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Physical Environment
Landscape
The Illawarra region lies
stratigraphically at the top of the Permian Shoalhaven group of rocks, which
consist of interbedded siltstones, sandstones and shales with various
intrusive igneous rocks of the Gerringong Volcanic Facies. Red Point is a
seaward extension of Gerringong Volcanic rocks that consist of intrusive and
extrusive latite (Wollongong Geological Series Sheet SI 56-9). Red Point marks
a geological boundary between sandy seabed to the south-west of the Point
(Perkins Beach) and rock and gravel seabed to the east and north of the Point.
Extensive reefs and rocky outcrops occur around Red Point and the Five Islands
group of islands are found offshore and to the north-east of Red Point.
Bathymetry &
Substrate
The outfall is located on the
south-east side of Red Point at the near vertical edge of a rocky reef
platform and discharges subtidally in approximately 8m of water. To the south
of the outfall are low relief, rocky cliffs of Red Point and then Perkins
Beach. To the north is Fishermans Beach, a small rocky headland, North Beach
and then Port Kembla Harbour.
Currents, Winds and Waves
Climate, wind and oceanographic
data for the area are available from AWT (1992a) and Patterson, Britton &
Partners, CEE & AWT (1998). These studies indicate:
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currents generally flowed to the
south, but northerly flow was experienced 10-20% of the time.
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currents towards the south tended to
be stronger in the summer months (February to March).
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about half the time there appeared to
be significant water movement suggested to be due to coastally trapped
waves. Current speeds associated with these waves was about 0.2 to 0.3 m/s
to north or south with a variable period (typically 3-10 days).
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there were no clear patterns between
the winds and water movement.
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wind directions in the nearshore
environment were significantly affected by the locally complex land
topography.
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in nearshore studies, the east
Australian current was rarely observed (less than 10% of the time).
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from the August 1991experiment, there
was clear evidence of secondary circulation cells in the lee of the
islands (Five Islands) near Port Kembla. These cells reached a diameter of
4km and produced current speeds of approximately 0.1m/s. these cells
appeared to be transient, but have the potential to move effluent towards
the shore.
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the islands offshore of Port Kembla
created a major restriction to the dominant southerly flow, diverting the
flow offshore. This resulted
in onshore currents in this region and a net northerly current in the
channel between Red Point (the site of the outfall) and Rocky Island.
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Recent studies by Lawson and
Treloar (1998 cited by Patterson Britton & Partners, CEE & AWT
1998) at the proposed deep water outfall site off Coniston Beach indicate:
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a net current to the south of 4 cm/s.
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southerly currents occurred much more
frequently than northerly currents, which in turn occurred more frequently
than offshore/onshore currents.
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currents measured over a one month
period revealed that they were generally weak, with longshore currents
averaging 4cm/s and onshore/offshore currents averaging 2cm/s.
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