With an average annual rainfall of 37 inches, it's no surprise that stormwater is one of Portland's biggest environmental challenges.
For over 10 years, the city has utilized a combination of policy, public education, and on-the-ground projects to incorporate natural functions into existing infrastructure to complement, enhance and strengthen its watersheds.
Their efforts have demonstrated how both new and existing impervious areas can be tailored to provide direct environmental benefits while being aesthetically integrated into the neighborhood streetscape.
Artistic touches, like the ornamental trench gate at right, are incorporated into many of Portland's green streets projects.
The Green Streets Program
"Green streets" are designed and landscaped areas along streets that collect stormwater runoff and allow it to soak into the ground as soil and plants filter pollutants. They work to:
- Reduce the amount of stormwater runoff that causes sewer overflows and flooding.
- Keep polluted stormwater out of rivers and streams. Portland's green street projects reduce peak stormwater flows by as much as 85 percent, stormwater volume by 60 percent, and pollution in runoff by up to 90 percent.
- Refresh groundwater supplies and help reduce urban heat islands that cause air pollution inversions.
- Create attractive streetscapes that enhance neighborhood livability by beautifying pedestrian areas and introducing park-like elements into urban neighborhoods;
Green streets can provide all these benefits and save money for sewer ratepayers and taxpayers. Traditional pipe and stormwater disposal systems can cost up to twice as much as green streets projects.
Learn more…
Examples of Green Street Technologies
Curb extensions
Curb extensions are created by carving out portions of the street’s parking zones and converting them into landscaped curb areas similar to the parkway. Curb extensions not only calm traffic and increase pedestrian safety, they are beautiful to look at and bring natural hydrologic functions back into the city.
Portland's award-winning curb extension project on NE Siskiyou Street (right) offers the added benefits of being simple to construct, maintenance-friendly, and cost effective.
Permeable Pavement
Permeable pavement (left) allows water to infiltrate the ground through the spaces between block pavers filled with fine rock.
Green roofs
In Portland, rooftops make up about one third of impervious surface area. Since 1996, more than 120 green roof projects (known in Portland as "ecoroofs") have been constructed, totaling approximately 10 acres.
Planters
Planters transform a street's pedestrian zone into attractive and sustainable stormwater management systems.
Rain Gardens
The Mount Tabor Middle School Rain Garden (right) won Portland a General Design Honor Award from the American Society of Landscape Architects in 2007.
Innovation and Cost Effectiveness
As with any new technology or innovation, Portland's early efforts required additional investments in research, planning and design. However, building on past experiences, their recent green street projects are increasingly cost-effective. Their most recent pre-design for green street projects identify design and construction savings of 20% to 63% over traditional storm sewer systems. These savings are calculated without accounting for the value of improved air and water quality, increased natural habitat, and other ecosystem benefits.
Monitoring and Design Improvement
Over the last 10 years, Portland has been systematically gathering performance data
on sustainable stormwater facilities in order to quantify benefits, improve design and function, and lower maintenance costs. Thus far these facilities have been shown to retain more than 90% of total annual rainfall. One of the most closely monitored facilities – the award-winning Glencoe Rain Garden – has performed extremely well. Rainfall and facility overflow have been monitored for over two years, and has retained 94% of the runoff.
More generally speaking, green streets have proven to reduce and manage stormwater runoff through interception, evapotranspiration, throughfall, and attenuation. They have also proven to be effective tools for inflow control of stormwater to the Combined Sewer Overflow (CSO) System.
Public Education
Portland has implemented many innovative public education strategies.
- The city
has effectively used small, interpretative signage (right) at project sites to show how the stormwater facilities function and to further engage the community,
- Public works officials use "street side chats" to gather residents' input on how much parking to remove for curb extensions, which planting schemes to use in swales, and to answer questions and address concerns.
- The city's Stormwater Solutions Handbook
offers guidance to anyone interested in managing stormwater on their property, planning or designing new construction projects, or making changes to existing development.
- Their downloadable walking tour map
serves as a detailed guide to green streets projects for both residents and visitors alike.
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