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Sunday, August 29, 2010

5 years ago - Hurricane Katrina

Five years ago today, Hurricane Katrina barrelled into the Louisiana and Mississippi coasts. The effects of this storm were both predictable and catastrophic. The idea of a major hurricane striking New Orleans causing the entire city to flood had been discussed for years before Katrina became a reality.

There have been many articles on the personal toll, the failure of government on all levels and the fact that much of the 9th Ward is still not re-built. Now that 5 years have passed we can begin to discuss what should have happened, what actually did happen and what needs to happen to prevent this type of catastrophe again. It is a certainty that some time in the future, New Orleans will be hit directly with a major hurricane head on. The city and the region must be prepared for a future landfalling hurricane.

First of all, the worst case scenario did not occur.

Hurricane Katrina did reach a Category 5 while in the Gulf but weakened to a Category 3 before coming ashore.

Additionally, the storm did not make a direct hit on the city. Just before coming ashore, Katrina veered to the east and actually made landfall near Bay St. Louis, MS.

What would happen if a Category 5 storm slammed directly into New Orleans? Would we be prepared? Is preparation even possible?

One thing that we need to look at is what was the intent and design of the levees in the first place and did they meet that design.

In the article "The levees didn't fail", Windell Curole explains that levees have always been considered successful in their task if they hold water back up to the point that the water spill over the top of the levees. At that point, the situation is beyond the design of the levee. Every system is designed to certain parameters and they are expected to work only within those parameters.

The levees didn't fail(HoumaToday)
The authorized projects for protection in the New Orleans area began with a barrier plan that would have protected the entire Pontchartrain basin, both north shore and south shore. Objections from an environmental organization and fishing groups forced the abandonment of the barrier plan. The Corps of Engineers was forced to develop the high-level plan, which consisted of flood protection, levees, gates and walls protecting the populated areas on the south shore.

A major weakness of the high-level plan was the failure to build flood protection where the drainage canals intersected the lake.

Where levees were built along the lake, the canals were left open and used thousands of feet of walls to connect the levees to the pump stations, which were near the heart of the city.
So the original plan to protect area was scrapped because the intersts of special interest groups took precidence over protecting the people and the city. In addition to leaving the canals open, the levees were designed for flooding from rainfall, not from storm surge.

Resources and attention of the public and the leaders in New Orleans were directed to rainfall flooding. Although rainfall flooding is a great hazard, it cannot match the devastation from tidal flooding. Sadly, this fact was emphatically proven by Hurricane Katrina. In effect, the Katrina event was a compromise to failure. The compromise to satisfy special interest groups led to a weakened system that destroyed a city, a city that misplaced its trust in a government that would not cater to special interest but would do its job for the greater good.

--snip--

One of the most inaccurate statements is that the levees failed.

In fact, even the poorest levees in New Orleans held the water back until there was overtopping. Even with the overtopping, only the levees along the MRGO had a large amount of levee destroyed. Seven miles were lost out of a 14-mile segment. In all other areas, most of the damage was associated with floodwalls and other non-levee flood-protection structures.

Prior to Katrina, if a levee held the water back until it reached the top of the levee, it was successful. If the water overtopped the levee, this was not considered a failure. It was understood the levee encountered a condition beyond the design of the levee. In other words, if the water level was higher than the level the levee was designed for, it was not a failure. The levee was considered a failure only if the levee failed before it was overtopped. This condition did not occur for any levees during Hurricane Katrina.

In comparison, the floodwalls along the 17th Street and London Avenue canals failed. These were considered failures because water had not reached the top of the wall before they broke, leading to the flooding of New Orleans proper. Another major problem contributing to the flood was the difficulty in measuring elevation accurately. Although officials were aware of this problem, there was limited money to correct it. Only with the recent development of GPS technology can elevations be determined quickly and inexpensively.

It was actually the floodwalls that failed. The levees held back the water until it reached their tops - the levees were too short! This may likely be due to a design based on flooding from rain ratehr than from storm surge.


The decision to build walls along the drainage canals instead of building gates doomed New Orleans proper. Comparisons between East Jefferson and New Orleans proper make a good distinction. (Emphasis mine)

The levees along Lake Pontchartrain for New Orleans and East Jefferson performed well. These levees were slightly overtopped, but performed well, which resulted in no flooding directly from the lake.

Those levees were attached to the walls at the 17th Street canal and London Avenue canal because the city did not move its pumps to the lake. With the pump stations at the lake, the canals would have been closed by gates that would have stopped the waters of Katrina. Those floodwalls failed with the water two feet from the top. Those failures allowed for scour holes through the system, which allowed floodwaters into New Orleans proper for over three days. Eighty percent of New Orleans flooded to a 4½-foot elevation due to these wall failures.

In contrast, East Jefferson suffered much less flooding because its side of the 17th Street Canal floodwall did not fail and there were no other canals open to the lake. The majority of the flooding occurred because there was no pumping of rainfall and storm surge entering through the pump stations. Once the water level receded from Lake Pontchartrain, the flooding through the pump station stopped. There were no scoured holes to continue to allow floodwaters in the system like there were in New Orleans proper.

So the barriers were not designed as they should have been in the first place. What is being done now to make certain that properly designed levees are in place when the next storm does come ashore in New Orleans?

Rebuilding New Orleans Infastructure(CBS Evening News)
The overhauled protection system will battle future hurricane flooding in three ways: first, with barriers to block the primary paths that storm surge can enter the city - from Lake Ponchartrain, the Mississippi River, and Lake Borgne.

Part of what the Corps of Engineers is doing is building their lines of defense as far away from the city of New Orleans as possible. The billion-dollar surge barrier is being constructed 12 miles from downtown New Orleans and 9 miles from the Lower Ninth Ward.

Along with blocking storm surge, the Corps has fortified the levees that failed in Katrina. They're building massive new levees that are anchored more than 100 feet below ground - and tall enough not to be overtopped by storm surge.

"We are raising, strengthening, improving the levee systems that were in place," said Col. Robert Sinkler Commander, Hurricane Protection Office. "So we went from something that had an elevation of 14 feet around St. Bernard Parish to something that is an elevation of 32 ft."

Finally, the Corps is storm-proofing existing pumping stations and building the largest new flood pump in the world - to quickly blast out any water that gets into the city.
Some residents, especially some in the Lower 9th Ward, are understandably skeptical. The fact that the levees will be over twice as high and anchored in a manner that they will hold against a storm surge is at least part of the right solution. The Army Corps has a plan that is not "more of the same". The new system has to be environmentally sound, but not be subject to uninformed special interests that compromise the protection of the city.

After seeing the destruction that nature caused 5 years ago, I'd like to think that putting a proper protection system in place will and is actually happening this time so that New Orleans can be prepared for the next big storm.

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