UPDATED DA - Attachment 7 - Flood Impact Assessment

     3.3    Temporal Patterns and Rainfall Intensity

     Temporal patterns are based on Australian Rainfall and Runoff (ARR) 2019 Ensemble Storm Temporal Patterns and
     have been sourced directly from ARR data hub. Rainfall intensities are typical for this area and have been sourced
     directly from the Bureau of Meteorology (BOM).

     3.4    Rainfall Durations

     Initially, flood modelling was undertaken for all rainfall durations ranging from 10 minutes to 360 minutes. This range
     of durations was simulated to ensure the critical durations for the catchment were captured. From reviewing the
     results, it was determined that the critical durations experienced at the proposed development site and immediately
     surrounding the site ranged from 20 minutes up to 120 minutes and therefore these were the durations adopted for
     this analysis.

     3.5    Rainfall Losses

     Adopted rainfall losses were sourced from ARR Data Hub. Rainfall losses for this region are as follows:
     •       Initial Losses – 27 mm; and
     •       Continuing Losses – 2.6 mm/hr.


     3.6    Pre-Burst Rainfall

     Rainfall losses adopted for the model are for complete storms. As such, pre-burst depths have been subtracted from
     the adopted initial losses to get the correct storm burst initial losses.
     From a review of the median and 75% pre-burst depths, it was concluded that the median pre-burst depths were not
     appropriate for this investigation, particularly given that the outcome of this investigation will determine minimum
     floor levels for residential properties. As such, adopting the 75% pre burst depths was considered more appropriate
     for this investigation.

     3.7    Areal Reduction Factor

     ARR 2019 guidelines recommend adopting Areal Reduction Factors (ARFs) for catchments greater than 1 km2. Given
     that the associated catchment area modelled as part of this simulation is approximately 2.87 km2, ARFs were adopted
     for this analysis. Refer to Table 3-1 for adopted ARFs.

                                                 Table 3-1 – Areal Reduction Factors

                                            Dur                    AEP (%)
                                           (min)         50          10                1
                                            20         0.975        0.973         0.970
                                            25         0.978        0.976         0.973
                                            30         0.980        0.978         0.974
                                            45         0.984        0.981         0.978
                                            60         0.986        0.983         0.979
                                            90         0.989        0.986         0.981
                                           120         0.991        0.987         0.981




Noosa Shire Council                                                                                    4
M25-0045Rpt – 244035– February 2025