Page 25 - SAICE book proof 2 LATEST JULY 2014

s a i c e
EASTERN CAPE PROVINCE

16. Plettenberg Bay pedestrian bridge over ◊ Below: Plettenberg Bay pedestrian bridge
the N2 ensures a safe crossing for residents and was at ◊ Below Centre: Hogsback Dam
its time a novel structural solution utilising steel tubing ◊ Bottom: Port Alfred
and other steel sections. To ensure a pleasing design an
asymmetrical arch, ten degrees out of the vertical was
used, therefore giving the bridge a sweeping feel across
the freeway at speed, leaning towards the horizontal
curve.

17. hogsback Dam is a flash back from the past
into the future. This water supply reservoir for a popu-
lar tourist resort was built in 2000 by labour intensive
methods according to a rubble masonry method. La-
bour intensive construction has contributed extensively,
albeit for limited time periods, to provide income for
people without formal jobs. In this case an environ-
mentally sound and aesthetically pleasing solution was
found which assisted a community in need of work. Al-
though relatively small in size with storage capacity of
100 000 m³, it is a tribute to sustainable development
and now even sports a trout population.

18. Chalumna River Bridge took design to a
new level when the box girder pre-stressed deck was
launched on a double curvature, i.e. horizontally and
vertically. Another unique and interesting feature is
that the design called for external pre-stressing cables
which are situated in sleeves that are accessible in case
the cables have to be replaced or strengthened at a
later stage.

33°14′ S, 27°35′ E

19. fresh water at the seaside has become
a necessity along portions of the coast where
development overtook the ability to supply potable
water from traditional sources such as rivers. At Port
Alfred to the south of East London fresh water wells in
amongst the sea dunes provided a solution. In other
places desalination plants have been installed in case
of emergency and at Port Elizabeth water comes all
the way from the Orange River dams 400 km away
via a series of transfer tunnels and rivers to augment and sell it at R5. At the SAICE Engineering Planet Future
the supply. Tourists are used to buying spring water Indaba in 2010 desalinated water from Sedgefield in the
from cafés and supermarkets at prices 1 000 times the Western Cape was indeed bottled, labelled and handed
price of water from the tap. Water from a desalination out to delegates as part of an environmental awareness
plant is almost as expensive at three times the price campaign at the conference, trying to convince people
of traditional water sources. A novel way would be to that water could really be drank from the tap instead of
bottle the desalinated water, costing 16c a litre, label it buying expensive spring water.

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