State of freshwater systems and resources: # 2
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Figure 3.12 Major rivers of South Africa
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There are 22 primary drainage regions (see Figure 3.12, map 7 Drainage regions - About South Africa) in South Africa, each
containing river systems of various length and MAR (Figure 3.12). Despite a high ecological and recreational value in a
generally arid landscape, the major concern of policy-makers and resource managers has been the role of rivers in supplying water
(through impoundment and interbasin transfer), and in their ability
to assimilate urban and industrial effluents.
Figure 3.13a-g.
shows long-term flow time
series for seven strategic rivers at a downstream point, either
before entering the sea (Orange, Palmiet, Mgeni and Tugela rivers),
or exiting the country (Crocodile river Mpumalanga) or before a
confluence (Vaal River). The exception is the station on the
Crocodile River (Gauteng), which is situated just before the river
enters Hartbeespoort Dam. These rivers have the following
characteristics:
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Figure 3.13a Annual flow for the Orange River at downstream point
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Orange River-the Orange River is the longest river in South Africa, and carries
more than 20% of the total river flow of the country. Including the
Vaal River (its largest tributary), the Senqu in Lesotho and the Fish River in Namibia (76 000
km2), the Orange River catchment is 682 059
km2 , covering most of Gauteng (mining, industry,
urban), the Free State (mining, agriculture) and the Northern
Cape (agriculture). It has five major dams along its length
(Katse, Gariep, Vanderkloof, Vaal and Bloemhof)as well as numerous weirs and barrages (Vaal barrage). The decrease in flow over the last 60 years Figure 3.13a is due to industrial and mining development in the catchment, and
abstraction for irrigation purposes in the Lower Orange
River.
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Palmiet River- the Palmiet River is a typical Western
Cape river (see Box 3.1), experiencing winter rainfall. It
has a small catchment area of 500 km2 and MAR of 228
million m3 a-1. It has five irrigation and
hydro-power dams along its length, and provides water for
agricultural and industrial uses, as well as to the city of Cape
Town. It is unclear why there has been an apparent increase in flow
over the last 30 years (Figure 3.13b).
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Figure 3.13b Annual flow for the Palmiet River at downstream point
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Mgeni River-the Mgeni River in KwaZulu/Natal, with a
catchment area of 4 439 km2 and MAR of 740 million
m3 a-1, serves the Pietermaritzburg-Durban
region. It is controlled by Midmar, Albert Falls, Nagel and Inanda
Dams and is augmented by inter-basin transfer from the Mooi River in
the Tugela Basin. Water in the river, including return flows from
Pietermaritzburg are fully utilised causing stoppage in flow, and an
additional augmentation from the Mooi River of about 200 million
m3 a-1 is planned. This will be fully utilised
by about 2007 (Basson et al.
1997).
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Figure 3.13c Annual flow for the Umgeni River at downstream point
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Tugela River-
the Tugela River, with a catchment area of
29 046 km2 and
MAR of 3 865 million m3
a-1, is one of the largest rivers in the country. It has
seven large dams along its length and provides water via interbasin
transfer to the Vaal, Mhlatuze and Mgeni Rivers. This river is
experiencing marked reductions in flow Figure 3.13d and will be fully
utilised by 2025.
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Figure 3.13d Annual flow for the Tugela River at downstream point
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Crocodile River (Mpumamlanga)-the Crocodile River in
Mpumalanga has a catchment area of 10 446 km2 and MAR of
1 236 million m3 a-1.It flows through the
Nelspruit industrial area, the lowveld agricultural area and the
Kruger National Park. The decrease in flow of the river is probably
due to abstractions for irrigated fruit farming (Figure
3.13e). Crocodile River (Gauteng) - the Crocodile River
(catchment area = 29 349 km2, MAR = 550 million
m3 a-1) flows from the
northern edge of the Witwatersrand to the Limpopo.
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Figure 3.13e Annual flow for the Crocodile River at downstream point (KNP)
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It is controlled
by the Hartbeespoort and Roodekoppies dams on the main river, as well as several smaller
dams on the tributaries. The volume of water in the river is showing
a steady increase Figure 3.13f
as a result
of return flows from the Witwatersrand urban area.
The virgin
MAR would have been significantly less
than current
MAR which includes these large volumes of
return flows of water originating from the Vaal river
system. The Crocodile drains a large, highly industrialised
and urbanised area, the return flows are largely of
treated sewage and industrial effluents, and is subject to
high levels of pollution.
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Figure 3.13f Annual flow for the Crocodile River at downstream point (Hartbeespoort)
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Vaal River - the Vaal River system, covering 196 438
km2 and with a runoff of 3 929 million
m3 a-1, supports about 37 % of the
countryeconomic activity.The greatest demand for water in
this catchment is for irrigation, follwed by mining and industrial
use, with a similar proportion going to urban and domestic use
(Basson et al. 1997). The river is controlled through the Vaal Dam,
the Vaal Barrage and Bloemhof Dam. It provides water to the
Crocodile and Olifants rivers, whilst receiving water from the
Assegaai, Buffalo, Tugela, Orange and Senqu.
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Figure 3.13g Annual flow of the Vaal River at downstream point
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There is also information about Freshwater Systems and Resources in the following reports:
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Metropolitan reports:
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Copyright © 1999 Department of Environmental
Affairs and Tourism. All Rights Reserved.
Site maintained by the Directorate Environmental Information and Reporting
Last update: October 1999
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