Mississippi Commons 

3721-3727 N Mississippi Avenue 

Portland, Oregon 

PROJECT SUMMARY 

Project Type: Complete onsite stormwater management for mixed-use commercial 

redevelopment—demonstration project 

Technologies: Downspout disconnection, innovative conveyance, infiltration planter, drywell, 

pervious gravel 

Major Benefits: • 500,000 gallons of stormwater is infiltrated and treated onsite each year 

instead of entering the combined sewer system. 

• The stormwater facilities are designed as amenities that contribute to the 

property’s public space. 

• The project adds a vegetative landscaped component to the surrounding built 

environment. 

Cost: $42,105; $25,000 paid by EPA grant funds 

Constructed: 2004 

Overview of the Stormwater System Mississippi Commons Before 

• The Mississippi Commons redevelopment 

project converted a collection of buildings 

from light industry to mixed-use artist space, 

offices, and retail. Part of the project involved 

providing complete onsite stormwater 

management. 

• Two downspouts were disconnected from the 

roof and directed to a two-level, steel-lined 

basin. The basin empties into a grate-covered 

trench in the ground, which in turn flows into 

an infiltration planter. Vegetation, soil, and 

material in the planter slow and filter the 

stormwater before it soaks into the ground. 

Mississippi Commons After, with Stormwater 

Infiltration Planter 

• The infiltration planter is designed as an 

architectural feature for the building’s public 

courtyard. 

• A third downspout is piped under the concrete 

and bubbles into the planter by way of a pipe. 

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• During large storm events, overflow enters a stand pipe within the planter and is directed 

underground to a drywell on the property. Overflow also spills onto an adjacent pervious 

gravel courtyard through an opening in the planter wall. 

STORMWATER CAPACITY AND SYSTEM COMPONENTS 

Stormwater Management Goal 

The goal was to provide complete onsite stormwater 

infiltration and treatment and reduce the volume of 

stormwater entering Portland’s combined sewer system. 

System Components 

Facility footprint: 550 square feet (infiltration planter) 

Catchment area: 25,000 square feet (21,800 roof and 

3,200 pervious gravel courtyard) 

Overflow system: Drywell; pervious gravel courtyard 

Downspouts disconnected to collection basin 

and conveyed along a trench to the planter Infiltration planter: The infiltration planter has a 12-inch 

sub-base of washed 3⁄4-inch gravel, which is separated 

from approximately 24 inches of soil by a layer of filter 

fabric. 

Landscaping: The largely native vegetation in the infiltration planter includes Juncus patens, 

Grooved rush; Cornus stolonifera, Red twig dogwood; Viburnum trilobum, American cranberry 

bush; Camassia leichtlinii, Camas lily; Sisyrinchium, Yellow-eyed grass, Scirpus acutus, 

hardstem bulrush, and Carex rupestris, Curly sedge. 

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BUDGET 

The cost for the stormwater management system was 

$42,105, with $25,000 paid for by an EPA Innovative 

Wet Weather Projects (IWWP) grant. Of this total, 

$12,496 (30%) was spent on non-construction 

activities, and $29,609 (70%) was spent on 

construction activities, as shown below. 

Budget 

Non-Construction Activities 

Design and engineering: $9,716 

Construction management 2,780

 $12,496 

Roof runoff conveyed to the newly vegetated 

planter 

Construction Activities 

Demolition, Excavation, grading, drywell: $10,560 

Stormwater collection and conveyance: 8,500 

Planter construction: 4,024 

Landscaping (soil, plants, drip irrigation): 6,525

 

 $29,609 

MAINTENANCE AND MONITORING 

The property owner is responsible for facility maintenance. 

The Bureau of Environmental Services (BES) provides periodic visual assessment of the facility. 

PUBLIC INVOLVEMENT 

A permanent interpretive sign at the project site provides information about the sustainable 

stormwater management techniques used. 

The project is used as an example of innovative stormwater management on the BES website and 

on tours of sustainable stormwater management facilities. 

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SUCCESSES AND LESSONS LEARNED 

Positive project example: 

Mississippi Commons is a good 

example of a successful 

public/private project. It is in a highly 

visible location in a fast-redeveloping 

area of the city, with other sustainable 

development projects occurring 

nearby. These projects provide 

opportunities for the public to 

become more aware of innovative 

stormwater management techniques, 

and other developers have expressed 

interest in using similar approaches. 

Creative approach: The steel 

stormwater basin and conveyance 

system are a creative and innovative 

approach to capture and convey 

runoff from the building roofs. 

Stormwater Infiltration Planter, looking north 

Bubbler: One downspout is directed underground to a bubbler within the infiltration planter; 

however, it does not work effectively and, when it is not raining, water remains stagnant in the 

pipe, creating a potential habitat for mosquito breeding. 

Stormwater rate reduction: Under the City’s Clean River Rewards program, the onsite 

stormwater management measures will allow the property owner to reduce a portion of the 

stormwater rates for the site. 

Plant survival: Since this was an early demonstration project, it was not known how some 

plants would behave in periodic standing water. All species appear to have survived except 

Polystichum munitum, sword fern; and Fragaria chiloensis strawberry; the Mahonia aquilfolium, 

Oregon grape, is surviving but is not growing with vigor. Continued visual assessments will 

determine the long term viability of the existing plants. 

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