The Okavango River may be best known for its dramatic demise in the sands of the Kalahari, but, as Mike Main explains, the pulse of life it brings to the delta each year is truly spectacular.
Wherever you go on the continent, Africa’s heartbeat is all around you. In the still of night at Victoria Falls, the earth trembles at the might of the flood. In the Congo, night skies are rent with flames from the deepest reaches of the earth. In the Sahara, powerful sand-laden winds roar and scour and endlessly reshape the land. In Botswana, the Okavango, like some gigantic lung, fills and empties to a slow, slow rhythm, marching in lockstep with the cycle of the seasons. What is the story of this enigmatic river? Where does it come from and where does it go? Why does it spill its waters fatally upon the blistering sands of the Kalahari so that they never see the sea?
The basic facts are simple enough. Botswana’s Okavango River rises 1600 km away on the Bié Plateau of Angola. First, as the Kubango, it drains a basin of more than 50,000 square kilometres, before flowing south to form the border with Namibia. It then crosses the Caprivi Strip and enters Botswana at Muhembo as the Okavango River, delivering nearly eleven cubic kilometres of water annually to the desert nation. It is there that it is transformed into one of the most unusual rivers in the world.
The first 95km of its journey through Botswana lies between two parallel faults that create a 12km-wide plain over which, in wide meanders, the river twists and turns through a floating sea of papyrus, like an enormous serpent. Locally this is known as the Panhandle because, downstream of it, the river fans out in a gigantic pan shape – the delta of the Okavango River.
The delta itself is created by two deep crustal faults that run at right angles to the flow: one at the base of the Panhandle and the other at the foot of the delta at Maun. In the 175km that lies between these two geologic features, the waters of the Okavango spread out in a magical mosaic of islands, wide rivers, narrow channels, lagoons, beautiful groves of towering riverine forest and vast mats of papyrus and reeds.
The difference in height between the start of the Panhandle at Muhembo and the base of the delta – a distance of 270km – is just 62m (200ft)! The slope is incredibly gentle – in the delta itself, just 1:3300. Thus the water moves slowly and, on the extremely flat landscape, spreads out to cover, at its greatest extent, almost 15,000 square kilometres.
The delta is not static – rather, it is highly seasonal. At the Okavango’s source in Angola, heavy rainfall towards the end of the year initiates a flood that courses through the catchment and reaches Muhembo between January and March. This is the start of the delta’s flood season. It takes three to four months for the mass of water to make its way through to the town of Maun in June or July, and so the peak of the flood in the heart of the delta occurs around April and May.
While peak flood months see the Okavango spread to its full size, the delta slowly shrinks after the flood has passed to as little as 6000 square kilometres. This happens in the hottest part of Botswana’s year – September to November – and will be the time of greatest stress for animals that live there. Water will be present as the delta never dries out completely, but its area will be much reduced, resulting in crowding and competition for grazing. This is the time of contented predators!
It is the impact of this pressure for food that causes many of the larger species to move out of the delta during Botswana’s rainy season, which runs from November to March. In the surrounding hinterland the rain will fill pans and rivers, replenish the grass and renew the biome, and thus drive the movements of the mammal population, especially elephant, to echo the ebb and flow of flood waters.
I once watched the arrival of the flood in the grasslands – I imagined it would be a quiet and peaceful event. I saw fingers of water seeping at walking speed through the stalks of tall grass, twisting here, turning there, searching, always searching for the lowest point and moving forward, ever forward. Small life panicked. Crickets, tiny reptiles and insects of all kinds crawled, leapt and jumped for their lives, some even going the wrong way, landing in the midst of the advancing flood. In seconds they were gulped down by a flotilla of hungry catfish. Jostling, pushing, sliding one against another as they muscled themselves over the wet ground in the open air ahead of the advancing water so as to be first to the feast. And whilst they did so, exposing themselves, other predators hovered, swooped and dived upon them in a devastating aerial attack. It was not a gentle flood but the front line of a killing zone.
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Giant fish eagles snatched squirming catfish high into the air or, if the fish were too big, hauled them along the wet ground to a gory death. Lesser birds sought the insects and smaller creatures, plucking them from their useless refuges. Half-eaten carcasses lined the edges of the advancing flood as sated birds bowed branches and still greater hordes fell upon the banquet, following its relentless progress through the grasslands.
Fish also move in response to the flood regime. Barbel seem to take it upon themselves spontaneously to migrate in huge shoals called ‘runs’, the causes of which are little understood. Especially in the upper reaches of the delta in October and November, where perhaps the fish sense that water levels are slowly falling, they congregate in huge numbers, causing the papyrus mats on either side of the channels to come alive with shoals of slapping, flapping fish as they make their way downstream in a chaotic rush towards the main body of water. Otters and fish eagles have a field day!
The fault lines defining the delta are considered to be an extension of the Great Rift Valley that scars the eastern side of Africa. It is this same feature that is believed to have created the Okavango itself. The central part, the down-faulted graben that lies beneath the heart of the delta, is now filled-in and covered by more than 300m of sand.
Of all the water that enters the delta, either from river flows or from local rain, a staggering 95 per cent evaporates into the atmosphere. Of the small amount that remains, two or three per cent sinks into groundwater and the tiny volume left over is collected by the Thamalakane River at Maun and led, by that river, either into Lake Ngami or into the Boteti River which itself, in modern times at least, goes nowhere and whose waters simply vanish into the sand of the Kalahari.
So this great river that came from the earth, returns to the earth. A river that in the course of its passing, sends a pulse of life flooding through the delta – a pulse, that in its turn, powers new life and reveals a place where one can, indeed, stand and see the slow heartbeat of Africa.
Plan your trip
There are no direct flights from Europe to Maun, the launching point for most trips into the Okavango Delta. Air Botswana (www.airbotswana.co.bw) has daily flights that connect Maun with Johannesburg.
Free 30-day tourist visas are available upon entry for most nationalities.
When to visit
The best months to see wildlife in the delta are during the dry season (April to October). The floods arrive in the delta between January and March, and typically start receding in September.
Bradt’s Botswana (3rd edition, 2010) and Lonely Planet’s Botswana & Namibia (2nd edition, 2010) are excellent companions for your Okavango trip. For more detailed information on the workings of the delta, check out Okavango Delta: Floods of Life by John Mendelsohn et al.
• Open, Velcro-strapped sandals without socks are the best answer for in-and-out-of-the-water explorations.
• Plastic dustbin bags, which fold into almost nothing, are wonderful emergency resources for keeping day-bags or people dry when unexpected storms appear.