Katse Dam is situated in the Malibamats’o River, three (3) kilometres downstream from where the Bokong River enters the main stream. The Dam is located in a valley between two mountains formed by basalt rock. The dam is a double curvature arch design.
The dam was built by Highlands Water Venture (HWV), a consortium of seven international contractors namely Imbregilo (a leading company) from Italy; Bouygues from France, Hochtief from Germany, Stirling and Kier from the United Kingdom and Concor and Group 5 from South Africa. The construction of the Katse Dam started in February 1991 and was completed in May 1997.
During excavation of the dam foundation, the rock conditions prompted a conservative modification to the dam design and resulted in the incorporation of the preformed joint which is 165 metres in length at the upstream heel of the dam. The joint is designed to reduce uplift pressures and increase the effective normal load of the dam.
Basalt aggregate that was used during construction was obtained at a quarry in a neighbouring valley and moved by a 2.4 kilometre long conveyor belt passing through a 1.4 km long tunnel to the tertiary crusher which was located next to the concrete batch plant.
The dam wall has got galleries that provided access during construction and were used for joint grouting. They are now being used for reading instruments, monitoring behaviour of the dam as well as for the control of seepage water through the use of sumps and dewatering pumps.
The construction of the dam wall was preceded by the construction of a 35 metre high upstream coffer dam which diverted the water from the Malibamats’o River through two diversion tunnels. Downstream of the wall, is a tailwater dam which is 17 metres high which creates a plunge pool to dissipate the energy of the flood waters which flow over the main dam wall through the spillway.
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Katse Intake Tower
The Katse Intake Tower is situated in the Katse reservoir, nineteen (19) kilometres upstream of the Katse Dam. The reservoir depth at the intake is 77 metres. To permit the selection of water at the optimum quality, four draw-off levels are provided, each with four inlets. The total capacity of the intake tower is 88m³ per second of water, through any four intake gates at a given draw-off level. The height of the tower from the foundation level to the top is 98.6 metres. The tower base is 5 metres thick with a diameter of 40 metres.
The Katse Intake Tower is the entry point of the water that is transferred from Lesotho to South Africa. The water begins its 82 km journey from Lesotho to South Africa from this structure.
The 45 km long Transfer Tunnel links the Katse reservoir with the Hydropower Station at ‘Muela in Butha-Buthe.
There are five (5) ventilation shafts along the length of the tunnel. The shafts have been lined to assist natural ventilation during inspections and to allow the escape of entrapped air.