Zambezi River Basin

Zambezi River runo 30 Thousand cubic metres per second

25

20

15

10

5

0

1939

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

Source: SARDC (2008) Southern African Environment Outlook, SADC, SARDC, IUCN, UNEP, Gaborone/Harare/Nairobi.

Figure 2.8 Flow Reduction in the Zambezi River Basin due to dam construction.

Reduced Runoff A major impact of the construction of the Kariba and Cahora Bassa dams from 1950–1970 was the reduction in the Zambezi River runoff. Before the dam construction, the Zambezi River was torrential with high flows during the wet season from November to March and relatively low flows in the dry season from April to October. On average, the river discharged 60 to 80 per cent of its mean annual flow during wet season. Since the dams were built, the wet season runoffs have been reduced by about 40 per cent, whereas the

dry season runoffs have increased by about 60 per cent (SADC and SARDC 2008).

Changing River Flows The generally arid southwestern part of the basin has produced some river flow regimes that are not consistent with the seasonality of the rainy and dry seasons. For example, the Savute River is uncharacteristically dry for long periods before flowing again, while the Lake Liambezi almost disappeared between 1985 and 2000 before in began filling up again.

After 28 years of aridity, the Savute Channel is flowing again, bringing an explosive growth of vegetation and drawing wildlife. The channel flowed from the 1850s to the 1880s, then stopped flowing and remained dry until it began flowing again in 1958. It stopped flowing in 1965, started again in 1967 then stopped in 1982, remaining dry for 28 years, until 2010 when water filled the channel again (Pfotenhauer 2011). This irregular flow of water explains the numerous dead trees that line the channel, as they have germinated and grown when the channel was dry and been drowned when it flowed again. Savute River in Botswana flowing again

The exceedingly high rainfall in the Angolan Highlands in the 2009-10 rainy season, along with the good floods of the year before, caused phenomenal flooding of the Okavango Delta in the winter of 2010, the highest ever recorded. Small tributaries of the Okavango River flow into the Selinda Spillway, now also flowing after many dry years. The spillway connects with the Kwando/Linyanti river system which, further north and east, flows into the Chobe River and eventually meets the Zambezi.

© Candice Bate, WWF

Elephants drinking from the Savute River.

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