Pervious Paving
Pervious pavement, also known as porous pavement, allows stormwater to seep into the ground where it is naturally filtered rather than contributing to runoff. It consists of a permeable surface course on top of layers of gravel and rock laid upon uncompacted soil. The permeable surface course can be one of the following types:
- Porous asphalt or concrete – low to no fine material in the mixture results in a course aggregate with a system of interconnected voids; concrete is more durable than asphalt.
- Structural pavers – support heavy vehicles; two types:
1. Open-celled, preassembled grids, usually made of recycled plastic, are filled and covered with gravel or soil topped with turf grass; prevent erosion.
2. Interlocking blocks made of concrete, brick or other material, with pervious material filling gaps between blocks; aesthetically appealing.
General considerations:
- Appropriate for use on well-drained soils and on flat or very gentle slopes
- Appropriate for pedestrian use, parking lots, roads with low-volume traffic, or similar uses
- Not appropriate in areas of highly contaminated runoff, such as gas stations or truck stops
- Not appropriate near groundwater drinking supplies
Rationale
Impervious surfaces disrupt natural hydrological cycles and contribute to the urban heat island effect. Stormwater cannot percolate into the ground and instead travels quickly across these surfaces, picking up many contaminants before reaching sewers and eventually lakes, streams and groundwater. Problems associated with stormwater runoff include poor water quality, erosion and degraded wildlife habitat.
Effort Required
- Hire qualified contractor with specialized pervious pavement experience
- Conduct geotechnical analysis of the site to determine technological feasibility
- Implement erosion and sediment control of surrounding areas
- Develop inspection and maintenance plan including vacuum cleaning 2 to 4 times per year and education of facilities staff Install signage to communicate restrictions on use
Benefits
- Among EPA’s Best Management Practices for Stormwater Management Reduces runoff, flooding and erosion
- Removes pollutants as water percolates through the pavement and underlying soil
- Allows replenishment of groundwater
- Reduces solar heat-gain thereby helping urban lower heat island effect
- May reduce overall project cost Frees land for other uses when other stormwater measures are eliminated
- Improved safety due to better traction, reduced glare and reduced icing hazards
Risks
- Improper site preparation or construction can result in low porosity and durability
- Clogging or damage can result when not maintained properly or if not protected from nearby construction activities or adjacent landscaping
- Groundwater contamination can result if applied in areas of highly contaminated runoff, such as fueling stations
Action Agents
Developer, facilities manager, landscape architect
Cost
Pervious pavement often results in lower overall construction costs due to elimination of the need for other stormwater management measures. Porous asphalt costs approximately 10-15% more than conventional asphalt, while porous concrete costs about 25% more than regular concrete. Structural pavers can be three or four times more expensive than conventional pavement. Maintenance for a porous parking lot costs on average $200 per acre per year.
Water from precipitation that flows over nonporous surfaces into sewer systems or receiving water bodies.Allows more than 50% absorption of water.Unwanted elements that may reduce the quality of natural systems (air, water, land). The absorption of heat by dark, non-reflective hardscapes (including pavement and buildings) and its radiation to surrounding areas. A problem in urban areas, the effect is exacerbated by vehicle exhaust, air-conditioners, and street equipment.Allows water to infiltrate into the ground. See PERMEABLE SURFACE.
