Articles / The Promise of Permeable Paving

Flooding and sewer overflow in West Haven, Connecticut. Credit: Christopher Zurcher

The impervious paving with which we are so familiar—the asphalt and concrete that covers most of America’s parking lots, driveways, sidewalks, highways and interstates—plays an outsized role in many of our water quality problems—including flooding, beach closures, contamination and groundwater depletion. Atop these surfaces sits motor oil, debris, bacteria, garbage and more. With storms come flooding and erosion—pollutants wash off paved surfaces and into waterways. And since much of the water washing off of roadways ends up in the stormwater system, there’s less to recharge local aquifers and so less water less water for lakes and rivers, posing a threat to aquatic habitat.

We can’t replace all the roads and parking lots with the forests and fields of yore, but given that paved surfaces in the U.S. cover an area almost the size of Ohio “permeable paving” is a partial solution to the runoff problem and has even become something of an environmental buzz-phrase. In part, this is because both concrete and asphalt can be engineered to be porous, and spaced-out pavers can create a permeable surface as well, offering engineers variety of ways to work.

Bruce Ferguson, the Franklin Professor of Landscape Architecture at the University of Georgia, explains the benefits of porous paving spread through the urban fabric: “In general, because it is porous and permeable, it restores natural environmental processes in place—right in the same place where the pavement is built to support urban land use, traffic, economy and human activity. Watersheds, aquifers, urban trees and natural systems all benefit.”

The Problems with the Standard

Impervious paving has been known to cause sewers to overflow, spilling polluted wastewater into nearby streams and waterways  and harming water quality. One of the problems is based on a complex system: If rainfall cannot infiltrate back into an aquifer, the water from underground sources for streams is lost, as are the wetlands fed by springs. The entire cycle is disrupted.

The speed of water runoff from impervious surfaces is as big a problem. It can come surging into watersheds fast enough to cause rapid rises in water levels and damage to habitats, and it can even trigger flash floods.

Implementing Permeable Paving

Permeable paving serves as a filter that lets rainwater trickle through to the soil below while trapping most pollutants in its porous composition. Oil breaks down in the permeable concrete, thanks to microbes that naturally thrive on the surface of its internal structure, leaving behind pollutants as rainwater seeps back down into the earth.

On roadways, permeable paving is also safer—a major spur to its implementation, as may be the case with policies that require permeable paving on certain roadways in Oregon and Georgia. Many of these only have a permeable layer on the surface, but this can reduce hydroplaning and accidents associated with wet weather. Although this technique does not allow as much water to infiltrate as paving that is permeable through-and-though, it drains more water into the soil on the edges of roadways than impervious surfaces from which more water evaporates, according to Ferguson as quoted in Environmental Health Perspectives.

One state with some of the greatest risks to wildlife habitat has also been one of the leaders in permeable paving. Oregon, with its cool salmon and trout streams, is working to protect its waterways from being flooded with hot water off black pavement that could raise water temperatures and threaten the aquatic life. Georgia, another state leading the trend, has other specific resources in mind to protect: for one, its stately, centuries-old live oak trees that require significant rainfall.

“We were able to work with Savannah to successfully get them to install porous pavers around old trees in our development,” says Tommy Linstroth, principal and CEO of Trident Sustainability and former head of the Georgia chapter of the U.S. Green Building Council. “The trees are able to get the water they need to the roots and to grow undisturbed.” There are no long-term results for the health of the trees, but Linstroth says it looks “promising.”

Permeable paving typically costs about 20 percent more, but with proper installation and maintenance, and with the financial incentives that many municipalities offer, it can mean great savings. One reason for this is that successful permeable paving renders stormwater retention ponds unnecessary, freeing up the land they require. According to Linstroth, “This gives developers more buildable area to maximize density rather than having to waste unleasable space on a giant pond." This may motivate developers and environmentalists alike. 

And this revolution isn’t just for urban planners and highway engineers: It’s also something a homeowner can think about. Consider the amount of pavement on your property: Have a driveway, patio or basketball hoop? If you’re redesigning or replacing your own pavement, consider permeable pavers, which can both help hydrate your lawn and protect your local waterways. Because pavement is so ubiquitous, this quiet, gradual change has the potential to make an enormous difference from coast to coast. For more ideas, see “Community Measures to Prevent Beach and Ocean Pollution.”