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Positioned partway down the hillside on favourable rock
conditions is the oval shaped Surge Headbay - a large reservoir with a
water surface area of about 3000m² and an internal wall depth of 31.5m.
In the centre of the northern wall, a bellmouth inlet from the pressure
tunnel guides the flow by a baffle structure set on the headbay floor.
Opposite the tunnel entry, blocks for four penstock
intakes are positioned, including a transition piece into which gate
frames are welded to hold in place the circular horizontal legs of the
penstocks terminating at a flange coupled to that of a PIV penstock inlet
valve. Foundations for the headbay, some 12m below ground level, require
excavation for 115 000m³. The spoil was used to fill the terraces for
parking area and for backfilling of the headbay structure.
The total concrete placed in the Surge Headbay came to
about 75 000m³.
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