ASLA Releases More than 475 Green Infrastructure Case Studies


The Environmental Protection Agency (E.P.A.) recently started a national rulemaking process, with the goal of creating a new, comprehensive program to reduce stormwater runoff. The E.P.A. announced that during this rulemaking it will evaluate green infrastructure design techniques that mimic natural processes to evapo-transpire, infiltrate and recharge, and harvest and re-use stormwater. Typical green infrastructure systems for managing stormwater include green roofs and walls, bioswales, rain gardens, bio-retention ponds, and permeable pavements. Street and park trees also provide great stormwater management benefits.

The E.P.A. asked ASLA to collect case studies on projects that successfully and sustainably manage stormwater. More than 300 ASLA members responded with 479 case studies from 43 states, the District of Columbia, and Canada. Not only do these projects showcase landscape architecture, but they also demonstrate to policymakers the value of creating green infrastructure policies and investing in these approaches.

Green infrastructure and low-impact development (LID) approaches, which are less costly than traditional grey infrastructure projects, can save communities millions of dollars each year and improve the quality of our nation’s water supply. Also, these systems provide multiple benefits: They store carbon, provide wildlife habitat, and clean and cool the air, creating more livable communities in the process.  

Here’s an analysis of the 479 stormwater case studies:

Project type:
Institutional/Education — 21.5% 
Open Space/Park  — 21.3%
Other  — 17.6%
Transportation Corridor/Streetscape  — 11.9%
Commercial  — 8.6%
Single Family Residential  — 5.5%
Government Complex —  4.2%
Multifamily Residential  — 3.7%
Open Space-Garden/Arboretum  — 2.9%
Mixed Use  — 1.8%
Industrial  — 1.1%

Estimated cost of green infrastructure:
$100,000–$500,000 — 29.2%
$1,000,000–$5,000,000 — 22.1%
$500,000–$1,000,000 — 13.2%
$50,000–$100,000 — 12.9%
$10,000–$50,000 — 12.1%
$10,000 — 3.5%

Green infrastructure type:
Retrofit of existing property — 50.7%
New development — 30.7%
Redevelopment project — 18.6%

How much impervious area was managed?
1 acre to 5 acres — 34.5%
5,000 sq/ft to 1 acre — 31.3%
greater than 5 acres — 24.8%
less than 5,000 sq/ft — 9.5% 

Did use of green infrastructure increase costs?
Reduced costs — 44.1%
Did not influence costs — 31.4.7%
Increased costs — 24.5%

Green infrastructure design approaches used:
Bioswale — 62.1%
Rain garden — 53.2%
Bioretention facility — 50.8%
Permeable pavement systems — 47.3%
Curb cuts — 37.9%
Cistern — 21.2%
Downspout removal — 18.1%
Green roof — 16.5%
Rain barrels — 5.7%

Other facts about the case studies:

  • 55 percent of the projects were designed to meet a local ordinance.
  • 88 percent of local regulators were supportive of the green infrastructure projects submitted.
  • 68 percent of the projects received local public funding.

Along with this effort, ASLA continues to work with Natural Resources Defense Council (NRDC) and American Rivers to promote green infrastructure policies.

View the 479 case studies organized by state.

Also, to learn more about green infrastructure, delve into Philadelphia’s cutting-edge program, watch an animation, and read an interview with Congresswoman Donna Edwards on her legislative proposal.

Image credit: Seattle Green Factor. City of Seattle Department of Planning and Development / Vulcan

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