A site layout comprises a number of elements that make up the public and private domain, as shown in Figure 29.
These include the building, the landscape yard, the street and the open space. WSD principles can be applied to each of these elements.
The private lot
Architecture and footprint
The following WSD treatment approaches can be applied within the footprint of buildings and structures:
- Combine the footprints of garages, utilities and ancillary structures to reduce impervious surfaces
- Provide an architectural response to slopes and vulnerable soils, e.g. pole or terraced housing which limits the earthworks required to accommodate the building
- Provide for flexible internal layouts of attached or semi-attached housing typologies to provide for diverse family groups and increased occupancy across land area
- Capture stormwater for re-use in buildings
- Use inert materials for construction that will not contribute contaminants to stormwater
- Consider living roofs, living walls and planter boxes to attenuate and treat stormwater.
The yard can be a useable open space or a buffer to adjacent land use. It may include private, semi-private, or communally operated areas. Yards can receive stormwater runoff as passive irrigation and contribute to stormwater management in the following ways:
- Share driveways between house lots to reduce impervious areas
- Utilise pervious paving options for drives and paths, and direct stormwater runoff from these surfaces to landscape areas
- Direct overflow from raintanks to purpose-built landscape areas as passive irrigation
- Utilise hedges, swales or filter strips to define boundaries
- Buffer existing natural areas
- Minimise fertiliser and pesticide inputs for landscape maintenance
- Investigate 'no mow' options using native plant substitutes
- Investigate the potential for communal overland flow paths, or even small streams across neighbouring yards
- Use tree planting to define boundaries, as summer shade, or to moderate prevailing winds, while also contributing a stormwater management function
- Investigate opportunities to direct stormwater runoff to raingardens and infiltration basins.
WSD streetsLaneways and pedestrian-oriented communities
WSD approaches can re-invent the function of streets in our communities to be lineal open spaces, pedestrian friendly environments and living ecosystems. Directing stormwater runoff to street trees and landscape berms not only delivers at-source treatment of stormwater runoff, it also irrigates and fertilises these plants.
The design of 'living street' environments can incorporate aspects of development such as stormwater management requirements, roading hierarchy, priority of transport mode, neighbourhood character and intersecting natural systems. For all WSD treatments, safety should be considered for street environments, including visibility for cars and pedestrians, response to road speeds, and 'turn off' areas for cyclists and pedestrians to escape erratic drivers.
Rural roads usually have increased speeds and less provision for amenity planting. However, there is still potential to enhance planting of swales and filter strips to reduce erosion and sediment entrainment. Parallel wetland systems can be located at the intersection of swales and stream environments to reduce instream erosion and provide further stormwater treatment (refer to Figure 30).
Production tree species can be included alongside swales or encouraged on adjacent boundaries to intercept rainfall, treat nitrogen in groundwater, and provide partial shade. However, tree planting alongside roads should allow for sunlight to pass through in order to foster plant growth in swales and to reduce the likelihood of frost on road surfaces.
Park streets refer to street environments that are integrated with adjacent open space areas, including stream corridors and wetlands. Park streets generally have a higher landscape amenity that can allow for appropriate vegetated WSD approaches.
There are examples of traffic-free communities in New Zealand and overseas, where car parking is placed outside of planned communities and generous access is provided for pedestrians and cycles. Another model is a pedestrian-oriented network where pedestrians and cyclists have priority access along building fronts where there are no driveways, while short feeder lanes provide automobile access at the back of houses.
These back lanes are often shared surfaces (with access for both pedestrians and automobiles) that act as semi-private spaces to connect residents within a block (refer to Figure 31). From a WSD perspective a low traffic laneway provides opportunities for pervious paving, above ground detention and overland flow to landscape areas. By removing parking from the front street, it reduces driveways and the carriageway on main roads, providing for more cycleways, street trees and landscape areas.
Roadways in industrial areas are often very wide to accommodate both extended carriageways and landscape berms. These streets may have sufficient space to accommodate open channels or lineal wetlands. WSD elements can be incorporated into berms or combined with landscape yards of individual lots.
Open channels provide the equivalent ecological function of intermittent streams, which are often lost to accommodate industrial lots. These watercourses can provide for increased flow capacity to reduce flooding risk. Vegetated stormwater features in general can play a part in a spill response, to capture and isolate contaminants before they reach the reticulated network and the receiving environment.
The installation of swales or lineal raingardens in industrial roads must accommodate turning circles for larger vehicles. These can be reduced through shared access points and internal private through-roads (refer to Figure 35). Internal road systems between industrial blocks can reduce traffic circulation requirements for individual lots, which can remove impervious surface requirements and optimise useable land area.
Garden streets / homezones
These streets, with the equivalent traffic movements of a 'neighbourhood' street, intentionally blur the distinction between streets, open spaces and private yards (refer to Figure 32). Ownership and management of the areas must be agreed between public and private entities. There is significant potential to integrate WSD stormwater responses into garden streets, including the following measures:
Combine automobile and pedestrian movement on the carriageway as a cue for lower speeds and to increase landscape areas in place of footpaths
Redirect or 'choke' the carriageway at specific junctures to slow traffic by increasing the extent of landscape elements, such as raingardens or street trees
Extend streetscapes across private lots and public open space to blur the distinction between roads and neighbourhood. This provides opportunities to retain existing vegetation and landform features as part of the roading corridor.
Provide shared surfaces where the road is a single kerb-less plane (described in further detail opposite). This requires the redirection of stormwater to multiple landscape features or pervious areas, since kerb and gutter systems are no longer applicable.
Provide for diffuse stormwater flows to landscape areas to allow passive irrigation
Provide overland flow paths contained within landscape areas and away from carriageways.
Shared space environments remove conventional traffic elements such as kerbs to re-prioritise pedestrians above vehicle movement. This may be accomplished in a number of ways, but generally these environments remove the visual cues defining a carriageway such as grade changes, signs, bollards, road markings and lineal berms in order to redirect driver behaviour.
The concept of shared space is based on civility and equitable use of public open space by all users. Shared spaces create an environment that encourages all users to think responsibly about the needs of others. Shared spaces generally function in street environments with less than 150 cars per hour at peak times (Boffa Miskell, 2010).
Shared space provides an opportunity for pedestrians to engage with a wider public realm and a unified space. In this way shared surfaces can be utilised for recreation and gathering. In combination with the removal of kerb and gutter systems, a WSD response is to direct stormwater to multiple landscape features or pervious areas for treatment and/or passive irrigation (refer to Figure 33).
WSD integration with open space
Public open space areas can act as default stormwater management areas by receiving stormwater runoff from adjacent impervious surfaces, as illustrated in Figure 34. Consideration needs to be given to the impact stormwater management structures can have on the amenity and values of the open space and its users. Stormwater reserves should provide the other functions of open space such as natural habitat, public amenity and recreation opportunities.
Combining public open space and stormwater function requires an integrated design approach between asset groups, community stakeholders, and operation and maintenance personnel. Some key considerations are provided below:
- Grade open spaces to allow recreation as well as stormwater attenuation/detention
- Provide pathways with appropriate width, cross slopes and drainage
- Keep structures above the 100 year ARI flood event for safety and to prevent water damage
- Limit the stormwater detention function of formal activity areas to less than 24 hours for a 2 year ARI event
- Design stormwater features that provide for landscape amenity, natural character values, social interaction and education/interpretation as appropriate
- Provide physical and/or visual access as appropriate to natural wetland environments and constructed stormwater features. Integrate with maintenance access where possible.
- Design stormwater management features to augment and/or buffer existing ecosystem functions and values
- Promote biodiversity from wetland to upland environments
- Include WSD responses to hard surfaces and structures such as car parking
- Design swales and watercourses so that they resist erosion and minimise maintenance requirements
- Where overland flow paths are accessible to the public (roads and pedestrian routes) AC CoP specifies a minimum depth of 200 mm and a maximum velocity of 0.6 m/s (see CoP 188.8.131.52).
- Rehabilitate soils and increase regenerating vegetation within open spaces to enhance stormwater attenuation potential
- Optimise the potential for stormwater and its entrained nutrients to be used as passive irrigation for open space planting
- Ensure maintenance regimes avoid close mowing for all areas, and place controls on the application of fertilisers, pesticides and herbicides
- Seek to connect discreet and separated open space areas within a community by linking through covenanted private land and/or 'living street' environments.
Industrial and contaminated sites
Contamination of soils can occur as a result of agricultural chemicals, industrial processing, vehicle use, storing of hazardous substances, dumping, and migration of contaminants from off-site. Where contaminants are present in the soil or groundwater, the risks may include short-term toxicity, long-term bioaccumulation by plants and animals, or unpredictable synergistic effects in the environment. In these instances, monitoring at variable groundwater levels and at various locations should be undertaken to determine whether to cap, export or phytoremediate contaminants.
In a site that is storing or using contaminants of concern, the potential source should be isolated through rain cover or similar, and any stormwater runoff generated should be separated either to an appropriate discharge location, or to storage for re-use in industrial processes. Part of stormwater management in this instance is appropriate pollution prevention and spill response plans.
Decentralised and discrete stormwater treatment practices such as gross pollutant traps, sand filters, swales or raingardens are appropriate to allow for localised spill containment without disabling wider stormwater systems. The separation of an industrial site into multiple sub-catchments also offers site flexibility for future tenants of the site.
Impervious surfaces are significant in industrial sites. However, the efficient use of impervious surfaces in industrial precincts can be provided by shared kerb breaks from main roads to increase landscape berms, and shared internal roads around buildings and between blocks to reduce turn-around requirements and increase available building footprints and staging areas (refer to Figure 35). Stormwater treatment practices such as swales or wetlands can also be shared across common boundaries.
A large volume of stormwater is available for capture and re-use in industrial sites, from large roof and paved areas. Alternatively, frame construction can be strengthened for 'extensive' living roof or living wall technologies. This might include a strip of planting on a strengthened area of rooftop to treat the first flush of contaminants, or brown roof technologies such as xeroscapes (arid, low soil plant systems).