Green Infrastructure

By Matthew Holdren

Although “green” and “sustainability” have been buzzwords for more than a decade, the concepts have recently gained significant interest for public infrastructure projects, both large and small.

Green infrastructure uses vegetation, soils, and natural processes shaped into aesthetically pleasing rain gardens, bioswales, green roofs, or constructed wetlands. The less aesthetic options, which include permeable, pervious, and porous pavements—like their vegetative counterparts—are also intended to manage water and create healthier environments.

By now, most people are familiar with green concepts with the goal of capturing precipitation while preventing fast entry into traditional storm sewers. However, my experience assisting in the development, construction, and maintenance of several green infrastructure projects within open parkland and roadway environments has helped me understand how to ensure project success. As I’ve found, successful green infrastructure projects address the following topics:

  • Green parking areas
  • Best-management practices
  • Construction and maintenance of bioswales and green pavements.

Green Parking Areas
As those in the Midwest know, snowfall totals can vary widely from year to year. Even with these variances, parking areas can have green components, but regional conditions might change how they are designed or operated. 

For example, on a project site with clay soils, the area may have to be over-excavated. This area could then be filled with a designed soil blend to retain a prescribed volume of precipitation. The volume of storage created would allow for a slower rate of infiltration (the downward entry of water into the ground) to mitigate clay soils’ limitation of slower infiltration rates. If the clay soils are too tightly compacted, subgrade drainage ways may have to be created to allow the precipitation to move to other more permeable soil areas adjacent to the parking area.

Whether pavement is permeable, pervious, or porous, avoid storing materials like mulch, sand, or other materials on a conventional parking lot—even temporarily. In addition, avoid stockpiling snow on these pavements as it will result in increased maintenance efforts to avert premature clogging. In a park setting, consider the tree canopy and the variety of trees atop the green pavement component. If possible, avoid trees that bear fruit, berries, and nuts as they will likely increase the frequency and need for maintenance activities.

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Best-Management Practices
With more communities looking to implement green infrastructure into long-term plans, it is essential to recognize that green-infrastructure, best-management practices (BMPs) must be followed to provide a return on investment.

Understanding how to plan for green construction and making sure everyone on the project understands what protocols must be followed—as well as how the green construction works with traditional or “gray” infrastructure—are necessary to get the most benefit from a project.

Many people may agree that pumps or settling tanks are critical to gray infrastructure’s treatment of water, but regardless of how critical they are, they will not provide the intended benefit unless they are constructed and installed properly. The same is true with bioswales and rain gardens. Like their gray counterparts, these critical green components must also be constructed and installed properly to provide their intended benefit. Having professional construction management and on-site inspection teams facilitate the proper construction of both gray and green projects is critical to their success individually, or when working together as a system.

The materials used and proper installations of green infrastructure are vital to project success. A rain garden may appear to be a simple project that involves merely installing plants. Likewise, a bioswale may seem like vegetation on top of layers of different material in a specific area. However, both of these green construction techniques are highly technical and must be constructed correctly to work efficiently.

A specific aggregate may be sourced for a bioswale because it helps promote drainage. However, before deciding to swap that type of aggregate for a less-expensive version or a type that is more readily available, know that it may change how the bioswale functions. A decision like this may prevent the bioswale from performing as intended because drainage calculations (a measure of the system’s functionality) are based on the gradation and materials specified in the design. Experienced and knowledgeable construction oversight can stop this from happening, preserving both the quality of the installation and avoiding additional costs. Insist on material testing and have a construction manager or design professional confirm that the materials meet the necessary specifications before bringing them to the project.

Due to their high visibility, green projects receive extra scrutiny from area residents. A construction manager and on-site inspector can ensure proper construction, providing the significant benefits for the community.

Constructing And Maintaining Bioswales And Green Pavements

Bioswales

1.       The contractor and crews must be educated on the importance of a properly constructed bioswale. It is essential that everyone on the project be aware of the design intent of individual elements.
2.       The soils must be non-compacted. Rely on the construction manager and on-site inspection team to keep people and equipment out of these areas.
3.       Select native plants for year-round cover. Certain plants tolerate different environments better than others, so involve an arborist or landscape architect to help select the plant varieties.
4.       If a bioswale is used as a temporary sedimentation basin, make sure the sediment is removed.

Green Pavements

1.       The subgrade must be uniform to allow proper drainage. Make sure the soil is not rutted or over-compacted.
2.       For pervious concrete, have a technical representative from the manufacturer or a testing firm on-site during placement.
3.       Prevent construction debris from choking off the pervious concrete. Have the contractor leave plastic on top of the concrete during any remaining construction activities.
4.       Plan for maintenance. Power-wash and vacuum the pavement at least twice a year (late spring and fall). If water ponds after a storm when similar areas are dry, be sure to investigate.

Key Points

  • Green infrastructure is here to stay.
  • Like other treatment components, green infrastructure must be installed correctly to provide its intended benefits.
  • A professional, qualified, and knowledgeable construction manager and on-site inspector should be present to view the installation of green infrastructure to protect the public owners’ interest.
  • Know the maintenance needs before selecting the right green option for a project, and have a plan in place to complete the maintenance.

An effective and aesthetically pleasing installation of any green project—large or small—can help promote the acceptance of additional green infrastructure projects in a community or district. So make the most of an opportunity and get it right. The environment will thank you!

Matthew Holdren is a project manager at H.R. Gray, a Columbus, Ohio-based firm providing program-management and construction-management services and a division of The Haskell Company. He has more than a decade of experience serving as a project manager and later deputy director of public service and engineering for a local municipality, providing oversight on projects, including roadway widening/reconstructions, as well as trail, utility, and traffic signal improvements both within private and municipal areas.. Reach him at (614) 487-1335 or mholdren@hrgray.com.