Att 4 - SWMP · MCU21/0117

            5. CONCLUSION

            This Stormwater Management Report has outlined how the stormwater run-off from the site
            is to be managed to minimise any adverse impacts to the downstream catchments.

            The existing site and upstream catchments’ drainage patterns currently discharge from the
            site as overland nuisance surface flows into adjacent properties to the north and east of the
            proposed development site. The legal point of discharge for the site will be to the
            stormwater drainage system on Pearl Street. As none of the existing catchments currently
            drain to the street, a pre-development to post-development comparison of site discharges
            is not suitable for the development. The network infrastructure has instead been modelled
            to demonstrate sufficient capacity exists withing the existing network to carry the
            developments discharge.

            The proposed development site, and the upstream and downstream catchments draining
            to the Pearl Street drainage system have been modelled under the 1% AEP storm event with
            a climate change increase factor of 20% being applied to represent the RCP8.5 scenario to
            2090. The modelling shows that with the combination of rainwater/attenuation tanks and
            bio-gardens, the proposed stormwater network within the site, the proposed drainage line
            in Pearl Street and the existing infrastructure (being the legal point of discharge for the
            development) are sufficiently sized to carry the 1% AEP design storm without exceeding the
            capacity of the existing network.

            During construction, erosion and sediment control measures including downstream
            sediment fencing of the property boundaries and of stockpile areas, a construction
            shakedown area at the entry/exit of the site and upstream diversion banks are to be
            implemented to minimise sediment and gross pollutants impacting the downstream
            receiving environment. These measures are to be inspected and maintained regularly
            during construction.

            In the operational phase of the development, a stormwater treatment train will provide
            quality improvements as required by the Noosa Council Planning Scheme Policy. Roof run-
            off is to be directed towards 4 5,000L rainwater reuse and attenuation tanks that will be
            fitted with first-flush divertors to will divert initial roof run-off to on site irrigation of vegetated
            areas. The tanks are to be plumbed for reuse for internal (laundry and toilets) and external
            (irrigation) purposes that will serve to provide both treatment and reduce the volume of run-
            off entering the drainage network. Overflows from the tanks, as well as overland flows from
            the ground areas are to be directed towards the site’s stormwater treatment devices. These
            are principally made up of two 12.5m2 bioretention areas that will treat the majority of run-
            off from the driveway areas while also attenuating run-off volumes. Ecosol litter baskets with
            200µm filter screens will also be provided to all pits within the development to ensure
            treatment for any run-off that bypasses or is unable to be captured by the bioretention areas.
            The development will connect into the existing stormwater infrastructure by providing a new
            drainage line within Pearl Street that will connect into the existing.

            The proposed stormwater treatment train has been modelled in MUSIC software in
            accordance with the Water By Design MUSIC Modelling Guidelines. By implementing the


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