This is an economical use of the land where the same area provides both parking and stormwater management. All soils have some permeability, ranging from several inches per hour to a fraction of an inch per hour. As discussed above, it is situations where bedrock is exposed or water table is at the surface, where recharge not feasible. Porous Paving differs from conventional bituminous asphalt paving by omitting the two smallest aggregate sizes from the mix. While recharge beds located under traditional impervious paving have been used in the past, recharge beds under porous paving is preferred since porous paving most closely mimics the previous infiltration response of the site.
Water is recharged evenly over the bed where it falls.
Porous paving parking lots constructed by Cahill Associates have never had a facility fail, with over forty systems constructed during the past seventeen years. They are generally located on the downhill side of any type of pavement such as roadways, driveways and walkways. These trenches can also be located in traditional drainage systems to reduce the volume of water that reaches a manhole. They convey water through a perforated pipe that infiltrates runoff along the way. Due to the volume of stormwater runoff, the University has a number of concrete channels conveying water that could be retrofitted.