Vegetated Geocellular Retaining Wall Designed as Flood Barrier for Reconstructed Levee

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.

To protect the Southport AWT plant and wastewater processing pond from a 500-year flood event from an adjacent creek and river, a wall system designed on the levee’s creek side would maintain a narrow profile and allow opening up the creek’s water capacity.

A Natural Erosion Protection Solution

The levee embankment along the north side of the wastewater treatment plant had received significant toe erosion resulting from flood events and high water flow from the adjacent creek. An erosion protection system to prevent future erosion from the creek’s varying depths and flows was required. Little Buck 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.

Project engineer, Christopher B. Burke Engineering, LLC, preferred a wall system that would incorporate native vegetation along the levee with enough sustainability to control erosive forces from the creek. The GEOWEB® vegetated wall system chosen would reduce environmental impacts, protect the levee from scour and erosion, and satisfy regulatory requirements.

Construction of the Levee Wall

The wall was designed as a gravity structure without reinforcement. Aggregate infill placed in the GEOWEB® wall’s back cells facilitate drainage and a blend of topsoil and #2 stone in the front outer cells support vegetation as well as provide stability and resistance to soil loss during larger storm events.

Wall Dimensions & Attributes

• Wall length: 1,500 ft. Wall heights: 5 to 12 feet.
• Open fascia cells allow infiltration of stormwater.
• Flexible wall performs well in soft soil environments; conforms well to a waterway’s geometry.
• HDPE material is unaffected by water contact.

Performance Update

Since installation seven years ago, the levee wall has performed well during several rain events. Significantly more economical than the U.S. Army Corps of Engineers’ (USACE) conventional riprap solution, 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

A natural alternative to MSE block walls, 3D geocellular walls offer green aesthetics through living plantings—as well as flexibility of design for a variety of wall configurations (gravity, reinforced, steepened slopes) and conformance to native landscapes and change-in-grade construction. Their stormwater benefit is ideally suited for Low Impact Development (LID) and Green Infrastructure (GI) design.