Traditional paving is impervious to water and directs stormwater runoff to street intakes or the nearest body of water without treatment. Permeable pavers are a stormwater friendly alternative to traditional pavement, allowing water to filter through the sides of the stone and into the layers of aggregate holding the layers in place and acting as a reservoir prior to the water percolating into a subgrade mix of sediment or being piped away through a perforated piping below the structure. Similar products include porous and pervious pavers, porous asphalt, pervious concrete, and grass or gravel pave systems. All have subtle variations to their design but each product will allow runoff to percolate directly into the hard surface to increase water quality and retention.
Roads, parking lots, and driveways account for the majority of impervious surfaces in urban areas. Even gravel roads are considered an impervious surface because it is difficult for water to soak into the packed gravel surface. This is also true for unpaved lawns with high clay content or packed soils from heavily trafficked areas.
Permeable paving provides the same functionality as traditional paving but with the ability for water to infiltrate directly into the subsurface rock chamber and percolate into the soils below or be carried off by an installed perforated sub drain. The more stormwater runoff that is absorbed means less runoff leaving the site and increases in groundwater recharge and water quality.
Permeable paver installation is a little more involved than a standard paver installation. The basic permeable paver installation begins with the placement of a perforated sub drain covered in various layers of compacted aggregate. The aggregate is then leveled before solid concrete pavers are placed on top with slight gaps between each one. The final step is distributing a granular fill between the gaps of the pavers. This granular fill is made of a granite chip or crushed stone designed to allow water to pass through with ease. A high flow geotextile fabric, specially designed for high water permeability is often used in the installation process to help hold or separate the aggregate between layers or as a base to separate aggregate from existing soils.
Permeable pavers can generally be used anywhere concrete or pavers would be found like driveways, parking lots, and patios. It is recommended to consult an engineer or professional installer before beginning. Rainscaping Iowa is an excellent place to start your search with their list of Certified Rainscapers that have experience installing many different Best Management Practices.