Here’s a good reason to build rain gardens and green roofs, and to plant and protect trees: It’ll save you money. That’s the conclusion of a new report from the American Association of Landscape Architects called “Banking on Green.”

The study surveyed green stormwater projects from across the US, plus a handful from Canada, and determined that in 41 percent of the cases, the environmentally friendly approach was cheaper than if a conventional solution for runoff was used.

The work builds on previous research by the US Environmental Protection Agency, ECONorthwest, the University of New Hampshire, Seattle Public Utilities, and others who have come to similar conclusions about cost savings.

The “Banking on Green” report also provides a list of 479 green infrastructure case studies organized by state. It does a nice job compiling current research that explains and quantifies the many problems caused by polluted runoff, and it offers the most effective solutions for addressing these problems. But it’s not everything I could hope for.

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  • Craving Rigor

    The report, whose other authors include American Rivers, the Water Environment
    Federation, ECONorthwest, and American Association of Landscape Architects, relies on case studies submitted by members of the landscape association. So it’s not a random, or even necessarily representative, sample of green stormwater projects.

    And in reviewing some of the 479 case studies submitted, I noticed that many don’t include green vs. gray infrastructure cost comparisons, so that 41 percent number must come from a subset. It is worth noting that nearly 25 percent of the projects reported that it was more expensive to go green, and 31 percent said there was no cost difference, so it’s not like only the rosiest cases made the self-selecting cut.

    Kids play along rain garden

    Kids play along rain garden at youth center at Joint Base Lewis-McChord near Tacoma; Flickr user JBLM.

    But it’s not like the authors of the report are trying to hide the limitations of their publication. In fact, the authors state in the second sentence of the report that “(i)t’s not intended to be an academic or technical document, but instead to be an ‘easy to read’ compendium of current experiences, analysis and knowledge.” On that, it delivers.

    The trouble is it would be so wonderfully useful to have a scientifically robust cost comparison performed, as fear about higher costs is cited again and again as one of the top hurdles to more widespread use of green solutions.

    Regardless, the report offers some nice project-by-project comparisons, including these examples:

    • “Chicago’s experience with its Green Alleys programs has shown that investing in permeable pavements, downspout disconnection, rain barrels, and tree planting are estimated to be 3 to 6 times more effective in managing stormwater per $1,000 invested than conventional methods.”
    • “Data from Seattle Public Utilities….indicate that the designs incorporating green infrastructure cost $217,253 less than a conventional street in overall construction costs and yield a cost savings equivalent to $329 per square foot.”
    • “The City of Portland, Oregon has integrated green and gray approaches to stormwater management in its CSO (combined sewer overflow) abatement program. A cost-effectiveness analysis….demonstrated that downspout disconnections, curb extensions that include vegetated swales, and parking lot infiltration were among the most cost-effective options (including conventional) for meeting CSO abatement goals. The costs for these approaches ranged from $0.89 to $4.08 per gallon removed.”

    Why green pencils out

    Seattle rain garden

    Seattle rain garden; Lisa Stiffler.

    The report goes on to explain where the construction and maintenance cost savings associated with environmentally friendly solutions to runoff come from, as well as the savings associated with better performance and other less obvious benefits.

    Green infrastructure can be cheaper to build because it doesn’t require expensive curb and drain systems or pipes and holding tanks. The report cites a 2003 US Department of Housing and Urban Development study that, while clearly dated, found that a conventional stormwater conveyance system of curbs and gutters typically ranges between $40–$50 per linear foot.

    Green infrastructure maintenance and replacement costs also are potentially less expensive. While green systems such as ecoroofs and rain gardens will likely require more routine, low intensity maintenance, they’re less likely to require big repairs and complete replacements. Ecoroofs should last longer as they protect roofing material from solar damage, which is a key source of wear and tear. Rain gardens have been shown to perform better over time, while conventional drain and tank systems wear out.

    The green systems can do a better job removing pollutants from the runoff. A recent study from Yakima examining permeable pavement found that stormwater that filtered through porous roadways contained lower amounts of toxic metals. Ongoing studies at Washington State University’s Puyallup Low Impact Development Research Program are working to quantify pollution treatment provided by rain gardens and porous asphalt.

    Other benefits cited:

    • Energy savings through improved insulation that comes with green roofs
    • Reduced heat-island effects thanks to increased vegetation
    • Reduced flooding when water infiltrates the ground, and recharge of groundwater supplies
    • Improved air quality due to trees and other vegetation filtering the air

    In 2010 Portland released its own study quantifying the less tangible effects of green infrastructure including health benefits, energy savings, and creating communities that are more livable.

    Speaking of Portland, the report includes a bunch of really interesting projects from the City of Roses. In particular, there were some great looking case studies showing rain gardens along roadsides — a green strategy that’s taken some heat and created some entrenched skepticism.

    And that leads me to another frustration with the report: couldn’t the projects have been presented in a more searchable format? It’s fine to have them listed by state, but I’d love to be able to zero in on certain types of projects, in this case roadside rain gardens, rather than clicking on each case study to figure out what kind of infrastructure it is.

    But all of the criticism aside, it’s great to see such a well articulated compilation of green stormwater projects and their economic, environmental, and societal benefits.