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What is Green Infrastructure?

Learn how green infrastructure works, and what types of green infrastructure are used in the City of Boston. 

“Green Infrastructure” (GI) is an umbrella term for stormwater management features that mimic nature. GI features use plants, soil and other natural materials to remove pollutants and allow stormwater to absorb back into the ground. These features help prevent flooding and reduce the amount of polluted water that goes to the City’s water bodies. GI also has many environmental, social and economic benefits. Learn more below. 

What is Stormwater

What is Stormwater?

Put simply, "stormwater" is "water" that comes from "storms." In nature, precipitation (e.g. rain or snow) soaks into the ground where it falls. In developed areas, like the City of Boston, “impervious” surfaces, like buildings, pavement and sidewalks, prevent water from passing through. Precipitation becomes stormwater runoff when it falls on impervious surfaces and “runs off,” rather than absorbing into the ground.

As stormwater runoff travels across impervious surfaces, it picks up litter and other unseen pollutants. Traditional stormwater management features, like catch basins and pipes, are known as "grey infrastructure." These features capture runoff and pipe it into nearby waterbodies, without treatment.

Fortunately, there are also "green infrastructure" features. These vegetated features capture precipitation where it falls and allow it to absorb back into the ground. They also use soil and plants to trap debris and filter pollutants out of stormwater. Read more, below!

What is a Stormwater Utility?

A Stormwater Utility is an increasingly common organizational structure used to equitably manage and fund stormwater programs. They often include a stormwater fee (or charge) based on impervious cover, as well as a credit program and grant program to help ratepayers reduce their fee.

The Boston Water and Sewer Commission is proposing to implement a Stormwater Utility in early 2024. Visit the Commission’s website for more information and to use the Commission’s “Bill Estimator” tool.

What is Green Infrastructure

What are the co-benefits of green infrastructure?
  • Stormwater Retention / Flood Mitigation

  • Groundwater Recharge

  • Stormwater Pollutant Removal

  • Urban Tree Canopy

  • Urban Heat Island

  • Air Quality

  • Biodiversity / Ecological Habitat

  • Food Security

  • Aesthetics / Quality of Life

  • Mental Health

How do we maintain green infrastructure?

Green infrastructure features require different types of maintenance throughout the year to keep them alive and well. Sometimes maintenance is repairing damage or replacing plants, and sometimes it's picking up coffee cups.

The City now has a variety of GI maintenance resources, including maintenance contracts and a Green Infrastructure Volunteer Program.  We're piloting the volunteer program in fall 2023 and the program will be launched citywide in spring 2024. More information coming soon!

The City is also hosting regular National Green Infrastructure Certification Program (NGICP) Trainings, open to all residents.  Send an email to green.infrastructure@boston.gov if you'd like to join our next session.  

Types of Green Infrastructure

Types of GI

A graphic of a rain garden

Bioretention Features are low lying areas that collect stormwater runoff from nearby surfaces. These features are typically shallow depressions that vary in size and shape. Sandy “bioretention soils” remove pollutants as stormwater passes through the soil and absorbs into the ground. Bioretention features also have plants that uptake stormwater while microorganisms that live around plant roots remove excess nutrients and other pollutants.  

Examples of Bioretention Features include:

  • Bioretention Areas
  • Rain Gardens
  • Bioswales

Constructed Wetlands

Constructed Wetlands are larger than most Bioretention Features, which allows them to manage runoff from large drainage areas (e.g. a campus, rather than a single parking lot). These features are designed to mimic natural wetlands and often contain a broad palette of plant species and soil types. Like natural wetlands, they provide excellent habitat for wildlife and can help improve the health of local ecosystems.

Green Roofs are made up of layers of soil and vegetation placed on the roofs of buildings. The size and makeup of these features varies from site to site. These features can be as simple as shallow trays and small planters or as complex as rooftop gardens with several feet of soil. Green roofs can be used instead of roof gutters, provide added insulation/energy savings and can help to lower nearby air temperatures.

Green Roofs

Infiltration Features

Infiltration Features are subsurface features filled with “clean washed” crushed stone or sand based structural soil that can hold and infiltrate large volumes of stormwater. These features often have perforated pipe or chambers that help distribute stormwater and increase the total storage volume. Infiltration features can be installed under a variety of surface materials, as well as in locations with limited space. 

Examples of Infiltration Features include:

  • Stone Infiltration Areas
  • Stormwater Chambers
  • Drywells

Porous Paving Materials are hard surfaces, like asphalt, concrete and pavers, with voids or gaps that water is able to pass through. These materials allow for urban uses, like driving, walking and parking, while still providing a path for stormwater to reach the soil underneath. They also experience less icing in the winter because ice melt is able to pass through the paving material, rather than refreezing on the surface. 

Examples of Porous Paving Materials include:

  • Porous Asphalt
  • Permeable & Porous Pavers
  • Porous Concrete

Porous Paving

Tree Pits and Tree Trenches are GI features with multiple components. The first is the underground stone infiltration area that can infiltrate large amounts of stormwater runoff from nearby hard surfaces, like roads and sidewalks. The second is the trees that are planted in these features, which can uptake hundreds of gallons of stormwater each year. These features help improve the health of urban street trees by providing tree roots with much-needed access to water and air.

Tree Pit

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