As storm intensity and floods increase, urban expansion is putting U.S. infrastructure at risk. According to a 2021 American Society of Civil Engineers report, stormwater floods lead to $9 billion in damages annually.
As hurricane Katrina eloquently demonstrated, seawalls are not the solution to preventing floods. Green infrastructure is our only hope in the face of rising median temperatures and increasing rainfall.
First Street Foundation analysts have estimated that the annual cost of floods in the U.S. could reach $32 billion by 2051. The bipartisan Infrastructure bill will deliver $50 billion to the EPA to improve drinking water, wastewater, and stormwater infrastructure to prevent some of these damages. This will be the largest investment our nation has ever made in its water infrastructure.
Each dollar spent on green infrastructure reduces the risk of catastrophic floods and massive waterway pollution. Unfortunately, most of the new infrastructure bill’s funds will be used to fix existing pipes, drains, and stormwater systems.
What our country needs is a complete transformation rather than a quick fix. We need to start working with nature rather than against it.
What is Green Infrastructure?
The Clean Water Act defines green infrastructure as infrastructure that “uses plant/soil systems, permeable pavement, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters.”
We call infrastructure green when it uses vegetation to harvest and filter stormwater or when it is carbon neutral. The green buildings of the future combine these two characteristics: they produce net-zero emissions and can filter rainwater and wastewater to feed their own water systems.
Rain gardens and street median planters serve the same purpose as storm sewers, but they are much more resilient and efficient. Runoff from rainstorms is not only absorbed by plants and soil; it can also be harvested and filtered to produce drinking water.
Global warming leads to more intense storms and heavier rainfall. As storms become more persistent, aging stormwater systems are overwhelmed, resulting in massive property losses and fatalities.
Green infrastructure is not only better for the environment; it is also more cost-efficient. A New York City study evaluated a combination of gray and green infrastructure in Queens and found that using only gray infrastructure would cost twice as much. In fact, according to the assistant administrator for the EPA's Office of Water, it is wrong to think “about the green and the gray separately;” the power lies in integrating them.
Green Infrastructure Projects Across America
Green infrastructure projects operating across America include downspout disconnection, which filters and redirects water from rooftops toward cisterns and permeable soil, and rainwater harvesting, which channels rainwater for irrigation or storage in tanks. Jurisdictions that have incentivized rainwater harvesting and downspout disconnection include Portland and Tucson.
Rain gardens are another convenient green alternative to grey stormwater systems. They can be installed almost anywhere to absorb water runoff from streets, sidewalks, and rooftops. Linear rain gardens installed in long narrow spaces are known as bioswales. They filter stormwater, providing treatment and retention, and are typically placed along roadsides and in parking lots.
The most interesting rain garden projects in the U.S. include Washington State University’s plan to install 12,000 rain gardens in the Puget Sound region. The program’s proponents estimate these gardens could soak 160 million gallons of contaminated runoff.
In 2019, NYC began installing 5,000 curbside rain gardens in Brooklyn, the Bronx, and Queens. Combined with 4,000 existing ones, the new rain gardens are expected to reduce overflows into local waterways by 500 million gallons each year.
Likewise, a series of bioretention gardens installed in 10 boulevard medians in Detroit’s Aviation neighborhood in 2021 will reduce the annual burden on the city’s centralized system by 37.3 million gallons of stormwater.
Planter boxes designed to absorb runoff from sidewalks, streets, and parking lots have also been successfully installed in downtown Minneapolis, Florence, SC, and San Jose, CA.
Some of the most ambitious and promising green infrastructure projects involve permeable pavements made of pervious concrete or porous asphalt, designed to infiltrate and treat rainwater. There are several working permeable pavement projects in the Pacific Northwest, including large-scale ones in Sultan, Washington, and Pringle Creek, Salem, Oregon.
Finally, green roofs prevent pollution by retaining 95 percent of rainwater's most dangerous contaminants, reducing energy consumption, and mitigating the “urban heat island” effect. Urban tree canopies serve a similar purpose while also providing shade. Successful urban forest initiatives have been implemented in Chicago and Philadelphia. In 2021, Chicago’s Mayor announced plans to invest $46 million to plant 75,000 trees over five years.
A recent paper published in Landscape and Urban Planning analyzed the impact of green infrastructure on urban flood risk. The researchers concluded that larger investments in green infrastructure in higher-income neighborhoods put non-white and low-income populations at a higher risk of rainwater flooding.
As U.S. cities work to direct newly available infrastructure dollars to the right mix of green and gray stormwater infrastructure, they must also focus on achieving equitable flood risk management.
Learn more about this and other pressing issues in Reframing America’s Infrastructure: A Ruins to Reinassance Playbook.