The Okavango Delta's Floods

June in Maun, at the bottom of the Delta, is a dry and dusty month. The locals regularly drive their 4x4s to check on the lifeless, empty Thamalakane River - everyone's waiting with mounting excitement for the arrival of the floods.

On average 9.4km³ of water tumbles down from the Angolan central highlands to seep several months later into the basin that is the Okavango Delta. The rise in water levels is at times imperceptible; other times you can walk alongside the trickle of water as it creeps along a dry channel.

Dusty, brown grasslands are transformed overnight into shimmering floodplains, glaring white salt-encrusted pans become shallow basins of chattering wildfowl and once parched ditches turn into clear rivers winding their way into the dry season's thirst lands.

The floods are, in essence, the lifeblood of the Delta: they bring water and precious nutrients to a world built on thick, leaching sands under a brutal and relentless sun. Without them the Delta would shrivel and dry into a stagnant, choking wasteland; with them the Delta is renewed and refreshed.

Water levels fluctuate by some degree - up to two metres at the Panhandle where the flow is at its most concentrated, to a few centimetres at its fringes. Percolating first into the deeper permanent swamps, the floodwaters slowly spread into the seasonal swamps and, in exceptional years, into the network of mysterious Kalahari rivers and lakes that lies to the south.

What surprises many people is the purity of the water - the word 'swamp' when applied to the Delta is a misnomer - you can usually drink the water straight out of the channel you are canoeing on. Crystal clear, largely free of salts and pollution, the cleanliness of the water has a downside - it's extremely deficient in nutrients, a fact that is borne out by the paucity of wildlife in the upper reaches of the Okavango. Happily for Botswana however is the fact that the Delta is a sink into which the nutrients are dumped and accumulated, making the Delta a far more biologically productive region than its northern watershed.

Along with the clear waters comes 170,000 tonnes of sand and sediment which is instrumental in changing the nature of the Okavango Delta: choking channels, switching flows, building islands and depositing nutrients - an everchanging mosaic.

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