Attachment 6 - Stormwater Management Plan and Engineering Response. · MCU23/0078

5.2.4   Source Nodes


        The second step taken in creating the MUSIC models was to define ‘Source Nodes’ or Sub-Catchments. Source nodes for
        modelling these catchments were based on the Water by Design reference material: Music Modelling Guidelines. The
        MUSIC model uses the split catchment approach and consists of commercial source nodes. Catchment areas are outlined
        in Table 25, 26 and 27 below with catchment extents illustrated in Appendix G for both proposed sites.


                                       Table 25: Source Node Information – Lot 3 Catchment
                                    Node type                             Area (ha)                  Fraction Impervious
                                Commercial Road                                    0.805                     90%
                                 Commercial Roof                                   1.504                     100%
                               Commercial Ground                                   0.516                     40%
                        South Site Future Commercial Road                          0.200                     90%
                        South Site Future Commercial Roof                          0.237                     100%
                       South Site Future Commercial Ground                         0.099                     40%
                 Private Access Roadway Un-Treated Road Areas                      0.116                     75%


                                   Table 26: Source Node Information – Lot 7 Northern Catchment
                                    Node type                        Area (ha)           Fraction Impervious
                                Commercial Road                            0.145                       80%
                                 Commercial Roof                           0.106                      100%


                                   Table 27: Source Node Information – Lot 7 Southern Catchment
                                    Node type                        Area (ha)           Fraction Impervious
                                Commercial Road                            0.216                       75%
                                 Commercial Roof                           0.110                      100%


        Note that the future business use within Lot 3 immediately to the south of the proposed development was included in the
        source node information found in Table 25 above. This is to ensure that the proposed bio-retention basin for the Lot 3
        catchment is adequately sized to also treat pollutant run-off from the future business development as well. Roof, road and
        ground areas for each source node within this future development area were calculated based on a 45% site coverage
        requirement of the Noosa Shire Council planning scheme for this future development.


        Note also that Table 25 above includes existing roadway catchments within the private access Road. As per the catchment
        extents illustrated in Appendix F and the engineering drawings shown in Appendix B, two of the existing bio-retention
        pods along the private access road are proposed to be removed to suit the proposed streetscape works. To mitigate this
        catchment area that will be discharged from the private access road without first going through treatment, an additional
        source note was added to the MUSIC modelling for Lot 3.


        The input parameters used are listed in Appendix G.


5.2.5   Treatment Methodology


        Runoff from the development site will be conveyed through three independent bio-retention basins owned and
        maintained by the development owners. Lot 3 is to have a single bio-retention basin in the south-west corner of the site,
        whilst each of the two sub-catchments within Lot 7 are to each have a bio-retention basin.




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