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Water Reconciliation Strategy Study for the Large Bulk Water Supply Systems: Greater Bloemfontein Area 6
3. AVAILABLE SUPPLY
3.1 Surface Water
Nearly 70% of the total surface runoff, which would flow through the Upper Orange Water Management
Area (WMA) under natural conditions, originates from Lesotho and just more than 30% from within the
WMA. The surface water resources, both within the WMA and in Lesotho, are well developed and have a
high degree of utilisation.
The two largest dams in this WMA are the Gariep and Vanderkloof dams, which reduce the incidence of
floods in the Lower Orange WMA by about 50%. Other major dams are the Welbedacht and Knellpoort
dams in the Caledon catchment and the Krugersdrift, Rustfontein, and Kalkfontein dams in the Modder-Riet
River catchment. A description of the major dams per sub-catchment is provided in the following sections.
3.1.1 Caledon River Sub-catchment
The Welbedacht Dam is situated on the Caledon River and supplies water to urban users in Bloemfontein,
Botshabelo, Dewetsdorp, and various other smaller users, as well as irrigators downstream of Welbedacht
Dam along the Caledon River. The irrigators downstream of Welbedacht Dam have no claim to any water
stored in Welbedacht Dam. Only the inflow can be released for irrigation purposes. The Welbedacht WTW
at Welbedacht Dam supplies water via the Caledon-Bloemfontein pipeline to Bloemfontein, Botshabelo, and
other minor consumers.
Due to the decreasing yield of the Welbedacht Dam as a result of siltation and the increasing demand on
the Caledon-Bloemfontein Regional Water Supply Scheme, the DWA supplemented the yield of the
Welbedacht Dam by constructing the Knellpoort off-channel storage dam on the Rietspruit, a tributary of the
Caledon River. Knellpoort Dam is supplied with water from the Caledon River by the Tienfontein Pump
station. Water pumped from the Caledon River into Knellpoort Dam is then released back into the Caledon
River to allow abstraction at Welbedacht Dam by Bloem Water all year round. Furthermore, the Novo
Transfer pump station is located at the Knellport Dam and is able to transfer water into the Modder River,
which supplied the Rustfontein and Mockes Dams.
Since 1973, when Welbedacht Dam was completed, the dam has lost more than 90% of its storage
capacity due to the high siltation rates. Since there is minimal storage capacity in Welbedacht Dam, the
Tienfontein pumps must operate at a high reliability on a run-of-river basis to supply Knellpoort Dam. The
current pumps have a total discharge of approximately 2.5 m 3 /s (design 3 m 3 /s) and have experienced high
maintenance costs as a result of fine debris and sediment which reach the pumps.
Tienfontein pump station is seen as the most critical component of the water supply infrastructure supplying
Bloem Water with raw water, as Bloem Water receives approximately 70% of its water supply from
Welbedacht Dam (via Tienfontein Pump station and Knellpoort Dam).
3.1.2 Modder River Sub-catchment
Krugersdrift Dam is located on the Modder River and supplies water for irrigation purposes to the Modder
River Government Water Scheme. More than 50 weirs are constructed in the Modder River between the
dam wall and the confluence with the Riet River.
Mockes Dam on the Modder River supplies water to Bloemfontein via the Maselspoort WTW. Groothoek
Dam is located on the Kgabanyane River, a tributary of the Modder River, and supplies water to Thaba
Nchu.
Interventions Report June 2012