As cities across the world grow, they give rise to more concrete, paved parking lots and miles of asphalt roads. During a large rain event in urban areas, these impervious surfaces cause runoff, which empties directly into drain systems that struggle to perform as infrastructure demand increases. In Atlanta, heavy rains repeatedly caused flooding problems in the neighborhoods of Summerhill, Peoplestown and Mechanicsville—areas located at a natural drainage point of a 1,500-acre watershed adjacent to the huge parking lots at Turner Field and directly centered where Interstates 20, 75 and 85 convene. The shared singular draining system combined with these impervious areas contributed to regular flooding. In 2012, a particularly fierce storm sent runoff and raw sewage into people’s homes and backyards, causing the city to take action.

The Solution

With a mandate from the mayor’s office to solve flooding problems, the Department of Watershed Management rose to the challenge, developing the Southeast Atlanta Green Infrastructure Initiative, which sought to create a holistic approach to managing stormwater runoff and reduce flooding while promoting sustainability and enhancing community amenities. A key aspect of green infrastructure is that it provides an alternative to traditional pipe replacement by incorporating elements designed to mimic nature to more effectively manage urban stormwater and reduce flooding, erosion and sewer overflows. One of the immediate projects undertaken by the Department of Watershed Management was the decision to install approximately four miles of permeable pavers in the Peoplestown, Mechanicsville and Summerville communities.

At the outset of planning the roadway renovations, Todd Hill, Director of Environmental Management for the Department of Watershed Management and his team asked, “What will get us the biggest bang for our buck?” Considering permeable interlocking concrete pavement, they agreed, “If we’re going to do a paver project, we want to have the greatest impact possible.”

Permeable Interlocking concrete pavement systems consists of concrete pavers with joint openings filled with permeable aggregate that allows stormwater to flow into layers of crushed stone that support the pavement while providing water storage and runoff control. As the rainwater sinks through the four feet of aggregate under the pavement, the rocks act as a filtration system to clean oils and chemicals from the street above. Geo-membrane dams and the aggregate detain the water and slowly release it into the existing stormwater sewer system. Since the water does not run directly to the curb gutter, flooding is significantly deterred during heavy rain.

After funding for the nearly $16 million project was secured, the Department of Watershed Management began excavation on the first of many streets upstream from the flood-prone areas. The goal was to use permeable pavers and the water storage capacity of deep aggregate reservoirs beneath them to provide downpipe capacity relief. “We picked residential streets that contributed to the flooding of our combined sewer system,” Hill said to Interlock Design magazine. Collectively, the four miles of permeable paver roads provided four million gallons of capacity relief.

Team leaders chose Belgard’s Aqualine™ L-Stone permeable paver—in the appropriate color of Georgia Blend. Economically sound and surpassing all EPA stormwater requirements, Aqualine is designed to withstand vehicular travel in high-traffic areas. The pavement also delivers results in both cost-effectiveness and long-term durability in harsh climates, particularly those with extreme freeze/thaw cycles.

Installation of the pavement was a three-step process. First, the asphalt was removed. Second, the street was excavated and filled with stone along with a terraced dam system that detains the water and eventually carries it to the proper drainage area. Finally, the individual pavers are put into place on top of the stone and installed 12 square feet at a time using a machine. The unique “L-shape” of the stone allows for minimal waste during installation and provides optimal interlock for vehicular traffic.

The Belgard team worked closely with Amec Foster Wheeler to help plan the design-build portion of the project. Using in-depth product knowledge and experience gained on past projects, Amec Foster Wheeler was able to better navigate challenges that occurred during installation such as unexpected utility cuts. In addition, Belgard and Southeastern Site Development worked together to develop a Permeable Interlocking Concrete Pavement Operations and Maintenance Guide for the City of Atlanta. The document provides in-depth details on short- and long-term maintenance ranging from replacing pavers to winter inspection. The guide will ensure that the city saves time and money, and maximizes its investment for years to come.

The Results

Atlanta adopted one of the most far-reaching post-development stormwater management ordinances in the nation, laying the groundwork for a robust green infrastructure program both for private development and the city’s capital improvement projects. Under the ordinance, new and redevelopment sites are required to treat the first inch of stormwater runoff with green infrastructure, such as bioretention (rain gardens) and permeable pavement. Over 2,000 construction projects that incorporate green infrastructure have been permitted in Atlanta since 2013, which equates to the removal of approximately 350 million gallons of polluted runoff from local streams and combined sewer systems each year.

“Permeable pavers are a very good solution for stormwater management, especially in highly urban areas with combined sewers that need capacity relief,” Hill said. “We have been surprised by and pleased with the amount of infiltration into the ground. We were estimating much less.”

Many of the sloped streets included check dam systems to encourage infiltration. The paver streets store runoff from a four-hour, 25-year storm yielding 3.68 inches of rainfall.

While achieving capacity relief was the main goal accomplished by this project, the decision to use permeable interlocking concrete pavement also contributed to increased property values for some communities and led to new development investments. “We know the houses that are on the permeable paver streets are more sought after than on other streets in these neighborhoods,” Hill said. “The residents who live in those areas really love the pavers and think they’re very beautiful,” stated Cameo Garrett, External Communications Manager for the Department of Watershed Management.

Belgard’s new PICP system is providing four million gallons of storage capacity, giving residents extra flood protection during heavy rain events.

In June 2016, the Metropolitan North Georgia Water Planning District awarded Watershed Management with a STREAM Award for its Post-Development Stormwater Management Ordinance in a celebration held at the Loudermilk Conference Center. The STREAM Awards recognize the outstanding sustainability achievements of Metro water utilities and local governments. The project has also drawn national attention with The Department receiving calls from other cities including Philadelphia, Washington D.C., San Francisco and Portland, Oregon.

Permeable interlocking concrete pavement systems continue to become an extremely popular choice for streetscapes and parking lots for municipalities and in the private sector. One of the biggest drivers for this technology is not just flood prevention, but also the Environmental Protection Agency’s Clean Water Act requiring builders to address their water quality impacts from stormwater runoff as well as neighborhood and street flooding. “A PICP system is the best of both worlds,” stated Aaron Faubli, Belgard Hardscapes Sales Manager. “You’re not just getting a pavement, you’re getting a pavement and a stormwater management system all in one.”

“Green Infrastructure and Low Impact Development practices are not new. However, the regional application by municipalities to solve flooding and capacity relief is a developing industry,” Cory Rayburn, Construction Project Manager for the Department of Watershed Management, said to Interlock Design magazine. “The social and economic development that can occur when these practices are done right is definitely an added benefit.”

In Atlanta’s case, the green infrastructure initiative has had a direct impact on new investment. “The Historic Fourth Ward stormwater pond adjacent to the Atlanta Beltline created a miniature ecosystem within the heart of Atlanta which reconnected surrounding residents to nature. The main function of the facility is combined sewer capacity relief, but we have seen over $500 million in private redevelopment in the surrounding area,” Rayburn said.

“We always look for opportunities to utilize green infrastructure where our historical response would have been a bigger pipe or vault,” Rayburn said. “That way, you can solve the problem while creating a real benefit for the community.”

PROJECT CREDITS:

Product: Aqualine™ 9” L-Stone 80 mm thickness
Color: Georgia Blend
Quantity: 850,000 SF
Installer: Four Seasons Landscape Management
Design Firm: Gresham, Smith and Partners
Design/Build Firm: Amec Foster Wheeler
General Contractor: Southeastern Site Development, Inc.

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