After a few close calls with category 5 cyclones, a heavy duty
rock wall is being constructed for protection.
Machans Beach seawall is reaching the final stages of construction and the
causeway that was used by trucks to take rock out for placement on the wall is
now itself being pulled up and placed on the wall to create a much thicker
layer of rock armour. As the causeway is
about 2 km long, removing the causeway is a huge job.
 |
| Causeway is located on left and is separated from rock wall by about 5 m |
A pair of excavators are working together at the end of the causeway. One fishes up rocks from the end of the
causeway and places then on the side of the causeway between the
excavators. These rocks are then picked
up by the second excavator and placed on the seawall. Each stone is carefully placed and tamped
down to ensure that it is unlikely to move.
It is a strange thing as the stability of seawalls increases when the
amount of open space between the rocks increases, so tightly placing the stones
possibly weakens the wall. However
people will climb over the wall so tightly placing stone improves public
safety.
 |
| Excavators passing stones from end of cause then on to rock wall |
 |
| Tamping down a rock |
At the top of the wall is a broad lip that is out of reach
of the excavators removing the causeway and rock is placed on the lip directly
by a smaller excavator equipped with a rock grab that lifts rock directly from a
conveniently parked semi and places/drops the rocks onto the wall directly. A white sheet of geo-fabric prevents soil
from washing into the gaps between the rocks.
 |
| Lifting rock from a semi and placing it on the seawall |
The truck has to negotiate some tight spaces when delivering
rock to the esplanade but with a bit of toing and froing, it gets around the
corners.
 |
| A heavy responsibility, you can't damage the pub |
Gradually sections of finished seawall are emerging. There is also a hidden part of the seawall, the base of the causeway will remain in place to provide support to the toe of the seawall.
 |
| Finished seawall |
As the causeway was built over a small beach that ran along the base of the old seawall, the local sand supply to Holloways Beach may
have been interrupted. The southern part
of the beach fared quite well as it is can receive sand from Barr Creek and
from an off-shore sandbar that has migrated in but the northern part of
Holloways Beach is again in trouble.
Fortunately, it seems that the sand supply is recovering and the
coastline around the Barr Creek Mouth appears to have prograded by as much as
20 m. It is hard to tell what contribution the seawall has as the beach also progrades due to floods pushing sand out of the creek and prevailing winds moving sand along the beach but these events have temporary effect and sand erodes away again.
 |
| Where the people are is new beach |
No comments:
Post a Comment