Welbedacht Dam

Dam in Free State, South Africa

29°51′35″S 26°53′26″E / 29.85985°S 26.89062°E / -29.85985; 26.89062Opening date1973Operator(s)Department of Water AffairsDam and spillwaysType of damConcrete gravityImpoundsCaledon RiverHeight32 mLength230 mReservoirCreatesWelbedacht Dam ReservoirTotal capacity10,330,000 m³Catchment area15,270 km²Surface area1017.5 ha

Welbedacht Dam is a concrete-gravity type dam situated in South Africa, and was established in 1973. Bloemfontein is the sixth-largest city in South Africa, with a population around 300 000. It is situated in the Modder River catchment, which has insufficient water resources to meet the growing water requirements. The water supply to Bloemfontein is, therefore, augmented from the adjacent Caledon River by means of the Caledon - Modder River Government Water Scheme (CMRGWS).

Bloemfontein was originally planned to receive Orange River water from Vanderkloof Dam and the outlet works for the transfer scheme still exist at the dam wall. For various reasons, however, constructing a smaller scheme on the Caledon River was implemented before completion of the Vanderkloof Dam. The Welbedacht Dam on the Caledon River was constructed as the main storage element of the CMRGWS and water is abstracted from this dam for transfer to Bloemfontein and various smaller users along the way.

The Welbedacht Dam is a concrete barrage-type dam on the Caledon River, which was designed and constructed by the Department of Water Affairs. The dam has a catchment area of some 15 245 km² with a natural mean annual runoff (MAR) around 1210 million m³/a (1920 to 1987) and was completed in 1973. Its purpose was to supply water to the city of Bloemfontein via the 115-km-long Caledon-Bloemfontein pipeline, which has a capacity around 1.157 m³/s. Due to the high sediment concentration in the water, the transfer from Welbedacht Dam is first purified at the Welbedacht Purification Plant, which is located just downstream of the dam. The purification plant has a capacity of 1.68 m³/s. The hazard potential of the dam has been ranked high.

Due to siltation, the storage capacity of the Welbedacht Dam reduced rapidly from the original 115 million m³ to roughly 16 million m³ during the 20 years since completion. This reduction in storage created problems in meeting the Bloemfontein demand at an acceptable level of reliability and as a result, the 50-m-high Knellpoort Dam was completed in 1988.