Parking lots cover some 5,000 acres of land in the Tualatin River basin, channeling a massive amount of runoff onto city streets and then into the river.

But what if a parking lot operated more like Mother Nature?

That’s what Tualatin Hills Parks & Recreation District and Tualatin Riverkeepers set out to do in a demonstration project at Sunset Swim Center in Washington County.

The center’s new parking lot is made of porous concrete that allows rainwater to pass through and soak into the ground. That’s part of a larger remodel project funded by the parks district’s 2008 bond measure.

Tualatin Riverkeepers then secured a grant from the Oregon Department of Environmental Quality to pay for linear tree wells in the parking lot. Those use “structural soil,” a mix of gravel, soil and other amendments, which supports the weight of pavement and vehicles and allows tree roots to grow and water to infiltrate. Using that soil mix allowed the addition of trees to the parking lot without losing any parking spaces.

A grant from the J. Frank Schmidt Foundation paid for the trees.

Tualatin Riverkeepers is hoping the new “runoff-free” parking lot becomes a standard for parking lot construction.

Steve Law can be reached at 503-546-5139 or This email address is being protected from spambots. You need JavaScript enabled to view it.

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