What Is Low Impact Development (LID)?
Types of Best Management Practices (BMP)
The 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 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.
Just 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?
(General LID information)
an LID site)
(EPA Low Impact Development Site)