Could permeable pavement reduce flooding in cities?

Total U.S. flood damage costs approached $200 billion from 1988 through 2017, according to a 2021 study in the National Academy of Sciences journal. Approximately $73 billion of those damages were due to excess precipitation over the 29-year period, the study said.

Various technologies and infrastructure strategies have been implemented to better manage stormwater in cities, but much of that infrastructure is aging. Pluvial flooding, or flooding from rainfall, is an increasing issue in urban areas that disrupts trucking routes and livelihoods around the world.

“Many contemporary cities are vulnerable to pluvial flooding, and its associated risks are projected to increase as the global climate changes, urban populations grow and existing infrastructure ages,” the 2018 study “Pluvial flood risk and opportunities for resilience” said.

Permeable pavement is a green infrastructure solution that was designed to let rainwater through to the ground below, reducing runoff and pluvial flooding while simultaneously refilling depleted aquifers. However, the pores in permeable pavements often get clogged, reducing the rate at which water can flow through.

The goal of Spokane, Washington-based company AquiPor’s co-founders Kevin Kunz and Greg Johnson was to create a more sustainable stormwater infrastructure with virtually cloggless permeable pavement, according to Kunz. AquiPor pavement has pores a fraction the size of hair follicles to prevent clogging, yet it maintains the strength and durability of conventional roads.

Permeable pavement details

The pavement has allowed more than 25 inches of rainfall per hour to flow through its 1-micron-diameter pores in tests, according to AquiPor. The extremely small pore size is what makes it unique, Kunz told FreightWaves. He noted that no matter the size of the pores, they eventually clog.

But, Kunz said, “The difference is, there has never been a sub-micron-sized filter made as cheaply and easily as this precast concrete material. That’s an important advantage because, once the material clogs, it can be easily and cost-effectively replaced.”

In an internal study, the permeable material prevented more than 80% of particulate matter and pollutants found in stormwater from getting through.

Kunz described the material as “fine sandpaper” to the touch. The goal is to reduce runoff and standing water, potentially making the permeable pavement less slippery for walkers, bikers and drivers. In an upcoming mock-up, the company plans to analyze texture, abrasion resistance, emissions and other factors in a full cradle-to-cradle analysis, spanning from production to end-of-life for the material.

Green infrastructure: Potential climate change, flooding solution in cities

Increased rainfall and flooding can damage roadways, bridges and tunnels, sometimes wiping out major freight routes. It can also reduce the life expectancy of highways and interfere with road construction, which could lead to more traffic delays for truck drivers.

That is particularly concerning in light of climate change.

“While the local impacts of climate change on annual precipitation totals remain uncertain, there is a general consensus that global climate change will result in more intense short-duration precipitation events in many regions of the world,” the 2018 study said.

Green infrastructure aims to filter and absorb stormwater where it falls, according to the Environmental Protection Agency. Reducing the distance that rainwater travels before it is absorbed mimics natural processes and saves money. Kunz said green infrastructure is proving more cost-effective than conventional stormwater management because it is much cheaper to manage stormwater on a smaller scale than it is to direct larger amounts of water to overwhelmed storm drains.

This mock-up shows standing water on the road, while the tan lane of permeable pavement allows water through it. (GIF: AquiPor)

What happens if the ground beneath permeable pavement becomes oversaturated?

“In practice, many types of [green infrastructure] rely primarily on the infiltration of stormwater to mitigate flooding and would be limited in their effectiveness when rainfall rates greatly exceed the maximum infiltration rates of their soils,” the 2018 study said.

While the AquiPor material may be able to let upwards of 25 inches of rain per hour flow through, there’s little data indicating that soil below would be able to absorb that much water at that pace, especially during heavy, prolonged rainfall.

While questions remain, green infrastructure may provide significant economic and environmental benefits.

“It’s refreshing to see that new, innovative solutions for replacing crumbling infrastructure are electing to focus on environmental upgrades alongside functionality,” said Tyler Cole, director of carbon intelligence at FreightWaves. “The hype around electrification and reducing emissions can at times overshadow other crucial areas of impact, such as efficient and safe water systems or gender equality. We need more firms like AquiPor to identify, develop and scale climate solutions.”

80-foot mock-up to provide additional data

Bricks of AquiPor’s pavement drying. (Photo: AquiPor)

AquiPor is building an 80-foot mock-up of permeable pavement at a Spilker PreCast location in Spokane, Washington. Kunz said he hopes the mock-up will be finished in the fall.

Half of the mock-up will be dedicated to demonstrations, while the other half will be tested over the coming years by the Washington Department of Ecology. The agency has a standard for treatment of stormwater quality that Kunz said is “stringent” and increasingly being recognized by states nationwide.

The mock-up is designed to provide empirical data and answer important questions about AquiPor’s permeable pavement, including whether it meets the Washington Department of Ecology’s standards.

The recycled aggregate and unique cement that make up this pavement should make the production-related emissions much lower than is the case for typically used road materials such as concrete or asphalt, Kunz said. But, he said, this will be backed by data following the mock-up.

After the mock-up and analysis of the manufacturing process are complete, Kunz said the company plans to begin educating PreCast manufacturers about how to make the permeable pavement in early 2022.

AquiPor’s goal is to build facilities within 500 miles of major cities where the material would be used for roads or sidewalks. Kunz said the cement and recycled aggregates needed for production are prevalent nationwide, and AquiPor hopes to source the materials near facilities.

“When we press go, we want to deploy this at scale,” Kunz said. “We have to identify the magnitude of the problem with climate change before we [breeze] through innovation into the market because this has to be done correctly the first time.”

Click here for more FreightWaves articles by Alyssa Sporrer.

Permeable pavement details

Green infrastructure: Potential climate change, flooding solution in cities

80-foot mock-up to provide additional data

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