Coast & Estuaries
Page 230
There is currently major sand accumulation at Largs Bay, while sand has been
depleted at Semaphore Park. Sand is carted from Semaphore to maintain this
beach and protect coastal properties.
The manual sand management to date has been carried out by the Coast
Protection Board and councils, and has involved beach replenishment by
carting sand from the northern to southern beaches, sand trapping and sand
bypassing at Patawalonga, West Beach, and Torrens River outlet.
The Department for Environment and Heritage have released ‘Adelaide’s Living
Beaches, A Strategy for 2005 – 2025’. The current system of sand
management has been reviewed, and the new plan recommended building a
series of pipelines to pump sand slurry from north to south. This sand will also
be supplemented by sand from external sources, most likely from Mount
Compass.
The cost implication of this action is being reviewed by the State Government.
Investigations also continue into coastal structures that will capture sand at a
few critical locations. An example is the breakwater or 'groyne' installed at
Semaphore South, constructed to trap sand which can also be used for beach
replenishment.
Sand Dunes
The Semaphore dunes have developed over the last 30 years. The pre-
European settlement dunes no longer exist due to housing development
fronting the esplanade.
There were no dunes at Semaphore in the 1970s but by 2001 the dune width at
the Semaphore jetty was approximately 100m. This occurred due to the
accumulation of sand on the beach as a result of changes in wave propagation
influencing the movement and deposition of sand, and further exacerbated by
the loss in offshore seagrasses (Townsend, 2005).
Accumulation of sand remains significant despite at least 700,000 cubic meters
of sand having been removed to replenish southern beaches.
As a result of the young age of the dunes, colonising vegetation is also recent.
The dunes are dominated by introduced species such as
Trachyandra
divaricata
(Dune Onion Weed) and
Euphorbia paralias
(sea spurge).
Off shore impact of Port Adelaide River Dredging
As part of the Flinders Ports development at Outer Harbour, dredging of the
Port Adelaide River was completed on the 14
th
February 2010, resulting in the
deepening of the channel by 2 metres (total depth 14.2 metres) and lengthening
the channel to approximately 3 km to accommodate large Panamax ships.
Land based disposal was not undertaken - the dredged soil was deposited off
shore in the Gulf St Vincent. It was suggested that this activity may threaten off-
