Book 4 of the Landcom series compiles a response to the practical issues raised by a focus group of over 10 local councils around maintenance issues for:
• Constructed wetlands
• Bioretention basins
• Sedimentation basin / ponds
The book assumes that any WSUD strategy for a particular project that has been developed meets best management practice objectives and design guidelines.
Section 4 discusses life cycle costing for the above devices. It contains excerpts from the (somewhat dated and patchy) life cycle costing data used by MUSIC (Model for Urban Stormwater Improvement Conceptualisation) – version 3.
Table 2 gives values for a range of key ‘life cycle costing’ parameters: Total Acquisition Cost (TAC ), Total Annual Maintenance (TAM ), renewal, and decommissioning costs. These values can assist with asset management planning – although practitioners need to know the assumptions and uncertainties attached to these values before applying them to their own asset portfolio.
Section 5 covers both predictive (event based) maintenance as well as programmed, regular ongoing maintenance and monitoring. The booklet emphasises that routine maintenance for the WSUD devices in question can be largely described as “landscape maintenance”. It also emphasises that the most time-intensive period of maintenance for a vegetated system is during plant establishment – typically two growing seasons – when supplementary watering, weeding and plant replacement may be required to ensure a good coverage of healthy vegetation.
For each WSUD device a three page table details a range of routine and preventative maintenance inspection criteria and appropriate maintenance activities.
Section 5.3 covers management and disposal options for typical ‘waste’ materials associated with WSUD devices (silt and sediments, dewatered silt, filter media, liquid waste from dewatering). This is practical, NSW specific information. At the time of publication the NSW Department of Environment and Climate Change (DECC) determined that silt from stormwater treatment devices or management systems is classified as “general solid waste” (non-putrescibles) under the Protection Of the Environment and Operations Act (1197) – Part 30 49. Such materials are to be either:
· Disposed in an appropriately licensed facility; or
· Recovered for appropriate reuse IF a ‘Resource Recovery Exemption’ is granted under Clause 51A of the POEO (Waste) Regulation 2005.
In either case, complexities arise if the asset owner believes that the material may have significant contaminant concentrations due to the nature of the upstream catchment. Refer to page 26 for details.
Section 6 outlines construction considerations that are vital to the proper establishment and commissioning of WSUD devices – and significantly influence ongoing maintenance issues and costs. This section is a good succinct summary of two pieces of current, detailed guidance:
- South East Queensland’s Construction and Establishment Guidelines: for vegetated stormwater systems (see related resources)
- The Faculty for Advancing Water Biofiltration (FAWB)’s recommended quality control requirements for biofiltration filter media.
The booklets’ Appendices contain a number of ‘checklists’ and sign off sheets, spanning: construction inspection sign off regular maintenance, and asset handover.