Low Impact Development

  Low Impact Development (LID) is a land planning and engineering design approach that focuses on minimizing adverse impacts of development on water quality. This approach is implemented by replicating the pre-development hydrologic regime of watersheds through infiltrating, filtering, storing, evaporating, and detaining stormwater runoff close to its source.^[1]

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Examples of LID site design include:

• diverting runoff from impervious surfaces such as parking lots by using bioretention areas (also called rain gardens);
• capturing rain water on a green roof;
• using grassed swales along roadways instead of curb-and-gutter drainage.

A concept that began in Prince George's County, Maryland in 1990, LID began as an alternative to traditional stormwater best management practices (BMPs) installed at construction projects.^[2] Officials found that the traditional practices were not cost-effective and the results did not meet water quality goals.

LID is a comprehensive technology-based approach to managing urban stormwater in small, cost-effective landscape features located near each site. This "source control" or pollution prevention concept contrasts with conventional "end-of-pipe" stormwater treatment designs, where runoff is conveyed and managed in large, costly pond facilities located at the bottom of drainage areas. Additionally, landscape vegetation working in tandem with a media filter can remove bacteria, metals and nutrients from runoff.

Hydrologic functions such as infiltration, frequency and volume of discharges to surface waters, and groundwater recharge levels can be maintained by minimizing the construction of impervious surfaces, and by use of functional grading, open section roadways, disconnection of hydrologic flowpaths, and bioretention/filtration landscape areas.

The LID design approach has received support from the U.S. Environmental Protection Agency (EPA) and is being promoted as a method to help meet goals of the Clean Water Act.^[3] Various local, state, and federal agency programs have used materials supplied by the LID Center (a non-profit group dedicated to advancing the practice).

LID techniques can also play an important role in Smart Growth and Green Infrastructure land use planning.

See also

• Conservation development
• Stormwater
• Surface runoff
• Sustainable development
• Water pollution

References