Reference Documents - MCU24 0141 & OPW24 0184 [As Published]

                Conductivity                                                  500 µS/cm

              4.2. Water Quality Modelling
                        4.2.1. MUSICX Model Parameters

              The MUSIC Modelling Guidelines – November 2018 was used to source base and storm flow concentration and
              runoff generation. The model used rainfall data published by eWater from the Cooroy Composite Station, over
              a ten (10) year period (1973-1983) at a 6 minute time step (as nominated in the Water by Design’s MUSIC
              Modelling Guidelines. All source nodes were set up in accordance with this guideline, specifically for the use of
              split catchments. Commercial and industrial rainfall-runoff parameters and industrial pollutant export
              parameters have been used for each split catchment course node. No routing of drainage links was adopted
              for the purpose of taking a conservative approach. This approach assumes that the flow through the drainage
              system takes no time, which overestimates the likely pollutant load. MUSICX version 1.40 was used for this
              assessment.
              MUSIC models are included in Appendix D.


                        4.2.2. Scenario Method

              The proposed development was split into two (2) catchments, with individual treatment options. Each
              catchment was modelled using split catchment nodes comprised of roof, carparking and landscaping nodes (as
              appropriate). It is considered that sub catchments are not required to meet the pollutant reduction targets as
              they both discharge to the same location. The modelling demonstrates that discharge from the site meets
              load reduction targets. The total development is approximately 0.29ha and consists of 17 industrial units. The
              development has been split into two catchments of approximately 0.23ha and 0.06ha.
              Refer to Table 3 and Appendix A for more detail.
              Table 3 - Catchment Characteristics

                                           Roof Area (ha)     Driveway Area (ha)     Landscape Area (ha)     Total Area (ha)
                Impervious Percentage            100%                 100%                    0%
                Catchment 1                     0.1670               0.0377                 0.0280                0.2327
                Catchment 2                        0                 0.0563                 0.0034                0.0597


                        4.2.3. Proposed Stormwater Treatment Train

              The stormwater runoff from catchment 1 will be treated with a bioretention basin and swale. Catchment 2
              will discharge to a vegetated swale before entering the stormwater network. The filter media of the
              bioretention basin was modelled using a total nitrogen content of 400mg/kg and an orthophosphate content
              of 30mg/kg. This is in accordance with MUSIC Modelling guidelines (consultation draft) by Water by Design
              (2018).
              Refer to Table 4 for the bioretention basin characteristics.




240127 – Stormwater Management Plan              7 of 10