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Green Retaining Walls Protect an Advanced Wastewater Treatment Plant from a 500-Year Flood Event

GEOWEB Green Retaining Wall

Flood Protection Plan

To meet federal requirements for flood mapping of levee-protected areas, a levee reconstruction project for the Indianapolis Southport Advanced Wastewater Treatment (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 erosion 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 system 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 impact, protect the levee from scour and erosion, and satisfy regulatory requirements.

Construction of the Levee Wall

levee wall being constructed with geocells

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 aggregate 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.

Wall Dimensions & GEOWEB Green Wall Attributes

  • Wall length: 1,500 feet; Wall height: 5 to 12 feet
  • Open fascia cells allow infiltration of stormwater.
  • Green fascia panels blend with natural environment.
  • Flexible wall performs well in soft soil environments; conforms well to a waterway’s geometry.
  • The GEOWEB HDPE material is unaffected by water contact.

Performance Update

Since its installation in 2012, the GEOWEB green wall continues to provide vital protection to the Southport ATW plant and wastewater-processing pond from major storm events. Significantly more economical than the U.S. Army Corps of Engineers’ (USACE) conventional riprap solution, the GEOWEB walls are a practical alternative for levee applications.

With native vegetation, the GEOWEB levee wall proved to be an attractive solution that effectively minimized environmental and permitting impacts.

Living Green Walls + Low Impact Development

An attractive alternative to MSE block walls or riprap, walls built with the GEOWEB geocells offer a green aesthetic and low-environmental impact approach to designing retaining walls. The GEOWEB Retaining Walls conform well to landscape contours, are resistant to environmental degradation, and install 25-30% faster than MSE block walls. The GEOWEB System also offers design flexibility for a variety of wall configurations, including gravity, reinforced, and steeped slopes.

Create Strong, Long-Lasting Mechanical Connections Using the New ATRA® Wall Key The new ATRA Wall Key is the most effective device for connecting the GEOWEB Retaining Wall sections, ensuring the long-term success of your project. Made of non-reactive, chemically inert high-density polyethylene, the ATRA Wall Key provides a more secure and permanent mechanical connection over staples or zip ties, and they are the only geocell connector specifically designed for use in exposed wall face applications.

The innovative ATRA Wall Key includes an integrated washer at the base of the handle to provide coverage of the I-slots, frictional barbs for an improved interlock with the GEOWEB sections, and an ergonomic handle with S-shaped contouring for ease of installation.

Formulated to withstand weathering and ultraviolet radiation, the ATRA Wall Keys will not corrode or photodegrade, even when exposed to harsh environments. Securing sections with the ATRA Wall Keys is faster than using staples or zip ties, requires no tools, and can be completed by one installer with one easy turn.

Design Support for Retaining Walls

Presto Geosystems offers fast and easy-to-use resources and tools for designing GEOWEB Retaining Walls. Let our Design Engineering Team prepare a complimentary project evaluation for your next project. We also offer free licenses for our GEOWEB® MSE Design software for retaining wall applications.