The SW 12th Avenue Green Street at SW 12th and Montgomery on the Portland State University campus utilizes a series of landscaped stormwater planters designed to capture and infiltrate approximately 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 both new and existing streets in downtown or highly urbanized areas can be designed to provide direct environmental benefits and be aesthetically integrated into the urban streetscape.
This green street project is effective and functional, and it also successfully integrates landscaped stormwater planters into the urban fabric.
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. Once inside the planter, the water is allowed to collect until it reaches a depth of six inches. The landscape system within each planter allows the water to infiltrate in the 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 a particular storm is, runoff will continue its downhill "dance" from planter to planter until all of the stormwater planters are at capacity. Once exceeding capacity, the water exits the last stormwater planter and enters the storm sewer.
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 was dedicated for people to access their vehicles without competing with the stormwater planters. Perpendicular pathways were located between each stormwater planter so that a pedestrian would not have to walk very far to access their cars or the sidewalk.
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.
The SW 12th Avenue Green Street Project has received a national award of honor from the American Society of Landscape Architects (ASLA). Bureau of Environmental Services green street specialist Kevin Robert Perry designed the innovative street stormwater project. The city completed the construction of the $30,000 demonstration project in June 2005 and has continually monitored its performance over the last 10 months.