What is Green Infrastructure?

Green infrastructure is an approach to wet weather management that is cost-effective, sustainable, and environmentally friendly. Green Infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies.

At the largest scale, the preservation and restoration of natural landscape features (such as forests, floodplains and wetlands) are critical components of green stormwater infrastructure. By protecting these ecologically sensitive areas, communities can improve water quality while providing wildlife habitat and opportunities for outdoor recreation.

On a smaller scale, green infrastructure practices include rain gardens, porous pavements, green roofs, infiltration planters, trees and tree boxes, and rainwater harvesting for non-potable uses such as toilet flushing and landscape irrigation.

{US Environmental Protection Agency, 2009}
Also see "What is Low Impact Development?" and Green Infrastructure and LID Resources

What is Low Impact Development?

Low Impact Development (LID) is an innovative, ecosystem-based approach to land development and stormwater management. The LID philosophy is modeled after nature: manage rainfall at the source. LID's goal is to mimic a site's natural hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source, resulting in a 'hydrologically functional' landscape and a protected watershed. Techniques are based on the premise that stormwater management should not be seen as stormwater disposal. LID is a versatile approach that can be applied equally well to new development, urban retrofits, and redevelopment / revitalization projects.

There are five basic principles of Low Impact Development:

1) Conserve natural areas
Planning is the first critical step in any LID project. Solid plans, based on natural resource inventories and assessments of the inventory data are important in identifying natural areas that should be conserved in the development process. These areas can be key for stormwater management, and their protection will help maintain the ecological integrity of the site. Regional, watershed, local, and site based plans, based on natural resource inventories and assessments are crucial for implementing LID strategies such as conservation subdivision design, stream and wetland buffers, and habitat conservation areas,

2) Minimize Development Impacts
There are many low- or no- cost LID strategies that can be implemented during subdivision design and building. Impervious surfaces can be reduced by minimizing road widths, shrinking parking lots, and building footprints, decreasing setbacks. Storm pipes, curbs, and gutters can also be reduced significantly (see #3 and #4). During development, preservation of sensitive soils, minimizing grading and lot disturbance help maintain the site's ecological integrity.

3) Maintain site runoff rate and control small storms
Maintaining the natural runoff rate from a site protects receiving waters, such as stream channels and wetlands, as well as the fish and wildlife habitat they provide. The goal is to maintain the historic, pre-developed volume, rate, frequency, and duration of stormwater discharges so that discharges are not excessively high during wet winter months or excessively low during dry summer months. Techniques include maintaining natural flow paths, using open drainage instead of closed (pipe) systems, flattening slopes, dispersing drainage, lengthening flow paths, maximizing sheet flows, and saving headwater areas.

4) Use integrated management practices (control volume and pollutant loads)
Instead of conveying stormwater and treating it in large, costly end-of-pipe facilities located at the bottom of drainage areas, LID addresses stormwater through small, cost-effective landscape features strategically distributed throughout the site. These landscape features, known as Integrated Management Practices (IMPs), are the building blocks of LID. Almost all components of the urban environment have the potential to serve as an IMP. This includes not only open space, but also rooftops (green roofs), streetscapes (rain gardens), parking lots (porous surfaces), sidewalks (tree filter boxes), and medians (vegetated swales). The use of these controls, in combination with the other LID principles listed here, creates a customized stormwater management strategy that helps maintain overall watershed integrity and functions.

5) Implement pollution prevention, proper maintenance, and public education programs
Pollution prevention and proper maintenance can help increase the efficiency and long-term success of integrated management practices and reduce the introduction of pollutants into the environment. Many practices are easier and less expensive to maintain than traditional stormwater facilities. For instance, many bioretention facilities need only to be cleared of any trash and then have mulch applied periodically. Individuals and groups that are responsible for maintaining LID facilities should receive educational brochures and other materials, and have access to workshops, so that they know their responsibilities and have the knowledge to carry them out.

What LID is NOT:
While LID can incorporate techniques of conservation subdivision design (or 'open space' design), it is not synonymous with conservation subdivision. Similarly, LID is not the same as smart growth or sustainable building. Each of these philosophies has overlapping goals and strategies, but the terms should not be used interchangeably.

Green Infrastructure and Low Impact Development Resources