Cities are increasingly turning to low impact development (LID) techniques to help meet water quality goals, promote natural conservation and reduce the need for costly stormwater infrastructure. One of the guiding principles of LID is to reduce impervious surfaces so that rainwater can soak into the ground where it lands instead of requiring construction of new drainage structures. For this reason, permeable pavement is often a key feature of LID projects.

Porous asphalt, pervious concrete and pavers are common permeable pavement systems. When installed properly, all three offer economic and environmental benefits including:

• Reduction in stormwater runoff
• Reduction in pollutants entering waterways
• Reduced need for drainage infrastructure
• Recharging of groundwater
• Reduced need for irrigation systems

Project type, location, budget and other factors should be considered before selecting a permeable pavement system. This 2016 study by the U.S. Environmental Protection Agency (EPA) compared the performance of porous asphalt, pervious concrete and permeable interlocking concrete pavers at its parking lot in Edison, N.J. The study found that while performance of the three systems varied, all three were effective tools for infiltrating direct rainfall and stormwater run-on. Here is a brief summary of each pavement system.

Porous asphalt

In most applications, porous asphalt is a cheaper option than pervious concrete or pavers. Although initial costs are typically higher than standard asphalt, it can be a cost-effective solution if it eliminates the need for stormwater infrastructure. According to the National Asphalt Pavement Association, porous asphalt can have a life span beyond 20 years.

According to the 2016 EPA Edison parking lot study, pervious concrete has the highest infiltration rate of the three pavement systems. Properly constructed parking areas utilizing pervious concrete will last 20 to 40 years, according the Southern California Ready Mixed Concrete Association. Just as standard concrete is more costly than standard asphalt, pervious concrete is typically more expensive than porous asphalt.

Application Opportunities: parking areas, subdivision streets, pedestrian walkways, sidewalks, driveways and bike lanes.

Pavers

For most applications, pavers are the most expensive solution, primarily due to labor costs required for installation. They are appealing for their ability to add character to a site and come in a variety of options. Generally, there are three types of pavers used in LID projects. Permeable pavers, porous pavers and pervious pavers all achieve similar stormwater management goals, but each are slightly different. A permeable paver system directs water to its surrounding joints, which contain porous, crushed aggregate. Porous pavers utilize a cellular grid system reinforced with dirt, sand, gravel or grass. Lastly, a pervious paver allows water to drain directly through its surface into the ground below.

Application opportunities: parks, plazas, street tree planting areas, driveways, public spaces and outdoor seating areas.

In making project design decisions, a qualified professional engineer must balance the water quality benefits provided by permeable pavement solutions versus the need to account for the volume of stormwater at a particular location to avoid flooding of properties.