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An estimated 10 trillion gallons a year of untreated stormwater runs off roofs, roads, parking lots, and other paved surfaces, often through the sewage systems, into rivers and waterways that serve as drinking water supplies and flow to our beaches, increasing health risks, degrading ecosystems, and damaging tourist economies. But cities of all sizes are saving money by employing green infrastructure as part of their solutions to stormwater pollution and sewage overflow problems.

Green infrastructure helps stop runoff pollution by capturing rainwater and either storing it for use or letting it filter back into the ground, replenishing vegetation and groundwater supplies. Examples of green infrastructure include green roofs, street trees, increased green space, rain barrels, rain gardens, and permeable pavement. These solutions have the added benefits of beautifying neighborhoods, cooling and cleansing the air, reducing asthma and heat-related illnesses, lowering heating and cooling energy costs, boosting economies, and supporting American jobs.

Video: Syracuse, New York

NRDC's Rooftops to Rivers II provides case studies for 14 geographically diverse cities that are all leaders in employing green infrastructure solutions to address stormwater challenges -- simultaneously finding beneficial uses for stormwater, reducing pollution, saving money, and beautifying cityscapes. These cities have recognized that stormwater, once viewed as a costly nuisance, can be transformed into a community resource. These cities have determined that green infrastructure is a more cost effective approach than investing in "gray," or conventional, infrastructure, such as underground storage systems and pipes. At the same time, each dollar of investment in green infrastructure delivers other benefits that conventional infrastructure cannot, including more flood resilience and, where needed, augmented local water supply.

NRDC identifies six key actions that cities should take to maximize green infrastructure investment and to become "Emerald Cities":

  • Develop a long-term green infrastructure plan to lay out the city's vision, as well as prioritize infrastructure investment.
  • Develop and enforce a strong retention standard for stormwater to minimize the impact from development and protect water resources.
  • Require the use of green infrastructure to reduce, or otherwise manage runoff from, some portion of impervious surfaces as a complement to comprehensive planning.
  • Provide incentives for residential and commercial property owners to install green infrastructure, spurring private owners to take action.
  • Provide guidance or other affirmative assistance to accomplish green infrastructure through demonstration projects, workshops and "how-to" materials and guides.
  • Ensure a long-term, dedicated funding source is available to support green infrastructure investment.

Click on the cities below to learn about their efforts to implement green infrastructure:

  • Aurora


    Achieving 4 of 6 Emerald City criteria, Aurora has successfully integrated green infrastructure (GI) into the planning done by all its city departments, has dedicated GI funding sources, and adheres to the county-wide retention ordinance. The city could benefit more by establishing private-party incentives and requiring the use of GI to reduce some portion of the existing impervious surfaces.

    case studies
  • Chicago


    Achieving 3 of 6 Emerald City criteria, Chicago has embedded green infrastructure (GI) into various city policies and initiatives and become a national leader on green roofs and permeable pavement. The city lacks a comprehensive plan, a requirement to reduce impervious surfaces and dedicated funding.

    case studies
  • Kansas City

    Kansas City

    Achieving 3 of 6 Emerald City criteria, Kansas City kicked off its green infrastructure (GI) strategy with a "10,000 Rain Gardens" initiative in 2005 and is now pursuing its first wide-scale pilot project that will use GI as the sole control method for combined sewage overflows in a 100-acre residential area.

    case studies
  • Milwaukee


    Achieving 5 of 6 Emerald City criteria, Milwaukee is a leader in its integration of green infrastructure (GI) into its combined sewer overflow reduction strategy, including specific reduction targets and a triple-bottom-line analysis. Dedicated capital funds support green roof grants, rain barrels, and rain gardens.

    case studies
  • Nashville


    Achieving 3 of 6 Emerald City criteria, Nashville identified potential green infrastructure (GI) projects and suggested incentives for private properties to participate in GI, such as stormwater fee discounts, rebates, installation financing, and awards and recognition programs.

    case studies
  • New York

    New York

    Achieving 5 of 6 Emerald City criteria, New York continues to expand one of the most extensive programs of public investment in green infrastructure in the United States, with an initial focus on greening municipal capital projects and implementing several neighborhood scale demonstration projects.

    Click to learn more about GI projects in New York. >>

    case studies
  • Philadelphia


    The only city achieving 6 of 6 Emerald City criteria, Philadelphia is the first city in the nation formally committed to using green infrastructure as the primary means to satisfy its combined sewer overflow obligations. The city will fund its share of the costs of the program with a stormwater fee based on impervious area.

    case studies
  • Pittsburgh


    Achieving 1 of 6 Emerald City criteria, Pittsburgh's most tangible step toward full-scale green infrastructure implementation is passage of an ordinance that establishes stormwater volume reductions standards, including a requirement that developments larger than 10,000 square feet retain the first inch of rainfall on-site.

    case studies
  • Portland


    Achieving 5 of 6 Emerald City criteria, Portland has made a strong community commitment to green infrastructure through a combination of required and voluntary measures, including a runoff retention standard and replacement program for city-owned impervious surfaces.

    case studies
  • Rouge River Watershed

    Rouge River Watershed

    Achieving 1 of 6 Emerald City criteria, Rouge River Watershed (which includes the city of Detroit) formed an alliance of local jurisdictions that prepared watershed-wide management plans that identify green infrastructure as one of several strategies to restore the watershed.

    case studies
  • Seattle


    Achieving 3 of 6 Emerald City criteria, Seattle has a strong program that includes strategies to help private parties implement green infrastructure (GI). Initiatives are now accompanied by a regulatory GI program called Green Factor, which requires that development projects achieve minimum scores based on landscaping features that promote GI.

    case studies
  • Syracuse


    Achieving 5 of 6 Emerald City criteria, Syracuse was the first community in the United States subject to a legal requirement to reduce sewage overflows with green infrastructure (GI). GI investments totalling nearly $80 million will account for nearly two-thirds of future combined sewage overflow reductions, funded by a combination of sewer fees and low-interest loans and grants from the state.

    case studies
  • Toronto


    Achieving 4 of 6 Emerald City criteria, Toronto made downspout disconnection mandatory, adopted construction standards to require buildings to include green roofs, established rainwater capture demonstration projects, and provided funding for tree plantings to double the city's existing tree canopy.

    case studies
  • Washington, D.C.

    Washington, D.C.

    Achieving 5 of 6 Emerald City criteria, Washington, D.C. has issued a federal stormwater permit that contains a 1.2-inch retention standard for new development and redevelopment -- to be achieved through evaportranspiration, infiltration, and harvesting -- and numeric retrofit targets for street trees and green roofs.

    Click to learn more about how Washington is handling stormwater runoff. >>

    case studies

Although cities and policy makers have taken enormous strides forward in their understanding and use of green infrastructure since the first Rooftops to Rivers report was published in 2006, much work remains at the local, state and federal levels. Local officials need better information about the benefits of green infrastructure and how to target investments to maximize benefits. States should undertake comprehensive green infrastructure planning, ensure permitting programs drive the use of green infrastructure, and eliminate hurdles (whether from building and development codes or funding) to ensure green infrastructure is adequately funded.

Most importantly, the U.S. Environmental Protection Agency (EPA) must reform the national Clean Water Act rules that apply to stormwater sources to require retention of a sufficient amount of stormwater through infiltration, evapotranspiration, and rainwater harvesting to ensure water quality protection. The rules should apply throughout urban and urbanizing areas. The EPA should also require retrofits in already developed areas and as part of infrastructure reconstruction projects. In so doing, the EPA will embody the lessons learned from cities across this country and the leaders who understand that, from an environmental, public health, and economic perspective, green infrastructure is the best approach to cleaning up our waters.


Wanted: Green Acres

Wanted: Green Acres

To reduce the impacts of urban stormwater runoff, Philadelphia's Greened Acre Retrofit Program is catalyzing low-cost green infrastructure retrofits on private property.

How Commercial Property Investment in Green Infrastructure Creates Value

The Green Edge: How Commercial Property Investment in Green Infrastructure Creates Value

There is a wide range of benefits that green infrastructure and stormwater management, when used on private property, can provide to commercial property owners and their tenants.

Creating Private Markets for Green Stormwater Infrastructure

Creating Private Markets for Green Stormwater Infrastructure

With the federal "Clean Water Needs Survey" identifying over $100 billion in needed infrastructure investment over the next twenty years to address stormwater and sewage overflows, the time for creating private markets for green infrastructure has arrived.

Financing Stormwater Retrofits in Philadelphia and Beyond

Financing Stormwater Retrofits in Philadelphia and Beyond

Stormwater runoff is a principal cause of urban waterway pollution nationwide, fouling rivers, lakes, beaches, and drinking water supplies. To reduce the environmental and public health threats posed by polluted stormwater and to comply with the Clean Water Act, cities nationwide are making significant investments to reduce stormwater runoff.

Looking Up

Looking Up: How Green Roofs and Cool Roofs Can Reduce Energy Use, Address Climate Change, and Protect Water Resources in Southern California

Southern California faces multiple threats stemming from urbanization and development, from increased stormwater runoff to higher energy use. Green roofs and cool roofs offer the potential to address some of the issues and improve the sustainability of urban areas.

Capturing Rainwater from Rooftops

Capturing Rainwater from Rooftops

Rooftop rainwater capture is a simple, cost-effective approach for supplying water that promotes sustainable water management and reduces pollution.

Thirsty for Answers

Thirsty for Answers: Preparing for the Water-related Impacts of Climate Change in American Cities

Cities across the United States face significant water-related vulnerabilities based on current carbon emission trends because of climate change, from water shortages to more intense storms and floods to sea level rise.

Energy Down the Drain

Energy Down the Drain: The Hidden Costs of California's Water Supply

California's water utilities and consumers burn large amounts of energy to treat, deliverheat, and cool water. A proper understanding of the close connections between water and energy can save both money and resources.

A Clear Blue Future

A Clear Blue Future: How Greening California Cities Can Address Water Resources and Climate Challenges in the 21st Century

As global warming threatens our water resources, low impact development can help communities ensure access to safe and reliable sources of water while reducing energy consumption and global warming pollution.

Climate Change, Water, and Risk

Climate Change, Water, and Risk: Current Water Demands Are Not Sustainable

Climate change will increase the risk that water supplies will fall short of demand in many areas of the United States. More than one-third of all counties in the lower 48 states will face higher risks of water shortages by mid-century as the result of global warming.

Video: Milwaukee, Wisconsin

Video: Santa Barbara, California

last revised 2/17/2015

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