Appendix 3 - Stormwater quality management plan

Stormwater Quality Management Plan – Commercial Development at Weyba Road, Noosaville           CC-3668



Rainfall Data

   Rainfall data for the site was chosen to give the best representation of actual conditions. In
    accordance with the recommendations of the MUSIC guidelines for Sunshine Coast (north), a
    time period of 10 years between 1973 and 1983 was selected from the Cooroy Composite
    station (40059), using a six minute time step. The evapotranspiration data for Sunshine Coast
    (north) was also adopted in the model, as per Table 3.1 of the MUSIC guidelines.




Treatment Nodes

The recommended MUSIC values for commercial source nodes have been used in MUSIC to generate
predicted pollutant loads from the site. The following devices have been used in the treatment train
to reduce these pollutant loads to achieve the Water Quality Objectives (WQOs) for this site.

   Gross Pollutant Traps – Although not included in the model it is proposed that all stormwater
    inlet pits on the site be fitted with a quality gross pollutant trap such as a stormwater 360
    enviropod.   These devices have not been modelled as they do not contribute to nutrient
    removal, which is the critical parameter in regard to utilising a MUSIC model to demonstrate
    that WQOs have been achieved by the proposed treatment train.


   Rain Water Reuse Tank – 15Kl of rainwater storage has been included in the model with 27% of
    the roof area connected to the tank and 73% of the roof area by-passing the tank. An irrigation
    reuse rate of 200kl per annum has been set in the model which equates to approximately
    435mm of irrigation per annum over 459m2 of landscaping. A daily reuse rate of 0.5Kl/day has
    also been modelled to represent 40x8l toilet flushes and 100l for external cleaning. This reuse
    rate is considered quite conservative and in reality it is suggested that the non-potable uses
    will actually be significantly higher than 0.5Kl/day.


   Bio-Retention Device – Designated bio-filtration areas with a total combined surface area of
    35m2 have been modelled with extended detention depths of 200mm, sandy loam filter media
    depths of 500m and a hydraulic conductivity of 200mm/hr. It is planned to locate the bio-
    retention areas within the landscaping throughout the site. Further details of the bio-retention
    area and there contributing catchments are shown within the Concept Drainage Layout Plans
    prepared by Empire Engineering, attached to this report as Appendix B. An exfiltration rate of
    0mm/hr was set for the bio-retention devices, a TN content of filter media of 800mg/kg,
    Orthophosphate content of filter media of 55mg/kg, a high flow bypass of 1m³/s and a low flow
    bypass set as 0m³/s.




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