Municipal engineers don’t exactly have reputations for being devil-may-care, live-on-the-edge risk takers. Speaking generally, they work hard, take their jobs seriously, and really really want their projects to work. Collapsed bridges and over-flowing sewers don’t look so hot on the resume.
But stormwater engineers in Gresham, a neighbor to Portland, and Issaquah, located in the foothills of the Cascades outside Seattle, have built some interesting — even a touch experimental — roads and parking lots using permeable pavement.
The main reason for using permeable pavement, which comes in two basic flavors: porous asphalt and pervious concrete, is to help shrink and clean polluted stormwater runoff. Instead of sheeting off pavement with a slug of toxic chemicals, rainwater trickles through pores in the pavement, soaking into the gravel and native soils below. In addition to treating stormwater, the pavement is safer for drivers because it reduces hydroplaning and the glare from wet pavement. Plus, it can save money by eliminating the need for traditional, costly stormwater pipes and retention ponds or vaults.
Permeable pavement is increasingly being turned to as a “green” technology for managing dirty stormwater, but the truth is, it’s still an approach that’s under development.
That’s why it’s interesting to see these two smaller cities tackling projects that stretch into uncharted territory for the Northwest. In Gresham, the city installed porous asphalt on a sloped road with less-than-perfect soils — two factors that tick up the degree of difficulty. Issaquah built a 1.5 acre porous asphalt parking lot at a formerly unpaved site that was so poorly drained, it was known for its muddy potholes.
“Everyone’s cautious on the public side,” said Steve Fancher, director of Gresham’s Department of Public Works. “You don’t want those failures.”
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