Food For Thought: Pavement

16 04 2008

Pavement, asphalt, cement–all of these qualify as impervious surfaces. Environmental scientists talk about them a lot, especially when trying to find ways to reduce pollution from runoff in urban, suburban, and (increasingly) rural areas. The chief problem with impervious surfaces, you see, is their absolute inability to absorb water from both the spring shower and the torrential thunderstorm. Hence, the name impervious–the surfaces are not permeable to liquids.

The design was loved, in its infancy, for exactly this quality; unlike dirt roads, pavement did not turn into a shape-shifting, liquid mire feared by all motorists. These days, however, as runoff from so many roads, parking lots, suburbs, and industrial parks is affecting nearly every inhabited watershed in the country with disturbed water quality and increased flooding, concerned citizens are looking for a better hard surface. There are now permeable pavement materials, but these are not yet stable enough to be considered for heavy traffic surfaces like highways, and are mostly used on parking lots. They are nevertheless a great start, allowing rainfall and snow-melt to trickle into the lower layers of surfacing and even to the ground, mimicking the natural ability of soil to return water to the groundwater system so crucial for humans and ecosystems alike.

This little lesson is all to say that you might do yourself and all other living things a favor if you try to reduce the amount of pavement in your own little corner of the world. This pertains mostly to those ready to build or modify their home, who can make choices about the amount of impervious surface associated with it. Permeable pavements are certainly a worthy option, but might be cost-prohibitive for some. Other options include brick and flagstone paving with spaces between stones to filter runoff through sand and gravel. The next, admittedly logical thought goes to grass, but to step up the green quotient, consider natural landscaping options like native plants. That is a subject with much to mine–for another day.

For now, consider that the ground has been controlling rain flows for as long as it has been around, which is longer than even cement. So, before you coat your lawn in black-top to make room for your RV, consider whether it’s really necessary. Besides, it reflects solar heat so well, you may have more global warming in your own back yard than you bargained for.

P.S.  For the scientifically minded and curious, here are some effects of impervious surface on aquatic organisms and stream health, from Maryland Department of Planning:

>2% impervious surface: brook trout and other pollution-intolerant species disappear;
>10% impervious surface: fish habitat is degraded with loss of fisheries and crab production;
>15% impervious surface: biotic integrity ranges from fair to poor;
>25% impervious surface: restoration is difficult, and only hardy species are present.

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2 responses

16 04 2008
Becky

Interesting stats…

I’d love to have a driveway made of permeable pavers…maybe someday!

18 04 2008
Mister Moone

Re:
“The next, admittedly logical thought goes to grass, but to step up the green quotient, consider natural landscaping options like native plants.”

Lately I have been considering those hexagonal cement sections with open centers that allow grass to grow up through them while allowing a hard/almost pavement like surface for parking…

Wayne

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