Reference Document - RAL23/0013.02 - Part 2 (As Published)

Figure 3-2: MUSIC Model Layout



3.3.       Treatment Measures
Runoff from the development will be treated through a bioretention basins. The locality of the treatment
devices servicing the development is shown in Figure 3-1.

3.3.1.     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 300mm, with a minimum filter media depth of 500mm. Table 3-5
summarises the proposed design parameters for the main bioretention system for this development, and
highlights the size of the existing bioretention basin approved as part of 25 Pavilion Street, along with the
upgraded size to account for the additional development from 33 Pavilion Street . As noted above this may
be split into several devices on detailed design. It is to be noted that the Orthophosphate content of the
filter media has been reduced to 30mg/kg in line with recent advice from Healthy Waterways.




23-0167SMP01-V3 | Stormwater Management Plan | 33 Pavilion Street, Pomona                            Page 32