City Parks, Clean Water: Making Great Places Using Green Infrastructure, a new report from The Trust for Public Land (TPL), makes a strong case for leveraging public parks to manage stormwater. The report offers several useful case studies that explain the challenges and opportunities involved in designing parks to act as systems for storing or absorbing excess stormwater.
The problem of stormwater, as many readers know, originates with the vast amount of asphalt and concrete used in urban areas. Where once stormwater would have filtrated into the ground, asphalt and concrete shed it toward sewer systems. That water, toting pollutants and grime from streets, gets conveyed to rivers, lakes, and other water sources that people use. It is never cleansed by soils and plants, never replenishes groundwater, and often overburdens sewer systems and local waterways, causing flooding.
A potential solution to this problem, according to report, is to use parks to do the work of traditional grates, pipes, and sewage and stormwater treatment facilities. Parks are ideal for providing this service because they already exist in most cities and can be designed from the beginning, or even retrofitted, to serve both recreational and ecological functions.
The report offers five case studies of cities that deployed parks as green infrastructure and were rewarded with working landscapes that beautify their neighborhoods and allow for recreation:
The award-winning Historic Fourth Ward Park, which is part of Atlanta’s Beltline, sits in a lowland, industrial area that was heavily prone to flooding. One of its major features, a 5-acre storage pond, serves the function of what was intended to be a $40 million underground tunnel, according to HDR Inc., the landscape architecture and engineering firm that designed the park. The pond can handle a 500-year flood.
Kevin Burke, ASLA, senior landscape architect for the Atlanta Beltline, said the stormwater storage function of the park is working well: “We’re in the position where the city has allowed two additional developers to tie their runoff to the pond.”
The park does not infiltrate or clean stormwater, its only job is to store it. The report strikes on this point repeatedly, that stowing and slowing water outflow with green infrastructure goes a long way to preventing flooding and lifting the burden off treatment plants.
The report also highlights Railroad Park in Birmingham, Alabama, designed by Tom Leader Studio, as another economic success. The park has incentivized $185 million in development in the area and receives 500,000 visitors annually. Many of these visitors come expressly to see the birds and wildlife that flock to its water-managing wetlands, according to Railroad Park Foundation director Camille Spratling.
“When the lake was built, it was the first time we saw the Birmingham skyline reflected in the water,” Spratling wrote. “That was a real point of pride.”
The report acknowledges it’s important to think out all the options, asking decision makers to consider the following about gray vs. green infrastructure: “Do both approaches work equally as well? Is one less expensive? Can they be combined? Are residents willing to put up with years of tunneling under then neighborhoods? Conversely, does the city have enough unbuilt land to capture water on the surface?”
Other questions to answer before turning to green infrastructure: should the park also absorb stormwater? If so, what is the cost to amend the soils of existing parks so they can better infiltrate stormwater?
“The mere presence of a grassy park does not guarantee water infiltration,” the report states. Water runoff rates of urban soil, which is often heavily compacted, can approximate that of asphalt. Factors such as budget, precipitation patterns, native soil porosity, and depth to water table must be considered when amending the soil of parks, the report suggests. Maintenance of parks and their water management features can add to the cost of green infrastructure.
But, according to Burke, the investment was well worth it: Historic Fourth Ward Park has spurred hundreds of millions of dollars in development in the neighborhood.