Site Based Stormwater Management Plan

5.2 OPERATIONAL PHASE

The internal drainage system has been designed to include Stormwater Quality
Improvement Devices (SQIDs) in the water quality treatment train for the proposed
development.




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)
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 5.1 below showing a typical cross section of a bio-
retention basin.




                            Figure 5.1 Typical cross section of a bio-retention basin



Bioretention for the development was sized according to Table B of Appendix 2 from the
SPP (2017) where the filter area is 1.5% of the contributing catchment area, therefore the
bioretention filter area required is 83m2. Refer to the Stormwater Drawings included in
Appendix A for the bioretention basin layout.




Site Based Stormwater Management Plan                                                   Page 14 of 19
2123-SBSMP-01_Version 1.0 (October 2021)