Reference Document - Flood & Stormwater Management Plan 28_8_2025

                 Table 2-4: External catchment overland flow (entering site) and pipe flow (diverted around site via Pavilion St)

                                Flow                10% AEP              5% AEP                 2% AEP              1% AEP                 1% CC AEP
                                             Area        Flow         Area       Flow        Area     Flow      Area          Flow      Area      Flow
                                             (ha)       (m3/s)        (ha)      (m3/s)       (ha)    (m3/s)     (ha)         (m3/s)     (ha)     (m3/s)
                             TOTAL           1.960       0.437        1.960     0.534        1.960   0.671      1.960        0.768     1.960     0.982

                    EX2      Overland           -          -          0.300     0.097        0.618   0.234      0.782        0.331     1.032     0.545

                             Pipe                        0.437                  0.437                0.437                   0.437               0.437
                             TOTAL           0.287       0.165        0.287     0.093        0.287   0.114      0.287        0.130     0.287     0.165

                    EX1      Overland           -          -          0.049     0.018        0.093   0.039      0.116        0.055     0.152     0.091

                             Pipe flow                   0.075                  0.075                0.075                   0.075               0.075



                 Table 2-5: Summary of Developed Catchment Parameters

                    Sub-catchment                   Downstream                  Area (ha)                  Imperviousness (%)
                                                     Catchment
                            Ex2                         SUB3                         1.960                              50
                            Ex1                         SUB1                         0.287                              50
                           SUB3                         SUB2                         1.780                              50
                           SUB1                         SUB2                         2.079                              50
                           SUB2                         SUB4                         1.354                              5
                           SUB4                         SINK                         0.819                              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 increased imperviousness and changes to catchment areas associated with the development resulted
                 in an increase in peak flows to the sites outlet as shown in Table 2-6. Mitigation will be required to ensure
                 non-worsening downstream and satisfy the lawful point of discharge requirements.

                 Table 2-6: Comparison of Peak Flows At Site Outlet (Existing Vs. Developed)

                       Event AEP             63.20%            50%            20%            10%         5%            2%             1%        1%CC
                    Existing (m3/s)            0.33            0.43           0.72           0.92        1.21        1.55             1.86       2.57
                  Developed (m3/s)             0.34            0.43           0.73           0.94        1.25        1.66             2.04       2.63
                    Change (m3/s)              0.01            0.00           0.01           0.02        0.04        0.11             0.18       0.06




                 23-0167SMP01-V4 | Stormwater Management Plan | 33 Pavilion Street, Pomona                                                      Page 22

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