RFI - Attachment 7 - Updated SWMP

3.2.6.     Bioretention System




Bioretention systems use ponding above a treatment surface to maximise the volume of runoff flowing
through the filtration media. They typically convey flows above the design event through overflow pits or a
weir. The treatment system operates by firstly filtering surface flows through surface vegetation and then
percolating runoff through prescribed filtration media. This media provides treatment through fine
filtration, extended detention, and biological uptake of nutrients. As these systems take approximately 12-
24hrs to drain, the maximum depth of pondage allowed to occur over the filter area has been limited to
300 mm.

Table 3-6 summarises the proposed design parameters for the main bioretention system for this
development.

(http://healthywaterways.org/initiatives/waterbydesign/stormwater).



3.2.6.1.   Rain Gardens.

Rain gardens (refer Figure 3-3) are a type of bio-retention system which use native plants and free draining
soils for treatment, they are designed to capture rainwater flow from gutters and rainwater tank, or
overland flow. Like bio-retention basins, they are used to slow the water down, decrease erosion, reduce
sediment, and filter pollutants out of the storm water (Brisbane City Council, 2024). This strategy has
incorporated 10 m2 of rainwater garden area to treat half of the roof area as illustrated in Figure 3-1,

Table 3-6 summarises the proposed design parameters of the raingardens.




                                   Figure 3-3: A raingarden (City of Sydney, 2019)




21-0211SMP01V1 | Stormwater Management Plan | Good Shepherd Lutheran College Arts Centre           Page 13