Reference Document - Flood & Stormwater Management Plan 28_8_2025

                 Table 2-1: Summary of Existing Catchment Parameters

                    Sub-catchment              Downstream               Area (ha)                  Imperviousness (%)
                                                Catchment
                            Ex2                     SUB3                  1.960                           50
                            Ex1                     SUB1                  0.287                           50
                           SUB3                     SUB4                  2.085                           21
                           SUB1                     SUB2                  2.079                           11
                           SUB2                     SUB4                  1.354                            5
                           SUB4                     SINK                  0.511                            5


                     Ex1 (<10% AEP)                                        0.0*                            -
                      Ex1 (5% AEP)                                       0.049*                           50
                      Ex1 (2% AEP)                                       0.093*                           50
                      Ex1 (1% AEP)                                       0.116*                           50
                    Ex1 (1% AEP CC)                                      0.152*                           50
                     Ex2 (<10% AEP)                                        0.0*                            -
                      Ex2 (5% AEP)                                       0.300*                           50
                      Ex2 (2% AEP)                                       0.618*                           50
                      Ex2 (1% AEP)                                       0.782*                           50
                    Ex2 (1% AEP CC)                                      1.032*                           50
                  * area factored based on flow rate for events greater than 10% AEP


                 The WBNM model has been run for events from 1 to 100-year ARI and for durations of 20 minutes to 3
                 hours. A WBNM catchment lag factor of 1.6 was applied which is within the recommended range. An initial
                 and continuing loss of 35mm and 2.4mm/hr in line with ARR2019 datahub values. The resulting peak flows
                 for the critical duration are provided in Table 2-2 for each event at the outlet reporting locations.

                 Table 2-2: Existing Catchment Peak Flows

                          Event AEP              63.20      50%        20%         10%           5%      2%       1%    1%CC
                                                  %
                  Existing (m3/s) – SUB3          0.13      0.16       0.30        0.38          0.47    0.58    0.68   0.88
                  Existing (m3/s) – SUB4          0.33      0.43       0.72               0.92           1.21    1.55   1.86       2
                                                                                                                                   .
                                                                                                                                   5
                                                                                                                                   7


                 2.1.2.      Rational Method Check
                 Pre-development peak flows have been checked against peak flows determined using the Rational Method
                 (RM) for SUB3, as shown in Table 2-3. A time of concentration of 20.6 minutes was determined for SUB3
                 rational method. It can be seen there is values are generally within ten percent difference across events
                 assessed, indicating that the WBNM model flows are suitable for use. Refer to Appendix B for a summary of
                 rational method parameters used.




                 23-0167SMP01-V4 | Stormwater Management Plan | 33 Pavilion Street, Pomona                               Page 20

Document Set ID: 24092538
Version: 1, Version Date: 02/09/2025