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| Porous surfaces control storm-water runoff |
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| Home & Building |
| Written by Jean Starr |
| Thursday, 05 July 2007 05:18 |
A puck-sized sample of pervious concrete.
We can’t do much about the weather, but there are options for patios, driveways, sidewalks, parking lots and other hard surfaces in the use of porous, or permeable materials. The move to permeable surfaces is driven by two things, said Drew Bender, regional manager of J.F. New, a natural-resources and ecological consulting firm headquartered in Walkerton, Ind. The first is regulations to require the control of flooding and to improve water quality. Second, there is a cost benefit to developers as space becomes a premium. "The opportunity to create green space and attractive features in sustainable development is catching on from a marketability standpoint," he said. Because porous concrete or asphalt is a relatively new process, it may seem costly. But that should improve as contractors become more experienced in the process. Engineers and scientists have made improvements in the design of storm-water filtration systems and have been successful with pervious surfaces. In Chesterton, Ind., the Coffee Creek Center is an example. The effort combines native plants, whose roots filter pollutants, and underground pipes that put wastewater to work, said Steve Barker, director of the Coffee Creek Watershed Conservancy. A series of pipes, called level spreaders, move water captured in an underground pond downhill to nourish the plants in an expansive prairie. Permeable paving is most appropriate for sidewalks, patios, driveways or alleys. It is not for high-traffic or high-speed areas because it has lower load-bearing capacity than conventional pavement. "{quotes align=right}The initial cost for permeable paving is competitive with conventional materials{/quotes}, sometimes lower, sometimes higher," says the Partnership for Advancing Technology in Housing. PATH is a public-private initiative dedicated to accelerating the development and use of technologies that radically improve the quality, durability, energy efficiency, environmental performance and affordability of America's housing. PATH is supported by the U.S Department of Housing and Urban Development. {sidebar id=14 align=right}Pervious surfaces may eliminate or reduce the need for detention ponds in subdivisions and office parks. Runoff in these areas is directed from impervious surfaces to the ponds where it slowly seeps into the soil or is piped to water treatment facilities. Land that isn’t used for a pond can be developed into homes or offices. Pervious surfaces also reduce or eliminate soil erosion and other damage from storm-water runoff. Pervious materials have more voids, or air spaces, which allow water to pass through. Traditional concrete has from 2- to 6-percent void structure, while pervious concrete contains around 25 percent, said Pat Kiel, executive director of Indiana Ready Mixed Concrete Association. Pervious concrete mixing and application require special training. "You design it according to its purpose," Kiel said. "We like to over-design in Indiana because of the clay soils." The method that is used for pervious concrete application is based partially on a soil’s percolation rate. The soil percolation rate is the amount of time water takes to move through soil, measured in minutes per inch. Finer-textured clay soils have slower percolation rates than sandy soils. {sidebar id=15}Jim Miller of Cicero, Ind., trains both permeable-concrete producers and contractors. "They are revocable certifications, and are only valid after they’ve completed two successful jobs with a certified consultant on hand," he said. As more crews are certified, the price should become more competitive, Miller said. For property owners and developers who would like to consider porous pavement, Miller recommends checking out the Indiana Ready Mixed Concrete Association’s Web site, www.irmca.com to find a certified contractor.
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About the author Jean Starr
Jean Starr is a freelance writer from Chesterton, Ind., who writes on many topics, including the environment.
Jean Starr is a freelance writer from Chesterton, Ind., who writes on many topics, including the environment.
