Approved Plans - RAL21/0033

               Response to Information Request
      An Information Request was received on 21 January, 2022 as part of Reconfiguration of Lot
      Application No: RAL21/0033. Items 22 to 25 relate to Flooding, with response to each item
      detailed below:
      Issue: Flooding
      The Flood investigation:
          i.    includes comments regarding the impacts of “blockage of stormwater culverts” but
                does not indicate the impacts (depth, velocity) of “blockage” on the proposed new
                road, and
         ii.    does not include any comment regarding the probable maximum flood (PMF)
        iii.    does not include sufficient detail to demonstrate that the development (access and
                all lots) achieve compliance with The Flood Hazard Overlay Code – Performance
                Outcome PO4
        iv.     the investigation recommends that the floor levels be a minimum of 500mm above
                the flood level while the planning scheme requires 300mm.
      Information Request:
      22.     Provide additional detail on the impacts (depth, velocity, safety) of 100% blockage of
      the stormwater culverts on the proposed new road

      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:




21-0288-FS001-V5 | Flood Investigation | 60 Glenridge Drive, Cooroibah                                 |4