Permeable Pavement FAQ
What's so great about holes in pavement?
(Hint: We're not talking about your garden variety cracks in driveways or sidewalks.)
- Permeable pavement allows water to flow through tiny, connected holes into the gravel substrata beneath the pavement surface, then into the soil.
- More widespread use of permeable pavement could help safeguard our fresh water resources.
How does permeable pavement work?
Permeable pavement can be used for sidewalks, driveways, parking lots and many other uses. It has three layers.
1. Surface layer or cover. The surface layer provides a solid surface over which people and vehicles move.
2. Gravel or aggregate layer. This base layer is immediately below the surface layer. It supports traffic on the surface layer and stores water during and right after a storm.
- This gravel layer, because of its surface area, helps cool the water. The cooler water also holds more oxygen, which is important when the water eventually reaches a body of water, such as a stream, pond, or lake.
- The gravel can hold bacteria that can help break down petroleum products and other contaminants.
3. Sub-base layer. The sub-base, also known as situ soil or underlying soil, is the soil just below the gravel layer. It filters water and removes pollutants.
What kinds of materials are available?
Many attractive, long-lasting new choices are coming onto the market. The Morton Arboretum has installed six types of permeable pavement on the grounds.
Why should I consider installing permeable pavement at my home or business?
- Fresh water is a precious resource. Only 2.7 percent of the water on earth is fresh water. Most is frozen in glaciers and ice caps. Less than .05 percent of all fresh water is available for living things. Pollutants and sediments reduce that percentage.
- Widespread use of impervious (hole-less) pavement contributes to water pollution. Asphalt and concrete roads, parking lots, and sidewalks don't allow water to penetrate the soil below. As water travels (we call this "water runoff") along the surface, it collects pollutants, such as oil and fertilizer, and eventually deposits them into water sources. Other common pollutants from water runoff are E. coli, sediments, phosphorus, zinc, cadmium, and copper.
- Polluted water runoff damages natural environments. Just as we need clean, healthy water to survive, so do plants and animals living around us. Water runoff eventually concentrates in an area where it pollutes soil. Or, runoff enters a waterway or wetland: a marsh, fen, sedge meadow, spring or other body of water that acts as nature's filtration and flood control center. This wetland ecosystem is fragile.
- Runoff into our waterways increases flooding. When we pave large expanses of land and send the runoff into waterways, the excess water can bring streams, lakes, and rivers to overcapacity. This causes flooding, which can damage our homes and communities. It also erodes waterway banks, exacerbating flooding problems.
What can the use of permeable pavement help achieve?
Studies have shown that the use of permeable pavement helps to:
- Reduce water runoff in parking lots and roadways
- Replenish underground water sources
- Ease flooding of nearby streams and rivers
- Cut costs for developing retention basins
- Decrease pollutants in water runoff
- Reduce irrigation of area plantings
Where can I find more information?
American Society of Landscape Architects' Sustainable Sites Initiative: www.sustainablesites.org/hydrology/
Interlocking Concrete Pavement Institute: www.icpi.org
Prairie Rivers Network Guide to Managing Stormwater with Green Infrastructure: http://prairierivers.org/wp-content/uploads/2008/07/PRN-StormwaterMgmnt-GuideBook.pdf
U.S. Green Building Industry's Green Home Guide: http://greenhomeguide.com
Description of the permeable parking lot at The Morton Arboretum Visitor Center