Double exposure of Hurricane Ida approaching New Orleans.Brian McGowan/Unsplash
On Aug. 29, Hurricane Ida struck Louisiana with maximum winds of 150 mph. The wind speed dropped as Ida continued inland, but, as the eye of the storm passed northeast of New Orleans, strong winds still left the entire city without power.
Compared with Hurricane Katrina in 2005, however, Ida led to much less flooding in New Orleans, which has been attributed in part to a redesign of the city’s levee system.
UW News asked Michael Motley, a UW associate professor of civil and environmental engineering who studies coastal resilience to tsunamis and related natural disasters, to explain how levees protect cities like New Orleans.
What are levee systems, and how do they work?
Levee systems, combined with large water pumps, are essentially used to maintain dry land when local water heights exceed the ground elevation in a city or town. These systems generally consist of more than just levees, including a series of engineered berms, seawalls and floodgates designed to prevent water from inundating the region, combined with strategically placed drainage systems and pumps that can be used to move water out. In many cases, these systems are there to mitigate the effects of natural disasters, but for some areas that lie below sea level, the levee systems are critical to maintaining day-to-day operation. Much of New Orleans lies below the local sea level, so the levee system there is vital, especially during tropical storms and hurricanes where the storm surge can cause a significant increase in water depth around the city.
After Hurricane Katrina, what did people do to improve the system?
Hurricane Katrina showed how important these systems are, as widespread failures across the system led to billions of dollars in flooding damage and significant loss of life. The failure of the levee system was the end result of a combination of factors, including miscalculation of the extent of the storm surge, poorly maintained and under-designed facilities, and budget shortfalls. Since 2005, various agencies have spent nearly $15 billion upgrading the levee system in and around New Orleans to resist a 100-year storm, or a storm with an annual probability of occurrence of 1%. These upgrades include reinforcement or armoring of the levees, increasing the size and scope of the seawalls, and improving the pumping system around the city.
How did these improvements do with Hurricane Ida?
Hurricane Ida was thus far the biggest system to impact the region since Katrina in 2005. After the failure of the levee system then, the redesigned system seems to have done its job. Moving forward, there are questions about the resilience of the system when we consider sinking elevations around the city (including sinking of some levees) and issues related to sea level rise.
For more information, contact Motley at [email protected].