updated flood investigation

      estimated upstream of the proposed Internal Road extension in the 1% (2100) AEP, however,
      this is contained within the site boundary.

      4.3.2.3. Flood Storage

      A flood storage assessment has been completed over the site to ensure there is no loss of
      flood plain storage as a result of the development. For the existing flood storage calculation,
      the existing peak 1% (2100) AEP flood surface was compared to the existing model terrain.
      Similarly with the proposed flood storage calculation, the proposed peak 1% (2100) AEP flood
      surface was compared to the proposed model terrain. Details of the flood plain storage in
      the existing and proposed cases is summarised below in Table 4-4, where it is shown there is
      an increase in the amount of flood storage as a result of the development, which is
      considered positive outcome.

      Table 4-4: 1% (2100) AEP Flood Storage Comparison.

        Scenario                              Flood Plain Storage (m3)
        Existing                                                             36,831
        Proposed                                                             45,932
        Difference                                                           +9,102

      4.3.2.4. Internal Road

      The Internal Road extension has been designed achieve flood immunity in the 10% AEP
      event, whilst allowing some overtopping in the 1% AEP (major event). The high point of the
      road (which acts as a weir) is at a minimum 12.81m AHD (refer Figure 4-1). This results in a
      flow depth of less 0.2m occurring over the road pavement in the 1% AEP, with flow velocities
      less than 1.6 m/s and flow hazard less than 0.3m2/s. These parameters are below the
      trafficability requirements of QUDM, which require a maximum depth of 0.2m and hazard less
      than 0.3m2/s in the 1% AEP event.

      The new culverts have a flow velocity of 3.9m/s. Outlet scour protection will be required to
      be provided with D50=500mm rock provided and extend 3.0m past apron.


                                                                                      Flow depth < 0.2m
                   1% AEP WSL




                                                                     Internal Road




      Figure 4-1: Section Across Internal Road Extension




21-0288-FS001-V1 | Flood Investigation | 60 Glenridge Drive, Cooroibah                                    | 10