Okavango River

The Okavango is the main river of an internally drained basin shared by Angola, Namibia, and Botswana. Its principal headwater systems, the Cubango and Cuito, rise on the Angolan plateau and flow generally south and southeast. After the Cuito joins the main stem near the Angola–Namibia border, the combined river continues east along the border and then turns into Botswana.

The same river carries different names along its course. Cubango is the usual name in Angola, Kavango is widely used in Namibia, and Okavango is used in Botswana and for the connected basin and delta. These names describe one continuous drainage system rather than separate rivers.

Unlike neighboring systems that reach the Atlantic or Indian oceans, the Okavango is endorheic. Its water enters a broad inland alluvial fan in northwestern Botswana. From there, evaporation, plant transpiration, infiltration, and groundwater movement account for almost all outflow; only during wetter conditions does surface water extend far into the distal channels.

The headwaters rise in the Bié and central Angolan highlands, where broad uplands stand roughly 1,500 metres or more above sea level. The terrain is not a single sharp mountain crest. It is an elevated, gently rolling plateau cut by shallow valleys, wetlands, and stream networks that gather summer rainfall and feed south-flowing rivers.

The western Cubango branch begins on relatively steeper ground and responds more quickly to rain. Bedrock reaches, rapids, and confined valleys occur along parts of its course. The Cuito drains gentler sandy terrain farther east. Water stored in headwater wetlands, peat-rich valleys, deep sands, and shallow groundwater is released more slowly, helping maintain base flow after the rainy season.

This difference between the two branches is central to the river's hydrology: the Cubango tends to produce sharper seasonal peaks, while the Cuito moderates the combined flow. Smaller Angolan tributaries enlarge both systems before their confluence. Although the mapped basin covers about 700,000 square kilometres, the principal perennial runoff comes from roughly 120,000 square kilometres of wetter Angolan headwater country. Much of the southern topographic basin is too dry or weakly connected to contribute regular surface flow.

After descending from the Angolan plateau, the Cubango reaches the Namibia border and becomes known as the Kavango. The river follows a long eastward boundary reach, joined by the Cuito from the north. Its valley alternates between sandy alluvial sections and local bedrock controls. Near the eastern end of the Namibian reach, the low rapids called Popa Falls expose resistant rock across the channel.

The river enters Botswana near Mohembo and passes into the delta's panhandle, a narrow, low-gradient valley about 150 kilometres long. Here the main channel meanders between floodplains before reaching the broader fan. Downstream, it separates into a shifting network of distributaries, including western, central, and eastern channel systems that convey floodwater across very slight relief.

The Okavango Delta is commonly called a delta because the river divides into distributaries and deposits sediment, but it lies inland rather than at a coast. Geomorphologically, it is a large alluvial fan occupying a shallow tectonic depression. Faults associated with the Okavango Rift Zone help define its margins and gradient, while old channels, levees, islands, and flood basins record repeated changes in the path of flow.

The river crosses a strong north-to-south rainfall gradient. Most runoff originates during the austral summer rainy season in Angola, where annual rainfall is substantially higher than in northern Botswana. Farther south, the delta lies in a semi-arid setting with high potential evaporation and a shorter, less dependable local rainy season.

Water released from the upper basin takes weeks to months to travel through the long river corridor. Inflow at the head of the delta commonly rises around the end of the local rainy season, and the flood front then advances slowly through channels and shallow floodplains. As a result, the greatest inundation across much of the delta usually occurs during the dry southern winter, well after the main Angolan rains.

Flood extent varies from year to year with rainfall in the headwaters, groundwater storage, channel condition, and losses along the route. Local rain falling directly on the delta also adds water, but it peaks earlier than the incoming river flood. The overlap and separation of these two water pulses create a distinctive annual sequence of local wet-season flooding followed by the delayed expansion of upstream water.

The Okavango carries relatively modest suspended-sediment loads into Botswana because much material is stored upstream and because the Cuito crosses extensive sandy wetlands with little exposed relief. Within the delta, the river deposits sand along channels and levees. Finer mineral material and organic matter settle in flood basins, while wind also supplies dust to islands and dry surfaces.

Vegetation slows water and traps sediment along channel margins. Over time, aggradation can raise a channel bed or obstruct a distributary, directing more water into another route. Fault scarps, even where they are subtle, also influence channel direction and the outer limits of flooding. The visible fan is therefore not fixed: its active channels and wet areas migrate over years and decades within a much older sedimentary landscape.

Dissolved salts enter with river water and are concentrated by evaporation, yet much of the flowing and seasonally flooded delta remains fresh. Salt is redistributed through groundwater and accumulates beneath or around some islands and distal basins. This subsurface transfer helps prevent uniform surface salinization even though the basin has no outlet to the sea.

As water reaches the lower fan, several distributaries converge toward the Thamalakane River near Maun, while western channels can extend toward Lake Ngami. The Thamalakane connects eastward with the Boteti, an intermittent outlet route that carries water away from the delta during sufficiently wet periods.

The Boteti descends toward the Makgadikgadi depression, linking the Okavango hydrologically to a much larger interior lowland. Surface water does not cross this entire route every year, and the river does not have a permanent terminal mouth comparable with a sea-flowing system. Instead, the position of the effective terminus shifts with flood magnitude, channel conveyance, evaporation, and infiltration.

Most Okavango water is ultimately returned to the atmosphere through evaporation and plant transpiration or enters shallow groundwater within the delta. This dispersed ending is the defining downstream landform process of the river: a concentrated highland flow becomes a broad, shallow pattern of channels, floodplains, islands, and dry terminal reaches.

The Okavango headwaters form part of a broad elevated water-source region in Angola. Nearby drainage lines lead north and west toward Atlantic-flowing systems and east toward the upper Zambezi network. Low relief and sandy terrain can make some divides subtle, but the present Okavango main stem carries its water south into the Kalahari interior.

Within Botswana, the delta occupies the northern part of the Kalahari Basin, a much larger structural and sedimentary depression. Its modern fan overlies older lake and river deposits associated with changing drainage patterns across the Makgadikgadi–Okavango region. The river therefore connects active seasonal hydrology with a longer history of faulting, sediment accumulation, and inland-basin reorganization.

For atlas comparison, the neighboring Zambezi River crosses plateau and gorge terrain before reaching the Indian Ocean, whereas the Okavango loses its flow within the continental interior. The contrast shows how subtle differences in regional slope and basin structure can send nearby headwaters toward very different termini.