2576 - SBSMP-01 (Feb 2026)

Bioretention Basin

Bioretention basins are densely vegetated filtration devices, where runoff (for small/frequent
storm events) enters the basin and is filtered through a filter media layer (e.g. sandy loam with
organics) as it percolates downwards. Bioretention basins often have an extended detention
volume above the filter media which increases the volume of runoff treated through the
system. The runoff is treated as it passes through the system through fine filtration, absorption,
and some biological uptake. Refer to Figure 3-1 below showing a typical cross section of a
bioretention basin.




  Figure 3-1 Typical cross section of a bioretention basin (Source: Healthy Waterways WSUD Technical Design Guidelines)




Bioretention provides a number of functions including:
        Reduce the total volume & velocity of runoff.
        Trap sediment and associated pollutants; and
        Reduce concentrations of nutrients such as Nitrogen and Phosphorous.




2576-SBSMP-01_Version 1.0 (February 2026)                                                                   Page 7 of 23
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