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LID Practices and Controls

Last updated: 09/27/2005

 

LID BMPs

Rain garden that collects roadway runoff. Source: LID Center
Rain garden that collects
roadway runoff.

Source: LID Center
(click on thumbnail
for enlarged view
)

Additional Information
 

 

Vegetated swales during a wet weather event. Source: LID Center
Vegetated swales during
a wet weather event.

Source: LID Center
(click on thumbnail
for enlarged view
)

Afforestation/Reforestation. Afforestation involves planting trees in an area where they were absent for a significant period of time (e.g. an old farm field or a riparian buffer). Reforestation is the planting of trees in an area that was forested in the recent past (e.g. an area that was cleared for residential development). Plantings may be seeds, seedlings, or semi-mature trees. Trees reduce runoff volume through evapotranspiration (ET) and interception and improve the infiltration capacity of the soil, thereby reducing runoff potential.  

Downspout Disconnection. In urban areas, downspouts are commonly directly connected to the sewer system.  The cumulative effect of thousands of connected downspouts can greatly increase the volume of stormwater entering the sewer system. Downspout disconnection is the process of separating roof downspouts from the sewer system and redirecting roof runoff onto pervious surfaces, most commonly a lawn. This simple act reduces the amount of directly connected impervious area in a drainage area.

 

Filter Strips. Filter strips are bands of densely vegetative slopes, designed to increase water quality entering a specific BMP. Filter strips increase water quality between a runoff source (i.e., impervious area) and another BMP, by filtration though the vegetated strip and encouraging infiltration. Filter strips are important components of a BMP treatment train.
 

Green Roofs. Green roofs are designed to support plants and mitigate the effects of urbanization on water quality by filtering, absorbing, and detaining rainfall. There are two basic types of green roofs: extensive and intensive. Extensive roofs form a thin vegetated sheath. Their low profile allows them to be added to existing buildings.  By contrast, intensive roofs are integral to the roof structure, permitting the use of trees and walkways. A greater depth of media and a greater roof structural capacity may be required to accommodate larger vegetation and surface features.
 

Infiltration Practices. Infiltration practices include designs that enhance water percolation through a media matrix that slows and partially holds stormwater runoff. Infiltration practices also promote groundwater recharge and facilitate pollutant removal. 
 

Pocket Wetlands. Pocket wetlands are constructed wetland systems designed to control stormwater volume and facilitate pollutant removal. Pocket wetlands generally have less biodiversity than natural wetlands, but still require a base flow through the wetland to support the aquatic vegetation present. Pollutant removal in these systems occurs through the settling of larger solids and coarse organic material and also by uptake in the aquatic vegetation.
 

Porous Pavement. Porous pavement includes pavers, asphalt, and concrete that allow stormwater to pass through voids in the surface and infiltrate into the subbase. The subbase provides storage for stormwater.  In unlined systems, infiltration into the underlying soil may also be possible.
 

Rain Barrels/Cisterns. Rain barrels are placed outside of a building at roof downspouts to collect and store rooftop runoff, which can later be reused for lawn and garden watering.

 

Rain Gardens. Rain gardens, also known as bioretention cells, are vegetated depressions that store and infiltrate runoff. Rain gardens are designed to encourage vegetative uptake of stormwater to reduce runoff volume and pollutant concentrations. A well design rain garden has an engineered soil which maximizes infiltration and pollutant removal while avoiding stormwater ponding for longer than 24 hours.

 

Soil Amendments. Soil amendments make the soil more suitable for the growth of plants and increase soil water retention capabilities through the use of both soil conditioners and fertilizers. Soil amendments also increase pollutant removal and promote groundwater recharge.

 

Tree Box Filters. Tree box filters are in-ground containers typically filled with bioretention type soil media containing street trees in urban areas. Runoff is directed to the tree box, where it is filtered by vegetation and soil before entering a catch basin. Tree box filters enhance pollutant removal and are ideal for ultra urban settings and spaces where rain gardens are not practicable. 

Vegetated Landscaping. Natural and reintroduced vegetation provides stormwater management and pollutant removal. Vegetated areas intercept and infiltrate rainfall, decreasing stormwater volumes. Plants, trees, and other vegetation remove pollutants from infiltrated stormwater through root zone uptake. Incorporating vegetation into the landscape is a stormwater management technique that utilizes environmentally beneficial mechanisms naturally occurring in the environment.  

Vegetated Swales. Vegetated swales are broad, shallow channels designed to convey and infiltrate stormwater runoff. The design of swales seeks to reduce stormwater volume through infiltration, improve water quality through infiltration and vegetative filtering, and reduce runoff velocity by increasing flow path lengths and channel roughness. 

Vegetative landscaping. Source: City of Vancouver Greenways Program
Vegetative landscaping.
Source: City of Vancouver Greenways Program

(click on thumbnail
for enlarged view
)


Additional information on LID BMPs is provided in a series of EPA fact sheets available at: http://cfpub.epa.gov/npdes/stormwater/menuofbmps/post.cfm

 


 

 

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