NE Fremont Street Green Street Project 

NE Fremont Street between NE 131st and NE 132nd avenues 

Portland, Oregon 

PROJECT SUMMARY 

Project Type: Stormwater retrofit of an existing residential collector street – demonstration project 

Technology: Stormwater curb extension 

Major Benefits: • The curb extension captures runoff from 4,500 square feet of paved surfaces. It 

treats and infiltrates most of the runoff it receives, providing volume and flow 

control and water quality benefits. 

• Runoff is managed onsite, instead of entering the storm sewer system. 

• The project includes a ramp that is ADA (Americans with Disabilities Act) 

compliant, providing for safe pedestrian crossing. 

 Cost: The total project cost, including project management (but not design), was $20,400. Of 

this, construction of the stormwater curb extension cost $16,400, or $3.64 per square 

foot of impervious area managed. The remaining $4,000 was required for ancillary 

sidewalk repairs and construction of a new ADA ramp on the opposite side of the 

street. These costs are not necessarily typical of other Green Street projects. 

Constructed: July 2005 

Maintenance The City of Portland maintains the facility. 

Before After. 

NE Fremont Stormwater Curb Extension

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Features 

• This project removed 300 square feet of paved street surface and 

transformed it into a vegetated system for stormwater management. 

The stormwater curb extension provides water quality treatment and 

maximizes infiltration of street runoff. It retains stormwater to a 

depth of about 6 inches. 

• This is Portland’s first Green Street project to integrate an ADAcompliant pedestrian crossing into the design of a stormwater curb 

extension facility. 

• The project provides an attractive addition to the neighborhood and 

enhances the urban environment.

BACKGROUND 

This was the first Green Street project jointly conceived and designed by the Portland Bureau of 

Environmental Services (BES) and the Portland Bureau of Transportation (BOT). BOT proposed 

a curb extension at the site to provide a safe pedestrian crossing that would accommodate school 

children in particular. BES suggested making it a vegetated facility that could also provide 

stormwater management, similar to stormwater curb extensions at NE Siskiyou Street and SE 

Ankeny Street. 

SITE SELECTION CRITERIA 

• Traffic Impacts: The project was not expected to have any traffic impacts. 

• Stormwater Catchment Area: The 4,500 square foot catchment area is considered 

representative of catchment sizes in the surrounding neighborhood. 

• Loss of Parking Spaces: The stormwater curb extension incorporates space that could 

accommodate parking for two cars. 

• Street Slope: The moderate, 2% street slope was suitable for the project. 

• Soil Infiltration Rates: Infiltration tests were not required at the site. (See “Geotechnical 

Evaluation” below.) 

• Available Space: It was possible to locate the project between the existing residential water 

service meters to minimize utility conflicts. 

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Fremont stormwater curb extension during 

a rainstorm

STORMWATER CAPACITY AND SYSTEM CONFIGURATION 

Stormwater Management Goal 

The goal was to maximize the retention, treatment, and 

infiltration of street runoff, while providing improved 

pedestrian safety and a visual amenity for the neighborhood. 

Geotechnical Evaluation 

An infiltration test was not required before construction 

because adequate documentation already existed concerning 

how well Portland’s east side soils drain. The Natural 

Resources Conservation Service soil survey for Multnomah 

County classifies the soils as 53B-Urban Land and welldrained Multnomah soils. The surface horizon typically is dark 

brown silt loam about 20 inches thick. Soil below this depth is 

gravelly silt loam and gravelly sand to a depth of approximately 60 inches. 

System Configuration 

Catchment Area (street, driveway, sidewalks): 

Constructing the stormwater facility; forming the curbs.

• 4,500 square feet 

Street Slope: 

• Approximately 2% 

Stormwater Curb Extension Dimensions: 

• Length: 65 feet 

• Width: 7 feet 

• Total landscape area: 300 square feet 

• Depth from sidewalk grade to finish grade of 

curb extension: 8 inches 

• Maximum ponding depth: Approximately 6 

inches 

• Radius of curb taper: 10 feet 

Internal Storage Volume: 

• 150 cubic feet 

Overflow: 

• Overflow exits the facility through a 6-inch curb notch at the downhill end, draining to the 

separated sewer via an existing street inlet. No modifications were made to the inlet. 

Additional Information: 

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• The curb extension was excavated to a depth of 18 inches below the sidewalk grade. The 

native soil was tilled before importing 12 inches of a three-way soil mix, consisting of sand, 

topsoil, and compost. No rock or sub-base material was added below the soil. 

• The three-way soil mix was tilled into the native soil and spread to create a shallow parabolic 

cross section. 

• The curb opening at the inflow point is 18 inches wide. 

• A 12-inch-wide grated concrete trench conveys stormwater under the pedestrian ramp. 

Landscaping 

Plants were selected for their drought tolerance, evergreen 

foliage, and height. The typical mature height of the plants is 

less than 2 feet. These characteristics were a priority because 

they minimize maintenance and address safety concerns. M

of the plants are native to the Pacific Northwest; some nonnative plants were included to provide seasonal color accen

Rushes are the dominant plant in the bottom of the facility 

because their stiff structure helps slow the passage of water 

and they survive well in the variable moist and dry soil 

conditions. 

ost 

ts. 

The plants were installed at a density greater than required by the city’s Stormwater Management 

Manual. This was done to reduce weeding and watering requirements and to quickly create an 

aesthetically appealing landscape. 

Initial plantings included: 

Scientific Name Common Name 

Hebe ‘Autumn Glory’ 

Lavandula angustifolia ‘Hidcote Blue’ 

Carex testacea 

Juncus patens 

Gaultheria shallon

Hebe 

Dwarf English lavender 

New Zealand orange sedge 

California grey rush or grooved rush 

Salal 

(See “Successes and Lessons Learned” below for notes on plant survival.) 

PROJECT COSTS 

The final project cost was $20,400, including project and construction management, curb 

extension and landscape construction, and ancillary construction activities. The cost does not 

include design. 

• Project and Construction Management 

Project and construction management cost $3,465, or 17% of the total cost. 

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• Curb Extension Construction 

The core curb extension construction activities cost 

$11,704, or 57% of the total cost. This included 

sawcutting and removing existing hardscape, 

excavation, concrete curb installation, ADA ramp 

construction, curb cuts and ornamental grate 

installation, soil import and preparation, and final 

grading. 

• Landscape Construction 

The landscape construction activities cost $1,230, o

6% of the total cost. This included fine grading, 

plant procurement, plant material, and mulching. 

r 

• Ancillary Construction Activities

Miscellaneous street and sidewalk repair activities cost $4,000, or 20% of the total. This 

included installing a new concrete ADA ramp on the north side of Fremont, opposite the new 

curb extension, as well as additional sidewalk repair. 

MAINTENANCE AND MONITORING 

Maintenance 

Maintenance includes hand weeding (no chemical 

applications are allowed), plant trimming, plant 

replacement, and sediment and debris removal. 

Portland Parks and Recreation maintained the curb 

extension during the 2-year plant establishment period. 

The city will continue long-term maintenance an 

average of four times per year. There is no permanent 

irrigation system. 

Monitoring 

BES will visually monitor the curb extension for maintenance requirements and plant success. 

SUCCESSES AND LESSONS LEARNED 

• This street retrofit project is an attractive demonstration of how to integrate vegetated 

stormwater management systems into the urban streetscape to provide direct environmental 

benefits and a sense of neighborhood identity. 

• The project is Portland’s first example of a stormwater curb extension that integrates an 

ADA-compliant pedestrian ramp into the design without compromising the function of the 

facility. 

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• All of the plants, with the exception of Gaultheria shallon (salal), grew vigorously during the 

first year. As a result, little weeding is required. Some plants appeared to suffer from cold 

east winds in the winter, evidenced by some browning of leaves. Most species of the salal 

died during the establishment period, probably as a result of cold winds and intense solar 

exposure at this location. The salal was replaced with more hebe plants. 

• In the first year, little sediment accumulated in the forebay. This may be because of a lack of 

contributing elements, such as street trees. Because there is little sediment input, city staff 

removes the sediment an average of twice per year, using a shovel and rake. 

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