Green infrastructure

What is green infrastructure?

Green infrastructure can have many forms, such as:

• a widened and replanted stream bank that helps to manage floodwater
• a permeable paved path that reduces the amount of stormwater entering the piped system
• a row of street trees or a whole urban forest
• a green roof or vertical wall
• a rain garden or an urban farm.

Broadly, the term refers to any system that fuses natural and built environments to reduce the environmental impact of core infrastructure and the built environment.

Further information on green infrastructure is available at:

United States Environmental Protection Agency website

ESRI Living Atlas of the World website

Examples of green infrastructure

Green roof and swale at the Auckland Botanic Gardens

The Auckland Botanic Gardens has planted native plants on the roof of its public toilet facilities, that absorb and treat rainwater.

This 'living roof' is combined with a vegetated swale – an area designed to manage water run-off – which further slows down and filters the flow of water, delivering relatively clean water to lakes in the gardens.

The swale works by increasing the time available for large sediment particles and contaminants to settle and be absorbed by the soils and plants.

Natural stormwater solution, Te Auaunga Awa / Oakley Creek

Significant flooding issues affected a 1.3 kilometre section of Te Auaunga Awa / Oakley Creek in Mt Roskill and Mt Albert. To overcome these issues, Auckland Council replaced the existing concrete channel with a wider, naturalised stream channel.

The use of natural plants – native trees, ferns and flaxes – increased the water-carrying capacity of the watercourse and provided greater potential for stormwater to naturally soak into the ground.

This had several effects:

• reduced the effects of flooding on surrounding areas
• provided natural filtration and cleaning of collected stormwater
• reduced the pressure on stormwater systems further downstream.

The landscaping and planting was designed to support the rehabilitation and restoration of native ecosystems in the area. It also established an accessible river park for the local communities.

By using a natural stormwater solution with greater and more flexible carrying capacity, the potential for climate change and population growth to increase the rate and intensity of flooding events was also alleviated.

The project involved:

• increasing the stream capacity by removing the existing concrete channel and providing a wider naturalised stream channel
• rehabilitating of Te Auaunga Awa / Oakley Creek through landscaping, planting and water quality improvement
• replacing Beagle Ave and Richardson Road culverts with new bridges to improve stormwater capacity
• constructing two new pedestrian bridges across the stream
• upgrading the park, including new paths and cycleways, an outdoor classroom and adventure playground and traditional Māori play elements.

Urban forests

Green infrastructure is often thought of as specific and isolated things, such as a green roof, or a rain garden. However, bigger systems can also support green infrastructure objectives.

For example, urban forest initiatives that focus on increasing the overall tree canopy cover of cities also deliver a range of benefits to the environment and local communities. Increasing the tree canopy can reduce the urban heat island effect, deliver better air quality and improve residents' mental and physical wellbeing.

The Auckland Mayor's Million Trees Programme aims to plan a million trees across Auckland over a three year period.

Auckland Council is also currently developing an Urban Forest Strategy that seeks to:

• green urban Auckland
• offset carbon emissions
• protect water quality by planting along rivers and coastlines
• improve our living environment.