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30th July 2022
Green Infrastructure: How to Manage Water in a Sustainable Way

By relying on plants, soil, and natural systems to manage rainfall runoff, green infrastructure tackles urban water woes and boosts climate resilience. Here’s how.

July 25, 2022 Melissa Denchak

From highways to bridges to airports, America’s infrastructure is in dire need of a face-lift. The critical systems we rely on nationwide endure chronic overuse and underinvestment, including our stormwater management systems. An estimated 10 trillion gallons of untreated stormwater runoff, containing everything from raw sewage to trash to toxins, enters U.S. waterways from city sewer systems every year, polluting the environment and drinking water supplies. In many urban and suburban areas, this runoff causes significant flooding as well. Not surprisingly, in 2021, the American Society of Civil Engineers bestowed a lowly D letter grade on U.S. stormwater and sewage systems. Meanwhile, the U.S. Environmental Protection Agency (EPA) estimates that upgrading our stormwater and other public wastewater systems will require at least $150 billion in investments over the next two decades.

The country’s urgent infrastructure needs also present a major opportunity. As an alternative to traditional water management systems, green infrastructure offers a cost-effective solution to many of our water woes, including how to handle flooding and stormwater pollution. Here’s a look at what green infrastructure is, what it does, and why we should invest so much green paper in it.

What Is Green Infrastructure?

Green infrastructure encompasses a variety of water management practices, such as vegetated rooftops, roadside plantings, absorbent gardens, and other measures that capture, filter, and reduce stormwater. In doing so, it cuts down on the amount of flooding and reduces the polluted runoff that reaches sewers, streams, rivers, lakes, and oceans. Green infrastructure captures the rain where it falls. It mimics natural hydrological processes and uses natural elements such as soil and plants to turn rainfall into a resource instead of a waste. It also increases the quality and quantity of local water supplies and provides myriad other environmental, economic, and health benefits—often in nature-starved urban areas.

What is gray infrastructure?

Gray infrastructure is the more traditional (and typically more expensive) water management systems that green infrastructure complements and can at times replace. It relies on hard infrastructure—such as storm drains, concrete, and pipes—to collect and channel stormwater (sometimes treated, oftentimes not) into waterways. It does not provide the same range of benefits as green infrastructure since it neither reduces the amount of stormwater that reaches waterways nor, for the most part, improves the quality of that runoff. Gray infrastructure also does not provide the same community benefits mentioned above.

Why Is Green Infrastructure Important?

Green infrastructure reins in stormwater runoff, which the EPA describes as “one of the fastest-growing sources of pollution” in the United States. Here’s what happens.

Stormwater Runoff

Runoff, the product of rainstorms or snowstorms, flows over the ground and into drains, sewers, and waterways. The more permeable (or absorbent) the surface, the less runoff there will be. Porous natural landscapes, such as meadows and forests, will readily soak up most of the rain or snowmelt they receive. This is then gradually released into the groundwater, nearby water bodies, and the atmosphere. In contrast, streets, parking lots, rooftops, and other hard, impervious (nonabsorbent) surfaces essentially repel stormwater, preventing it from soaking into the land and forcing it to flow whichever way gravity takes it. The average city block can generate more than five times as much runoff as a forested area of equal size.

Stormwater Pollution

When rainfall hits an impervious surface, it meets whatever pollutants reside on that surface. That could include road salt, sediment, or trash; oil, heavy metals, or toxic chemicals from cars and trucks; pesticides or fertilizers from lawns and gardens; and even viruses or bacteria from animal waste. These contaminants turn pristine rainfall into dirty runoff, an estimated 10 trillion gallons of which enter U.S. waters from cities, untreated, each year. How exactly does that happen? Point the blame at our stormwater management systems and impervious surfaces.

Water that drains from bathrooms, kitchens, and other sources with plumbing gets channeled via sewers to sewage treatment plants before it’s discharged into public waterways. However, most storm drains funnel rainfall directly into waterways without treatment, bringing with it whatever it carries in a raw state, including trash, toxins, pathogens, excess sediment and nutrients, and thermal pollution (hot water that causes a sudden upswing in ambient water temperatures). The following are just some of the ways in which stormwater pollution impacts rivers, streams, lakes, oceans, and all of us.

Impaired water quality

According to the EPA, urban stormwater is the "leading remaining cause of water quality problems" in U.S. rivers and streams, as well as a good chunk of our lakes and coastal waters. Impaired waters wreak havoc on ecosystems and vegetation, imperil drinking water supplies and public health, and ruin recreational areas.


Just an inch of rainfall on one mile of a narrow, two-lane road can produce 55,000 gallons of stormwater runoff. When funneled through a storm drain, the sudden entry of so much runoff can damage and erode delicate banks of waterways, resulting in land and habitat loss and changing a waterway’s basic morphology.

Sewage overflows

Instead of separate storm drains, nearly 860 municipalities across the United States use combined sewer systems, which dump stormwater runoff into the same pipes that are used for domestic sewage and industrial wastewater. Unfortunately, these sewer systems are designed to overflow when stormwater exceeds their capacity. A big storm, in other words, can cause an excess mess of both runoff and raw sewage to be released into waterways. In New York City alone, about 27 billion gallons of this noxious mixture pour from nearly 460 outfalls every year.

Economic toll

Stormwater runoff contributes to the frequency and severity of small-scale urban floods. Although localized flood events are not as damaging as catastrophic ones, they can create a greater overall economic burden because of their repetitive nature. In the United States, more than 30,000 properties in 2017 had been flooded an average of five times each (with some homes getting inundated 30-plus times). And those figures will likely rise as climate change takes its toll, which is why it’s critical that FEMA update its standards for the National Flood Insurance Program. The EPA estimates that annual flood damages, due in part to runoff, will increase by $750 million by century’s end. And stormwater comes with other costs too. When water quality deteriorates, fish and shellfish populations—along with the economies that rely on them—decline as well. There can also be a public health cost. One study estimated that in Los Angeles alone, stormwater runoff causes $14 to $35 million in health costs annually just from people who contract gastrointestinal illnesses after swimming in contaminated oceans.

Health toll

Stormwater runoff impacts the water we drink, the seafood we eat, and the recreational areas we visit. It introduces disease-causing pathogens into water supply sources that treatment facilities can’t always filter out. And it can contaminate fish and shellfish, which in turn can sicken us. Rainfall runoff also inundates beach water with bacteria at levels that violate public health standards and sicken people, causing rashes, hepatitis, and gastrointestinal illnesses. As climate change creates more frequent, extreme weather events, our exposure to stormwater runoff pollution will increase.

Stormwater Management

A key part of managing the pollution from stormwater runoff is prevention. Green infrastructure keeps waterways clean and healthy in two primary ways:

Water retention

Green infrastructure prevents runoff by capturing rain where it falls, allowing it to filter into the earth (where it can replenish groundwater supplies), return to the atmosphere through evapotranspiration (when water evaporates directly from the land or plants), or be reused for another purpose, such as landscaping.

Water quality

Green infrastructure improves water quality by decreasing the amount of stormwater that reaches waterways and by removing contaminants from the water that does. Soil and plants help capture and remove pollutants from stormwater in a variety of ways, including adsorption (when pollutants stick to soil or plants), filtration (when particulate matter gets trapped), plant uptake (when vegetation absorbs nutrients from the ground), and the decomposition of organic matter. These processes break down or capture many of the common pollutants found in runoff, from heavy metals to oil to bacteria.

What Are Other Benefits of Green Infrastructure?
In addition to influencing the quantity and quality of runoff that reaches waterways, green infrastructure provides the following benefits.

Reduced flooding

Heavy rains have gotten more frequent—and intense—in the United States over the past 50 years, with climate change making matters worse and increasing the risk of flooding and sewer system overflows. Indeed, the average size of a 100-year floodplain is likely to increase 45 percent by century’s end, according to the EPA. Another growing problem is urban flooding: Caused simply by too much rain on impervious surfaces (not by storm surges or overflowing bodies of water), urban floods can destroy neighborhoods. They particularly affect low-income neighborhoods and communities of color and can leave behind health problems like asthma and illness caused by mold. Green infrastructure reduces flood risks and bolsters the climate resiliency of communities by capturing rain where it falls and keeping it out of sewers and waterways.

Increased water supply

More than half of the rain that falls in urban areas—which are covered mostly by impervious surfaces—ends up as runoff. Green infrastructure practices reduce runoff by capturing stormwater and allowing it to recharge groundwater supplies or be harvested for purposes like landscaping and toilet flushing. That reduces demand on municipal water supplies (even more important because of decreased rainfall, reduced snowpack, and earlier snowmelt brought on by drought and hotter temperatures that can come with climate change). Green infrastructure promotes rainfall conservation through the use of capture methods and infiltration techniques (for instance, bioswales, discussed below, absorb runoff that can recharge aquifers). As much as 75 percent of the rainfall that lands on a rooftop can be captured and used for other purposes. A study in Wisconsin estimated that green infrastructure could capture or reallocate up to four billion gallons of stormwater; and in California, it could save up to 4.5 trillion gallons.

....Continued in Part 2