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Annual floods Okavango Delta

Annual floods Okavango Delta

The start of Southern Africa's cool dry season is May/June, when data is coming in thick and fast from hydro measuring stations throughout the region reporting the state of flows in the rivers here.  This includes data from the water authorities in Namibia, Angola, Botswana, and Zimbabwe and Zambia, outlining the flows in the catchments of the Kunene, Zambezi, Kwando and Okavango Rivers.

The record flood occurred in 1957/58 when the coffer dam and the suspension bridge over the Kariba gorge, during the construction of the Kariba Dam wall, were destroyed. 2009 marked the highest flood of the Upper Zambezi River since 1969 but floods in 2010 were also extremely high.

When will ‘Nyaminyami’, the Zambezi River God strike again?

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Intertropical Convergence Zone (ITCZ)

Due to a combination of higher than normal Indian Ocean temperatures, a low pressure system centred over central Botswana, Zimbabwe and Zambia and a southward movement of the moist Inter Tropical Convergence Zone (ITCZ), the rains were above average during 2009.  This was particularly so over the 16 and 17 Degrees South latitude in a band across the African Continent and which, fortuitously, includes the catchments of most of the great rivers mentioned. 

During March 2009 this band received about 120% above average rainfall, followed by localized but heavy falls along the Zambia/Angola border region as well as over the Okavango Delta itself.  Above average heavy rain was also recorded in Central Zimbabwe and Zambia, also important catchment areas for the middle and lower Zambezi.

Okavango_flood_2009

Flood effects in the Okavango and Linyanti

The flood effects in the Okavango and Linyanti are fantastic, as large grassland areas and floodplains which have not been inundated for many months and sometimes decades, become flooded, and a complete recharge of groundwater takes place.

Islands which have been dehydrated through no ground water flows rejuvenate and distal lakes such as Ngami and Mababe fill.  These two terminal sinks along with a major increase in flows down the Boteti River,  which connects the Okavango to the Magadikgadi, create wide ranging habitats for many, many waterfowl and mammal species.

Okavango_flooding_2009

Linked to the Mababe Lake and fed from the Linyanti/Kwando system the Savute Channel has a major increase in flow, which may result in the re-establishment of the famed Savute Marsh at the Chobe National Park end of the channel, which has been dry since 1984.

On the 8th May 2009 we flew along the Selinda Spillway, (that connects the North eastern arm of the Okavango Delta to the Savuti channel in the Linyanti region) and it was full of water along its entire length!

The availability of so much water over a large area has extremely beneficial effects on the distribution of the region’s high elephant numbers.

Most, if not all of the camps in the Okavango are situated on islands and higher ground with many being on lifted walkways and stilts.  There is little, if any, effect on the camps themselves, although some camps have to adjust the road networks somewhat since many were located on lower ground during the dry years. (In the Okavango a meter can make a huge difference to wet and dry).

The Caprivi Strip, the section of Namibia that separates Botswana and Zambia and culminates in the four countries of Namibia, Zambia, Zimbabwe and Botswana joining together, is sometimes completely under water as the Zambezi pushes its waters back up the Chobe River, forcing the Chobe to flow backwards from East to West (if its normal the river flows from West to East).

Okavango sunset 2009

This is in fact a natural phenomenon which only happens very occasionally in the wet and dry cycle as mentioned, and is a grand opportunity to see the waters of this fascinating region in all their glory. The river levels of the Chobe and Zambezi can drop 2 metres in as little as 2 weeks, exposing newly fertilised grasslands. The Okavango Delta continues to fill as the waters filter through the vast reed beds and papyrus.

NASA have some excellent images of the floods NASA Earth Obvservatory to check it out. Be warned - images are huge and take a while to load!



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