From rooftops to rivers: green infrastructure yields economic and environmental benefits

Nancy Stoner, Director, Clean Water Project, Natural Resources Defense Council, Washington, D.C.; Alexandra Dapolito Dunn, Esq., Assistant Dean of Environmental Law Programs, Pace University School of Law, White Plains, New York

Most urban and suburban waterways in the United States are polluted, and wet weather impacts are a huge part of the problem. While boating or other non-contact recreation may be possible, many urban and suburban streams, lakes or coastal waters are often unsafe for swimming or other direct contact after it rains. Rainfall carries trash, toxins and bacteria into waterways, increasing the risk of illness for swimmers and making these waters unhealthy for fish, amphibians and birds. If these same urban rivers, lakes and coastal waters are clean, they can become a tremendous community resource, providing fishing, swimming and other recreational opportunities as well as a higher quality source of drinking water for cities and suburbs. However, if polluted, they can be a potential health hazard as well as an eyesore, lowering property values and detracting from community revitalization efforts.

As rain comes into contact with streets, parking lots and rooftops, an environmental chain reaction occurs. This rain picks up oil, grease and toxins, as well as pathogens, nutrients and other pollutants, and deposits them into lakes, streams and coastal waters. The high-volume, high-velocity flows cause additional adverse environmental consequences, including flooding, streambank scouring, riparian habitat loss, flashy streams, increased stream temperatures, and, because the rainwater cannot soak into the ground, depleted groundwater resources. These problems will only continue to grow as our nation's population increases and, even more importantly, as development continues to spread across the landscape—at twice the rate of population growth.

These problematic impacts are exacerbated in the over 770 cities in the United States served by combined wastewater and stormwater pipes, as these peak wet weather flows cause Combined Sewer Overflows (CSOs). The United States Environmental Protection Agency's (EPA's) 2004 Report to Congress on sewer overflows estimated the volume of CSO discharged nationwide at 850 billion gallons per year.(1) Despite diligent efforts by cities to mitigate the impacts of CSOs, these efforts can be hindered overall by the failing condition of the nation's wastewater infrastructure. This critical system of underground pipes and conveyances is in dire need, as evidenced by its recent D- grade assessed by the American Society of Civil Engineers.(2) As miles and miles of underground pipes age they become more likely to fail,(3) at the same time that they are taxed further due to increasing population and development. For example, at our current rate of investment, EPA has projected that sewage pollution will be as high in 2025 as it was in 1968—before the passage of the Clean Water Act—that is, when Lake Erie was declared dead and the Cuyahoga River was on fire.(4)

Add to this mix the projected impacts of global warming on water resources and shorelines. Global warming is anticipated to have adverse effects on available freshwater resources. For example, the Natural Resources Defense Council's (NRDC's) recent report, In Hot Water, projects that global warming will decrease snowpack in the American West, reduce water supplies, increase the magnitude and frequency of floods and droughts, and degrade aquatic habitat by reducing stream flows and increasing the temperature of waterways.(5) EPA reports that while data are inconclusive, some models predict that global warming will increase the frequency of Combined Sewer Overflows by up to 12 percent, as well as the volume and velocity of stormwater flows.(6) EPA also notes that the costs of adapting existing CSO mitigation plans to manage the long-term risks associated with climate change could significantly increase funding requirements, exacerbating what is known as the "infrastructure gap"—the difference between available funding and the actually needed funding.(7)

With global warming, failing infrastructure and a land development rate of twice that of population growth, our nation faces a water quality problem that is literally begging for attention, investment and innovation. Continuing to use the approaches of the past to deal with these pollution sources is likely to be both costly and largely unsuccessful. Public works managers are challenged to change traditional ways of thinking. It is time to revisit the long-embraced philosophy that the best course is to move stormwater as rapidly as possible into pipes—recognizing that in many cases this volume goes untreated into waterways or worse, causing sewage pipes to exceed capacity and overflow. Fortunately there are alternatives, and one is catching on in progressive cities and towns across the United States. It is called green infrastructure, which does not just mean "green" as in environmentally sound, but instead green as the color of the vegetation that it relies upon as its principal wastewater treatment mechanism. The term "green infrastructure" has many definitions because it is used on a variety of scales—watershed or subwatershed, neighborhood, or site. In this article it applies to natural systems or designed or engineered systems that use soil and vegetation to mimic natural processes to protect and enhance environmental quality and provide utility services.

Green infrastructure in cities, where stormwater-induced pollution is most severe, includes green roofs, trees and tree boxes, rain gardens, vegetated swales, pocket wetlands, infiltration planters and vegetated median strips—really anywhere where soil and vegetation can be worked into the urban landscape. Green infrastructure is often accompanied by other decentralized storage and infiltration approaches, including the use of permeable pavement and rain barrels and cisterns to capture and reuse rainfall for watering plants or flushing toilets. All of these have the benefit of keeping rainwater out of the combined system so that it does not cause sewage overflows, allowing it to be absorbed and cleansed by soil and vegetation, and then reused or allowed to flow back into groundwater or surface water resources.

Green infrastructure benefits include improved water quality, expanded wildlife habitat, enhanced drinking water supplies, protected open space and parks, energy savings, smog reduction, decreased flooding, improved aesthetics and higher property values. Green infrastructure often saves taxpayers money as well by not only reducing sewage and stormwater pollution, but also by minimizing the amount of water that needs to be conveyed to centralized treatment facilities, thereby making those facilities more cost-effective to operate. Use of green infrastructure approaches in addition to modernization of aging, decaying treatment plants, collection systems and distribution systems can forestall the need for even more costly approaches and investments in the future.

NRDC's 2006 report, Rooftops to Rivers, reported on the green infrastructure strategies already employed by forward-thinking communities that are stretching wastewater infrastructure investments to achieve more by focusing on multi-benefit approaches, by leveraging private as well as public investment, and by weaving green infrastructure controls into a broad range of ongoing municipal activities, such as repair and rehabilitation of roads. And both the clean waterways themselves and the green infrastructure that keeps them clean increase property values, revitalize blighted neighborhoods, enhance street life and community aesthetics, and provide free recreation.(8)

In 2007, NRDC, EPA, the Low Impact Development Center, the National Association of Clean Water Agencies, the Association of State and Interstate Water Pollution Control Administrators, and a whole host of other organizations, including the American Public Works Association, joined together to promote use of green infrastructure in stormwater and sewer overflow control programs. Since that time, EPA has compiled and developed a number of green infrastructure resources that offer information and guidance to communities nationwide.(9) EPA also has named a green infrastructure coordinator at EPA Headquarters in Washington, D.C., and in each of the ten Regions, making it even easier for cities to gain information and guidance about green infrastructure projects.(10)

Active green infrastructure programs in several U.S. cities, including Chicago, Portland and Seattle, have yielded early and significant success. Green infrastructure offers the advantage of managing rain where it falls, often preventing it from reaching the sewer system. Less water in the sewer system means less pollution discharged from CSOs or separate stormwater sewers and lower treatment costs at wastewater treatment plants. Cost savings have also been gained from either avoiding the addition of new infrastructure or diminishing the size and scope of capacity improvements.

An $8 million subsidized downspout disconnection program in Portland has saved $250 million in infrastructure improvements by diverting one billion gallons of rain annually from the combined sewer system and allowing the rain to soak into the ground. Seattle's first Street Edge Alternative (SEA) pilot project has retained 99 percent of the rain that has fallen during the five years of monitoring and prevented it from being discharged to sensitive receiving waters that are home to salmon.

The benefits of introducing green infrastructure are not confined to water quality. Green infrastructure filters airborne pollutants, helps to offset urban heat island effects, and can reduce the heating and cooling demands of buildings. Temperatures above Chicago's City Hall green roof average 10-15 degrees F lower than a nearby black tar roof, with the difference being as much as 50 degrees F in August. The associated energy savings for the building are estimated to be $3,600 annually. And one benefit of green infrastructure is often a critical factor for thriving and sustainable communities: the aesthetic benefits gained from trees and vegetation.

A further good example of green infrastructure practices is the restoration of highly urbanized areas by using existing wetlands for stormwater management, as well as creating new wetlands for the same purpose. In the Rouge River area of Michigan, the Inkster Wetlands demonstration project uses 14 acres of wetlands (approximately nine of which are constructed) adjacent to the river to naturally treat stormwater before it enters the river. Prior to the project, "hard infrastructure" discharge pipes routed stormwater past the existing wetlands and directly to the river; however, the demonstration project rerouted stormwater through the existing wetlands which were supplemented with new, constructed wetlands. The project was completed in 1997 at a cost of $465,000. The results of a subsequent five-year monitoring study evaluated the effectiveness of the project at improving the quality of the stormwater runoff and found that in addition to dampening stormwater flows, the wetlands also reduced concentrations of total suspended solids by 80 percent, total phosphorus by 70 percent, and both oxygen depleting substances (BOD) and heavy metals by 60 percent.

These cities that have shown innovation adopting green practices have also been at the forefront of the policy and institutional changes necessary to encourage new programs. Public funding has been critical to the adoption and acceptance of green infrastructure. Public financing has been used directly to install pilot projects and subsidize community programs and provide grant money for private efforts. Chicago's Department of the Environment announced that it would provide twenty $5,000 grants in 2006 for small-scale commercial and residential green roofs and received 123 applications. Policy changes have required that green infrastructure be the first option for new development and offered financial incentives for green infrastructure retrofits. Several cities have revised their stormwater regulations to place an emphasis on onsite retention and treatment and state a preference for green infrastructure approaches. Cities have also structured their utility fees to provide a fee discount when green controls are installed.

Another emerging advantage of green infrastructure is its link with the green jobs movement. Where it is being applied, green infrastructure creates jobs for architects, designers, engineers, construction workers, maintenance workers and a variety of small businesses engaged in designing and building green roofs, rain gardens, tree boxes and other types of green infrastructure.(11) Green infrastructure approaches can achieve cleaner bodies of water, a greener environment and better quality of life.

The cities that have shown innovation adopting green practices are at the forefront of the policy and institutional changes necessary to encourage new green programs. In many cities, however, green infrastructure remains a garnish, not the meal. So, what can we do to eliminate obstacles—real or perceived—to green infrastructure solutions?

First, we need to refine and make readily accessible user-friendly models to quantify effectiveness of green infrastructure solutions and its life-cycle cost, and tools for measuring economic and environmental benefits realized from the use of green infrastructure. Measurement of small-scale projects can be done with general ease. For example, to address localized flooding caused by runoff from one alley, the City of Chicago removed the asphalt from the 630-foot-long, 16-foot-wide area and replaced it with a permeable paving system. The City then measured that, instead of generating stormwater runoff, the alley will infiltrate and retain the volume of a three-inch, one-hour rain event. The permeable pavement requires little maintenance and has a life expectancy of 25 to 35 years. In other areas of the country, studies in Maryland and Illinois show that new residential developments using conservation design approaches saved $3,500 to $4,500 per lot (quarter- to half-acre lots) when compared to new developments with conventional stormwater controls. These developments were conceived and designed to reduce and manage stormwater runoff by preserving natural vegetation and landscaping, reducing overall site imperviousness and installing green stormwater controls. Cost savings for these developments resulted from less conventional stormwater infrastructure and paving and lower site preparation costs. Importantly, in addition to lowering costs, each of the sites discharges less stormwater than conventional developments. Adding to the cost savings, developments utilizing green infrastructure normally yield more lots for sale by eliminating land-consuming conventional stormwater controls, and lots in green developments generally have a higher sale price because of the premium that buyers place on vegetation and conservation development. Methods for predicting the effectiveness of large-scale or large-area green infrastructure projects prove more challenging and are still evolving, but absolutely exist today. For example, researchers at the University of California at Davis have estimated that for every 1,000 deciduous trees in California's Central Valley, stormwater runoff is reduced nearly one million gallons—a value of almost $7,000. EPA, in fact, now has gathered in a single location a variety of accepted predictive models and calculators for green infrastructure, putting these tools in the hands of city managers and planners nationwide and helping to debunk the myth that the effectiveness of green solutions cannot be measured.(12)

Second, we need to identify—and take proactive steps to create—sources of federal, state and local funding for green infrastructure projects. The billions of dollars necessary to mitigate water pollution simply and absolutely cannot be found at the local level alone. Experience shows that when public financing is on the table, entities will pick up the green infrastructure ball and run with it. As an example (and as previously mentioned), in 2006 Chicago's Department of the Environment announced that it would provide twenty $5,000 grants for small-scale commercial and residential green roofs—and received 123 applications. EPA recently cataloged a variety of federal programs where funding for green infrastructure projects may be available.(13) Meaningful funding for such projects at the state and local levels remains generally elusive, but is starting to become more common.(14)

There are a variety of other ways to create funding for green solutions. These include the creation of stormwater utilities, similar in function to water and wastewater utilities, which then allow for the assessment and collection of user fees dedicated to a stormwater management program. The dedicated funds can then be applied in part to green infrastructure solutions or they can include incentives to encourage voluntary use of green infrastructure. For example, Portland's River Rewards program provides a credit of up to 35 percent of the standard stormwater fee for properties that retain stormwater onsite. Another option is dedicating a certain portion of collected local tax revenues to a stormwater fund, thereby removing stormwater management from volatile and competitive general revenue funding at the local level. These dedicated stormwater funding sources could identify a preference for green infrastructure or establish a funding scale based upon the relative use of green management techniques. Frankly, the organizational structures and possibilities are many—but they have to be entertained and seriously considered, and existing revenue collection mechanisms may need to be abolished or changed. And while change can be hard, it is far from impossible—especially when the environment stands to benefit.

Third, the role of regulatory requirements must be explored—both in terms of how they facilitate and also hinder the use of green infrastructure. In the category of facilitation, research shows that a common driver among many cities using green infrastructure is, in fact, the need to assure compliance with regulatory requirements. For example, a catalyst for Portland, Oregon's active green infrastructure program is a need to satisfy a number of environmental regulatory requirements, including limitations on Combined Sewer Overflows, discharges into groundwaters used as drinking water supplies, and total maximum daily load (TMDL) allocations.

However, these same regulatory requirements have shown themselves to hinder opportunities for creativity and willingness on the part of municipal decision makers to actively promote and introduce green infrastructure. For example, models have shown that trees with mature canopies can absorb the first half-inch of rainfall—but trees can't be planted with mature canopies. In contrast, a pipe can capture water as soon as it is installed and online. Because our regulatory and enforcement system revolves around compliance and immediate results, and because green solutions can take time to come into their own, green infrastructure can be snubbed in favor of a tried-and-true hard infrastructure solution that can produce measurable results to regulators. For example, many cities are reluctant to use green infrastructure as part of their CSO remediation programs because enforcement officials generally prefer to see water quality benefit realized expressed in traditional terms, such as percent capture. Percent capture through green solutions is seen as unreliable—and thus, possibly less enforceable. We need to ensure that green infrastructure projects become an acceptable alternative to hard infrastructure solutions in federal, state and local permitting and enforcement contexts—even if they may take more time to become fully effective. For example, a tree can take 20 years or more to develop a full canopy that will maximize its stormwater retention and other environmental benefits, which makes regulators reluctant to include them in long-term control plans for Combined Sewer Overflows; but it can take almost as long to design and build underground storage tunnels to retain wet weather flows, and those tunnels provide no benefits until they are completed. At least trees provide some stormwater retention, shade, property enhancement, air quality benefits and aesthetics while they are growing. Regulatory and enforcement officials should focus on the big picture and ensure that the remedies they seek are the most beneficial over the long haul.

Many stormwater regulations focus on peak flow rate control and flood control, and not on retention of stormwater and recharge of groundwater resources. Revision of these regulations to require minimizing and reducing impervious surfaces, protecting existing vegetation, maintaining pre-development runoff volume and infiltration rates, and providing water quality improvements can encourage green infrastructure because it can meet these objectives. New Jersey's stormwater management standards require 300-foot riparian buffers and stipulate a preference for non-structural best management practices (BMPs). These standards also institute water quantity as well as quality regulations. The water quantity standards require no change in groundwater recharge volume following construction and that infiltration be used to maintain pre-development runoff volumes and peak flow rates. Any increase in runoff volume must be offset by a decrease in post-construction peak flow rate. Water quality standards require a reduction in stormwater nutrient loads to the "maximum extent feasible" and total suspended solids reductions of 80 percent. If the receiving water body is a high-quality water, the required total suspended solids reduction is 95 percent.

Further, existing local zoning requirements and building codes often inadvertently discourage the use of green infrastructure. Provisions requiring downspouts to be connected to the stormwater collection system prohibit disconnection programs and the use of green space for treatment of rooftop runoff. Mandatory street widths and building setbacks can unnecessarily increase imperviousness. Stormwater treatment requirements that favor centralized collection and treatment and prescribe treatment options offer little opportunity or incentive to use green infrastructure. Jurisdictions should review their applicable stormwater and wastewater ordinances and revise them to remove barriers to green infrastructure use and encourage more environmentally friendly regulations. Those looking to see what other jurisdictions have done can consult a variety of resources, such as the comprehensive, publicly available compilation of ordinances maintained by Pace University School of Law's Land Use Law Center in its Gaining Ground database. This resource contains local ordinances on all subjects, including low impact development and stormwater management, and groups them by state, EPA region, and topic.(15)

It is also critically important to recognize that some of the most significant barriers to incorporating green infrastructure into existing urban areas are the costs and challenges associated with retrofitting these systems into built-out and space-constrained urban areas. For example, green infrastructure solutions may be more appealing to developers and cities when they are part of a large investment of capital for new projects that are projected to substantially overhaul and upgrade existing infrastructure. For example, it is often less expensive to install a green roof when an existing roof needs to be replaced, and rain gardens or trees in road median strips are often installed along with other street improvements when a street is already likely to be torn up and construction crews are onsite.

Fourth, we need to increase the public's and policy makers' awareness and acceptance of green infrastructure options. Although green infrastructure is in many cases less costly than traditional methods of stormwater and sewer overflow control, it often is easier to continue the habit of investing in existing conventional controls rather than trying an alternative approach. It is incumbent on local decision makers, leaders and citizens to promote and publicize cleaner, more environmentally attractive methods of reducing the water pollution that reaches their communities. Green infrastructure presents an opportunity for community outreach and education. Downspout disconnections, rain barrels, rain gardens and green roofs may individually manage a relatively small volume of stormwater, but collectively can have a significant impact. Green infrastructure can be introduced into a community one lot or one neighborhood at a time.

A commonality among cities that have incorporated green infrastructure is a commitment from city personnel. Whether elected officials or professional staff, these city leaders have recognized the benefits of green infrastructure and have successfully communicated its value to the public. These cities have also been innovative with their regulations and environmental policies, looking for existing and alternative avenues to encourage adoption of new stormwater and CSO control strategies. These efforts are often popular because of the public's positive response to the "greenscaping" that accompanies the programs. As many local leaders have found, using green infrastructure in place of or in combination with less effective conventional methods of managing water pollution and stormwater runoff can have benefits beyond just economic cost savings and reduced pollution.

Finding an effective approach to achieve urban water quality has been elusive. However, it should be clear now that many cities are developing a track record of success in the green infrastructure arena. They are demonstrating convincingly that green infrastructure is an economically and environmentally viable approach for water management and natural resource protection in urban areas. So with that, let's do what it takes, city by city, to start enjoying the environmental and quality-of-life benefits green infrastructure delivers.

Nancy Stoner is the Director of the Clean Water Project at the Natural Resources Defense Council, an organization that uses law, science and the support of 1.2 million members to ensure a safe and healthy environment for all living things; she can be reached at (202) 289-2394 or Alexandra Dapolito Dunn is the Assistant Dean of Environmental Law Programs at Pace University
School of Law, which is nationally recognized for its environmental law program; she can be reached at (914) 422-4209 or

(1) Report to Congress, Impacts of CSOs and SSOs, August 2004, EPA 833-R-04-001 at ES-5; Report available at


(3) U.S. EPA, The Clean Water and Drinking Water Infrastructure Gap Analysis, EPA-816-R-02-020 (Sept. 2002) (projects that 47% of sewer pipes will be in poor, very poor, or life-elapsed condition by 2020, up from 10% in 1980 and 23% in 2000).

(4) U.S. EPA, The Clean Water and Drinking Water Infrastructure Gap Analysis, EPA-816-R-02-020 (Sept. 2002).

(5) In Hot Water, pp. 4-16.

(6) "A Screening Assessment of the Potential Impacts of Climate Change on Combined Sewer Overflow (CSO) Mitigation in the Great Lakes and New England Regions'' (EPA/600/R-07/033A); available at

(7) Id. at 26.

(8) NRDC, Rooftops to Rivers: Green Strategies for Controlling Stormwater and Combined Sewer Overflows (June 2006).



(11) (projects creation of 50,000 new jobs from green infrastructure initiative)




(15) See; look under "browse resources," no password needed.