Keep a close eye on construction to make sure the design drawings and specifications are followed. A few simple mistakes can cause plants to not survive or thrive.
A meeting should be held before construction begins, as it can save time during construction and help prevent issues. This meeting should include representatives from the design and construction teams.
The pre-construction meeting should ensure:
- safety considerations are covered
- all design documentation and drawings are available and clearly understood
- construction hold points, materials validation and required signoffs are understood
- locations of underground services are marked
- asset protection measures are understood
- environmental controls follow the Site Environmental Management Plan
- traffic controls are covered (if applicable)
- measures to limit public access are covered
For subdivision developments within growth areas, the pre-construction or pre-commencement meeting should also comply with Chapter 18 of the Metropolitan Planning Authority's Engineering Design and Construction Manual for Subdivisions in Growth Areas.
Hold points are needed during construction to validate the quality of construction and materials. The design package should contain specific construction checklists, but general checklists can be used if they are not available.
Some of the construction phase checks will be common to all WSUD assets, for example:
- maintenance access provided
provision for high flows during construction (e.g. high flow by-pass, erosion control measures), which should be checked at the beginning of construction and during construction after heavy rain
connection to existing drainage lines is correct
soil specifications are correct
plant species, maturity, density and number are as specified
An inspection is necessary at the completion of construction. The design drawings must be updated with any changes made during construction, to 'as constructed' versions.
Operation and maintenance plans
Operation and maintenance plans should be developed and approved during the construction phase, and should clearly outline the roles and responsibilities for the WSUD asset.
The plans may be a generic council plan for a particular WSUD asset type or specific to the project. They should take into account maintenance considerations noted during design, and any issues or changes as a result of construction.
The need for an operation plan should be determined on a case-by-case basis, but they are typically required for WSUD systems that are difficult to operate – such as stormwater harvesting schemes with complex control systems, or wetlands with penstocks to control water levels.
Operation plans include the details and requirements for the operational components of a WSUD asset, and may include:
photographs and locations of relevant components, which should be clearly marked – for example with a bollard or sign
make and manufacturer
purpose of each component
expected frequency of operation
All WSUD assets should have plans that clearly identify maintenance requirements and state who is responsible for ongoing maintenance. All plans should be approved before the maintenance period begins.
Maintenance plans should include a description or plan showing the location of assets requiring maintenance. Marker locations may also be needed for pits or other infrastructure that need maintenance but cannot be easily found, for example, once vegetation is established.
Maintenance tasks can include:
- asset cleaning
- litter, debris, silt and sediment removal, and safe, legal disposal in accordance with EPA standards
filter media removal and replacement
edge control and erosion management
vegetation management, including weed removal, mowing, tree pruning and plant and mulch replacement
pump, control and wiring maintenance
ongoing monitoring and reporting
Other maintenance plans should also include:
required inspections and frequencies
maintenance procedures and any specific equipment required
materials list and supplier details
manufacturers' documents, warranties and schedules
maintenance access – note frequency and timing (for example if all weather access is needed), safety requirements, environmental impacts and aesthetics
any site-specific requirements, such as locks to prevent vandalism
an estimate of ongoing maintenance costs to be included in budgets
It is common for construction contracts to include a defect and liability period of up to two years for plant growth and establishment. During this time, the builder or developer is responsible for maintaining the asset and fixing any defects. At the end of this period, a final inspection and asset handover check is performed.
The handover from the construction phase to maintenance phase should only occur after the plants are established and mature. This should involve handover of the operation and maintenance plans, and inspection and handover of the WSUD asset.
All relevant parties, including council representatives and external stakeholders, should be involved in this process so everyone has a clear understanding of the roles and responsibilities for ongoing maintenance of the WSUD asset.
Common mistakes and issues
Common mistakes during construction and handover include:
not adding the asset to an asset management system
not keeping records of “as constructed” drawings, or operation and maintenance plans
signing off construction completion or the defects and liability period when the asset is in poor condition
not properly budgeting for and overseeing maintenance
poor quality planting