Porous asphalt provides better water quality - Pt3
Posted by Jesse Willoughby on Thu, Apr 23, 2009 @ 06:33 AM
Image: Hydrograph comparison showing how porous pavement reduces peak flow and total volume of runoff
Source: Cahill Associates
Impact on groundwater
Asphalt pavements are compatible with clean water. Studies show that asphalt pavements and stockpiles of reclaimed asphalt pavement do not leach.
Contaminants on the surface of pavements tend to become part of runoff, but with a porous pavement, they are washed into the stone bed. From there they flow down into the soil, where beneficial bacteria and other natural processes cleanse them. Data are limited, but indicate a very high removal rate for total suspended solids, metals, and oil and grease.
Figure 1 shows the effect of a porous asphalt pavement on the hydrology of a developed site.
Cool cities
Porous asphalt pavements have been shown to mitigate the urban heat island effect. Open-graded asphalt roads and highways-which use the same surface material as porous parking lots-have been shown to lower nighttime surface temperatures as compared to impervious pavements. In at least one city, the hottest heat signature is at the airport, with its thick, dense, impervious runways.
Comparisons to other asphalt pavements
The surface of a porous asphalt pavement wears well. While slightly coarser than some pavements, it is attractive and acceptable. Most people driving or walking on the pavement will not notice (or believe) that it is porous.
Like all asphalt pavements, porous pavements are ADA-friendly.
Environmental applications
Asphalt pavements have been used for many years to enhance water quality. At landfills, asphalt liners and caps keep contaminants from leaking into groundwater. Drinking water reservoirs lined with asphalt pavement have been used in California since the 1950s. Salmon hatcheries and fish rearing ponds in the Pacific Northwest use asphalt liners.
Variations on the theme
Porous asphalt can be used successfully in parking lots, walkways, and playgrounds. Several current suburban projects are exploring its use in subdivision roads. A few porous highways and city streets have been constructed, both in the U.S. and in Europe, and have performed well.
The open-graded asphalt surface used for porous pavements has been used extensively to surface high-volume highways that carry heavy trucks. Its benefits include noise reduction, a decrease in splash and spray kicked up by vehicles in heavy downpours, and mitigation of the urban heat island effect.