Click the photograph for a enlarged view
|
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.
|
