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For many years, large areas in the Eastern Cape experienced severe water shortages with
the result that thousands of hectares of irrigable soil which previously obtained water
from one or other of the dams in the region could not be irrigated. The situation was
aggravated by the reduction in capacity of many of the existing dams due to heavy silt
deposits.
The Orange-Fish Tunnel, together with its network of canals, weirs and balancing
dams , has enabled these areas to be restored and has made the irrigation of thousands of
hectares of additional land possible.
The Orange-Fish Tunnel was completed in 1975 and is the key structure by which water is
delivered from the Gariep Dam, to the Teebus Spruit and the Great
Brak River and from there to the valley of the Great Fish River and the Sundays River
valley. With a length of 82,8 km, the 5,35 m diameter tunnel is the longest
continuous enclosed aqueduct in the southern hemisphere and the second-longest water
supply tunnel in the world. The main purpose of the tunnel is to divert water to the
Eastern Cape for irrigation, urban and industrial use. Over 200 000 m3
of concrete was used to line the tunnel which has a maximum capacity of 54 m3/s.
Click image for full size photo
The intake tower is situated on the south bank of the Gariep
Reservoir at Oviston, approximately 19 km upstream of the dam wall. Seen from above, the
intake tower is shaped like a four-leaf clover with each leaf containing an inlet gate -
all at different levels. In this manner, water can be drawn from different levels to help
control the water quality. Each of the four inlets can be sealed to allow complete
de-watering of the tunnel for routine maintenance.
Click image for full size photo
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