Pioneering Low Impact Design
The urbanisation of the Long Bay catchment has been a long time coming. After an Environmental Court hearing in 1996, ten years of planning to preparing the Long Bay Structure Plan, a Council hearing in 2005 and second Environmental Court process that lasted from 2007 to 2011, the Long Bay Structure Plan became operative on the 6th of October, 2011.
The Long Bay Structure Plan allows for 360 hectares of greenfield development to house 7,500 people and is one of Auckland’s largest greenfield developments.
The development fronts onto the Long Bay Regional Park and has two streams, The Awaruku Stream and Vaughan’s Stream, which discharge directly into the Long Bay/Okura Marine Reserve.
To protect and preserve the ecological values in Long Bay, Low Impact Design (LID) practices have been incorporated throughout the development. The guiding principle behind LID is that a newly developed site should have as little impact on the natural state of a site as possible. This means mimicking the natural hydrology as closely as possible, i.e., where would stormwater flows naturally go and where would they pond in small and large rainfall events? How much water is generated before development and after development? LID also targets pollutant removal and so places an emphasis both on the amount of stormwater and the quality of stormwater.
For the Long Bay development, stormwater design was aligned with LID principles in the following way:
- Minimising site disturbance and earth working activities over the development area
- Managing stormwater at source through rain tanks for non-potable reuse, permeable paving instead of concrete for driveways and parking areas, raingardens, swales and local ponds
- Reducing impervious coverage on site so that less area will need mitigation provided for and more area will be available for stormwater treatment devices. In Long Bay, this included reducing carriageway widths on roads and allowing space for the stormwater management devices such as raingardens
These devices become a part of the streetscape, providing amenity value, and at the same time treating stormwater runoff to a level suitable for discharge into the environment. Raingardens and wetlands were used to provide treatment and volume reduction. The devices used were economical and cost-effective to construct and were designed to ensure minimal maintenance with regards to planting. The stormwater devices worked together providing scour protection prior to discharge into the sensitive marine environment. At the time this was a radical approach to a new development and was well ahead of the Auckland Unitary Plan and SMAF rules that make this approach now a relatively standard affair. Woods have and continue to look at how we can improve the outcomes and performance of our clients’ development and help them realise the full potential of their projects.
Engineering Manager - Senior Associate