Engineering Hydrology Plans (IWMP)

   The bioretention systems proposed to treat the runoff generated from the
   development site are to be located within the landscape area within the carpark
   area. Runoff from the carpark areas are to be directed to these small bioretention
   basins, before entering the underground drainage network.
   Roadside bioretention cells are proposed to treat runoff from the new road.
   As these systems take approximately 12-24hrs to drain, the maximum depth of
   pondage allowed to occur over the filter area has been limited to 200mm in the
   carpark and 100mm in the road reserve. The depth of the filter media has been
   limited to 500mm. The basin is to be planted out with native species which are
   adaptable to a wet/dry soil environment. The basin will require maintenance such as
   weeding and replanting if plants are damaged or die. Table 9 summarises the
   proposed design parameters for the bioretention basin for this development.
   As bioretention systems are scalable, modeling has been undertaken representing
   each sub-catchment as a whole. Final sizing and location of bioretention systems
   will be dependent on the detailed design of the drainage catchments / system. The
   areas identified in Table 9 are the minimum areas that are to be implemented within
   each sub-catchment. Indicative bioretention locations are highlighted in Figure 6.

   Table 9: Bioretention Basin Design Parameters

              Parameter                            A       B            C           D
     Extended Detention Depth (m)              0.2        0.2          0.2         0.1
                                   2
       Storage Surface Area (m )               120        65           45          40
                               2
         Filter Media Area (m )                90         50           35          30
   Unlined Filter Media Perimeter (m)         0.01       0.01         0.01        0.01
Saturated Hydraulic Conductivity (mm/hr)       200        200          200         200
            Filter Depth (m)                   0.5        0.5          0.5         0.5
  TN Content of Filter Media (mg/kg)           800        800          800         800
Orthophosphate Content of Filter Media
                                               55         55           55          55
                (mg/kg)
      Exfiltration Rate (mm/hr)                0.0        0.0          0.0         0.0
           Overflow Weir (m)                   2.0        2.0          2.0         2.0




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