Green Infrastructure
What is Green Infrastructure, or Low Impact Development (LID)?
LID is an approach to land development (or redevelopment) that works with nature to manage stormwater as close to its source as possible.
The goal of LID is to reduce runoff and to mimic a site’s predevelopment hydrology by infiltrating, filtering, storing, evaporating, and detaining stormwater runoff. LID employs principles such as preserving and recreating natural landscape features and minimizing imperviousness to create functional and appealing site drainage that treats stormwater as a resource, rather than a waste product.
The goal of LID is to reduce runoff and to mimic a site’s predevelopment hydrology by infiltrating, filtering, storing, evaporating, and detaining stormwater runoff. LID employs principles such as preserving and recreating natural landscape features and minimizing imperviousness to create functional and appealing site drainage that treats stormwater as a resource, rather than a waste product.
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By implementing LID principles and practices, water can be managed in a way that reduces the effects of developed areas and promotes the natural movement of water in an ecosystem or watershed. Applied on a broad scale, LID can maintain or restore a watershed’s hydrologic and ecological functions and provide numerous other environmental, economic, and social benefits.
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LID is also known as:
• Green Infrastructure • Conservation Site Design • Sustainable Stormwater Management LID is one of many strategies and techniques used to counteract the impact of development. Many of the strategies have things in common and a few of the terms have been used interchangeably, but each may have a different frame that sets it apart from the others. |
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Bioretention Cell
Level Spreader |
Bioswales slowly convey water to storm sewer inlets or surface waters and filter the ‘first flush’ of runoff.
The first flush occurs during the first few moments of a rain event when pollutants are most concentrated. Rain gardens are native, perennial gardens, strategically located to capture runoff from impervious surfaces. Rain gardens increase aesthetic value, absorb water, reduce runoff, protect water quality and prevent flooding.
Bioretention cells are shallow, landscaped depressions that can handle large volumes of water. They are well-suited for commercial, institutional, industrial, or residential settings.
Level spreaders dissipate water velocity and prevent erosion by spreading water flows over a wide area, rather than releasing them from a point source of discharge, such as a pipe.
Native plants have a tremendous root structure that builds soil quality and increase organic matter content to facilitate infiltration.
Permeable paving surfaces may include permeable paver blocks, porous concrete, or porous asphalt. They provide support of traditional parking surfaces, but they allow a significant amount of annual precipitation to be filtered.
A green roof is a low-maintenance vegetated roof system that reduces stormwater runoff by absorbing and retaining the water in the soil medium for plant growth.
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LID Benefits
LID offers a number of advantages over traditional, engineered stormwater drainage approaches, including:
LID offers a number of advantages over traditional, engineered stormwater drainage approaches, including:
- Addresses stormwater at its source
LID practices seek to manage rainfall where it falls, thereby reducing or eliminating the need for detention ponds and flood controls. - Promotes groundwater recharge
Many LID techniques allow stormwater to infiltrate the earth, thereby recharging groundwater aquifers and providing baseflow to streams during dry weather. The stormwater, cooled as it flows underground, helps keep stream
temperatures low. - Allows for more flexible site layouts
Whereas traditional stormwater management required large stormwater ponds that consume valuable real estate, the small-scale, dispersed nature of LID practices means that designers can include stormwater management in a variety of open spaces and smaller landscaped areas. - Preserves streams and watersheds
Because LID practices infiltrate rainfall and prevent runoff, they reduce both pollutant loads and streambank erosion associated with peak flows. - Enhances aesthetics and public access/use
Well-designed vegetated practices, such as rain gardens, can provide a visual amenity, particularly when compared to hardened drainage infrastructure such as pipes, curbs, gutters, and concrete-lined channels. Some practices can double as park space, offering recreational amenities. - Reduces costs
A common myth is that LID costs more than traditional stormwater management, but case studies have shown the opposite to be true. Savings can arise from the reduced amount of pipes, asphalt, detention basins or other infrastructure needed to handle runoff, reduced energy costs, and increases in developable land area, which otherwise would not have been available had traditional stormwater management approaches been employed.
