In 2004, Environmental Services paved three blocks of streets in the Westmoreland neighborhood with permeable pavement that allows water to go through the street surface and into the ground. It is the first use of this type of permeable paving material on a public street in Portland, although similar materials are used locally in parking lots and private driveways.
Environmental Services paved about 1,000 feet of street surface with interlocking concrete blocks. They look like brick but are actually high-strength concrete. One block of SE Knapp Street was paved curb-to-curb with permeable blocks. The other streets – SE Rex Street and SE 21st Avenue – were paved with a center strip of standard asphalt and permeable pavement in both curb lanes. A fourth block was paved curb-to-curb with standard asphalt.
A More Natural Approach
The project is an alternative to the standard approach of capturing stormwater in a pipe, treating it, and discharging it to a surface stream. The permeable pavement allows water to infiltrate the ground through the spaces between the blocks filled with fine rock. Two layers of rock below the pavers provide a strong base for the street and help the infiltration process. Geotextile fabric layers below the base rock further reduce pollutants carried into the soil as the water infiltrates.
Portland uses several innovative approaches to reduce the amount of stormwater that flows through sewer pipes and discharges to rivers and streams. Approaches include downspout disconnection, vegetated infiltration areas, constructed wetlands, increased tree canopy, ecoroofs, green streets, and permeable pavement. The goal is to replace the pipe it, treat it, discharge it method with models that improved water quality in a more natural way.
Stormwater contributes to several problems in Portland’s sewer system. Heavy rains cause combined sewer overflows (CSOs) to the Willamette River. Stormwater discharges to streams can pollute water. Intense storms can also overload the sewer system and cause sewer backups in basements.
By removing stormwater from the combined sewer system, the Westmoreland project can reduce CSOs, stream pollution and basement sewer backups. It will also reduce the total volume of wastewater in the sewer system, reducing long-term costs of operating and maintaining the system.
The Westmoreland project will help evaluate the costs of building permeable streets and their performance over time. Several monitoring points in the project area will allow technicians to collect water samples to monitor how well the pavement infiltrates water and if it helps improve water quality. The Portland Office of Transportation will evaluate how well the street holds up to residential use, as well as the costs and challenges of maintaining the new surface. New methods and equipment – like vacuum sweepers - will be used to clean the streets and keep them free of weeds and debris.
A Cooperative Effort
The Portland bureaus of Environmental Services, Water and Transportation designed and built the Westmoreland project jointly. Additional funding came from an Innovative Wet Weather Program grant from the U.S. Environmental Protection Agency. The construction cost was $412,000.
Learn more about innovative stormwater management programs, and view Portland’s stormwater management manual online.
In 2003, large diameter sewers were built in the streets now included in the Westmoreland Permeable Pavement Pilot Project. Because of the deteriorated condition of the original concrete & asphalt section, lack of base material, and the heavy equipment used for the sewer work, full street reconstruction was needed.
The scope of the resurfacing meant the City of Portland had to meet the water quality standards for redevelopment required by the city’s stormwater management manual. The permeable pavement project was designed and built as a cooperative effort of three City bureaus: Environmental Services, Water, and the Office of Transportation.
SE 21st Avenue and SE Rex Street
The existing street is removed to a depth of about 8-12 inches below street grade. Temporary rock ramps are placed, allowing residents to access their driveways.
Repairs are made to damaged or missing sections of curb. In some cases, driveways are rebuilt to accommodate the planned street grade.
Water mains are re-built at greater depth in 21st and in Rex. Water services are installed on 21st (no services exist on affected blocks of Rex or SE Knapp Street).
New water service lines are reconnected by the Portland Water Bureau.
Streets are excavated to full depth, about 13 to 18 inches below top of curb. Drainage geotextile fabric is placed on the ground surface, and a layer of 2”-minus rock drainage blanket 6-10 inches deep is laid on top of the fabric and compacted.
A modified concrete curb 12” wide and about 10” deep is formed and poured on top of the drainage blanket rock. The modified curb serves to separate the asphalt center lane from the paver-block curb lanes on 21st and on Rex.
Subgrade geotextile fabric is placed on top of the drainage blanket rock.
The center asphalt lane is paved with two two-inch lifts of asphalt on two inches of
¾”-minus aggregate base.
For the curb lanes, a leveling bed of 3/8”-minus rock three inches deep is placed and compacted above the geotextile fabric.
The permeable pavers are then installed on the leveling bed. The space between paving blocks is filled with the fine rock, and rock and pavers are compacted.
Following street construction, sidewalk and surface restoration is completed.
SE Knapp Street
The construction sequence on Knapp is the same as above, except there is no water work and no center asphalt lane. Permeable pavers on Knapp extend curb-to-curb.
SE 20th Avenue and All Intersections
SE 20th Avenue and all intersections are reconstructed using standard asphalt. Water quality standards are met by planting trees in the drainage basin.
In summer 2005, the City of Portland completed paving four blocks of North Gay Avenue where Environmental Services installed large-diameter sewer pipes in 2001. The project area is on Gay between North Wygant and North Sumner Streets.
Commissioner Sam Adams briefs news media as concrete crews finish the last block of North Gay pilot project.
The project is a joint effort of Environmental Services, the Portland Office of Transportation, and the Portland Water Bureau. Parker-Northwest Paving of Oregon City was the City’s contractor.
The North Gay Avenue Pervious Pavement Pilot Project had two main goals:
- To permanently re-pave streets damaged during the sewer work in 2001. The old concrete streets cracked badly, and the current asphalt is of temporary quality.
- To provide information on how porous concrete and asphalt perform as a street surface. Porous pavement allows rain to soak through street and into the ground.
Why Porous Pavement?
When it rains, stormwater runs off North Gay Avenue into the City’s combined sewer system where it mixes with sanitary sewage. Some of the combined sewage goes to the wastewater treatment plant and some overflows to the Willamette River. With porous pavement, most or all of the stormwater will filter through the street surface into layers of rock below the street, and then into the ground. The existing storm inlets will remain to take any excess runoff.
The porous pavement provides several benefits:
- Reducing combined sewer overflows (CSOs) to the Willamette River;
- Reducing basement flooding caused by rain storms that overload sewers; and
- Creating a more natural stormwater management system that allows stormwater to be absorbed, filtered and cleaned before recharging groundwater.
Environmental Services received grants from the federal Environmental Protection Agency (EPA) in 2002 and 2003 to allow the City to test new ways of handling stormwater. The Gay Avenue project is one of several partly funded by the EPA grant.
|Pervious pavement works! Water sprayed from a flusher truck disappears into the new pervious asphalt pavement on North Gay Avenue before it reaches the gutter.|
This is a pilot project to learn how well different pavement materials handle stormwater and hold up as a street surface. For this reason, the City installed four different pavement combinations on Gay:
- Between Wygant and Humboldt, porous concrete curb-to-curb.
- Between Humboldt and Alberta, porous concrete in both curb lanes, standard concrete in the middle travel lanes.
- Between Alberta and Webster, poruous asphalt curb-to-curb.
- Between Webster and Sumner, porous asphalt in the curb lanes only.