Cooperative Extension Fact Sheet FS1197 | December 2012
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.
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.
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.
A green roof is a roof covered in plants that allows for stormwater management (see picture 5). 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 pictures 6a & 6b). The container can range in size from a rain barrel (picture 6a), typically 55 or 90 gallons, to a cistern (picture 6b) 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 picture 7). 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.
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