Request to Amend Application and Response to DSDIP's Information Request · MCU14/0009

2 Stormwater Quality
2.1 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.
The load based Water Quality Objectives (WQO’s) stipulated in the State Planning
Policy 4/10 - Healthy Waterways and Urban Stormwater Quality Planning Guidelines
2010 (DERM, 2010) for the South East Queensland region will be adopted for the
site. The applicable water quality design objectives for the site are shown in Table 1
below.
Table 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

2.2 Stormwater Quality Treatment
2.2.1 Strategy
The objective of this report is to assess the stormwater quality measures required
based on the development layout prepared in support of the Material Change of Use
application for the site. The treatment for the proposed development consists of
runoff from the site being collected and directed to a bioretention system located
along the western boundary of the site prior to discharge from the site. Whilst
majority of the site is currently impervious (developed), the treatment facility has
been sized to treat the entire site and not just the new development area.

2.3 Modelling Approach
2.3.1 MUSIC Parameters
An assessment of stormwater runoff quality from the proposed development site
has been assessed using the Model for Urban Stormwater Improvement
Conceptualisation (MUSIC) – Version 6.01, released in 2013.
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 2 and Table 3 outline the adopted source node parameters from “MUSIC
Modeling Guidelines” (Water By Design, 2010) that were used in the MUSIC model.
In setting up the model a fraction impervious of 89% was applied to represent the
portion of hardstand and roof the will exist over the site post development




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