|
The key to the Lesotho Highlands Water
Project is the breathtaking Katse Dam which has recently (1997) been completed in the
Malibamatso Valley just below the Bokong River confluence.
The Katse Dam is a major international undertaking and is now the highest dam in Africa
with a height of 185m. The dam was designed by a consortium of South African and overseas
consultants and the construction contract was awarded to Highlands Water Venture, a
consortium of Italian, French, South African, German and British contractors on 14
December 1990.
Click on image for full size picture
The dam forms part of the first phase of the Lesotho Highlands Water Project (LHWP) and
is usually referred to as Phase 1A of the LHWP. It forms the main collecting storage in
Lesotho from which all transfers to South Africa will be made through approximately 80 km
of concrete lined tunnels.
Click on image for full size picture
The reservoir formed by the Katse Dam is very narrow, winding and deep with a surface
area at full supply level of only 35.8 km2. The relatively small surface area
together with the low evaporation rate at the dam result in very low evaporation losses
from the reservoir water surface - approximately 10% of the evaporation experienced at Vaal Dam for the same storage.
Click on image for full size picture
The intake tower is located approximately 18km north of Katse Dam and has been designed
to accommodate 70 m3/s which was the maximum transfer originally envisaged for
full implementation of the LHWP. The intake tower is 23m in diameter and 98m high to
accommodate the large range in reservoir storage elevation as well as to facilitate the
draw-off at four distinct lake levels. This will enable the quality of the transferred
water to be controlled at all times. Due to the position and design of the intake tower,
there is a certain volume of water in the reservoir that cannot be accessed via the
transfer tunnels. This dead storage is approximately 430 million m3 with the
result that the effective live storage behind Katse Dam is reduced from the total storage
capacity of 1 950 million m3 to 1520 million m3.
The Katse Dam is a double curvature concrete arch dam with a crest length of 710m and
contains 2.3 million m3 of concrete. The catchment area of the dam is 1867 km2
and the natural Mean Annual Runoff (MAR) is approximately 560 million m3/a -
the Katse reservoir therefore has a live storage of approximately 3 MAR. The overflow
crest spillway comprises 10 ungated bays each 16m wide. The jet from the spillway will be
dispersed before dropping into a plunge pool created by a 17m high tailwater dam.
|