Stormwater runoff occurs when rain or snowmelt flows over hard surfaces such as roads, driveways, and parking lots, instead of soaking into the ground. Stormwater runoff collects pollutants such as heavy metals, nutrients, sediment, and pathogens as it flows to the storm sewer system and is discharged to local waterways without treatment. Historically, municipalities have managed their stormwater utilizing "gray" infrastructure practices made up of gutters, basins, and pipes that transport stormwater quickly to local streams, rivers, and lakes. Many municipalities struggle to maintain this aging stormwater infrastructure due to lack of funding. The result is frequent flooding and nonpoint source pollution degrading local watersheds.
Additionally, in many older communities, stormwater and raw sewage from homes and businesses flow through the same pipes to wastewater treatment plants. During heavy rain events, when the treatment plant reaches capacity, both untreated stormwater and raw sewage are discharged directly to local streams and rivers through combined sewer overflows (CSOs). There are over 200 CSOs in New Jersey, many in underserved, low income communities. These CSOs degrade water quality and threaten human health by discharging pathogens, toxic pollutants, and excess nutrients directly to our waterways. Swimming or fishing in these waters can cause waterborne infections and diseases. CSOs also cause beach and shellfish bed closures, contaminate drinking water supplies, and harm aquatic life. Separating combined sewer systems is an expensive process that disrupts daily life within communities, as pipes are slowly separated piece by piece.
What Is Green Infrastructure?
Green infrastructure is often defined based on the scale that is being discussed. At its broadest, green infrastructure refers to an "interconnected network of green space that conserves natural systems and provides assorted benefits to human populations" (McMahon and Benedict, 2006). At the local scale, green infrastructure is an approach to managing stormwater by infiltrating it in the ground where it is generated using vegetation or porous surfaces, or by capturing it for later reuse. Green infrastructure is often used interchangeably with the term "low impact development", but there are nuanced differences between the two. Low impact development (LID) is an approach to land management that aspires to restore or maintain pre-development hydrological conditions. Green infrastructure refers to the techniques used to implement low impact development with regard to stormwater. This fact sheet will focus on green infrastructure practices that can be installed at the local scale to effectively manage stormwater.
What Are the Benefits of Green Infrastructure?
There are many benefits of green infrastructure, and they can generally be categorized into three major objectives: improved stormwater management, reduced costs, and enhanced individual and community well-being.
Green infrastructure practices can improve stormwater management by:
- Reducing stormwater volume. Runoff is captured or absorbed by the green infrastructure practice thereby reducing the flow of stormwater to the storm sewer, reducing the occurrence of CSOs where they exist, and reducing flooding in local waterways.
- Reducing impervious cover. Surfaces that allow water to penetrate are "pervious" or "permeable" while those that do not are "impervious". Examples of impervious cover are roads, driveways, and parking lots. Some green infrastructure techniques replace impervious cover with permeable surfaces, which leads to reduced stormwater runoff when it rains.
- Decreasing and delaying peak discharge. Peak discharge is the highest rate of flow in a stream, which is influenced by the land cover in the surrounding watershed. In areas with high impervious cover, in addition to decreasing runoff to streams, green infrastructure practices capture and absorb stormwater volume, slowly infiltrating water into the ground, which attenuates peak volumes thereby reducing the burden on the sewer system.
- Preventing pollution. Many green infrastructure practices filter or remove stormwater pollutants such as heavy metals, nutrients, sediment, and pathogens, which leads to improved water quality. Additionally, green infrastructure often prevents pollution-carrying runoff from reaching the local waterway by absorbing and treating stormwater near its source.
- Recharging groundwater. Green infrastructure techniques that absorb runoff allow water to penetrate into the soil, which replenishes the groundwater supply. Groundwater provides base flow to local rivers and streams as well as provides the drinking water supply to many New Jersey municipalities.
Green infrastructure practices can reduce costs by:
- Reducing energy needs. Green infrastructure practices that utilize vegetation insulate surfaces in cooler months, provide evaporative cooling in the summer months, and provide shade while reducing wind speeds. These benefits lead to reduced heating and/or cooling costs. Additionally, rainwater harvesting provides a local source of water for free as opposed to potable water which requires an energy-intensive treatment and transportation process.
- Reducing potable water demand. Many homeowners use drinking water to irrigate their lawns, even though plants do not require treated water to thrive. Rainwater harvesting can reduce potable water usage, leading to lower water bills and less demand on the water supply. Additionally, replacing turf with a bioretention system such as a rain garden or vegetated swale reduces the need for irrigation once plants are established, leading to lower water usage.
- Reducing maintenance costs. Many green infrastructure practices are open systems, allowing for easy access during maintenance. Traditional stormwater management systems are closed and require machinery to access the pipes for maintenance. Permeable pavement installations do not have pothole issues like conventional pavement because the water moves through the surface without freezing. Permeable pavement systems also require less salt in the winter because of the reduced occurrence of black ice on the surface. The maintenance of many green infrastructure practices can be done by hand and does not require expensive machinery to keep them operational.
Green infrastructure practices can improve individual and community well-being by:
- Improving human health. Green infrastructure practices can reduce the potential for human exposure to raw sewage through decreased incidence of flooding and CSOs. With green infrastructure homeowners are less likely to have stormwater and raw sewage flooding their basements. CSOs may be triggered less often which results in reduced exposure to waterborne pathogens and toxic chemicals. With the reduction in CSOs, water quality is also improved, which could make those waterways safe for fishing and swimming.
- Improving neighborhood aesthetics. Many green infrastructure practices utilize flowers, shrubs, and other plants to improve runoff absorption and to reduce stormwater pollution. These plants complement the existing landscaping and enhance the beauty of the surrounding environment.
- Cooling cities and improving air quality. Asphalt absorbs heat throughout the day and releases it at night, keeping city air at elevated temperatures with no opportunity for cooling. Green infrastructure practices allow for greater air movement, reflection of heat, and provide shading that can cool urban environments. Air quality is improved by green infrastructure because lower temperatures can lead to reduced smog formation, while plants used in these practices absorb air pollutants and reduce carbon dioxide levels.
- Increased recreation opportunities and property values. People are more likely to participate in outdoor activities when vegetation has been added to a neighborhood (Stratus, 2009) and research has shown that property values increase when trees and other vegetation are present in urban areas (Shultz and Schmitz, 2008).
What Are the Types of Green Infrastructure?
- Bioretention cells, or rain gardens, are shallow landscaped depressions that utilize soil and both woody and herbaceous plants to remove pollutants and infiltrate stormwater runoff (USEPA, 1999). Bioretention cells (see Figure 1) consist of different zones that perform specific functions for treating and infiltrating stormwater. Ideal for various locations from residential properties to parking lot islands, bioretention cells can even be installed in areas with high clay content by amending the soil with sand and compost and installing an under drain. Within 24 hours of a rain event, a properly designed bioretention cell should be fully drained and no standing water should be seen. Avoid locations with high water tables or steep slopes.
- Similar to rain gardens, planter or tree boxes utilize soil, gravel, and plants to infiltrate and filter stormwater runoff from impervious surfaces (see Figure 2). Planter boxes are typically smaller than rain gardens and are used in urban communities such as along sidewalks, roadways, and within parking lots. They are typically rectangular with concrete sides and an inlet that allows stormwater to enter the planter box.
- Vegetated swales are shallow channels that convey, slow down, and infiltrate stormwater runoff (see Figure 3). They also help to trap pollutants such as particulates and fine metals. Swales are best placed in residential, industrial and commercial areas, with small drainage areas that will generate low volumes of runoff. Swales are best used in combination with other green infrastructure practices. They can be used to replace curbs and gutters. Swales are not practical in areas with large drainage areas. Municipalities will often restrict the use of swales because of concerns about erosion during large flow events and the potential for breeding mosquitoes.
- Permeable pavement is a stormwater drainage system that allows rainwater and runoff to move through the pavement's surface to a storage layer below, with water eventually seeping into underlying soil (see Figures 4 and 5). Types of permeable pavement include pervious concrete, porous asphalt, interlocking concrete pavers, and grid pavers. These pavement systems are ideal for parking lots, driveways, alleys, sidewalks, and playgrounds. Permeable pavement can be used on all soil types including clay and have no freeze-thaw issues. Maintenance involves using a regenerative air vacuum instead of a street sweeper.
A green roof is a roof covered in plants that allows for stormwater management (see Figure 6). Green roofs normally consist of an insulation layer, a waterproof membrane, a growing media layer, and vegetation (Oberndorfer, 2007). Adding a green roof can lessen the negative effects of buildings on the environment and can reduce the energy use of the building itself. Energy use decreases because vegetation and planting media intercept and dissipate solar radiation (Del Barrio, 1998). Green roofs also reduce stormwater runoff by retaining precipitation and reducing runoff to the storm drain system. They are meant to be low maintenance and more functional then a roof garden which would have more extensive design and larger plants.
Green roofs are heavier than normal roofs due to the storage of water, the growing media, and the plants. The integrity of the building must be studied prior to installing a green roof on an existing structure. Many green roofs are installed with new construction to avoid this constraint.
Rainwater harvesting involves collecting runoff from an impervious surface and storing it in a container or basin for later use (see Figures 7a & 7b). The container can range in size from a rain barrel (Figure 7a), typically 55 or 90 gallons, to a cistern (Figure 7b) which can hold hundreds or thousands of gallons of water. Harvested rainwater can supply water for various uses including irrigation, toilet flushing, clothes laundering, car washing, and fire fighting. Currently, harvested rainwater cannot be used as a drinking water supply in New Jersey. Rainwater harvesting helps reduce dependence on the drinking water supply for non-consumptive uses and reduces stormwater runoff.
Downspout disconnection is a technique for reducing stormwater runoff from roof surfaces by cutting and/or redirecting the downspout to a pervious area such as a lawn, garden, or porous walkway or driveway. The downspouts can also be re-routed to a cistern or rain barrel. This practice often can be implemented easily and inexpensively with basic household tools (hack saw or tin snips). Downspouts should be extended approximately 6 feet from a home foundation where there is a basement, and approximately 2 feet when there is a crawl space. Caution should be exercised in neighborhoods with small lots sizes to avoid redirecting roof runoff onto a neighbor's property.
The addition of trees to a landscape is one of the simplest green infrastructure techniques (see Figure 8). Tree canopy can reduce stormwater runoff by intercepting rainfall, as well as by improving stormwater infiltration in soils. Shade trees can lead to improved air quality and reduced energy usage due to their cooling capabilities. The presence of trees in urban areas has also been linked to improved human health, reduced crime risk, and an increased feeling of community at the neighborhood level (USDA Forest Service, 1994, Branas et al., 2011). Many New Jersey municipalities have shade tree commissions that can provide resources related to tree planting in local communities.
Green infrastructure is an approach to stormwater management that is becoming widespread throughout New Jersey and across the nation. Multiple resources exist to guide communities in the implementation of these practices. In addition to the resources listed below, please contact your local Cooperative Extension office for assistance in planning green infrastructure projects.
Potential state and federal funding for green infrastructure:
- The New Jersey Environmental Infrastructure Financing Program (low interest loans)
- New Jersey Statewide Nonpoint Source Pollution Program Grants (Section 319h Program)
- Department of Transportation Enhancement Activities
- Environmental Protection Agency's Targeted Watershed Grants Program
- An Introduction To Permeable Pavement FS1177
- Rooftop Rainwater Harvesting For Plant Irrigation I: Design Concepts and Water Quantity FS1162
- Rooftop Rainwater Harvesting for Plant Irrigation II: Water Quality and Horticultural Considerations FS1165
- Rain Barrels Part I: How to Build a Rain Barrel Bulletin E329
- Rain Barrel Part II: Installation and Use FS1118
- Rain Gardens FS513
- US EPA Green Infrastructure Website
- Philadelphia Combined Sewer Overflow Long Term Control Plan Update Supplemental Documentation Volume 2: Triple Bottom Line Analysis (PDF)
- Green Infrastructure: Converting Dry Detention Basins to Natural Ecosystems FS1195
- Benedict, M. A., & McMahon, E. T. (2006). Green Infrastructure: Linking Landscapes and Communitities. Island Press.
- Del Barrio, E. P. (1998). Analysis of the green roofs cooling potential in buildings. Energy and Buildings, 27 (2), 179-193.
- Oberndorfer, E., Lundholm, J., Bass, B., Coffman, R. R., Doshi, H., Dunnett, N., et al. (2007). Green roofs as urban ecosystems: Ecological Structures, functions, and services. BioScience, 57 (10), 823-833.
- United States Environmental Protection Agency (1999). Storm Water Technology Fact Sheet Bioretention. Office of Water. Washington, D.C.: US Environmental Protection Agency.
- United States Environmental Protection Agency (1999). Storm Water Technology Fact Sheet Vegetated Swales. Office of Water. Washington, D.C.: US Environmental Protection Agency.
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