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Types of Green Infrastructure
Types of Green Infrastructure

Multiple, cost-effective treatment practices located throughout a development project or property will most effectively manage stormwater. Some types of GI are described below, accompanied by examples.

Site Design

Site design refers to a variety of techniques, including conservation development, vegetated buffers, permeable pavement, and other innovative strategies to decrease impervious cover and maximize efficiency. A key attribute of conservation development is smaller-sized plots to allow for more open space shown at right.

  • Image comparing conservation with traditional development from UCONN NEMO publication: Developing A Sustainable Community.
  • Plan showing traditional development from The Rhode Island Conservation Development Manual...
  • ...and a plan for conservation development on the same land. Note how lots are clustered together (The Rhode Island Conservation Development Manual).
  • This image and the next from Georgetown Climate Center show that GI can be used in urban settings in place of impervious surfaces.
  • The illustration above depicts how green roofs, rain gardens, plastic grid paver parking lots and infiltration trenches absorb stormwater and allow it to filter into the ground.

Bioswales

A bioswale is typically a long, narrow channel planted with grasses or other native vegetation that may convey stormwater to another LID practice or capture and treat stormwater directly.

  • Bioswale with river rock inlets at Lowes, North Kingstown.
  • Bioswale at Kent Hospital, Providence.

Cisterns and Rain Barrels

Cisterns and rain barrels are water collection techniques to capture runoff from rooftops and other paved surfaces for various non-potable water uses, such as lawn watering or fire control.

  • Rain barrel connected to downspout, Providence.
  • Cisterns are sometimes underground as shown in the diagram above from PennState Extension.
  • A cistern connected to roof to catch runoff. US EPA.
  • Cistern connected to roof decorated with art. Alisha Goldstein, EPA.

Dry Wells and Infiltration Trenches

Infiltration trenches and dry wells are trenches or chambers filled with crushed stone to capture and temporarily store stormwater before allowing it to infiltrate into the soil.

  • Infiltration trenches are made of gravel or crushed stone and are generally 1-3 ft deep.
  • Large drywells are installed under Capitol Square in Providence.

Naturalized Landscaping

Naturalized landscaping takes the place of a lawn and is characterized by native vegetation. Native plants have deeper roots that require less water (drought-tolerant), do not need to be fertilized, and are beneficial for pollinators. Naturalized landscaping may be used in an area that was depaved in an effort to decrease the amount of impervious surface.

  • Naturalized landscaping is ideal for slopes with a steep grade
  • Naturalized landscaping can appear alongside traditional turf.
  • Native plants used in naturalized landscaping are beneficial for pollinators.
  • Native plants used in naturalized landscaping are beneficial for pollinators.
Rain Gardens and Bioretention

Rain gardens and bioretention areas are shallow depressions that collect and filter stormwater through layers of mulch, soil, and plants. Small rain gardens can be integrated onto residential lots, while larger bioretention systems are suitable for cul-de-sacs, roadsides, or parking lot drainage. Bioretention can take many forms as seen in the images below.

Rain garden resources on RI Stormwater Solutions

  • Residential rain garden image courtesy of University of New Hampshire.
  • An aboveground filter planter is being connected to a downspout in Providence.
  • A vegetated median strip on Wickenden Street, Providence.
  • Bioretention area at Kent Hospital, Providence.
  • Bioretention areas can serve as sizeable BMPs that receive large amounts of runoff.

Trees

Trees can absorb and use large amounts of stormwater. Street trees accept some runoff from the sidewalks and surrounding buildings as well as providing shade and beauty. Tree filters are plantings designed to receive and infiltrate stormwater runoff. Reforesting broader areas of trees is another way in which trees can be used to reduce stormwater runoff.

  • A row of tree filters on Dexter Street, Providence.
  • Street trees are located within the right-of-way, South Kingstown.
  • A tree box filter at URI with visible overflow, inlet pipe, and adjacent stormdrain, Kingston.
  • A curb bump-out with a tree filter planting. US EPA.

Green Roofs

A green roof is either partially or completely covered in vegetation to absorb and capture rainwater, reducing the amount of water available to runoff.

  • The green roof on Environmental Packaging International, Jamestown.
  • The green roof on Potter League for Animals showcases sedum plants, in Newport.

Permeable Paving

Permeable pavement is a method of paving that allows stormwater to seep into the ground through openings within the paving material.

Permeable pavement factsheet series

  • Permeable block pavers are designed to interlock with void spaces between bricks, allowing stormwater to infiltrate.
  • Conventional asphalt on the left, porous asphalt on the right at Cottages on Greene in East Greenwich. Photo courtesy of Jonathan Ford.