When heavy rainfall exceeds the ground’s capacity to absorb water, a natural process called runoff occurs. Water flows over the saturated ground and into streams, rivers, and lakes; however, there are many problems associated with runoff in today’s urban jungles. As cities and suburbs continue to expand outward, more and more non-permeable pavement is put into place. Runoff from non-permeable surfaces is not a natural process. As water runs off non-permeable surfaces, it picks up pollutants such as tar, salt, construction chemicals or waste, car oil, and antifreeze, carrying them to storm drains and into rivers and streams. Additionally, when water flows in rushes to rivers and streams, it does not percolate through layers of soil and porous rock to recharge the water table. This process is not only a vital step in the water cycle, for water tables and aquifers supply drinking water for many cities, it also is a natural filtration process of chemicals such as fertilizers and detergent. Runoff from non-permeable pavement is a real issue. According to Sierra Club, “a 30 foot by 30 foot patch of concrete can shed over 550 gallons of water from 1 inch of rain.” To mitigate the host of problems resulting from non-permeable pavement, including groundwater depletion and pollution of rivers and streams, individuals can replace non-permeable concrete and asphalt in residential driveways with permeable pavement options.
Installing permeable, rather than non-permeable pavement, in residential home drives and walkways is beneficial to more than just the environment. Permeable pavement, particularly interlocking pavers, can truly increase a homeowner’s property value. Permeable pavement also fights the heat-island effect, resulting in much cooler temperatures around one’s home. There have also been instances where homeowner’s have received credit from their municipality for the storm water functions provided by permeable pavement. Permeable pavement that is installed and maintained correctly can percolate between 5.6 to 18.5 gallons of water per minute per square foot based on design. Such high percolation rates can reduce the storm water maintenance required of the city, such as unclogging gutters and drains.
It is important to know that installing permeable pavement in your residence will make a positive impact upon the water cycle, the biological health of waterways and surrounding ecosystems, and the quality of drinking water. All types of permeable pavement are laid on top of a geotextile fabric and aggregate stone layer. First, rainfall is caught in the pores or spaces in the permeable pavement. The water then trickles through the stone aggregate and geotextile fabric. This assisted filtering process provides water the chance to slowly absorb into the soil beneath your drive. The permeable pavement and its sub-layers essentially provide a holding area, allowing the water to infiltrate slowly, unlike the non-porous pavements that act as a slip and slide right into the storm drain. Residential permeable pavement driveways provide the first step to recharging aquifers and the filtration of pollutants. They also lower the risk of flooding around your home during heavy storms and result in less ice buildup during the winter. The benefits of permeable pavement should outweigh the higher installation costs in most instances. There are a few types of permeable pavement typically available to homeowners: small stones, plastic or concrete grid, interlocking pavers, the Hollywood driveway, porous asphalt, and permeable concrete. There are different pros and cons for each type of pavement. Before selecting a type, consult with a professional contractor or installer who can advise upon the best option for your home. The maintenance required for porous asphalt, permeable concrete, and in some cases, interlocking pavers is annual vacuuming of debris to prevent clogging of pores. Talk to your contractor about the details of maintenance.
Small Stones: must be smooth, not gravel (water does not seep well between gravel particles). Small stones are by far the cheapest permeable option, but they are more easily displaced, especially during snow removal.
Concrete or Recycled Plastic Grid: form a honeycomb or lattice pattern where grass can grow in the free spaces. It is important to note that vegetated pavers require occasional mowing, like any other grassy lawn, and that grass will not grow in places where cars are parked permanently.
Interlocking Pavers: the most aesthetically pleasing of permeable pavement options. Some styles utilize small stones between pavers. There are many patterns and designs in which to array your pavers.
Hollywood Driveway: consists of two parallel strips of concrete or asphalt for cars to drive upon leading up to the house. This option is not optimal for multiple car driveways or for long driveways, for it can be difficult to maneuver up them on the strips.
Porous Asphalt: like traditional asphalt, but lacking the finer particles, leaving pores for water to trickle through.
Permeable Concrete: like traditional concrete, but lacking the finer particles, so there are many pores where water can trickle through. It resembles a Rice Krispie treat.
Permeable pavement is undoubtedly more expensive to install and requires some maintenance; however, permeable pavement can increase your property value, it does not have to be replaced as frequently as non-permeable options, and it can reduce storm water related problems.
Written by Claire Zinser, 2013 Summer Intern at The Conservation Foundation.
Works Cited
Balogh, Anne. “Permeable Surfaces: A Hot New Installation Segment.” LandscapeOnline.com: The Largest Landscape Database on the Internet. Landscape Communications Inc., n.d. Web. 28 Aug. 2013.
Eisenberg, Sheryl. “Permeable Pavement – NRDC.” Permeable Pavement – NRDC. Natural Resources Defense Council, n.d. Web. 28 Aug. 2013.
Ferguson, Bruce K. “Water Conservation Newsletter.” American Society of Landscape Architects. American Society of Landscape Architects, 2010. Web. 28 Aug. 2013.
“Permeable Paving.” City of Chicago: Water Management. N.p., n.d. Web. 28 Aug. 2013.
“Permeable Paving–The Environmentally Friendly Driveway.” Sierra Club Green Home: It Begins Where You Live. SCGH, n.d. Web. 28 Aug. 2013.
“Permeable Surfaces.” PREC – Program for Resource Efficient Communities Home. University of Florida: IFAS Extension, 2008. Web. 28 Aug. 2013.
Pineo, Rebecca, and Susan Barton. “Permeable vs. Impermeable Surfaces.” Sustainable Landscape Series. Cooperative Extension University of Delaware College of Agriculture & Natural Resources Botanical Gardens, 31 Jan. 2009. Web. 28 Aug. 2013.
“UNI ECO-STONE® FAMILY OF PERMEABLE PAVERS.” Eco-Stone Family of Permeable Pavers. Uni-Group U.S.A., n.d. Web. 28 Aug. 2013.