RFI - Appendix G SWMP by MPN Consulting

 16 December 2021


5.5       Proposed Stormwater Quality Treatment Devices

5.5.1 Locations

The location of the proposed stormwater quality treatment device is shown on MPN Plan 8293-
CP.1.01 attached in Appendix 3.

5.5.2 Device and Size

The device type and size are depicted on MPN Plan 8293-CP.1.01 attached in Appendix 3.

5.5.3 Operation

The bioretention basin operates by filtering runoff through densely planted surface vegetation,
then percolating the water through a sandy loam filter media with details as per MPN Plan 8293-
CP.2.01 attached in Appendix 3. As the water is percolated through the soil, pollutants are
captured by fine filtration, adsorption and biological uptake.


5.5.4 Maintenance

For the initial maintenance of the bioretention basin it is important to remove weeds and debris,
with regular watering until plants are established and actively growing.

Watering is to be undertaken following the construction of the basin at the following frequency:

      •   Week 1 – 6, 5 times/week
      •   Week 6 – 10, 3 times/week
      •   Week 11 – 15, 2 times/week

If there is no rain, each plant should receive 2.5 – 5.0 litres of water per week during establishment
in the first 6 weeks (40mm/week).

Watering requirements to sustain healthy vegetation should be determined during ongoing
maintenance visits.

Detailed establishment techniques can be found in the Water By Design Construction and
Establishment Guidelines.

Inspections are also recommended following large storm events to check for scour and other
damage.


Maintenance of the bioretention basin will include:

      •   Routine inspections of surface profile to identify areas of sediment buildup, scour and
          erosion or clogging of the filter media;
      •   Routine inspection of the overflow pits and under drains for blockages and litter buildup;
      •   Removal of sediment where it is smothering the basin vegetation; and
      •   Repair all basin damage due to scour or erosion by replacement of filter media and
          vegetation.


 Excellence with Economy in Engineering                                                                  15
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