SW 12th Avenue Green Street

Designers: Kevin Robert Perry | City: Portland, OR | Project Type: stormwater management, retrofit, streetscape
Date Visited: 12.12.12

Locations: SW 12th Ave between SW Mill and SW Montgomery
Size: 0.92-acre
Construction Cost: $38,850
Construction Finished: May – June 2005

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The urban street retrofit stretching along SW 12th Avenue between SW Mill and Montgomery marked Portland’s first Green Street project that successfully integrated stormwater management into the urban landscape. The Green Street Project was built in the summer of 2005 and received the 2006 ASLA General Design Award of Honor.

Consisting of four consecutive street stormwater planters, this award-winning design is capable of capturing runoff from approximately 7,500 square feet of paved surfaces. By treating runoff onsite, this stormwater system reduces the amount of pollutants that would have normally flowed directly into the Willamette River.

Site Plan. Image Credit: asla.org

PortlandOnline’s Project Summary of the site describe the process for the capture and treatment of stormwater:

• Stormwater runoff from the street flows downhill along the existing curb until it reaches the first of four consecutive stormwater planters.
• A 12-inch-wide trench drain channels the street runoff into the first stormwater planter. The trench drain moves the water under the vehicle step-out area and into the facility. The runoff is directed over a concrete pad, where sediment and debris are deposited for easy removal.
• Stormwater is allowed to pond to a depth of 7 inches before infiltrating through the soil at a rate of approximately 4 inches per hour. During large storm events, water may enter the planter at a rate faster than the soil can infiltrate, resulting in a ponding depth greater than 7 inches. In that case, the runoff exits a second curb cut, flows back into the street, and enters the second (downhill) planter. This process continues for the third and fourth planters. If the fourth planter ponds to capacity, it overflows to the existing storm system.
• The adjacent sidewalk slopes toward the planters, and sidewalk runoff enters the planters through curb cuts.

In addition to attractive green space and stormwater management capabilities, the SW 12th Avenue Green Street is also lauded for integrating the planters in a way that also accommodated pedestrians, vehicular access, street furniture and on-street parking.

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