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[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Togo
 
 
  '''Lire cette page en français: [[Hydrogéologie du Togo | Hydrogéologie du Togo ]]'''  [[File: flag_of_france.png  | 50px]]
 
 
[[File:CC-BY-SA_logo_88x31.png | frame | This work is licensed under a [https://creativecommons.org/licenses/by-sa/3.0/ Creative Commons Attribution-ShareAlike 3.0 Unported License]]]
 
 
In historical times, present-day Togo lay between the powerful kingdoms of Ashanti and Dahomey. From the 11th to 16th centuries, various peoples migrated there from neighbouring regions, including Ewe people from the area of present-day Nigeria, who comprise the majority ethnic group today. European slave trading posts were established on the coast in the 16th century. In the late 19th century German claimed control over what was called Togoland, and after World War I this was claimed and divided by Britain and France. British Togoland voted to join the Gold Coast, becoming independent as part of the nation of Ghana in 1957. French Togoland remained separate and became independent as the Togolose Republic in 1960.
 
A military coup in 1963 replaced an elected government, and another coup in 1967 saw Gnassingbé Eyadéma assume the presidency, maintaining a one-party state until 1991, when under political pressure, opposition parties were legalised. Eyadéma remained in power until he died in 2005, and amidst further unrest was replaced by his son, who has won elections since. Anti-government protests that began in August 2017 have faced government suppression.
 
 
Togo’s economy is based on exports of phosphate and commercial plantation agricultural crops, including coffee, cocoa and groundnuts. The phosphate industry was nationalised in the 1970s, but has declined since the 1990s, in part due to falling world prices and increasing foreign competition. Tourism has become less important to the economy since the 1990s because of political issues.
 
 
Togo has relatively high, but seasonal, rainfall. There are no major rivers in much of the country, and many smaller rivers are ephemeral. Groundwater supplies most public water schemes in the country, including many major cities. Groundwater is also widely used in the phosphate and other industries.
 
 
 
 
==Authors==
 
==Authors==
  
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'''Kpadja Agouda''', Department of Water Resources, Togo
 
'''Kpadja Agouda''', Department of Water Resources, Togo
 
   
 
   
'''Dr Kirsty Upton''', '''Brighid Ó Dochartaigh''', British Geological Survey, UK
+
'''Kirsty Upton''' & '''Brighid Ó Dochartaigh''', British Geological Survey, UK
 
 
'''Dr Imogen Bellwood-Howard''', Institute of Development Studies, UK
 
 
 
Please cite this page as: Gnazou, Sabi, Tauirou, Akakpo, Agouda, Upton, Ó Dochartaigh and Bellwood-Howard, 2018.
 
 
 
Bibliographic reference: Gnazou MD-T., Sabi EB, Tairou SM, Akakpo W, Agouda K, Upton K, Ó Dochartaigh BÉ and Bellwood-Howard, I. 2018. Africa Groundwater Atlas: Hydrogeology of Togo. British Geological Survey. Accessed [date you accessed the information]. http://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Togo
 
 
 
==Terms and conditions==
 
 
 
The Africa Groundwater Atlas is hosted by the British Geological Survey (BGS) and includes information from third party sources. Your use of information provided by this website is at your own risk. If reproducing diagrams that include third party information, please cite both the Africa Groundwater Atlas and the third party sources. Please see the [[Africa Groundwater Atlas Terms of Use | Terms of use]] for more information.
 
  
==Geographical Setting==
+
==Geographical & Political Setting==
  
[[File:Togo_Political.png | right | frame | Togo. 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 | geography resource page]].]]
+
[[File:Togo_Political.png | right | frame | Political Map of Togo (For more information on the datasets used in the map see the [[Geography | geography resources section]])]]  
  
 
===General===
 
===General===
  
Togo is a narrow country extending from the border with Burkina Faso in the north to the Atlantic Ocean (Gulf of Guinea) in the south. The north of the country is dominated by savannah while the coast is generally a low lying plain with numerous lagoons and marshes. The Togo Mountains extend from the south west border with Ghana to the north east border with Benin, reaching a maximum elevation of over 900 m.
 
  
 
{| class = "wikitable"
 
{| class = "wikitable"
 
|-
 
|-
|Capital city || Lome
+
|Estimated Population in 2013* || 6,816,982
 +
|-
 +
|Rural Population (% of total)* || 61%
 +
|-
 +
|Total Surface Area* || 54.390 sq km
 +
|-
 +
|Agricultural Land (% of total area)* || 71%
 +
|-
 +
|Capital City || Lome
 +
|-
 +
|Region || West Africa
 
|-
 
|-
|Region || Western Africa
+
|Border Countries || Benin, Burkina Faso, Ghana
 
|-
 
|-
|Border countries || Benin, Burkina Faso, Ghana
+
|Annual Freshwater Withdrawal (2013)* || 169 Million cubic metres
 
|-
 
|-
|Total surface area* || 56,790 km<sup>2</sup>  (5,679,000 ha)
+
|Annual Freshwater Withdrawal for Agriculture* || 45%
 
|-
 
|-
|Total population (2015)* || 7,305,000
+
|Annual Freshwater Withdrawal for Domestic Use* || 53%
 
|-
 
|-
|Rural population (2015)* ||4,439,000 (61%)
+
|Annual Freshwater Withdrawal for Industry* || 2%
 
|-
 
|-
|Urban population (2015)* ||2,866,000 (39%)
+
|Rural Population with Access to Improved Water Source* || 40%
 
|-
 
|-
|UN Human Development Index (HDI) [highest = 1] (2014)*|| 0.4835
+
|Urban Population with Access to Improved Water Source* || 91%
 
|}
 
|}
  
<nowiki>*</nowiki> Source: [http://www.fao.org/nr/water/aquastat/data/query/index.html?lang=en FAO Aquastat]
+
<nowiki>*</nowiki> Source: World Bank
  
  
 
===Climate===
 
===Climate===
 +
 +
Togo is a narrow country extending from the border with Burkina Faso in the north to the Atlantic Ocean (Gulf of Guinea) in the south. The north of the country is dominated by savannah while the coast is generally a low lying plain with numerous lagoons and marshes. The Togo Mountains extend from the south west border with Ghana to the north east border with Benin, reaching a maximum elevation of over 900 m.
 +
  
 
The climate of Togo is classified as Tropical Savannah. Annual average temperatures are slightly higher in the north and lower in the south. They also decrease with altitude in the mountainous regions. Precipitation is generally lower in the north and higher in the south but also increases slightly over the mountainous regions.
 
The climate of Togo is classified as Tropical Savannah. Annual average temperatures are slightly higher in the north and lower in the south. They also decrease with altitude in the mountainous regions. Precipitation is generally lower in the north and higher in the south but also increases slightly over the mountainous regions.
 +
 +
 +
<gallery widths="375px" heights=365px mode=nolines>
 +
File:Togo_ClimateZones.png |Koppen Geiger Climate Zones
 +
File:Togo_ClimatePrecip.png |Average Annual Precipitation
 +
File:Togo_ClimateTemp.png |Average Temperature
 +
</gallery>
 +
  
 
Precipitation and temperature vary throughout the year. Average temperature across the country shows two peaks throughout year in March and November. When averaged spatially across the country, precipitation shows a relatively wet period between April and October; however this is split into two distinct wet seasons in the south of the country, which occur during April-July and September-October.
 
Precipitation and temperature vary throughout the year. Average temperature across the country shows two peaks throughout year in March and November. When averaged spatially across the country, precipitation shows a relatively wet period between April and October; however this is split into two distinct wet seasons in the south of the country, which occur during April-July and September-October.
  
[[File:Togo_ClimateZones.png | 375x365px |Koppen Geiger Climate Zones]][[File:Togo_ClimatePrecip.png | 375x365px |Average Annual Precipitation]][[File:Togo_ClimateTemp.png | 375x365px |Average Temperature]]
 
  
[[File:Togo_pre_Monthly.png| 255x124px| Average monthly precipitation for Togo showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Togo_tmp_Monthly.png| 255x124px| Average monthly temperature for Togo showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Togo_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Togo_pre_Mts.png|255x124px | Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)]]
+
[[File:Togo_pre_Monthly.png| 255x124px| Average monthly precipitation for Togo showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall]] [[File:Togo_tmp_Monthly.png| 255x124px| Average monthly temperature for Togo showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature]] [[File:Togo_pre_Qts.png | 255x124px | Quarterly precipitation over the period 1950-2012]] [[File:Togo_pre_Mts.png|255x124px | 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 | climate resources section]].
 +
 
  
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 | climate resource page]].
 
  
 
===Surface water===
 
===Surface water===
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The River Mono drains south from the Togo Mountains, marking the border with Benin, before entering the Gulf of Guinea in the south east of the country.   
 
The River Mono drains south from the Togo Mountains, marking the border with Benin, before entering the Gulf of Guinea in the south east of the country.   
 +
  
 
The largest lagoon along the coastal region is Lake Togo, which is fed by the Zio River draining the south western part of the Togo Mountains.
 
The largest lagoon along the coastal region is Lake Togo, which is fed by the Zio River draining the south western part of the Togo Mountains.
 +
  
 
The Department of Water Resources, which sits within the Ministry of Water, is responsible for river flow gauging. All observed data is held within the Department of Water Resources and will be made available online through the Systèmes Intégrés d’information sur l’eau project.  
 
The Department of Water Resources, which sits within the Ministry of Water, is responsible for river flow gauging. All observed data is held within the Department of Water Resources and will be made available online through the Systèmes Intégrés d’information sur l’eau project.  
  
  
| [[File:Togo_Hydrology.png | frame | Major surface water features of Togo. 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:Togo_Hydrology.png | frame | Surface Water Map of Togo (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]
 
|}
 
|}
 +
  
  
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{|
 
{|
 
|-
 
|-
 +
| [[File:Togo_soil.png | frame | Soil Map of Togo (For more information on the datasets used in the map see the [[Soil | soil resources section]])]]
 +
 
|Clay-rich Lixosols, which are common in the northern part of Togo, generally reflect stable geological conditions and natural savannah vegetation.  
 
|Clay-rich Lixosols, which are common in the northern part of Togo, generally reflect stable geological conditions and natural savannah vegetation.  
  
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Fluvisols have developed along the valley of the River Oti in the north and the River Zio in the south.
 
Fluvisols have developed along the valley of the River Oti in the north and the River Zio in the south.
 
| [[File:Togo_soil.png | frame | Soil Map of Togo, from the European Commission Joint Research Centre: European Soil Portal. For more information on the map see the [[Soil | soil resource page]].]]
 
|
 
 
|}
 
|}
  
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{|
 
{|
 
|-
 
|-
|
+
|General information about COUNTRY land cover.
| [[File:Togo_LandCover.png | frame | Land Cover Map of Togo, from the European Space Agency GlobCover 2.3, 2009. For more information on the map see the [[Land cover | land cover resource page]].]]
 
|
 
|}
 
 
 
===Water statistics===
 
  
{| class = "wikitable"
+
| [[File:Togo_LandCover.png | frame | Land Cover Map of Togo (For more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]
| || 1996 ||2002||2005||2014||2015
 
|-
 
|Rural population with access to safe drinking water (%) || || ||  || || 44.2
 
|-
 
|Urban population with access to safe drinking water (%) || || ||  || || 91.4
 
|-
 
|Population affected by water related disease || No data || No data || No data  || No data || No data
 
|-
 
|Total internal renewable water resources (cubic metres/inhabitant/year) || || ||  ||1574 ||
 
|-
 
|Total exploitable water resources (Million cubic metres/year) || No data || No data || No data  || No data || No data
 
|-
 
|Freshwater withdrawal as % of total renewable water resources || ||1.15 || || ||
 
|-
 
|Total renewable groundwater (Million cubic metres/year) ||  || || ||5,700 ||
 
|-
 
|Exploitable: Regular renewable groundwater (Million cubic metres/year) || No data || No data || No data  || No data || No data
 
|-
 
|Groundwater produced internally (Million cubic metres/year) || || ||  ||5,700 ||
 
|-
 
|Fresh groundwater withdrawal (primary and secondary) (Million cubic metres/year) || No data || No data || No data  || No data || No data
 
|-
 
|Groundwater: entering the country (total) (Million cubic metres/year) || 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
 
|-
 
|Industrial water withdrawal (all water sources) (Million cubic metres/year) || || ||6.3|| ||
 
|-
 
|Municipal water withdrawal (all water sources) (Million cubic metres/year)  || || ||140.7|| ||
 
|-
 
|Agricultural water withdrawal (all water sources) (Million cubic metres/year) || || 76|| || ||
 
|-
 
|Irrigation water withdrawal (all water sources) <sup>1</sup> (Million cubic metres/year) || ||46||  || ||
 
|-
 
|Irrigation water requirement (all water sources) <sup>1</sup> (Million cubic metres/year) ||6.6 || ||  || ||
 
|-
 
|Area of permanent crops (ha) || || ||  ||170,000 ||
 
|-
 
|Cultivated land (arable and permanent crops) (ha) || || ||  ||2,820,000 ||
 
|-
 
|Total area of country cultivated (%) || || ||  || 49.66||
 
|-
 
|Area equipped for irrigation by groundwater (ha) || No data || No data || No data  || No data || No data
 
|-
 
|Area equipped for irrigation by mixed surface water and groundwater (ha) || No data || No data || No data  || No data || No data
 
 
|}
 
|}
  
These statistics are sourced from [http://www.fao.org/nr/water/aquastat/main/index.stm 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 [http://www.fao.org/nr/water/aquastat/data/query/index.html?lang=en Aquastat Main Database].
 
  
<sup>1</sup> More information on [http://www.fao.org/nr/water/aquastat/water_use_agr/index.stm irrigation water use and requirement statistics]
 
  
 
==Geology==
 
==Geology==
 
+
[[File:Togo_Geology.png | right]]
This section provides a summary of the geology of Togo. More detail can be found in the references listed at the bottom of this page. Many of these references can be accessed through the [http://www.bgs.ac.uk/africagroundwateratlas/archive.cfm Africa Groundwater Literature Archive].
 
 
 
The geology map on this page shows a simplified overview of the geology at a national scale (see the [[Geology | Geology resource page]] for more details).
 
 
 
[https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html '''Download a GIS shapefile of the Togo geology and hydrogeology map'''].
 
 
 
 
[[File:Togo_Geology4.png | center | thumb| 500px | Geology of Togo 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]]. [https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html Download a GIS shapefile of the Togo geology and hydrogeology map].]]
 
  
 
{| class = "wikitable"
 
{| class = "wikitable"
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|Key Formations||Period||Lithology||Structure
 
|Key Formations||Period||Lithology||Structure
 
|-
 
|-
!colspan="4"| Coastal Basin Sedimentary
+
!colspan="4"|Precambrian Craton
 +
|-
 +
|Dorsale de Leo ou de Man (West African Craton)
 +
||Neo-Archean (2064±90 Ma) – Lower Proterozoic (2300-1600Ma)
 +
||Acidic to basic ortho-metamorphic rocks (gneiss, migmatite, amphibolites, pyroxenite) and granitic plutonic rocks.
 +
||Polycyclic basement that outcrops in the north of Togo.
 +
|-
 +
!colspan="4"| Precambrian Metasedimentary
 
|-
 
|-
|Coastal Basin
+
|Bombouaka and Oti Supergroups (Volta Basin mega-sequences)
||Cretaceous – Pleistocene (Quaternary)
+
||Neo-Proterozoic
||Basal unconsolidated sands, limestone, marl, phospharenite, continental sediments and Quaternary sands.  
+
||Continental rift deposits consisting of megasequences of sandstone (Bombouaka Supergroup) and mudstone (Oti Supergroup).
||Sequence deposited in a compartment of the Adina Fault in the south of Togo.
+
||
 
 
 
|-
 
|-
 
!colspan="4"| Precambrian Mobile/Orogenic Belt
 
!colspan="4"| Precambrian Mobile/Orogenic Belt
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||The Dahomeyide Belt was deformed during five phases of the Pan-African event.
 
||The Dahomeyide Belt was deformed during five phases of the Pan-African event.
 
|-
 
|-
!colspan="4"| Precambrian Metasedimentary
+
!colspan="4"| Sedimentary – Coastal Basin
 
|-
 
|-
|Bombouaka and Oti Supergroups (Volta Basin mega-sequences)
+
|Coastal Basin
||Neo-Proterozoic
+
||Cretaceous – Pleistocene
||Continental rift deposits consisting of megasequences of sandstone (Bombouaka Supergroup) and mudstone (Oti Supergroup).
+
||Basal unconsolidated sands, limestone, marl, phospharenite, continental sediments and Quaternary sands.
||
+
||Sequence deposited in a compartment of the Adina Fault in the south of Togo.
 +
 
 +
|}
 +
 
 +
 
 +
==Hydrogeology==
 +
 
 +
There are three main hydrogeological environments in Togo:
 +
 
 +
 
 +
*Basement aquifers, including the West African Craton and Dahomeyides Chain
 +
*The Volta Basin aquifer
 +
*Coastal Sedimentary aquifers
 +
 
 +
 
 +
The basement aquifers and Volta Basin aquifer represent 94% of the area of Togo. The basement is predominantly composed of low permeability granite, gneiss and migmatite and groundwater occurs in the weathered horizon or fractures. The Volta Basin comprises sandstone and quartzite while the Coastal Basin is a layered sedimentary sequence that dips gently from north to south.
 +
 
 +
 
 +
 
 +
===Aquifer properties===
 +
[[File:Togo_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]
 +
 
 +
 
 +
====Basement====
 +
{| class = "wikitable"
 +
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
!colspan="4"|Precambrian Craton
+
|West African Craton and Dahomeyides Chain
|-
+
 
|Dorsale de Leo ou de Man (West African Craton)
+
|| The West African Craton (north of Dapaong) and the Dahomeyides Chain are the principal groundwater-bearing formations of the basement. However, these are generally discontinuous aquifers, either related to fracturing or alteration/weathering of the bedrock.
||Neo-Archean (2064±90 Ma) – Lower Proterozoic (2300-1600Ma)
+
 
||Acidic to basic ortho-metamorphic rocks (gneiss, migmatite, amphibolites, pyroxenite) and granitic plutonic rocks.
+
The properties of the basement aquifers are controlled by the frequency of fracturing, which varies depending on the nature of the rock, bedding, structural position and tectonic history. Harder rocks are generally more fractured, while schistose rocks are more deformable and therefore less fractured.
||Polycyclic basement that outcrops in the north of Togo.
+
 
 +
Alteration or weathering of the bedrock, along cracks and towards the surface, creates aquifers of limited volume that are unevenly distributed in space. These aquifers generally only have thicknesses of 3 to 15 m and are usually exploited by large diameter wells.
 +
 
 +
Aquifers related to alteration or weathering typically have porosities of 2-5%, with hydraulic conductivity on the order of 10-3 m/d. Fractured basement aquifers have lower porosity (1%) and may produce yields of up to 120 m3/day (1 l/s).
 +
 
 +
The weathered basement aquifers are generally unconfined while the fractured basement aquifers may be confined by the altered overburden. The thickness of the water-bearing fractured zone is largely unknown.  
 +
 
 +
In the basement aquifers of the West African Craton the depth of the water table typically varies between 0.5 and 20 m, and boreholes are generally drilled to depths of 14-60 m. In the Dahomeyides Chain the water table may extend to a depth of 30 m and boreholes are generally drilled to depths of 35-70 m.
  
 +
||The basement aquifers do not always provide sufficient borehole yields to be considered a viable source.
  
|}
+
||Groundwaters from the West African Craton aquifers typically have low mineralisation, while those from the Dahomeyides Chain can be highly mineralised (up to 1700 microSiemens/cm).
  
==Hydrogeology==
+
High nitrate concentrations (50-620 mg/l) have been reported in parts of the plateau region. 
  
This section provides a summary of the hydrogeology of the main aquifers in Togo.  More information is available in the references listed at the bottom of this page. Many of these references can be accessed through the [http://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].
+
||Recharge to the basement aquifers is typically from rainfall and surface water.
 +
|}
  
The hydrogeology map on this page shows a simplified overview of the type and productivity of the main aquifers at a national scale (see the [[Africa Groundwater Atlas Hydrogeology Maps | Hydrogeology map resource page]] for more details).  
+
====Consolidated Sedimentary - Fracture Flow====
 +
{| class = "wikitable"
 +
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 +
|-
 +
|Volta Basin Aquifers
 +
||Discontinuous aquifers occur in the sandstone, quartzite and silexite of the Volta Basin. These are generally unconfined in the north of the basin, but confined by the Mango Clay Formation in the south.
  
[https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html '''Download a GIS shapefile of the Togo geology and hydrogeology map'''].
+
Borehole yields are reported between 10 and 250 m3/day (0.1-3 l/s).  
  
There are three main hydrogeological environments in Togo:
+
Typical aquifer thicknesses are unknown however boreholes are generally drilled to depths of 20-100 m. In the unconfined regions, the depth of the water table is usually 3-39 m.
  
*Coastal Sedimentary aquifers
+
||The aquifers of the Volta Basin are generally exploited by hand pumps so there are few issues of groundwater availability.
*The Volta Basin aquifer
 
*Basement aquifers, including the West African Craton and Dahomeyides Chain
 
  
The basement aquifers and Volta Basin aquifer represent 94% of the area of Togo. The basement is predominantly composed of low permeability granite, gneiss and migmatite and groundwater occurs in the weathered horizon or fractures. The Volta Basin comprises sandstone and quartzite while the Coastal Basin is a layered sedimentary sequence that dips gently from north to south.  
+
||Groundwater from the Volta Basin aquifers have low mineralization.  
  
 +
||The Volta Basin aquifers are recharged by rainfall and surface water in the northern unconfined region. 
 +
|}
  
[[File:Togo_Hydrogeology4.png | center | thumb| 500px | Hydrogeology of Togo at 1:5 million scale. For more information on how the map was developed see the [[Africa Groundwater Atlas Hydrogeology Maps | Hydrogeology map]] resource page. [https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html Download a GIS shapefile of the Togo geology and hydrogeology map].]].
 
  
 +
====Consolidated Sedimentary - Intergranular ====
  
====Sedimentary Aquifers - Intergranular and Fracture Flow====
+
Although classified as predominantly intergranular flow, the coastal basin sedimentary aquifer (Keta Basin) is a multi-layered aquifer and fracture flow is important at depth. The coastal basin contains the following aquifers in a layered system (see cross section):
  
The coastal basin sedimentary aquifer (Keta Basin) is a multi-layered aquifer, which generally has high productivity and groundwater potential. Intergranular flow dominates in the shallower systems, but fracture flow is important at depth. The coastal basin contains the following aquifers in a layered system:
 
  
 
*Quaternary Sand Aquifer
 
*Quaternary Sand Aquifer
Line 264: Line 247:
 
*Maestrichtian Aquifer
 
*Maestrichtian Aquifer
  
These aquifers are separated by thick, low permeability aquicludes.
+
 
 +
 
 +
These aquifers are separated by thick aquicludes.
 +
 
  
  
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| Quaternary Sand Aquifer
 
| Quaternary Sand Aquifer
 
||This forms a 2-3km wide aquifer along the coast and is typically exploited by wells for domestic use. Flow is predominantly intergranular and the aquifer is unconfined.  
 
||This forms a 2-3km wide aquifer along the coast and is typically exploited by wells for domestic use. Flow is predominantly intergranular and the aquifer is unconfined.  
The properties of this aquifer are largely unknown. The aquifer thickness varies from 10 - 30 m and the water table depth varies from 0.5 - 3 m.  
+
The properties of this aquifer are largely unknown, however the aquifer thickness varies between 10 and 30 m and the water table depth varies between 0.5 and 3 m.  
 
||
 
||
 
||
 
||
 
||
 
||
 +
 
|-
 
|-
 
| Continental Terminal Aquifer
 
| Continental Terminal Aquifer
|| This is the most heavily exploited aquifer in the coastal basin, providing the drinking water supply for the city of Lome. Flow is predominantly intergranular and the aquifer is unconfined. Transmissivity is typically on the order of 10-³ – 10<sup>-2</sup> m²/s. Storage is typically 1-8%. Borehole yields generally vary between 10 and 200 /h.
+
|| This is the most heavily exploited aquifer in the basin, providing the drinking water supply for the city of Lome. Flow is predominantly intergranular and the aquifer is unconfined.
 +
 
 +
Transmissivity is typically on the order of 10-3 – 10-2 m2/s
 +
 
 +
Storage is typically 1-8%
 +
 
 +
Borehole yields generally vary between 10 and 200 m3/h
  
 
The aquifer thickness varies between 20 and 80 m, the water table depth varies between 1.5 and 50 m, and boreholes are generally drilled to depths of 10-60 m.
 
The aquifer thickness varies between 20 and 80 m, the water table depth varies between 1.5 and 50 m, and boreholes are generally drilled to depths of 10-60 m.
Line 295: Line 288:
 
|-
 
|-
 
| Paleocene Limestone Aquifer
 
| Paleocene Limestone Aquifer
||This is a confined aquifer in which fracture flow is dominant. Transmissivity is typically on the order of 10-³ to 10-² m²/s. Borehole yields generally vary between 20 and 150 /h. The aquifer thickness varies between 15 and 40 m.
+
||This is a confined aquifer in which fracture flow is dominant.  
 +
 
 +
Transmissivity is typically on the order of 10-3 – 10-2 m2/s
 +
 
 +
Borehole yields generally vary between 20 and 150 m3/h
 +
 
 +
The aquifer thickness varies between 15 and 40 m.
 +
 
 
||
 
||
 +
 
||
 
||
 
*Conductivity varies from 400 to 1600 microSiemens/cm
 
*Conductivity varies from 400 to 1600 microSiemens/cm
Line 302: Line 303:
 
*pH values vary between 6.7 and 7.6
 
*pH values vary between 6.7 and 7.6
  
||Recharge occurs in the north of the basin by infiltration through the Continental Terminal aquifer.
+
|| Recharge occurs in the north of the basin by infiltration through the Continental Terminal aquifer.
  
 
|-
 
|-
|Maestrichtian Aquifer
+
| Maestrichtian Aquifer
||The Maestrichtian Aquifer comprises sandstone (and sometimes sandy limestone) and flow is predominantly intergranular. It is mainly exploited in the northern part of the basin where it is more easily accessible, although it remains confined across the basin. The lateral extent of this aquifer towards the south of the basin is currently unknown due to the significant depth of the sediments.  
+
|| The Maestrichtian Aquifer comprises sandstone (and sometimes sandy limestone) and flow is predominantly intergranular. It is mainly exploited in the northern part of the basin where it is more easily accessible, although it remains confined across the basin. The lateral extent of this aquifer towards the south of the basin is currently unknown due to the significant depth of the sediments.  
 +
 
 +
Transmissivity is typically on the order of 10-3 – 10-2 m2/s
 +
 
 +
Storage is typically 1-3%
 +
 
 +
Borehole yields generally vary between 15 and 140 m3/h
  
Transmissivity is typically on the order of 10<sup>-3</sup> – 10<sup>-2</sup> m²/s. Storage is typically 1-3%. Borehole yields generally vary between 15 and 140 m³/h. The aquifer thickness varies between 5 and 25 m and boreholes are generally drilled to depths of 80-150 m (these would need to be significantly deeper in the southern part of the basin).
+
The aquifer thickness varies between 5 and 25 m and boreholes are generally drilled to depths of 80-150 m (these would need to be significantly deeper in the southern part of the basin).
  
 
||
 
||
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|}
 
|}
  
====Sedimentary Aquifers - Fracture Flow====
 
{| class = "wikitable"
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|Volta Basin Aquifers
 
||Discontinuous aquifers occur in the sandstone, quartzite and silexite of the Volta Basin. These are generally unconfined in the north of the basin, but confined by the Mango Clay Formation in the south.
 
  
Borehole yields are reported between 10 and 250 m3/day (0.1-3 l/s).
+
===Groundwater Status===
  
Typical aquifer thicknesses are unknown however boreholes are generally drilled to depths of 20-100 m. In the unconfined regions, the depth of the water table is usually 3-39 m.
 
  
||The aquifers of the Volta Basin are generally exploited by hand pumps so there are few issues of groundwater availability.
+
The basement aquifers are laterally discontinuous and thus relatively unproductive. However, exploitation is predominantly by hand pump and the aquifers are generally capable of sustaining low rates of abstraction. Nitrate concentrations in the basement aquifers are often elevated to >50-620 mg/l.  
  
||Groundwater from the Volta Basin aquifers have low mineralization.
 
  
||The Volta Basin aquifers are recharged by rainfall and surface water in the northern unconfined region.
+
The Continental Terminal aquifer in the coastal basin supplies 70% of the public water supply in Lome, through the Togolese Company of Water (TdE). In addition to TdE boreholes, there are many industrial and private boreholes (estimated around 2500 in the Lome Region) that also exploit this aquifer in the Agoe Plateau region. As a result, groundwater levels in the Continental Terminal aquifer have fallen by between 0.5 and 12 m. Saline intrusion is also an issue as a result of overexploitation in the coastal region.  
|}
 
  
  
 +
==Groundwater use and management==
 +
=== Groundwater use===
  
====Basement Aquifers====
 
{| class = "wikitable"
 
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|West African Craton and Dahomeyides Chain
 
  
||The West African Craton (north of Dapaong) and the Dahomeyides Chain are the principal groundwater-bearing formations of the basement. However, these are generally discontinuous aquifers, either related to fracturing or alteration/weathering of the bedrock.
+
Around 85% of the total public national water supply in Togo comes from groundwater (DGEA, 2009).  
  
The properties of the basement aquifers are controlled by the frequency of fracturing, which varies depending on the nature of the rock, bedding, structural position and tectonic history. Harder rocks are generally more fractured, while schistose rocks are more deformable and therefore less fractured.
 
  
Alteration or weathering of the bedrock, along cracks and towards the surface, creates aquifers of limited volume that are unevenly distributed in space. These aquifers generally only have thicknesses of 3 to 15 m and are usually exploited by large diameter wells.
+
The main groundwater dependent cities are listed in the table below, along with the volume of groundwater abstracted per year by the Togolese Company of Water (TdE, 2010).  
  
Aquifers related to alteration or weathering typically have porosities of 2-5%, with hydraulic conductivity on the order of 10-³ m/d. Fractured basement aquifers have lower porosity (1%) and may produce yields of up to 120 m³/day (1 l/s).
 
 
The weathered basement aquifers are generally unconfined while the fractured basement aquifers may be confined by the altered overburden. The thickness of the water-bearing fractured zone is largely unknown.
 
 
In the basement aquifers of the West African Craton the depth of the water table typically varies between 0.5 and 20 m, and boreholes are generally drilled to depths of 14-60 m. In the Dahomeyides Chain the water table may extend to a depth of 30 m and boreholes are generally drilled to depths of 35-70 m.
 
 
||The basement aquifers do not always provide sufficient borehole yields to be considered a viable source.
 
 
||Groundwaters from the West African Craton aquifers typically have low mineralisation, while those from the Dahomeyides Chain can be highly mineralised (up to 1700 microSiemens/cm).
 
 
High nitrate concentrations (50-620 mg/l) have been reported in parts of the plateau region. 
 
 
||Recharge to the basement aquifers is typically from rainfall and surface water.
 
|}
 
 
 
===Groundwater Status===
 
 
The basement aquifers are laterally discontinuous and thus relatively unproductive. However, exploitation is predominantly by hand pump and the aquifers are generally capable of sustaining low rates of abstraction. Nitrate concentrations in the basement aquifers are often elevated to >50-620 mg/l.
 
 
The Continental Terminal aquifer in the coastal basin supplies 70% of the public water supply in Lome, through the Togolese Company of Water (TdE). In addition to TdE boreholes, there are many industrial and private boreholes (estimated around 2500 in the Lome Region) that also exploit this aquifer in the Agoe Plateau region. As a result, groundwater levels in the Continental Terminal aquifer have fallen by between 0.5 and 12 m. Saline intrusion is also an issue as a result of overexploitation in the coastal region.
 
 
==Groundwater use and management==
 
=== Groundwater use===
 
Around 85% of the total public national water supply in Togo comes from groundwater (DGEA, 2009).
 
 
The main groundwater dependent cities are listed in the table below, along with the volume of groundwater abstracted per year by the Togolese Company of Water (TdE, 2010).
 
  
 
{| class = "wikitable"
 
{| class = "wikitable"
Line 394: Line 361:
 
|}
 
|}
  
The main groundwater dependent industries are the phosphates industry (with an estimated groundwater abstraction of 4 M m³/yr) and the brewing industry (with an estimated groundwater abstraction of 0.35 M m³/yr).
 
  
The amount of groundwater removed by aquifer, both by the TdE and through private boreholes (where known), is given in the table below (MEAHV/DGEA 2013, TdE).
+
The main groundwater dependent industries are the phosphates industry (with an estimated groundwater abstraction of 4 M m3/yr) and the brewing industry (with an estimated groundwater abstraction of 0.35 M m3/yr).
 +
 
 +
 
 +
The amount of groundwater removed by aquifer, both by the TdE and through private boreholes (where known), is given in the table below (MEAHV/DGEA, 2013; TdE).
  
 
{| class = "wikitable"
 
{| class = "wikitable"
|Aquifer||Volume abstracted by TdE (M /yr)||Volume abstracted by industry and private boreholes (M m3/yr)||Volume abstracted rurally (M /yr)||Total (M /yr)
+
|Aquifer||Volume abstracted by TdE (M m3/yr)||Volume abstracted by industry and private boreholes (M m3/yr)||Volume abstracted rurally (M m3/yr)||Total (M m3/yr)
 
|-
 
|-
 
|Continental Terminal||10.6||4.3||1.7||16.6
 
|Continental Terminal||10.6||4.3||1.7||16.6
Line 412: Line 381:
 
|}
 
|}
  
It is estimated that there are around 6442 boreholes with hand pumps and 108 improved springs in Togo (DGEA 2009). Electric pumps are used in 80 boreholes by the TdE and in thousands more privately owned boreholes.   
+
 
 +
It is estimated that there are around 6442 boreholes with hand pumps and 108 improved springs in Togo (DGEA, 2009). Electric pumps are used in 80 boreholes by the TdE and in thousands more privately owned boreholes.   
 +
 
  
 
=== Groundwater management===
 
=== Groundwater management===
  
 
The key groundwater legislation in Togo is Loi No 2010-004 Portant Code de l'Eau (Groundwater Code).  
 
The key groundwater legislation in Togo is Loi No 2010-004 Portant Code de l'Eau (Groundwater Code).  
 +
  
 
The main institutions responsible for groundwater supply and management in Togo are:
 
The main institutions responsible for groundwater supply and management in Togo are:
  
;Le Ministère de l’Eau, de l’Assainissement et de l’Hydraulique Villageoise (MEAHV) (Ministry of Water, sanitation and village hydraulics)
 
  
Responsible for the implementation of national policy related to water and sanitation, and for monitoring in collaboration with other ministries or institutions.
+
;Le Ministère de l’Eau, de l’Assainissement et de l’Hydraulique Villageoise (MEAHV)
 +
:Ministry of Water, sanitation and village hydraulics
 +
:Responsible for the implementation of national policy related to water and sanitation, and for monitoring in collaboration with other ministries or institutions
  
;La Société Togolaise des Eaux (TdE) (Togolese Company of Water)
 
  
Responsible for supplying the greatest possible number of urban households at the lowest possible cost, and for ensuring the collection and disposal of waste water in urban centres where the equipment exists.
+
;La Société Togolaise des Eaux (TdE)
 +
:Togolese Company of Water
 +
:Responsible for supplying the greatest possible number of urban households at the lowest possible cost, and for ensuring the collection and disposal of waste water in urban centres where the equipment exists
  
;La Société de patrimoine Eau, Assainissement Urbain (SP-EAU) (Heritage Society of Water and Urban Sanitation)
 
  
Ensures the management and development of state-controlled drinking water supply and sanitation in urban areas.
+
;La Société de patrimoine Eau, Assainissement Urbain (SP-EAU)
 +
:Heritage Society of Water and Urban Sanitation
 +
:Ensures the management and development of state-controlled drinking water supply and sanitation in urban areas
  
=== Groundwater monitoring===
 
  
The Department of Water Resources, which sits within the Ministry of Water, is responsible for groundwater monitoring. However, there are currently no national groundwater level or groundwater quality monitoring programmes.
 
  
 
=== Transboundary aquifers===
 
=== Transboundary aquifers===
  
 
Togo shares the sedimentary coastal aquifer with Ghana, Benin and Nigeria but to date there are no significant transboundary issues.
 
Togo shares the sedimentary coastal aquifer with Ghana, Benin and Nigeria but to date there are no significant transboundary issues.
 +
  
 
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]
 
For further information about transboundary aquifers, please see the [[Transboundary aquifers | Transboundary aquifers resources page]]
  
  
==References==
+
=== Groundwater monitoring===
Many of the references below, and others relating to the hydrogeology of Togo, can be found in the [https://www.bgs.ac.uk/africaGroundwaterAtlas/atlas.cfc?method=listResults&title_search=&author_search=&category_search=&country_search=TG&placeboolean=AND&singlecountry=1 Africa Groundwater Literature Archive].
 
 
 
===Key Geology References===
 
 
 
AFFATON P. 1987. Le bassin des Volta (Afrique de 1'Ouest): une marge passive d'âge Protérozoïque supérieur, tectonisée au Panafricain (600 ± 50 Ma). Thèse Doct. d'Etat, Fac. Sci. St Jérôme, Univ. Aix-Marseille III, Fr., 462 p.
 
 
 
AFFATON P, SOUGY J et TROMPETTE R. 1980. The tectono-stratigraphic relationships between the Upper Precambrian and Lower Paleozoic Volta Basin and the Pan-African Dahomeyide  Orogenic Belt (West Africa). Amer.  J. Sci., vol. 280, pp. 224 - 248.
 
 
 
AFFATON P, RAHAMAN MA, TROMPETTE R et SOUGY J. 1991a. The Dahomeyide orogen : tectonothermal evolution and relationships with the Volta basin. In Dallmayer and Lécorché (Edit.) : The West-African Orogen and Circum Atlantic Correlatives. Projet  233. 1CGP, IUGS, UNESCO, pp 107 - 122.
 
 
 
AFFATON P, SEDDOH FK et SIMPARA N 1991b. Caractéristiques et affinités géodynamiques des métamagmatites de l’unité structurale du Buem. Act. jour. Sci. Univ. Bénin, (3), pp. 87 - 90.
 
 
 
AFFATON P, GELARD JP et SIMPARA N. 1991c Paléocontraintes enregistrées par la fracturation dans l’unité structurale de l’Atacora (Chaîne Panafricaine des Dahomeyides, Togo). C.R. Acad. Sci., Paris, t. 312 pp. 763 – 768.
 
 
 
AFFATON P, AGUIRRE L et MENOT R-P. 1997. Thermal and geodynamic setting of the Buem volcanic rocks near Tiélé, North west Benin, West Africa. Precambrian Research, 82, pp 191-209.
 
 
 
AFFATON P, KRÖNER A et SEDDOH K F. 2000a. Pan African granulites formation in the Kabye of northen Togo (West Africa) : Pb–Pb zircon ages. Int. Jour. Earth Sci. 88, pp. 778 – 790.
 
 
 
AFFATON P, GAVIGLO P et PHARISAT A. 2000b. Réactivation du craton ouest–africain au panafricain : paléocontraintes déduites de la fracturation des grès néoprotérozoïques de Karey Gourou (Niger, Afrique de l’Ouest). C. R. Acad. Sci. Paris, Sci. de la Terre et des Planètes, 331, pp. 609 – 614.
 
 
 
AGBOSSOUMONDE Y. 1998. Les complexes ultrabasiques de la chaîne panafricaine au Togo (Axe Agou – Atakpamé, Sud-Togo). Etude pétrographique, minéralogique et géochimique. Thèse Doct. Lab. Géol. Pétro. Univ. Jean Monnet St. Etienne Fr., 306 p.
 
 
 
AGBOSSOUMONDÉ Y, MENOT RP et GUILLOT S. 2001. Metamorphic evolution of Neoproterozoic eclogites from South Togo (West Africa). Jour. of Afr. Earth Sc. Vol. 33, n°2, pp. 227 – 244.
 
 
 
AGBOSSOUMONDE Y, GUILLOT S et MENOT R-P. 2004b. Pan-African subduction – collision evidence by hight-P coronas in metanorites from the Agou – massif (southern Togo). Precambrian Research, 135, pp. 1 – 21.
 
 
 
SABI BE. 2007. Etude pétrologique et structurale du Massif Kabyè, Nord-Togo. Thèse Doctorat, Univ. Lomé,  256 p.
 
 
 
SOUGY J. 1970. Le bassin des volta et son contexte (Ghana, Niger, Togo, Dahomey, Haute-Volta). Etude bibliographique interprétée. Tra. Lab. Sci. Terre, St. – Jérôme, Marseille, Fr., (X), 12, 78 p.
 
 
 
SYLVAIN J P, COLLART J, AREGBA A et GODONOU S. 1986. Notice explicative de la carte géologique 1/500.0000è du Togo, Mém. n°6, D.G.M.G./B.N.R.M., Lomé – Togo.
 
 
 
===Key Hydrogeology References===
 
 
 
AGBEFU NOMESI YT. 2013. Caractérisation hydrogéologique et hydrochimique des aquifères de socle de la plaine des Dahoméyides  dans la région des Plateaux-Togo. Mém master Environnement-eau et santé. Univ. Lomé, 30p
 
 
 
ARI A. 2000. Etude géochimique et hydrogéologique des eaux souterraines d’un bassin sédimentaire côtier en zone tropicale. Implications sur la gestion, la protection et la préservation des ressources en eau du Togo (Afrique de l’ouest). Thèse Doct., Univ. de Paris VI. 158p + annexes.
 
 
 
ASSOUMA D. 1988. Etude par modèle mathématique de la structure et du fonctionnement d’un aquifère de socle exploité en région tropicale. (Alimentation en eau potable de la ville de Dapaong -TOGO). Thèse de 3e cycle, Univ. d’Orléans. 183p.
 
 
 
DGEA. 2009. Rapport de synthèse : Gestion intégrée des ressources en eau (GIRE) ey objectif du Millénaire pour le Développement. 119p, UNDESA.
 
 
 
Direction de l’Hydraulique et de l’Energie. 1983. Alimentation en eau de Lomé. Ressource en eau souterraine. Synthèse des données hydrogéologiques. Rapport 83 AGE 040 BCEOM/BRGM 37p
 
 
 
Direction de l’Hydraulique et de l’Energie. 1984. Alimentation en eau de Lomé. Modèle mathématique préliminaire des nappes du Continental Terminal et du Paléocène. Simulation de plusieurs scénarios d’exploitation. Rapport 84 AGE 008. BCEOM/BRGM 66p + annexes.
 
 
 
Gendron-Lefevre. 1977. Etude de factibilité d’approvisionnement en eau potable pour la ville de Lomé et de neuf villages avoisinants. République du Togo. Tome I : Ville de Lomé. ACDI. 126p.
 
 
 
GNAZOU MDT. 2008. Etude hydrodynamique, hydrochimique, isotopique et modélisation de l'aquifère du bassin sédimentaire côtier du Togo. Thèse Université de Lomé. 204p
 
 
 
PNUD. 1975. Prospection des eaux souterraines dans la zone côtière (TOGO) : conclusions et recommandations. DP/UN/TOG-70-511/1. Nations Unies, New York,. 83p + annexes.
 
 
 
PNUD. 1982. Stratégie d’aménagement des eaux, ressources et besoins en eau. Laboratoire Centrale d’Hydraulique de France. 11 notices et 11planches.
 
 
 
  
 +
The Department of Water Resources, which sits within the Ministry of Water, is responsible for groundwater monitoring. However, there are currently no national groundwater level or groundwater quality monitoring programmes.
  
  
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[[Category:Hydrogeology by country|t]]
 
[[Category:Hydrogeology by country|t]]
[[Category:Africa Groundwater Atlas]]
 

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