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Stormwater is a major source of pollution to the Mystic River. This is largely due to developments and the excessive amounts of impervious surfaces - those that do not allow water to pass through them (such as concrete).

Low Impact Development (LID) A green roof acts as a rainwater sponge atop Chicago's City Hall. Photo courtesy of City of a method of site planning that works to reduce the impacts of development while still allowing development to occur. According to the Natural Resources Defense Council, "LID is grounded in a core set of principles based on the paradigm that stormwater management should not be seen as stormwater disposal and that numerous opportunities exist within the developed landscape to control stormwater runoff close to the source. Underlying these principles is an understanding of natural systems and a commitment to work within their limits whenever possible. Doing so creates an opportunity for development to occur with low environmental impact."

LID has shown itself to be effective, flexible, economical, and aesthetically pleasing. LID works to include multiple site-specific stormwater controls that work with the natural landscape and are cost effective, in the design process.

Most of the LID methods try to control runoff at the source in order to replicate the predevelopment hydrology. Controlling water at the source reduces the need for stormwater conveyances, lowering costs for developers and municipalities.

As a tool, Low Impact Development can:

  • Reduce stormwater runoff
  • Save developers and municipalities money
  • Increase lot values
  • Add beauty to the site
  • Protect the environment

In addition, LID can be used in new developments, redevelopments, and even ultra urban redevelopments.

LID for New Developments

New developments, especially ones is suburban area, have more choices of LID methods. Many methods aim to reduce the amount of impervious surfaces that are created. Examples include: reducing the width of streets, reducing the size and number of parking spaces, creating alternative designs for cul-de-sacs, employing innovative development designs that increase the amount of open space, such as cluster developments, and having sidewalks on only one side of the street. All of these methods increase open space and decrease stormwater runoff, and many of them are more cost-effective than their alternatives.

For example, a California study found that an excessively wide street (36 feet as compared to 24 feet) cost about $12,500 more per 100-foot section (HUD). A 130 acre development in Arkansas that was redesigned to save an additional 22 acres of open space and include LID practices ended up saving the developer $2.2 million and allowed for the creation of a neighborhood park with some of the savings (HUD).

LID for Redevelopments and New Developments

The following methods can be used for both redevelopments and new developments and are very common in LID projects: rain gardens or bioretention areas, green roofs, vegetated swales, filter strips, tree preservation, rain barrels and cisterns, permeable pavements, soil amendments for increased permeability, impervious surface reduction and disconnection, and pollution prevention.

The city of Bellingham, Washington created two rain gardens instead of the traditional vault method of stormwater storage. Not only do they have two beautiful gardens to enjoy, but they saved $62,000 in construction costs. A developer in Maryland created bioretention areas that eliminated the need for a stormwater pond, allowed for the development of an extra six lots, and saved the developer over $4,000 per lot.

Green roofs, such as the one on city hall in Chicago, have many benefits including: extending the life of the roof (green roofs last twice as long as conventional roofs), cleaning the air, beautifying the area, reducing cooling and heating costs, increasing sound insulation, adding open space, reducing urban heat islands, and reducing stormwater runoff.

Sources & More Information


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