Cape Town Dams
Cape Town is supplied by 14 dams with a collective capacity of approximately 900 000 Ml
(900 000 000 000 litres). Most of this capacity is provided by five large dams: the Theewaterskloof, Voëlvlei, Berg River, Wemmershoek and the Steenbras Upper and Lower dams. The remaining dams are much smaller and only contribute 0.4% to total capacity. The three largest dams are owned or managed by the National Department of Water and Sanitation.
Until 1897, Cape Town relied on spring river water which usually reduced to a trickle in the summer months. This supply challenge changed with the construction of Cape Town’s first dam, the 954 Ml Woodhead Dam on Table Mountain. These days, the city has access to water storage of nearly 1 000 times greater capacity, provided by 14 dams, and is integrated into the wider Western Cape Supply System.
Table Mountain dams
The Woodhead Dam (pictured) was completed in 1897 and is Cape Town’s oldest dam currently in use. It was one of the first dams
to be built in the country. It is still in service and provides water to Camps Bay and the high-lying areas of the City Bowl.
Hely Hutchinson Dam
The water supply was augmented by the Hely-Hutchinson Dam which was completed seven years after Woodhead Dam opened. It was built upstream from Woodhead Dam and is also situated on Table Mountain’s Disa River. Both have masonry dam walls constructed of sandstone blocks which were carved out of the mountain by stone masons. A small railway line and a cable car connecting the top of Kasteelspoort to Camps Bay were constructed to assist with the dams’ construction. A small waterworks museum (pictured below), which includes the original locomotive, is located next to the dams.
Water from these two dams is treated at the Kloofnek Water Treatment Plant. The water takes an interesting route to get there. First, it is released into the Disa River Gorge where it flows as a small river towards Hout Bay. Closer to Hout Bay, the water is fed through the 700 metre Woodhead Tunnel that runs through the Twelve Apostles mountains to the Camps Bay side. From there it is piped into cast iron pipes that run along the popular Pipe Track hiking trail to the Kloofnek Treatment Works.
Victoria, Alexandra and De Villiers Dams
The three other dams on Table Mountain are Victoria, Alexandra and De Villiers dams. Completed before 1910, the dams are closer to the Constantia Nek side of the mountain and were the only water suppliers to the former Wynberg Municipality for many years. Water from these three dams is treated at the Constantia Nek Water Treatment Plant.
Steenbras Lower Dam
Steenbras Lower Dam (pictured) is located in the mountains above Gordon’s Bay and was completed in 1921. It was the first dam in Cape Town to bebuilt at a remove from Table Mountain. The original Steenbras Water Scheme included an 820 m tunnel through the mountain to Gordon’s Bay and a 64 km cast iron pipe (750 mm in diameter) which linked the dam to the Molteno Reservoir in Oranjezicht.
This project proved to be so expensive that the independent municipalities of Cape Town, Claremont, Green Point, Sea Point, Kalk Bay, Maitland, Mowbray, Rondebosch, Woodstock and, at a later stage, Wynberg, combined to form the Greater Cape Town Municipality in order to afford it. Further work included the building of a new, higher dam wall in 1926 and then raising it still higher in 1954. A second (1926) and third (1949) pipeline to Newlands Reservoir were also constructed.
Steenbras Upper Dam
The Steenbras Upper Dam (pictured) was completed in 1977 and almost doubled the storage capacity on the Steenbras River. It is located just upstream of the Steenbras Lower Dam and can be seen from the N2 highway. In addition to storing water, the Steenbras Upper Dam also plays an important role in generating electricity as it forms the upper reservoir for the City of Cape Town’s Steenbras pumped storage scheme, the first such scheme to be built in Africa.
Pump storage schemes are used to generate additional electricity in peak demand periods. During the night they use surplus electricity available on the national grid to pump water back up to the upper reservoir.
Steenbras Upper Dam is also linked by an open canal and pipeline to the Rockview Dam that forms the upper reservoir of the Palmiet Pumped Storage Scheme, which is a separate pump storage scheme operated by Eskom and the Department of Water and Sanitation. The link allows water from the Palmiet River to be transferred the dam.
Wemmershoek Dam (pictured at right) was completed in 1957 and was the second of Cape Town’s dams to be constructed at a remove from Table Mountain. It is nearly double the capacity of the Steenbras Lower Dam and is the largest dam owned by the City of Cape Town.
In an engineering first in South Africa, it was constructed using a clay wall and rockfill embankment rather than a traditional masonry and cement dam wall, which significantly reduced the cost. The dam is in a beautiful setting in the Wemmershoek Mountains and contains very high quality water that requires relatively little treatment.
Simon’s Town dams
Simon’s Town is supplied by two small dams: the Kleinplaats and Lewis Gay dams. Following local government restructuring of 1997, Simon’s Town’s water system has been connected to the wider City of Cape Town water system.
Voëlvlei Dam is Cape Town’s second largest supply dam, even though it is not built on any major river. Instead, it is supplied with water from two canals that divert water from the Klein Berg, Leeu and Twenty-Four rivers, which have catchment areas in the Porterville and Tulbagh mountains.
Voëlvlei Dam was built by the Department of Water and Sanitation and was completed in 1971. However, the infrastructure required for the city to use this water, including the water treatment works, pumping stations and the 80 km of 1 500 mm pipeline connecting the dam to the city were constructed by the City of Cape Town.
Theewaterskloof Dam is located near Villiersdorp and is the largest dam supplying Cape Town. It is the seventh-largest dam in South Africa. It is larger in capacity than the other 13 dams combined.
Theewaterskloof is connected to an extensive system of pipelines and tunnels that, in turn, connects it to the broader Western Cape Water Supply System. Particularly impressive is the 30 km of tunnels that pass through the Franschhoek, Groot Drakenstein and Stellenbosch mountains. To put this in perspective, this tunnel system is nearly eight times longer than the Huguenot Tunnel that one travels through on the N1 highway near Paarl. The tunnels link the Theewaterskloof Dam with the Cape Town water system near Somerset West via the Kleinplaas Balancing Dam (not to be confused with the Kleinplaats Dam near Simon’s Town) in the Jonkershoek Valley near Stellenbosch. The tunnels also connect to pipelines in the Franschhoek Valley linking it to the Wemmershoek and Berg River dams.
Western Cape Water Supply System
The dams in and around Cape Town form part of the Western Cape Water Supply System, which is integrated and collectively managed system of dams, pump stations, pipelines and tunnels. In addition to servicing Cape Town, the system supplies water to towns in the Overberg, Boland, West Coast and Swartland areas as well as providing irrigation water for agriculture. The integrated system helps optimise the use of water resources in the region as it allows water to be transferred between dams and catchment systems. Dams that are running low can be topped up from another source, and excess water flows in the Berg River in winter can be transferred to Theewaterskloof Dam for storage. During the dry months the water is transferred back and released into the Berg River as required.
Berg River Dam
The Berg River Dam (pictured at right, and originally called the Skuifraam Dam) is located in the mountains near Franschhoek and is the newest supply dam. It was completed in 2009, or 112 years after Cape Town’s first supply dam was constructed on Table Mountain in 1897. In future, the City will need to find other means of meeting its increasing water requirements. As there is no more suitable land on which to build dams in the Cape Town area, no further dams will be built.