Proposed works

The proposed works would comprise:

– Approximately 200 x 0.75m3 geobags arranged in a step profile five units high and typically two units wide.
– A slope of approximately 1V:1.5H.
– An overall approximate (buried) height of 2.1 metres.
– An encapsulated self healing toe comprising an additional geobag incorporated in the bottom layer on the seaward side and tied back to the double layer structure.
– A westward return at the northern limit of the extension to mitigate the out-flanking risk.

There are already approximately 300 x 0.75m3 geobags that are filled and stockpiled near the northern limit of the extension (far more than is required for this task). These geobags were filled with sand from the commercial sand extraction operation at Chinderah. No sand was used from the beach or dune system.

The placement of the geobags would be supervised by a suitably experienced Coastal Engineer. Particular care would be taken in the installation of the ‘encapsulated self-healing toe’ to ensure the geotextile encapsulation of the third geobag in the bottom layer is suitably tied to the double-layer main section of the works.

Where the works are located seaward of the existing erosion escarpment, the area between the crest of the works and the escarpment will be back filled and battered back at a stable slope. The two geobags at the crest will be left exposed to facilitate along shore pedestrian access unless the crest level is below the existing beach berm level at the time of construction. Where the works are located wholly with the dunal system they will be completely back filled.

Excavation of the beach berm and dune would be required to install the geobags to the proposed level and alignment. The estimated total quantity of excavation is 1,200m3. All excavated material would be temporarily stockpiled and reused in the restoration/reshaping of the beach and dune profile. No excavated sand would be removed from the beach and dune system.

The aim of the excavation would be to place the geobags as low as possible in the sand profile while avoiding or minimising the need for excavation below the water table, which would otherwise affect buildability and the quality of construction. In the event it became necessary to remove any groundwater or wave washover from the excavation, this would be pumped to a nearby depression (sump) created in the beach berm to allow natural infiltration. The groundwater would not be pumped directly to the estuary or to the sea.

Approximately 800m3 of sand would be imported from the commercial sand extraction operation at Chinderah to assist in re-establishment of the dune profile. This would address the volume of sand ‘locked up’ behind the extension to the geobag coastal protection works.

Fencing would be incorporated around the construction works on the landward side to prohibit unauthorised access. Star pickets with bunting/flagging or the like would be utilised on the beach to manage access, coupled with observers employed by the Contractor.

Erosion and sediment controls would be installed in accordance the ‘Blue Book’ (Landcom, 2006), as required, to manage the potential effects of land disturbance activities on the Belongil Estuary.

At the completion of works, vegetation of the dune areas will be undertaken using suitable species.