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Don Paul: New Orleans' redone levees are already in trouble

Don Paul

“Well, that didn’t take long.” I’m referring to the lessening stability and reliability of massive improvements in New Orleans’ levee systems since the flooding disaster following Hurricane Katrina’s landfall on Aug. 29, 2005.

More than 1,800 people died in one of the worst continental U.S. disasters of the modern era when the failure-prone previous levees, designed to withstand storm surge and wave action from a Category 2 Hurricane did, in fact, fail before killer Katrina

Through what’s known as a rapid intensification cycle over the Gulf, Katrina underwent explosive intensification from Category 3 to maximum Category 5 in just 9 hours over the Gulf’s hot waters, with top winds reaching 175 mph and central pressure falling to 29.60 inches:

Had the storm made landfall at that extraordinary intensity, the horrendous disaster would have been considerably worse. On Aug. 28th, the National Weather Service office in New Orleans had to assume Katrina would make landfall at cat 5 intensity. On that basis, they issued this bulletin, the most ominous I’ve ever seen:

 

But an eyewall replacement cycle prior to landfall produced a timely reduction to still major status of Category 3, with top winds of 125 mph. The actual highest storm surge took place near Gulfport, Miss., east of New Orleans. Here is New Orleans National Weather Service Doppler radar imagery of the approach of Katrina.

This is a New Orleans diagram of topography and levee heights at the acknowledged inadequately federally funded levees of the time.

The Army Corps of Engineers and other institutions could not, with that previous funding, build the kinds of levees recommended by multi-disciplinary experts. As you can see, a substantial portion of the city lies beneath sea level.

Without going into details about inadequate federal, state, and local responses to the disaster greatly adding to the massive number of fatalities, eventually efforts were undertaken to engineer and build drastically improved levees for the city. The hope was such a massive undertaking would afford New Orleans a long period of greater security against future storms and rising sea levels. Such is not to be the case.

An article in Scientific American reprinted from Climatewire outlines the unexpected rapidity of deterioration in the new structures. A $14 billion network of new levees and floodwalls, just completed 11 months ago, is already sinking.

The Army Corps reports the new system will stop providing adequate protection in as little as four years from now. The main problem isn’t the integrity of the levees and floodwalls themselves. It’s a matter of rising sea levels combined with subsiding landmass. Quite a few stretches of the Gulf and Florida coastlines are subsiding, with soft soils and subsoils in the wet environment. Combining that subsidence with rising sea levels due to climate change (causing ice melt and warming oceans with expanding water volumes) is hastening the lessening of protection which many residents in New Orleans now consider “fixed” for the foreseeable future. There is a false sense of security in much of the New Orleans population.

The protection systems were constructed over a decade, and were not designed within an information vacuum. Army Corps engineers knew subsidence and rising sea levels would someday again slowly diminish levels of protection. But earlier studies have proven inadequate in assuming lower rates of these two processes. The Corps is already having to reassess what it will take to buttress these systems to keep them from being rendered dangerously inadequate, as was the case in 2005. Sea level rise is outpacing earlier climate model projections in many (not all) parts of the world, and subsidence has accelerated as well. Protective marshlands and barrier islands south of New Orleans are eroding away rapidly. The projections made in 2007 have turned out to be overly optimistic. In 2016 the National Academy of Sciences warned that New Orleans remained among the world’s most vulnerable cities to sea level rise, along with Manila, Jakarta and Bangkok.

Now, questions are raised as to whether the already high standard protective system has to be repaired and, in places, restructured to an even high standard for the future.

After receiving public comment on any future projects, the Corps will have to consider whether and how much to lift the levees: “Reinforcing the levees—a process known misleadingly as “lifting"— involves scraping off the top layer of grass and a fabric mattress and piling on additional earth before restoring the surface layer. It is unclear how much earth will need to be added to the levees, which stand as high as 35 feet.”

We can assume whatever choices are made will be expensive. There is no chance sea level rises will stop, and little chance they will slow down in the next century, owing to projections of continued warming and ice mass losses on glaciers, Greenland and Antarctica. There is also no reason to expect any real improvement in land subsidence, hastening the impact of rising waters.

Before any armchair generals comment with proposals of abandoning New Orleans in the face of its threatened environment, there are two things to keep in mind. It is one of the nation’s unique cultural centers with assets too numerous to list here. And, the Port of New Orleans is one of the nation’s busiest and most important of all ports, and is also ranked within the world’s 10 busiest ports. New Orleans’ contributions to our economy go far beyond that of many larger cities and metropolitan areas.

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