Response to Information Request 20220004 -Tunba Court

            The proposed concrete spoon drain channels at the top of batters will convey stormwater
            run-off from the upstream catchments and from the earthworks pad to the drainage gully
            to the north of the development area which maintains consistency with the flow paths of
            the pre-development site so that impacts to downstream environments and neighbouring
            properties are minimised.

            A rock energy dissipator has been sized in accordance with QUDM Section 8.7.2 to
            ensure that the outlet of the drainage system is sufficiently protected such that the risks of
            erosion or scour in the receiving waters are mitigated.

            An erosion and sediment control plan has been prepared by Aussie Environmental to
            manage the water quality of receiving waters during construction. Construction is to be
            carried out in accordance with this plan to reduce impacts of the construction phase.

            At the post construction phase, any disturbed or exposed areas of the development are to
            be stabilised using grass seeding as soon as practicable to prevent sediment being lost
            from the development site and stabilise the earthworks surface.

                    PO2
                    Stormwater drainage infrastructure is planned, designed and constructed to:

                       1. incorporate allowance for increased flood risk and tidal inundation through
                          pipework as a result of cilmate change and sea level rise;
                       2. ensure the development is adequately drained; and
                       3. ensure stormwater is managed and lawfully discharged without altering
                          stormwater drainage characteristics external to the site.

            The concrete spoon drains proposed as the drainage infrastructure for the development,
            will provide the batter slope protection required by the geotechnical slope stability
            assessment to ensure water does not infiltrate into the batters. The spoon drains have
            been sized based on the 1% AEP storm event, allowing a climate change increase of 20%
            to the BoM IFD rainfall intensities for the site with the details of these calculations
            attached. An assumed 20% impervious area has been taken into account in sizing the
            lower earthworks pad to allow for any future development of this area

            Finished surfaces are to be graded locally towards the drainage lines so that run-off from
            the development will be collected in the drainage infrastructure. Minimum slopes of 1%
            are proposed for the drains to ensure the site will be free draining, and also achieving the
            required capacity for the major storm event.

            The proposed point of discharge within the subject site is through a rock energy
            dissipator falling towards of an existing drainage gully. The drainage gully is the eventual
            point of capture of pre-development flows, so discharging to this location is considered to
            maintain the existing flow paths from the site. The energy dissipator is located
            approximately 30m from the adjacent property boundary and has been sized to prevent
            erosion or scour of the gully and disperse concentrated flows so that when run-off crosses
            the property boundary it will be sufficiently similar to pre-existing conditions that any
            impacts to drainage characteristics external to the site are expected to be minimal.




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