Porous pavement, vegetation to curtail stormwater

by: SUBMITTED PHOTO - New native plantings in linear tree wells work with the newly installed porous concrete pavement at Sunset Swim Center to filter and minimize stormwater runoff.When the rainy season kicks back into gear this fall, at least one additional parking lot in Cedar Mill will be equipped to process rainwater runoff in an environmentally sensitive manner.

A collaboration between Tualatin Hills Park and Recreation District and Tualatin Riverkeepers created a porous-pavement parking lot interspersed with runoff-absorbing native plants at Sunset Swim Center, 13707 N.W. Science Park Drive.

The porous concrete pavement allows rainwater to be absorbed into the ground, while linear tree wells —

upheld by “structural soil” that supports the weight of pavement and vehicles — allow tree roots to grow and water to infiltrate.

The renovated 70-space parking lot is one of the park district’s projects funded by a $100 million bond measure voters approved in 2008. Landscape, sidewalk, curb and driveway upgrades were also part of the $525,000 project, said Bob Wayt, park district spokesman.

For its part, Tualatin Riverkeepers secured a $50,000 Oregon Department of Environmental Quality grant from a funding pool dedicated to vegetation and stormwater and erosion management. A smaller grant from the J. Frank Schmidt Foundation paid for the actual trees planted in the linear wells.

Brian Wegener, Tualatin Riverkeepers advocacy and communications manager, said the project is unique for the nonprofit watershed advocacy and management organization.

“We normally don’t get involved with construction projects,” he noted.

An Environmental Protection Agency program administered by the DEQ devoted to nonpoint source pollution abatement created an opportunity for the Riverkeepers to make a positive change in the Tualatin River watershed.

“We applied for a grant through the EPA and DEQ related to stormwater abatement,” Wegener explained. “They were looking for partners.”

The successful application provided $50,000 to retrofit the drainage and landscape systems in the parking lot, one of 5,000 in the Tualatin River basin.

This is the first of two demonstrations in what’s called the 5,000 Acres Initiative, funded by the DEQ and EPA’s 319 Nonpoint Source Pollution Grant. Another, much smaller project is on track to be completed this fall at the Portland Community College’s Sylvania Campus.

This is the park district’s second pervious concrete parking lot project, following a paving project at the Aloha Swim Center in 2010.

Unlike forest land, where rainwater is soaked up like a sponge, parking lots paved with impervious asphalt send whatever’s landed on or stuck to the surface since the last rain into the nearest stream.

More than 650,000 gallons of rain fall on the swim center parking lot in a typical year.

“A lot of stormwater comes off them,” Wegener said, “and it’s usually piped into the nearest creek. Rushing water creates erosion that stirs up legacy pollutants: oil dripping off automobiles, dust off of brakes, any kind of garbage on the parking lot gets washed off the storm drain into the nearest creek.”

The park district focused on its part of the project earlier this summer. The porous pavement parking lot was built on “structural soil,” a mix of large gravel, soil and other amendments engineered to support the weight of pavement and cars but able to absorb water and the growth of tree roots. Using the structural soil made it possible to add trees to the parking lot without losing any parking spaces.

Green Girl Land Development Solutions 3J’s Engineering & Consulting Firm and D&T Excavation, Inc., the park district’s contractor, all played key roles in the project.

Trees were planted in the wells in early August.

“We applied for the grant three years ago,” Wegener noted. “Finalizing the agreement with DEQ and finding partners took over a year of discussions. This summer, all the construction happened very quickly.”

Any funding left over from the $50,000 grant, which expires at the end of the calendar year, will be used for on-site landscape architecture demonstrations.

“We can show others how we did it,” he said, “and encourage others to follow suit.”

For more information, visit or SUBMITTED PHOTO - New native plantings in linear tree wells work with vegetation bioswales, above, and newly installed porous concrete pavement to filter and minimize stormwater runoff in the Sunset Swim Center parking lot.

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