According to the National Oceanic & Atmospheric Administration (NOAA), flooding causes more damage in the United States than any other severe weather related event. Flooding damages cost an average of $5 billion a year in the United States, and flooding occurs in all fifty states yearly.
Flooding in cities is frequently exacerbated by the issue that water has nowhere to go downtown. Sidewalks, roads, parking lots, concrete, brick, stone - these are all impervious sources that rainwater can't penetrate through to reach the soil below. In most United States cities, about 40% of the land area is impervious. When rainwater hits impervious surfaces, it becomes runoff and officially becomes a problem.
With the increase in frequency and strength of severe storms, the issue of what to do with all that runoff is just getting more and more complicated. So, what's the answer?
One company in the United Kingdom thinks they have a solution in their new fast-draining concrete, Topmix Permeable. Topmix Permeable can absorb up to 1,000 liters of water per minute per square meter. Check out this mesmerizing video of 4,000 liters of water disappearing into a parking lot surface to see Topmix Permeable in action.
Tarmac, the company that makes Topmix Permeable, was able to accomplish permeable pavement by simply removing the fine crushed stone and sand that typically goes into road paving material. The resulting material is porous enough to let water flow through it. Topmix Permeable is typically layered on top of an aggregate sub-base of crushed stone, which typically sits directly on top of the soil. These layers provide the added benefit of filtering contaminants, such as motor oil, out of the rainwater as it filters down to the water table below.
It's hard to find any perfect product, and like others before it, Topmix Permeable has its faults. Heavy use of areas paved with Topmix Permeable will degrade the surface area faster than normal, but at this point, it is still the strongest and most resilient permeable paving product out there. Part of Tarmac's secret is the high void space, or amount of air space, in their product. Typically, permeable pavement has a void space of about 20%, however Topmix Permeable's void space is around 35%. This allows water to run through the mix and reach the water table below.
There are so many benefits to permeable pavement, from reducing the risks of hydroplaning and flash flooding to reducing the urban heat island effect and pollution in storm water runoff. So, the next time you hear that your town needs to repave some roads be sure to let your officials know about the benefits of permeable pavement.