It also seeks to protect headwater environments, which represent 90% of Auckland streams (O'Brien 1999). Headwater environments are ephemeral and intermittent watercourses upstream of permanent watercourses. A watercourse classification may be carried out (consult an ecologist) as part of the Site Assessment phase to determine the classification of watercourses in the development.
An environmental framework must take into account the relative values and functions of riparian systems from a catchment and regional perspective, as well as the vulnerability of these systems to catchment stressors. The framework looks at the long-term sustainability of these riparian systems, including providing for appropriate riparian buffers, flood mitigation and ecological value.
If streams are already affected by existing adverse catchment conditions, the project team may consider rehabilitation of a stream or increasing the stormwater management functions of these systems through some of the responses discussed below.
Promotion of continuous stream corridors
Greenways, also known as lineal parks, wildlife corridors or riverways, were previously discussed in Section B. They are lineal open spaces linking natural, cultural and recreational areas in coincidence with streams or other lineal landscape features. Greenways provide the framework to protect, conserve and link natural resources and open spaces, including fragmented urban habitats. An example of a greenway in the Auckland region is the Twin Streams project that aligned asset managers and community groups behind a collective vision for two significant Waitakere watercourses and their associated open space. Currently, greenways are being promoted by Auckland Transport and Local Boards for walkways and cycleways while including the "green" elements of streams, green infrastructure and ecological corridors where possible.
Stream corridors in Auckland are often marginal areas for built development due to flooding constraints and climatic conditions, but they can have significant value as open space linkages between coastal open space, ridgelines and volcanic cones.
Protecting and enhancing natural stream morphologies
Streams are dynamic systems that change frequently along their length through natural pool-riffle-run sequences (refer to Figure 16), and across their width from stream margin, to banks, floodplains and tributaries. To ensure a sustainable stream system, a project design team must consider the underlying geology, hydrology and ecology to provide for a stream in equilibrium with its floodplain and catchment.
WSD promotes the use of bioengineering approaches to stream restoration, which utilise natural materials working in combination with appropriate stream morphologies to detain and convey stream flows. Additionally, aquatic diversity can be deliberately included in stream restoration projects through purpose-built habitat or enhanced fish passage.
Promotion of riparian buffers
A riparian zone is the area of land adjacent to streams and rivers that is the transition between land and water (Becker et al., 2001). This includes land from the water's edge, stream banks and adjacent floodplains that are periodically inundated. Riparian buffers and natural floodplains can be accommodated within development as part of a broader open space network, or enhanced for an inherent stormwater management function.
It is appropriate to apply a flexible approach to riparian buffers accounting for the following attributes:
- Geotechnical stability of adjacent land
- Spring seepages, isolated wetlands and extent of flooding
- The values of existing riparian vegetation
- A sustainable buffer width to achieve minimal ongoing maintenance of weeds
- A predicted stream profile based on an urbanised catchment
- The predicted meander alignment of a stream
- Safe public access, including visibility
- Parallel stormwater management treatment opportunities
- Pedestrian and road crossing points
- Priority ecological connections for distribution of flora and fauna between catchments
- Stream habitat diversity.