Click the photograph for a enlarged view
|
Physical Environment
Landscape
Wonga Point consists
of the Clifton Sub-group of Narrabeen claystone, sandstone and shale (Sydney
Geological Series Sheet S1 56-5). To the north of the outfall is Blue Lagoon
and Shelley Beach. To the south of the outfall is Bateau Bay and then rocky
cliffs until Crackneck Point.
Bathymetry &
Substrate
The
water off Wonga Point is shallow (5-10m) and the area of rocky bottom is
small, although it dominates the sea bed in the vicinity of the outfall (Laxton
& Laxton 1978). The reef area is widest off the center of Wonga Point and
breaks up into a series of ridges to the north and south before giving way to
sand (Laxton & Laxton 1980).
Currents, Winds and Waves
MHL (MHL249
1978) studies indicate:-
-
nearshore
current systems are set up in the vicinity of Wonga Point in response to
north or south offshore current systems.
-
A large
proportion of the effluent discharged from Wonga Point moves parallel to
the coastline within the offshore current system and not directly onto
beaches in the area.
-
An
anti-clockwise eddy system is established in Bateau Bay under either a
north or south offshore current.
-
If effluent
is ‘blocked’ against the shoreline by waves, wind and currents, it
will move into Bateau Bay between the perimeter of the eddy and the
shoreline, irrespective of the offshore current direction. This mode of
effluent movement occurs frequently.
-
Effluent
sometimes moves with nearshore waters into Shelley Beach, but this is
relatively rare.
- When ocean water levels reach 1.3m above tide
datum (70%-80% of all high tides), effluent is pushed up onto the Wonga
Point rock platform and moves south-west into Bateau Bay and north-west
into Shelley Beach. Most of this effluent moves into Bateau Bay.
|
