Change to Existing Approval - OPW11/0116.01

Impacts on Shoals

No change expected.


Erosion of Mangroves


While the rock wall is expected to successfully prevent further erosion along its length, natural erosion of the adjacent
mangroves has been substantial to date and while the proposed works may help to stabilise a more shorward alignment of
mangroves in the longer term, ongoing erosion remains expected in the short term regardless of the change to rock and
should not automatically be considered to be a result of the construction of the works without further investigation. As
erosion occurs, a step in the shoreline will develop and works may need to be extended or modified in response to
monitoring. Extension of the works in response to ongoing erosion or modification of the structure will likely be simpler, more
responsive to actual conditions and lower impact with a rock profile than would have been the case with mega-containers.

Flooding

No change expected.


Flushing

No change expected.


Swimmer safety near submerged closure


No change expected.


Navigation

Toe depth is adequate to maintain existing channel depths so that access and navigational safety is not compromised.
Tolerances are such that as-constructed levels will not be higher than -2.7m AHD. As the channel deepens adjacent to the
wall, undermining will result in reforming of the flexible toe and a corresponding lowering of the levels of the toe.

Vandalism I Vessel impact with the structure


Rock is not vulnerable to damage from vandalism or vessel impact.


Structural aspects


Design of the rock wall profile has been undertaken to ensure that the protection provided is equivalent to the level of
protection and impacts provided by the approved mega container profile, including:
     .    Rock sizes to withstand expected 100yr ARI wave and current conditions (2.5m/s current and 0.75m waves).
     .    Flexible toe can withstand deepening of the channel to -6m AHD (with further rock top-up possible if required).
     .    Depth of rock at the crest can withstand some loss of backfill as a result of overtopping during high tides I flood
          events (with further backfill or rock top-up post-flood possible if required).


Visual Impact


As the crest remains level with adjacent top of bank, the visual impact is expected to be minimimsed. The dark colour of the
rock is expected to stand out less than the sandy coloured mega-containers.


Acid Sulphates


The depth of the toe for the rock profile has been limited to a depth of -4.5m AHD with required tolerances giving an absolute
maximum dredge depth of -4.7m AHD. This eliminates the expected disturbance of material which is potentially contains
ASS I PASS along this section of the structure since soil testing only revealed PASS material below -4.75m AHD. There is
also a substantial reduction in the overall volume of disturbance required [Figure 8].