Hydrogeology of Botswana

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Africa Groundwater Atlas >> Hydrogeology by country >> Hydrogeology of Botswana

The textual information on this page was taken from a number of different sources, which are listed in the References section, below. If you have more information on the hydrogeology of Botswana, please get in touch.

Compilers

Dr Kirsty Upton and Brighid Ó Dochartaigh, British Geological Survey, UK

Geographical Setting

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

General

Botswana is a land-locked country. It is predominantly flat, forming a gently rolling plateau with an average elevation of 1,100 m. Up to 70 percent of the country - most of the centre, west and south - is covered by the Kalahari Desert. In the northwest is the Okavango Delta.

Estimated Population in 2013* 2,011,100
Rural Population (% of total) (2013)* 43.1%
Total Surface Area* 566,730 sq km
Agricultural Land (% of total area) (2012)* 45.7%
Capital City Gabarone
Region Southern Africa
Border Countries South Africa, Namibia, Zimbabwe, Zambia
Annual Freshwater Withdrawal (2013)* 194 Million cubic metres
Annual Freshwater Withdrawal for Agriculture (2013)* 41.2%
Annual Freshwater Withdrawal for Domestic Use (2013)* 40.1%
Annual Freshwater Withdrawal for Industry (2013)* 18.0%
Rural Population with Access to Improved Water Source (2012)* 92.8%
Urban Population with Access to Improved Water Source (2012)* 99.3%

* Source: World Bank


Climate

Botswana’s climate is mostly semi-arid. Rainfall is low - less than 250 mm/year over most of the country, and less than 100 mm/year in the Kalahari - and is unevenly distributed and highly variable from year to year. Drought is a recurrent phenomenon. The east and north of the country receive the highest rainfall, but very few areas receive more than 600 mm/year.

Potential evaporation is around 2,000 mm/year (United Nations 1989).

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

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

Surface water

Many rivers in Botswana are ephemeral, flowing only during wet seasons. The major perennial river systems in the north of the country are the Chobe river, which is a tributary of the Zambezi river, and flows north into Zambia; and the Okavango river, which drains into the Okavango Delta. The east of Botswana lies in the Limpopo river basin, and a number of tributaries in Botswana flow into the Limpopo river. The Notwane river in the south provides water to the capital city through the Gabarone Dam. The Molopo river forms the border with South Africa to the south.

There are a number of dams in the country.



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

Soil

Much of the country is covered with arenosols typical of arid, desert areas. Only in the east is there widespread development of other soil types.
Soil Map of Botswana (For map key and more information on the datasets used in the map see the soil resources section)

Land cover

Up to 70 percent of the country is covered by the Kalahari Desert, with grassland and savannah vegetation that is often sparse. The east of the country has more forest cover. The northwest of Botwana lies in the Okavango Delta, with extensive wetlands.




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


Geology

This section provides a summary of the geology of Botswana. More information is available in the Africa Groundwater Literature Archive.

The geology maps below show a simplified version of the geology at a national scale (see the Geology resources page for more details).

















Summary

Much of Botswana is covered by unconsolidated sediments of Tertiary to Quaternary age, related to the Kalahari Desert, and known as the Kalahari system.

The pre-Kalahari geology of the country includes sedimentary rocks - largely sandstones - of Karoo type, sometimes capped by volcanic rocks; and large areas of Precambrian rocks. The Precambrian rocks are divided into sedimentary basins, which are also sometimes capped with volcanic rocks; dolomites; and basement type crystalline rocks.

Botswana is rich in mineral resources, including coal, diamonds, and metals such as nickel and copper.


Geological Environments
Key Formations Period Lithology
Kalahari
Kalahari Tertiary to Quaternary Predominantly terrestrial and highly variably deposits, comprising a sequence of aeolian sands, calcretised sands, calcretes, silcretes and marls, with variable thickness from 10 to 150 m (Farr et al. 1981).
Karoo
Karoo sedimentary rocks - uncovered Carboniferous - Jurassic The Karoo system comprises a predominantly terrestrial, arenaceous sedimentary sequence, partially capped by volcanic basaltic lavas (Farr et al. 1981). The maximum thickness of Karoo rocks in Botswana is unknown, but is thought to be of the order of 1,000 to 1,200 m in the axial regions of the Central basin and parts of the Southwest basin (Farr et al. 1981). From oldest to youngest, the main units are the Dwyka; the Ecca Group; the Beaufort; the Red Beds; the Cave Sandstone; and the Stormberg Basalts.

The Dwyka group consists largely of tillites, shales and siltstones associated with glacial and glaciofluvial deposition (Farr et al. 1981).

The Ecca group passes upwards from siltstones to, successively, coarse grained arkosic sandstones, finer grained sandstones, shales, coals, and argillaceous siltstones and mudstones. Basal conglomerate units also occur where middle Ecca strata lie directly on pre-Karoo basement. Impure limestones are recorded rarely. Finer grained sandstones passing into shaley sandstones and sandy shales and siltstones are often interbedded with the coarser units (Farr et al. 1981).

The Beaufort group has little coals or carbonaceous matter, but has conglomerates with calcareous concretions, and mudstones and siltstones with calcareous cement (Farr et al. 1981).

The Red Beds consist of a sequence of mudstones and siltstones, red shales, marls and fine grained calcareous sandstones.

The Cave Sandstone is the most widespread Karoo unit in Botswana, comprising largely aeolian sandstones, usually massive, and often loosely cemented. The sandstones are mostly fine-grained, sometimes almost siltstone grade, but includes extensive coarse-grained horizons. They include non-aeolian silt beds, calcareous concretions and thin limestones and chert nodular horizons (Farr et al. 1981).

The youngest Karoo unit in Botswana comprises volcanic rocks of the Stormberg Basalts. Much of the older Karoo rocks are covered by these relatively flat lying plateau basalts, formed of lava flows that vary in thickness from less than one metre to several tens of metres. The junctions of individual lava flows are often marked by fracturing. Tuffs are rare and impersistent, but occur near the base of the basalts, along with minor intercalations of Cave Sandstone and, higher in the sequence, occasional thin intraformational sandstones, siltstones, marls and/or palaeosoils (Farr et al. 1981).

Precambrian
Metasedimentary basins Significant basins of metasedimentary rocks of Precambrian age occur across Botswana, and include sandstones, conglomerates, limestones and quartzites (United Nations 1989).
Dolomites of the Transvaal system This series includes dolomites, cherts, quartzites and schists, but dolomites are dominant, and widespread across the country (United Nations 1989).
Crystalline Basement Granitic and metamorphic rocks, including amphibolites, quartzites and schists (United Nations 1989).

Hydrogeology

This section provides a summary of the hydrogeology of the main aquifers in Botswana. More information is available in the Africa Groundwater Literature Archive.

The hydrogeology map shows a simplified version of the type and productivity of the main aquifers at a national scale (see the Aquifer properties resource page for more details).


Unconsolidated

Named Aquifers Period General Description Water quality
Kalahari system Tertiary - Quaternary Aeolian and alluvial sands and gravels, particularly in the base of river valleys. These form an important water source in rural areas, as groundwater levels are shallow.


Sedimentary - Intergranular & Fracture Flow

Named Aquifers Period General Description Water quality
Karoo system The Karoo system forms a stratified aquifer, in which permeable layers (dominantly sandstone) are separated by layers with low permeability. A large proportion of groundwater storage and flow is via fractures in the aquifer layers. Semi-vertical fault zones and fractures form some connection between aquifer layers. The highest potential aquifers within the Karoo system are fractured sandstones with high transmissivity and storage capacity, particularly the Ecca and Cave sandstones. Typical transmissivity values are at least 350 m²/day, with relatively low storage coefficients of 2.5 to 3.5 percent. Typical borehole yields from the Cave sandstones are around 2.5 litres/second (l/s).

Sedimentary - Fracture Flow (including karstic)

Named Aquifers Period General Description Water quality
Dolomites Precambrian These rocks form karstic aquifers, with high potential where karstic features are well developed - where they are not well developed, yields are likely to be low. Transmissivity values of at least 250 m²/day are common, and values of more than 550 m²/day are seen occasionally, with storage coefficients of 0.1 to 6.
Volcanic rocks Stormberg lavas typically have transmissivity values of around 25 m²/day. Typical borehole yields are around 2.5 l/s.
Metasedimentary rocks Precambrian Quartzites can have moderately high yields.

Basement

Named Aquifers Period General Description Water quality
Precambrian Small local aquifers are formed in fractured zones and/or weathered basins. Yields are generally low.


Groundwater Status

There have been a number of estimates of the volume of Botswana’s groundwater resources. One puts the total groundwater resource at around 100 billion m³, with an average annual recharge of 1,600 million m³/year (Department of Surveys and Mapping, Government of Botswana, 2001); another gives a much lower estimated sustainable yield of 96 million m³/year. These different figures illustrate that further groundwater exploration work is needed to estimate the sustainable amount of groundwater in the country (Department of Water Affairs, Ministry of Minerals, Energy & Water Resources, 2013)

Only a small part of the estimated available groundwater resources can be economically abstracted, due to high abstractions costs, poor water quality and remoteness of productive aquifers in relation to water demand (Department of Water Affairs, Ministry of Minerals, Energy & Water Resources, 2013).


Groundwater use and management

Groundwater use

Groundwater is abstracted mostly for use in rural water supply, mines, power plants and irrigation, through well fields and individual boreholes.

Groundwater management

Groundwater monitoring

Transboundary aquifers

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


References

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

Many of these, and others, can be accessed through the Africa Groundwater Literature Archive

Useful web resources

Department of Surveys and Mapping, Government of Botswana. The Botswana National Atlas

Published literature

Department of Water Affairs, Ministry of Minerals, Energy & Water Resources. 2013. Botswana Integrated Water Resources Management & Water Efficiency Plan, Volume 1: Main Report. (L. Dikobe, Ed), Gabarone, Botswana: Government of Botswana.


Farr JL, Cheney CS and Baron JH. 1981. GS10 Project: Evaluation of underground water resources: Final report. Republic of Botswana, Department of Geological Survey.

United Nations. 1989. Groundwater in Eastern, Central and Southern Africa: Botswana. United Nations Department of Technical Cooperation for Development. Natural Resources / Water Series No. 19, ST/TCD/6


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