The focal point and centrepiece of the LHWP, Katse Dam, is a monumental piece of engineering, inspiring awe in anyone who sees it. The dam is a double curvature concrete arch, 185m high, and 710m along the crest.
The design was chosen because it was the most cost-effective of the viable designs to span the wide U-shaped valley of the Malibamatso River, downstream of its confluence with the Bokong River. It also allowed water to be impounded at low risk while construction was taking place.
Some 2,32 million cubic metres of concrete were produced to build the wall, using a basalt aggregate taken from quarries in the surrounding mountains. Cement and fly ash, transported by road from Ficksburg, were delivered at 40-minute intervals during the construction phase. All of this material now forms a wall 60m thick at the base and 9m at the crest consisting of 46 cantilever blocks. The joints between the blocks were filled by high-pressure cement grout, applied from the passages (called "galleries") that traverse the wall. These galleries contain the precision instruments that monitor the behaviour of the dam, and also act as drainage channels for seepage water.
Katse Dam has a preformed joint at the bottom of the wall. This joint extends laterally across the middle 11 (out of 46) blocks and into the upstream 1Om of the base of the dam. It was decided to incorporate the joint to compensate for instability detected in the bedrock below the dam during excavation for the foundation. The joint allows the wall to flex under the pressure of the two million tons of water when the reservoir is full, preventing possible cracks in the wall area under most pressure.
The contractor for Katse Dam was an international consortium made up of companies from Italy, France, Germany, the UK and South Africa.
The dam was completed in May 1997 and due to the good rains of that year and the previous season, it filled to its full supply level by early 1998, when nature tested the free- flowing spillway and the performance of the dam under full loading conditions.
Since then a balance of good rain and the delivery of water to South Africa has kept the dam at or near to its full supply level.
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