Permeable or perforated paving materials or pavers with spaces between pavers allow transmission of water to an aggregate base, reducing runoff volume and improving water quality. Runoff is temporarily stored in the base and slowly evaporated and released to storm sewers. Paving blocks and grids, the most common and available type of permeable pavement, are modular systems containing openings filled with gravel or rock chips. Porous pavement, concrete, and asphalt contain larger than typical aggregates and pore space to allow water percolation, but are less common with greater design concerns. Variations on gravel are a third type of permeable practice.

Applicability

Permeable pavement is appropriate for new and retrofit projects on existing streets, full and temporary (overflow and special event) parking lots, alleys, sidewalks, utility and access roads, emergency access lanes, fire lanes, and driveways. Not appropriate for vehicle service stations, gas stations, and other areas used for transfer or storage of hazardous materials.

Benefits

• Reduces stormwater runoff volumes by 20% or more depending on depth of the aggregate base.
• Reduces stormwater runoff rates, by up to 95%.
• Filters sediments, hydrocarbons, nutrients, and other urban pollutants from runoff and reduces runoff temperatures.
• Can help meet detention requirements and reduce stormwater conveyance and detention infrastructure needs (detention storage can be provided within the gravel base below the surface.)
• Reduces need for deicing salt and salt impacts to water quality.
• Less ponding of water on the driving or parking surface reduces skidding, hydroplaning, and ice buildup.