PROJECT PARNTER(S)
designers: Kevin Robert Perry and Brandon Wilson, Portland Environmental Services
clients: City of Portland and Portland Public Schools

LOCATION
Portland, Oregon

GREEN INFRASTRUCTURE ELEMENTS
2Sy, 3RG

DESCRIPTION (from ASLA website) The Mount Tabor Middle School Rain Garden project is unique to Portland and the United States in the way this schoolyard has been transformed to sustainably manage stormwater runoff. The project demonstrates the City of Portland’s commitment to promote a more natural approach to stormwater management, and many regard this “urban rain garden” project as one of Portland’s most successful stormwater management retrofit projects to date. In a collaborative effort between the City of Portland and Portland Public Schools, the Mount Tabor Middle School Rain Garden project converts what was previously 4,000 square feet of underutilized asphalt parking area abutting the school’s courtyard entrance into an innovative rain garden designed to capture, slow, cleanse, and infiltrate nearly an acre of the school’s runoff. Prior to the rain garden’s installation, the students and staff described the parking lot courtyard space immediately adjacent to their classrooms as an “asphalt oven”. Even on the mildest of days, the heat generated from the asphalt parking lot would send the temperature within their classrooms soaring. After a careful site analysis, the design team recognized several inefficiencies in the layout of the parking lot. By reorganizing the courtyard space, the design team was able to provide sufficient room for a 2,000 square foot rain garden and an entry plaza with bike parking and student seating, while maintaining adequate parking for school staff. What is particularly unique about this rain garden project is that it is first of several stormwater retrofit projects specifically designed at Mount Tabor Middle School to help solve a chronic neighborhood problem of local basement flooding. It is important to understand this context in order to help gauge the success of the rain garden project.

PHOTOS AND DRAWINGS


LESSONS LEARNED
(from ASLA website) The Mount Tabor Middle School Rain Garden project essentially disconnects a portion of the school’s stormwater runoff from the neighborhood’s combined sewer system and manages it on-site using a landscape approach. Approximately 30,000 square feet of impervious area runoff generated by the school’s asphalt play area, parking lot, and rooftops, is elegantly captured and conveyed into the rain garden via a series of trench drains and concrete runnels. Once inside the landscape space, the water is allowed to interact with both plants and soil while soaking into the ground. Depending on how intense a particular storm event is, runoff will rise within the rain garden until it has reached the 8-inch design depth. Once exceeding capacity, the water exits the landscape system and enters the combined sewer system. The rain garden’s infiltration rate varies from 2-4 inches per hour, meaning that any runoff that is retained in the rain garden is completely gone within a couple of hours. Since its completion in September 2006, the Mount Tabor Middle School Rain Garden’s performance has been very impressive. All of the rainfall captured within the rain garden has infiltrated without ever overflowing into the combined sewer system. As a result, approximately 500,000 gallons of stormwater runoff has been infiltrated on-site. For illustration purposes, the amount of runoff infiltrated equates to a volume of water that would stand 36 feet tall within the footprint of the rain garden. It is also estimated that the successful performance of the rain garden, along with the other stormwater improvements planned for the school, will ultimately save $100,000 in future sewer infrastructure replacement costs within the neighborhood.

ADDITIONAL RESOURCES
ASLA Honor Award webpage: http://asla.org/awards/2007/07winners/517_nna.html
City of Portland website: http://www.portlandonline.com/bes/index.cfm?&c=45382&a=172138