This following is excerpted from Managing Wet Weather with Green Infrastructure Action Strategy 2008 by American Rivers, Association of State and Interstate Water Pollution Control Administrators, National Association of Clean Water Agencies, Natural Resources Defense Council, The Low Impact Development Center and the U.S. Environmental Protection Agency. More information on this can be found at http://www.epa.gov/npdes/greeninfrastructure
Many communities, ranging from highly developed cities to newly developing towns, are looking for ways to assure that the quality of their rivers, streams, lakes, and estuaries is protected from the impacts of development and urbanization. Traditional development practices cover large areas of the ground with impervious surfaces such as roads, driveways, and buildings. Once such development occurs, rainwater cannot infiltrate into the ground, but rather runs offsite at levels that are much higher than would naturally occur. The collective force of such rainwater scours streams, erodes stream banks, and thereby causes large quantities of sediment and other entrained pollutants to enter the water body each time it rains.
In addition to the problems caused by stormwater and nonpoint source runoff, many older cities (including many of the largest cities in the United States), have combined sewage and stormwater pipes which periodically and in some cases frequently overflow due to precipitation events. In the late 20th century, most cities that attempted to reduce sewer overflows did so by separating combined sewers, expanding treatment capacity or storage within the sewer system, or by replacing broken or decaying pipes. However, these practices can be enormously expensive and take decades to implement. Moreover, piped stormwater and combined sewer overflows ("CSOs") may also, in some cases, have the adverse effects of upsetting the hydrological balance by moving water out of the watershed, thus bypassing local streams and ground water. Many of these events also have adverse impacts and costs on source water for municipal drinking water utilities.
A set of techniques, technologies, approaches and practicesâ€”collectively referred to as "green infrastructure"â€”can be used to eliminate or reduce the amount of water and pollutants that run off a site and ultimately are discharged into adjacent water bodies. As cities move towards sustainable infrastructure, green infrastructure can be a valuable approach.
"Green infrastructure" is a relatively new and flexible term, and it has been used differently in different contexts. Thus, to date, there is no universally established definition of the term. For example, Benedict and McMahon, in their book Green Infrastructure (Island Press, 2006), have defined it broadly as "an interconnected network of natural areas and other open spaces that conserves natural ecosystem values and functions, sustains clean air and water, and provides a wide array of benefits to people and wildlife." However, for the purposes of our efforts to implement the Green Infrastructure Statement of Intent (discussed below), we intend the term "green infrastructure" to generally refer to systems and practices that use or mimic natural processes to infiltrate, evapotranspirate (the return of water to the atmosphere either through evaporation or by plants), or reuse stormwater or runoff on the site where it is generated.
What is Green Infrastructure? Green infrastructure is management approaches and technologies that utilize, enhance and/or mimic the natural hydrologic cycle processes of infiltration, evapotranspiration and reuse. Green infrastructure approaches currently in use include green roofs, trees and tree boxes, rain gardens, vegetated swales, pocket wetlands, infiltration planters, porous and permeable pavements, vegetated median strips, reforestation/revegetation, and protection and enhancement of riparian buffers and floodplains. Green infrastructure can be used almost anywhere soil and vegetation can be worked into the urban or suburban landscape. Green infrastructure also includes decentralized harvesting approaches, such as the use of rain barrels and cisterns to capture and re-use rainfall for watering plants or flushing toilets. These approaches can be used to keep rainwater out of the sewer system so that it does not contribute to a sewer overflow and also to reduce the amount of untreated runoff discharging to surface waters. Green infrastructure also allows stormwater to be absorbed and cleansed by soil and vegetation and either re-used or allowed to flow back into groundwater or surface water resources. In managing wet weather, green infrastructure practices, like all types of practices, need to be implemented at multiple scales: site, neighborhood, and regional or watershed. The most beautifully designed site, even if multiple green infrastructure practices are used, may actually result in an overall increase in impervious surfaces and thus stormwater discharges, if new or expanded roads, parking lots and commercial development are needed to serve it. For that reason, we include approaches such as infill, redevelopment and preserving natural areas in our suite of green infrastructure approaches. For more information on specific green infrastructure practices and how they function, visit: >http://www.epa.gov/npdes/greeninfrastructure.
Green Infrastructure BenefitsGreen infrastructure has a number of environmental and economic benefits in addition to reducing the volume of sewer overflows and runoff.
- Cleaner Water â€“ Vegetation, green space and water reuse reduce the volumes of stormwater runoff and, in combined systems, the volume of combined sewer overflows, as well as reduce concentrations of pollutants in those discharges.
- Enhanced Water Supplies â€“ Most green infiltration approaches involve allowing stormwater to percolate through the soil where it recharges the groundwater and the base flow for streams, thus ensuring adequate water supplies for humans and more stable aquatic ecosystems. In addition, capturing and using stormwater conserves water supplies.
- Cleaner Air â€“ Trees and vegetation improve air quality by filtering many airborne pollutants and can help reduce the amount of respiratory illness. Transportation and community planning and design efforts that facilitate shorter commute distances and the ability to walk to destinations will also reduce vehicle emissions.
- Reduced Urban Temperatures â€“ Summer city temperatures can average 10ÂºF higher than nearby suburban temperatures. High temperatures are also linked to higher ground level ozone concentrations. Vegetation creates shade, reduces the amount of heat absorbing materials and emits water vapor â€“ all of which cool hot air. Limiting impervious surface and using light colored impervious surfaces (e.g., porous concrete) also mitigate urban temperatures.
- Increased Energy Efficiency â€“ Green space helps lower ambient temperatures and, when incorporated on and around buildings, helps shade and insulate buildings from wide temperature swings, decreasing the energy needed for heating and cooling. Further, diverting stormwater from wastewater collection, conveyance and treatment systems reduces the amount of energy needed to pump and treat the water. Energy efficiency not only reduces costs, but also reduces generation of greenhouse gases.
- Source Water Protection â€“ Green infrastructure practices provide pollutant removal benefits, thereby providing some protection for both ground water and surface water sources of drinking water. In addition, green infrastructure provides groundwater recharge benefits.
- Community Benefits â€“ Trees and plants improve urban aesthetics and community livability by providing recreational and wildlife areas. Studies show that property values are higher when trees and other vegetation are present.
- Cost Savings â€“ Green infrastructure may save capital costs associated with paving, creating curbs and gutters, building large collection and conveyance systems, and digging big tunnels and centralized stormwater ponds; operations and maintenance expenses for treatment plants, pumping stations, pipes, and other hard infrastructure; energy costs for pumping water around; cost of treatment during wet weather; and costs of repairing the damage caused by stormwater, such as streambank restoration.
Wayne County Department of Environment is championing the development of Green Infrastructure in Wayne County as well as promoting it in southeastern Michigan. Green infrastructure has a number of environmental and economic benefits in addition to reducing the volume of sewer overflows and runoff. These benefits includeâ€¦
- Cleaner Water
- Enhanced Water Supplies
- Cleaner Air
- Reduced Urban Temperatures
- Increased Energy Efficiency
- Source Water Protection
- Community Benefits
- Cost Savings
Southeastern Michigan Urban Ecosystem Report
Guidelines for Home Rain Gardens
Riparian Corridor Management
Grow Zone Initiative
Green Infrastructure Reports
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