Development Application part 7 of 10 Stormwater Management Report - MCU13/0092

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5.      Maintenance


The following maintenance protocols detailed in Section 5 have been adapted from the Healthy Waterways Water
Sensitive Urban Technical Design Engineering Guidelines for South East Queensland        -
                                                                                           Version 1 June 2006. They
should generally be adopted as standard maintenance procedures upon the installation and or construction of
Bioretention Basins.


5.1 Bioretention Basins


Bioretention Basins require ongoing maintenance to ensure water treatment efficiencies are maintained. Attached in
Appendix D is a Bioretention Checklist.

Vegetation plays a key role in maintaining the porosity of the filter media of a bioretention basin and a strong healthy
growth of vegetation is critical to its performance. Therefore the most intensive period of maintenance is during the
plant establishment period (first two years).

Inflow systems and overflow pits require careful monitoring, as these can be prone to scour and litter build up. Debris
can block inlets or outlets and can be unsightly, particularly in high visibility areas. Inspection and removal of debris
should be done regularly, and debris should be removed whenever it is observed on a site. Where sediment forebays
are adopted, regular inspection of the forebay is required (3monthly) with removal of accumulated sediment

undertaken as required.


For larger bioretention basins, it is essential that a maintenance access point is designed for and maintained in the
bioretention basin. The size and complexity of the system will guide its design and may involve provision of a
reinforced concrete ramp/ pad for truck or machinery access.


Typical maintenance of bioretention basin elements will involve:

     .   Routine inspection of the bioretention basin profile to identify any areas of obvious increased sediment
         deposition, scouring from storm flows, rill erosion of the batters from lateral inflows, damage to the profile
         from vehicles and clogging of the bioretention basin (evident by a ’boggy’filter media surface).
     .   Routine inspection of inflows systems, overflow pits and under-drains to identify and clean any areas of
         scour, litter build up and blockages.
     .   Removal of sediment where it is smothering the bioretention basin vegetation.
     .   Where a sediment forebay is adopted, removal of accumulated sediment.
     .
         Repairing any damage to the profile resulting from scour, rill erosion or vehicle damage by replacement of
         appropriate fill (to match onsite soils) and revegetating.
     .
         Tilling of the bioretention basin surface, or removal of the surface layer, if there is evidence of clogging.
     .
         Regular watering/ irrigation of vegetation until plants are established and actively growing.
     .   Removal and management of invasive weeds (herbicides should not be used).
     .   Removal of plants that have died and replacement with plants of equivalent size and species as detailed in
         the plant schedule.
     .
         Pruning to remove dead or diseased vegetation material and to stimulate growth.
     .
         Vegetation pest monitoring and control.

Resetting (i.e. complete reconstruction) of the bioretention basin will be required if the system fails to drain
adequately after tilling of the surface. Maintenance should only occur after a reasonably rain free period when the soil
in the bioretention system is dry. Inspections are also recommended following large storm events to check for scour
and other damage.
                                                       P age   113

Level 2, 39 Sherwood Road                       [email protected]                                     P: 07 3870 8888
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