Design Considerations for Vegetated Permeable Pavement

Creating open, multifunctional spaces and providing green benefits

Angela D. Dye, FASLA, LEED AP

Permeable paving systems, in general, continue to grow in scope and practicality as we search for ways to reduce our carbon footprint, improve water quality, diminish flooding and erosion, reduce the “urban heat island” from reradiated (building and pavement) heat in our cities and environment, and add attractive open space to building sites and neighborhoods. The current varieties of permeable pavements are permeable asphalt, permeable concrete, permeable interlocking concrete pavers, and vegetated permeable pavements. Most research on any permeable pavement considers all these types to “substantially and significantly” reduce stormwater runoff.¹ Results from a study in 2007 at the North Carolina State University (NCSU) Permeable Pavement Research Lab showed that “all permeable pavements significantly and substantially reduced surface runoff volumes and peak flow rates when compared to standard asphalt…”

Vegetated permeable pavement will be the focus of this article, exploring some of the current environmental regulations, codes, and guidelines that incorporate their application, design considerations, modular options, and sustainable landscape benefits to help you make an informed decision. The main types of vegetated permeable pavements are flexible concrete mats, concrete grid slab, concrete grid paving units, and plastic geocells, each of which can be planted with turf or groundcover, or filled with aggregate or crusher fines.

Demonstrating Environmental Leadership

Using permeable pavement, whether vegetated or not, is one of several strategies within a comprehensive site design and green infrastructure approach to creating more functional and sustainable landscapes. The Environmental Protection Agency (EPA) considers “stormwater runoff in urban and developing areas to be one of the leading causes of water pollution in the United States.”² Since 2007, using Section 438 of the Energy Independence and Security Act, EPA has required federal agencies to reduce stormwater runoff from federal projects, compelling agencies to “lead by example” to clean up water resources by using “green infrastructure and low-impact development” techniques. In 2011, the EPA compiled a list of green infrastructure case studies nationwide. As part of a national rule-making process to create an EPA program to reduce stormwater runoff, 47.3 percent of the 479 case studies used some type of permeable pavement system, with just over half of the projects being retrofits of existing properties. Various projects are represented, from commercial, institutional/education, open space/parks, and transportation. The EPA's website Green Infrastructure provides information on each case study, its location by region, and research associated with infrastructure types.

Photo courtesy of Soil Retention Products, Inc.

 

What is Permeable Paving? Permeable paving is a range of sustainable materials and techniques for permeable pavements with a base and subbase that allow the movement of stormwater through the surface. In addition to reducing runoff, this effectively traps suspended solids and filters pollutants from the water.3

“The primary motivation for using permeable pavement,” according to Neil Weinstein, executive director of the non-profit Low Impact Development (LID) Center in Washington, D.C., “is that it doesn't eat up the land (like surface retention basins, bioswales, and filtration basins do). This is especially important in urban areas where sites are smaller and must meet stormwater regulations.” The LID Center works with many government agencies including the EPA, various universities, and the National Academy of Sciences to set standards of practice for use of permeable pavement of all types. Weinstein goes on to point out, “since stormwater regulation is so prevalent, use of permeable pavement is becoming much more known and used more often as a matter of course (to meet national pollution and stormwater requirements). It's available and has become more attractive.” LID finds the largest users are commercial properties such as offices and shopping centers with large parking areas. However, transportation and residential applications are also becoming more commonplace.

Main types of vegetated permeable pavements Photo courtesy of Soil Retention Products, Inc.

 

Reducing Flooding and Erosion While Cleaning Our Water
All permeable pavements have shown their ability to clean polluted urban runoff water before it reaches local streams and rivers by filtering out heavy metal contaminants such as lead, zinc, cadmium, and copper as well as acid rain and phosphorus. Individual projects, whether public or private, can potentially use them to meet local and federal flood control and stormwater pollution regulations under the Clean Water Act's National Pollution Discharge Elimination System (NPDES). According to EPA's website, “the NPDES permit program controls water pollution by regulating point sources (pipes and ditches) that discharge pollutants into waters of the United States. Industrial, municipal, and other facilities must obtain permits if their discharges go directly to surface waters.” Cities with separate stormwater systems, known as MS4s (Municipal Separate Storm Sewer Systems), are now required to control the quality of what flows off parking lots and other sites into their stormdrains. The value of permeable pavement systems to mitigate the flow of this type of pollution has increased its role in green infrastructure design, helping cities and private landowners alike to comply with these regulations. These pavements are strong enough to carry the loads from vehicles yet allow for rainfall infiltration through the pavement surface. This infiltration quality lessens the potential for flooding and erosion as well as cleaning stormwater.

Following on EPA's leadership in green infrastructure, many of the most recent and developed handbooks for best management practices (BMPs) and stormwater regulations are at the municipal level, in locations near bodies of water—streams, rivers, lakes, and coastal areas. This is where permeable pavement has seen its greatest public benefit—the cleaning of urban runoff into fisheries and water supplies. Areas with BMPs, guidelines, and regulations include the East Coast seaboard around Chesapeake Bay, Virginia; North Carolina; Washington, D.C.; and Maryland; the Great Lakes region especially around Lake Michigan; the City of Chicago; and the West Coast cities of Seattle, Portland, San Francisco, and San Diego, to list a few.

Research on the use of permeable pavement for stormwater and erosion control is extensive and compelling. Non-profit organizations such as LID Center and American Rivers tout permeable pavement and green infrastructure investment as important to the rebuilding of our aging national infrastructure. Several examples exist in the United States where local and state governments have adopted regulations, codes, BMPs, and guidelines specifying the use of permeable pavements.

The North Carolina Department of Environment and Natural Resources (NCDENR) guidelines adopted in 2008 consider permeable pavement as a stormwater design feature, giving credit for pollution prevention for runoff reduction. For NCDENR, permeable pavement is now considered equal to the permeability of turf, requiring 20 percent of parking lots be permeable pavement (or a suitable, environmentally friendly, alternative stormwater management practice).

The City of Santa Monica, California, recently adopted a municipal code to reduce stormwater volume and improve water quality from existing properties and new development into Santa Monica Bay. Developers must now reduce by 20 percent any projected runoff through an Urban Runoff Mitigation Plan, achieved by increasing permeable areas such as parking lots and driveways, while also increasing the percentage of green space. This is a perfect application for vegetated permeable pavement. A source for stormwater BMPs is the Stormwater Managers Resource Center (SMRC), a website established by the Center for Watershed Protection through an EPA grant. The SMRC is “designed specifically for stormwater practitioners, local government officials, and others that need technical assistance on stormwater management issues.”

Benefits of Vegetated Permeable Pavement

Photos courtesy of Soil Retention Products, Inc.

When permeable pavement is vegetated with turfgrass or groundcover, the overall effect can be stunning, and serves to integrate a project into its environment. Vegetation over pavement has the ability to absorb carbon dioxide, emit oxygen, and biodegrade pollutants. As a living plant material, its evapotranspiration naturally makes it cooler than inert surfaces such as concrete, reducing albedo and the Urban Heat Island (UHI) effect. The turfgrass surface reduces glare and absorbs noise, while adding to green open space on a developed site.⁴ In addition to this comfort factor, there is a distinct design advantage to vegetated permeable pavement systems since hardscape can be disguised and better integrated into the project's environment and ecology. Using vegetation or “soft” materials such as sand, gravel, or decomposed granite, for instance, the otherwise overwhelming effect of parking lot concrete or asphalt can be mitigated. Another advantage is that valuable space can now be considered multifunctional, creating a better aesthetic appeal and often a better neighbor without sacrificing buildable land (see photo 1 above).

Suitable for a variety of scales, vegetated permeable pavement is typically not used for major streets, except perhaps for parallel parking spaces. These pavements' ability to add vegetation into the voids, and even to cover the paved area, creates site area that becomes more a part of the landscape. Many applications are perfect for site areas infrequently used, such as fire lanes, utility easements, and drainage ways. Areas like these which use large amounts of space, but are seldom used, leave an under-utilized vacant area in a project. Vegetated permeable pavement is especially helpful to the designer and developer when site design or city code dictates accommodating these facilities. Critical when site area is limited, vegetated permeable pavement can add green space, giving additional landscape and usable area back to the project (see photo 2).

In one of the most recent examples of the effectiveness of vegetated permeable pavement, a 2008 study responded to the need to clean up beachfront runoff. An Oceanside, California, fire station tested the viability of using vegetated permeable pavement for washing fire trucks. The fire station is near one of the most polluted beach outlets in southern California. The test was prompted by a mandate of the San Diego Regional Water Quality Control Board to clean runoff from the washing of fire trucks several times a day. The trucks were washed on the asphalt driveway in front of the station, which drained directly into the San Luis Rey River just upstream. The installation of a vegetated flexible concrete mat was used to resolve both polluted runoff and sustain daily truck loads. Placed over a bed of granular infill and base material, the site experiences no runoff, storing up to 0.40 inch of water at the surface and infiltrating at a rate of more than 3.0 inches per hour (see photo 3).

Design Considerations for Vegetated Permeable Pavement

Design of a vegetated permeable pavement system for any site is a multidisciplinary effort. Once a project is envisioned, important site planning factors must be considered for building layout, access, circulation, and parking, not to mention federal, state, and local code requirement compliance. Vegetated permeable pavements can satisfy several objectives for stormwater management, while adding value and aesthetics to the project.

Structural and Stormwater Design
In one of the most concise summaries to date, a 2008 Australian conference paper, by engineering professors at the Universities of New South Wales and South Australia, lays out several distinct objectives to ask early on: “Flood mitigation/stormwater retention or detention? Water quality improvement, whether filtration or retention? Water conservation for collection and reuse? And ability to carry the intended site traffic.” In the chart below, a design decision flowchart clearly illustrates the process for designing a vegetated permeable pavement. A key design consideration is the composition of the subgrade (native soils below the paving section) and their infiltration rates. Depending on the composition of the subbase (structural base material), in some cases enough rainfall can be collected to offset and store a percentage of the increased runoff from site development. For some projects, this may eliminate an expensive and separate “hard” drainage system. For other projects, with native soils with low infiltration, excess water could be detained and stored. Use of this excess stored water may have to be considered. For example, this excess water could be harvested for reuse, or alternatively, piped away with an elevated underdrain. The paper points out another key design question, in addition to pavement system design life, rainfall absorption, infiltration, and retention: how thick the pavement should be to carry the intended traffic. Permeable pavement thickness may be slightly thicker for managing stormwater than for load bearing, but there is usually an associated economic benefit for its use.

 

Turfgrass Considerations
Vegetation, specifically turf, is commonly used as a surface for applications with light pedestrian traffic, such as parks or ballfields. For it to be a viable cover under vehicle traffic, the pavement design fundamentally needs to prevent soil compaction so that the living root zone for these plants is both porous and permeable to both air and water. Vegetated permeable pavement has void spaces between a load-bearing pavement material, which distributes the imposed load to the underlying base and/or bedding materials. “A reinforced turf surface bears traffic equally directly, …(and) assists the turf in resisting wear and compaction.”⁵ This support condition allows the plants the ability to stand up to increased traffic weight and volume. Root zone areas for vegetated permeable pavements vary by type of pavement, but the more access to root space, the more likely the turfgrass will survive.

Graphic courtesy of Soil Retention Products, Inc.

 

The soil area between cells is also an important factor to turfgrass health. Vehicle tires are flexible, so when void spaces are too large and overfilled, soil compaction will occur, which cuts off the air and water needed for plant growth. For example, choosing sod to top the permeable pavement for a fire lane (hopefully never used) may be an appropriate design choice. However, if the use is daily parking, applying turf by seed, and not over-filling the void space, is likely to give greater protection to the emerging root system. Choosing the appropriate method of turf establishment for the intended use can be especially critical when the pavement is saturated. With heavy and/or constant traffic, significant compaction in the void space can occur along with turf damage.

Another aspect of turf establishment and maintenance is to realize that the width of the load-bearing portion of any vegetated permeable pavement system is important to retaining turfgrass as well as carrying the traffic load. The greater area of contact between the pavement and the vehicle tire, the better the pressure is distributed and the root zone is protected. A relevant ingredient for healthy turfgrass is a bedding course, defined as the underlying sandy material between the pavement and its often heavily compacted base, which allows for a continuous symbiotic root zone and moisture for the plants. The depth of pavement can also have an impact on the ability for roots and moisture to spread along with similar-sized materials for infill and bedding course. That is because root zones are complex systems, with physical, chemical, and biological components. Each of these components together determines the quality of the turfgrass. Pavement systems which maximize the root zone area, while allowing for filtration and aeration, are likely to result in the best long-term vegetative cover.

Specifying the type of grass species or groundcover, and whether to seed or sod turfgrass over the pavement surface depends greatly on the location and intended use. Many geographic locations receive sufficient moisture to support turf without irrigation. Choosing the appropriate vegetation for the site conditions, and anticipating cold climate factors such as freeze/thaw cycle are also important design considerations. A pavement system can be designed to capture rainwater and collect the runoff for reuse as irrigation. If the vegetated permeable pavement also serves to enhance stormwater regulation, this may be considered an appropriate application of water in an arid environment.

Selection of a turf species must take into consideration microclimates like shade, slope, temperature variations, and seasonal conditions. Parking can create a microclimate that casts shade for a portion of the day over the turfgrass. This may affect the density and growth of some turfgrasses; therefore, specifying the correct species can be an important long-term maintenance decision.

Whether to use a warm-season grass or cool-season grass, bunchgrass or spreading grass type, one that is salt tolerant to de-icing or is shade tolerant, are all design considerations that are site and project specific. Ferguson, in his book Porous Pavement (2005), states that a warm-season grass such as Bermuda stands up well to traffic as does Tall Fescue (cool-season). However, some grasses may be considered an invasive species to native ecosystems. Local cooperative extension agents, state agricultural offices, and landscape architects can offer advice on which species are best.

Maintenance Concerns
As with any new construction, concern is always expressed for long-term maintenance and durability of the product. The non-profit organization LID Center has found that as with all the pavement systems—permeable concrete, permeable asphalt, permeable interlocking concrete pavers, and vegetated permeable pavements—“maintenance is low and has been shown to be quite resilient over time, as long as the openings remain permeable.”⁶ The pollution-trapping benefit of vegetated permeable pavements is apparent, but there may be some concern about this diminishing over time. With maintenance, these systems can reasonably last up to 20 years, according to several sources.

Here are some tips on keeping these systems functioning: 1) make sure drainage from other areas with sediment loads does not flow over the pavement, clogging the voids; 2) perform periodic inspections following storms greater than ½ inch in depth to observe any standing water; 3) consider choosing salt-tolerant grasses where de-icing is common, and adding Teflon runners to snow plow blades to prevent damage; 4) monitor the turfgrass for diseases, fungi, and insect infestations, using biological controls such as ladybugs and organic controls; and 5) consider implementing “resting periods” that vary access points and parking stall use to reduce wear on turf and giving it time to recover from heavy use; and 6) consider the benefits of overseeding and top dressing to promote healthy living turf. The City of Chicago, for instance, recommends special care during snow removal and might even require mowing turf at times.

Differentiating between Vegetated Permeable Pavements

Each type of vegetated permeable pavement system is designed to promote infiltration of rain and snowmelt. Each system contains openings to be filled with sand, soil, or a sand/soil mixture that in combination with the bedding layer becomes a rooting zone for vegetation such as turf or groundcover. Note that comparison of the four types of vegetated permeable pavements is very difficult based on their diversity and different properties. As Ferguson states, “Many manufacturers supply guidelines for installation of their products. However, the reinforced plastic/geocell-producing industry does not have the benefit of an industrial association to set uniform standards of comparison or to educate potential users about appropriate applications. Manufacturers' reports of strength and other characteristics are too often based on tests that are inconsistent between one manufacturer and another, and between geocells and other types of paving materials. In the absence of uniform measures of performance, potential users are left to rely on experience with specific models in specific types of settings.” He goes on to suggest that “An impartial industrial association would give guidance to users and credibility to suppliers. The formation of an industrial association or ASTM (American Society for Testing and Materials) committee to formulate uniform standards of plastic paving geocells is called for.”

It is noteworthy to understand that compressive strength is often used to compare plastic and concrete products. On the one hand, concrete products have a required compressive strength for load bearing; however, unit dimensions and resistance to wear ultimately determine their performance. Compressive strength for plastic products, on the other hand, can be derived from sand-infilled vertical plate lab tests. A substantial portion of the load is taken by the sand infill which increases the compaction of the material in the void space.

Flexible Concrete Mat
A precast mat unit with a network of concrete pads cast around a polymer grid that flex and conform to irregular ground surface contours.

Basic Product Composition: Wet cast concrete mat with an engineered grid cast inside. Individual pads are intended to crack at the joints and grid is designed to allow for long-term settlements. Individual mats are butted up similar to conventional pavers. The concrete can use recycled material such as fly ash or slag.
Flexible or Rigid: Flexible
Typical Infill and Bedding Course: Specifies 80% sand and 20% organic infill and bedding course. Bedding course is typically 2 inches thick.
Typical Void Width: 1.5 inches
Typical Unit Load-Bearing Surface Area: 40%
Typical Dimensions: 24 inches x 24 inches x 1.5 inches
Measure of Performance: ASTM. No specific ASTM for this type of product.
Testing: Manufacturer's reports: Permanent Deflection and Performance Study Sept. 2005 – Feb. 2006⁷; Runoff 911 Test Section Performance⁸
Limitations: Steel track vehicle areas. No certified installation program.

Concrete Grid Slab
Concrete grid slabs are a cast-in-place, monolithic pavement with voids from forms, with steel reinforcement.

Basic Product Composition: Cast-in-place, monolithic, pervious concrete pavement that is continuously reinforced with steel. The concrete can use recycled material such as fly ash or slag.
Flexible or Rigid: Rigid
Typical Infill and Bedding Course: Infill not specified; typically set on 1 inch of bedding sand
Typical Void Width: 4 inches
Typical Unit Load-Bearing Surface Area: Not available
Typical Dimensions: continuous slab, 5.5 inches thick
Measure of Performance: ASTM, ACI. No specific ASTM for this type of product.
Testing: Common concrete strength testing and reinforcement per ASTM. Manufacturer's report: One-day test 1986 structural load test with Grumman ladder truck 23,000 lb per axle. RAM testing 1994—lateral load testing of the protruding concrete surface posts.⁹ One-day test 1980 City of El Segundo Fire Department.
Limitations: Contoured installations. Accessibility to utilities below installation. Long-term oxidation of rebar. Lack of continuous bedding course for root zone.

Concrete Grid Paving Units
Most people know these as the waffle-like, commonly available individual concrete block pavers with voids.

Basic Product Composition: Dry cast modular concrete blocks. Some products include steel reinforcement to allow for heavier vehicles (typical spec for any modular block is the length / thickness <= 4). The concrete can use recycled material such as fly ash or slag.
Flexible or Rigid: Individual units are rigid.
Typical Infill and Bedding Course: Top soil infill or sand, if non-vegetated; ½ inch to 1 inch of bedding sand
Typical Void Width: 3 inches
Typical Unit Load Bearing Surface Area: 61%
Typical Dimensions: 24 inches x 24 inches (L x W) or less. Minimum thickness of 3.125 inches
Measure of Performance: ASTM, ICPI, NCMA
Testing: Common concrete strength testing. Several light-duty case studies through academic research available. No published field studies with heavy vehicles found.
Limitations: Steel track vehicle areas. Heavy loads on larger units without reinforcement (based on ASTM 936) resulting in cracking at surface from base or subgrade settlement. Elaborate contoured installations. Lack of continuous bedding course for root zone.

Plastic Geocells
Reinforced plastic cells are made of a recycled plastic—high-density polyethylene (HDPE)—the #2 category for recycling.

Basic Product Composition: Plastic. Most commonly HDPE plastic in modular tray units or standard roll sizes covering 108 to 538 square feet. Rings connected by tensile members or a network of square or hexagonal cells.
Flexible or Rigid: Flexible and rigid
Typical Infill and Bedding Course: Infill varies between top soil and sand. No bedding course is typically specified. Rolled units require staking into the base or subbase material.
Typical Void Width: 2 to 3 inches
Typical Unit Load-Bearing Surface Area: 5 to 13%.
Typical Dimensions: 1 to 1.5 inches thick. Varying dimensions for trays and roll sizes.
Measure of Performance: None at this time.
Testing: Different laboratory tests per manufacturer for sand filled and unfilled compression tests. A.G. Wassenaar Geotechnical compression resistance/load-bearing capacity test 1991. No published heavy vehicle field tests.
Limitations: Steel track vehicle areas. Memory in the material once disturbed. Movement of plastic under stress (plastic is susceptible to thermal expansion /contraction). Strength of narrow sidewalls in a saturated environment. Lack of continuous bedding course for root zone. No common measure of performance or certified installation program.

Green Infrastructure Initiatives

Other decisions that should be part of the initial design process are whether the project is pursuing LEED® and SITES® (in development), other pavement design factors that might be important for your project type, potential first and life-cycle costs will be, and the level of commitment that the client plans for maintenance. The goals of reducing stormwater runoff and improving stream health are inherent in both green building/green infrastructure rating systems such as LEED® and SITES® (in development). Cities and regional planning agencies often provide BMPs with details and specifications within their green building/green infrastructure development standards and/or guidelines. Vegetated permeable pavement can be used in bioswales, bioretention areas, or rain gardens, for adding to the site's biomass index (BMI), or to prevent erosion, recharge the groundwater, or reduce UHI.

In New York's Green Infrastructure Plan (2011): A Sustainable Strategy for Clean Waterways the goal is to reduce by 10 percent its combined sewer overflow through the use of retention and infiltration by 2020. Within nearly each land-use type in this large metropolitan area, from streets and sidewalks to parks and parking lots, there are opportunities to use permeable pavement to achieve that 10 percent goal. The City of Chicago, through its Green Alley Handbook, and extensive green infrastructure design efforts, lists “Permeable Paving” as one of its preferred materials, being “most effective in areas closer to Lake Michigan that are underlain with sandy, permeable soils…Permeable pavement may have aesthetic and marketing advantages over conventional pavement, depending on the materials selected. Vegetated pavers, in particular, could substantially improve the aesthetic appeal of paved areas...(and) effective in reducing the 'urban heat island' effect.” To this city, permeable pavement is particularly appropriate for “…overflow and special event parking, driveways, utility and access roads, emergency access lanes, fire lanes, and alleys.”

The City of Seattle Public Utilities (SPU) Department and Office of Sustainability recommends use of permeable pavement for their Stormwater Facility Credit (SPU) program. The SPU program grants discounts on drainage bills for private stormwater systems that “reduce stormwater flow and/or provide water quality treatment…” Permeable pavement is among the stormwater structures that qualify for up to a 50 percent credit. In theState of Virginia's Stormwater Design Specification #7: Permeable Pavement (Version 1.8 3/1/11), BMPs are enumerated at length primarily for permeable pavements. The specification details the properties for each type of pavement, material specifications, maintenance recommendations, and construction installation sequence. This type of BMP information is common among those cities and regions leading the way in the use of permeable pavements.

LEED® and SITES®

To set a green building leadership example, the U.S. General Services Administration (GSA) increased its stipulation for LEED certification for its facilities in 2010. The GSA now requires all new federal buildings and major renovation projects to achieve at least a LEED Gold certification, up from the previous Silver rating. “Sustainable, better-performing federal buildings can significantly contribute to reducing the government's environmental footprint,” former GSA Commissioner of Public Buildings Robert A. Peck has said. “This new requirement is just one of the many ways we're greening the federal real estate inventory to help deliver on President Obama's commitment to increase sustainability and energy efficiency across government.” The GSA's portfolio includes more than 361 million square feet of space in 9,600 federally owned and leased facilities occupied by more than 1.2 million federal employees.

Coronado, California sewer pump station—sod over flexible concrete mat Photo courtesy of Soil Retention Products, Inc.

Vegetated permeable pavement options can help projects achieve LEED® and SITES® credits. Points for LEED® Credit 1 Water Efficient Landscape, when planted with drought turf and tolerant groundcover; Credit 4 Recycled Content for HDPE, fly ash or slag; Credit 5.0, 5.1 & 5.2 Site Development for use in parking stalls and pathways, and use of regional materials, where applicable; Credit 6.1 & 6.2 Stormwater Design for water quality and quantity control; and Credit 7.1 & 7.2 Non-roof (parking) and Roof (pathways).

Within the proposed point system for SITES® (the Sustainable Sites Initiative), potential credits may be reached for Site Design/Water (3.3 protect and restore riparian areas, 3.4 rehabilitate streams, 3.5 manage stormwater, 3.6 protect and enhance on-site water resources and water quality), Site Design/Soil and Vegetation (4.6 restore biomass, 4.7 use native plants, 4.9 restore vegetation native to the ecoregion, and 4.12 reduce urban heat island effects); Site Design/Materials Selection (5.3 deconstruction design, 5.5 recycled content, 5.7 regional materials); Site Design/Human Health and Well Being (6.5 site accessibility, 6.6 opportunities for physical activity, 6.8 provide outdoor spaces); Construction (7.2 restore soils disturbed during construction), and Monitoring and Innovation.

Conclusion

The use of a vegetated permeable pavement system is becoming very popular with urbanized areas near coastal and riparian environments, and those adjacent to lakes and rivers, essentially where the bulk of all our cities are located. Use of these green infrastructure techniques can have huge significance to efforts to be more sustainable and to lessen our impact on the environment. Infiltration of water through vegetated permeable pavement, with its ability to slow and clean runoff full of pollutants like motor oil, salts, and urban detritus, is but one reason to use vegetated permeable pavements.

The applications for vegetated permeable pavements will continue to grow, as noted in the green infrastructure plans for Chicago, New York, and other major metropolitan areas. All elements of site design can benefit from permeable pavement. Whether a large-scale or small-scale project, the use of vegetated permeable pavement gains valuable space for the site designer and developer in companion with its stormwater benefits. Site landscapes can become more multifunctional, creating more usable open space and a sustainable landscape.

 

ENDNOTES
1	Brattlebo & Booth 2003; NCSU 2007
2	Foreword, Technical Guidance/EPA
3	Wikipedia
4	Ferguson, Porous Pavement (2005)
5	Ferguson, Porous Pavement (2005)
6	Weinstein, 2012
7	GMU Geotechnical
8	SR Designs Inc.
9	Twining Laboratories field testing

 

Since 1987 Soil Retention Products, Inc. has been manufacturing and distributing Plantable concrete systems®. Soil Retention’s product line includes Drivable Grass®, a permeable, flexible, and plantable concrete pavement system; Verdura®, a fully plantable retaining wall system; and Enviroflex®, a permeable and plantable ACB revetment system. www.soilretention.com