Landcom Book 4 Maintenance - WSUD

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Water Sensitive Urban Design Item to be Monitored Purpose of Monitoring Performance Target Schedule Maintenance or Investigation Immediate Action Required Maintenance Action Required Plant Condition Plants are crucial to the performance of a bioretention system. Healthy vegetation Poorly growing or visibly stressed Die back / dead plants Schedule an investigation into the cause of plant die-back or poor health. During dry periods: Plants help maintain the structure and porosity of the filter media. During rainfall events: Vegetation aboveground acts to retard and distribute flows, and provides scour protection if the bioretention system is designed as a swale. Below ground the roots provide an important media for trapping or absorbing pollutants as they percolate through the media. Maintenance action will depend on the cause of die-back or poor plant health. Once the problem is rectified, infill planting may be required, especially if more than 1 square meter of plantings has died. Infill planting must be as per the original planting schedule. The accumulation of dead plant material can detract from the visual amenity of the bioretention system. Litter (organic) Organic litter can provide an additional source of nutrients to the bioretention system, introduce non-native species, which out-compete native plants and block the filter media. Accumulated organic matter / litter can also cause offensive odours (such as methane gas and hydrogen sulphide, i.e. rotten egg gas) and can reduce percolation of water into the filter media. No litter visible Litter visible Litter thickly covers filter media surface or detracting from visual amenity Identify source of organic litter and address with appropriate response action: e.g. change of landscape maintenance practices; community education re: litter dumping (appropriate for repeat incidences). In the interim, all litter must be removed by maintenance crews. Litter (anthropogenic) Litter can potentially block the inlet and outlet structures of the bioretention system resulting in flooding, as well as detract from the system’s visual amenity. No litter visible Litter visible Litter blocking structures or detracting from visual amenity Identify source of rubbish: e.g. from catchment (commercial precinct); overflow of rubbish bins; accumulation in backwater area and schedule general maintenance to remove rubbish. Where required address source of rubbish (e.g. increase in frequency of rubbish bin emptying; gross pollutant traps in high load generation land uses). In the interim, all litter must be removed by maintenance crews. WARNING: Contact with sharp objects, including hypodermic needles is a risk when removing litter. All workers must be made aware of this risk, wear appropriate protective gear and use caution. Oil slicks Oil spills / inflows are not necessarily an impedance to bioretention system function. Bioretention systems are designed to remove oils from stormwater; hydrocarbons decompose relatively quickly in the presence of soil microbes and water. It is expected that fuel or oil trapped in the bioretention basin would decompose within two to three weeks, depending on the size of the oil spill. No visible oil Persistent but limited visible oil Extensive or localised thick layer of oil visible Do not isolate bioretention system in the case of an oil spill - it is better that the oil is contained within the system than allowed to flow to the downstream water course. Notify the EPA of the spill and clean-up requirements NOTE: do not add any fertiliser, or other nitrogen based product to the system. The microbes within the filter media are capable of decomposing hydrocarbons. 26 Book 4 | MAINTENANCE
Water Sensitive Urban Design 5.2.4 Constructed Wetlands and Ponds A pond treats runoff by providing extended detention and allowing sedimentation to occur. NOTE:- A separate maintenance checksheet has been developed for ponds as provided in the appendix to this booklet. Wetlands treat runoff by filtering it through vegetation and providing extended detention to allow sedimentation to occur. In addition, they have a flow management role that needs to be maintained to ensure adequate flood protection for local properties and protection of the wetland ecosystem. Ponds are frequently designed downstream of a wetland to provide further polishing of stormwater as well as detention (either to meet reuse requirements or attenuation of flows). A pond treats runoff by providing extended detention and allowing sedimentation to occur. This same principle applies for ponds designed for primary treatment. To ensure the functionality of the system, routine monitoring and maintenance of constructed wetlands will require: •• Checking flow paths in and out of the system are unobstructed •• Ensuring vegetation is healthy and is sufficiently dense •• Preventing undesired vegetation from taking over the desirable vegetation •• Removal of noxious plants or weeds •• Re-establishment of plants that die •• Removal of accumulated sediments •• Litter and debris removal Of the above items, debris removal should be the only action requiring ongoing attention. Debris, if not removed, can block inlets or outlets, and can be unsightly if located in a visible location. Inspection and removal of debris should be done regularly, but debris should be removed whenever it is observed. The monitoring and maintenance requirements of ponds are similar to constructed wetlands in maintaining flow into and through the system, ensuring healthy vegetation, minimising establishment of evasive and noxious plants and removal of accumulated sediment, litter and debris. The guidance given for monitoring and maintaining constructed wetlands can in general be adopted for ponds, (refer to note) noting the following: •• Artificial turnover of the lake may be required (because of long residence times). A mechanical system will need to be employed and will require specific maintenance •• Ponds designed to provide primary treatment will typically be more maintenance intensive due to the higher loads of nutrients delivered and captured Book 4 | MAINTENANCE 27
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Level 2, 330 Church Street Parramat
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Landcom Book 4 Maintenance - WSUD

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