Posted on November 6, 2024
For decades, engineers and disaster-response planners have evaluated levee vegetation health – a key indicator of a levee’s ability to withstand an overtopping event – by visually grading vegetation on a simple three-option scale: good, average or poor. Researchers from the U.S. Army Engineer Research and Development Center (ERDC) believe they can do better than that, and possibly save lives and whole communities in the process.
A multidisciplinary ERDC team is working to modernize widely used flood models such as StormSim and Hydrologic Engineering Center software by developing a vegetation index that more comprehensively quantifies vegetation stability on coastal levees. The index will incorporate an array of ecological measurements, such as root/shoot ratios, evapotranspiration rates, soil moisture, vegetation shear, root strength, and vegetation age, size and type.
“Although most people envision dunes protecting coastlines, thousands of miles of inland levees protect areas from coastal flooding, including the city and port of New Orleans,” said Dr. Simone Whitecloud, a research ecologist at ERDC’s Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, New Hampshire, who is leading the project. “The current method of evaluation was created in the 1970s by hydraulic engineers who did not consider the bigger picture of vegetation, such as what plants are present? Are they healthy? What is the soil like? These factors contribute to the ability of vegetation to either promote or inhibit levee stability.”
Understanding that “bigger picture,” is important, Whitecloud says, because “healthy vegetation is going to be able to withstand overtopping events better than unhealthy vegetation” as the roots help hold the soil in place so that erosion won’t take place.
A Potential Gamechanger
The team plans to develop the index using tried-and-tried methodologies familiar to any ecologist – field sampling and greenhouse experiments – but also by incorporating remote sensing via satellites, UAVs, and planes.
“The hope is that we will be able to use remotely sensed data,” said Whitecloud. “There are various indices that can look at the quality of light reflected off plants that give you a sense of their health, so you could use that to say ‘this is a healthier stand’ versus a less healthy stand.”
The potential use of remotely sensed data is tantalizing, because if successful it would allow flood models to incorporate real-time data, a potential gamechanger in disaster planning and response.
“We could point satellites to get data in pretty much real time, so if we knew a storm was coming in, we could evaluate the health of the levees and know where to prioritize evacuation,” said Whitecloud.
Levees in the United States
The impact of the team’s work is underscored by the importance of levee safety in the United States. According to the U.S. Army Corps of Engineers (USACE), the average age of the nation’s 6,675 levees is 60 years old. Twenty-three million Americans in 2,375 communities across the country live behind levees.
“It is really mind boggling when you think about all the people, all the homes and businesses and critical infrastructure that are protected by our nation’s levees,” said Dr. Ivan Beckman, CRREL’s acting director. “Levee safety is one of the most important missions that the Corps of Engineers has and I truly believe that this project can help us maintain and build safer levees. That is truly impactful work.”
Inter-laboratory Collaboration
The project, says Beckman, is also a good illustration of the multi-disciplinary, inter-laboratory collaboration that ERDC is well known for.
Besides CRREL, the project team also includes research scientists and engineers from ERDC’s Coastal and Hydraulics Laboratory (CHL) and Geotechnical and Structures Laboratory (GSL), both located in Vicksburg, Mississippi.
While CRREL is largely focusing on vegetation health measurements and model developments, GSL is assisting with test site selection through its network of USACE districts, and CHL with model development, geotechnical engineering and StormSim simulations.
“This is a great example of the strengths of multiple laboratories being leveraged to create even more robust research capabilities, and ultimately, greater impact,” said Beckman. “This is exactly the type of cooperation that was envisioned when ERDC formed more than 25 years ago.”
The project is funded by the Geophysical Computational Modeling work package of the Comprehensive Water Risk Management Strategic Focus Area.
Even age affects the size and strength of plants. A multidisciplinary ERDC team is working to modernize widely used flood models such as StormSim and Hydrologic Engineering Center software by developing a vegetation index that more comprehensively quantifies vegetation stability on coastal levees. The index will incorporate an array of ecological measurements, such as root/shoot ratios, evapotranspiration rates, soil moisture, vegetation shear, root strength, and vegetation age, size and type.
ERDC-CRREL invented a specialized tool that measures vegetation shear strength, or how much force is required to pull the plant out by the roots. A multidisciplinary ERDC team is working to modernize widely used flood models such as StormSim and Hydrologic Engineering Center software by developing a vegetation index that more comprehensively quantifies vegetation stability on coastal levees. The index will incorporate an array of ecological measurements, such as root/shoot ratios, evapotranspiration rates, soil moisture, vegetation shear, root strength, and vegetation age, size and type.
