Reference Document - RAL23/0013.02 - Part 2 (As Published)

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
                                             2
                    Filter Media Area (m )                              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-V3 | Stormwater Management Plan | 33 Pavilion Street, Pomona                                   Page 33