The SW 12th Avenue Green Street at SW 12th and Montgomery on the Portland State University campus contains a series of landscaped stormwater planters that capture and infiltrate about 8,000 square feet of street runoff.

This innovative streetscape project effectively manages street runoff while still maintaining strong pedestrian circulation and on-street parking.

Built in summer 2005, this street retrofit project demonstrates how to design both new and existing streets in downtown or highly urbanized areas that have direct environmental benefits and are aesthetically integrated into the urban streetscape.

This effective, functional green street project successfully integrates landscaped stormwater planters into an urban area.

How It Works

The 12th Avenue Green Street project disconnects street stormwater runoff from a storm sewer that drains directly into the Willamette River and manages it on-site using a landscape approach. Stormwater runoff from SW 12th flows downhill along the existing curb until it reaches the first of four stormwater planters.

A 12-inch curb cut channels the street runoff into the first stormwater planter. Inside the planter, the water collects until it reaches a depth of six inches. The landscape system within each planter allows the water to infiltrate into the ground soil at a rate of four inches per hour.

If a rain event is intense enough, water will exit through the planter’s second curb cut, flow back out into the street and eventually enter the next downstream stormwater planter. Depending on how intense the storm is, runoff will continue flowing downhill from planter to planter until all the planters are at capacity. If they all exceed capacity, the water exits the last planter and enters the storm sewer.

This system manages nearly all SW 12th Avenue’s annual street runoff, estimated at 180,000 gallons.

Design Challenges

The main challenge for retrofitting SW 12th Avenue was finding enough space for pedestrians, on-street parking, street trees, landscaping, street lighting, signage, and stormwater planters within an eight-foot wide space.

A three-foot wide parking egress zone allows people to reach their vehicles without competing with the stormwater planters. Perpendicular pathways between each planter shorten the distance between the sidewalk and parked cars.

A four-inch curb exposure at each planter indicates to the pedestrian that there is a drop in grade. Each curb cut that allows the street runoff to enter the stormwater planters has an ADA accessible grate to allow for unencumbered pedestrian flow along the parking egress zone.