National Research Council,
Robert S. Kerr Environmental Research Center
US Environmental Protection Agency,
Robert S. Kerr Environmental Research Center
*Adapted from: http://water.epa.gov/infrastructure/greeninfrastructure
THE PROBLEM WITH PAVEMENT
Large paved surfaces keep rain from infiltrating the soil and recharging groundwater supplies. Impervious surfaces like streets, parking lots, sidewalks, and rooftops transport stormwater in volumes up to 16 times higher than natural areas1. This stormwater runoff delivers pollutants from motor oil, lawn chemicals, sediments, and pet waste to streams, rivers, and lakes untreated. Higher flows can also cause erosion and flooding that can damage property, infrastructure, and wildlife habitat.
In 2008 the EPA reported the total wastewater and stormwater infrastructure maintenance and repair needs for the United States to be $298.1 billion2. Conventional stormwater infrastructure or gray infrastructure is largely designed to move stormwater away from urban areas through pipes and other man-made conduits. A potentially less expensive but effective alternative, green infrastructure uses natural processes to reduce and treat stormwater in place by soaking up and storing water. These systems provide many environmental, social, and economic benefits that promote urban livability and add to the bottom line.
WHAT IS GREEN INFRASTRUCTURE?
Green infrastructure techniques use vegetation, soils, and natural processes to manage stormwater and generate healthier urban environments. Green infrastructure systems mimic natural hydrology to take advantage of interception, evapotranspiration, and infiltration of stormwater runoff at its source thus disconnecting impervious surfaces from gray infrastructure. This approach provides multiple benefits of flood protection, cleaner air, and cleaner water.
Green Infrastructure Techniques
- Downspout Disconnection – the rerouting of rooftop drainage pipes to permeable areas, rain barrels, or cisterns. This allows stormwater to infiltrate into the soil and/or stores stormwater for later use
- Rainwater Harvesting – systems that collect and store rainfall for later use. These systems provide a renewable water supply and can slow and reduce runoff. Such systems can reduce demands on increasingly limited water supplies in arid regions
- Rain Gardens – also known as bioretention or bioinfiltration cells, these are shallow, vegetated basins that collect and absorb runoff by infiltration and evapotranspiration. Rain gardens can easily be installed in many unpaved spaces.
- Planter Boxes – structures with vertical walls and open or closed bottoms filled with gravel, soil and vegetation that collect and absorb runoff. Planter boxes are ideal for space-limited sites in dense urban areas.
- Bioswales – broad and shallow vegetated, mulched, or xeriscaped channels that provide stormwater treatment and retention. Bioswales slow water flow and allow infiltration into soils, thereby filtering stormwater flows. As linear features, they are appropriate along streets and parking lots.
- Permeable Pavements – porous paved surfaces that allow rain to permeate into soils. Permeable pavements can be constructed from various materials such as pervious concrete, porous asphalt, permeable interlocking pavers.
- Green Streets and Alleys – transform impervious streets into landscaped green spaces by integrating green infrastructure elements such as bioswales, planter boxes, and trees into street and alley design. Green streets and alleys are designed to store, infiltrate, and evapotranspire stormwater while adding to the aesthetics of landsapes.
- Green Parking – integrate green infrastructure elements such aspermeable pavements and rain gardens into parking lot designs. Such structures manage stormwater on site, mitigate urban heat islands, and create a more pedestrian-accessible environment.
- Green Roofs – roofs covered with growing media and vegetation. Green roofs are cost effective in dense urban areas or where stormwater management costs may be high.
- Urban Tree Canopy- Trees intercept rain in their leaves and branches thereby reducing and slowing stormwater runoff. Homeowners, businesses, and cities can all participate in the planting and maintenance of trees.
- Land Conservation – Open spaces and natural areas within and adjacent to cities can protect water quality, mitigate flooding impacts, and provide recreation. Important natural areas that help protect water quality and mitigate flooding include riparian areas, wetlands, and steep hillsides where construction may exacerbate erosion.
OKLAHOMA’S WATER CHALLENGES
Oklahoma is facing population growth, land use change, aging infrastructure, and climate change2. All of these factors will increase demands for good quality water to be used in the public water supply, protection of fish, shellfish, and wildlife, as well as recreational, agricultural, industrial, energy exploration, and navigational purposes3.
Oklahoma Water Facts4
- Oklahoma has approximately 55,646 miles of shoreline along lakes and ponds.
- Oklahoma contains approximately 1,401 sq miles of water area in its lakes and ponds.
- The majority of the state’s surface water (approximately 54%) is used for public water supply.
- Groundwater accounts for 73% of total Oklahoma irrigation water use.
- OCWP5 estimates approximately $44 billion (in 2010 dollars) will be required to meet the wastewater infrastructure needs for the next 50 years.
BENEFITS OF GREEN INFRASTRUCTURE
Conventional gray stormwater infrastructure is designed mainly to move urban stormwater away from urban environments, but green infrastructure reduces and treats stormwater in place while delivering environmental, social, and economic benefits. Here’s how:
Water Quality: by soaking up and storing water in place, green infrastructure reduces stormwater discharges. Lower stormwater volumes means reduced gray infrastructure overflows and lower pollutant loads. Infiltration and storage of stormwater can also help remove pollutants.
Flooding: Slowing and reducing stormwater discharges and peak flows can mitigate flood risk.
Water supply: Rainwater harvesting and practices that increase infiltration can provide a renewable, water supply alternative. Harvested rainwater can be used for outdoor irrigation and certain indoor uses thereby significantly reducing municipal water use. Water infiltration practices also recharge groundwater, an important source of drinking water.
Private and Public Cost Savings: Incorporation of green infrastructure into stormwater management systems can lower capital costs. Lower costs for site grading, paving, and landscaping, and smaller or eliminated piping and detention facilities provide savings for developers. In cities with combined waste and stormwater sewer systems, green infrastructure control measures can cost less than conventional controls, and green-gray approaches can reduce stormwater infrastructure costs.
ECONOMIC BENEFITS OF GREEN INFRASTRUCTURE
Case studies have shown that, in the vast majority of the cases, implementing well-chosen green infrastructure practices saves money for developers, property owners, and communities while protecting and restoring water quality6. For example, the Gap Creek subdivision in Sherwood, Arkansas was redesigned to include green infrastructure elements. In this project open space was increased from 1.5 acres to 23.5 acres, lots sold for $3,000 more and cost $4,800 less to develop, resulting in $2.2 million in additional profit for the developer.6
Examples of Economic Benefits7:
• Reduce flooding – a reduction in flooding can increase property values in floodplains by up to 5%.
• Improved water quality – can increase market value by 15% for properties near lakes, rivers, streams, or coastal areas.
• Reduced filtration costs – along the Anacostia River in Washington, DC, bioretention methods saved $250,000 over the use of piped stormwater and sand filters.
• Infrastructure cost savings – replacing curb, gutter, and storm sewers with roadside bioswales saved one developer $70,000 per mile.
• Increased property values – lots in green infrastructure neighborhoods sold for $3000 more than lots using conventional stormwater infrastructure
• Protecting water quality – green infrastructure helps maintain clean water, which is usually less expensive than cleaning contaminated water. Not having to clean contaminated water is an avoided cost.
Table 1. Adapted Summary of Cost Comparisons between
Conventional and Green Infrastructure Approaches.6
|Project||Conventional Costs||Green Infrastructure Costs||Percent Difference|
Green infrastructure is an approach that communities can choose to maintain water quality, provide environmental and social benefits, and support sustainable communities. Unlike gray stormwater infrastructure, which uses pipes and other man-made conduits to dispose of rainwater, green infrastructure uses vegetation and soil to manage rainwater in place. By regenerating natural processes in the urban environment, green infrastructure provides not only stormwater management, but also flood mitigation, lower infrastructure costs, increased property values, and improved urban livability.
Oklahoma is facing greater demands for water quality and supply at a time when stormwater infrastructure needs replacement or repair. In these tough and uncertain economic times, we need resilient, flexible and affordable solutions that satisfy several objectives at once. Green infrastructure is one solution.
REFERENCES AND RESOURCES
Green infrastructure information, general benefits, and summary were adapted from:
*This website contains most links to PDFs cited in this document as well as much more information and resources.
1 Schueler, T. 1995. The importance of imperviousness. Watershed Protection Techniques 1(3):100-111.
2 State of Oklahoma Water Resources Board. 2011. Oklahoma Comprehensive Water Plan 2012 Update: Water Demand Forecast Report.
3 State of Oklahoma Water Resources Board.(Viewed 2012, June 20) Fact Sheet: Water Quality Standards. http://www.owrb.ok.gov/about/about_pdf/Fact-Standards.pdf
4 State of Oklahoma Water Resources Board. (Viewed 2012, June 20). “Oklahoma Water Facts”. http://www.owrb.ok.gov/util/waterfact.php
5 State of Oklahoma Water Resources Board. 2012. Oklahoma Comprehensive Water Plan 2012 Update: Wastewater Infrastructure Needs Assessment by Region. http://www.owrb.ok.gov/supply/ocwp/pdf_ocwp/WaterPlanUpdate/draftreports/OCWP_WasteWaterInfrastructureAssessment.pdf
6 USEPA. 2007. Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices EPA 841-F-07-006: http://www.epa.gov/owow/NPS/lid/costs07/documents/reducingstormwatercosts.pdf
7 NC State University, A&T State University Cooperative Extension (Viewed 2012, June 20). Low Impact Development – an economic fact sheet: http://www.ces.ncsu.edu/depts/agecon/WECO/nemo/documents/WECO_LID_econ_factsheet.pdf
“The Value of Green Infrastructure” document from American Rivers provides a framework to help communities measure and value the air quality, energy use, and many other benefits that green infrastructure provides.
Low Impact Development: A Design Manual for Urban Areas introduces general audiences to designing landscapes for urban stormwater runoff—a primary source of watershed pollution.
The Green Values® Stormwater Toolbox was developed primarily for use by planners, engineers and other municipal staff and provides tools to learn how the use of green infrastructure saves money and understand the costs and benefits of using green infrastructure to mitigate the need for different types of built water infrastructure, such as sewers and detention basins. This includes two easy to use stormwater management calculators.
Contact for More Information:
This article has not been subjected to internal policy review of the U.S. EPA. Therefore, the research results do not necessarily reflect the views of the Agency or its policies.