Mt Tabor Middle School

Integrated stormwater management techniques

Location: 5800 SE Ash Street

Stormwater facilities: rain garden, parking lot swale, downspout planters, drywells, curb extension 

Date of installation: 2006-2007

Impervious area managed: Approximately 2 acres

(please visit only during non-school hours)

This school retrofit protects nearby residents from basement sewer backups, provides an outdoor classroom for students and helps cool the building and surrounding impervious surfaces. A variety of landscaped stormwater management technologies intercept stormwater runoff from about two acres of impervious surfaces. The facilities keep stormwater out of the sewer system and help reduce combined sewer overflows (CSOs) and basement sewer backups. 

Rain Garden:

The rain garden sits between the two wings of the building on the south side of the school and collects runoff from the adjacent roof and asphalt play areas. Runoff from the roof enters via concrete splash blocks or “runnels.” Runoff from the asphalt area enters the forebay of the system through an 18 inch wide trench drain. The forebay helps filter out sediment and debris. The main compartment can pond to a depth of 8 inches before overflowing to the storm collection system through a catch basin in the northwest corner of the facility. The bottom of the facility is planted with a mixture of sedges and rushes. The trees are Tupelo and Aspen. 

Parking Lot Swale:

A 1,400 sq. ft.swale and a 200 sq. ft.planter in the parking lot manage runoff from 15,000 sq. ft.of asphalt. The swale has multiple check dams with adjustable weirs 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. In large storm events, the swale and planter overflow safely to the stormwater curb extension and an underground sump in the street. 

Downspout Planters:

There are five infiltration planters along the north and west sides of the building. Each of the four planters on the north side has a footprint of about 150 sq. ft. A single planter along the southwest edge of the building has a footprint of about 250 sq. ft. The planters together manage runoff from about 15,000 sq. ft. of roof. All planters are roughly 7 feet from the building, adjacent to existing downspouts that were disconnected and diverted into the facilities. Splash pads (concrete runnels) convey runoff from the disconnected downspouts into the planters. 

Drywells:

Three drywells beneath the asphalt playground on the east side of the school manage runoff from about 25,000 sq. ft.of roof and asphalt. The drywells are 4 feet in diameter and 17-20 feet deep. Runoff enters the drywells through standard inlet and sedimentation manholes, with overflow connections back to the sewer should they ever reach capacity. 

Curb Extension:

A single stormwater curb extension on the east side of SE

57th, down-slope from the entrance to the school parking lot, captures overflow from the parking lot swale and street surfaces. The facility is 64 feet long and has an overall slope of 4.2% (the upper end is steeper). Eight flat-bottomed compartments separated by check dams maximize the internal volume of the facility. The overall width is 4 feet (planted width is 3.5 feet). It manages runoff almost 6,000 sq ft of pavement.

Project Design: Nevue/Ngan, Landscape Architects