Welbedacht Dam
| Welbedacht Dam | |
|---|---|
| Official name | Welbedacht Dam |
| Location | Free State, South Africa |
| Coordinates | 29°51′35″S 26°53′26″E / 29.85985°S 26.89062°ECoordinates: 29°51′35″S 26°53′26″E / 29.85985°S 26.89062°E |
| Opening date | 1973 |
| Operator(s) | Department of Water Affairs and Forestry |
| Dam and spillways | |
| Type of dam | concrete gravity |
| Impounds | Caledon River |
| Height | 32 m |
| Length | 230 m |
| Reservoir | |
| Creates | Welbedacht Dam Reservoir |
| Total capacity | 10 330 000 m3 |
| Catchment area | 15 270 km2 |
| Surface area | 1017.5 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 of approximately 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).
It was originally envisaged that Bloemfontein would 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, it was decided to construct a smaller scheme on the Caledon River which could be 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) of approximately 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 of ~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 (3).
Due to siltation, the storage capacity of the Welbedacht Dam reduced rapidly from the original 115 million m³ to approximately 16 million m³ during the twenty 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. It was the first arch gravity Roller Compacted Concrete (RCC) dam in the world and comprises almost 64 600 m³ rollcrete and 14 200 m³ concrete with a gross storage capacity of 137 million m³.