Green infrastructure has a reputation for increased costs compared to traditional or “grey” infrastructure projects. That reputation is not always deserved.

The American Society of Landscape Architects, American Rivers, ECONorthwest, and the Water Environment Federation co-authored a 2012 study that examined 479 green infrastructure projects across the U.S. Their report states that only about one-fourth of the projects cost more than comparable “grey” infrastructure projects. Of the remaining projects, 31 per cent cost about the same while 44 per cent actually cost less than grey projects.

The term “green infrastructure” comprises many varied components. At the University of Melbourne, the Green Infrastructure Research Group (GIRG) defines green infrastructure as:

“The network of natural and designed vegetation within our cities and towns, in both public and private domains. It includes public parks, recreation areas, remnant vegetation, residential gardens and street trees, as well as innovative urban greening technologies such as green roofs, green walls and rain gardens.”

The GIRG studies green infrastructure to determine “the effectiveness of green roofs and more traditional green infrastructure elements such as street trees as a cost-effective and socially acceptable climate change adaptation strategy for buildings, communities and cities.”

Projects the group is studying include:

● Green roofs
● Green walls
● Parks, gardens, golf courses
● Urban agriculture
● Urban woodlands
● Suburban street trees
● Urban street trees
● Water-sensitive urban design, such as porous pavement, rain gardens, and bioswales.

Growing cities need new approaches

Increasing population combined with smart growth strategies is leading to denser cities worldwide, with already overtaxed grey infrastructure systems. In many cities, antiquated sewer systems quickly become overloaded during rains and can discharge raw sewage into waterways. Green infrastructure projects can manage stormwater, diverting it to bioswales and rain gardens so it filters through the soil and stays out of the sewer system. This approach can also deliver cleaner water to streams, ponds, wetlands, and bays that previously received polluted runoff.

Green infrastructure such as street trees, urban woodlands, and parks can mitigate urban heat islands, sequester carbon, clean the air of pollutants, and provide the connection to green space that humans need. In addition, green infrastructure can be regenerative, such as parks that sequester carbon and produce oxygen. Adding green roofs, bioswales and other features which supplement or even take the place of grey infrastructure can be more functional and more cost effective than grey infrastructure alone.

Green infrastructure in Sydney

The City of Sydney recently updated its policy for green roofs and walls. In recognition of the environmental and aesthetic benefits of green infrastructure, the new policy now encourages green roofs and walls for homes and businesses. The city is also looking to support businesses that install green roofs and walls by “investing in research and technology, reducing installation costs and educating the community on the benefits of green roofs and walls.”

The city currently enjoys about 15 per cent green canopy coverage, with a goal of bumping that to 23.5 per cent by 2030.

 Green Parks

Another type of green infrastructure project in Sydney is the stormwater harvesting project in Sydney Park’s wetlands. Using water-sensitive urban design elements such as a bioretention system and some sweeping natural forms, the project improves water quality, provides flood mitigation, and blends naturally with the adjacent wetlands.

 Green infrastructure professionals from around the world will travel to Sydney for the World Green Infrastructure Network 2014 Congress from October 7–10, 2014.