Urban areas are blanketed with roads, sidewalks, parking lots and buildings that seal the ground off from water that would otherwise be absorbed and filtered by soils and plants. Whenever it rains, water runs through the streets, down storm drains and into local waterways without being cleansed of all the impurities it picks up along the way. This stormwater can be managed, however, by replacing typical pavements with porous asphalt, cement and pavers that allow water to pass through them. This reduces flooding and pollution by allowing the water to be absorbed and filtered naturally by the underlying soil. These "pervious" pavements perform best in pedestrian walkways, sidewalks, driveways, parking lots and low-volume roadways.
Viewer Tip: If you'd like to replace a driveway, walkway or patio at your home, here are some tips:
- Porous Asphalt: This material is best suited for your driveway. Make sure that the pavement contractor is using asphalt that has 16 percent of its space devoted to air voids to maximize its permeability. The asphalt should be 2-4 inches thick and laid upon several layers of different-sized rocks.
- Pervious Cement: This type of pavement works well for footpaths and driveways. Make sure that the pavement contractor is using cement that has an average void space of between 15 and 35 percent to maximize permeability. The cement should be 4-5 inches thick and laid upon several layers of different-sized rocks.
- Permeable Pavers: This pavement structure uses interlocking blocks of concrete or stones that devote 5 to 15 percent of surface area to voids filled with sand, gravel or sod. This type of pavement can also be laid out in a lattice grid to maximize permeability.
(Sources: U.S. Environmental Protection Agency. “National Pollutant Discharge Elimination System: Pervious Concrete Pavement.” Accessed Online May 8, 2012.; U.S. Environmental Protection Agency. “National Pollutant Discharge Elimination System: Porous Asphalt Pavement.” Accessed Online May 8, 2012.; U.S. Environmental Protection Agency. “Greening EPA: Permeable Pavers.” Accessed Online May 8, 2012.; Images courtesy EPA.)