MCU21.0117 OPW21.0199-Att 5 Stormwater · MCU21/0117

            5. CONCLUSION
            This Stormwater Management Report has outlined how the stormwater run-off from the site
            is to be managed to comply with the relevant requirements and minimise any adverse
            impacts to the downstream catchments.

                    •   The existing site and upstream catchments’ drainage patterns currently discharge
                        from the site as overland (potentially nuisance) flows into adjacent properties to the
                        north and east of the proposed development site.

                    •   The proposed 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 existing capacity of the Pearl Street drainage system has been
                        analysed to determine an allowable discharge from the development to the legal
                        point of 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 conditions to determine an appropriate discharge rate from the site that
                        will serve to minimise the impacts to the upstream or downstream network and
                        adjacent properties. It was found that with a maximum pump out rate of 64L/s from
                        the site, both the proposed internal stormwater network and the street drainage
                        system can suitably convey storms up to the 1% AEP.

                    •   During construction, erosion and sediment control measures will be implemented
                        to minimise potential contaminants 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 x 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 toward 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 stormwater system will convey run-off to a
                        manhole chamber providing further attenuation storage prior to pump-out from the
                        site. Water pumps, to be specified by a hydraulic engineer, will be used to pump


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