WSD promotes the protection of ecosystem resources, including existing vegetation and vulnerable soils.
The construction phase of development requires best practice methodologies to ensure this outcome.
Implementing a detailed site survey (including a topo survey with mark-out) will allow a limit of work around areas to be protected and allow set out of access points and staging areas. This reduces the area of the site that is left 'open' and directs specific areas for construction traffic. In general, the lightest equipment and the fewest passes necessary should be applied to achieve site works.
Construction practices should also protect rootzones around trees, establish wind protection around remnant vegetation, protect groundwater interface for wetland areas, and retain 'clean water' surface runoff onto existing vegetation, where appropriate. Sediment and erosion controls should follow best practice guidance in accordance with Auckland Regional Council Technical Publication TP90 Erosion and Sediment Control Guidelines for Land Disturbing Activities in the Auckland Region (1999).
To ensure appropriate environmental management of a construction site, it is imperative to have representation from the project design team at pre-determined control points of the construction phase. Contractors undertaking developments with WSD approaches should be experienced and/or show a clear understanding through a detailed construction methodology and programme. The construction methodology and programme submitted in the tender phase should be given a high weighting, in reference to expectations for best practice.
Bioengineering uses natural construction materials to stabilise slopes and overland flowpaths.
The approach starts with slope profiles that emulate a natural morphology, applies biodegradable materials for short-term protection, and utilises planting to achieve long-term regenerative slope stabilisation. Bioengineering approaches are flexible enough to allow natural systems to find their own equilibrium over time, and as environments change.
During the operational phase of development, there may still be high sediment loads from unexpected erosion in the catchment or from modifications to individual sites.
An increase in fine sediment loads can cause critical failure in pervious paving or bioretention practices and should be controlled. Possible approaches to minimising sediment and contaminants entering stormwater runoff during the operational phase, thereby increasing the lifespan of stormwater management devices, include:
- Education of homeowners and local contractors on the function of WSD stormwater management strategies and practices
- Erosion and sediment control plans (ESCP) for individual sites appended to ownership deeds
- Temporary 'capping' of stormwater practices with a sand layer, rolled turf or geotextile, and ideally a combination of these, to protect practices from localised earthworks in the contributing catchment
- Filter strips to remove coarse sediments in stormwater prior to entering bioretention practices and to additionally protect these practices from accidental contaminant spills
- Landscape maintenance that reduces fertiliser and pesticide use
- Encouraging the use of inert materials in building construction and isolate treated timber and galvanised materials from stormwater runoff
- Provision of control pads for specific treatment systems
- Training contractors to maintain WSD approaches
- Access to private lots for maintenance of public stormwater management practices
- Provision of integrated maintenance contracts for roading, open space and stormwater practices including maintenance priorities and specifications
- Regular road sweeping, catchpit clearance and litter removal from swales and bioretention
- Following storm events, checking WSD devices for performance and operation relative to design intent.