To decrease flooding and sewer overflows in three southeastern neighborhoods in Atlanta, officials in the city’s Department of Watershed Management opted for a less conventional, but green, solution: Permeable pavement made from interlocking concrete pavers.

By retrofitting more than 4 miles of paved streets with permeable pavers instead of concrete or asphalt, the DWM dramatically reduced flooding from stormwater runoff and overflows from combined sewers during heavy rainstorms, says Mikita Browning, the agency’s commissioner.

“To our knowledge, it’s the largest use of permeable pavement to retrofit existing roads,” Browning says of the $15.8 million project.

Roughly 570,000 square feet of Aqualine permeable pavers, made by Belgard Commercial Hardscapes, were installed in the Summerhill, Peoplestown and Mechanicsville neighborhoods. These neighborhoods are located near Center Parc Credit Union Stadium (formerly known as Turner Field).

Work started in January 2015 and finished in September 2016, Browning says. (The color of the bricks, appropriately enough, is called Georgia blend.)

“Our engineering analysis has shown that the permeable pavers provide additional capacity overall within our combined sewer system,” she explains. “They definitely have reduced the flooding from heavy rains, so we think they’ve been very beneficial in remedying the flooding.”

In addition, the permeable-pavement solution was substantially less expensive and much less disruptive than tearing up streets and separating the combined sewer systems. About 10% of Atlanta’s sewers remain combined, Browning says.

Flow-through filtering

Permeable pavers use built-in spacers that create slightly wider-than-normal joints between pavers. Those joints are filled with small aggregate through which stormwater flows. The stormwater then passes through layers of crushed stone below the pavers. These layers act as a natural filtration system to remove pollutants such as oil.

In the Atlanta project, the average depth of the crushed-stone layers was 44 inches.

The system also relies on a geomembrane that lies under the layers of aggregate, providing yet another layer to trap pollutants. The bottom line: Runoff that normally flows directly to curbs and into sewers instead slowly seeps in between the pavers, where it’s contained and filtered naturally, reducing entry into sewer systems.

Installation required four basic steps: Asphalt removal, excavation to a specific depth, filling the excavation with aggregate and laying the pavers, which was done by a machine in 12-square-foot sections. The L-shaped bricks allowed for optimal interlocking to withstand the weight of vehicular traffic.

In addition, an impermeable liner was installed on the sides of the excavation. Impermeable-liner check dams also were installed to break up the subsurface flows below the pavers on streets that had a significant slope, she says.

“The contractor was able to install about 5,000 square feet of pavers per day,” Browning says. “Installation went pretty quickly.”

Installation, however, was not free of complications. Project contractors encountered issues with subsurface utility lines and service connections while preparing the subgrade for installation, which contributed significantly to the time it took to finish the project.

The project also included installation of 32 stormwater planters, plus a 6-million-gallon 

concrete vault in the Center Parc Credit Union Stadium, all of which work in concert with the pavers to reduce flooding. The vault stores peak flows during heavy rains, then slowly releases it back into the combined sewer system.

Floods spurred action

The permeable-pavement project was spurred by severe flooding in 2012 that sent storm runoff and raw sewage into the yards and homes of many residents in the three neighborhoods. That prompted city officials — already contending with consent decrees from the Environmental Protection Agency that mandated reductions in sewer overflows — to look at stormwater runoff mitigation strategies.

After performing topography and hydraulic studies and analysis, officials began considering their options. They opted for a more sustainable and holistic — and less expensive — approach.

So far, DWM officials are pleased with the results.

“They’ve worked great,” Browning says. “But a maintenance program is key. Pavers are no different than roads. You have to be sure you establish a preventive-maintenance schedule.”

When asked what advice she would give other municipalities considering the use of permeable pavement, Browning says it’s “imperative” for agencies to collaborate and locate subsurface utility lines. “That helps ease the construction process,” she says.

Browning also recommends installing permeable pavers upstream from the flooding areas.

More pavers possible

Browning says strategic use of permeable pavement in other areas of Atlanta is a possibility. “We still have quite a bit of work to do as it relates to the consent-decree program.”

The key takeaway, Browning says, is that utilities shouldn’t be afraid to consider less traditional and more environmentally friendly techniques for controlling stormwater runoff.

“I would say every city is different, but here in Atlanta, we try to think outside of the box and be innovative by using sustainable solutions to address environmental issues,” she notes. “You need to keep in mind that everything is site specific … as well as understand clearly the nature of the issue, then look at a menu of solutions.

“Here in Atlanta, we try to balance ‘gray’ solutions with ‘green’ solutions,” she continues. “Sometimes a gray structural approach is more beneficial and sometimes a green approach is more beneficial. We try to strike a balance between those two practices.”