Mount Tabor Middle School Bioretention Area

Mount Tabor Middle School Bioretention Area

from www.portlandonline.com

In 2007, the City of Portland Bureau of Environmental Services worked with Portland Public Schools to complete a stormwater retrofit project at Mt. Tabor Middle School, 5800 SE Ash Street in Portland. The project is designed to protect nearby residents from sewer backups into basements when combined sewer pipes fill to capacity during heavy rains. The project includes a rain garden, a swale, six planters, and three drywells. Environmental Services also constructed a stormwater curb extension adjacent to the school on SE 57th at Pine Street. The facilities manage runoff from about two acres of roof, playground, parking lot, and street surfaces.

The Tabor Rain Garden, on the south edge of the school, is technically an infiltration planter, built in summer 2006. It has a footprint of 1,900 square feet and a maximum ponding depth of six to eight inches. The flat-bottomed facility collects runoff from about 30,000 square feet of roof and asphalt play area. Runoff from the roof enters through concrete runnels and through a large trench drain from the asphalt area. When the system reaches capacity, it sends overflow back to the storm collection system through a standpipe in the northwest corner. The bottom of the facility is planted with a mixture of sedges and rushes. The trees are Tupelo and Aspen.

Parking Lot Landscape Systems

In 2007, Environmental Services finished the project with the retrofit of the parking lot with two landscaped facilities; a 1,400 square foot swale that runs east-west down the center of the parking lot, and a 200 square foot planter in the northwest corner. The systems together manage runoff from 15,000 square feet of asphalt.

The swale has multiple check dams to retain runoff and promote infiltration. Runoff enters along the north side of the swale through curb cuts. The south edge has a flush curb that allows runoff to enter along the entire length of the facility. Runoff enters the planter through a single curb cut on the north end of the unit.

Both the swale and planter are designed to safely overflow – in very large storm events – to the entrance of the parking lot, and into the street.

The bottom of the parking lot swale is planted with rushes and sedges; the drier upslope areas are planted with compact Oregon Grape, Dwarf Heavenly Bamboo, Hebe, and Euonymus. The trees are Tupelo and Aspen. The flat-bottomed planter in the northwest corner of the parking lot has plants similar to those in the bottom of the rain garden and the parking lot swale.

Planters Along the Building Edge

In August 2007, Environmental Services built five infiltration planters along the north and west edges of the building. The four planters on the north side of the building are identical; each has a footprint of about 150 square feet. There is a single planter along the southwest edge of the building. It has a footprint of about 250 square feet. The planters together manage runoff from about 15,000 square feet of roof. All of the planters are roughly seven feet from the building, adjacent to downspouts. Splash pads, or concrete runnels, carry runoff from the disconnected downspouts into the planters. The outside edges of the planters are flush with the adjacent grass for easy mowing. The units are designed to overflow onto the grass when they reach a ponding depth of about six inches. There are two plant types in the facilities: sedges and rushes.

Drywells

Environmental Services installed three drywells under the playground on the east side of the school. They manage runoff from about 25,000 square feet of roof and asphalt.

Street Curb Extension

In January 2007, Environmental Services built a single curb extension on SE 57th, down-slope from the entrance to the school parking lot. It manages runoff from the street and the parking lot entrance, a total of about 6,000 square feet of asphalt. The facility is 64 feet long, has an overall slope of 4.2%, and has eight compartments separated by check dams. The curb extension is 3.5 feet across, from curb to curb, and is planted with rushes.

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