Project Statement
The Mount Tabor Middle School Rain Garden is regarded as one of
Portland’s most successful examples of sustainable stormwater management. This project transformed an underutilized
asphalt parking area into an innovative rain garden that melds the concepts of art, education, and ecological
function. Built in the summer of 2006, the Mount Tabor Middle School Rain Garden has not only turned a “gray
space” into a “green space”, but it is also helping solve the local neighborhood’s
combined sewer infrastructure problems.
Introduction: Transforming Gray Space into “Green Space”
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.
The 80-year old combined sewer pipes serving
the Mount Tabor neighborhood are inadequately sized
to effectively manage the amount of impervious area
runoff generated from neighborhood buildings, streets,
and parking lots. During intense rainfall events, the
overload of stormwater entering the neighborhood combined
sewer system will “push” sewer water back
into the basements of local residences. The City of
Portland, dedicated to solving this problem, began working
with Portland Public Schools to reduce, as much as possible,
the amount of stormwater entering the combined sewer
system from Mount Tabor Middle School. After several
months of planning, the design team developed a multi-phased
plan to retrofit the entire school footprint with landscape
stormwater facilities- the rain garden being the first
improvement. During the summer of 2006, after only 59
days of construction, the parking lot courtyard space
was completely transformed from a “gray space”
into a “green space” that manages stormwater,
helps cool the school’s south-facing classrooms,
and provides a canvas for environmental education for
the students, staff, and overall community. As a model
for sustainable stormwater design, the Mount Tabor Middle
School Rain Garden’s simple and cost-effective
design demonstrates how stormwater management can be
aesthetically integrated into urbanized space, provide
direct environmental benefits, and act as a community
amenity.
How Does The Mount Tabor Rain Garden Work?
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.
Simple Design Solutions
The paramount design challenge for retrofitting the Mount Tabor Middle School Rain Garden was creating
simple, cost-effective, and low-maintenance design solutions while still maintaining a well integrated, visually
intriguing, and functional site design. Most of the rain garden’s design is predicated on the concept
of enhancing the beauty of the site while minimizing future maintenance efforts. For example, the use of
a diverse blend of low-growing rushes and sedges within the rain garden not only provides a tapestry of texture
and color, but this design approach also allows the occasional weed to grow and blend with the landscape
relatively unnoticed, thus reducing the need for intensive maintenance in the future. Another example is the design
of a 2-foot wide pea gravel “corridor” that visually connects the rain garden from end to end. Not
only does this prominent design feature allow the visitor to observe stormwater cascading into the rain garden
from multiple directions, but it also serves as a pathway for maintenance crews to access the rain garden without
disturbing the plantings or soil structure. Overall, the design of the Mount Tabor Middle School Rain Garden
has met three primary goals: 1) it is low-cost in its design and execution; 2) it benefits the environment
and embodies community livability; and 3) it acts a model for other sustainable stormwater retrofit projects.
Community Partnerships
The success of innovative stormwater projects like the
Mt. Tabor Middle School Rain Garden is dependent on
community partnerships. Representatives from Portland
Public Schools, Mount Tabor Middle School, and the local
neighborhood were active participants in the project’s
design process. Communication with school representatives
and the neighborhood continues to this day to determine
the overall success of the project from the neighborhood
perspective. In addition, many school groups throughout
the Portland area visit Mount Tabor Middle School to
learn about sustainable stormwater management and to
take back ideas and inspiration to potentially help
retrofit their own school grounds. Despite the fact
that the Mt. Tabor Middle School has not even reached
its first anniversary, the project has caught the attention
of both Portland locals and visitors from all over the
United States. The aesthetic appeal and intrigue of
the new rain garden has created a community asset that
promotes both environmental stewardship and education
at the neighborhood level within the urban core of the
city.
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