In all, some 50 serious failures occurred throughout New Orleans’s web of canals and shorelines, so that the whole system was overwhelmed. Even if the three major breaches on the drainage and navigation canals had not occurred, about 40 percent of the areas flooded by Katrina still would have flooded, says Walter Baumy, chief engineer for the Army Corps’ New Orleans district. The Katrina flooding exceeded levee design levels by as much as two meters in much of the city [see photo, ”Devastation”].
During recent visits by this reporter to the New Orleans district office and to the corps’ major group of engineering laboratories, in Vicksburg, Miss., leaders of the district’s hurricane protection operations described the challenges they face and the implications of the IPET report.
In many ways, as the corps’ top managers describe the situation, it’s a recipe for haste-makes-waste decision making. Having already spent more than $1 billion in barely more than a year and now well into its second $1 billion, the corps undoubtedly will run into problems with contractors and specifications. Some work, decided on too quickly, will have to be redone. And no doubt some work already completed will turn out to have been misguided to begin with, as the corps resolves issues of what’s needed for 100-year protection.
For example, in some areas of the city where waterways branch like veins in a hand, the corps already is raising the levees along them to higher levels. But it may discover on further analysis that it would have done better to build single dikes closer to potential flooding sources, to protect whole neighborhoods. The absence of effective local government, combined with a lack of strong leadership from the federal government, will make it all the harder for such difficult and sometimes unpopular choices to be made correctly and in time.
But surely the thorniest of all dilemmas for the corps is the need to proceed with planning and contracting to meet Congress’s 100-year mandate, without knowing just what that mandate means. And even when the reports assessing storm probabilities and risks are more or less complete, this month or next, they are bound to be controversial.
To begin with, defining 100-year storm levels is an immensely complex task in analysis, computation, and simulation. Katrina, which corps experts believe may have been something like a 300- or 400-year storm, threw off all the received risk estimation curves, which are historically based. Then, too, history is continuing to change before the simulators’ eyes. With climate change, hardly anybody still expects the next 100 years to be just like the last 100.
A group headed by Don Resio of the Corps’ Engineers Research and Development Center, in Vicksburg, has been working since last summer to define a family of worst-case scenarios—basically, maximum wave heights and storm surges to be expected in a 100-year interval, given a variety of storm conditions. Some of the group’s conclusions will feed into Foster’s risk assessment, which is part of the IPET endeavor, though Resio’s team is not, strictly speaking, part of that project.
Resio and a second researcher have done a study of Gulf hurricanes, in which they found two major peaks in hurricane activity: in the 1960s and in the last decade. Though they discerned no long-term trend, as a what-if exercise they asked what the effect would be if the number of high-activity years doubled in the future. Their conclusion is that while the results would be serious, they would not be apocalyptic—expected 100-year surge levels would increase 15 percent and 100''year maximum wave heights 12 percent.
Resio’s group has discarded the obsolete concept of thinking in terms of just a single 100-year storm. Instead it starts with a model of typical local hurricanes and their characteristics; estimates their probabilities and likely consequences; and after a lot of numerical manipulation, obtains a range of wind speeds, wave heights, and storm surges. Though the group has been able to pare down the number of storm possibilities by focusing on the storm tracks typical of big hurricanes, it’s still an immense undertaking, ”really first of a kind,” says Resio.
The IPET risk group, relying partly on the storm probabilities developed by Resio’s team, is using a model of the whole hurricane protection area along the Gulf coast to assess risks. It will be up to the corps’ New Orleans district office to determine how those risks translate into specifications for the improved protection system. Foster anticipates that as the district prepares plans, the risk group will be asked to evaluate them, as a follow-up to its IPET work—a further feedback loop, or circularity.
When the conclusions of Resio’s team and the IPET risk group are released, which will be soon, they are bound to give rise to new questions. Is the methodology used to calculate 100''year-storm scenarios sound? Does it adequately factor in projected climate changes? Is Congress’s 100-year mandate itself adequate?
Kerry Emanuel, an atmospheric scientist at MIT, comments that if you separate out Gulf hurricanes the way Resio has done, you’ll end up with too small a data set to detect a trend. Only about a fifth of the hurricanes originating in the Atlantic end up in the Gulf, says Emanuel, whose work asserting a sharp increase in Atlantic hurricanes has aroused considerable debate. ”You have to get away from history and bring in physics,” he says.
Katrina certainly was a history-changing event. Though only a Category 3 storm by landfall, it nonetheless kicked up the highest waves ever recorded off North America, generating surges ”larger than any previous storm to strike the area or [indeed] the North American continent,” as IPET put it. Katrina flooded about 80 percent of New Orleans—a sprawling city consisting largely of low-lying ranch-style homes—killing 1600 to 2000 people in the region and displacing at least two-thirds of the city’s population.
The Federal Emergency Management Agency (FEMA), which has inherited the job of setting insurance rates in coastal areas, has always based those rates on 100-year-flood scenarios. But if Katrina itself was a 300-year or 400''year storm, as Resio surmises, does it make sense now to be preparing for only a 100-year storm?
Then, too, there will be questions about whether the corps’ district office in New Orleans, given a legacy of shoddy work and wide public mistrust, can be counted on to translate conclusions about waves and surges into proper new elevations; set specs for better levees, floodwalls, and gates; and actually get the work done. ”It’s not just the levee system, it’s the system that gave us that system,” comments Paul Kemp, a faculty member at Louisiana State University and a researcher at the LSU Hurricane Center, in Baton Rouge. The center has often been at loggerheads with the corps.
Kemp claims that before Katrina, the corps said more than once that it already had given the city 300-year-storm protection, only to be proven catastrophically wrong.
The draft final report of the IPET group evaluating the operational risk and reliability of the New Orleans hurricane protection system will be posted when complete at https://ipet.wes.army.mil.