18-0165B Stormwater Management Report_Issue D

The model was calibrated using the Bureau of Meteorology (BoM) data from thr Cooroy Composite, 1973 – 1983, at a
6-minute time step. The annual rainfall for this site is listed in Table 4 below:

                                                      Table 4 - Annual Rainfall

 Year        1973          1974       1975        1976       1977      1978          1979   1980      1981    1982      1983
Annual
Rainfall    2135.5        2796.1      1178.9    2108.7       950.2    1468.5      1023.7    1232.4   1507.3   1332     2040.8
 (mm)


8.3 MUSIC Model Results


The proposed treatment train modelled with MUSIC, includes the following water quality treatment measures:

A bio-retention basin will be constructed within landscaped areas to the south-east corner of the site adjacent the
                                                                            2                                  2
existing bushland. The bio-retention basins is to have a total area of 213m and a filter media area of 114m and is to
accept runoff for all roofs, hardstand and majority of landscaped areas prior to discharging into the existing drainage
infrastructure. The basin has been modelled with an extended detention depth of 300mm, a hydraulic conductivity of
200mm/hr and a filter media depth of 500mm.

The tabulated results are shown below:

                                               Table 5 – Treatment Train Effectiveness

                                                                     Reduction          Target
                              Unmitigated          Mitigated                                         Compliance
              Pollutant                                              Achieved          Reduction
                                (kg/yr)             (kg/yr)                                            (Y/N)
                                                                        (%)               (%)
                 TSS               3470               490              85.7                80            Y
                 TP                13.1               3.61             72.7                60            Y
                 TN                29.3               15.0             49.2                45            Y
                 GP                 352                 0               100                90            Y


                                               Table 6 – Mean Annual Pollutant Loads

                                          Pre-Development             Post-Development        Compliance
                          Pollutant
                                               (kg/yr)                      (kg/yr)             (Y/N)
                            TSS                 2060                          490                 Y
                            TP                  5.27                         3.61                 Y
                            TN                  34.8                         15.0                 Y


                                                   Table 7 - Daily Pollutant Loads

                                   WQO’s            Pre-Development            Post-Development       Compliance
               Pollutant
                                   (mg/L)                (mg/L)                      (mg/L)             (Y/N)
                    TSS              6                    15.7                        0.973               Y
                    TP              0.05                  0.044                       0.035               Y
                    TN              0.5                   0.299                       0.178               Y


As demonstrated in Tables 5, 6 and 7, the stormwater quality management strategies proposed for this development
exceed the taget reduction rates required by the NSC and the State Planning Policy (2014).



HR DESIGN                                              Reference No: 18-0165D                                      Page 9 of 15