Managing stormwater is a challenging task for most urban landscapes across the world. Among the many sustainable strategies being used to manage stormwater, the tactic of “green streets” is one of the most compelling. The City of Portland, Oregon has one of the most successful green streets programs in the United States that not only has assisted with stormwater management, but also brought nature back into cities.

According to the City of Portland, a “green street” can be defined as a “street that uses vegetated facilities to manage stormwater runoff at its source.” Green streets’ initiatives have many positive effects on communities ranging from improving water quality and reducing flows to beautifying urban settings with native plants.

With three feet of rainfall each year and approximately seventy square miles of impervious surfaces from rooftops and pavement, it is easy to understand why Portland must prioritize stormwater management. A traditional hard infrastructure system left the city facing sewer overflows, flooding, and water pollution leading to a Clean Water Act lawsuit.

With the lawsuit requiring a series of mandates, Portland could spend $150 million in increasing pipe networks or consider other ways to absorb and filter excess stormwater. To grapple with these issues, Portland, Oregon created a two-pronged approach in 2007 that included a traditional pipe system, but also incorporated green infrastructure. Green streets have been used as part of this green infrastructure approach and include a range of strategies from simple street planters and green strips to more ambitious retention ponds and parks.

Portland’s green street initiative includes four different strategies. The first is modifying an existing planting strip to allow stormwater in and add plantings that absorb and filter water. The second is to create curb extensions where plantings replace street parking and the curb is, therefore, extended. This helps to shorten pedestrian crossing while also increasing permeable surfaces. Street planters are another way of “greening” streets when surface planting is not feasible. These planters usually consist of concrete boxes along parking spaces that divide the street parking from the sidewalks. Finally, identifying un-used urban spaces that can be transformed into park-like settings is another example of a Portland green street strategy.

Design is not the only tactic that Portland city officials have used to attain stormwater management goals. The city has developed many policy tools to support and extend the green streets’ efforts including a watershed management plan, stormwater management manual, green street policy, city building eco-roof policy, and a Green Street Inventory sheet.

In addition to the many environmental and social benefits, Portland’s experiment with green streets saved the city an estimated $60 million dollars in pipe replacement costs.  Green streets have been a win-win for Portland, Oregon and for many communities across the world.

Post by Carla Jones

Biophilic Cities Project Researcher, UVA Department of Urban & Environmental Planning