Hydrogeology of Guinea Bissau

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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.


Compilers

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 and Bellwood-Howard, 2018.

Bibliographic reference: Upton, K, Ó Dochartaigh, B É and Bellwood-Howard, I. 2018. Africa Groundwater Atlas: Hydrogeology of Guinea Bissau. British Geological Survey. Accessed [date you accessed the information]. http://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Guinea_Bissau

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Geographical Setting

Guinea Bissau.Map developed from USGS GTOPOPO30; GADM global administrative areas; and UN Revision of World Urbanization Prospects. For more information on the map development and datasets see the geography resource page

General

Guinea Bissau's territory includes the Bijagos archipelago, made up of more than 30 offshore islands. Most of the country is flat and low lying, with a maximum elevation of 40 m, and many areas of wetlands, including coastal mangrove swamps. The exception is the flat topped Boé Colline hills in the southeast, which reach 300 m elevation.

Capital city Bissau
Region Western Africa
Border countries Senegal, Guinea
Total surface area* 36,130 km2 (3,613,000 ha)
Total population (2015)* 1,844,000
Rural population (2015)* 962,000 (52%)
Urban population (2015)* 882,000 (48%)
UN Human Development Index (HDI) [highest = 1] (2014)* 0.4196

* Source: FAO Aquastat


Climate

Guinea Bissau has a wet tropical climate, with a wet season typically from April to October and a dry season from November to March. The eastern part of the country has lower rainfall, and the western coastal zone has higher rainfall.

Koppen Geiger Climate ZonesAverage Annual PrecipitationAverage Temperature

Average monthly precipitation for Guinea Bissau showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for Guinea Bissau 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)


More information on average rainfall and temperature for each of the climate zones in Guinea Bissau can be seen at the Guinea Bissau climate page.

These maps and graphs were developed from the CRU TS 3.21 dataset produced by the Climatic Research Unit at the University of East Anglia, UK. For more information see the climate resource page.

Surface water

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.

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 resource page

Soil

Soil Map of Guinea Bissau, from the European Commission Joint Research Centre: European Soil Portal. For more information on the map see the soil resource page

Land cover

Much of Guinea Bissau was originally dominated by wooded savannah and forest, but there has been widespread clearance of forest and woodland in recent decades, for local or exportable timber use or for cultivation.
Land Cover Map of Guinea Bissau, from the European Space Agency GlobCover 2.3, 2009. For map key and more information on the datasets used to develop the map see the land cover resource page


Water statistics

1996 2000 2005 2012 2014 2015
Rural population with access to safe drinking water (%) 60.3
Urban population with access to safe drinking water (%) 98.8
Population affected by water related disease No data No data No data No data No data No data
Total internal renewable water resources (cubic metres/inhabitant/year) 8,677
Total exploitable water resources (Million cubic metres/year) No data No data No data No data No data No data
Freshwater withdrawal as % of total renewable water resources 0.5573
Renewable groundwater resources (Million cubic metres/year) 350
Groundwater produced internally (Million cubic metres/year) 14,000
Fresh groundwater withdrawal (primary and secondary) (Million cubic metres/year) 31
Groundwater: entering the country (total) (Million cubic metres/year) No data No data No data No data No data No data
Groundwater: leaving the country to other countries (total) (Million cubic metres/year) No data No data No data No data No data No data
Industrial water withdrawal (all water sources) (Million cubic metres/year) 11.9
Municipal water withdrawal (all water sources) (Million cubic metres/year) 34.1
Agricultural water withdrawal (all water sources) (Million cubic metres/year) 144
Irrigation water withdrawal (all water sources) 1 (Million cubic metres/year) No data No data No data No data No data No data
Irrigation water requirement (all water sources) 1 (Million cubic metres/year) 26.3
Area of permanent crops (ha) 250,000
Cultivated land (arable and permanent crops) (ha) 550,000
Total area of country cultivated (%) 15.22
Area equipped for irrigation by groundwater (ha) 530
Area equipped for irrigation by mixed surface water and groundwater (ha) 7,371

These statistics are sourced from FAO Aquastat. They are the most recent available information in the Aquastat database. More information on the derivation and interpretation of these statistics can be seen on the FAO Aquastat website.

Further water and related statistics can be accessed at the Aquastat Main Database.

1 More information on irrigation water use and requirement statistics


Geology

The geology map below shows a simplified version of the geology of Guinea Bissau at 1:5 million scale (see the Geology resources page for more details).

A more detailed geology map of Guinea Bissau is available to view and interrogate online at the 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 (LNEG).

This report provides more information on the Geology of Guinea Bissau (Geologia da Guiné-Bissau) (Alves 2010).


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 resource page.



Summary

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 carbonates of Silurian age; and some Precambrian rocks; and
  • a western zone with mainly late Mesozoic to Cenozoic sediments. The Cretaceous to Cenozoic sediments are mainly of marine origin (University of Guelph).


Geological Environments
Period Lithology
Quaternary unconsolidated
Quaternary Coastal sediments, including beach sands; river and coastal alluvium. Including sands, silts, and clays.
Upper Cretaceous - Tertiary sedimentary
Maastrichtian, Palaeocene-Eocene, Oligocene, Miocene A sequence of largely marine sedimentary rocks, including limestones, marls, clays, silts, sands and phosphates. Drilling investigations have proved a ~5m thick phosphate layer in the Palaeocene-Eocene sequence, with 25-50m of overlying sediments.
Igneous
Little is known of the igneous rocks in Guinea-Bissau.
Palaeozoic sedimentary
Devonian Shales and sandstones, including the Upper Devonian Bafata Group, and Lower Devonian sandstones in the Cusselinta-Saltinho area.
Silurian Rocks of the Buba Group, including sandstones with some organic rich/carbonaceous black shales.
Cambrian-Ordovician Sandstones, shales, conglomerates and rare limestones.
Precambrian metamorphic complex
Neoproterozoic A volcanic and metasedimentary complex, including schists, quartzites and metavolcanic rocks.

Hydrogeology

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 resource page for more details).

More information on the hydrogeology of Guinea Bissau is available in the report United Nations (1988) (see References section, below).

Hydrogeology of Guinea Bissau at 1:5million scale. For more information on how the map was developed see the hydrogeology map resource page




Groundwater use and management

Groundwater use

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 (Aquastat).

Groundwater management

The main agencies involved in water management in Guinea Bissau are (http://www.fao.org/nr/water/aquastat/countries_regions/GNB/ Aquastat):

  • 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.

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

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.


Transboundary aquifers

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

References

References with more information on the geology and hydrogeology of Guinea Bissau can be accessed through the Africa Groundwater Literature Archive.

Alves PH. 2010. 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. 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.

University of Guelph. Rocks for Crops.

WES. Guinea Bissau: Country Profile. Water, Environment and Sanitation (WES), UNICEF.

United Nations. 1988. Groundwater in North and West Africa: Guinea-Bissau. United Nations Department of Technical Cooperation for Development and Economic Commission for Africa.

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