Difference between revisions of "Hydrogeology of Tanzania"
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Revision as of 07:37, 5 June 2015
- 1 Authors
- 2 Geographical and Political Setting
- 3 Geology
- 4 Hydrogeology
- 5 Groundwater use and management
Hosea Sanga, Department of Water Resources, Ministry of Water and Irrigation, Tanzania
Kirsty Upton & Brighid Ó Dochartaigh, British Geological Survey, UK
Geographical and Political Setting
Tanzania lies in the area between the Great Lakes (Victoria, Tanganyika and Malawi) and the Indian Ocean. The lakes mark the trace of the western branch of the East African Rift System. The coastal area of Tanzania comprises a low-lying flat plain. The centre of the country is dominated by a plateau, which varies in height between 900 and 1800 m above sea level. In the north and south of the country are highland areas, with the highest mountain in Africa, Mount Kilimanjaro (5895 metres above sea level), situated in the northern Pare Range. Tanzania also includes several islands, located off the east coast in the Indian Ocean. The largest of these are Pemba (north), Zanzibar (centre), and Mafia (south).
|Estimated Population in 2013*||49,253,126|
|Rural Population (% of total)*||70%|
|Total Surface Area*||885,800 sq km|
|Agricultural Land (% of total area)*||46%|
|Border Countries||Kenya, Uganda, Rwanda, Burundi, Democratic Republic of the Congo, Zambia, Malawi, Mozambique|
|Annual Freshwater Withdrawal (2013)*||5184 Million cubic metres|
|Annual Freshwater Withdrawal for Agriculture*||89%|
|Annual Freshwater Withdrawal for Domestic Use*||10%|
|Annual Freshwater Withdrawal for Industry*||<1%|
|Rural Population with Access to Improved Water Source*||44%|
|Urban Population with Access to Improved Water Source*||78%|
* Source: World Bank
The central plateau region of Tanzania is classified as a hot arid steppe climate, while the northern and southern regions are predominantly tropical savannah. The highland areas in the northeast and southwest of the country have temperate climates with dry winters and warm or hot summers. These climate regions are reflected in the spatial variations in observed average annual temperature and precipitation across Tanzania.
There are temporal variations in precipitation and temperature across Tanzania. Temperature is generally lower during the winter months of June to August, and highest during November and December. Precipitation is consistently low from June to September, and is higher and more variable during the summer months.
Rainfall time-series and graphs of monthly average rainfall and temperature for each climate zone can be found on the Tanzania Climate Page.
For further detail on the climate datasets used see the climate resources section.
|The main surface water features in Tanzania are Lake Victoria in the north, Lake Tanganyika in the west, and Lake Malawi in the south.
The main river draining the plateau region into Lake Tanganyika is the Gombe River. Several smaller lakes, including Lake Manyara, Lake Eyasi and Lake Rukwa, also receive discharge from rivers draining the central plateau.
The main rivers flowing from the plateau region into the Indian Ocean are the Pangani (north), Wami (centre) and Rufiji (south).
The Ministry of Water, through its nine Lake/River Basins, is responsible for river flow gauging. River flow data are stored in each of the Lake/River Basin offices, and also stored centrally at the Ministry of Water.
Tanzania National Parks (TANAPA) have river gauging stations at selected areas of interest within National Parks.
Tanzania Electric Supply Company (TANESCO) also monitor lake levels and river flow in selected locations.
|The soils of Tanzania are very varied, reflecting the complex interaction of climate, topography and geology.
Volcanic activity associated with the East African Rift System typically gives rise to Andosols, while erosion of weathered basic volcanic rocks typically produces Vertisols.
Widespread Cambisols reflect continuous uplift of the area surrounding the East African Rift System. These are young soils that generally lack distinct horizons and show limited evidence of soil forming processes.
Acidic Acrisols and clay-rich Luvisols represent soil development in areas with significant relief.
Extensive Lixosols in the south of Tanzania reflect the predominance of grassland savannah.
Fluvisols are widespread in central Tanzania along the floodplain of the Rufiji River and its tributaries.
|General information about COUNTRY land cover.|
|Sedimentary – Coastal Basin|
|Palaeozoic - Recent||The coastal basin comprises sedimentary rocks of various ages, including parts of the Karroo Sandstone, which extends south-westwards from the coast at the border with Kenya to Lake Malawi. The coastal basin includes sandstone, mudstone and limestone.||There are two major structural trends associated with faulting: the NNE-SSW Tanga Fault and the NNW-SSE Lind Fault.|
|Sedimentary – Cretaceous-Tertiary|
|Cretaceous Sedimentary||Cretaceous||The Cretaceous sedimentary rocks are associated with marine regression, and consist predominantly of continental and deltaic sedimentary rocks, interbedded with thin marine beds.
The continental units include sandstone, siltstone and mudstone; the marine units contain coral limestone, silty shale and mudstone.
|The majority of the marine sedimentary rocks occur in southern Tanzania, with isolated deposits in the central-east and northeast of the country.|
|Sedimentary – Mesozoic-Paleozoic|
|Karroo System||Carboniferous to Lower Jurassic||In southwest Tanzania the Karroo sedimentary rocks are of continental origin; in the northeast they are predominantly marine.
The Karroo system consists mainly of sandstone, siltstone and shale, with some coal deposits.
|The major basins of the Karroo System trend NNE. The smaller basins are aligned in a NW direction between Lake Nyasa and Lake Tanganyika.
The sedimentary sequence of the Karroo System reaches 7000 m thick.
|Upper Mesozoic Sedimentary||Upper Mesozoic||Sedimentary rocks of Upper Mesozoic age overlie the Karroo System and Precambrian basement. They were deposited in coastal basins that formed during the breakup of Gondwana, and represent alternating transgressive and regressive deposits. They comprise largely limestone, sandstone, shale, marl and local evaporites.||The Upper Mesozoic rocks occur along the coastal margin of Tanzania and in parts of the rift trough.|
|Bukoban System and Mozambique Belt||Upper Proterozoic||The Bukoban System comprises sedimentary rocks of anorogenic and continental origin, amygdaloidal basalts, and andesites. The sedimentary rocks of the Bukoban System include sandstones, siltstone, shales, red beds, chert, conglomerates, quartzites, greywackes, and dolomitic limestones.
The Mozambique Belt contains granitoids, granulite, meta-anorthosites, gneisses, amphibolites, marbles, pegmatites, mafic and ultramafic rocks, migmatites, quartzites and schists.
|The rocks of the Bukoban System are unmetamorphosed, except where they have been subjected to local cataclasis.
The rocks of the Mozambique Belt are intensely metamorphosed and deformed.
|Granitic Rocks||Archean - Proterozoic||Granitic rocks are subdivided into syn-, post-, and late-orogenic.
The late-orogenic granites typically form the cores of gneiss domes, or occur in complex intrusions.
Various types of late-orogenic granites exist: granites that are typically intruded into Archaean and Proterozoic rocks, micro-granites, and granodiorites.
|Granites within the Archean and Proterozoic rocks of Tanzania are scarce, small and discordant with the general structural trend.
Micro-granites typically occur as lenticular masses within syn-orogenic granites in the Lake Victoria Goldfield.
Granodiorites occur in several places including the Archean Lake Victoria Goldfield and Proterozoic Lupa Goldfield.
|Pegmatite||Different types of pegmatite occur in syn-orogenic granites, migmatites, and metamorphic rocks of the Archean and Proterozoic terrains.||Pegmatites are abundant in the Proterozoic Usagaran and Ubendian Systems; they are rare in the Archean Dodoman System; almost absent in the Archean Nyanzian System; and do not occur in rocks younger than Proterozoic age.|
|Shinyanga-Mwadui, Mabuki, Speke Gulf, Lake Eyasi and Iramba Plateau kimberlite provinces||Cretaceous||Diamondiferous kimberlites||Kimberlites are concentrated in the Tanzania Precambrian Craton (see below), mainly south of Lake Victoria, with outliers in the Precambrian (Proterozoic) mobile/orogenic belts (see below).|
|Precambrian Mobile/Orogenic Belt|
|Ubendian, Usagaran, and Karagwe-Ankolean Systems||Lower and Middle Proterozoic||The Ubendian System includes granulite, amphibolite, migmatite, gneiss, schist, quartzite and marble. Intrusive rocks are predominantly granite, but also include gabbronorites, eclogites, metamorphosed amphibolites, dolerites, peridotites and carbonatites.
The Usagaran System comprises sedimentary and volcanic rocks of the Konse Group and gneisses, amphibolites and lenses of granulites of the Isimani Suite.
The Karagwe-Ankolean System comprises argillaceous formations that have been slightly metamorphosed to argillites, phyllites and schists. Arenaceous formations have also been metamorphosed to quartzite.
|Rocks of the Usagaran System were largely deposited in geosynclinals troughs.
The Konse Group of the Usagaran System trends NE-SW and is bordered by the Tanzania Craton to the West and Isimani Suite to the East.
The Isimani Suite is highly metamorphosed and is unconformably overlain by the Konse Group.
|The Archean Granitoid Terrains, Dodoman System and Greenstone Belts||Archean||The craton is a composite of several different terrains of variously metamorphosed Archaean rocks.
The Dodoman System is the oldest and is of amphibolites facies.
There are also rocks of the Nyanzian and Kavirondian Systems, which include gneiss, schist, quartzite, migmatite, amphibolite and granulite.
The Greenstone Belts to the south and east of Lake Victoria are regionally metamorphosed to greenschist facies, and locally metamorphosed to epidote and amphibolites facies near granitic intrusions. The Greenstone Belts include ultramafic rocks, gabbros, dolerites, granites, syenites, diorite and lamprophyries.
|The Dodoman System is intruded by ultramafic, mafic, and felsic rocks (granites and pegmatites discussed above).
The Greenstone Belts are also intruded by mafic to felsic intrusions of various ages.
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge|
|Name of aquifer||Alluvial deposits are confined to delta regions along river valleys. Borehole yields vary depending on lithology, but the greatest potential lies within the volcano-pyroclastic and alluvium deposits of the Kahe Basin and Sanya Plain near Kilimanjaro. Yields typically vary between 0.2 and 2 l/s.
The coastal plain consists of largely unconsolidated sediments (beach sands, dunes and salt marsh), with some consolidated limestone deposits.
The thickness of the alluvial aquifers is not well defined, but the water table depth tends to vary between 10 and 20 m. Boreholes are often drilled to depths of 100-200 m.
|There are no major groundwater quantity issues.||Groundwater quality is generally good, with the exception of the coastal plain deposits, which are vulnerable to saline intrusion.||Rainfall is the dominant source of recharge, but infiltration also occurs from rivers and lakes.|
Consolidated Sedimentary - Intergranular & Fracture Flow
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge|
|Coastal Sedimentary Aquifer and Karroo Sandstone Aquifer||The groundwater potential of the Coastal Sedimentary Aquifer varies depending on its lithology, with higher productivity provided by the sandstones and limestones. Marls and shales are generally unproductive. The aquifer is also generally unconfined. Borehole yields in the Coastal Sedimentary Aquifer are highest in the limestone (1-6 l/s) and slightly lower in the sandstone (up to 2.5 l/s).
Sandstones and conglomerates of the Karroo System are characterised by intergranular flow and storage, which may be locally enhanced by secondary fracture porosity. They are generally unconfined. Boreholes in the Karroo sediments commonly provide yields of 0.1-5 l/s, but yields up to 15 l/s have also been reported.
The sedimentary aquifers generally vary in thickness from 5-30m. The water table typically sits at a depth of 10-35 m. Boreholes are not normally drilled below a depth of 80 m.
|The productivity of the Coastal Aquifer is limited due to issues with saline intrusion.||Salinity and nitrate are common groundwater quality issues.|
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge|
|Basement Complex||Groundwater occurrence in Basement Complex rocks is largely limited to secondary permeability, such as weathered zones, joints, fractures, faults or solution features. The potential of weathered zones depends on the degree and depth of weathering and associated fracturing, and the saturated thickness. The aquifers are generally discontinuous, and often confined.
Higher yields are encountered in narrow bands of gneisses and metasediments, in which permeability can be enhanced by a greater degree of fracturing due to their proximity to fault zones. Such zones occur in the Pangani Basin.
Higher yields are also obtained where thick weathered zones are associated with bedrock fracturing, such as in the Makutapora Basin in Dodoma, and in fractured quartzite and metasediments in otherwise dense gneisses.
Borehole yields in the basement complex rocks are generally around 3 l/s and vary with lithology. A maximum yield of 13 l/s is recorded in the Pangani Basin.
Transmissivity in the Pangani Basin ranges significantly. Hydraulic conductivities of between 1 and >16 m/day have been reported.
Studies in the weathered fractured aquifer of the Makutupora Basin have indicated a transmissivity of 670 m²/day in the basement rocks, while overlying sand and gravel deposits have a transmissivity of around 490 m²/day.
The basement aquifers are typically up to 50 m thick. Boreholes are typically drilled to depths of 70-120 m in the Dodoma System and 40-250 m in the Usagaran System.
|There are no major groundwater quantity issues.||There are no major groundwater quality issues.||Recharge generally occurs through fracture zones, faults or lineaments.|
In Tanzania there is inadequate data and information available for the major aquifers. Data that exists are often scattered, fragmented and incomplete.
Some of the key groundwater issues in Tanzania are:
- Parts of the Makutupora Basin, which supplies the Dodoma Municipality, are showing declining water levels;
- There has been a decrease in borehole yields, particularly within the Sanawari area;
- Overexploitation has led to saline intrusion in coastal regions, particularly around Dar es Salaam;
- There is no country-wide monitoring network to fully understand issues of overexploitation;
- There is a lack of groundwater resources management to deal with issues of overexploitation.
- There is no established safe distance between groundwater abstractions and potentially contaminating human activities;
- Polluting activities are increasingly encroaching on important recharge areas;
- Many aquifers are showing deteriorating groundwater quality;
- There is inadequate public awareness of potential sources of pollution and their impact on the groundwater environment.
Management of abandoned wells
- Poor borehole construction can lead to borehole collapse, which leaves deep aquifers vulnerable to pollution;
- There is inadequate institutional regulation of groundwater resources;
- There is inadequate government control of the private drilling sector.
Generally, the natural groundwater quality in Tanzania is considered potentially good and acceptable for use, with notable exceptions in some parts of the country:
- High chloride concentration (salinity) is a problem in the coastal regions of Lindi and Mtwara, and in central regions such as Singida and Shinyanga where there is a high evaporation rate and poor drainage.
- In Lindi and Mtwara regions, high levels of carbon dioxide have been reported in groundwater (Kongola et al. 1999), which causes issues with corrosion.
- High fluoride concentrations are a common problem in the areas surrounding the Rift valley system (e.g. Kilimanjaro, Arusha, Singida and parts of Shinyanga regions) (Mato et al. 2002).
- High iron content in groundwater has been observed in Mtwara and Kagera regions (Kongola et al. 1999).
- Nitrate levels of more than 100 mg/l were reported in the Makutupora basin, Dodoma and Singida town (Nkotagu, 1996; Kongola et al. 1999).
There are several groundwater dependent ecosystems in Tanzania that are dependent on the Makutopora aquifer in the Dodoma Region. The Little Kinyasungwe River and the Hombolo lake/wetland are discharge points for this aquifer and are important sources of water for domestic supply, livestock and irrigation in the Chamwimo District.
Groundwater use and management
Groundwater is a vital source for both rural and urban water supply schemes in Tanzania. Towns such as Dar es Salaam, Singida, Babati, Arusha, Moshi and Dodoma depend largely on groundwater for public water supply. Many rural water schemes are also built on groundwater sources. Most sources consist of boreholes with electric or hand pumps.
The current volume of groundwater used across Tanzania (1,265,000 m³/day) is estimated to be 12% of the total available volume. The main uses of groundwater are:
- Urban water supply (10% of total volume)
- Rural water supply (50% of total volume)
- Agriculture (10% of total volume)
- Industry and mining (2% of total volume)
- Other uses including livestock and dry land fishing (28% of total volume)
Source: Ministry of Water, 2009
Groundwater use in industry is more concentrated in urban areas, particularly in Dar es Salaam, where around 80% of Tanzania's industrial activity takes place.
The principal legal instruments that regulate water resources in Tanzania are:
- The Water Resources Management Act, No. 11 of 2009, which regulates water resources management.
- The Water Supply and Sanitation Act, No. 12 of 2009, which regulates water supply delivery.
These pieces of legislation are based on the 2002 National Water Policy.
The Water Resource Management Act outlines the institutional and legal framework for the sustainable management and development of water resources, outlines principles for water resources management, provides for the prevention and control of water pollution, and provides for the participation of stakeholders and the general public in the implementation of the National Water Policy.
The Water Resource Management Act also addresses issues such as groundwater control areas, and abstraction and discharge permits. Under Section 62 of the Act, the Ministry of Water is responsible for:
- Groundwater exploration licences (issued to any person who is engaged in groundwater exploration);
- Groundwater drilling licences (issued to any person who wishes to undertake groundwater drilling activities);
- Drilling licences (issued to all drillers, allowing them to operate a drilling rig).
Part IV of the Water Resource Management Act outlines the different institutions which are to be responsible for the development and management of water resources, including groundwater.
Institutions mentioned in the Act are: The Directorate of Water Resources (DWR), the National Water Board (NWB), Basin Water Boards (BWB), Catchment and Sub-catchment Water Committees and Water Users Associations (WUAs). The Act also specifies the duties and responsibilities of these institutions.
Other key institutions and organisations are:
- The Ministry of Water – responsible for forming regulations and guidelines;
- 9 Lake/River Basin Water Boards – act as a point for data collection, assessment, monitoring and management;
- Drilling and Dam Construction Agency – responsible for government agency drilling of boreholes;
- Higher Learning Institutions – responsible for providing groundwater water related courses:
- University of Dar es Salaam (UDSM)
- Ardhi University
- Sokoine University of Agriculture and Water Development and Management Institute (Formerly Rwegulurila Water Institute)
The main transboundary aquifers in Tanzania are:
- Kagera aquifer (Uganda)
- Kilimanjaro aquifer (Kenya)
- Coastal sedimentary aquifer (Kenya to the north and Mozambique to the south)
- Karoo sandstone aquifer (Mozambique)
There are currently no significant issues concerning the management of these aquifers.
For more general information about transboundary aquifers, please see the Transboundary aquifers resources page
The Ministry of Water has established groundwater monitoring stations in four basins: Pangani, Wami/Ruvu, IDB and Rufiji.
Groundwater level monitoring is carried out in the Makutapora Basin in the Dodoma region, where ten automatic water level recorders are installed.
Groundwater level monitoring is also performed in observation wells in Arusha by the Arusha Urban Water Supply Authority and in TPC-Moshi. Most of these measurements are taken manually on a daily basis.
The Ministry of Water, through its nine Lake/River Basins, also has a water quality monitoring network. Each Basin is responsible for the management and operation of its respective monitoring network and monitoring is generally carried out on a quarterly basis. Physical, chemical and biological monitoring is carried out through sampling of the following:
- pH, Electrical Conductivity, Turbidity, Odor, Taste and Temperature;
- Nitrate, Nitrite, Sulphate, Fluoride, Iron, Hardness, Alkalinity, and Ammonium;
- Total Coliform, Faecal coliform, and E coli.
- Bacteriological monitoring is performed in Makutapora only.