Walking along Lake Washington in Seattle recently, we noticed that one of the city's boating centers had repaved its rather large parking lot. What struck us about the paving project was that the city had repaved the lot using impervious black asphalt--surprising for a city that prides itself on being "green" (cf. our recently adopted "zero waste strategy"), but shocking considering the parking lot sits mere meters from a large, heavily used body of water.

What reminded me of that incident was a story in the Salem, Oregon Statesman Journal about a system of porous streets in that city's Pringle Creek Community, a housing development that has gotten national praise (even landing on Natural Home's list of the top 10 "green" housing developments in the US) for its green building and sustainable-design practices. Community members had worried that the system would not be able to stand up to Oregon's wet winters; so far, with February getting underway, residents have been hard-pressed to so much as find a puddle.

Pringle Creek, a 30-acre, 139-lot development, boasts the largest porous street system in the country, although interest has been increasing exponentially, according to the Oregon Asphalt Pavement Association, whose director, Jim Huddleston, told the Portland Journal of Commerce that he looked forward to a day when cities routinely used porous asphalt to pave roads, not just parking lots.

Porous pavement has been around since the 1970s. It consists of regular asphalt from which the smallest particles have been removed, allowing the vast majority of liquid that hits the pavement to pass through. Stormwater drains through the asphalt and infiltrates slowly into the underlying soil. Although it does cost more, it holds up as well as or better than traditional asphalt; a test street in North Portland demonstrated that porous streets can hold up to regular city traffic.

Most importantly, unlike impervious pavement it allows 90 percent of stormwater to infiltrate back into the ground. Impervious pavement, in contrast, gets rid of stormwater in the form of runoff; that in turn leads to more polluted waterways, more frequent and severe flooding, loss of natural storage capacity in plants, wetlands, and soil, and reduced groundwater recharge. Other solutions include reducing the amount of impervious surface in new developments, routing water to areas with soil and grass, building retention basins, and (my favorite!) xeriscaping.

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