The Okavango River (formerly spelled Okovango or Okovanggo), Also known as the Cubango River, is a
river
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
in southwest
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
. It is the fourth-longest river system in southern Africa, running southeastward for . It begins at an elevation of in the sandy highlands of
Angola
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. Farther south, it forms part of the border between Angola and
Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...
, and then flows into
Botswana
Botswana (, ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label= Setswana, ), is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory being the Kalaha ...
. The Okavango does not have an outlet to the sea. Instead, it discharges into the
Okavango Delta
The Okavango Delta (or Okavango Grassland; formerly spelled "Okovango" or "Okovanggo") in Botswana is a swampy inland delta formed where the Okavango River reaches a tectonic trough at an altitude of 930–1,000 m in the central part of the en ...
or Okavango Alluvial Fan, in an
endorheic basin
An endorheic basin (; also spelled endoreic basin or endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but drainage converges instead into lakes ...
in the
Kalahari Desert
The Kalahari Desert is a large semi-arid sandy savanna in Southern Africa extending for , covering much of Botswana, and parts of Namibia and South Africa.
It is not to be confused with the Angolan, Namibian, and South African Namib coastal d ...
.
Flow
In Angola, the upper reaches of the Cuito (a tributary river to the Okavango) suffers clogging due to
controlled burns of the vegetation, reducing water flow downstream as the accumulated water instead
flows into the sand.
Before it enters Botswana, the river drops 4 m in a series of rapids known as Popa Falls, visible when the river is low, as during the dry season.
In the rainy season, an outflow to the
Boteti River in turn seasonally discharges to the
Makgadikgadi Pan
The Makgadikgadi Pan ( Tswana pronunciation ), a salt pan situated in the middle of the dry savanna of north-eastern Botswana, is one of the largest salt flats in the world. The pan is all that remains of the formerly enormous Lake Makgadi ...
s, which features an expansive area of rainy-season
wetland
A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The p ...
where tens of thousands of
flamingo
Flamingos or flamingoes are a type of wading bird in the family Phoenicopteridae, which is the only extant family in the order Phoenicopteriformes. There are four flamingo species distributed throughout the Americas (including the Caribbea ...
s congregate each summer. Part of the river's flow fills
Lake Ngami
Lake Ngami is an endorheic lake in Botswana north of the Kalahari Desert. It is seasonally filled by the Taughe River, an effluent of the Okavango River system flowing out of the western side of the Okavango Delta. It is one of the fragmented remn ...
. Noted for its
wildlife
Wildlife refers to undomesticated animal species, but has come to include all organisms that grow or live wild in an area without being introduced by humans. Wildlife was also synonymous to game: those birds and mammals that were hunted ...
, the Okavango area contains Botswana's
Moremi Game Reserve
Moremi Game Reserve is a protected area in Botswana. It lies on the eastern side of the Okavango Delta and was named after Chief Moremi of the BaTawana tribe. Moremi was designated as a game reserve, rather than a national park, when it was ...
.
Flood
Every wet season, Angola receives three times more rainfall than Botswana, discharging a higher than usual flow into the Okavango, turning swathes of outlying desert into a huge wetland.
Although the summer rains fall in Angola in January, they take a whole month to travel the first 1,000 km of the Okavango River, and then they take a further four months to
filter
Filter, filtering or filters may refer to:
Science and technology
Computing
* Filter (higher-order function), in functional programming
* Filter (software), a computer program to process a data stream
* Filter (video), a software component tha ...
through the plants and numerous channels of the final 250 km of the delta. As a result, the flood is at its biggest sometime between June and August, during Botswana's dry winter months. The delta then swells to three times its permanent size, attracting animals from kilometres around and creating one of Africa's greatest concentrations of
wildlife
Wildlife refers to undomesticated animal species, but has come to include all organisms that grow or live wild in an area without being introduced by humans. Wildlife was also synonymous to game: those birds and mammals that were hunted ...
.
At its widest point in a big flood year, the seasonal
swamp stretches to 150 km across from east to west; one of the factors that leads to the ever-changing nature of the delta is the flatness of the area. If one were to take a cross section of the delta at its widest point, one would find that the height variation from the mean over that 150 km is less than 2 m, which means that a minor sand deposition can cause major changes.
[http://blog.africabespoke.com/okavango-delta-part-2/ Okavango River Flooding]
In very wet years, a part of the river's flow may extend along the Magweggana River (actually a northeastern distributary of the Okavango Delta) and enter the
Zambezi River
The Zambezi River (also spelled Zambeze and Zambesi) is the fourth-longest river in Africa, the longest east-flowing river in Africa and the largest flowing into the Indian Ocean from Africa. Its drainage basin covers , slightly less than hal ...
, bypassing the Kalahari.
Sediment transport
The river carries annually 28,000 tonnes of
suspended sediment
The suspended load of a flow of fluid, such as a river, is the portion of its sediment uplifted by the fluid's flow in the process of sediment transportation. It is kept suspended by the fluid's turbulence. The suspended load generally consists of ...
and a similar amount of bedload to the terminal swamps.
Most of the particulate sediment carried by the river is fine sand, with some silt and mud, thanks to the geological makeup of the Okavango River catchment which is largely underlain by Kalahari sand. There is low concentration of dissolved solids in the river water - around 40 mg/L, made up mostly of silica, calcium and magnesium bicarbonates - but these dissolved solids form the largest component of sediment carried into the delta because the annual water volume is so large.
History
During colder periods in Earth's history, a part of the Kalahari was a massive lake, known as
Lake Makgadikgadi
Lake Makgadikgadi ( tn, Letsha la Makgadikgadi, label=Setswana, ) was a paleolake that existed in what is now the Kalahari Desert in Botswana from 2,000,000 years BP to 10,000 years BP. It may have once covered an area of from and was 30 m de ...
. In this time, the Okavango would have been one of its largest tributaries.
Water conflict
Both Namibia and Botswana experience drought, and as a result, concerns have been expressed about possible conflict over use of the river's water. Namibia has built a water canal, measuring about 300 km long, and has proposed a project to build a 250 km pipeline to divert water from the river into Namibia to help relieve the drought.
Botswana, however, uses the Okavango Delta for both tourism income and a water source. The Department of Water Affairs in Botswana has submitted that 97% of the water in the river is lost through evaporation, so the country cannot afford to lose any extra water.
Namibia, in turn, has argued that it will only divert half of one percent of the river's flow, and that it is entitled to any water that flows through its territory. To deal with such issues, in September 1994, Angola, Namibia, and Botswana signed an agreement to form th
Permanent Okavango River Basin Water Commission to provide advice to the three countries about the best ways to share the Okavango River's resources.
References
External links
OKACOM Homepage
{{Authority control
Rivers of Angola
Rivers of Namibia
Rivers of Botswana
International rivers of Africa
Kalahari Desert
Angola–Namibia border
Water conflicts
Border rivers