedimentary formations of tuffs, breccias, and green rocks. These form bands running from north-northeast to south-southwest, and are heavily folded, sometimes vertical. | ||Metamorphic rocks, mainly of sedimentary origin. These are generally schists, with meta-sandstones and meta-conglomerates in places. In places there are granitic intrusions, accompanied by volcano-sedimentary formations of tuffs, breccias, and green rocks. These form bands running from north-northeast to south-southwest, and are heavily folded, sometimes vertical. | ||
|- | |- | ||
− | | | + | |Prebirrimian |
||Lower Precambrian | ||Lower Precambrian | ||
||The oldest basement formations include crystalline gneiss, granites and migmatites. They are most common in the west of the country (although migmatites are found everywhere). | ||The oldest basement formations include crystalline gneiss, granites and migmatites. They are most common in the west of the country (although migmatites are found everywhere). | ||
|} | |} | ||
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==Hydrogeology== | ==Hydrogeology== | ||
− | This section provides a summary of the hydrogeology of the main aquifers in Côte d'Ivoire. More information is available in the report [ | + | This section provides a summary of the hydrogeology of the main aquifers in Côte d'Ivoire. More information is available in the report [ADD LINK UN] (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 hydrogeology map shows a simplified version of the type and productivity of the main aquifers at a national scale (see [[Aquifer properties| the Aquifer properties resource page]] for more details). |
− | [ | + | [[File:Côte d'Ivoire_Hydrogeology.png]] [[File: Hydrogeology_Key.png | center | 500x195px]] |
− | + | '''Note:''' the term Continental Terminal is sometimes used to describe the whole of the coastal basin aquifer, from Cretaceous to Quaternary, and sometimes to describe only the Quaternary, or only the Tertiary, or both the Cretaceous and Tertiary formations. Here, it is used to describe the Cretaceous-Tertiary aquifer in the coastal basin that underlies the Quaternary aquifer. The Quaternary aquifer is described separately, highlighting its unconsolidated nature and high vulnerability. | |
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|Coastal basin | |Coastal basin | ||
||Quaternary | ||Quaternary | ||
− | ||The southern part of the coastal basin consists of Quaternary formations, including coastal and marine sands. In their upper part, these form a moderately to highly productive aquifer, capable of sustaining borehole yields of at least 5 to 50 m³/hour. In some places with very permeable coarse sands, a borehole yield of at least 210 m³/hour for a drawdown of 3.1 m was recorded (a specific capacity of at least 1600 m³/day/m) ( | + | ||The southern part of the coastal basin consists of Quaternary formations, including coastal and marine sands. In their upper part, these form a moderately to highly productive aquifer, capable of sustaining borehole yields of at least 5 to 50 m³/hour. In some places with very permeable coarse sands, a borehole yield of at least 210 m³/hour for a drawdown of 3.1 m was recorded (a specific capacity of at least 1600 m³/day/m) (an underlying clay layer protects the aquifer from intrusion by the underlying salt water). |
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The aquifer is recharged by direct infiltration of rainwater, and recharge is high, with effective infiltration of 50 percent of rainfall. | The aquifer is recharged by direct infiltration of rainwater, and recharge is high, with effective infiltration of 50 percent of rainfall. | ||
− | Fresh water lies in density equilibrium on a layer (or wedge) of salt water, or on impermeable strata | + | Fresh water lies in density equilibrium on a layer (or wedge) of salt water, or on impermeable strata. |
− | ||Where there is no seawater intrusion, groundwater in the upper layers is fresh. | + | ||Where there is no seawater intrusion, groundwater in the upper layers is fresh. The salt water at depth has salinity ranging from 100 to 2500 mg/l. |
|} | |} | ||
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|Continental Terminal - coastal basin | |Continental Terminal - coastal basin | ||
||Cretaceous-Tertiary | ||Cretaceous-Tertiary | ||
− | ||This aquifer is buried below the shallow Quaternary aquifer in the coastal basin, and they may be in hydraulic continuity. Groundwater flow is dominantly intergranular, and the aquifer is likely to be largely unconfined. Transmissivity is high, with values of up to and possibly more than 10,000 m²/day, and storage coefficients of 10 to 15 percent. Sustainable borehole yields may be on the order of 10 | + | ||This aquifer is buried below the shallow Quaternary aquifer in the coastal basin, and they may be in hydraulic continuity. Groundwater flow is dominantly intergranular, and the aquifer is likely to be largely unconfined. Transmissivity is high, with values of up to and possibly more than 10,000 m²/day, and storage coefficients of 10 to 15 percent. Sustainable borehole yields may be on the order of 10 and 200 m³/h. |
||Groundwater generally has low mineral content, with dry residue usually between 40 and 150 mg/l; calcium and magnesium of 1 to 4 mg/l; bicarbonate of 3 to 6 mg/l; and chloride of 7 to 14 mg/l. It is almost always acidic, with pH close to 4.5. | ||Groundwater generally has low mineral content, with dry residue usually between 40 and 150 mg/l; calcium and magnesium of 1 to 4 mg/l; bicarbonate of 3 to 6 mg/l; and chloride of 7 to 14 mg/l. It is almost always acidic, with pH close to 4.5. | ||
|} | |} | ||
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====Basement==== | ====Basement==== | ||
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||Groundwater has moderate mineral content, with dry residues of between 250 and 500 mg/l, sometimes up to 650 mg/l, and a pH close to 7 (neutral). | ||Groundwater has moderate mineral content, with dry residues of between 250 and 500 mg/l, sometimes up to 650 mg/l, and a pH close to 7 (neutral). | ||
|- | |- | ||
− | | | + | |Granitogneiss aquifers |
− | ||Lower Precambrian | + | || Lower Precambrian |
− | || | + | ||In the quartz grained granitogneiss rocks, groundwater occurs in shallow weathered zones, where the rock has weathered to sand and gravel; and in deeper fractures in unweathered bedrock. |
The weathered zone is 20 to 30 m thick on average, but sometimes as much as 60 m. Transmissivity values for this zone are in the order of 8 to 85 m²/day. Generally speaking, the most weathered (the most sandy and gravelly) zones, which have the highest permeability, are found at the base of the weathered zone. | The weathered zone is 20 to 30 m thick on average, but sometimes as much as 60 m. Transmissivity values for this zone are in the order of 8 to 85 m²/day. Generally speaking, the most weathered (the most sandy and gravelly) zones, which have the highest permeability, are found at the base of the weathered zone. | ||
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||Groundwater has moderate mineral content, with dry residues of between 250 and 500 mg/l, sometimes up to 650 mg/l, and a pH close to 7 (neutral). | ||Groundwater has moderate mineral content, with dry residues of between 250 and 500 mg/l, sometimes up to 650 mg/l, and a pH close to 7 (neutral). | ||
|} | |} | ||
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==Groundwater Status== | ==Groundwater Status== | ||
− | + | Groundwater in the coastal Quaternary and Continental Terminal aquifers is highly vulnerable to contamination, both by seawater intrusion and by pollution from urban industry and domestic waste. Many studies have been done of the risks to and effects on groundwater, particularly in the Abidjan area (e.g. Douagui et al. 2012, Kouassi et al. 2013 and Issiaka et al. 2006). | |
− | Seawater intrusion may be caused by falling groundwater levels, which themselves may be linked to intensive groundwater pumping and/or to rainfall variability (Oga et al. 2006). | + | Seawater intrusion may be caused by falling groundwater levels, which themselves may be linked to intensive groundwater pumping and/or to rainfall variability (Oga et al. 2006). |
==Groundwater use and management== | ==Groundwater use and management== | ||
− | + | Groundwater from the Quaternary aquifer is the main source of drinking water supply in Abidjan and most of the rest of the coastal zone. Groundwater from shallow boreholes and hand dug wells in the basement aquifer is the main source of water in rural areas across the rest of the country. | |
− | + | At least 13,000 groundwater sources had been recorded in the country in 2008, mostly boreholes, with hand dug wells the next numerous. | |
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==References== | ==References== | ||
− | The following references provide more information on the geology and hydrogeology of | + | The following references provide more information on the geology and hydrogeology of Cote d'Ivoire. |
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− | + | These, and others, can be accessed through the [http://www.bgs.ac.uk/africagroundwateratlas/searchResults.cfm?title_search=&author_search=&category_search=&country_search=CI&placeboolean=AND&singlecountry=1 Africa Groundwater Literature Archive] | |
− | Douagui et al. 2012. | + | Douagui et al. 2012. Assessment of the bacteriological quality and nitrate pollution risk of Quaternary groundwater in the southern part of Abidjan District (Côte d’Ivoire). Journal of Hydro-environment Research, Vol.6, Issue 3, pp 227-238 |
Issiaka et al. 2006. Vulnerability assessment of the Abidjan Quaternary aquifer using the DRASTIC method. In: Groundwater quality in Africa, ed. Y Xu and B Usher, Taylor and Francis/Balkema, Rotterdam, pp 115-124 | Issiaka et al. 2006. Vulnerability assessment of the Abidjan Quaternary aquifer using the DRASTIC method. In: Groundwater quality in Africa, ed. Y Xu and B Usher, Taylor and Francis/Balkema, Rotterdam, pp 115-124 | ||
− | + | Kouassi et al. 2013. Modeling of Quaternary Groundwater Pollution Risk by GIS and Multicriteria Analysis in the Southern Part of Abidjan District (Côte d’Ivoire). Journal of Hydro-environment Research, Vol.6, Issue 3, pp 227-238. | |
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− | + | Oga MS, Marlin C, Dever L, Filly A and Njitchoua R. 2008 . Hydrochemical and isotopic characteristics of coastal Groundwater near Abidjan. In: Adelana and MacDonald (eds) Applied Groundwater Studies in Africa, pp 371-389. | |
− | + | United Nations. 1988. [http://www.bgs.ac.uk/africagroundwateratlas/fulldetails.cfm?id=AGLA060034 Groundwater in North and West Africa: Côte d'Ivoire]. 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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− | Return to the index pages | + | ==Return to the index pages== |
− | [[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] | + | [[Overview of Africa Groundwater Atlas | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Cote d'Ivoire |
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[[Category:Hydrogeology by country|c]] | [[Category:Hydrogeology by country|c]] | ||
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