The role of Ceres municipality (now Witzenberg municipality) before the combined dam (municipal & agricultural use) was constructed.
The Koekedouw river is the main water source of Ceres town and a prominent source to the surrounding agricultural development in the well known Ceres valley situated in the Western Cape approximately ±180km from Cape Town. The original dam in the form of a concrete arch dam and main supply line was completed around 1953 supplying water to Ceres town as well as the then state-of-the-art hydro-electric power station.
The original pipeline from the arch dam was approximately ±2150m long consisting of a 900mm underground concrete pipe plus an 760mm overland steel pipe with cement liner. Shortly after the earthquake of 1969 the damaged concrete pipe segment was replaced by a Ø900mm asbestos cement pipe which subsequently was replaced by a Ø900mm overland galvanized steel pipe in 2013.
The role of Ceres Koekedouw Management Committee (Witzenberg municipality & Koekedouw irrigation board) with the combined dam (municipal & agricultural use).
The first phase of the Koekedouw irrigation scheme was completed around 1973, delivering surplus winter water to a number of farms in the valley. The arch dam was then demolished and replaced with the current state of the art rockfill dam which was completed in 1998 meeting the ever growing water demands of the town while also adding a summer water supply component to the Koekedouw irrigation scheme.
The Koekedouw pipeline was built in 1973 as a 600mm overland bitumen lined steel pipe ±1700m long all the way to the foot of the mountain. Subsequently the bitumen liner was stripped out and replaced with an orange-peel finish cement liner in 1998 at the time when the new dam was built.
The bulk water supply system consists of three branches as follows:
Interestingly, in 1994, Ceres was one of the fastest-growing towns in the Western Cape and South Africa.
The industrial and domestic water demand during dry summer months, when the dam’s inflow was at its lowest, had led to multiple water restrictions. The unsafe, aging dam’s inadequacy spurred the construction of the much larger new dam.
Negotiations between the Ceres Municipality and the Koekedouw Irrigation Board gave rise to the inaugural collaboration agreement between an irrigation board and a local government in South Africa, with the objective of constructing a dam independently, without government assistance, to meet the community’s water requirements.
In January 1996, the initial phase of the dam project commenced. The new dam, a pioneering endeavor in Africa, was positioned at the same site above the previous structure. Given its location in a seismically active zone, it necessitated special design techniques. A rock-fill dam with an asphalt-concrete core was the chosen design to provide flexibility during earthquakes, requiring the engagement of Norwegian expertise and subcontractors, alongside local contractors.
A road paver was adapted for asphalt concrete placement, employing a continuous movement method. The 50 cm wide asphalt concrete layer was applied in layers, building to a 20 cm height, with laser equipment ensuring uniform thickness. For effective bonding, the surface of the prior asphalt concrete layer was heated to 150°C before the next layer was laid.
The dam project encompassed two primary components:
A. The interim water supply scheme, ensuring a consistent water supply to the municipality and the Koekedouw Irrigation Board during larger dam construction, composed of three distinct projects:
A1. The initiation of an access road and cofferdam, sharing the storage capacity of the old dam, commencing in January 1996 and completing by December 1996.
A2. The establishment of a borehole pumping system, delivering water from three points to a new reservoir at Groenplaatjie, where modern lime dosing and chlorination now occur. This project began in April 1996 and reached completion in December 1996.
A3. The construction of an additional concrete reservoir, boasting a 5 megaliter capacity at Groenplaatjie, was initiated in August 1996 and was fully operational by June 1997.
B. The construction of the new dam, which commenced in October 1996, with a target completion date of August 1998.
The new dam boasts a 60-meter wall height, a voluminous capacity of 640,000 cubic meters, and storage space for 17,000,000 cubic meters. It features a concrete-lined syphon overflow, while the outlet infrastructure includes a 140-meter tunnel beneath a mountain slope equipped with two 90mm pipes. A concrete outlet tower, complete with an access bridge over the flood overflow channel, controls water extraction from the dam.
The dam wall’s rock was excavated from an on-site quarry situated below the water table in the Table Mountain Sandstone. Explosives were employed for excavation, and filter material was prepared on-site using rock crushers.
Grinaker, the contractor for the project, engaged 40 senior personnel, 100 skilled workers, and approximately 75 temporary workers from the Ceres area.
The dam’s cost totaled R80,000,000, jointly financed by the Witzenberg Municipality and the Koekedouw Irrigation Board, with the municipality covering 41% of the construction costs, while the Koekedouw Irrigation Board bore the remaining 59%.
This collaborative endeavor proved to be a unique and highly beneficial venture for both parties. The town secured a substantial water supply for another 40 years, significantly accelerating the already impressive 6-8% growth rate in agricultural development in the region.
Therefore, this project proved to be of immense benefit to the Ceres community.
It was agreed upon by all parties involved that for the initial 20 years following completion, farmers would have access to 10,000,000 cubic meters, while the town would receive 7,000,000 cubic meters. Afterward, the allocation was to shift to 7,000,000 cubic meters for farmers and 10,000,000 cubic meters for the town.
Following the dam’s completion, an additional 800 hectares of farmland became available for irrigation. Plans were also underway to allocate 130 hectares of irrigated land to emerging small-scale farmers from the larger dam. This component of the project advanced as envisioned, enhancing the region’s agricultural prospects.
The Witzenberg Municipality is using its allocation to supply precious drinking water to the towns of Ceres, Bella Vista, Nduli and Prince Alfred’s Hamlet.
