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ASLA Offers Guide to Green Infrastructure

The goal of the earliest design stages for Richland College in Dallas was that every drop of rain would be captured in bioswales, directed to cisterns and used on site. The goal of the landscape design and subsequent planning was to minimize impact on the downstream watershed.
Photo: Charles Smith, for Linda Tycher & Associates, Inc.

The American Society of Landscape Architects (ASLA) has launched a guide that explains the many benefits of "green infrastructure" -- designed systems that harness nature to create proven benefits for communities
and the environment.

"Green" infrastructure includes park systems, urban forests, wildlife habitat and corridors, green roofs and green walls. These infrastructures protect communities against flooding, excessive heat, and help to improve air and water quality.

That nature is also infrastructure isn't new, but it's now more widely understood to be true, according to Nancy Somerville, Hon. ASLA, executive vice president and CEO of ASLA. Researchers are amassing evidence to demonstrate that green infrastructure is often more cost-effective than outmoded models of grey infrastructure -
a term used for the concrete tunnels created to move water--and also provides far more benefits for both people
and the environment.

"At all scales, green infrastructure provides real ecological, economic, and social benefits," asserts Somerville.
"Cities need as much green infrastructure as possible, and landscape architects are implementing it in communities
across the country."

Among the benefits of green infrastructure is sequestering atmospheric carbon dioxide (CO2); filtering air and water pollutants; stabilizing soil to prevent or reduce erosion; providing wildlife habitat; decreasing solar heat gain; lowering the public cost of stormwater management infrastructure and providing flood control; and reducing energy use through passive heating and cooling. In contrast, grey infrastructure usually provides just a single benefit.

The guide, part of ASLA's series of sustainable design resource guides and toolkits, includes hundreds of research studies by leading scientists, news articles and case studies on innovative uses of green infrastructure.

Resources are organized into seven sections:

Overview: The Benefits
Forests & Nature Reserves
Wildlife Habitat & Corridors
Constructed Wetlands
Green Streets
Green Roofs & Walls

There are descriptions of the many types of green infrastructure, quantifiable benefits, and the role of
landscape architects.

In the cities section there are two powerful examples of the benefits of green infrastructure:

In Philadelphia, a comprehensive green infrastructure approach is estimated to cost just $1.2 billion over the next 25 years, compared to over $6 billion for "grey" infrastructure. The city calculates up to 1.5 billion pounds of carbon dioxide emission to be avoided or absorbed through green infrastructure each year, the equivalent of removing close to 3,400 vehicles from roadways. The city also estimates 20 deaths due to asthma will be avoided, and 250 fewer work or school days will be missed. Lastly, the economic benefits are also outstanding: the new greenery will increase property values by $390 million over 45 years, also boosting the property taxes the city takes in.

New York City's green infrastructure plan is projected to cost $1.5 billion less than a comparable grey infrastructure approach. Green stormwater management alone will save $1 billion, at a cost of about $0.15 less per gallon. Also, sustainability benefits in NYC range from $139-418 million over the 20-year life of the project, depending on measures implemented. The plan estimates that "every fully vegetated acre of green infrastructure would provide total annual benefits of $8.522 in reduced energy demand, $166 in reduced CO2 emissions, $1,044 in improved air quality, and $4,725 in increased property value."

Landscape architects were deeply involved in the creation and management of the Philadelphia and New York City plans. Many more contribute to making these plans a reality by planning and designing urban forests, parks and green roofs and walls.

ASLA says the guide is a living resource, and invites anyone to submit additional research studies, news articles and case studies on green infrastructure (e-mail ASLA at

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October 21, 2019, 2:17 pm PDT

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