RFI - updated flood investigation report

      Response: Whilst it is not a design requirement for the 100% blocked scenario to achieve
      QUDM design requirements, a comparison against the QUDM road drainage criteria has
      been made for some context. In the 100% blocked scenario, the depth of flow exceeds the
      0.2m QUDM depth criteria in the upstream lane (with depths up to 0.25m noted), however, is
      less than 0.2m on the downstream lane. Flow velocity is up to 1.75m/s. Approximately 80m
      of the road has a hazard greater than the 0.3m2/s QUDM hazard criteria (with hazard up to
      0.5m2/s noted).

      Information Request:
      23.    Include additional comments regarding the probable maximum flood (PMF) and the
      impacts on the safety of residents (within the site and on adjoining properties) and road
      users.

      Response: An assessment of the PMF event found that flood levels in the PMF event are
      approximately 0.5m higher that the 1% (2100) AEP flood levels. It is recommended that floor
      levels be constructed to a minimum PMF level so as to provide a refuge for residents in this
      event. It also noted that the cul-de-sac end of the internal road is also above the PMF level
      and could act as a refuge.

      Information Request:
      24.    Provide additional comment in regard to the recommended minimum floor levels
      and the potential impacts of the PMF.

      Response: The Planning Scheme requires a minimum floor level of dwellings to be 0.3m
      above the 1% (2100) AEP event. An assessment of the PMF event found that flood levels in
      the PMF event are approximately 0.4m to 1.0m higher that the 1% (2100) AEP flood levels.
      The recommended minimum building envelope / finished floor level (FFL) for each lot has
      been taken as the greater of the DFE + freeboard (0.3m) or the PMF, as summarised in Table
      4-5, so as to provide a refuge for residents in this event.

      Information Request:
      25.   Provide additional detail to demonstrate that the development (access and all lots)
      achieves compliance with The Flood Hazard Overlay Code – Performance Outcome PO4.

      Response: The Planning Scheme requires a minimum floor level of dwellings to be 0.3m
      above the 1% (2100) AEP event. An assessment of the PMF event found that flood levels in
      the PMF event are approximately 0.4m to 1.0m higher that the 1% (2100) AEP flood levels.
      The recommended minimum building envelope / finished floor level (FFL) for each lot has
      been taken as the greater of the DFE + freeboard (0.3m) or the PMF, as summarised in Table
      4-5, so as to provide a refuge for residents in this event. Lot 8 has flood free access to
      Glenridge Road, which is located above the PMF level. If a PMF event were to occur, they
      would be able to safely seek refuge on Glenridge Road.




21-0288-FS001-V3 | Flood Investigation | 60 Glenridge Drive, Cooroibah                                |5