Stormwater Treatment & Water Quality Management Plan_April2014

                                                                              Callaghan & Toth


The mean Annual Rainfall for Cooroy      92 – 02 = 1585mm
The mean Annual Rainfall for Cooroy      72 – 02 = 1650mm

The MUSIC Modelling Guidelines (2010) details that Cooroy data for 1973 to 1983 should be
used. This data has an annual average Rainfall of 1600mm. It is considered that the 10 year
period from 1992 – 2002 has a relatively close mean annual Rainfall to the recommended 10
year period and as such is acceptable to use in this case.

Urban Residential rainfall-runoff parameters from the draft guidelines have been used.

4.3      MUSIC Modelling Results

The MUSIC modelling program has been used to investigate the performance of various
treatment options in the treatment train. MUSIC Version 6.0.1 is the current version and was
used to assess this development proposal.

4.3.1 Water Quality Objectives

This proposed stormwater treatment system for the development, when modelled using MUSIC
meets the pollution load reduction target as detailed in DSDIP’s State Planning Policy
December 2013 – Appendix 2, Table B. The following have been included in Appendix 2.
           The treatment train effectiveness for the system.
           The MUSIC Version 6.0.3 Summary Report.

The treatment train effectiveness for the system is shown below in Table 4.2. The results
indicate that the proposed stormwater treatment train will be effective in achieving the
reductions as outlined in the State Planning Policy December 2013 – Appendix 2, Table B. It
reduces sediment and nutrient concentrations and loads to an acceptable level and also
reduces runoff concentrations.


TABLE 4.2:      COMPARISON OF LOAD REDUCTIONS
                            MUSIC REDUCTION                  POLLUTANT LOAD
        PARAMETERS
                                RESULTS                     REDUCTION TARGETS
    Flow                           3%
    Total Suspended Solids        81%                                 80%
    Total Phosphorous             58%                                 60%
    Total Nitrogen                51%                                 45%
    Gross Pollutants              99%                                 90%

4.3.2 Assessment of Results

The developed site has been modelled as a series of Urban Residential sub-catchments, which
incorporate Water Sensitive Urban Design (WSUD) treatment trains. Figure 3.1 and Figure 3.2
show the proposed locations of the treatment systems. The reductions listed in Table 4.2 above
generally comply with Council’s requirements, Water by Design Deemed to Comply Solutions
and the State Planning Policy December 2013 – Appendix 2, Table B. Therefore, it is
considered that the proposed stormwater treatment system is currently sufficient to reduce the
pollutants prior to exiting the site and entering the tributary of the Six Mile Creek.




55 Lake MacDonald Drive – Stage 1 to 5                                                   pg. 16