LATE RFI - SCG 33114 (SWM) Rev A

5.0        STORMWATER QUALITY
In the absence of adequate controls, urban development can increase both stormwater runoff volumes
and peak discharge rates. In addition, this urban development has the potential for increased creek
erosion and the stressing of in-stream aquatic ecosystems. The use of stormwater detention or retention
systems aims at reducing these threats by limiting property flooding to acceptable levels and also
filtering stormwater runoff through a vegetated soils media layer, thus reducing the threats caused by
urban development.


The following factors have been identified as potential contributors which can adversely affect
stormwater quality draining from the site:-
           •    Silt and sediment erosion
           •    Gross Pollutants
           •    Hydrocarbon runoff
           •    Nutrient runoff


5.1        State Planning Policy and Water by Design Assessment
The proposed development has been assessed against the State Planning Policy 2017 and the Water By
Design (Stormwater Quality Deemed to Comply Solutions – 2010).


The proposed residential development involves a land area less than the trigger value of 2500m2 for
stormwater quality measures as required in the State Planning Policy 2017 and the Water By Design -
Stormwater Quality Deemed to Comply Solutions - 2010. Therefore, stormwater quality treatment is
not required for the proposed development. However, to promote sustainable building design,
stormwater harvesting has been proposed for stormwater re-use for communal landscaping. The
proposed water re-use tank has been sized in accordance with the Sunshine Coast Council Flooding and
Stormwater Management Guidelines adopting 1kl per 25m2 of communal landscaping area.


However as per Noosa Council information request dated 04.03.2023 (MCU23/0109 & OPW23/0123),
Noosa Council have requested the following targets for stormwater quality treatment.
      -   60% reduction in total phosphorous
      -   45% reduction in total nitrogen.


5.2        Construction Phase
Sediment generated during the construction phase shall be controlled in accordance with a site-specific
Erosion and Sediment Control (ESC) Plan and kept on site throughout construction.


5.2.1      Silt and Sediment Erosion
A potential for sediment mobilisation/transportation exists during and beyond the construction of the
proposed development. This can elevate turbidity levels of stormwater runoff.
A RUSLE assessment of the site confirms proposed development is a Low Risk for soil loss (< 150
Tonnes).

SCG Consulting Engineers                    Page 7                               SCG Ref: 33114(SWMP)