H - Revised Integrated Water Management Plan by Cardno (inc MUSIC file) (13.09.19)

1.4 Stormwater Treatment (Bioretention) in WSUD Street Trees
WSUD street trees are a combination of a bioretention (biofiltration) system and a street tree.
Bioretention systems are shallow depressed vegetated filter beds which are designed to collect and treat stormwater
runoff. The Figure 1 depicts a typical bioretention profile




Figure 1 – Typical Bioretention Profile
Stormwater runoff intercepted by a bioretention system is treated via a number of natural processes including
sedimentation, physical filtration by soil and plants, chemical adsorption, biological processing by plants and bacteria
within the soil. Depending on the configuration, treated water may drain into the surrounding soils or via perforated pipes
that connect into the downstream drainage system.
As well as improving the quality of stormwater, bioretention systems can improve urban hydrology by storing and detaining
water, and reducing the volume of runoff through evapotranspiration and in some cases infiltration into the surrounding soil.
In a Strataflow tree pit, filter media is used as a replacement for typical growing media at the pavement opening, and
stormwater runoff from surrounding hardstand areas is directed towards the tree where the stormwater is cleaned as it
drains through the bioretention media. Tree pit openings are usually small systems, accommodating a single tree and are
usually a few square metres in size.




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