Increasing the Resilience and Improving the Environmental Performance of Earthen Flood Defense Structures with High Performance Turf Reinforcement Mat Reinforced Vegetation

Thompson, R. and Loizeaux, D. (2018) Increasing the Resilience and Improving the Environmental Performance of Earthen Flood Defense Structures with High Performance Turf Reinforcement Mat Reinforced Vegetation. In: Protections 2018 (3rd International Conference on Protection against Overtopping), 6-8 June 2018, Grange-over-Sands, UK.

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Abstract

Adding resilience to earthen flood defense structures, such as dams and levees, is critical to future risk mitigation as building higher and stronger structures to prevent overtopping waves, storm surge, and flood waters becomes more prohibitive. To add resilience riprap, articulated concrete blocks, concrete slope paving, and other traditional hard armor solutions are often used typically at a great cost to the owner and the environment. The United States Army Corps of Engineers (USACE) sought to mitigate these costs when selecting an armoring system for the earthen levees in the 214 km (133 miles) of the Hurricane & Storm Damage Risk Reduction System for southeast Louisiana. The USACE armoring focus turned to High Performance Turf Reinforcement Mats (HPTRMs) after a levee armored with vegetation reinforced by this synthetic mat in Lafitte, Louisiana survived the storm surge and wave overtopping produced during Hurricane Ike in 2008. This success encouraged the USACE to begin a 10 year intensive research program to determine the hydraulic performance threshold, cost effectiveness, and long-term durability of vegetation reinforced by a HPTRM for adding resilience to the re-built levee system destroyed by Hurricane Katrina. Research at the Hydraulics Laboratory of Colorado State University has established the HPTRM reinforced vegetation performance in both outdoor flume testing and in the world’s largest, full scale Wave Overtopping Simulator. As a result of this research, this paper will focus on using hydraulic data to reposition HPTRMs as a suitable alternative to traditional hard erosion control solutions and explain the importance of key material properties when comparing different HPTRMs. This paper will show that HPTRMs with a more closed structure and a smaller percent vegetation establishment perform better than the more open HPTRMs with a higher percentage of vegetation establishment. More research is required to determine specific design guidelines for correlating percent HPTRM openness to vegetation densities in different soil types as it relates to hydraulic performance. Even with low vegetation densities, HPTRM reinforced vegetation provides improved environmental outcomes and lower carbon emissions when compared to traditional hard armor solutions. Countries around the world may benefit greatly from investing in HPTRM reinforced vegetation to provide resilience on earthen flood defenses as an alternate to traditional hard armor systems that are more expensive, less aesthetically pleasing, and more detrimental to the environment.

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