Dr. Robert Gilbert, the risk expert on the ASCE panel and a civil engineering professor at The University of Texas at Austin, noted that their risk analysis confirms the vulnerable nature of the city's hurricane protection system. In the report, the panel estimated that despite the levees and floodwalls, New Orleans residents' pre-Katrina risk was at a 1,000-fold higher rate than considered minimally acceptable for a major U.S. dam.

"A thousand people died in New Orleans, and the system failed once in 40 years," said the international risk assessment expert. "That's way off the chart of acceptable risk if you compare the system to major U.S. dams, which have governmental oversight and must meet federal safety guidelines."

Determining the factors that directly or indirectly led to this high risk was a major goal of the ASCE panel as an essential step to help the city make informed decisions about the future.

"Given the high risk, some very significant decisions need to be made about how New Orleans is going to be redeveloped and function in the future," Gilbert said. "The risk of flooding should influence everything from how people are evacuated to where and how houses are re-built and land is re-developed. Building houses on ground that is 5 to 10 feet below sea level and assuming they will never get wet is nonsensical."

The U.S. Army Corps of Engineers is expected in June to release its assessment of the inherent risk of the 350-mile, New Orleans' hurricane protection system.

As part of assessing the risk and making recommendations for future improvements, the panel considered factors that included:

+ how inconsistencies in the features of the levees and floodwalls - including their varying heights and construction from erodible materials - resulted from their piecemeal development and disjointed oversight, and how this fed into the failure at 50 locations along the system during Hurricane Katrina;

+ how the hurricane protection system was under-designed to handle a major storm surge produced by hurricane winds that would reach New Orleans. No one had ever estimated the height of the surge likely to reach different points of the levee system using the standard benchmark - a major hurricane that would hit an average of every 100 years.

Despite the importance of engineering improvements, Gilbert cautioned that fortification steps alone aren't enough.

"It isn't just about improving the reliability of the levees and making them taller," he said. "Spending federal money towards developing a way to evacuate people effectively is crucial, and very little emphasis has been put on this or on determining how to rebuild the city in a way that will keep people and property safe."

Relying only on levees isn't the answer, Gilbert said, because upgrading them is expensive, and it's difficult to anticipate the magnitude of future storms, which can impact a small portion of a levee system and have catastrophic consequences. He also noted that higher levees can create greater danger because of the higher wall of water that is released if they fail.

"I'm hopeful that getting this report out into the public forum about all these challenges will help motivate the people involved in making tough decisions about the future of New Orleans to start doing so."

In August 2006, the U.S. Army Corps of Engineers and the ASCE External Review Panel each published lists of steps to take to protect New Orleans, and since then several improvements have been made. An amendment to Louisiana's constitution has led to two new levee boards in New Orleans, replacing roughly a dozen agencies who previously handled oversight.

These boards involve engineers and others with flood control experience who oversee the maintenance and operations of the hurricane protection system. In addition, legislation has been proposed to require the U.S. Army Corps of Engineers to have external peer review of major flood control and navigation projects.

The external review provided by the ASCE of the Corps' levee investigation occurred at the request of Lt. General Carl A. Strock, the chief of engineers for the U.S. Army Corp of Engineers. For their role in the ASCE External Review Panel's work, Gilbert, the Hudson Matlock Professor of Civil Engineering and two other University of Texas at Austin engineering alumni received the U.S. Army's Outstanding Civil Service Medal this past February.

A PDF copy of the ASCE panel's "What Went Wrong and Why" report is available online.

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