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A Parking Lot That Drinks Stormwater

Topmix Permeable concrete soaks up 4,000 liters in 60 seconds.

Permeable pavement is one of those super-wonky infrastructure items—incredibly important but not always easy to care about. Thanks to the mesmerizing video above, however, a new and improved variety of concrete developed in the U.K. called Topmix Permeable has been turning heads. The video shows a parking lot paved with Topmix absorbing 4,000 liters of water in a minute, and it’s kind of magical to watch it disappear.

This new concrete, from Lafarge Tarmac, could potentially be a very useful tool in combating urban flash flooding from sudden, heavy storms—the type that are likely to become increasingly common because of climate change. In its promotional materials, the company uses the example of the 2007 floods that devastated Great Britain, costing the economy some $4.8 billion. Of the 57,000 homes affected by the floods, two-thirds were damaged not by rivers that overflowed but by stormwater runoff.

In the U.S., stormwater routinely overwhelms antiquated wastewater systems, causing untreated sewage to be dumped into local waterways and befouling public beaches. Storm runoff is also a significant source of pollution for rivers, streams, and reservoirs around the globe. Topmix pavement filters pollutants such as motor oil residue, even as it allows water to drain into the ground below.

There are some caveats to the technology, which works the way it does because there are empty spaces between particles that allow water to flow through. Topmix concrete, which is applied over a base layer of gravel that further filters water, is less able to handle heavy vehicle loads and intense traffic than conventional paving materials. So while it’s appropriate for driveways, many parking lots, quiet residential streets, bike paths, and the like, it isn’t going to be right for highways and heavily traveled streets.

Also its ability to absorb water can be compromised by dirt and other particulate waste, such as sawdust or silt. Damage from freezing water is a potential concern with permeable pavement, although Lafarge Tarmac says its product has “excellent freeze-thaw resistance.”

Still, as more and more of the world gets paved over, the need to reduce the amount of impermeable surface we create, however we can, becomes more urgent. Parking lots that soak up rainwater like sponges are part of the solution. And pretty fun to watch in action.

About the Author

  • Sarah Goodyear
    Sarah Goodyear is a Brooklyn-based contributing writer to CityLab. She's written about cities for a variety of publications, including Grist and Streetsblog.