Porous pavements have potential as a technology for maintaining predevelopment runoff levels by allowing infiltration and groundwater recharge. By acting as an attenuation and runoff reduction device, these pavements can decrease the volume and peak flow rate and increase lag time. Porous asphalt pavements have been used in highway and airport runway construction. This open-graded asphalt mix has been referred to as 'popcorn mix', or 'porous friction course'. The material is laid to a thickness of 0.75 to 1 in. The resulting pavement has a course surface texture and a high void space-ratio. The course surface texture provides pressure relief channels to remove water under excess pressure between the pavement and vehicle tire. Temporary storage is minimal because rainfall is diverted in nearby drains.