In the United States, stormwater and water runoff significantly threaten water quality.
As more areas are urbanized and developed, the landscape is increasingly covered with impervious materials, which prevents water from soaking into the ground. This change boosts the volume and speed of stormwater runoff that rushes into our streams, lakes, and rivers.
Unfortunately, this runoff carries sediments, waste, toxic chemicals, pollutants such as vehicles’ oil, pesticides and nutrients from gardens and farms, viruses and bacteria from pests, failing septic systems, and road salts. There’s also the issue of thermal pollution from these hard surfaces.
The impact of these pollutants and toxic substances can severely damage the environment, wildlife, and their natural habitats.
Green infrastructure
The benefit of green infrastructure is already felt in many communities across the United States. The Environmental Protection Agency, states, and municipalities have made significant progress in protecting their waters through the Clean Water Act, and implementing green infrastructure is a way to comply with the CWA.
Historically, the U.S. has used gray infrastructure, such as gutters, pipes, and tunnels, to quickly remove stormwater runoff, which is then directed to wastewater treatment plants or local water bodies.
Still, this approach prevents treating or managing stormwater at its source. Many of the country’s stormwater and sewer systems are aging, and population and urbanization growth are pushing them beyond their capacity. The EPA estimates that the country needs $115 billion to upgrade its stormwater system. This is where green infrastructure practices can help.
Low-impact development (LID) practices, also called green infrastructure, are designed to infiltrate, evaporate, filter, capture, and facilitate the beneficial use of stormwater. Common LID practices include green roofs, rain gardens, sidewalk planters, curb extensions, street trees, permeable pavements, and cisterns.
The EPA actively endorses the widespread adoption of green infrastructure in LIDs in municipalities across the United States, allowing them to enjoy the many environmental, social, and economic benefits of green infrastructure.
According to the Agency, they partner with various levels of government, agencies, non-profits, and stakeholders to overcome barriers to advancing green infrastructure. The EPA has also identified existing policies, legislation, and funding mechanisms to support integrating and implementing LIDs nationally and locally.
EPA presents case studies of Green Infrastructure across many states, its benefits in reducing runoff, flooding risks, and pollution, and the savings it provides to the municipality. These are some examples:
Michigan Avenue Bioretention Planter Boxes
In 2006, the Lansing, Michigan community installed planter boxes along four blocks of Michigan Avenue, a busy five-lane street. The planters can treat the runoff from 1 to 4 inches of rain falling on the adjacent street and sidewalk.
Flow meters were used to monitor the system. The results show that the model treated around 90% of the annual stormwater volume; it absorbed 16% and discharged 84% of the total volume of stormwater received, delaying the excess discharge into the local water body. It also lowered the peak flow rate of the water released through the underdrain by 87%, reducing the overall impact of the stormwater runoff.
Sterncrest Drive Bioswale and Rain Gardens, Cuyahoga County, Ohio
In 2007, an EPA grant allowed the installation of nine rain gardens designed to handle 0.75-inch rain falling on the adjacent roadway and replacing 1,400 feet of roadside ditch with a grassed bioswale. The U.S. Geological Survey monitored the effect of these on stormwater runoff on-site from 2008 to 2010.
A 2-foot-square slightly elevated grate in the center of each rain garden was also installed to allow excess stormwater runoff to overflow into the storm sewer. The result shows that these rain gardens and bioswale can absorb several rainfall events exceeding 0.75-inch which means they performed better than expected. In the three years of monitoring, the system overflowed only 19 times during the 47 rainfall events over 0.75 inches and fell within a 96-hour (4-day) span.
Bioretention cells in sloped areas: 110th Street Cascade, Seattle, Washington
Seattle Public Utilities installed 12 cascading bioretention cells in 2002 alongside a sloped residential road to manage the runoff from a 2-acre drainage area. The goal is to reduce the volume of stormwater, encourage infiltration, slow the flow rate, and trap sediment and pollutants.
The design used concrete walls, vegetation, soils, and rocks to slow down, infiltrate and filter the stormwater. These G.I.s were monitored for their effectiveness between 2003 and 2006, and the result shows that these bioretention cells absorbed 186 of the 235 precipitation events (79%) recorded. They were able to absorb the runoff and pollution. Storms with up to 1-inch rainfall depths were thoroughly infiltrated in dry conditions. The bioretention cells have retained 48% to 74% of the incoming water for all stormwater runoff events.
Barrier Busters fact sheets
The EPA has released a series of Barrier Busters fact sheets, concise two-page documents that deliver straightforward and accessible insights into green infrastructure and Low-Impact Development (LID) practices.
These fact sheets explore various important topics, including the benefits of implementing these methods, their design and aesthetic considerations, maintenance requirements, and how they can be applied across different soil types and landscapes, whether flat or sloping. They cover large-scale applications, such as parking lots, road islands, street berms, and smaller projects, like individual front yards and backyard gardens. Furthermore, the sheets offer guidance on how communities can identify local regulations that may impede these practices and work towards revising them for smoother implementation.
Green infrastructure’s proven effectiveness in reducing runoff and preventing pollutants from entering the freshwater source, as well as its other social, recreational, and economic benefits and low cost of application, makes it an ideal solution for addressing the challenges posed by aging infrastructure, climate change, and the need to protect water quality.
Infrastructure management perspective
Green infrastructure forms part of the network for managing stormwater and associated runoff. Like all other infrastructure, it must be recorded, operated, maintained, and worked on throughout its lifecycle.
Sources:
About Green Infrastructure. (2024, August 29). EPA. Retrieved from https://www.epa.gov/green-infrastructure/about-green-infrastructure
Nonpoint Source: Urban Areas. (2023, November 30). EPA. Retrieved from https://www.epa.gov/nps/nonpoint-source-urban-areas
Green Infrastructure Strategic Agenda 2013. EPA. Retrieved from https://www.epa.gov/sites/default/files/2015-10/documents/2013_gi_final_agenda_101713_0.pdf
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