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Auckland, New Zealand
Habitat and Biodiversity. Green streetscapes enhance urban biodiversity as native species provide habitats for birds, insects, and other species. Native vegetation is better suited to the rainfall of the local area. Enhancement of biodiversity in cities can increase environmental awareness among urban residents.
Water Quality. Green infrastructure improves stormwater quality by reducing the load of sediment, unwanted minerals, and other contaminants that are carried with runoff from impermeable surfaces.
Flow Management. Retaining runoff in landscaped areas and slowing the rate of flow from the catchment area reduces the risk of erosion of the soil bed. Slower
flow rates reduce stress on downstream waterways as well.
Natural Hydrology. Where local soils are suitable, rain gardens are used to treat stormwater before it permeates the groundwater.
Passive Irrigation. Directing stormwater to irrigate the planting reduces the need for manual watering and increases soil moisture.
Amenity and Landscape Design. Landscape design contributes to a city’s character and identity. Planting complements the built environment, softens appearance of hard surfaces,
and provides a visual screen.
Urban Cooling. Trees and green infrastructure provide significant reductions in urban temperatures. Large trees with good soil moisture can reduce local temperatures through shading and evapotranspiration. Trees can reduce air temperatures in parks and green areas by as much as 2–8°C, and they have been linked to the prevention of unnecessary loss of life during heatwaves.1
Encourage Outdoor Activity. Green cover encourages outdoor activity, including walking, cycling, and other recreation.
Air Quality. Vegetation improves air quality and reduces greenhouse gases. Trees remove carbon dioxide, nitrous oxides, sulphur dioxide, carbon monoxide, and ozone from the atmosphere. The most effective species in trapping pollutants are those with large leaf surface areas and high transpiration rates.
Energy. By reducing local temperatures and shading building surfaces, green infrastructure reduces the cooling demand of buildings, thus cutting energy needs.
Lifespan of Infrastructure. Green infrastructure complements grey infrastructure such as catch basins and drainage pipes, and lengthens the lifespan of grey infrastructure.
Water Systems. The impacts on drainage systems and the cost of managing erosion in waterways can be significant. Streets with green infrastructure slow the rate of runoff, reducing the pressure on these systems and lowering maintenance costs.
Property Values and Marketability. Street trees and green infrastructure enhance aesthetic qualities and provide a significant neighborhood amenity. Properties on tree-lined streets are valued at up to 30% more than those on streets without trees.2
Diagram showing bioswale cross-section with drainage pipes that connect to the larger stormwater collection system. The engineered soil mixture should consist of 5% maximum clay content, maintain a clearance of at least 1.5 m from the bottom of the bioswale to high groundwater table, raise the overflow/ bypass drain system above soil surface to manage storms larger than the water quality event, and discourage pedestrian trampling by using low curbs or barriers, or hardy vegetative ground covers.
1. Doick Kieron and Hutchings Tony, “Air temperature reduction by urban trees and green infrastructure” (Research Note, Forestry Commission, February 2013), accessed June 6, 2016, http://www.forestry.gov.uk/pdf/FCRN012.pdf/$FILE/FCRN012.pdf. Tara Zupancic, Westmacott Claire, and Bulthuis Mike, Impact of Green Space on Heat and Air Pollution (Vancouver, BC: David Suzuki Foundation, March 2015).
2. Dan Burden, “Urban Street Trees, 22 Benefits Specific Application,” accessed June 6, 2016, http://www.michigan.gov/documents/dnr/22_benefits_208084_7.pdf.2006.
Adapted by Global Street Design Guide published by Island Press.