Okavango River

The Okavango River (formerly spelled Okovango or Okovanggo) is a river in southwest Africa. It is the fourth-longest river system in southern Africa, running southeastward for 1,600 km (990 mi). It begins in Angola, where it is known by the Portuguese name Rio Cubango. Farther south, it forms part of the border between Angola and Namibia, and then flows into Botswana, draining into the Moremi Game Reserve.

Okavango
Okavango in Kavango, Namibia
Okavango river basin map
Location
CountryAngola, Namibia, Botswana
Physical characteristics
Mouth 
 • location
Moremi Game Reserve, Botswana
Length1,700 km (1,100 mi)
Basin size530,000 km2 (200,000 sq mi)
Discharge 
 • average475 m3/s (16,800 cu ft/s)
 • minimum350 m3/s (12,000 cu ft/s)
 • maximum1,000 m3/s (35,000 cu ft/s)

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.[1]

Discharging to an endorheic basin, the Okavango does not have an outlet to the sea. Instead, it empties into a swamp in the Kalahari Desert, known as the Okavango Delta or Okavango Alluvial Fan. In the rainy season, an outflow to the Boteti River in turn seasonally discharges to the Makgadikgadi Pans, which features an expansive area of rainy-season wetland where tens of thousands of flamingos congregate each summer.[2] Part of the river's flow fills Lake Ngami. Noted for its wildlife, the Okavango area contains Botswana's Moremi Game Reserve.

During colder periods in Earth's history, a part of the Kalahari was a massive lake, known as Lake Makgadikgadi. In this time, the Okavango would have been one of its largest tributaries.

Confluence of Cuito (from top) and Okavango (flowing from left to right) (2018)
18°01′40″S 020°47′31″E

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.[3][4]

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 country. To deal with such issues, in September 1994, Angola, Namibia, and Botswana signed an agreement to form the Permanent Okavango River Basin Water Commission, to provide advice to the three countries about the best ways to share the Okavango River's resources.[4][3]

Flood
Popa Falls (2018)

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 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 miles around and creating one of Africa's greatest concentrations of wildlife.

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.[5]

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, bypassing the Kalahari.

Sediment transport

The river carries annually 28,000 tonnes of suspended sediment and a similar amount of bedload to the terminal swamps.[6]

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References
  1. Siyabona Africa Travel (Pty) Ltd, "Popa Falls | Okavango River | Botswana" webpage: TravelZA-PopaFalls
  2. C. Michael Hogan (2008) Makgadikgadi, The Megalithic Portal, ed. A. Burnham
  3. Basedau, Matthias (2005-01-01). Resource Politics in Sub-Saharan Africa. GIGA-Hamburg. p. 294. ISBN 9783928049917.
  4. Varis, Olli; Tortajada, Cecilia; Biswas, Asit K. (2008-03-15). Management of Transboundary Rivers and Lakes. Springer Science & Business Media. p. 96. ISBN 9783540749288.
  5. Okavango Delta | Okavango River Flooding
  6. Hanibal Lemma, and colleagues (2019). "Bedload transport measurements in the Gilgel Abay River, Lake Tana Basin, Ethiopia". Journal of Hydrology. 577: 123968. doi:10.1016/j.jhydrol.2019.123968.

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