Appendix 3 - Stormwater quality management plan

Operational Management and Maintenance Manual for Stormwater Quality Improvement Devices         CC-3668




4. BIORETENTION SYSTEM
4.1.     Background
Bioretention systems treat stormwater by filtering runoff through densely planted vegetation and
then percolating the runoff through a prescribed filter media. Bioretention systems serve as tertiary
stormwater treatment devices in stormwater treatment trains. Bioretention systems contribute to
stormwater quality management outcomes by removing fine sediments, metals, particulates and
dissolved nutrients (Water by Design, 2009). The primary functions of a bioretention system, as
outlined in Maintaining Vegetated Stormwater Assets (Water by Design, 2012a) are to:

   Capture and filter stormwater through dense vegetation;
   Percolate stormwater through prescribed filter media and infiltrate it into surrounding soils
    and/or discharge it to downstream drainage;
   Allow high flow to bypass or pass over the bioretention area in a controlled manner; and
   Provide visual amenity and promote ecology within urban zones.

The operational management and maintenance activities outlined below are consistent with the
recommendations provided in Concept Design Guidelines for Water Sensitive Urban Design (Water By
Design, 2009), WSUD Technical Guidelines for South East Queensland (Water By Design, 2006),
Maintaining Vegetated Stormwater Assets (Water By Design, 2012a) and Rectifying Vegetated
Stormwater Assets (Water By Design, 2012b).

4.2.     Vegetation Establishment
The most intensive period of maintenance is during the first two years whilst the plants are established.
During this time regular watering and weeding is required.

4.2.1.    Watering
Regular watering of the bioretention system is essential for successful establishment. The frequency of
watering is dependent on rainfall during the establishment phase however the following program should
be used as a guideline:

        Week 1-2         3 waterings per week
        Week 3-6         2 waterings per week
        Week 7-12        1 watering per week
        After Week 12, water as required during extended dry periods

4.2.2.    Weeding
Weed management will need to be undertaken manually on a fortnightly basis until such time that the
plants are established with sufficient density to effectively prevent weed propagation. Surface mulching
of the bioretention system with organic material such as bark chips should not be undertaken as most
organic mulch floats and runoff typically causes this material to be washed away with a risk of causing a
drain blockage.


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