14 Target Hard Surfaces Impervious surfaces generate the most runoff. Reducing the amount of impervious surface at the park can have a big impact on water quality and localized flooding. Options include: • Evaluate parking demand and convert underused parking spaces to landscaped area. • Convert low-traffic stalls and lanes to permeable pavement. • Use pervious asphalt or concrete for basketball courts and other paved areas. Another way to reduce the impact of impervious surfaces is to direct the runoff they generate to pervious areas rather than the storm drain system or nearby waterbodies. Options include: • Disconnect gutter downspouts so that water flows over landscaped, pervious areas or is captured for later use. • Reconfigure parking lots (e.g., cut curbing at strategic spots) so runoff drains to landscaped areas. • Grade walkways and plazas to drain toward turf grass, natural areas, and other pervious areas. Case Study: Converting Concrete to Green Space at Historic Fourth Ward Park Atlanta, Georgia Completed in 2011, Historic Fourth Ward Park is a 17-acre urban park located along Atlanta’s BeltLine, a former railway being redeveloped as a multi-use trail. It is situated in a lowland area that had experienced flooding and sewer overflows during storms. The site of the park was originally a mix of industrial and commercial property, including areas that had become vacant or blighted. City planners wanted to provide the surrounding neighborhood with a multipurpose green space in which residents could gather, while at the same time improving stormwater management. The park includes: • A 2-acre stormwater retention pond bordered by plantings and a walkway that can capture runoff from a 100-year storm. • An underground cistern that allows for the reuse of nonpotable water, and rain gardens with constructed wetlands. • An increase in pervious groundcover. • Recreational amenities including open meadows and lawns, an amphitheater, a skate park, playgrounds, and a multiuse field. The park is owned and managed by the city of Atlanta and supported by the Historic Fourth Ward Park Conservancy. The land for the park was donated by Georgia Power and BB&T, with funding provided by the Atlanta BeltLine Partnership Capital Campaign, the Department of Watershed Management, Park Improvement Bonds, and the Atlanta BeltLine Tax Allocation District. It is estimated that the green infrastructure features in the park saved Atlanta more than $15 million compared with installing conventional gray infrastructure drainage alternatives. Development of the park has allowed Atlanta to meet a federal consent decree regarding combined sewer overflows and waste treatment. Figure 6. Top: Historic Fourth Ward Park. Bottom: conditions before construction. (Source: Steve Carrol, HDR)
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