Okavango Delta

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NASA view of Okavango Delta

Typical region in the Okavango Delta, with a rag rug of free canals and lakes, swamps and islands

The Okavango Delta (or Okavango Swamp), in Botswana, is the world's largest inland delta.

The area was once part of Lake Makgadikgadi, an ancient lake that mostly dried up by the early Holocene, except for seasonal flooding. Today, the Okavango River has no outlet to the sea. Instead, it empties onto the sands of the Kalahari Desert, irrigating 15,000 km² of the desert. Each year some 11 cubic kilometres of water reach the delta. Some of this water reaches further south to Lake Ngami.^[1]

The waters of the Okavango Delta are subject to seasonal flooding, which begins about mid-summer in the north and six months later in the south (May/June). The water from the delta is evaporated relatively rapidly by the high temperatures, resulting in a cycle of cresting and dropping water in the south. Islands can disappear completely during the peak flood, then reappear at the end of the season. This process of evaporation was badly understood as late as the early 20th century:

[edit] Geography

[edit] Flood

If you think of the channels in the delta as the arteries of this gigantic living organism, then its heart is 1 250 km away in the Angola highlands. This distant heart beats but once a year when Angola receives three times the amount of rainfall that Botswana does. Sending a giant pulse of water coursing across Africa which eventually drains its lifeblood into the waiting arteries of the Okavango. This is referred to as the flood but unlike in the rest of the world where a flood has negative connotations, in the Okavango the flood is always welcome!

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. And the delta 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. And one of the factors that leads to the ever changing nature of the Delta is the flatness of the area. To give you an idea of how flat it is, if you were to take a cross section of the Delta at its widest point, along this cross section you would find that the height variation from the mean over that 150km is less than 2m. So a little sand deposition can cause major changes.^[2]

[edit] Where The Water Goes

Every year 90 million litres of water flow into the delta and although one would think that the water was simply swallowed up by the thirsty sands of the desert, an incredible 60% of this water leaves into the atmosphere via transpiration, in other words via the leaves of the plants rather than via evaporation. Amazingly only 2% of the water soaks into the desert and about the same amount flows out at the southern end of the delta. Little wonder then that Aurel Schultz, one of the first Europeans to clap eyes on the swamps, said “Where all this water goes is a mystery.”

With all of that water leaving the Delta into the atmosphere the Delta is unable to flush itself of the minerals carried in by the river and the water should become salty and uninhabitable like the Dead Sea. But remarkably it hasn’t and there are two reasons for this. Firstly, the water itself has a very low salt content, and secondly as so much of the water is leaving via the plants rather than evaporation the salt from that water collects around the roots of the plants rather than being left behind in the water.

[edit] Salinity

The catchment area of the Okavango is on Kalahari sands and for the people who live along the river and around the Delta this is a mixed blessing. The drawback is that the farmers don’t get a good silt load enriching their lands during flooding since there are very few nutrients in the waters of the flood. In fact your average urban tap water contains three times as many nutrients as the waters of the Delta! But the upside is that because the sands are so barren the Delta has not ended up as a lifeless salt pan, but rather as the host of a rich diversity of flora and fauna. And in turn those plants keep transpiring and inadvertently taking the salts out of the water and thus saving themselves and the Delta from a salty end.

[edit] Salt Islands

If you are ever fortunate enough to fly into the Delta you will see thousands of little islands, many of which have bare white patches in their centre. These islands grow each year because of the salts that are deposited on them as the water is drawn up by the trees on the island. As the water enters the roots it leaves some of the salts behind, these salts concentrate in the sands of the island, causing the islands to grow a little each day. It is for this same reason that the islands have bare, white patches in their centres. Those parts of the island have become too salty to support plants, aside from the odd salt resistant palm tree. The sand near the edges of the islands has yet to become that salty and the trees and grasses can still grow there.

[edit] Termite Islands

Approximately 70% of the islands in the delta began as termite mounds. Termite mounds are the soil homes that termites or flying ants, as they are more commonly known, construct. Some termites build a mound of earth and then a tree takes root. And from those small beginnings these islands have grown.

The water entering the delta is unusually pure, due to the lack of agriculture and industry along the Okavango River. It passes through the sand aquifers of the numerous delta islands and evaporates/transpirates by leaving enormous quantities of salt behind. These precipitation processes are so strong that the vegetation disappears in the center of the islands and thick salt crusts are formed.

[edit] Chief’s Island

The largest Island in the Delta is Chief’s Island and it wasn’t formed by either of these processes but rather by a fault line which uplifted this part of the Delta. Historically the island was reserved as an exclusive hunting area for the chief, hence its modern name. Chief’s Island is over 70km long and 15km wide and provides the core area for much of the Delta’s resident wildlife, especially as the waters rise and dry land shrinks. So here we have an irony common in many parts of the world, the hunting grounds of yesterday are the core conservation areas of today.

[edit] Wildlife

The Okavango is home to a prosperity of wildlife and attracts thousands of visitors a year. There are simple camps as well as luxury resorts within the delta region that cater to these visitors.

The delta provides a seasonal habitat to numerous different species. Among these are African Bush Elephants, the African Buffalo, the Hippopotamus, the Lechwe, the Topi, the Blue Wildebeest, the Giraffe, the Nile crocodile, the Lion, the Cheetah, the Leopard, Brown and Spotted Hyenas, Greater Kudu, the Sable Antelope, both the Black and the White Rhinoceros, the Plains Zebras, the Warthog and the Chacma Baboon. Notably the endangered African Wild Dog is present within the Okavango Delta,^[3] exhibiting one of the richest pack densities in Africa. The delta also includes over 400 species of birds, including the African Fish Eagle, the Crested Crane, the Lilac-breasted Roller, the Hammerkop, Ostrich, and the Sacred Ibis.

[edit] Animals

There are an estimated 200 000 large mammals in and around the Okavango Delta. Many of these animals live in the Delta but the majority move in and out. They leave with the summer rains to find renewed fields of grass to graze on and trees to browse. And then as winter approaches and the countryside dries up they make their way back to swamps. This leads to some of the most incredible sightings as large numbers of prey and predators get squashed into a smaller and smaller area. And certain areas of the Delta provide some of the best predator action that you can see anywhere in the world.

[edit] Lechwe

The most populous large mammal in the Delta is the lechwe. There are more than 60 000 lechwe and perhaps you will be lucky enough to see or hear a herd of these swamp dwelling antelope dashing through the shallow waters of the swamps. They are a little larger than impala and like the impala only the males have horns. The lechwe have adapted to live in marshy areas and occur throughout these swamps and those in Zambia. They live off aquatic plants and their elongated hooves and a water repellent substance on their legs enable them to move rapidly through knee deep water. And like the better known Waterbuck they also take to water when threatened by predators.

Aside from lechwe you can also see large herds of buffalo and elephants in the Delta, both of which total about 30 000. And together with the other animals, birds, plants and the beautiful environment, they make the Okavango Delta a truly remarkable destination.

[edit] Plants

The plants of the Delta play an extremely important roll provide cohesion for the sand. The banks or levees of a river normally have a high mud content and this combines with the sand in the river’s load to continuously build up the river banks. Here in the Delta, because of the clean waters of the Okavango, there is almost no mud and the river’s load is comprised almost entirely of sand. It is the plants that capture the sand, acting as the glue and making up for the lack of mud and in the process creating further islands on which more plants can take root.

This process is important in the formation of the other type of islands that you see in the swamps, linear islands. They are long and thin and often curved like a gently meandering river. The reason for that is that they are actually the natural banks of old river channels. Which over time have become blocked up by plant growth and sand deposition, resulting in the river changing course and the old river levees becoming islands. Due to the flatness of the Delta, and the large tonnage of sand flowing in to it from the Okavango River, the floor of the delta is slowly but constantly rising. And were channels are today islands will be tomorrow and new channels may wash away these existing islands. ^[4]

[edit] People

The Okavango Delta peoples consist of five ethnic groups, each with its own ethnic identity and language. They are Hambukushu (also known as Mbukushu, Bukushu, Bukusu, Mbukuschu, Ghuva, Haghuva), Dceriku (Dxeriku, Diriku, Gciriku, Gceriku, Giriku, Niriku), Wayeyi (Bayei, Bayeyi, Yei), Bugakhwe (Kxoe, Khwe, Kwengo, Barakwena, G/anda) and ||anikhwe (Gxanekwe, //tanekwe, River Bushmen, Swamp Bushmen, G//ani, //ani, Xanekwe). The Hambukushu, Dceriku, and Wayeyi are all Bantus who have traditionally engaged in mixed economies of millet/sorghum agriculture; fishing, hunting, and the collection of wild plant foods; and pastoralism.

The Bugakhwe and ||anikwhe are Bushmen who have traditionally practised fishing, hunting, and the collection of wild plant foods; Bugakhwe utilized both forest and riverine resources while the ||anikhwe mostly focused on riverine resources. The Hambukushu, Dceriku, and Bugakhwe are present along the Okavango River in Angola and in the Caprivi Strip of Namibia, and there are small numbers of Hambukushu and Bugakhwe in Zambia as well. Within the Okavango Delta, over the past 150 years or so Hambukushu, Dceriku, and Bugakhwe have inhabited the Panhandle and the Magwegqana in the northeastern Delta. ||anikhwjjje have inhabited the Panhandle and the area along the Boro River through the Delta, as well as the area along the Boteti River.

The Wayeyi have inhabited the area around Seronga as well as the southern Delta around Maun, and a few Wayeyi live in their putative ancestral home in the Caprivi Strip. Within the past 20 years many people from all over the Okavango have migrated to Maun, the late 1960s and early 1970s over 4,000 Hambukushu refugees from Angola were settled in the area around Etsha in the western Panhandle.

The Okavango Delta has been under the political control of the Batawana (a Tswana sub-tribe) since the late 1700s. Most Batawana, however, have traditionally lived on the edges of the Delta. Small numbers of people from other ethnic groups such as Ovaherero and Ovambanderu now live in parts of the Okavango Delta, but since the majority of the members of those groups live elsewhere and the habitation is recent they are not considered as part of the Okavango Delta peoples. There are also several Bushmen groups represented by a handful of people. These groups were decimated by diseases of contact in the middle part of the 20th century, and most of the remaining members have intermarried with the ||anikwhe.

[edit] Hydropower proposals

The Namibian government have presented plans to build a hydropower station in the Caprivi region, which would regulate the Okavango's flow to at least some extent. While proponents argue that the effect would be minimal, environmentalists argue that this project could destroy most of the rich wildlife and plant life in the Delta.^[5] The proposal is also a prime example of the potential for cross-border conflicts over water use.^{[citation needed]}

[edit] Gallery

Okavango Delta seen from Spot Satellite	Elephants in the Okavango Delta seen from a makoro (small boat).	A buffalo herd in the Southern part of the Okavango Delta.	A Lechwe Antelope "flying" over a patch of clear water
The Okavango Delta viewed from a Cessna at 1,200 ft.	Mokoro trip in the Okavango Delta	Water lillies in the delta	Girl gathering food in the Okavango Delta
Waiting for the hippos in the delta	Hippos as seen from a small boat in the Okavango	A pair of Saddle-billed Storks	Hyperolius argus (Reed Frog) in the Okavango Delta

[edit] References

P. Allison. 2007. Whatever You Do, Don't Run: True Tales Of A Botswana Safari Guide
J. Bock. 2002. Learning, Life History, and Productivity: Children’s lives in the Okavango Delta of Botswana. Human Nature 13(2). 161-198. Full text
C. Michael Hogan. 2009. Painted Hunting Dog: Lycaon pictus, GlobalTwitcher.com, ed. N. Stromberg
Cecil Keen. 1997. Okavango Delta

[edit] Line notes

^ Cecil Keen. 1997
^ http://blog.africabespoke.com/okavango-delta-part-2/ Okavango Delta
^ C. Michael Hogan. 2009
^ http://blog.africabespoke.com/okavango-delta-part-2/
^ Namibia: Power plans face wall of objections

[edit] External links

Wikimedia Commons has media related to: Okavango Delta

Coordinates: 19°15′S 22°45′E / 19.25°S 22.75°E / -19.25; 22.75

[0] Cecil Keen. 1997

[1] ttp://blog.africabespoke.com/okavango-delta-part-2/ Okavango Delta

[2] C. Michael Hogan. 2009

[3] ttp://blog.africabespoke.com/okavango-delta-part-2/

[4] Namibia: Power plans face wall of objections

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