Green Streets are neighborhood streets with stormwater management features, often utilizing natural elements, which can remove and filter storm water runoff before it reaches the storm drain. These features are visible from the street, allowing interaction by the public by opportunities for maintenance and upkeep, and education about human interaction with the natural environment.
You may want to check out the Portland Bureau of Environmental Services “What is a Green Street?” flyer for a succinct overview.
Bioswales, also called biofiltration swales or grassy swales, are one possible feature of Green Streets.
“Swales are gently sloping depressions planted with dense vegetation or grass that treat stormwater runoff from rooftops, streets, and parking lots. As the runoff flows along the length of the swale, the vegetation slows and filters it and allows it to infiltrate into the ground. Where soils do not drain well, swale are typically lined and convey runoff to a drywell or soakage trench. Swales can include check dams to help slow and detain the flow. A swale can look like a typical landscaped area.”
-The Portland Community Watershed Stewardship Program Stormwater Solution Handbook
Bioswales often integrate into green streets at curb extensions where upstream and downstream cuts in the street curb allow rainwater to exit the street and filter through the swale. Overflow exits through the downstream curb-cut and continues to the storm drain.