SMPs are sometimes prepared in conjunction with 'structure' or 'comprehensive development' plans (CDP). These are spatially-based land use planning documents that take into account the ecological and hydrological gradients across the catchment to provide an appropriate development response, potentially including clustered and mixed use development approaches.
Catchment headwaters
Headwater environments make up a significant proportion of Auckland's land area, due to the prevalence of low order streams and intermittent gullies within the region. The steep and intermittent nature of these streams requires vegetation to protect against erosion and to attenuate stormwater runoff to prevent it rapidly concentrating in overland flow paths.
Stormwater management in the upper catchment is often associated with source control, including capture and re-use of rainwater, or retention and treatment in bioretention practices. Groundwater infiltration is also a relevant stormwater management response within Auckland's volcanic fields. Auckland is fortunate to have retained open space associated with many of its volcanic cones, which protects steep slopes and aquifer recharge areas.
The steep nature of headwaters, as well as the need for resource protection, lends itself to a clustered form of urban development, where dense residential or institutional buildings are dominated by planted slopes and generous open space (refer to Figure 27). In rural areas, woodlots and other longer term productive landscapes may be an appropriate response to steeper slopes.
Mid catchment
The mid catchment is generally associated with rolling slopes where stormwater runoff coalesces into larger stream and wetland systems. These riparian systems require the protection of planted buffers and appropriate land management. This protects the natural drainage patterns through the mid slopes and upper valleys of urban environments, which can provide important open space connections along low valley gradients.
Stream and wetland widths can vary according to adjacent land use, with thick vegetation supporting narrow stream corridors in dense urban areas, and wider and more open floodplain environments in suburban neighbourhoods allowing for a combination of diverse riparian habitats and open space opportunities.
Lowland and coastal environments
The primary WSD issues in the lower catchment are protection of coastal and estuarine environments, and the prevention of flooding impacts. In terms of urban form, lowland environments are usually undulating to flat areas, which provide optimal site conditions for large scale, dense and specialised urban typologies such as commercial centres, ports and industrial zones.
The resulting land use pattern is a contrasting environment between the built form and open spaces. Wide open spaces in association with floodplains, estuaries and recreational open space sit directly beside dense development or industrial and commercial precincts.
Flat environments often require widely distributed WSD responses such as raingardens and swales. Wetland environments are also common in flat environments, where they can accommodate surface flooding and high groundwater levels.
Careful planning is required to minimise environmental impacts for greenfield situations, and to provide remediation of ecosystems if brownfield development opportunities arise.
Reconciling the urban grid
Urban design principles, discussed previously in Section A, promote a grid-like street pattern to provide for greater community connectivity, traffic dispersal and wayfinding. However, there is inevitably a creative tension between the dendritic pattern of natural stream systems and the rigid street patterns of urban form. The means to reconcile these patterns occurs at the fundamental level of movement within the site. It is a matter of interlacing natural and built elements in the most appropriate ways to rationalise objectives for each system. Some potential responses may include (illustrated in Figure 28):
- Adapting the urban street grid pattern in response to existing topography and landform
- Creating 'naturalised' drainage patterns to receive runoff from increased imperviousness, placed along boundaries and within streetscapes
- Allowing flexibility for both road carriage width and riparian buffers
- At strategic stream crossing points, favouring pedestrian and bike crossings over roads
- Assisting vehicle movements by prioritising street connections and potential stream crossings based on neighbourhood density and travel distances
- Creating streetscapes and street alignments which draw from and extend riparian open spaces
- Increasing neighbourhood cycle/pedestrian connections through stormwater reserves
- Mitigating the occupation of the floodplain by road crossings by enhancing stream habitats elsewhere (internal to blocks)
- Providing for wider stream corridors at road crossings to accommodate bridge abutments, landscape transitions, and habitat refuges above and below culverts.