Swmp

       SUB1-Ex                                   0.287                                    50
       SUB1-Ex (<10% AEP)                         0.0*                                    -
       SUB1-Ex (5% AEP)                         0.047*                                    50
       SUB1-Ex (2% AEP)                         0.095*                                    50
       SUB1-Ex (1% AEP)                         0.138*                                    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 2-5.
      Mitigation will be required to ensure non-worsening downstream and satisfy the lawful point
      of discharge requirements.
      Table 2-5: Comparison of Peak Flows At Site Outlet (Existing Vs. Developed)

       Event AEP                     63.2%        50%        20%        10%         5%         2%     1%

       Existing (m3/s)                0.34        0.42       0.64           0.80   0.95        1.12   1.27
       Developed (m3/s)               0.41        0.49       0.72           0.88   1.05        1.25   1.41
       Change (m3/s)                  0.06        0.07       0.08           0.09   0.10        0.13   0.13



      2.1.4. Mitigation Scenario

      When comparing the peak flows in the existing and developed scenarios, increases in the
      peak discharge are predicted at the site outlet. A detention basin is proposed to attenuate
      peak flows discharging from the site to demonstrate non-worsening and meet the legal point
      of discharge requirements.
      All modelling parameters remain consistent between the developed and mitigated
      scenarios, with the addition of detention basins. The proposed basin structure details are
      summarised in Table 2-6 with Concept Engineering Drawings included in Appendix A.
      Table 2-6: Summary of Basin Structure Details

                                  Basin A1

           Elevation (RL)                    Storage (m3)

                   0                                0
                  0.1                              26
                  0.2                              55
                  0.3                              87
                  0.4                              123
                  0.5                              162
                  0.6                              205
                  0.7                              251
                  0.8                              301
                 0.87                              338




21-0166SMP01-V1 | Stormwater Management Plan | 25 Pavilion Street, Pomona                                    |7