Volume II - The Northern Cape Provincial Spatial Development ...

Northern Cape PSDF
Volume 2
Map C.5: The Orange River Basin (Source: WRP in Earl et al 2005).
December 2011
The Province largely falls within 4 Water Management Areas, namely the Lower Orange
(WMA 06), Upper Orange (WMA 12), Olifants/Doorn (WMA 15) and the Lower Vaal (WMA
20) Water Management Area (WMA) (refer to Map C.6 below).
C.2.4.1 LOWER ORANGE WMA
This WMA largely corresponds to the boundaries of the Northern Cape Province with
Botswana and Namibia, as well as having small portions located in the Western Cape and
Free State Provinces. Most of the water requirement is met from releases from major dams
in the Upper Orange WMA. The area receives the lowest mean annual rainfall in the country,
ranging from 20mm at the coast and 400mm on the eastern boundary. Evaporation can be
several times more than the rainfall received, being as high as 3,000 mm per annum. The
area is also characterised by prolonged droughts often interspersed with severe flooding.
57% Of the natural runoff is generated in Lesotho, 33% in the Upper Orange WMA and the
remaining 10% in the Lower Orange WMA. The Vaal River is the main tributary to the Orange
River with the confluence near the town of Douglas. Other tributaries are Ongers,
Hartebeest and Molopo rivers, as well as the Fish River in Namibia. Most of the runoff
generated in the WMA is coming from the Fish River and enters the main Orange River close
to the river mouth. The WMA is extremely dependent on water from upstream WMAs. Over
95% of water available in the WMA is released from the Vanderkloof Dam in the Upper
Orange WMA. Water is transferred within the WMA from the Orange River to the Coastal
sub‐area. This water transfer supplies 75% of the requirements for water in the sub‐area.
The Orange River’s negative yield within the Lower Orange WMA is a result of evaporation
Office of the Premier &
Department of Rural Development & Land Reform
20
Dennis Moss Partnership