Reverse Water Loadings for Levee Systems - A Lesson from Hurricane Ida

ABSTRACT ONLY - Hurricane Ida made landfall at Port Fourchon, Louisiana on August 29, 2021. The hurricane was a Category 4 at landfall with sustained winds of 150 mph and gusts up to approximately 175 mph. In some South Louisiana coastal locations, the storm brought with it up to 10 ft. of storm surge. The various levee systems and flood structures in the New Orleans and South Louisiana areas mostly performed well. However, some structures, especially those in the Morganza to the Gulf system, experienced significant damage due to reverse loadings that were in excess of original design levels. For roughly 6 to 12 hours, the hurricane location provided unique wind and surge conditions that contributed to water levels dropping suddenly on the Gulf of Mexico side of flood structures by as much as 6 feet. This sudden drop in water level led to reverse loadings from the Lake Boudreaux side of the structures of approximately 6 to 8 feet, well above the design level of 1.5 feet. These reverse loadings led to multiple structures being damaged to the point of inoperability.
In October 2021, a team of engineers from the U.S. Army Corps of Engineers (USACE), Geotechnical Extreme Events Reconnaissance (GEER) Association, American Society of Civil Engineers (ASCE), and Louisiana State University (LSU) performed after-action site visits and observed the damages caused by Hurricane Ida firsthand. These site visits included meeting with representatives from Port Fourchon, Coastal Protection and Restoration Authority (CPRA), South Lafourche Levee District, Southeast Louisiana Protection Authority - East, and Southeast Louisiana Protection Authority - West to better understand the extent of damage caused by Hurricane Ida.
Our technical paper and presentation will consider typical design and evaluation approaches for reverse water loading conditions within levee systems, impacts of the reverse loadings experienced during Hurricane Ida, and will discuss how levee designs may need to account for larger reverse loadings in the future.