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.

http://flickr.com/photos/eyefruit/51110795/

How well does it work in areas where the ground freezes (New England etc...)?

Posted by: Garth on February 1, 2008 6:46 AM

Same question as Garth essentially... Does it work in areas with a repeated freeze/thaw cycle during the winter months? (For me: Ohio)

Posted by: Eric on February 2, 2008 4:26 AM

Pervious pavement systems work in low speed situations and in freeze thaw situations. The key is having sufficient void space from a layer of crushed stone below the pavement layers to store water as is infiltrates the soil. As soon as a rain event is over, or a warm day where snow is melting, the water is below the pavement, thereby not having the adverse affects one would think when it freezes again. There are some pictures out there of two grocery stores nextdoor, one with a normal parking lot, and one with the pervious one. The pervious one needs far less salting and ice removal through the winter because not puddles form. And thus far has held up very well.

Posted by: greg on February 3, 2008 7:03 AM

There is a similar technology that was developed in Mexico City, but has representation in the US, called EcoCreto (http://www.ecocreto.com/home.html). The porous concrete does well in cold weather and the company claims that for each square foot of EcoCreto pavement up to 45 gallons of water is returned to the aquifer per year.

Posted by: Sara Standish on February 3, 2008 8:16 AM

I live in Austin, and though there's tremendous interest in protecting our fairly fragile but much loved watershed, there doesn't seem to be much interest in porous pavement- something I find absurd or at least unfortunate.

Are there any initiatives to require parking lots and low-traffic residential streets to be pervious in any major cities or towns right now? This one seems like such an easy one to pull off politically.

Posted by: Donald Jackson on February 3, 2008 1:34 PM

Here's a piece from the International Herald Tribune about Chicago's use of permeable pavement in it's alleys.
http://www.iht.com/articles/2007/11/26/america/chicago.php

Posted by: Todd on February 8, 2008 12:56 PM

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