What Is Low Impact Development (LID)?
Types of Best Management Practices (BMP)
BioretentionThe type of LID shown to the right is called a Rain Garden, or Bioretention cell. The Stormwater pools in the engineered soil fill and then percolates into the soil or is absorbed by the vegetation, rather than running straight into the storm drain. This allows an opportunity for the run-off to be treated by the Bioretention cell. Many of these are being put into practice in place of retention cells to address water quality and quantity from impervious surface run-off.
Green RoofsGreen Roofs treat runoff from another type of impervious surface; roof tops. They can be constructed on roof tops up to a 45 degree slant and have multiple benefits besides the asthetics of having a garden on your roof. The soil and vegetation help to regulate temperature. The BMP absorbs the worst of the heat during the day to keep buildings cool and acts as a heat retainer at night to keep heat from escaping. They also retain rainwater that falls on roof tops, holding the precipitation until it evaporates or treating it through percolation before it leaves the roof.
Permeable PavementJust as there are many variations of BMP and LID, there are different kinds of permeable pavement, but the main idea is consistent; they aim to make traditionally impervious surfaces permeable. The picture shown is an example of concrete pavers that are layed with a stone underdrain similat to the bioretention cell, and with soil planted with grass seed filled into the permeable space in the pavers. An EPA study found that "The use of permeable pavement systems dramatically reduced surface runoff volume and attenuated the peak discharge".
Where is LID being used?
http://www.lowimpactdevelopment.org/ (General LID information)http://www.lid-stormwater.net/ (Design an LID site)http://water.epa.gov/polwaste/green/ (EPA Low Impact Development Site)