Reference Document - Flood & Stormwater Management Plan 28_8_2025

                 Table 3-5: Bioretention Design Parameters

                                           Parameter                             Existing Basin       Upgraded Basin

                                 Extended Detention Depth (m)                           0.30                  0.30
                                   Storage Surface Area (m2)                             80                   130
                                     Filter Media Area (m2)                              80                   130
                               Unlined Filter Media Perimeter (m)                       0.01                  0.01
                      Saturated Hydraulic Conductivity (mm/hr)                          200                   200
                                        Filter Depth (m)                                 0.5                  0.5
                               TN Content of Filter Media (mg/kg)                       400                   400
                  Orthophosphate Content of Filter Media (mg/kg)                         30                   30
                                   Exfiltration Rate (mm/hr)                             0.0                  0.0
                                       Overflow Weir (m)                                 2                     2
                 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                                    Value

                                       Site Catchment (ha)                              2.645
                                    Min Area of Forebay (m2)                             26
                                     Removal Efficiency (%)                              80

                 3.4.           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. Calculations for mitigated loads are shown in Table 3-8.

                 Table 3-7: MUSIC Results – Load Based Pollutant Outputs
                                                               Mitigated
                                       Unmitigated           (Less External    Reduction           Target
                   Pollutant                                                                                         Compliance
                                         (kg/yr)              Catchment)      Achieved (%)        Reduction
                                                                 (kg/yr)
                        TSS                4,660                  900             81                80%                  ✓

                          TP               9.27                  2.38             74                60%                  ✓

                        TN                 51.8                  24.5             53                45%                  ✓

                        GP                 485.0                   0              100               90%                  ✓




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

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