BELLAMBI OUTFALL

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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. The beaches in the vicinity of Bellambi Point consist of Quaternary sand dunes (Wollongong Geological Series Sheet SI 56-9) which are aeolian (wind formed) north-south oriented dunes 5-15m high. Soils consist of deep calcareous sand on the beaches, siliceous sands on the foredunes and isolated podzols in the swales (Patterson Britton & Partners, CEE & AWT 1998). The

Bathymetry & Substrate

Bellambi Point outfall is on a shallow rocky reef region formed from Hawkesbury sandstone. The once high foredunes fronting onto the reef have been drastically lowered by sand mining and are now approximately 0.5m above sea level in places. The outfall is located approximately 150m offshore in 5m water depth (Water Board 1991a). The seabed around the existing Bellambi outfall is predominantly rock, except for a nearshore strip of sand just to the north and south of the point. To the north of the outfall are Bellambi Harbour and Bellambi Beach. To the south of the outfall are Bellambi Reef, Sandspit Point and Corrimal Beach.

Currents, Winds and Waves

Studies by AWT (1992a), Patterson, Britton & Partners and CEE & AWT (1998) indicate:-

- currents generally flow to the south, but northerly flow is experienced 10-20% of the time.

- currents towards the south tended to be stronger in the summer months (February to March).

- 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).

- there were no clear patterns between the winds and water movement.

- wind directions in the nearshore environment were significantly affected by the locally complex land topography.

- in nearshore studies, the east Australian current was rarely observed (less than 10% of the time).

- there was some evidence of secondary circulation cells in the lee of the Bellambi Reef, however, the current records from this region were highly variable and it was not possible to adequately quantify the intensity and duration of these features (AWT 1992a).

Studies by Lawson and Treloar (1998 cited by Patterson Britton & Partners, CEE & AWT 1998) indicate:-

- a net current to the south of 1cm/s at the proposed deep water outfall site off Coniston Beach (1km offshore, 20m water depth, current meter deployed at 8m below surface).

- southerly currents occurred much more frequently than northerly currents, which in turn occurred more frequently than offshore/onshore currents.

- measurements over a one month period revealed that currents were weak, with longshore currents averaging 4cm/s and onshore/offshore currents averaging 2cm/s.

Outfall Site

Outfall Site

Bellambi

(Bell_5) Last updated June 2000