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[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Guinea Bissau | [[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Guinea Bissau | ||
+ | '''This page is being updated - please check back soon for more information''' | ||
− | + | '''Do you have more information on hydrogeology of Guinea Bissau? Please get in touch.''' | |
+ | Present-day Guinea Bissau was once part of the Gabu kingdom and the ancient Mali empire. From the 15th century, the coast became a centre of slave trading by Portuguese merchants, which, as well as inland areas, became fully colonised by the Portuguese in the 19th century. An armed rebellion against colonial rule from the 1950s led to independence in 1974. The rebels were allied to an extent with independence fighters from another Portuguese colony, Cape Verde, although the two countries never unified. Since independence, Guinea Bissau has experienced constant political change, with a succession of coups. | ||
− | + | Guinea Bissau adopted the CFA currency in 1997. There is some potential for mineral exploitation and possibly offshore hydrocarbon exploitation, but their development has been impeded by political instability and armed conflict. The economy remains dominated by agriculture and fishing, with cashew nuts and groundnuts the most important export crops. GDP and HDI remain some of the lowest world-wide. Illegal drug trafficking is significant, with the country used as a transit point for drugs between South America and Europe. | |
− | + | A tropical country with high but seasonal rainfall, Guinea Bissau has relatively abundant seasonal surface water resources, but dry season water supplies are largely sourced from groundwater. | |
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− | Guinea Bissau has relatively abundant seasonal surface water resources | ||
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The larger rivers in Guinea Bissau include the Corubal and the Geba rivers, which rise in neighbouring Senegal or Guinea. Smaller coastal rivers include the Cacheu, Mansoa, Geba-Corubal, Grande de Buba, Tombali, Cumbidja and Cacine rivers. | The larger rivers in Guinea Bissau include the Corubal and the Geba rivers, which rise in neighbouring Senegal or Guinea. Smaller coastal rivers include the Cacheu, Mansoa, Geba-Corubal, Grande de Buba, Tombali, Cumbidja and Cacine rivers. | ||
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| [[File:Guinea-Bissau_Hydrology.png | frame | Major surface water features of Guinea Bissau. Map developed from World Wildlife Fund HydroSHEDS; Digital Chart of the World drainage; and FAO Inland Water Bodies. For more information on the map development and datasets see the [[Surface water | surface water resource page]]]] | | [[File:Guinea-Bissau_Hydrology.png | frame | Major surface water features of Guinea Bissau. Map developed from World Wildlife Fund HydroSHEDS; Digital Chart of the World drainage; and FAO Inland Water Bodies. For more information on the map development and datasets see the [[Surface water | surface water resource page]]]] | ||
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|Freshwater withdrawal as % of total renewable water resources || || 0.5573|| || || || | |Freshwater withdrawal as % of total renewable water resources || || 0.5573|| || || || | ||
|- | |- | ||
− | | | + | |Renewable groundwater resources (Million cubic metres/year) || || || ||350 || || |
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|Groundwater produced internally (Million cubic metres/year) || || || || ||14,000 || | |Groundwater produced internally (Million cubic metres/year) || || || || ||14,000 || | ||
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<sup>1</sup> More information on [http://www.fao.org/nr/water/aquastat/water_use_agr/index.stm irrigation water use and requirement statistics] | <sup>1</sup> More information on [http://www.fao.org/nr/water/aquastat/water_use_agr/index.stm irrigation water use and requirement statistics] | ||
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==Geology== | ==Geology== | ||
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A more detailed geology map of Guinea Bissau is available to view and interrogate online at the [http://geoportal.lneg.pt/geoportal/mapas/index.html?mapa=CartaGuine '''Visualizador de Mapas geoPortal'''] (published 2014). This map was created by the Uidade de Informacao Geocientifica of the Portugese National Laboratory of Energy and Geology ([http://www.lneg.pt/Default.aspx LNEG)]. | A more detailed geology map of Guinea Bissau is available to view and interrogate online at the [http://geoportal.lneg.pt/geoportal/mapas/index.html?mapa=CartaGuine '''Visualizador de Mapas geoPortal'''] (published 2014). This map was created by the Uidade de Informacao Geocientifica of the Portugese National Laboratory of Energy and Geology ([http://www.lneg.pt/Default.aspx LNEG)]. | ||
− | This report provides more information on the Geology of Guinea Bissau | + | This report provides more information on the Geology of Guinea Bissau ([http://repositorio.lneg.pt/handle/10400.9/1227?locale=en Geologia da Guiné-Bissau]) (Alves 2010). |
− | [[File:Guinea- | + | [[File:Guinea-Bissau_Geology2.png | center | thumb| 500px | Geology of Guinea Bissau at 1:5 million scale. Based on map described by Persits et al. 2002/Furon and Lombard 1964. For more information on the map development and datasets see the [[Geology | geology resource page]].]] |
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Guinea-Bissau lies between the Fouta Djallon massif, of uncertain Palaeozoic age, and the Mesozoic-Cenozoic Senegal basin (UN 1988). It can be roughly divided into two geological units: | Guinea-Bissau lies between the Fouta Djallon massif, of uncertain Palaeozoic age, and the Mesozoic-Cenozoic Senegal basin (UN 1988). It can be roughly divided into two geological units: | ||
− | * an eastern zone with predominantly clastic sedimentary Paleozoic rocks, and some Precambrian rocks; and | + | * an eastern zone with predominantly clastic sedimentary Paleozoic rocks, and some carbonates of Silurian age; and some Precambrian rocks; and |
− | * a western zone with mainly Cenozoic sediments | + | * a western zone with mainly late Mesozoic to Cenozoic sediments. The Cretaceous to Cenozoic sediments are mainly of marine origin (University of Guelph). |
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− | + | There is a buried sequence of earlier Mesozoic sedimentary rocks thought to rest on the Palaeozoic sequence, which is the equivalent of the 'intercalated continental' series known in Senegal. These do not crop out at the surface in Guinea Bissau, and so are not shown on the geology map. Little is known of these rocks in Guinea Bissau, as they are buried at depths of over 800 m (UN 1988). They are thought to include schists with some sandstone and limestone intercalations in the northeast, and a dominantly continental series of schists with intercalations of fine sandstone in the centre of the country. This series is 120 m thick at Safim and 330 m thick at S. Domingos (UN 1988). | |
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||Coastal sediments, including beach sands; river and coastal alluvium. Including sands, silts, and clays. These often overlie similar lagoonal-coastal Oligocene-Miocene sediments (see below). | ||Coastal sediments, including beach sands; river and coastal alluvium. Including sands, silts, and clays. These often overlie similar lagoonal-coastal Oligocene-Miocene sediments (see below). | ||
|- | |- | ||
− | !colspan="4"|Tertiary | + | !colspan="4"|Cretaceous - Tertiary sedimentary |
|- | |- | ||
− | | | + | |Maastrichtian, Palaeocene-Eocene, Oligocene, Miocene |
− | ||A sequence of largely marine, coastal or lagoonal sedimentary rocks, including limestones, marls, clays, silts, sands and phosphates. | + | ||A sequence of largely marine, coastal or lagoonal sedimentary rocks, including limestones, marls, clays, silts, sands and phosphates. |
+ | |||
+ | The Oligocene-Miocene 'continental terminal' series comprises Oligocene lagoonal fine grained, clayey sandstones at the base, overlain by Miocene marine limestone-marls that are sometimes sandy (UN 1988). | ||
The Palaeocene-Eocene sequence is dominantly marine, formed of sandy marl-limestone formations with dolomitic intercalations (UN 1988). | The Palaeocene-Eocene sequence is dominantly marine, formed of sandy marl-limestone formations with dolomitic intercalations (UN 1988). | ||
− | The | + | The Middle and Upper Cretaceous series is very thick (1360 m at S. Domingos and 600 m at Safim). The base of the sequence consists of schists with some limestone-dolomitic intercalations, overlain by dark shales with some sand, and terminating at the top in a thick sandstone layer of Maastrichtian (top Cretaceous) age (UN 1988). This top sandstone is up to 490 m thick in the northwest (S. Domingos) and 540 m in the west (Cangongue) (UN 1988). |
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!colspan="4"|Igneous | !colspan="4"|Igneous | ||
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|- | |- | ||
|Devonian | |Devonian | ||
− | ||Shales and sandstones over a large area in the east of the country, forming a northwest/southeast syncline. | + | ||Shales and sandstones over a large area in the east of the country, forming a northwest/southeast syncline. The base of the series consists of the sandstones of Lower Devonian age in the Cusselinta-Saltinho area, which are mostly well consolidated micaceous and feldspathic sandstones. Overlying this is the Upper Devonian Bafata Group, comprising argillaceous schists with intercalactions of fine grained quartz sandstone. |
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− | Overlying this is the | ||
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|Silurian | |Silurian | ||
− | || | + | ||Rocks of the Buba Group, including sandstones with some organic rich/carbonaceous black shales. Drilling in the southeast of the country showed very compact black, carbonaceous schists with fine grained sandstone intercalations, and some doloritic layers. In the northeast, schists interbedded with dolerite were seen, with varying indications of metamorphism, and fine grained, clay-rich sandstones at the top at the transition to the overlying Devonian rocks. |
|- | |- | ||
− | |Ordovician | + | |Cambrian-Ordovician |
||Sandstones, shales, conglomerates and rare limestones. These are found in the northeast of the country, overlying older Neoproterozoic metamorphic rocks. | ||Sandstones, shales, conglomerates and rare limestones. These are found in the northeast of the country, overlying older Neoproterozoic metamorphic rocks. | ||
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Cambrian rocks are dominated by fine grained sandstones and shales, including shales of Pirada and Canquelifa, schist-sandstones of Cantari, and the younger Caium sandstones of Upper Cambrian age. | Cambrian rocks are dominated by fine grained sandstones and shales, including shales of Pirada and Canquelifa, schist-sandstones of Cantari, and the younger Caium sandstones of Upper Cambrian age. | ||
+ | Ordovician rocks are dominated by the Gabu sandstone series, which is thought to be mostly steeply dipping at up to 50 degrees. At its base is a white, coarse grained sandstone unit up to 170 m thick, overlain by less compact, sandier strata of considerable thickness, and then by a fine grained sandstone unit that is 10-30 m thick (UN 1988). | ||
|- | |- | ||
− | !colspan="4"|Precambrian | + | !colspan="4"|Precambrian metamorphic complex |
|- | |- | ||
|Neoproterozoic | |Neoproterozoic | ||
− | ||A volcanic and metasedimentary complex, including schists, quartzites and metavolcanic rocks. There are few outcrops | + | ||A volcanic and metasedimentary complex, including schists, quartzites and metavolcanic rocks. There are few outcrops of these rocks, as they generally lie below fairly thick younger geological formations. |
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|} | |} | ||
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The hydrogeology map below 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). | The hydrogeology map below 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). | ||
− | + | A little more information on the hydrogeology of Guinea Bissau can be found in the report [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060039 United Nations (1988)] (see References section, below). | |
− | [[File:Guinea- | + | [[File:Guinea-Bissau_Hydrogeology2.png| center | thumb| 500px | Hydrogeology of Guinea Bissau at 1:5 million scale. For more information on how the map was developed see the [[Hydrogeology Map | hydrogeology map]] resource page]] |
'''Summary''' | '''Summary''' | ||
− | + | Relatively little is available to describe the hydrogeology and groundwater potential of the aquifers in Guinea Bissau. | |
− | In the eastern part of the country, | + | In the eastern part of the country, Basement and Palaeozoic Sedimentary (Fracture flow) aquifers are dominant. These rocks typically have low permeability and form small and discontinuous aquifers, controlled by the distribution, nature and degree of fracturing and weathering. Boreholes must be sited and drilled with great care to locate them in the most productive zones. |
− | In the west of the country, the Cretaceous-Tertiary-Quaternary sequence forms more continuous aquifers. The three main aquifers are: | + | In the west of the country, the Cretaceous-Tertiary-Quaternary sequence forms more continuous aquifers. The three main aquifers here are: |
* Maastrichtian sands | * Maastrichtian sands | ||
* Palaocene-Eocene (limestone)-Oligocene (sand), and | * Palaocene-Eocene (limestone)-Oligocene (sand), and | ||
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====Unconsolidated==== | ====Unconsolidated==== | ||
{| class = "wikitable" | {| class = "wikitable" | ||
− | |Aquifer | + | |Aquifer||Description |
|- | |- | ||
− | |Quaternary | + | |Dominantly Quaternary |
− | || | + | ||Coastal/marine silty sands and laterite. These are usually unconfined. |
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|} | |} | ||
====Sedimentary - Mixed Intergranular and Fracture flow==== | ====Sedimentary - Mixed Intergranular and Fracture flow==== | ||
{| class = "wikitable" | {| class = "wikitable" | ||
− | |Aquifer|| | + | |Aquifer||Description |
+ | |- | ||
+ | |Tertiary (Oligocene-Miocene) | ||
+ | ||The Oligocene-Miocene series of Eocene largely unconsolidated sands and Miocene limestones form significant aquifers. | ||
|- | |- | ||
− | |Tertiary (Palaeocene-Eocene | + | |Tertiary (Palaeocene-Eocene) |
− | || | + | ||The Palaeocene-Eocene marine sandy marl-limestones are an important aquifer, which has been explored by a number of deep boreholes for groundwater reconnaissance and exploitation (UN 1988). The sandstones are likely to be dominated by intergranular flow, and the limestones by fracture flow. |
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− | |Cretaceous | + | |Cretaceous |
− | + | ||The main Cretaceous aquifer is the thick sandstone bed of Maastrichtian age, at the top of the Cretaceous sequence, which is an aquifer of major importance in Guinea Bissau. It has been explored and exploited most intensively and at shallowest depths close to its outcrop zone in central and southern regions, and by a number of deeper boreholes 200 - 260 m deep on the island of Bissau and at Farim (UN 1988). The aquifer productivity declines in the direction of the Silurian rocks, because they become shallower and change from poorly consolidated sand to a more compact, well consolidated sandstone that has lower permeability (UN 1988). | |
− | ||The main Cretaceous aquifer is the thick sandstone bed of Maastrichtian age, at the top of the Cretaceous sequence, which is an aquifer of major importance in Guinea Bissau. It has been explored and exploited most intensively and at shallowest depths close to its outcrop zone in central and southern regions, and by a number of deeper boreholes 200-260 m deep on the island of Bissau and at Farim (UN 1988). The aquifer productivity declines in the direction of the Silurian rocks, because they become shallower and change from poorly consolidated sand to a more compact, well consolidated sandstone that has lower permeability (UN 1988). | ||
− | Test pumping | + | Test pumping showed a range of permeability XXX |
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The aquifer is largely confined, except at rare points where it crops out. Artesian heads occur across much of the centre and west of the country, but not in the southern part of the coastal zone. Artesian heads at Farim and Mansoa were measured at +6m and +7m. Close to the sea and estuaries, groundwater heads are affected by tides. The main direction of groundwater flow appears to be towards the northwest and west (UN 1988). | The aquifer is largely confined, except at rare points where it crops out. Artesian heads occur across much of the centre and west of the country, but not in the southern part of the coastal zone. Artesian heads at Farim and Mansoa were measured at +6m and +7m. Close to the sea and estuaries, groundwater heads are affected by tides. The main direction of groundwater flow appears to be towards the northwest and west (UN 1988). | ||
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====Igneous==== | ====Igneous==== | ||
{| class = "wikitable" | {| class = "wikitable" | ||
− | |Aquifer | + | |Aquifer||Description |
|- | |- | ||
− | | | + | | |
− | || | + | || |
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|} | |} | ||
====Sedimentary - Fracture flow (Palaeozoic aquifers)==== | ====Sedimentary - Fracture flow (Palaeozoic aquifers)==== | ||
{| class = "wikitable" | {| class = "wikitable" | ||
− | |Aquifer | + | |Aquifer||Description |
|- | |- | ||
|Devonian | |Devonian | ||
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||Drilling into these rocks at shallow depths to about 20 m in the Nhabijocs plain (Bombadinca) showed them to be well consolidated with low permeability and to form a poor aquifer. | ||Drilling into these rocks at shallow depths to about 20 m in the Nhabijocs plain (Bombadinca) showed them to be well consolidated with low permeability and to form a poor aquifer. | ||
|- | |- | ||
|Silurian | |Silurian | ||
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||The Buba Group has been explored by drilling water boreholes in a number of places at Buba, Guilege, Gadamael and Sangonha in the northeast and southeast of the country. The dominantly fine grained, sometimes clay-rich sandstones, black carbonaceous shales and intercalations of dolerite, sometimes metamorphosed, all have low permeability and formed very poor aquifers. | ||The Buba Group has been explored by drilling water boreholes in a number of places at Buba, Guilege, Gadamael and Sangonha in the northeast and southeast of the country. The dominantly fine grained, sometimes clay-rich sandstones, black carbonaceous shales and intercalations of dolerite, sometimes metamorphosed, all have low permeability and formed very poor aquifers. | ||
|- | |- | ||
|Cambro-Ordovician | |Cambro-Ordovician | ||
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||The Cambrian rocks, dominated by fine grained, well consolidated sandstones and shales, generally form very poor aquifers. Small local aquifers can be found in shallow weathered zones, and particularly in sandstones, which typically have slightly higher permeability. | ||The Cambrian rocks, dominated by fine grained, well consolidated sandstones and shales, generally form very poor aquifers. Small local aquifers can be found in shallow weathered zones, and particularly in sandstones, which typically have slightly higher permeability. | ||
Little is known of the groundwater potential of the Ordovician sandstones, although drilling in the Canjadude region showed the sandstone to be compacted, with low permeability, and unproductive. | Little is known of the groundwater potential of the Ordovician sandstones, although drilling in the Canjadude region showed the sandstone to be compacted, with low permeability, and unproductive. | ||
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====Basement==== | ====Basement==== | ||
{| class = "wikitable" | {| class = "wikitable" | ||
− | |Aquifer | + | |Aquifer||Description |
|- | |- | ||
− | | | + | | |
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|} | |} | ||
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==Groundwater use and management== | ==Groundwater use and management== | ||
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===Groundwater use=== | ===Groundwater use=== | ||
− | Groundwater is the main source of rural water supply | + | Groundwater is the main source of rural water supply in the dry season, for drinking water and small scale (garden) irrigation. |
− | + | Traditional small scale irrigation typically uses groundwater from shallow, hand dug wells. Groundwater is not used much for large scale commercial irrigation, although in at least one area - Granja de Pessub - drilled boreholes up to 300 m deep are used for irrigation ([http://www.fao.org/nr/water/aquastat/countries_regions/GNB/ Aquastat]). | |
===Groundwater management=== | ===Groundwater management=== | ||
− | The | + | The main agencies involved in water management in Guinea Bissau are (http://www.fao.org/nr/water/aquastat/countries_regions/GNB/ Aquastat): |
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− | * | + | * the Ministry of Agriculture, Forestry, Hunting and Livestock, through the Directorate of Rural Engineering Services (DSER), which deals with the developments use and management of water for agricultural use. |
− | + | * the Directorate General of Water Resources of the State Secretariat for Industry, Natural Resources and the Environment (SEIRNA) | |
− | * | ||
* the Council Interministerial for Water Resources (CIMA) and the Water Technical Committee, which exist to harmonise water management activities between different sectors and to drive water policies. | * the Council Interministerial for Water Resources (CIMA) and the Water Technical Committee, which exist to harmonise water management activities between different sectors and to drive water policies. | ||
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At a local level, the operation of water infrastructure is largely managed by the beneficiaries themselves through associations or management committees, in collaboration with the DSER, extension services, NGOs and other relevant authorities. | At a local level, the operation of water infrastructure is largely managed by the beneficiaries themselves through associations or management committees, in collaboration with the DSER, extension services, NGOs and other relevant authorities. | ||
− | + | ====Groundwater policy==== | |
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− | ====Groundwater | ||
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− | + | The Water Code, 1992, established the general regime for the management, use and conservation of water resources, and determines the institutional framework. It recognises that water is a public good whose development and management must be planned. Use rights are granted by the State, taking into account the productivity of water, the respect of pre-existing rights and the protection of the environment. The State is responsible for the conservation and protection of the water environment both qualitatively and quantitatively. Customary water law is enforced and respected at the local level by rural people. | |
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===Transboundary aquifers=== | ===Transboundary aquifers=== | ||
− | + | For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]. | |
− | |||
− | For further | ||
==References== | ==References== | ||
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Alves PH. 2010. [http://repositorio.lneg.pt/handle/10400.9/1227?locale=en Geologia da Guinée-Bissau]. X Congresso de Geoquimica dos Paises de Lingua Portuguesa, XVI Semana de Geoquimica. LNEG – Laboratório Nacional de Energia e Geologia / IICT – Instituto de Investigação Científica Tropical | Alves PH. 2010. [http://repositorio.lneg.pt/handle/10400.9/1227?locale=en Geologia da Guinée-Bissau]. X Congresso de Geoquimica dos Paises de Lingua Portuguesa, XVI Semana de Geoquimica. LNEG – Laboratório Nacional de Energia e Geologia / IICT – Instituto de Investigação Científica Tropical | ||
− | + | Fussi F, Asplund F, Fumagalli L, Caruba M, Rotiroti M and Bonomi T. 2017. [https://upgro.files.wordpress.com/2015/09/t224_fussi-presentation-iah2.pdf Characterization of shallow aquifer in Guinea Bissau to support the promotion of manual drilling at country level]. Presentation at 44th IAH Congress, 25-29 Sept 2017. | |
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− | Fussi F, Asplund F, Fumagalli L, Caruba M, Rotiroti M and Bonomi T. | ||
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University of Guelph. [http://www.uoguelph.ca/~geology/rocks_for_crops/30guinea_bissau.PDF Rocks for Crops]. | University of Guelph. [http://www.uoguelph.ca/~geology/rocks_for_crops/30guinea_bissau.PDF Rocks for Crops]. | ||
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United Nations. 1988. [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060039 Groundwater in North and West Africa: Guinea-Bissau]. United Nations Department of Technical Cooperation for Development and Economic Commission for Africa. | United Nations. 1988. [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=ViewDetails&id=AGLA060039 Groundwater in North and West Africa: Guinea-Bissau]. United Nations Department of Technical Cooperation for Development and Economic Commission for Africa. | ||
− | + | ==Return to the index pages== | |
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− | Return to the index pages | ||
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Guinea Bissau | [[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Guinea Bissau | ||