RFI - Stormwater management (flood report)

      3.3.2. Sediment Forebays

      To ensure that the deposition of coarse sediment on the filter media surface does not affect
      its function, bioretention systems should be designed with pre-treatment to limit the amount
      of coarse sediment reaching the filter media. The sediment forebay has been sized in
      accordance with the WaterByDesign’s Bioretention Technical Design Guideline. Table 3-6
      summarises the proposed design parameters for the proposed sediment forebay.
      Table 3-6: Sediment Forebay Design Parameters

                                           Parameter                         Bioretention Basin
                                                                                     A

                                      Site Catchment (ha)                          1.384
                                    Min Area of Forebay (m2)                        15
                                     Removal Efficiency (%)                         80



             Results
      MUSIC modelling of the proposed treatment train for the developable area of the
      development at 25 Pavilion Street, Pomona was performed to ensure the WQO’s were
      achieved. Table 3-7 presents the load-based outputs that are represented by this
      application. As the bioretention basin is treating an external catchment, the loads
      generated from the external catchment have been subtracted from the mitigated loads.
      The results show the mitigated scenario, which achieves compliant load reductions set out
      within the NSC Planning Scheme.
      Table 3-7: MUSIC Results – Load Based Pollutant Outputs

        Pollutant       Unmitigated          Mitigated         Reduction         Target           Compliance
                          (kg/yr)          (Less External     Achieved (%)     Reduction
                                            Catchment)
                                              (kg/yr)
            TSS             2,780                539                 81           80%                 ✓
            TP               5.33               1.33                 75           60%                 ✓
            TN               27.9               13.31                52           45%                 ✓

            GP              208.8                 0                 100           90%                 ✓




21-0166SMP01-V1 | Stormwater Management Plan | 25 Pavilion Street, Pomona                                      | 18