Industry paper

Increasing the resiliency of earthen flood defense structures with HPTRM reinforced vegetation

Authors: Randy Thompson, PE, and Drew Loizeaux, PE

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. Traditional hard armor structures, such as riprap or ACBs are often used to add resilience to earthen flood defense structures. The USACE sought to mitigate these costs when selecting an armoring system for the earthen levees in the Hurricane & Storm Damage Risk Reduction System for Louisiana. The USACE began focusing on High Performance Turf Reinforcement Mats (HPTRMs) after a levee armored with HPTRM reinforced vegetation survived the storm surge and wave overtopping produced during Hurricane Ike. This led the USACE to an intensive research program to determine the hydraulic performance threshold, cost effectiveness, and long-term durability of HPTRM reinforced vegetation for adding resilience to re-built levee systems. Research at 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. This paper will focus on the results of the wave overtopping test as it applies to different HPTRM levee protection systems. Testing indicates that the HPTRM’s performance may not require a 100% vegetative cover in order to improve the resilience of an earthen embankment. HPTRMs with a more closed structure and a smaller percent vegetation establishment may perform better than more open HPTRMs with a higher percentage of vegetation establishment. Emerging research also indicates HPTRM reinforced vegetation provides improved performance and produces significantly less carbon emissions when compared to traditional hard armor solutions. This paper presents field and laboratory data in combination with the USACE’s research to establish guidance on the use of HPTRM technology to increase the resiliency and reduce the carbon footprint of earthen flood defense structures.