Permeable Pavement Systems to sustainably manage stormwater runoff
Managing stormwater runoff from parking lots, driveways and roadways is essential to prevent pollution and absorb runoff from asphalt pavement. The MA DEP has a Stormwater Policy with ten performance standards that must be met in order to comply depending on certain factors, such as impervious cover. The overall goal of the policy is to mimic natural hydrologic condition by having stormwater retained, treated and infiltrated or re-used onsite. Impervious paved surfaces can have adverse impacts on water quality, including transporting sediments and petroleum by products, and there are effective ways to prevent it. Constructed wetlands, raingardens and underground chambers are part of these innovative pavement alternatives. But there are also permeable pavement technologies (also known as porous pavement technologies) for civil engineers and project owners that are powerful tools to protect watersheds.
Many projects incorporate permeable pavement systems, and there are many products as well as custom designs that be implemented to meet site specific needs.
A brief summary of these options is:
- Proprietary BMPs (Best Management Practices) :
BodPave85 is a cost-effective porous paving solution with very little maintenance installed in parking stall areas. This system is composed of 100% post-consumer recycled plastic. This highly porous reinforced gravel profile stabilizes the area, drains water and provides a storage capacity during rainfall events. The 4-inch clean gravel profile will accommodate an additional 0.75 inch to 1 inch of rainfall over its relative area.
GravelPave2 is another permeable paving system. This system can be used for the entrance road but also for driveways and onsite parking. This system provides a natural gravel road look. The structure is composed of cylinders connected by a grid with an attached geotextile fabric and it is anchored to a base course with ring-shank spikes.
Another example of a low-impact parking improvements project is Geoblock. This is a porous pavement system linked with sustainable design practices. To be more precise, Geoblock is a vegetated parking lot that suits the needs of an unfrequent use traffic parking (i.e. overflow parking areas). It provides infiltration of rainfall with minimal amount of runoff and the grass surface reduces heat island effects associated with the asphalt.
The University of New Hampshire (UNH) Stormwater Center provides research of stormwater treatment system in order to help water managers, planners and design engineers in New England and in the United States in their projects by providing them resources. Its main goal is to protect water resources by managing stormwater effectively. The UNH Stormwater Center has developed an effective permeable paving profile for which most engineering designs are based, it is as follows.
Typical Parking Area Cross-Section for Pervious Pavement System
Porous pavement systems should be installed on pedestrian-only areas and for low-volume, low-speed areas such as overflow parking areas, residential driveways, bikepaths. It is not appropriate for high traffic areas, because it has lower load-bearing capacity than conventional pavement and area has a risk of transporting petroleum hydrocarbons to the groundwater table if not sited properly. The permeability of the underlying soils has to be of at least 0.17 inches per hour. This system does not require any additional land, thus it is a perfect technical solution for dense urban areas.
Porous pavement systems are really efficient for recharging groundwater and reducing stormwater runoff volume. Porous paving can infiltrate as much as 70% to 80% of annual rainfall. This is an excellent technique to reduce peak discharge rates significantly by diverting stormwater into the ground and away from pipe-and-basin stormwater management systems. Porous paving can also increase the effective development area of a site by reducing the need for large stormwater management structures.
However, requirements must be observed:
- Porous paving must not receive stormwater from other drainage areas (i.e. rooftops, walkways, parking area)
- Porous paving has to be used only on gentle slopes (less than 5%)
- This system cannot be used in high traffic areas
Concerning the design, there are three different types of permeable paving, constructed over a storage bed:
- Porous asphalt and pervious concrete
- Paving stones
- Grass pavers
Some designs incorporate an “overflow edge”. This is a trench surrounding the edge of the pavement.
Porous pavement can be successfully installed in cold climates and they perform well there, because the design includes features to reduce frost heaving. This system can reduce meltwater runoff and avoid excessive water on the road during the snowmelt period.
- Maintenance requirements :
Maintenance is essential and required in any porous pavement systems. Cleaning the pavement surface helps prevent clogging. If the surface clogs, the system efficiency will considerably decrease because stormwater will flow over the surface and into the trench, and infiltration and treatment loss will occur.
Surface cleaning consists in frequent vacuum sweeping (monthly) along with jet washing of asphalt and concrete pavement. Annually, the surface must be inspected for deterioration or spalling. And periodically, grass pavers must be reseeded to fill in bare spots.
Some rules must be known and respected too as: minimizing salt use during winter months, avoiding winter sanding, monitoring the paving surface (to make sure it drains properly after storms), posting signs identifying porous pavement areas or never re-seal or re-pave with impermeable materials.
For more information about the permeable pavement systems, please contact John McAllister at firstname.lastname@example.org or at (508) 747 - 7900 x 117.