Hydrogeology of Benin: Difference between revisions

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The hydrogeology map on this page shows a simplified description of the type and productivity of aquifers in Benin, at 1:5,000,000 scale. More detailed hydrogeological maps, at 1:500,000 scale and 1:200,000 scale, are produced by GIZ Germany/DGEau Benin (Achidi et al 2012).  
The hydrogeology map on this page shows a simplified description of the type and productivity of aquifers in Benin, at 1:5,000,000 scale. More detailed hydrogeological maps, at 1:500,000 scale and 1:200,000 scale, are produced by GIZ Germany/DGEau Benin (Achidi et al 2012).  


[[File:Benin_Hydrogeology2.png]] | center | border| 500px| Simplified aquifer types and productivity]]
[[File:Benin_Hydrogeology2.png | center | border| 500px| Simplified aquifer types and productivity]]


====Unconsolidated====
====Unconsolidated====

Revision as of 13:21, 9 June 2015

Authors

Moussa Boukari, Faculté des sciences et techniques, Université d’Abomey-Calavi, Benin

Henri Totin, Université de Parakou, Benin

Kirsty Upton & Brighid Ó Dochartaigh, British Geological Survey, UK

Geographical and Political Setting

Political Map of Benin (For more information on the datasets used in the map see the geography resources section)

General

Benin extends from the Atlantic Ocean (Gulf of Guinea) in the south to the Niger River in the north, a distance of around 700 km. The country is relatively flat, with a granitic plateau in the centre of the country which rises to the Atakora mountain range in the northwest. The highest point is at an elevation of 658 m above sea level.

Estimated Population in 2013* 10,323,474
Rural Population (% of total)* 57%
Total Surface Area* 112,760 sq km
Agricultural Land (% of total area)* 33%
Capital City Porto Novo
Region West Africa
Border Countries Nigeria, Niger, Burkina Faso, Togo
Annual Freshwater Withdrawal (2013)* 130 Million cubic metres
Annual Freshwater Withdrawal for Agriculture* 45%
Annual Freshwater Withdrawal for Domestic Use* 32%
Annual Freshwater Withdrawal for Industry* 23%
Rural Population with Access to Improved Water Source* 69%
Urban Population with Access to Improved Water Source* 85%

* Source: World Bank


Climate

The majority of the country is classified as a tropical savannah climate, apart from the far north, which transitions into a hot and arid climate towards the Sahel region. Average annual rainfall across the majority of the country is between 1000 and 1100 mm. This decreases in the northern zone to almost 700 mm per year. Average temperatures also show a north-south transition, increasing by a relatively small amount towards the north.

There are temporal changes in precipitation and temperature throughout the year. The principal rainy season occurs between April and August, and a second, shorter and less intense rainy season occurs during September and October. Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the Benin Climate Page.

Average monthly precipitation for Benin showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for Benin showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature Quarterly precipitation over the period 1950-2012 Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)


For further detail on the climate datasets used see the climate resources section.

Surface water

The main rivers in the north of Benin are tributaries of the Niger River, and flow northwards, out of the country. The main perennial river in the south of Benin is the Oueme River, which, along with some other smaller rivers, drains into the network of lagoons which has developed along the coast - there is no natural river discharge directly into the Atlantic Ocean.

The General Directorate of Water (DG-Eau) maintains 48 river flow gauging stations across Benin. Records cover the period 1950 - 2014, with daily observations. River flow data are stored in the Department of Water Information within the DG-Eau.

The Early Warning System (SAP) project also collects river flow data.

Surface Water Map of Benin (For more information on the datasets used in the map see the surface water resources section)

Soil

Soil Map of Benin (For more information on the datasets used in the map see the soil resources section)
Lixosols are the dominant soil type in Benin, reflecting stable geological conditions, a savannah climate and grassland vegetation.

Leptosols are found in the mountainous region in the north west of the country while Arenosols (large sand deposits) occur in the Sahel region along the northeastern border.

Productive Nitisols have developed on the alluvium in the coastal region. On the sandbars and lagoons of the coastal region are Gleysols and Arenosols.

Land cover

Land Cover Map of Benin (For more information on the datasets used in the map see the land cover resources section)

Geology

This section provides a summary of the geology of Benin. More detail can be found in the references listed at the bottom of this page.

The geology map on this page shows a simplified version of the geology of Benin. A more detailed geological map at 1:200,000 scale was produced by BRGM (1978).

Simplified geological map
Simplified geological map
Geological Environments
Key Formations Period Lithology Structure
Unconsolidated Sedimentary
Alluvium Quaternary Sand, clay, silt and sometimes gravel deposits, forming outwash fan, channel and floodplain deposits along river channels. Variable thickness but generally less than 100 m.
Sedimentary - Coastal Basin
Benin Sedimentary Coastal Basin Lower Cretaceous - Quaternary Marine deposits (sandstone, limestone, clay, marl and conglomerate) belonging to the Keta Basin, deposited along the Atlantic coast of Ghana, Togo, Benin and Nigeria.

Fine grained unconsolidated lacustrine sediments are also deposited along the coast.

Marine deposits have highly variable thickness (10 - 2000 m).

Unconsolidated coastal deposits are on average 50 m thick.

Sedimentary - Iullumeden Basin
Were, Goungoun, Kandi, Sende & Continental Terminal Formations Lower Palaeozoic - Cretaceous Conglomerate, sandstone, siltstone & clay. These Continental deposits, belonging to the southern part of the Iullemeden Basin, also occur in Nigeria, Niger and Mali. Variable thickness (20 - 400 m). The Continental Terminal Formation contains small extensional features.
Precambrian Metasedimentary
Voltaian (or Pendjari) Basin Late Precambrian - Lower Palaeozoic Sandstones, shales and siltstones. Highly variable thickness.
Buem (Volcanic-Sedimentary) Series Late Precambrian Sandstone, quartzite, rhyolite and andesite Highly variable thickness (estimated 250 - 2000 m).
Precambrian Mobile/Orogenic Belt
Basement Complex Precambrian Crystalline gneiss and granulite with granite and syenite intrusions. Highly metamorphosed and deformed during several orogenic phases which gave rise to various episodes of igneous activity. Often intensely folded. Folds are generally isoclinal. Not generally steeply dipping.
Atacora, Kande and Kouande Series Precambrian Quartzite and schist. Highly metamorphosed during the Panafrican Orogeny.

Hydrogeology

This section provides a summary of the hydrogeology of the main aquifers in Benin. More information is available in the references listed at the bottom of this page, many of which are available through the Africa Groundwater Literature Archive.

Aquifer properties

The hydrogeology map on this page shows a simplified description of the type and productivity of aquifers in Benin, at 1:5,000,000 scale. More detailed hydrogeological maps, at 1:500,000 scale and 1:200,000 scale, are produced by GIZ Germany/DGEau Benin (Achidi et al 2012).

Simplified aquifer types and productivity
Simplified aquifer types and productivity

Unconsolidated

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Alluvial and barrier beach deposits The alluvial and barrier beach deposits of Benin are highly variable both laterally and vertically. The alluvial deposits are found along the major river valleys, the most significant of which is the River Niger valley in the north. The barrier beach deposits are found along the coast and are dominated by relatively impermeable clays. However, interbedded, generally poorly sorted, coarser grained sands and gravels can form aquifers of local importance along the coast.

Yields are highly variable but are often reported around 5 l/s, and sometimes higher from sand and gravel layers. Transmissivity is generally 10 to 400 m²/d. Storage coefficient is typically 10-2 - 10-1.

The thickness of the unconsolidated aquifers typically varies between 10 and 20 m. The water table is generally shallow, less than 7 m below ground level. Boreholes are typically drilled to depths of 5 to 20 m.

There are no known issues with water quantity and availability. The unconsolidated deposits are particularly vulnerable to contamination from latrines and agriculture. Saline intrusion is an issue in the littoral area and high salinity is also reported in parts of the alluvial aquifer along the Oueme River valley. Recharge is not well quantified.

Coastal Sedimentary Basin aquifers (Consolidated Sedimentary - Intergranular Flow)

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Coastal sedimentary basin aquifers There are 4 main aquifers in the Coastal Basin, and they are the main source of drinking water for southern Benin. They are, in order of decreasing age, the Upper Cretaceous, Paleocene, Continental Terminal and Quaternary aquifers. They are separated by low permeability clays and marls, and may be confined or unconfined depending on the local geology.

Yields are generally 2 to 50 l/s. Transmissivity is generally 80 - 900 m²/d. Storage coefficient is typically 10-6 - 10-5.

The coastal sedimentary aquifers typically range from 20 to 150 m thick, with boreholes extending to depths of 10 to 100 m. Where the aquifers are unconfined, the water table depth may vary from 5 to 50 m below ground level.

Storage decreases where aquifer thickness is low (typically towards the upstream limits), which can lead to issues with groundwater availability. Total dissolved solids (TDS) is generally less than 500 mg/l and usually around 200 mg/l. pH is typically neutral to acidic. Saline intrusion is an issue in the littoral zone.

Unconfined aquifers are particularly vulnerable to contamination from latrines and agriculture, especially where the water table is very shallow.

Recharge is not well quantified.

Sedimentary - Kandi (Iullemeden) Basin and Precambrian - Voltaian (or Pendjari) Basin aquifers (Consolidated Sedimentary - Intergranular & Fracture Flow)

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Kandi Basin (Iullemeden) aquifer and Voltaian (or Pendjari) basin aquifer The Kandi Basin can be divided into two principal aquifers: a younger Cretaceous sandstone aquifer, and an underlying Cambro-Ordivician sandstone aquifer. The two aquifers are separated by low permeability fine sandstones and argillites of Silurian age. The Cretaceous aquifer comprises coarse sandstone; groundwater is unconfined and in hydraulic continuity with overlying unconsolidated alluvial deposits along the Niger River.

The underlying Cambro-Ordovician aquifer is also composed of coarse sandstone and is largely confined. It becomes unconfined in the south and west of the basin where the sandstone outcrops adjacent to Precambrian basement.

The Voltaian Basin aquifer has similar regional characteristics to the aquifers in the Kandi Basin.

Yields are rarely higher than 1.5 l/s. Transmissivity varies from <1 to >600 m²/d.

The total thickness of these aquifers is unknown. Boreholes typically vary in depth from 30 to 100 m. Where unconfined, the depth of the water table varies between 5 and 45 m below ground level.

There are no known issues with water quantity and availability. Conductivity, and thus total dissolved solids, is generally lower for the unconfined Cretaceous aquifer with values of 25 - 60 micro siemens per cm reported for the upper aquifer and 130 - 425 micro siemens per cm reported for the lower aquifer. Recharge is not well quantified.

Basement

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Basement Complex Sandstone (central Benin) and Atacora Series (northwest Benin) Basement aquifers have very low intergranular permeability in their unweathered state. Aquifer productivity depends on the development of a weathered zone. Coarser grained granites and gneiss generally weather to a more permeable sandy material which typically forms a low-moderate productivity aquifer. Weathered areas typically form shallow basins separated by largely unweathered rock. The presence and thickness of the weathered zone is highly variable, but is best developed on plateaus (often 10 to 30 m thick). Weathered basins typically thin towards outcropping inselbergs.

Yields are generally 0.25-0.5 l/s but can reach 2.0 l/s.

Hydraulic conductivity is generally 0.5 to 15 m/d. Tranmissivity is generally 5 to 35 m²/d. Storage coefficient is typically 10-3 - 10-2.

The basement aquifers are typically unconfined. Water table depths are generally 5 to 15 m below ground level, but can be deeper (up to 30 m below ground level). Seasonal water table fluctuations are thought to be between 1 and 5 m.

Boreholes are typically drilled to depths of 45 to 60 m.

Boreholes are usually fitted with handpumps, and therefore abstraction rates are typically low. Total dissolved solids (TDS) is generally less than 1000 mg/l and usually around 500 mg/l. pH is usually neutral to slightly basic. High salinity is occasionally reported.

The weathered basement is vulnerable to nitrate contamination from agricultural sources and latrines.

Recharge is not well quantified.

Groundwater Status

Low yields from basement aquifers, which cover most of Benin, lead to difficulties with fresh water availability in medium to large cities.

Potable water supply is also an issue in parts of the coastal basin, where the saturated thickness of the shallow aquifers is not sufficient for large supplies. Where the shallow deposits are unable to sustain sufficient yields, boreholes are drilled deeper into the weathered basement below.

Groundwater in shallow aquifers is often of poor quality due to contamination. Saline intrusion is a particular problem in the coastal aquifers.

The Oueme River loses water to the permeable coastal sedimentary aquifer, and river flow depletion is therefore an issue in this river downstream of the contact between the Precambrian basement aquifer and the coastal sedimentary aquifer.

The surface water coastal lagoons around Godomey in central-south Benin often dry up due to intensive pumping from the adjacent Godomey well field.

Groundwater use and management

Groundwater use

The main uses of groundwater in Benin are domestic supply (both urban and rural), agriculture, livestock and fish farming, tourism, industry and transport.

Groundwater sources vary from boreholes with electric pumps, hand pumps and foot pumps, modern and traditional wells, and traditional and improved springs.

Groundwater management

The key groundwater institutions in Benin are:

  • National Company of Urban Water Supply (SONEB) - responsible for groundwater supply in urban areas.
  • General Directorate of Water (DG-Eau) - - responsible for groundwater supply in rural areas.

The "Code of Water in Benin" is the key piece of legislation related to groundwater management. Permits are required for drilling and groundwater abstraction. These are issued by the government through the Ministry of Justice and the Ministry of Water. Groundwater protection is very difficult particularly in more densely populated areas because the disposal of waste is largely uncontrolled.

Transboundary aquifers

In the coastal region the Quaternary and Continental Terminal aquifers are shared with Nigeria, Benin, Togo and Ghana.

The aquifers of the Iullemeden Basin are shared with Niger, Mali and Nigeria.

For further general information about transboundary aquifers, please see the Transboundary aquifers resources page

Groundwater monitoring

Groundwater monitoring is carried out by the National Company of Urban Water Supply (SONEB), the General Directorate of Water (DG-Eau) and the National Institute of Water.

The Laboratory of Climatology carries out work to look at climate change impacts on groundwater.

References

The following references provide more information on the geology and hydrogeology of Benin.

Geology References

Affaton P. 1975. Etude géologique et structurale du Nord-Ouest du Dahomey, du Nord Togo et du Sud-Est de la Haute Volta. Travaux Laboratoire Sciences de la Terre, St-Jérôme, Marseille, France, (B) 201 p.

Alidou S. 1983. Etude géologique du bassin paléo-mésozoique de Kandi, Nord-Est du Bénin (Afrique de l’Ouest). Thèse de doctorat ès-Sciences, 328 p. Université de Dijon, France.

Alidou S et Oyédé LM. 1984. Quaternaire du Bénin. ASEQUA, Dakar. Bulletin de Liaison, 72-73, 42-43.

Boussari WT. 1975. Contribution à l’étude géologique du socle cristallin de la zone mobile Pan-africaine (région central du Dahomey). Thèse de 3ème cycle, 105 p. Université de Besançon, 236.

BRGM. 1978. Carte géologique au 1/200 000 du Bénin et du Togo entre les 9ème et 10ème degré de latitude Nord. Rapport, OBEMINES. Cotonou, Bénin. 78 RDM 055 AF. 2 feuilles, 1 notice explicative.

Guiraud R et Alidou S. 1981. La faille de Kandi (Bénin), témoin du rejeu fini-Crétacé d’un accident majeur à l’échelle de la plaque africaine. Comptes Rendus Académie des Sciences. Paris, France. 293 (II) 779-782.

Houessou A et Lang J. 1979. La "Terre de Barre" dans le Bénin méridional (Afrique de l’Ouest). Bulletin ASEQUA 56-57, 49-58.

IRB ou Istituto recerche Breda. 1982. Etude de cartographie géologique et prospection minière de reconnaissance au Nord du 11ème parallèle. Rapport final OBEMINES, Cotonou, Bénin.

IRB ou Istituto recerche Breda. 1987. Etude de cartographie géologique et prospection minière de reconnaissance au Sud du 9ème parallèle. Rapport, 80 p. OBEMINES, Cotonou, Bénin.

Konaté M. 1996. Evolution tectono-sédimentaire du bassin paléozoïque de Kandi (Nord-Bénin et Sud-Niger): un témoin de l’extension post-orogénique de la chaîne panafricaine. Thèse doctorat, 281 p. Université de Bourgogne et Université de Nancy I. France.

Konaté M, Guiraud M, Alidou S, Clermonté J, Drouet J-J et Lang J. 1994. Structuration et dynamique sédimentaire du bassin paléozoïque en demi-graben de Kandi (Bénin, Niger). Comptes Rendus Académie des Sciences. Paris, France. 318 (II) 535-542.

Lang J, Kogbe C, Alidou S, Alzouma K, Bellion G, Dubois D, Houessou A et Trichet J. 1986. Le sidérolithique du Tertiaire oust-africain et le concept du Continental Termial. Bulletin de la Société. Géologique de France. 8, (II) 605-622.

Oyédé LM, de Klasz I, de Klasz S, Lang J, Carbonnel G, Grosdidier E, Legoux O et Martini E. 1992. Datation de la discordance dite «oligocène» sur la partie terrestre du bassin sédimentaire côtier béninois (Afrique de l’Ouest). Comptes Rendus Académie des Sciences. Paris, France. 315(II), 971-977.

Oyédé LM. 1991. Dynamique sédimentaire actuelle et messages enregistrés dans les séquences quaternaires et néogènes du domaine margino-littoral du Bénin (Afrique de l'Ouest). Thèse de doctorat, 302 p. Université de Bourgogne, Dijon, France.

Pougnet R. 1955. Le Précambrien du Dahomey. 186 p. Bulletin de la Direction Fédérale des Mines de l’Afrique Occidentale française. Dakar, Sénégal. 22.

SERHAU ou Service d’Etude et de Recherche pour l’Habitat et l’Urbanisme. 1992. Atlas cartographique de la région nord du Bénin. Rapport, 54 p. MEHU. Cotonou, Bénin.

Slansky M. 1962. Contribution à l'étude géologique du Bassin sédimentaire côtier du Dahomey et du Togo. Thèse de doctorat, 241 p. Université de Nancy, Nancy, France.

TECHNOEXPORT. 1980. La constitution et les substances utiles de la République Populaire du Bénin entre les 10ème et 11ème parallèles de latitude nord. Rapport Office Béninois des Mines. Cotonou, Moscou, Bénin, URSS.

TECHNOEXPORT. 1984. La constitution et les substances utiles de la partie Est de la République Populaire du Bénin, entre les 10ème et 11ème parallèles de latitude nord (rapport du levé et de prospection géologiques à l’échelle de 1/200 000 effectués en 1981-1984). Rapport, 331 p. Office Béninois des Mines. Cotonou, Bénin.

Wakuti KE et Gall KG. 1968. Reconnaissance géophysique et sondages mécaniques dans le Centre, Nord-Est et Nord-Ouest du Dahomey. Rapport Direction Hydraulique, Mines et Travaux Publics. Cotonou, Bénin.


Hydrogeology References

Key references are highlighted in bold.

Achidi, J-B, Bourguet L, Elsaesser R, Legier A, Paulvé E et Triboullard N. 2012. Cartes hydrogéologiques du Bénin au 1/500 000 and 1/200000. GIZ Germany or DGEau Benin.

Alassane A. 2004. Etude hydrogéologique du Continental Terminal et des formations de la plaine littorale dans la région de Porto-Novo (sud du Bénin): identification des aquifères et vulnérabilité de la nappe superficielle. Thèse 3ème cycle, 145 p. Université Cheik Anta Diop, Dakar, Sénégal.

Alidou S et Oyédé LM. 1984. Quaternaire du Bénin. ASEQUA, Dakar. Bulletin de Liaison, 72-73, 42-43.

Boukari M. 1980. Contribution à l’étude hydrogéologique des régions de socle de l’Afrique occidentale : mise au point des connaissances relatives à la République Populaire du Bénin. Rapport Département de Géologie. No 4. Nouvelle série. Mémoire de DEA, 141 p. Université de Dakar, Sénégal.

Boukari M. 1982. Contribution à l’étude hydrogéologique des régions de socle de l’Afrique intertropicale : l’hydrogéologie de la région de Dassa-Zoumé (Bénin). Thèse 3ème cycle, 140 p. Université Cheik Anta Diop, Dakar, Sénégal.

Boukari M. 1989. Etude de synthèse et de cartographie relative au cadre physique et aux ressources naturelles de la région nord du Bénin. Rapport SERHAU, 68 p. Cotonou, Bénin.

Boukari M, Alidou S, Oyédé LM, Gaye CB et Maliki R. 1995. Identification des aquifères de la area littorale du Bénin (Afrique de l'Ouest) : hydrodynamique, hydrochimie et problèmes d'alimentation en eau de la ville de Cotonou. African Geoscience Review 2 (1), 139-157.

Boukari M, Gaye CB, Faye A et Faye S. 1996. The impact of urban development on coastal aquifers near Cotonou (Bénin). Journal of African Earth Sciences 22 (4), 403-408.

Boukari M. 1998. Fonctionnement du système aquifère exploité pour l’approvisionnement en eau de la ville de Cotonou sur le littoral béninois. Impact du développement urbain sur la qualité des ressources. Thèse de doctorat ès Sciences, 278 p. Université Cheik Anta Diop, Dakar Sénégal.

Boukari M. 2002. Réactualisation des connaissances hydrogéologiques relatives au bassin sédimentaire côtier du Bénin. Rapport du programme d’Appui à la Gestion des Ressources en Eau (AGRE), 134 p. Direction Hydraulique. Cotonou, Bénin.

Boukari, M. 2007. Hydrogéologie de la République du Bénin (Afrique de l’ouest). Africa Geoscience Review (2007), Vol. 14, N° 3, pp. 303-328. France.

Boukari M et Alassane A. 2007. Les ressources en eaux souterraines du bassin sédimentaire côtier de la République du Bénin. Africa Geoscience Review (2007), Vol. 14, N° 3, pp. 283-301. France.

Bouzid M. 1971. Développement de l’utilisation des eaux souterraines, Dahomey : hydrogéologie. Rapport technique 1, 88 p. PNUD-FAO. SF/DAH3. Rome, Italie.

BURGEAP-BRGM. 1986. Programme d’hydraulique villageoise du Nord-Borgou (Bénin). Etudes d’implantation et contrôle des travaux de points d’eau. Rapport final, 74 p. Direction de l’Hydraulique. Cotonou, Bénin.

BURGEAP-BRGM. 1994. Projet d’alimentation en eau potable des areas lacustres des Départements de l’Atlantique et de l’Ouémé. Rapport final, 64 p. Direction de l’Hydraulique, Cotonou, Bénin. CEFIGRE ou Centre de Formation Internationale à la Gestion des Ressources en Eau. 1984. Synthèse des connaissances sur l’hydrogéologie du socle cristallin et cristallophyllien, et du sédimentaire ancien de l’Afrique de l’Ouest. Rapport Ministère des Relations Extérieures. 121 p. Valbonne. France.

CEFIGRE. 1984. Synthèse des connaissances sur l’hydrogéologie du socle cristallin et cristallophyllien, et du sédimentaire ancien de l’Afrique de l’Ouest. Rapport Ministère des Relations Extérieures. Valbonne. France.121 p.

Collin JJ et Mangin, A. 1985. Evolution récente de l'hydrogéologie: de la prospection à la gestion des ressources en eau. Bulletin de la Société. Géologique de France. 7, 999-1008. Descloitres, M., Séguis, L., and Wubda, M. (2006). Caractérisation des aquifères sur les sites AMMA CATCH au Bénin, apport de la résonnance magnétique des protons. Rapport de mission. Direction de l’Hydraulique. 2000. Vision Eau 2025 Bénin. Rapport 28 p. Direction de l’Hydraulique, Cotonou, Bénin.

Descloitres M, Séguis L and Wubda, M. 2006. Caractérisation des aquifères sur les sites AMMA CATCH au Bénin, apport de la résonnance magnétique des protons. Rapport de mission.

Dray M, Giachello L, Lazzarotto V, Mancini M, Roman E et Zuppi GM. 1988. Etude isotopique de l’aquifère crétacé du bassin côtier béninois. Actes du Séminaire sur le développement des techniques isotopiques et nucléaires en hydrologie dans les pays du Sahel. Niamey, Niger. 21-35.

El Fahem T. 2008. Hydrogeological conceptualisation of a tropical river catchment in a crystalline basement area and transfer into a numerical groundwater model, Case study for the Upper Oueme catchment in Benin. PhD thesis, Université of Bonn, Germany.

Engalenc M. 1978a. Les modalités de la recherche d’eau dan les roches cristallines fracturées de l’Afrique de l’Ouest. Bull. CIEH, nº 33-34, 22-30.

Engalenc M. 1978b. Méthode d’étude et de recherche de l’eau souterraine des roches cristallines de l’Afrique de l’Ouest. Rapport CIEH, 318 p. Ouagadougou. Haute-Volta.

Falola E et Sotognon FC. 2002. Impact de l’utilisation des intrants agricoles sur la qualité Chimique des nappes d’eaux souterraines dans les Départements du Borgou et de l’Alibori. Mémoire de Maîtrise, 59 p. Université d’Abomey-Calavi, Bénin.

GEOHYDRAULIQUE-BURGEAP. 1988. Projet d’hydraulique villageoise de l’Atlantique et du Sud du Zou. Rapport final, 185 p. Direction de l’Hydraulique, Cotonou, Bénin.

GEOHYDRAULIQUE. 1985. Note explicative de la carte hydrogéologique à 1/200 000 du bassin sédimentaire côtier du Bénin. Rapport, 23 p. Direction de l’Hydraulique, Cotonou, Bénin.

GEOHYDRAULIQUE. 1985b. Hydraulique villageoise dans les provinces de l’Atacora, du Mono et de l’Ouémé. Rapport final, 236 p. 1. Direction de l’Hydraulique, Cotonou, Bénin.

GIGG ou Groupement IGIP-GKW-GRAS. 1983. Plan Directeur Alimentation en eau potable ville de Cotonou : les ressources en eau. 2 volumes. Rapport, Société Béninoise d’Electricité et d’Eau, Cotonou, Bénin.

Gnaha EFC et Adjadji ChA. 2001. Evolution quantitative et qualitative des ressources en eaux souterraines captées dans le périmètre de pompage intensif de Godomey: impact sur l’approvisionnement en eau potable de l’agglomération de Cotonou. Mémoire Maîtrise, 53 p. Géologie Appliquée. Université.Abomey-Calavi, Cotonou, Bénin.

Guiraud R. 1975. Eléments pour une orientation nouvelle de la recherche des eaux souterraines dans les régions à substratum métamorphique ou éruptif de l’Afrique Occidentale. Réunion de Porto-Alegre. Mémoire AIH, XI, 15-19.

Guiraud R. 1976. Sur la présence des nappes aquifères de fissures dans le socle précambrien de l’Afrique intertropicale. 4ème Réunion Annuelle des Sciences de la Terre. Société Géologique de France. Paris.

Guiraud R. 1988. L’hydrogéologie de l’Afrique. Journal of African Earth Sciences 7, 519-543.

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