Oregon: Portland (Mt. Tabor Middle School)

Green Infrastructure Type: Green Campuses

Types of Green Infrastructure Used: Rain Garden, Bioswale, In-ground Planters, Dry Wells, and Street Curb Extensions

Summary:

Completed rain garden at Mt. Tabor Middle School

Description:
In 2007, the Portland Bureau of Environmental Services, in partnership with Portland Public schools implemented a stormwater retrofit project at the Mt. Tabor Middle School to transform a 4,000 square foot south side asphalt parking area into a rain garden; to install a vegetated swale and planter in the main parking lot; to install planters along the building and connect downspouts to three drywells; as well as build a single curb extension on 57th Street next to the school entrance. The retrofit project was designed to reduce the flow entering the combined sewers, and protect residents in the surrounding area from sewer backups in basements when the city's combined sewers exceed their capacity, by disconnecting the runoff from the school to the combined sewer.

The 1,900 square foot rain garden collects runoff from 30,000 square feet of impervious area generated the school's playground and roof top. Runoff from the roof is conveyed directly to the rain garden through concrete runnels, and runoff from the playground enters the rain garden through a large trench drain. The system is designed to have a ponding depth of six to eight inches with an infiltration rate of 2-4 inches per hour, depending on the size of the storm event. Overflow from the rain garden is directed the combined sewer system through a stand pipe. The rain garden is planted with a diverse blend of low growing rushes, sedges, and trees, which reduces maintenance needs. The rain garden also provides shade and cooling benefits to the adjacent classrooms. Since its construction, the rain garden has captured and infiltrated approximately 500,000 gallons of runoff.

In addition to the rain garden, the Portland Bureau of Environmental Services also installed two landscaped facilities in the school's main parking lot: a 1,400 square foot swale that runs down the center of the parking lot, and a 200 square foot planter in the northeast corner of the parking lot. The two facilities in combination manage runoff from 15,000 square feet of asphalt. Both facilities are planted with similar species as the rain garden and are designed to promote infiltration and safely allow overflow in large storm events.

The Bureau has also installed planters along the building edge and drywells under the playground to disconnect roof downspouts. Four 150 square foot planters and one 200 square foot planters are located seven feet from the downspouts on the north and west edges of the building. Runoff is carried by splash pads and concrete runnels to the planters from the disconnected downspouts. The planters have flush edges to allow for easy mowing and are designed to overflow onto the grass. Furthermore, three drywells were installed under the playground on the east side of the school. Together these two practices manage runoff from 40,000 square feet of roof top and asphalt.

Lastly, the Bureau installed a street curb extension along 57th Street and the entrance of the school parking lot. The curb extension manages runoff from the street and the parking lot entrance. The curb extension is 64 feet long and has eight compartments with vegetation to promote infiltration and plant uptake to manage runoff.

The Mt. Tabor Middle School retrofit project is one of the more successful sustainable stormwater management projects and has turned areas into green space to help solve the combined sewer infrastructure problem.

For more information, visit the Portland Bureau of Environmental Services Web site at http://www.portlandonline.com/BES/index.cfm?a=172138&c=45382 .

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Last updated on September 10, 2009 10:55 AM
URL:http://cfpub.epa.gov/npdes/greeninfrastructure/gicasestudies_specific.cfm