Attachment 3 - Revised Engineering Report (rec. 7.04.2025) MCU24-0165 & OPW24-0222

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However, AO6.2 of NSC Water Quality and Drainage code indicates that all developments must achieve
water quality objectives and must use natural processes wherever possible. Therefore natural treatment
through a bio basin system has been adopted and designed in the following sections.
5.6.2.1 MUSIC Modelling
MUSIC (MUSICX by eWater), a pollutant export modelling program, has been used to model the
expected pollutant loads generated by each catchment within the development and the effectiveness
of WSUD treatment options selected.
5.6.2.2 Catchment Approach
The MUSIC model is based on a split catchment approach, modelled as various catchments
representing the different surface types in accordance with the guidelines and available site information.
Split catchment surface information was informed by taking measurements of the site layout in
accordance with HLW guidelines and are shown in Table 3.
TABLE 3: ADOPTED AREA & PERCENT IMPERVIOUS – URBAN RESIDENTIAL

       Surface Type                 Area (ha)            Percent of Site (%)       Percent Impervious
                                                                                           (%)
           Roof                       0.096                       51                            100
         Driveway                     0.043                       23                             80
          Ground                      0.049                       26                             30

5.6.2.3 MUSIC Meteorological Data
Weather data from Cooroy station 40059 was used for the MUSIC analysis. The 10-year climate period
was selected from 01/01/1973 to 31/12/1983 in accordance with HLW guidelines. The rainfall and
evapotranspiration data with a 6-minute time step, was used in the model.
Input parameters for the rainfall-runoff, source nodes and treatment devices were also obtained from
the guidelines. The following parameters were selected based on urban residential development.
5.6.2.4 Rainfall-Runoff Parameters
The rainfall-runoff parameters listed in Table 3.7 of MUSIC guidelines were used in the model. The
parameters recommended by the guideline are as shown in Table 4.




 15 November 2024                                                                                         Page 12