Low Impact Development (LID) refers to a set of stormwater management approaches that are implemented to reduce runoff and pollutant loadings as close to their source(s) as possible.Through these approaches, permanent water quality can be micromanaged at various locations around the site in leiu of larger BMPs near the outfall of the drainage area.
LID is designed to mimic, as close as possible, the naturally hydrologic conditions of a site thereby reducing the adverse impacts caused by increased runoff that is typically associated with traditional development laden with impervious areas.
The fundamental principle behind Low Impact Development is to both reduce the volume of runoff and to divert stormwater flows away from a common collection point. There are various practices that can be used in conjunction with one another to accomplish this goal. Some examples of these practices include open space preservation, infiltration basins/trenches, rain gardens, rain barrels/cisterns, eliminating curves/gutters, bioretention, vegetated swales and converting turf areas to trees and shrubs.
Infiltration areas designed to mimic natural, predevelopment hydrology and address water quality.
Drainage swales equipped with native vegetation to slow down conveyance, improving infiltration.
Green spaces provide wildlife, recreational, hydrologic, aesthetic and educational benefits.
The majority of Low Impact Development practices can be assigned to one of six categories: Conservation Design, Infiltration, Runoff Storage, Runoff Conveyance, Filtration, and Low Impact Landscaping. For more information please visit the EPA's LID website via the link below.
Rain Barrels and Cisterns – Runoff Storage Practices. Runoff off from impervious surfaces such as roofsand parking lots can be diverted into small storage tanks to be later gradually infiltrated, evaporated, used in irrigation systems or in other rainwater reuse systems. Collecting runoff in this manner may help reduce peak flow discharges and may reduce the amount of runoff volume released into downstream areas that may be prone to flooding. These small storage tanks may be installed as above ground rain barrels or underground cisterns.
Cluster Development – Conservation Designs. The premises behind cluster development is to minimize the amount of impervious area by slightly reducing the proposed land disturbance, and to preserve open space that could then be used for recreation, visual aesthetics, wildlife habitats, or as an area to place additional LID practices. Residential developers have been able to provide residents with recreational areas or undisturbed natural vistas by utilizing cluster development.
Permeable Pavement – Infiltration Practices. Asphalt, concrete, and other traditional pavement materials can be engineered to allow for runoff to infiltrate through the pavement into the underlying soils. Not only will permeable pavement help reduce the volume of runoff discharged offsite but may also help recharge ground water, maintain stream temperatures, or even provide additional aesthetic benefits.
Grass Swales – Runoff Conveyance Practices. Typically installed as an alternative to curb-and-gutter systems, these permeable, vegetated swales are used to route runoff from large impervious surfaces through the site in a manner that either slows the runoff's velocity, lengthen the runoff time of concentration or delays the peak flow. Certain vegetation can be added to theses swales that will enhance the performance of these swales especially when it comes to evaporation, settling of solids, and even biological uptake of pollutants.
Bioretention Area – Filtration Practices. These areas, often described as rain gardens, are designed to treat runoff by filtering through grass buffers, sand beds, and organic layers of planting soil and vegetation in order to capture pollutants before releasing the runoff from the site. Typically these areas consist of a ponding area, landscaped with native plants and grasses, that collect runoff allowing it to filter through the soil media below. Bioretention may help reduce the volume of runoff, the thermal impact of receiving water, and it may help increase ground water recharge.
Xeriscaping – Low Impact Landscaping. This is a style of landscaping in which plants, native to the area, can be used within other LID practices such as Bioretention and swales, along with proper soil conditions, to take full advantage of rainfall. The proper utilization and placement of indigenous flora can reduce runoff volumes, increase visual aesthetics, and could even reduce maintenance requirements.