How Green Streets Can Improve Your Stormwater Mitigation

By Ingrid Bauer, PE, LEED AP, B+C

Across the Country, agencies with all levels of government are employing a variety of methods to curb the negative impacts of stormwater runoff and restore natural water resources and processes. When selecting projects, it is important to not overlook options that work to address issues close to their source. While these projects can be challenging to implement due to right of way complexities and navigating public reaction, they can provide important benefits to multiple facets of community life.

In 2010, Entrix, Inc., prepared a study for Oregon’s Bureau of Environmental Services (BES) that attempted to quantify the health, energy and community livability benefits of Portland’s green infrastructure. The study investigated the effects of 700 green streets facilities that had been implemented at the time, accounting for a planned total of 920 green streets projects, which would manage flow from 92 acres. The results of the study projected that at the end of the planned green streets implementation, these 920 projects would lead to:

  • an overall peak stormwater flow reduction of 93%
  • an additional 68.2 million gallons of water per year re-entering groundwater systems
  • an 80% reduction in total suspended solids in the local waterways, and
  • an addition of 6.3 acres of habitat around the city for birds, insects, and other animals.

So, what are green streets?  Green streets are stormwater Best Management Practices (BMPs) constructed along roadways that use vegetation and soil to decrease, slow, and filter contaminants from stormwater runoff. They mimic nature’s typical processes to address street runoff quantity and quality at the source. During a rain event, runoff from the right-of-way is directed into the green street planting feature, sometimes using curb cuts, depressions, grates, or check dams. Special soil mixtures used in the planting areas are able to retain a significant amount of water, and some designs also use aggregate beneath the soil to collect even more runoff; the porous soil and aggregate allow runoff to infiltrate into the groundwater system both during and after a rain event. At this point, the infiltration process and uptake by plants help to cleanse the stormwater. Green streets features also have overflow outlets or underdrains so that planted areas do not fill beyond capacity, which could cause safety issues or damage the feature (plus, who wants to have to walk through puddles?).

In the study of Portland’s green streets, Entrix, Inc., also found that green streets can positively impact air quality.  They estimated that through the combined impacts of the vegetation and soils, as well as the reduced need for electricity at the city’s combined sewer system treatment plants, the planned 920 green streets features would provide an annual reduction of 40.8 pounds of PM10 (particulate matter less than 10 μm in diameter, which is “associated with adverse impacts on respiratory health”) and 304 tons of CO2 from the atmosphere.

Apart from providing environmental benefits, green streets improve the livability of the communities they are built in. Researchers from Portland State University conducted a study comparing a neighborhood with green streets projects to a nearby neighborhood without green streets using surveys to poll residents. 61% of respondents felt that green streets made their neighborhood a better place to live and nearly 75% felt that green streets made walking in their neighborhood more pleasant. Researchers noted that “respondents in green street areas were significantly less likely to say that driving is now more difficult in their neighborhood” and that there was essentially equal, or fewer concerns of parking to residents of green streets neighborhoods compared to those in the control neighborhoods. The Entrix, Inc., study similarly noted that green streets enhance mental and physical health of those who live and work in these areas and provide a 3-5% increase in home values.

There are also transportation safety benefits associated with green streets projects. Some green streets features are used to shrink intersections by utilizing excess space from oversized street lanes, making traffic at the intersection more predictable for motorists, cyclists, and pedestrians. These same features extend the sidewalk, shortening the crossing distance and lessening pedestrian exposure to lines of traffic. The open areas created by green streets features also allow for longer sight lines, allowing additional time for users to assess the intersection’s situation, reducing the potential for negative interactions among motorists, cyclists, and pedestrians. Studies in Philadelphia also showed that green infrastructure construction tends to cause less traffic disruption, in both length of time and physical area disturbed, than construction on traditional infrastructure.

Green streets are a viable and attractive option for stormwater management in urban and suburban communities. They handle storm water effectively by leveraging more natural processes while providing the added benefits of improving human health and community livability. Incorporating green streets BMPs when doing roadway projects or projects adjacent to roadways can help manage stormwater while also increasing curb appeal and making the community a greener and healthier place to live!


References

Ciarlo, Catherine. Portland Mayor’s Transportation Policy Director. “Green Streets: Making Our Streets Safe and Keeping Rivers Clean.” Mayor Sam Adams’s videos. 2010 http://vimeo.com/10272405

Dill, Jennifer, et al. “Demonstrating the Benefits of Green Streets for Active Aging: Final Report to EPA.” Portland State University, 2010. https://friendsoftrees.org/images/stories/pdf/psu_green_streets_active_aging_report.pdf

Entrix, Inc. “Portland’s Green Infrastructure: Quantifying the Health, Energy, and Community Livability Benefits.” BES, 2010. https://www.portlandoregon.gov/bes/article/298042

Kurtz, Tim. “Managing Street Runoff with Green Streets.” 2008 International Low Impact Development Conference: Low Impact Development for Urban Ecosystem and Habitat Protection. ASCE, 2008. https://ascelibrary.org/doi/10.1061/41009%28333%2920

Milwaukee Metropolitan Sewer District. “Fresh Coast, Green Solutions: Weaving Milwaukee’s Green & Gray Infrastructure into a Sustainable Future.” MMSD, 2009. https://www.mmsd.com/application/files/8514/8779/6598/SustainBookletweb1209.pdf

Oregon Environmental Council. “Stormwater Solutions: Turning Oregon’s Rain Back into a Resource.” OEC, 2007.http://www.oeconline.org/wp/wp-content/uploads/2014/11/Stormwater-Solutions-Report.pdf

Portland Bureau of Environmental Services. Portland Green Street Program, website. BES, 2012. http://www.portlandonline.com/bes/index.cfm?c=44407

Portland Bureau of Environmental Services. “Green Streets: Frequently Asked Questions.” BES, 2008. https://www.portlandoregon.gov/bes/article/319876

Stratus Consulting. “A Triple Bottom Line Assessment of Traditional and Green Infrastructure Options for Controlling CSO Events in Philadelphia’s Watersheds.” City of Philadelphia Water Department, 2009. https://www.michigan.gov/documents/dnr/tbl.assessmentgreenvstraditionalstormwatermgt_293337_7.pdf

USEPA. “Green Infrastructure Case Studies: Municipal Policies for Managing Stormwater with Green Infrastructure.” Office of Wetlands, Oceans, and Watersheds. Report EPA-841-F-10-0004. 2010. https://nepis.epa.gov/Exe/ZyNET.exe/P100FTEM.TXT?ZyActionD=ZyDocument&Client=EPA&Index=2006+Thru+2010&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C06thru10%5CTxt%5C00000033%5CP100FTEM.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL

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