I've read in numerous places that the New Orleans levee system was designed to withstand a storm of category 3 on the Saffir-Simpson scale I've also read that Hurricane Katrina took a last minute turn and missed a direct hit on New Orleans. This NOAA report from 4 AM last Monday indicates that hurricane force winds extended 105 miles from the center, and the 8 AM report says "NEW ORLEANS LAKEFRONT AIRPORT RECENTLY REPORTED SUSTAINED WINDS OF 69 MPH WITH A GUST TO 86 MPH." The 10 AM report indicates that the storm had weakened to category 3, and gives the position as 35 miles East Northeast of New Orleans, but does not give specific wind speeds for New Orleans.
My understanding, confirmed by Wikipedia of the scale is that it's the sustained winds that matter, and category 4 means sustained winds of 131-155 MPH. Clearly it was a terrible storm, with category 4 winds on the Mississipi delta where it first made landfall and in the State of Mississippi, but the highest reported sustained wind in New Orleans that I have been able to find doesn't even make it up to the category 1 minimum of 74 MPH. I presume there were some higher measurements that never made it onto the NOAA reports, but was it really category 4 in New Orleans? Did it really exceed what the levees were supposed to handle? At the moment I'm not convinced that it did. The wind data for weather stations in New Orleans must exist. I'd wager that the Army Corp of Engineers has their own data. I wonder if we'll ever see it.
1. Bruce Perry09/05/2005 09:53:37 PM
Here's a post on Daily Kos from a professional meteorologist:
He's got some info about the wind speeds, some criticism of the current hurricane scale, and info about the storm surge (which was huge). He says the storm came ashore as a Category 4, though dropping to a Category 3 at Gulfport. No word on the wind speed at NO though.
2. Jeff Crossett09/05/2005 10:18:38 PM
I'll echo Bruce's comments and add that New Orleans got a double whammy on this one with the storm surge doing a ton of damage, and then the flood of water draining into the gulf from all the rains. From what I understand, the levee breaks came from this second surge of water.
Oddly enough, according to this article, one of the breaks occurred in a recently upgraded section.
3. Richard Schwartz09/05/2005 11:35:24 PM
@Bruce: Great thread there. Thanks. Some info on the NOLA wind speeds there now. The levees survived the winds, which were probably Cat 2 in NOLA, but canal walls breached later due to factors not yet known, but Jeff's theory that it was the wash back to the Gulf makes sense.
4. Bruce Perry09/05/2005 11:54:03 PM
@Jeff: I'd heard somewhere that the upgrade on that section had been started, but wasn't complete. More dirt had been added, but it wasn't fully compacted and/or faced with concrete.
5. Curt Stone09/06/2005 12:12:46 PM
Sounds to me that the system could not even handle a cat 3 and no one had an effective plan to evacuate. First, the local gov. should have made the evacuation mandatory for the people that had the means to get out. For the others, they needed those buses ready to take people out a lot sooner. I can't believe the time it took to mobilize the National Guard from the Feds.
What will happen if a larger city needs to evacuate in a terror attack?
6. Jeff Crossett09/06/2005 06:54:08 PM
I recently learned that in 2004 the feds gave themselves the power to insert troops into any state amidst an emergency. Evidently, the criteria for this determination is pretty vague so even though FEMA and the LA National Guard were at work, it took a while for the governor of LA to officially ask for additional assistance. In fact, she still refuses to give the federal government control over the NG troops there now.
I even saw the New Orleans mayors office press release that allowed the use of school buses in the evacuation; it was dated 3 days after the storm :/
Big fubar all around. Funny how our strength of having independent states kind of flopped here.
7. Jerry Glover09/08/2005 02:29:29 AM
They do know exactly why the concrete wall levees failed; it was overtopping - i.e. Katrina's storm surge raised the level of Lake Pontchartrain to the point where it spilled over a section of the levee (the break on the 17th St. Canal was at one of the shortest sections of levee wall in the city - see maps).
The mode of failure for an overtopped levee is well-known by the Corps of Engineers (engineers in general I suppose). The spillover of water causes turbulence at the toe (base) of the levee where it is undermined and eventually fails.
Pontchartrain was at record levels from Katrina's storm surge; it was just a matter of time. If there's interest, I can supply more info/references tomorrow night when I'm not supposed to be asleep.
8. leilei391502/28/2017 02:18:05 AM
9. zzzzz02/28/2017 08:45:40 PM