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      3. STORMWATER QUALITY
             Design Objectives
      This report identifies the stormwater quality management objectives for the operational
      phase (post-construction phase) of the proposed development. Construction based
      stormwater quality management objectives will need to be addressed as part of operational
      works documentation.
      NSC Planning Scheme (2020) defines the post-construction phase Water Quality Objectives
      as shown in Table 3-1.
      Table 3-1: Site Stormwater Quality Objectives (Operational Phase)

              Minimum reductions in mean annual loads from unmitigated development (%)

          Total Suspended           Total Phosphorous             Total Nitrogen   Gross pollutants
             Solids (TSS)                   (TP)                       (TN)            >5 mm
                  80                         60                         45               90



             Stormwater Quality Treatment
      3.2.1. Strategy

      The objective of this report is to assess the stormwater quality measures required based on
      the development layout to support the development application. Runoff from the
      development will be collected in a stormwater drainage system and discharged into a
      bioretention basin prior to being discharged from the site.
      This report sizes the required bioretention basins to treat runoff from the proposed
      development of this site only.

      3.2.2. MUSIC Parameters

      An assessment of stormwater runoff quality from the existing conditions and proposed
      developed conditions has been undertaken using the Model for Urban Stormwater
      Improvement Conceptualisation (MUSIC) – Version 6.3, released in 2018.
      Climate data for the catchment was sourced from the MUSIC model database. The rainfall
      and evaporation data template for this site has been based on data from Cooroy from
      1/1/1973- 31/12/1983 with six (6) minute rainfall duration.
      Table 3-2 and Table 3-3 outline the adopted source node parameters from “MUSIC
      Modelling Guidelines” (Water By Design, 2010) that were used in the MUSIC model.
      The site density of 10 dwellings per hectare, with the source nodes being assigned
      percentage impervious values based on 10 dwellings per hectare




21-0166SMP01-V1 | Stormwater Management Plan | 25 Pavilion Street, Pomona                             | 10