Design Options for Greening Urban Environments  

With each new project, architects, landscape architects, engineers, and other design professionals are being asked to provide solutions that are sustainable, meet criteria for low-impact development (LID), and provide holistic environments that enhance the social, psychological, and economic aspects of a community as well as the living systems of the earth. As designers, our ability to turn existing man-made or “grey” infrastructure into “green” infrastructure can assist in achieving these holistic goals.

The Center for Green Infrastructure Design (CGID)¹ defines green infrastructure as “an interconnected network of natural and social systems that provide a diverse range of environmental, cultural, recreational, psychological, public health, and economic benefits.” The CGID states that “green infrastructure conserves environmental values and functions, sustains clean air and water, promotes a sustainable economic regional framework, and contributes to the health and quality of life for our residents.”

The new International Green Construction Code (IgCC) as well as LEED® and SITES™ criteria provides a framework of standards that focus on achieving green infrastructure for projects.

The IgCC code establishes minimum green requirements for both new and existing buildings and includes sustainability measures for the entire construction project and its site starting with the design and going through construction to the certificate of occupancy and project commissioning. The new code is looking to address the built environment from a holistic perspective, making buildings more efficient, reducing waste, and creating positive impacts on health, safety, and community welfare.

The LEED for Neighborhood Development (ND) criteria will expand the LEED criteria beyond the building envelope and the immediate site and will provide criteria for sustainable neighborhoods. LEED ND categories of Neighborhood Pattern and Design and Green Infrastructure and Buildings provide credits in areas that stress heat island reduction, tree-lined and shaded streets, building energy efficiency, building water efficiency, stormwater management, and recycled content in infrastructure.

The guidelines and benchmarks for The Sustainable Sites Initiative or SITES™ present nine categories with standards for protecting and restoring hydrology, soil and vegetation, repairing damaged ecosystems and resources, minimizing the effects of construction, and supporting and maintaining sustainability.

These new codes and criteria provide a framework for designers as they work to achieve green environments. However, urban areas present many challenges towards the creation of a green environment. This article will highlight some recent innovations that help achieve and sustain green infrastructure within the framework of man-made (grey) infrastructure and will review current trends and materials that help to recapture and enhance urban green space, enhance urban arboriculture, enhance water quality and reduce stormwater runoff, achieve energy efficiency, and overall, integrate sustainable design solutions for bridging the building-site (grey-green) interface.

At 5c Studios in Tempe, Arizona, green façade systems or green walls provide a building-site interface to improve urban air quality and building energy efficiency. Photo courtesy of greenscreen®

The Visionaire, NYC

Modular decking on the green roof of the Visionaire Condominium in New York City meets LEED credit in Materials and Resources. Photo courtesy of Bison Innovative Products The Visionaire is New York City’s first LEED Platinum-certified condominium project. This project used a modular decking system for their roof patio and as access to their green roof plantings. The Visionaire features a green roof covering 70 percent of the rooftop. The decks on the Visionaire used FSC Massaranduba Tiles and thus qualified for LEED credits. The pedestals have recycled content and thus provided a credit through Materials and Resources. This project also qualified for a tax credit through a 2008 New York City bill (A.11226) that allowed building owners in New York City who install green rooftops to receive a property tax credit. Under this law, building owners in New York City who install green roofs on at least 50 percent of available rooftop space can apply for a one-year property tax credit of up to $100,000. These modular decking systems protect and extend the life of costly roofing and waterproofing systems, and reduce heat and cold penetration into the building so they provide a means of reducing energy and the related costs.

 

Sustainable green infrastructure begins with providing appropriate conditions for the growth and maintenance of vegetation. It is essential that planting areas provide sufficient room for plant growth and provide a planting medium that is loose, friable, and containing sufficient organic matter so that soil can retain porosity for air circulation and water absorption. Sustainable urban green space can be attained through a number of innovations that provide plantable soils, pervious and flexible pavement systems, urban tree protection, vertical planting frames, and flexible surfaces for roof insulation.

Recapturing and Enhancing Urban Green Space

According to the U.S. Forest Service Urban and Community Forestry Report, June 2010, Sustaining America's Urban Trees and Forests: Forests on the Edge, “...tree cover in urban areas of the conterminous United States is estimated at 35.1 percent (20.9 million ac). As urban areas expand, the amount of urban forest will increase and urban forests will become increasingly critical to sustaining environmental quality and human well-being in urban areas. Careful planning and management will be crucial to maintain and enhance urban forest benefits.”

Mature urban forests provide innumerable benefits to a community. They reduce and slow stormwater runoff; serve as habitat for birds, mammals, and insects; reduce energy consumption; mitigate extreme temperature fluctuations; reduce heat island effects; enhance air quality; remediate contaminated soils; help to moderate climate change; and provide attractive, healthy living environments for people. However, urban trees rarely live to their mature age due to the challenges of survival in the urban environment. These challenges include compacted soils, poor hydrology, and constraints to trunk expansion and root growth from urban infrastructure.

Providing Better Soil Structure for Urban Forests

Structural soils are one means of providing urban trees with the medium essential to proper growth and sustainable long-term viability. A study conducted at the Urban Horticulture Institute at Cornell University (N. Bassuck, J. Grabosky, P. Trowbridge, J. Urban) introduced structural soils as a medium for integrating trees into pavement. Structural soils are designed to meet or exceed pavement design standards so that pavement compaction levels can be achieved while the soil remains sufficiently “porous” for root growth and stormwater penetration. Structural soils also provide a continuous base course under pavements for tree root growth.

Expanding Plantable and Structural Soil Areas
However, structural soils—which are 80 percent rock and only 20 percent soil—in and of themselves are not sufficient in sustaining urban trees. At the 2011 Greenbuild conference, James Urban, FASLA, a contributor to the Cornell University study stated, “structural soils, which combine broken up rock and soil, have issues so urban tree planters came up with a new idea: suspended pavements.” Suspended pavements are constructed with either custom concrete systems or modular products like underground bioretention cells. Modular underground bioretention cells support the pavement while allowing plantable soil as well as underground irrigation systems to be installed below pavement. These cells contain the soil volume that nurtures trees and also slows and treats water before it is piped out. Leda Marritz, ISA-certified arborist for DeepRoot Green Infrastructure, states that modular underground bioretention cells may be used in urban environments such as streets, plazas, parking lots, green roofs, and more in order to expand urban tree plantings and manage stormwater on-site. (See case studies.)

This diagram shows how a combination of structural soils, modular underground bioretention cells, and pervious flexible pavements improves the hydrolic cycle in urban areas, allowing stormwater to penetrate to planting areas below the pavement surface. Image courtesy of DeepRoot Green Infrastructure

 

Reducing Urban Heat Islands and Stormwater Runoff

Paved urban environments present challenges with the management of stormwater and the excessive heat that emanates from these pavements. Urban pavements are traditionally non-pervious rigid materials. Flexible pavements are defined by AASHTO (American Association of State, Highway and Transportation Officials) as being one of four standard pavement surfaces. By AASHTO definition: “Flexible pavements in general consist of an asphalt-bound surface course or layer on top of unbound base and sub base granular layers over the subgrade soil. In some cases, the sub base and/or base layers may be absent (e.g., full-depth asphalt pavements); while in others the base and/or sub base layers may be stabilized using cementitious or bituminous admixtures. Drainage layers may also be provided to remove water quickly from the pavement structure.”

Although newer porous asphalt and concrete pavements are by design sufficiently permeable so that water can penetrate through, their inherent density and their subsurface design and compaction requirements, which provide a suitable surface for vehicular traffic, do not allow for the installation of structural soils underneath.

The Koll Center in Irvine, California provides 6,000 square feet of grass pervious surface as a fire lane. Photo courtesy of Invisible Structures, Inc.

 

Pervious Flexible Pavements

A pervious flexible paving system can provide another design solution in addition to suspended pavements for enhancing green space and transitioning from grey to green infrastructure. Pervious flexible paving systems can utilize either sand with seed/sod/groundcovers or gravel as filler materials. Both options provide benefits toward filtering and mitigating stormwater runoff and enhancing site ecology. Unlike standard gravel pavement surfaces, a gravel pervious flexible pavement system has added stability and prevents gravel migration as the gravel is contained by the grid paver system. It is dust free, easy to install, and very low maintenance.

Dustin Glist, media and information director for Invisible Structures, Inc., cites the following benefits of pervious flexible paving systems:

• Reduced site disturbance
• Enhanced stormwater management
• Reduced heat island effect
• Reduced water use through water efficient landscaping
• Erosion and sediment control
• Enhanced safety as a result of emergency access to tight urban areas
• Enhanced urban green space

The primary applications for grass/lawn pervious flexible pavements include residential drives and parking areas, pedestrian traffic zones, utility access areas, fire/emergency access areas, and parking lots. Some examples of this include the parking lot at the West Farms Mall in West Hartford, Connecticut; the parking lot at Reliant Stadium, Houston, Texas; road shoulder reinforcement in Calgary, Alberta, Canada; and fire/emergency access lanes at the Koll Center in Irvine, California.

The Koll Center used 6,000 square feet of grass pervious flexible pavement system to create a porous fire lane around the building. The grass pervious flexible pavement system is located on the south end of the building and within a parking lot. Koll Center is a complex of buildings centered around a beautifully designed outdoor fountain and pedestrian mall.

Pervious Flexible Pavement System Standards
A grass pervious flexible pavement system is best used for light to moderate vehicular use and to reinforce turf. It helps to filter and treat stormwater pollution, reduce heat island effect, and enhance tree growth in parking areas. Since porous pavers drain more rapidly than regular pavers, more water must be applied during the first year after initial seeding to ensure a solid stand of grass. Chemicals cannot be used to remove snow from a grass pervious flexible pavement as these chemicals will degrade the grass and can rapidly leach into the ground water. As with any type of porous pavement, there are also slope restrictions with the use of pervious flexible pavement systems, which include the following:

• 5 percent maximum slope for fire lanes
• 8 percent maximum slope for parking areas
• 15-20 percent slopes for trails and walkways

Pervious flexible paving systems that involve the development of a lawn/grass help to recharge groundwater, reduce stormwater runoff volume, capture suspended solids, clean hydrocarbon drips and pollutants, and protect the grass root zone from compaction so a healthy lawn can be maintained.

A gravel pervious flexible pavement system can be used for parking aisles and bays, ADA and multiple use trails, service and access drives, fire lanes, driveways, RV parking, boat and truck storage, boat ramps, and high-use pedestrian areas. A gravel pervious flexible pavement system has unlimited use in lower-speed vehicular traffic. It can also be used for ADA multiple use trails. The benefits include providing a pervious load-bearing surface, reducing heat island effect, and filtration and treatment of stormwater.

Both grass and gravel systems are made from high-density polyethylene and from second-generation post-industrial recycled products. This material also has a UV protective coating to prevent breakdown from exposure to the elements. Both grass and gravel systems also meet industry standards to support the compressive strength and weight of heavy vehicles such as fire trucks.

Restoring Urban Arboriculture

The Society of Municipal Arborists (SMA) has a slogan that reads “Green Communities are Smart Communities—That's Why Trees!” The SMA provides resources and studies relating to the many ways that trees improve the environment. In urban areas, trees assist in traffic calming along streets, reduce energy through shading, mitigate drainage and flooding problems through stormwater management, and improve quality of life and health through reduction in pollutants and aesthetic enhancement. Urban reforestation would help to achieve many of the above-mentioned goals and attain LEED® and SITES™ credits for certifications.

In a 2002 report, David J. Nowak of the USDA Forest Service summarized the energy effects of trees on buildings. “Trees reduce building energy use by lowering temperatures and shading buildings during the summer and blocking winds in winter. However, they also can increase energy use by shading buildings in winter, and may increase or decrease energy use by blocking summer breezes. Thus, proper tree placement near a building is critical to achieve maximum building energy conservation benefits.”

Although urban forests provide many benefits to the health and welfare of urban communities, there are many challenges to proper placement and installation of trees within the urban infrastructure. Structural soils, modular underground bioretention cells, suspended pavements, and pervious flexible pavement systems are all options for providing sustainable planting environments for trees and lawn areas with the man-made infrastructure. Providing the appropriate volume and planting medium for trees is not the only consideration. Tree placement on sidewalks must also consider universal accessibility and safety for pedestrians.

A 40-foot run of tree grates along this Chicago streetscape provides a larger pervious planting bed for sustaining urban trees. Photo courtesy of IRONSMITH, INC.

Integrating Trees into the Urban Landscape

Tree grates have been used for many years to help integrate trees into the urban hardscape. Tree grates provide surface exposure to air and water that trees require and provide a walkable surface for pedestrians. Tree grates also keep areas around trees free of litter and animal waste so they provide a sanitary benefit as well. Tree grates come in a range of sizes, colors, and grate patterns. In Chicago, for example, a square steel tree grate with small 1/2-inch square openings set in a grid pattern was selected to create a 40-foot run of individual tree grates that provided an extended street tree planting area. By providing extensive tree planting along the street edge, this installation greatly reduced the urban heat island effect within this urban area.

Another case study that illustrates a solution for reduction of urban heat islands and energy consumption is Civic Space Park in Phoenix, Arizona. Sustainable requirements led the design focus for this gathering space in the heart of downtown Phoenix. Rainfall is sparse and then intense when it occurs in the southwest. Downtown Phoenix can be ten degrees hotter than areas on the perimeter. It was essential that a solid, sustainable tree canopy be established to create a pleasant urban park that users could enjoy. Seventy percent of the park will be shaded when the trees reach their maturity and this percentage meets the City of Phoenix's design guidelines. A suspended paver system of tree grates was used in conjunction with structural soils to allow the planting of over 100 trees.

Enhancing Arboriculture with Suspended Paver Systems

As traditional tree grates can limit the location and placement of urban trees in constrained areas, the new suspended paver system extends the amount of planting area. According to D'Arcy Deeks, vice president at IRONSMITH, the new suspended paver system “buys more sidewalk in urban areas while still protecting tree roots and allowing necessary air and water into the root system.” Such systems allow the installation of unit pavers over the tree planting area, thus providing more room under the pavement for a larger volume of planting medium and more room for root growth. Suspended paver systems provide the following specific design benefits:

• Expand walking surfaces in tight pedestrian walk areas.
• Greatly reduce weeds and trash accumulation.
• Reduce tree area maintenance.
• Prevent compaction around the root ball
• Prevent roots from lifting pavers or sidewalk pavement
• Allow easy fertilization and irrigation.
• Present more design options for paving materials.
• Provide expansion to allow for trunk growth.

From the broader perspective, these suspended paver systems provide more flexibility with respect to tree placement and thus trees can be located to maximize on reduction of heat islands and energy consumption in urban environments. With greater flexibility in the number and placement of trees, urban reforestation can be more readily achieved. In addition, these systems also lend themselves to being integrated with other tools such as structural soils and modular underground bioretention cells, thus providing healthier growing environments for urban trees. Healthier trees are more sustainable and enable expansion of urban green space as well as mitigating stormwater runoff and extreme temperature fluctuations.

Civic Space Park in Phoenix, Arizona used a suspended paver system of tree grates to provide more space for tree planting, thus reducing the urban heat island effect. Photo courtesy of IRONSMITH, INC.

Design Criteria for Suspended Paver Systems
Some key design factors to consider when utilizing suspended paver systems are (1) maximize on the external tree trunk opening within the constraints of project budget, the local code and ADA compliance and (2) specify the tree opening appropriate to the tree being specified.

Suspended paver systems and tree grates are fabricated of recycled steel, which does meet LEED Materials and Resource Credit 4 and both must meet transportation engineering standards. Through these newer reduced opening tree grates and suspended paver systems, arboriculture and reforestation can be enhanced in the urban environment and this will assist in reducing the heat island effect and energy consumption.

Using Modular Decking to Green the Street

In addition to expanded tree grates and suspended paver systems, modular wood decking can be used to create seasonal green parks. Seasonal green parks can be set up or “popped up” along narrow streetscapes and then broken down if and when necessary. These seasonal parks are being used in Chicago, San Francisco, and other urban municipalities to “green the street” between spring and summer. The parks are then removed for winter storage. Private restaurants use the modular decking and planter systems of the seasonal green parks to create outdoor dining areas that are shaded and screened by small trees set in the modular planters. In Wheatridge, Colorado, a seasonal park system is being used to provide traffic calming. Although the planters provided as part of the seasonal green park system will only support shrubs and very small trees, this does provide added green space in tight urban areas.

The seasonal green “pop-up” park in San Francisco provides a means for greening an urban environment. Photo by: Matthew Roth; courtesy of Bison Innovative Products

 

These modular decking systems have been widely used in the United States for over a decade. There has been extensive testing done on these products and a few are now 100 percent made in the USA. The deck support system is gravity based and must have perimeter containment such as a curb or parapet walls, on all sides, and therefore does not require mechanical attachment to the pavement or the roof membrane for anchoring. Compared to traditional joist and plank installations the pedestal deck systems yield significant labor savings to the installer.

At ground level, these seasonal green parks systems add aesthetics to the street as well as adding a flexible type of urban green space that can be used either temporarily or long term.

Improving Urban Air Quality and Energy Efficiency

How do you expand urban green space and enhance the urban environment in tight areas? How do you obtain those LEED® and SITES™ credits and meet new development code requirements for stormwater management when there is no room for green infrastructure at street level? Dean Hill, ASLA, director of sustainability at greenscreen®, would suggest that you look up and consider green walls and green roofs. He considers vertical space as another layer in planting design. The incorporation of vertical vegetation through the use of green walls and green façade walls in particular can contribute to building energy efficiency, water efficient landscapes and the reduction of Urban Heat Island (UHI) effects. It can also provide landscape architects with an additional design dynamic to increase habitat connectivity, seasonality, native plant incorporation and the enhancement of overall planting designs.

Using Green Façade Systems and Green Walls

Vertical frame systems (green façades) help to expand the planting of vegetation in tight urban areas where there is no room for street trees. Green façade technology provides a direct interface between architecture and landscape architecture—between site and building—between grey infrastructure and green infrastructure. Rigid, green façade systems can stand independently away from a building or can be set back from the building façade through mounting clips. In both situations, the structural integrity of the building is maintained and waterproofing membranes are not penetrated or compromised.

A number of studies have been done with respect to green walls including a study completed by Thomas A. M. Pugh, A. Robert MacKenzie, J Duncan Whyatt and C. Nicholas Hewitt of Lancaster Environmental Centre, Lancaster University, Lancaster, UK on The Effectiveness of Green Infrastructure for Improvement of Air Quality in Urban Street Canyons. In a 2012 interview with BBC News, Professor A. Robert MacKenzie says “The benefit of green walls is that they clean up the air coming into and staying in the street canyon. Planting more (green walls) in a strategic way could be a relatively easy way to take control of our local pollution problems.” In addition, researchers in the UK found that trees were also effective in controlling air pollution, but “only if care is taken to avoid trapping pollutants beneath their crowns.

Green façade systems or green walls are being used throughout Europe and the United States in a variety of climates and settings to increase urban green space, mitigate stormwater runoff and assist in reducing energy consumption. In addition to having a direct interface with building façades, green walls are also being used on green roofs.

The Department of Public Works in Lexington, Massachusetts used wall mounted trellis panels to create a green wall that is part of a green infrastructure rain garden at a new regional office facility. This project received a Silver LEED® citation. In Oakland, California, large sections of trellis panels were placed on a multistory parking facility at the Kaiser Permanente Parking Lot. The trellis panels provide a support structure for vines that are part of a stormwater filtering rain garden. In the southwest, trellis panels were installed at the waiting stations throughout the Valley Metro Light Rail transit system in Phoenix, Arizona. The planted vines provide shade and reduce the heat from adjacent hardscape surfaces. In addition to use as independent green walls, green façade systems have been used in conjunction with on-site stormwater management plans such as the HOK design for the National Wildlife Federation Building in Washington, D.C.

When designing with green façades and trellis panels, consideration must be given to selecting appropriate plant materials (vines and herbaceous plants only) that are native to the area and providing regular maintenance for plant material and soil mediums. Landscape architects and architects are encouraged to reference regional plant lists and to consult with local nurseries regarding availability of recommended vines, hardiness of vines in windy urban areas, and solar requirements for the plant.

The Value of Vertical Green Space
There is some debate as to whether the cost of maintaining green walls offsets its value for addressing a site's environmental considerations. greenscreen's Hill states that further research is being done around soil volumes and maintenance with respect to vertical planting systems but notes that “the trellis systems facilitate the natural growth of the plant materials so the integrity of the screen is not compromised as plants mature.”

Overall, green walls add to the palette of materials and methods that can help to increase and enhance urban green space and bridge the interface between human man-made and green infrastructure. Studies have shown that green walls on building façades help to mitigate outdoor air quality but they also reduce indoor ambient air temperature which adds to energy and cost savings and provides a greater return on investment to projects. Green walls present an additional option for implementing urban green space and enhancing the urban environment.

The National Wildlife Federation Building in Washington, D.C. utilizes a green façade system in conjunction with on-site stormwater management. Photo courtesy of greenscreen®

 

Bridging the Building—Site Interface

Green walls are not the only building-site interface for enhancing green space in tight urban areas. Green roofs have been an integral part of the design palette for both architects and landscape architects since the 1960s when they were first constructed in Germany. As green roofs become more an integral part of the urban environment, accessing their components for maintenance and long term sustainability is important. Modular decking systems have been developed to provide easier access to maintain green roofs. These modular decking systems also protect the roofing materials and thus prolong the roof lifespan. In addition, the modular decking systems cover unsightly rooftop penetrations, provide space for irrigation systems and facilitate water drainage from green roof planters.

Modular Decking for Green Roofs

Modular decking components include prefabricated wooden squares and high density plastic adjustable deck supports. According to Lisa von Gunten, vice president and general manager of Bison Innovative Products, some manufacturers offer prefabricated commercial grade wooden squares or tiles that are “pre-assembled and are “constructed from select cut Brazilian hardwoods that are harvested in an environmentally responsible method, FSC Certified and qualify for LEED points.” To comply with LEED ® and SITES ™ criteria for certification, designers should verify the origin of the wood and confirm the exact species. Deck supports are typically made from polypropylene and contain 20 percent post industrial recycled material so they qualify for points under LEED® Materials and Resources Credit 4. The decking is designed for ADA accessibility. This modular roof decking is held in place via perimeter containment so it does not require anchoring to or penetration of the roof membrane.

Urban Streetscapes and Storm Water Minneapolis, Minnesota

The streetscape at Marquette and 2nd Downtown in Minneapolis, Minnesota uses modular underground bioretention cells to meet regulatory stormwater compliance. The modular cells also allow utilities to be constructed around them. Photo courtesy of DeepRoot Green Infrastructure Modular underground bioretention cells have been used in Minneapolis, Minnesota on the Marquette and 2nd Downtown Streetscape to meet regulatory stormwater compliance. The Marquette and 2nd Avenue (MARQ2) project was a transit-way streetscape renovation in a 48-block mixed-use stretch of downtown Minneapolis. A modular underground bioretention cell system was installed under pervious pavers to allow stormwater infiltration to tree pits. The streetscape was designed to route stormwater to the soil in the underground bioretention cells and thus eliminates irrigation and reduces runoff. Bob Kost, project landscape architect and director of SEH (Short, Elliot, Hendrickson, Minneapolis, Minnesota), stated that “we were immediately attracted to this cell because of its holistic nature of providing heavy-duty structural pavement support, stormwater treatment and the horticultural benefits of highly accessible soil volumes. Unlike structural soil alternatives, this bioretention cell makes large volumes of lightly compacted soil available to soak up urban stormwater runoff while making this resource available for uptake by the street trees, completing the hydrologic cycle. For the first time in my 30 years of design practice, we finally have a product that allows street trees to function as a measurable, long-term component of civic infrastructure.” For this project 167 street trees were installed and over 19,000 cubic feet (0.45 acre feet or 558.3 m3) of stormwater can be treated with 90 percent of the stormwater from rain events being captured.

Utilities and Urban Green Space Seattle, Washington

Aurora Avenue Secret Rain Garden uses modular underground bioretention cells to create a green corridor along Route 99 in Seattle, Washington. Photo courtesy of DeepRoot Green Infrastructure Among the key benefits to modular underground bioretention cells in an urban environment is that they allow existing utilities to stay in place because the system is modular and can be constructed around them. This can be a major construction cost savings. There are a number of simple ways to work with and around utilities using these cells. Use of modular underground bioretention cells around existing utilities was a factor considered by the designers of the Aurora Avenue Secret Rain Garden along Route 99 near Seattle, Washington. A rain garden was designed along one side of a road way to provide a separation for pedestrians. The designer, Curtis LaPierre, Otak, Inc., created a system that integrated permeable pavers, curb cuts and modular underground bioretention cells. The cells extend the rain garden underneath the pavement, the stormwater from the road enters the rain gardens through the pavement and curb cuts and is absorbed into the soil, providing irrigation for the plantings and recharging the groundwater. The project area had a limited right of way and large paved areas. The solution provided additional traffic lanes, wider sidewalks, better stormwater management and increased green space. Modular underground bioretention cells are designed to meet AASHTO H-20 loading standards. When considering the use of these cells for your site, it’s important to specify soil volumes that are appropriate for both mature tree growth and stormwater management. As more municipalities update their codes and design guidelines for increased onsite stormwater management and increased urban forest canopy, modular underground bioretention cells provide an option for achieving both these criteria in a single system. These cells provide the structure to support pavement while creating an underground vault for containing soil and managing water. This integrated system of structural soils and underground bioretention cells provides a larger and better planting medium for urban trees, creates a simple and effective method of capturing and treating rain and stormwater at source, and allows designers to plan for more extensive, functional, and sustainable urban green space.

 

Grass Pervious Flexible Pavement Systems

Reliant Stadium’s grass parking area provides seven acres of porous pavement surface. Photo courtesy of Invisible Structures, Inc. The parking lot at Reliant Stadium includes seven acres of pervious flexible pavement system, making it the largest grass-porous paving system in the world. This grass replaces seven acres of asphalt and it has cooled the site sufficiently to allow almost three more months of use during the year. This porous grass parking lot has the ability to store and clean 60,000 cubic feet of stormwater, thus preventing down stream flooding and non-point source pollution. In addition, trees can now survive in this parking lot as the permeable nature of the surface provides sufficient air and water to the tree’s root zone. The increased forest canopy has increased shade and reduced the heat island effect.

Conclusion

As we continue to experience severe weather episodes and extreme shifts in weather patterns and temperatures, concern grows regarding the effects that human infrastructure is having on climate change. More municipal, state, and federal agencies are requiring that projects meet LEED®, SITES™ or IgCC criteria and/or are initiating their own sustainable design and code standards. In 2010, three northeastern states established new stormwater regulations and guidelines that require more green open space or the creation of rain gardens and bioswales to address stormwater runoff at the point source.

Compliance with these new regulations and criteria can be met through the use of one or more of the methods and solutions described in this article. Structural soils, modular underground bioretention cells, pervious flexible pavement systems, suspended paver grate systems, tree grates, modular decking systems, and seasonal green parks are design techniques that either directly or indirectly provide a means to increase urban green space, reduce heat island effect, improve water and air quality, and enhance the health and well-being of people within the urban environment.

 

ENDNOTE
1	The Center or Green Infrastructure (CGID) www.greeninfrastructuredesign.org/green-infrastructure