6.5.22 - Further advice response 6 may

    C. Update the fill level for the building envelope of proposed Lot 8 to the PMF
       Level.

Lot 8 to include a 1,100m2 fill envelope (adjacent to the existing house) above the PMF.
The Flood Investigation modelling has been remodelled to accommodate the changes in
the subdivision design and all lot envelopes are above the PMF, while also having no
impact to adjoining properties.


    D. Provide a Risk Assessment Report that demonstrates compliance with PO7
       and AO7.1 to AO7.3 of the Flood Hazard Overlay Code and addresses
       management of risks to occupants of the site having regard to Mckinnon
       Drive being not trafficable during a PMF event.
    E. Amend Table 4-5 of the Flood Investigation – 60 Glenridge Dve, Cooroibah
       Version 4 prepared by PeakUrban dated 01/04/2022 to address the
       following:
          i.  The minimum fill level for proposed Lot 8 is to be amended to the
              PMF level. All works are to be carried out generally in accordance
              with the updated flood investigation report.
         ii.  The updated flood investigation report is to be submitted to Council
              for approval prior to the issue of Development Permit.

Brendon Bolt from Peak Urban Consulting Hydraulic Engineers provides an updated
section in the Flood Investigation Report (4.3.2.8) discussing the Flood Risk from the site.
The relevant section of the report is included below (highlight’s emphasis) as well as the
GCCC Flood Refuge Guideline:
       4.3.2.8.Flood Risk
       This development has been designed to provide flood free access to all lots via the new internal road
       in events up to the 10% AEP and will remain trafficable in events up to the 1% AEP event in
       accordance with the Queensland Urban Drainage Manual (QUDM). Further consideration of flood
       risk has been undertaken in events greater than the 1% AEP event, with assessment of the PMF
       event taking place. The assessment found that the lots within the development would become
       isolated in extreme events such as the PMF, with the internal access road having flow conditions that
       would not be trafficable.
       An assessment was completed as to the length of time the internal access would be considered not
       trafficable (flow depths> 0.2m) along the warning time between the start of the rain event to when
       the internal crossing becomes not trafficable. The assessment was completed for the PMF event for
       a number of durations and is highlighted below. From this, it is considered that a site flood warning
       system would not be appropriate in this situation due to the short response times for flood waters to
       rise. It would be safer outcome for residents to seek refuge within their houses and communication
       about a extreme weather system come from Council or State Disaster Management Services.
       This assessment highlights that there would be a limited amount of time to warn / evacuate residents
       due to the relatively short amount of time it takes for the internal road to become inundated in an
       extreme (i.e PMF) event. This would be typical of all catchments where the upstream catchment is
       relatively small. From this, the time of submergence is also relatively small with times ranging from
       2.0 to 8.0 hours depending on the event duration. From this, it is considered that the provision of
       suitable flood refuge or evacuation to higher ground (i.e.to Glenridge Drive) would be the preferred
       risk management measure as opposed to evacuating the area to a formal evacuation centre. Each
       lot is provided with an1,100m2 building envelope above the PMF level that would be suitable to act
       as a flood refuge until flood waters recede. The application of a flood refuge is recommended in
       similar circumstances as means to address flood risk and potential burden by Gold Coast City Council
       (GCCC), who have large amount of flood plain on which developments are managed. The Guideline
       developed by GCCC is presented in Appendix J, and in summary states “a shelter-in-place
       approach” provides an opportunity to address the risks of isolation and subsequent risk to life and
       potential burden to emergency services and has been commonly used in development assessment
       for larger developments”. Further to this, that subsequent that Council Disaster Management Plan
       includes communications to these future residents that their building envelopes serve as a flood
       refuge should anevent greater than the 1% AEP event occur. This information could also be
       conveyed via property note.




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