Spongier Surfaces Reducing Stormwater Runoff

By Trey Cody

Think about the sponge on your kitchen sink.  When you hold it under the running faucet, it absorbs a surprising amount of water.  But what if the sponge was covered in plastic wrap?  The water would hit the surface and flow right off.  We can see this same concept at work in our urbanized watersheds where, in many areas, green space that once absorbed rainfall has been replaced by hard surfaces that water can’t penetrate.

There are lots of ways that cities and towns are trying to get closer to their original, spongy state.  Having a surface that is porous and permeable reduces the effects of stormwater runoff on receiving streams, like stream bank erosion and negative effects on aquatic plant and animal life.

That’s why porous paving projects are popping up all over the place.  Permeable paving refers to a different way of mixing or constructing concrete or asphalt that allows water to flow through the pavement and into the ground instead of over it.

            One project can be found in our neighboring EPA Region 2’s Laboratory in Edison, New Jersey (above), where three permeable surfaces are being tested on the site of a former concrete parking lot. The performance and capabilities of these systems are being documented as part of a long term project to study the effects of paving materials such as porous asphalt, porous concrete, and interlocking concrete paver blocks. The parking lot will be monitored for its ability to accept, store, and infiltrate stormwater, water quality performance, urban heat island mitigation, maintenance effects, and parking behavior.

Closer to our regional office home, the first porous street in Philadelphia was recently unveiled.   AndWashington D.C. has done a number of Green Alley Projects using permeable pavement for the street surfaces.  Have you seen other examples of pervious pavement near you?

To learn more about permeable pavement and other green infrastructure techniques, and how it benefits water quality, check out EPA’s Green Infrastructure Page.