updated flood investigation

              Results - Existing Scenario (E01)
      The TUFLOW hydraulic model been assessed for a range of flood events including the 63.2%,
      39%, 10% and 1% AEP storm events. The assessment has considered a range of storm
      durations to ensure that the critical storm is defined. The results of the hydraulic assessment
      are presented as a series of flood maps to illustrate the flooding characteristics of the
      overland flow path and the resulting flood behaviours including flooded depth, height,
      velocities, hazard and afflux.
      The flood maps are presented in Appendix D and Appendix G.

      4.3.1. Existing Scenario

      The existing scenario flood maps are shown in Appendix D. This details the existing flood
      extent and behaviour in relation to the development site. The results of this have been used
      as the basis for assessing the potential impacts that may result from the development.

      4.3.2. Proposed Scenario

      The proposed scenario flood maps are shown in Appendix E. This details the proposed flood
      extent and behaviour in relation to the development site. An indicative lot plan is overlaid on
      this map set to highlight how the development relates to the flood plain.

      It is noted that the building envelopes of Lot 1 and 4 have been filled to achieve flood
      immunity requirements, will some minor shaping of the land beside the Lot 1 building
      envelope to manage afflux cause by flooding backing up behind the building envelope.

      4.3.2.1. Peak Discharge

      The assessment found the peak discharge at the site boundary are predicted to decrease
      across all modelled events. This is shown in Table 4-3 which compares the Existing and
      Proposed peak discharge at the site boundary for each event. As such it is considered that
      a formal detention is not required to service this development as the design has achieved
      the required non-worsening outcome.
      Table 4-3: Existing and Proposed Peak discharge at the Site Boundary.

        Design            Critical Duration       Existing Peak          Proposed Peak      Difference (m3/s)
        Event (AEP)       (min) / Temporal        Discharge (m3/s)       Discharge (m3/s)
                          Pattern
        1% (2100)              120 (TP3)                  48.36               48.19               -0.18
        1%                     120 (TP6)                  36.85               35.78               -1.07
        10%                    180 (TP8)                  20.94               20.20               -0.74
        39%                    540 (TP5)                  9.23                 9.17               -0.07
        63.2%                  540 (TP5)                  6.19                 6.16               -0.02



      4.3.2.2. Afflux

      Afflux mapping has been undertaken for the 63.2%, 39%, 10% and 1% AEP to identify whether
      there are any impacts resulting, and if so, whether an alternative development arrangement
      needs to be investigated. Afflux maps have been provided in Appendix F.
      The afflux mapping shows that there are no external impacts resulting to any adjoining
      properties as a result of the development. An increase in flood levels of up to 330mm is




21-0288-FS001-V1 | Flood Investigation | 60 Glenridge Drive, Cooroibah                                          |9