RMS

Five Years Later – How New Orleans Flood Risk Has Changed Since Hurricane Katrina

	Significant investments have been made in levees over the last five years; however, flood threat continues as the city continues to sink and sea levels rise.
	Key findings stress the need for a risk-based approach to flood management.
	In 2011, RMS will release an upgrade to the RMS® U.S. Hurricane Model, which offers an up-to-date view of the levee and storm defense risk in New Orleans.

On August 25, 2005, Hurricane Katrina first made landfall on the Florida Peninsula as a moderate Category 1 hurricane. Devastating the city of New Orleans, Katrina made landfall again as a strong Category 3 storm on the morning of August 29, 2005. Although the storm weakened as it passed through the city, it maintained the characteristics of a Category 5 hurricane offshore, causing storm surge to reach maximum elevations of more than 25 ft (7.6 m) along the south-facing Mississippi Coast. Because Katrina exceeded the standard surge for a Category 3 hurricane (the "standard project" Category 3 hurricane was used to design the city's flood defenses), some of New Orleans' levees and pumping systems failed.

"Hurricane Katrina was one of the most destructive natural disasters to occur in the United States, but also one in which large amounts of the damage and loss of life reflect the failings of human systems of engineering, planning, and disaster management," said Dr. Claire Souch, vice president of Natural Catastrophe & Portfolio Solutions, RMS.

A number of investigations have already been conducted in order to understand these failings, with the results published in FEMA, 2006; ILIT, 2006; USACE, 2006. Each stressed the need to identify lessons to be learned from the disaster to reduce the chances of a recurrence in the future. A number of major points have emerged relating to flood risk in New Orleans, stressing the need for risk-based approaches to flood management.

Since Katrina, a significant amount of reconstruction and strengthening of the levee systems in New Orleans has taken place, with several billions invested. The U.S. Army Corps of Engineers is committed to providing a 100-year level risk reduction for southeast Louisiana in 2011 through its Hurricane and Storm Damage Risk Reduction System (HSDRRS). A 25 ft-high surge barrier is being constructed eight miles east of the city, where the Gulf Intracoastal Waterway (GIWW) and the Mississippi River Gulf Outlet (MRGO) meet.

However, while steps have been taken to prevent a similar reoccurrence, the flood threat to New Orleans continues to increase due to a combination of three factors:

	New Orleans is located on thick, relatively young delta sediments along the edge of an oceanic basin; the city is sinking at geologically rapid rates.
	Over the last decade, global sea level rise has increased as a result of climate change and is predicted to accelerate in the future.
	The level of Atlantic Basin hurricane activity has also risen, with the biggest increases for the strongest storms (with the largest surges). These factors all serve to increase the storm surge flood hazard faced by New Orleans, and will significantly raise the risk of flooding in the city through the 21st century.

In early spring 2011, RMS will release the latest version of its U.S. Hurricane Model, incorporating high-resolution modeling capabilities to assess the city's flood risk from storm surge today. RMS' storm surge model dynamically links to the wind model throughout the entire lifecycle of the storm, allowing for the simulation of storms, like Katrina, with significantly greater storm surge than their landfall characteristics would suggest. This builds on the 2006 post-Katrina update of the model, which already incorporated significant lessons learned from the event.

The 2011 model incorporates an up-to-date characterization of levee and storm defense risk, including the potential for failures to occur at surge water levels below the design standards. The model also incorporates housing stock improvements resulting from new regulations that require all rebuilt coastal property be elevated significantly above ground level. Unfortunately, many of the properties destroyed by Katrina have yet to be rebuilt.

Please follow the links below for more information on Hurricane Katrina:

In 2006, RMS published the research report Flood Risk in New Orleans: Implications for Future Management and Insurability, which discusses the impact of Hurricane Katrina on the city of New Orleans and analyzes the future storm surge flood risk at different geographical locations within the city and how this risk in expected to change into the future.

References:

Federal Emergency Management Agency (FEMA), 2006. Mitigation Assessment Team Report: Hurricane Katrina in the Gulf Coast - Building Performance Observations, Recommendations, and Technical Guidance (July 2006). http://www.fema.gov/library/viewRecord.do?id=1857

Independent Levee Investigation Team (ILIT), 2006. Investigation of the Performance of the New Orleans Flood Protection Systems in Hurricane Katrina on August 29, 2005 (July 31, 2006). http://www.ce.berkeley.edu/~new_orleans/

U.S. Army Corps of Engineers (USACE), 2006. Draft Final Report of the Interagency Performance Evaluation Task Force (1 June 2006). https://IPET.wes.army.mil

Editorial Contacts

Jackie Barber

RMS U.K.

+44 20 7444 7723

jackie.barber@rms.com

Carolyn Krehel

RMS U.S.

1.201.498.8712

carolyn.krehel@rms.com