SDA-1116-034770 - Proposed nbn Facility at 23 Jirrima Cres Cooroibah - Response to Information Request

        •   The proposed culvert is to feature a larger, cell cross-sectional area compared to the existing
            culvert configuration. This will prevent increased water depth upstream of the barrier, which can
            result in loss of in-stream plants, leading to reduced food supply or loss of breeding habitat;
        •   The proposed culvert cell has been adopted to provide equal or better fish passage for the
            waterway;
        •   The waterway bed is to be retained with natural substrate comparable to the natural substrate
            size and consistency; and
        •   During and after construction, the works will be undertaken as per the requirements of
            WWBW01 Part 3 Section 5.1, including:
                o The waterway will be restored to its existing condition immediately on completion of the
                     works;
                o Impacts on water quality during construction will be minimised by undertaking works
                     set out in the Best Practice Erosion and Sediment Control guidelines 2008;
                o Construction works will not occur during times of elevated flows; and
                o Provision will be made to minimise the risk of fish killing during construction, such as
                     through entrapment of fish upstream of work site.

5. PO20 - Fish passage is provided for:
(1) in the inherent design of the waterway barrier works
(2) over the in-situ life of the barrier in that position through adequate construction and maintenance
of the barrier.

Please confirm through providing detailed plans that the culvert design will comply with the design
provisions of the self-assessable code WWBW01- Part 3 Culvert Crossings for Amber waterways.

If the plans are not in line with the self-assessable code, please provide detail on the following, in
relation to the culvert crossing:
     - The expected drown out characteristics of the culvert crossing and the ability for fish to
         cross the barrier under all flow conditions – i.e. water velocities will not exceed 0.3ms
         through the low flow channel
     - The expected timing and duration of drown out events and the delay expected to fish
         passage when there are flows in the system but no fish passage being provided.

As shown on the detailed plans, the culvert design complies with the design provisions of the self-assessable
code WWBW01- Part 3 Culvert Crossings for Amber waterway, whereby fish passage is provided by the
following culvert design features:

        •   The culvert will be installed at approximately 550mm below the bed level;
        •   The culvert will be backfilled with bed material won from the site to maintain and simulate natural
            bed surface;
        •   The culvert will be installed at a minimum of 1200mm wide to allow for fish passage; and
        •   The culvert will be installed at no steeper gradient than the waterway bed gradient to limit
            velocity increases through the culvert.

6. PO23 - Waterway barriers that are culverts provide adequate fish passage for the site, and:
(1) fish passage is provided for the life of the crossing
(2) hydraulic conditions (depth, velocities and turbulence) from the downstream to the upstream
limit of the structure allow for fish passage of all fish attempting to move through the crossing at all
flows up to the drownout of the structure.




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