RFI - Attachment 4 - Engineering Response Package · MCU22/0171

DME Projects Pty Ltd
P.O. Box 7481
Sippy Downs, QLD, 4556
Tel 0438 157 612
ABN 79 224 274 637

                                        Response to Information Request – 128 Gympie Tce Noosaville
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        Issue – Variation in Flood Gate between Plans
        The location of the proposed flood gate is shown along the west boundary in DME Projects’
        Stormwater Details (220508-05), while it is shown at the peak of the downward slope of the
        driveway in Sparks Architects’ Driveway (DD 1.4).

        Information Required
        9. Clarify the proposed location of the proposed flood gate.
        10. Provide comment discussing why the proposed location is the most suitable for the
        proposed flood gate. Noting that the proposed development must not adversely affect
        the existing drainage conditions of the subject site and neighbouring properties.

The amended engineering drawings show the flood gate in the location as per the Architectural
Plans. This is considered to be the most appropriate location as the flood gate installation will also
incorporate a separate strip drain to capture surface water runoff to function as the driveway
drainage system in ordinary rainfall events, discharging to the street. A very small catchment from
the easement driveway (8m2) reports to the drainage pit at the front of the subject site and is
discharged to the street. This is considered to be a cost-effective drainage outcome, minimising the
infrastructure required. There are no other external catchments impacted by the proposed works.

        Issue – Flooding
        The subject site is located in Council’s Flood Hazard overlay and is adjacent to the Noosa
        River and Canal. Council are concerned regarding the functionality of the proposed
        stormwater system and associated infrastructure during, up to and including, 1% AEP events
        and at the end of the development’s lifespan. Council predict that the yearly average rainfall
        will increase approximately 20% towards the end of the development’s life span (2100).

        Information Required
        11. Provide additional detail and comment demonstrating how the proposed stormwater
            system and associated infrastructure will function during, up to and including, 1% AEP
            events and when experiencing an average annual rainfall increase of 20% by the year
            2100. The additional detail and comment must be prepared by a suitably qualified
            person (RPEQ – Registered Professional Engineer of Queensland) and include, but not
            be limited to:
            a. the functionality of the proposed kerb outlet during a flood event in which the outlet
            is submerged

The engineering drawings now include additional details, specifically surface levels and pipe invert
levels for the proposed drainage system. These clearly show that there is sufficient hydraulic grade
for the system to function as intended in a design event (5%AEP Roofwater and surface water). The
kerb invert level at the outlet is approx. 1.25m AHD. Noosa Council infrastructure mapping shows
underground stormwater networks to the east and west of the subject site, discharging to
appreciable open channel in Mill St and canal system in close proximity to the development site.
These both discharge directly into the Noosa River. A brief drainage assessment concludes that a
difference in water surface level of >350mm is achieved between the lowest internal drainage