Blacksburg, Va. — Ten years have passed since Hurricane Katrina struck the Gulf Coast of the United States.
Deemed one of the strongest storms to impact the coast during the last 100 years, Katrina made landfall with a Category-3 rating on the Saffir-Simpson Hurricane Scale, bringing with it sustained winds of 100-140 miles per hour, a span of some 400 miles, and massive flooding over 80 percent of New Orleans.
The aftermath was catastrophic.
Overall, Hurricane Katrina displaced thousands of inhabitants from Louisiana, Mississippi and Alabama, killed nearly 2,000 people and affected approximately 90,000 square miles of the United States. Over $110 billion in damages was estimated by FEMA, making it the costliest hurricane in U.S. history.
Tom Brandon, professor of the Via Department of Civil and Environmental Engineering at Virginia Tech, was one of the experts called to help with evaluation and reconstruction. A decade later he continues to conduct research and provide expertise on flood protection design methods.
The U.S. Army Corps of Engineers issued its June 1, 2006 follow-up study of the hurricane protection system for New Orleans and Southeast Louisiana. Among its findings, it said: "The system did not perform as a system: the hurricane protection in New Orleans and Southeast Louisiana was a system in name only…The system's performance was compromised by the incompleteness of the system, the inconsistency in levels of protection, and the lack of redundancy. Incomplete sections of the system resulted in sections with lower protective elevations or transitions between types and levels of protection that were weak spots."
Brandon, director of Virginia Tech Geotechnical Program's W. C. English Geotechnical Research Laboratory, facilitated much of the Virginia Tech research associated with the failures of the New Orleans levees.
In collaboration with Mike Duncan, civil and environmental engineering distinguished professor emeritus at Virginia Tech and a member of the National Academy of Engineering, and Stephen Wright, professor emeritus at University of Texas at Austin, they were a part of the Interagency Performance Evaluation Task Force (IPET), working with the Corps' Division and District engineers to investigate the multiple breaches in the floodwall and levee system. Their conclusions concerning failures at 17th Street and London Avenue Canal are case studies documented in their book, Soil Strength and Slope Stability.
A few years after Katrina, the Corps of Engineers conducted a full-scale test of the flood protection wall on London Avenue Canal. Brandon was part of the technical committee charged with designing and conducting the test. Soon after, Brandon submitted a proposal to analyze the data collected from the London Avenue Canal load test with the intent of integrating the findings into current flood protection design methods. Several papers have resulted from this study and the results will impact the forthcoming levee design manual.
At the London Avenue test-site between the north and south failures that occurred during Hurricane Katrina, a 150-foot section of the I-wall was hydraulically loaded with pressures and displacements measured in the vicinity of the I-wall through an extensive instrumentation system. After assessment and analysis of the data, parameters for future canals were recommended in a 2013 paper, "Analytical Calibration Approach to Develop a Seepage Model for the London Avenue Canal Load Test," written by Abeera Batool, a Virginia Tech doctoral student at the time, and Brandon.
Brandon also collaborated with Batool and Daniel VandenBerge, postdoctoral associate at Virginia Tech, comparing the results of using the U.S. Army Corps of Engineers' blanket theory and finite-element analysis (FEA) to assess conditions in which the two methods provide essentially the same solution.
"The results of combined research were helpful in the design of the permanent canal closures for the outfall canals," said Brandon of the London test project completed in 2013 and the theory comparison study completed in 2015.
The soils on which the levees are built are also an important element of the post-Katrina research and levee construction standards in general.
"During the reconstruction of the flood protection system, there was a shortage of soils to be used a construction material," said Brandon.
Flood protection research continues
A report released in February 2015 by the Corps states concerns that a five mile section of Lake Borgne District's post-Katrina levees were built on highly unstable soil. Shifting soil under levees could possibly damage the pilings supporting them, undermining their ability to withstand a hurricane.
In their 2015 paper "Highly Organic Fill for Levee Stability Berms," published in the Geotechnical Testing Journal by VandenBerge, Brandon, and Michael Wielputz, materials regional technical specialist for the Corps of Engineers, they reported findings from testing samples of organic clay from Louisiana for compaction characteristics, undrained strength, and erodibility, evaluating their potential use for stability berms.
Earth berms constructed of cohesive fill are often used to improve the stability of levees. In some parts of the United States, many of the locally available cohesive soils contain high organic content, which has historically prevented their use for stability berms.
"Our research shows materials that had historically been considered poor construction soils could be used effectively in the flood protection system," said Brandon.
They found the target total unit weight was almost impossible to achieve in soils with organic content above about 9 percent. The desired minimum undrained strength was easily attained for all of the organic contents at water contents up to 6 percent wet of optimum. The erosion resistance stayed the same or increased as the organic content of the fill increased.
Based on the test results, soils with organic content in excess of 9 percent are suitable for use as stability berm fill, provided that a lower total unit weight can be used in design.
Currently Brandon is being funded by the Corps to work in transient seepage analysis through dams and levees at its Engineering Development and Research Center (ERDC) in Vicksburg, Mississippi. Instruments have been installed in four levees to record responses to flood waters. Two of the levees are near the Vicksburg center, one near Cairo, Ill., and one close to Seattle. The project is to be concluded in 2018.
From 2011 to present, Brandon has been retained by the U.S. Department of Justice to serve as its expert on Hurricane Katrina related litigation.
In January 2015, the USACE released a report recommending a "complete reanalysis" of the levee system by 2018, as part of a regular review process that would then be repeated every 10 years.
Brandon has been involved in aspects of a new levee design manual to be released in 2016. And the standards continue to be developed for systems in New Orleans and beyond.
"The Corps of Engineers can only build what is authorized by congress, said Brandon. "What many people tend to forget is that the engineers at the New Orleans District mostly live within the flood protection system. They have a personal vested interest in the proper performance of the flood protection system."