Phase 1B Description
Phase 1B is designed to supplement the inflow into Katse Reservoir and to increase the average flow to South Africa from the 16.8m3/s of Phase 1A to 28.5m3/s, utilising nearly the full theoretical capacity of the Phase 1A Transfer and Delivery Tunnel network. The three principal structures in Phase 1B comprise: Mohale Dam to the south-west of Katse which will create a new 958 million m3 reservoir on the Senqunyane River; a 32km-long Interconnecting Tunnel of about 4.5m in diameter to link the Mohale and Katse Reservoirs; and the Matsoku River diversion weir, from where water will be diverted via a 5.6km-long gravity feed tunnel also into Katse Reservoir. Mohale will contribute 9.5m3/s to Katse's inflow while Matsoku will contribute 2.2m3/s when the two diversions are complete.
Mohale Dam
Mohale Dam is a concrete-faced rock-fill embarkment 145 metres high. It is built on the confluence of the Senqunyane arid Likalaneng rivers that drain into the Senqu River. Atotal concrete volume of 100 thousand cubic metres and a volume of 7.2 million cubic metres of rock-fill have been used on completion of construction, making Mohale Dam the highest of its type in Africa and one of the top ten highest such dams in the world. The dam creates a reservoir storage capacity of over 950 million cumecs of water. It has a crest length of 600 metres and is 12 metres thick at the crest.
Mohale Tunnel
Mohale Tunnel provides for an approximately 32km long water conveyance
tunnel through the mountain massif separating the Senqunyane catchment from
the Malibamats'o catchment, so connecting the Mohale Reservoir to the Katse
Reservoir. The tunnel is Tunnel Boring Machine (TBM) driven predominantly
through basalt on two headings. The unlined intake drive averages 5.1m
internal diameter while Outlet drive is approximately 4.9m in diameter.
Pre-cast concrete segmental lining is applied to protect basalt gradation
and the final internal diameter of the lined tunnel will be approximately
4.2m. The capacity of the tunnel will be 9.5 m3/s and estimated
to be complete by year 2002.
Matsoku Weir & Tunnel
Matsoku Diversion will consists of a 19m high , 180 m long, mass gravity
diversion weir on the Matsoku River and a 5.6km long tunnel leading from the
weir to Katse Reservoir. The tunnel will discharge into the reservoir at
full supply level of the latter at a point some 16km upstream of the Katse
Dam wall. Associated works include 4.8km long gravel access road to the
tunnel outlet, and 1.5km gravel access road to the weir site with a low
level bridge over the Matsoku River just downstream of the weir.