NORTHERN BEACHES FIELD TRIP
YR 10 GEOGRAPHY/ RAP ASSIGNMENT:
21 MARCH 2013ADDITIONAL NOTES AND INFO
1.WIND AND WATER ARE CONTINUALLY TRYING TO EQUALISE
THEMSELVES- This creates the movement of tides, waves and cycle of
accretion ( see below ) and high and low pressure systems in our weather.
The movement of air from high to low pressure systems is the process which
creates wind.
2.ONSHORE WIND- wind blows on shore
3.OFFSHORE WIND-wind blows off the beach
4.LONGSHORE WIND- wind blows in the direction/follows the path of the
shoreline. Therefore, the name, longshore drift. Objects and seaweed may
accumulate at one end of the beach as it is forced/tunneled down there by
longshore wind, creating what can be seen to be longshore drift.
5. RIPS- occurs when there is a build up of water ( swash and backwash
collide + the addition of storm water from drains as the case at Collaroy ). The
water is constantly trying to equalize itself. As the collided water tries to
equalize itself, it flows to the path of least resistance. All the water rushes to
this point as it tries to equalize, causing the dangerous rips. Rips are seen by
an area with no waves breaking or white foam as it is an area of deeper water
from water rushing into the area.
6.ACCRETION CYCLE- describes the construction/destruction cycle of waves
adding to the beach and then taken in away. This is a natural cycle and is
ongoing.
7.COASTAL DEVELOPMENT ON COLLAROY BEACH:

BEACHFRONT- is the area from the waters edge to the escarpment. It
therefore includes, beach, beachfront homes, Pittwater Road, shops,
homes, flats.

Stormwater drains / pipes: collect water from entire area and direct out
to sea from 9 stormwater pipes that feed into the beach waters at
Collaroy. Only 1/10 left.

SEAWALLS / BEACHFRONT HOMES / 14 STOEY FLIGHT DECK
APARTMENT TOWER: can be seen at the foreshore right at the front
of buildings that have been built on the shore line. These have some
spinifex and very low vegetation currently growing on them. These
buildings were built here during a period of NO building controls on
beachfront areas in the mid 1900’s.
These homes, especially the cute wide weatherboard house ( see pic
in worksheet of 1967 storms ) and the 14 storey building ( flight deck )
have had several periods of their foundations eroded over time. Eg
During the 1967 storm/flooding and the 1974 king storms where the
beach waters crossed the main road Pittwater Road.
Massive rubble, boulders and even car bodies were placed under and
at the base of these homes to prevent against further destructive wave
damage during these storm events. The sand that was dumped there
stayed after the storms left to cover the masses underneath and
vegetation has grown . This forms the sea wall as we see it now, but
another massive king storm will erode the sea wall as it is and expose
the foundations if these buildings again !!
This process is completely the result of NO planning or management.

GRASSED AREA ON BEACH FRONT: This occurred after the 1920
storm. The weatherboard homes that were in that area were
destroyed. The Warringah Council bought the homes/land and
restored the area to a “ green space “. Therefore it eliminated the risk
on the occurring again to these homes…. Later years they didn’t do
these. WHY ???

EXISTING SEA WALL : needs continual sand “ top up “ to maintain it
as a “ barrier “. Local opposed a 2002 1 km sea wall proposal with the
“ line in the sand “ campaign. WHY ? costly, ugly, a short term
solution as wouldn’t stop the natural effect of wave action, especially
since the man made sea wall would change the natural system.

DEE WHY BEACH SAND PROFILE: As move further away from
waters edge, sand gets darker in colour and smaller in size. This is
because :
 Water acts as a “ cleaning “ agent.
 Some very small shell in sand sample closest to water
edge
 Finer particles furthers away as these are lightest and
wind carry them further
 Darker colour shows, nutrients, decomposed tree matter
and leaf litter that has fallen to base of tree and
leeched/decomposed into the soil at the base of the tree.