NORAH HEAD OUTFALL

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Physical Environment

Landscape

Norah Head consists of the Clifton Sub-group of Narrabeen claystone, sandstone and shale (Sydney Geological Series Sheet S1 56-5). The seabed in the vicinity of the outfall is mainly rock inshore with patches of coarse sand and gravel (Laxton & Laxton 1983b). To the north of the outfall are Lighthouse Beach and Cabbage Tree Harbour. To the south of the outfall are rocky headlands, Pebbly (Gravelly) Beach, Soldiers Point and Soldiers Beach. Waters immediately surrounding the headland are of the order of 10m below ISLW (PWD 1980).

Bathymetry & Substrate

Currents, Winds and Waves

Limited climate, wind and oceanographic data for the area are available from MHL (MHL554 1988). PWD (1980) studies indicate:-

- The average current speed past Norah Head ranged from near calm to 0.4 m/s with a tendency towards lower values during the winter period sampled.

- Both southerly and northerly currents occurred.

- The southerly flow pattern was characterized by currents west of Bull Rock being diverted east by the land mass approximately 1.5km north of the headland, sweeping past Norah Head, generally with an increase in speed and rejoining the mainline currents originating from east of Bull Rock. In the area of Cabbage Tree Harbour currents were generally weak.

- South of the headland shear induced recirculation was sometimes present in the area of Pebbly (Gravelly) Beach and to a lesser extent in Soldiers Beach.

- The northerly flow pattern consisted of flow lines normally parallel to the southern coast only occasionally inducing recirculation near Soldiers Beach and then splitting past the headland and Bull Rock.

- On the western side of Bull Rock the current speed decreased.

- No evidence of strong recirculation eddy north of the headland was found, although small weak eddies were observed occasionally.

- In general, the region west of the headland and towards the beach was a low activity area, uninfluenced by northerly and north-westerly currents.

Outfall Site

Outfall Site

Norah Head

(Nora_5) Last updated June 2000