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

Northern Cape PSDF
Volume 2
December 2011
losses and evapo‐transpiration by riparian vegetation along that part of the river, which by
far exceed the run‐of‐river yield contributed by local inflows. The WMA is also most
impacted upon by upstream developments. It is the most downstream of five WMAs
covering the Orange/Vaal River Basis, with extensive inter‐catchment transfers into and from
most of these WMAs. Water use in Lesotho, and transfers from Lesotho to the Upper Vaal
WMA, as well as the sharing of water with Namibia and underground resources with
Botswana, also have an influence on the WMA.
The Orange River Estuary is a transboundary Ramsar site. The in‐stream and estuarine flow
requirements are approximately 280 million m³ per annum and this water is currently being
released from the Vanderkloof Dam. The three sub‐areas of the water management area are
the Orange, the Orange Tributaries and the Orange Coastal sub‐areas.
C.2.4.2 UPPER ORANGE WMA
This WMA lies predominantly within the Free State. As with the Lower Orange WMA, the
Orange River, which rises in the eastern highlands of Lesotho where it is known as the Senqu
River, is the main river in this WMA. The Orange River is the largest and longest river in
South Africa and discharges into the Atlantic Ocean some 2 300 km from its origin in
Lesotho. The climate over the Upper Orange WMA is cool to temperate and ranges from
semi‐arid to arid. Rainfall mainly occurs as summer thunder showers and reduces
dramatically from as high as 1 000 mm per year at locations in the east to about 200 mm per
year in the west. In Lesotho rainfall varies between 600 mm per year to about 1 500 mm per
year. Potential evaporation within the Upper Orange WMA is also well in excess of the
annual rainfall. Main storage dams in the WMA are:
a) The Gariep and Vanderkloof dams, which command the two largest reservoirs in
South Africa. Hydropower for peaking purposes is generated at both sites.
b) The Armenia and Egmont dams on tributaries in the Caledon sub‐area, the
Welbedacht Dam on the Caledon River, and the Knellpoort Dam that supplements
the water to Bloemfontein.
c) The Rustfontein, Mockes and Krugersdrift dams that are situated on the Modder
River, and the Tierpoort and Kalkfontein dams on the Riet River.
C.2.4.3 LOWER VAAL WMA
The Vaal River is the only major river in the Lower Vaal WMA flowing across its south‐
eastern corner connecting it to the Middle Vaal and Lower Orange WMAs. The Harts River is
the only significant tributary to the Vaal River as it enters the Lower Orange WMA. The
largest part of the Lower Vaal WMA falls within the catchment of the Molopo River, a
tributary to the Orange River. However, the Molopo is an endorheic river with its flow not
reaching the Orange River. Intensive irrigation is practiced at Vaalharts and along the Vaal
River. The Vaalharts Irrigation Scheme is the largest in the country and of its 35,302 ha,
31,732 ha is located in the Northern Cape. There are no distinct topographic features in the
Lower Vaal WMA and most of the terrain is relatively flat with no climatic barriers. Climate
over the Lower Vaal WMA therefore varies gradually according to the larger regional
patterns. Annual rainfall ranges from about 500 mm in the east to as low as 100 mm in the
Office of the Premier &
Department of Rural Development & Land Reform
21
Dennis Moss Partnership