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Green Retaining Walls Protect an Advanced Wastewater Treatment Plant from a 500-Year Flood Event
Flood Protection Plan To meet federal requirements for flood mapping of levee-protected areas, a levee reconstruction project for the Indianapolis Southport Advanced Wastewater Treat- ment (AWT) plant along Little Buck Creek was part of a more extensive Deep Rock Tunnel Connector project—one of the largest combined sewer overflow projects for the City of Indianapolis. The project included plans to protect the Southport ATW plant and wastewater- processing pond from a 500-year flood event from an adjacent creek and river. To accomplish this, a wall system designed on the creek side of the levee would have to maintain a narrow profile to increase the water capacity of the creek. A Natural Erosion Protection Solution Flood events and high water flow from the adjacent creek caused significant toe ero- sion of the levee embankment along the north side of the wastewater treatment plant. The AWT required a long-term soil stabilization solution to combat erosive forces from Little Buck Creek's varying depths and flows. The creek flows as low as a 1-foot depth with velocities of 3 feet per second (fps) to as high as 8 fps with a depth of 12 to 15 feet during a flooding event. The project engineer preferred a wall sys- tem with native vegetation along the levee that would be robust enough to withstand erosive forces from the creek. They chose the GEOWEB® Vegetated Retaining Wall System to reduce the environmental im- pact, protect the levee from scour and ero- sion, and satisfy regulatory requirements. Construction of the Levee Wall
Working within a limited footprint to maintain a narrow profile, the engineer designed the GEOWEB Retaining Wall as a gravity structure. Installers filled the back cells of the GEOWEB System with aggre- gate to promote drainage and placed a mixture of topsoil and #2 stone in the front outer cells to support vegetation and provide stability and resistance to soil loss during larger storm events.
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csengineermag.com
October 2022
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