Portland, Oregon, is known as one of the greenest cities in the U.S., receiving high marks for public transportation, bicycle/carpool commuting, renewable energy usage, recycling, and number of LEED-certified buildings. It also has quite a few innovative environmentally-sustainable sites, including several “green streets”. These streetscapes incorporate special planters that decelerate runoff and filter pollutants from the water before it reaches the storm pipe system.

During a recent visit to Portland, I had the opportunity to see a couple of these green street projects in the downtown area: one on Southwest 12th Avenue within Portland State University, and another on Southwest Park Avenue across from Director Park. There are several other green streets scattered around the city, and many of these have their own unique design.

The 12th Avenue site was the first of its kind, built in 2005. In addition to its stormwater management function, it has enhanced the visual quality of the existing streetscape. In this case, stormwater flows into the first of four planters, and settles into the soil. During heavy storms, if the water level in this planter reaches more than 6 inches, the excess amount will flow back out into the gutter and then flow into the next planter for infiltration, repeating the process. Water exceeding 6 inches height in the last (lowest) planter will flow out to the street and enter the storm drain system. The number of planters functioning in this manner depends on the intensity and duration of each rain event. The planters are filled with a native species called Grooved Rush (Juncus patens), and each also includes a Black Gum tree (Nyssa sylvatica). Both of these species tolerate saturated soil conditions. In addition, a 3’-wide strip of pavers is located along the street side, providing space for access to parked cars. Pedestrian walkways are also situated between the planters, bounded by small shrubs.

The Southwest 12th Avenue planters include a strip of pavers for parked vehicle access.

Excess runoff from the lowest planter enters the storm drain system.

The planters and vegetation fit nicely into the urban streetscape.

Each street-side planter inlet includes a small hump in the asphalt to direct water into the planter.

The planters on Park Avenue are designed in a different manner. The largest planter (pictured below) is divided into three sections. Water enters the planters from drain inlets along the street side, and from gaps in the curbing along the sidewalk. When water in the highest planter section exceeds the height of the divider during large rain events, that runoff will flow over the divider into the next section. Most of the water will filter into the soil in the planters, but during the heaviest storms it may reach the third (lowest) planter section. If the water level in this section reaches the height of the elevated drain inlet located within it, this excess water will enter the inlet and flow into the storm pipe system.

Southwest Park Avenue planter with drain inlets connecting to each divided section

Raised drain inlet within the lowest planter section

Gaps in curbing along the sidewalk receive runoff.

One of several individual tree planters along Southwest Park Avenue only receives runoff from the walkway side. A small raised drain in the planter takes in excess water during heavy storms.

Photos by Alice Webb