Ray in New Orleans

Right. And do the 1% maps mean "If the levees break again, you're this much more protected because of the floodgates"? Because the 1% (100Year?) map looks a LOT like the actual depth maps for Katrina. I still have those .kmz google earth files on my PC and the 1% map overlays seem to just be the "what katrina did" map. So I want to know, is the corps actually implying that there levees will break again, but we're that much more protected because of the floodgates?

I believe according to the Corps Katrina would be classified as a "one in 400 year" storm...or so I've read.

As for my Gentilly neighborhood, I don't see any difference between the three "protection before Katrina" maps and the "protection now" maps. Essentially what they're telling me is that after they've installed a flood gate and pumps at the mouth of the London Avenue Canal, I still have the same risk I had before they did any of their work. For the record, I show up as being "dry" for the "1 in a 100 year storm" and under 4 to 6 feet of water for the "1 in 500 year storm"...which is roughly what happened under the Katrina scenario.

Stepchild not included on maps......so what else is new.

I know, sweetie, I know. Some of us still remember that Walnut Bend is as much a part of New Orleans as Lakeview and Gentilly.

It gets murkier, according to page 2 of this article on the NY Times ( http://www.nytimes.com/2007/06/21/us/21orleans.html?pagewanted=1&ei=5090&en=95a82457370a9506&ex=1340078400&partner=rssuserland&emc=rss )
"One of the biggest problems, Mr. Powell said, is that people have lived in New Orleans for generations and believe that the city would have been largely undamaged if the levees had held, but the new report says that the force of Hurricane Katrina would have caused extensive damage even if the levees had held."

As I said before, the "before katrina" maps look a lot like the actual Katrina results. What powell is saying is that those maps represent how much flooding would have happened if the levees held. I think powell is misunderstanding or misrepresenting the maps. the NYtimes own flood graphic derived from the corps maps shows the intial item as 8/31/2005 flooding as I suspect it is.

That's not murky, that's clearly bullshit. If the levees had held, Gentilly would have got 8+ feet of flooding from rainwater? Powell needs to pull his head out of George W.'s ass. The new report doesn't say that the neighborhoods would have flooded if the levees had held, the new report says that the levees are still 1% likely to fail every year.

Its annoying the overlays don't scale on zoom. Still, I can see a tinu difference on my own little atoll in the Isles d'Orleans: no water in my street in the 50 map.

Powell is buying into the overtopping theoru that Katrina would have overtopped areas of the system, which is probably true for some areas (the low wall on either Orleans Avenue or 17th Street; I forget).

The overtopping theory is bullshit no matter which way you slice it.

Either overtopping scours the unarmored dry side of the levee, and then you end up with a breach. Or else overtopping only pushes water over the levee during the small window of time that the storm surge is higher than the height of the levee in that place. I don't buy it that that latter scenario would put 6+ feet of water in half the city, which you have even in the 50-year scenario.

Just looking at the FQ/Garden District map, I see negligable difference in the 50-year and 500-year scenarios between current and pre-K. And in the 100-year scenario, if you flip back and forth between current and pre-K, it looks like just a 2-foot flood difference between the two maps.

So all the work that has been done has lowered expected flood heights by only 2 feet in a 100-year scenario, i.e., a scenario that everybody is expected to see in their lifetime?

Dat shit sucks. And that's assuming that the maps are honest and accurate.

I wonder if analogous maps exist for Amsterdam.

Whoa, wait a second.

Powell says, "The new report says that the force of Hurricane Katrina would have caused extensive damage even if the levees had held."

What was the extent of the damage between when the winds died down and the levees broke? Not much except for roof and tree damage as already suffered. Does Powell imply that Katrina intended to make a U-turn and run over New Orleans proper to cause this extensive damage?

Also, how does Tchoup get flooded (with standing water) if it's above sea level?

Ok, Powell was trying to say that overtopping would have done a lot of damage, but it would never have been as critical and deadly as the levees actually breaking (and creating the flash floods in the Lower Ninth). Again, weren't things alright between the passing of the storm and the levee breaks?

Also, Scott and Ray, take a look at the NYT's interpretation of the Corps' maps. The flooding gets increasingly worse when going from 1 in 50 to 1 in 100 and then 1 in 500 year scenarios. I can't get Google Earth to come up at work because the IT nazis turned up the user restrictions (and they keep forgetting I'm a developer and should have my computer unlocked, for the love of code), but will look at the overlays in more detail at home before passing final judgment.

It makes sense that the flooding would get worse when going from 1 in 50 to 1 in 500 year scenarios. Catastrophic flooding all the way from the lake to the river is much less likely.

Tchoupitoulas is only shown getting 2-4 feet of flooding in the 500-year flood, which presumably entails massive storm surge and systemic levee failures. You can get bad flooding above sea level...ask Trent Lott.

I wonder if these maps consider spring flood simulations that put the river levee system at risk. Now that we have spillways, how bad of a flood would it take for a river levee failure to flood the city?

The big problem is that NOAA has significantly changed hurricane forecasting. The levees we have were supposed to protect from the 1% storm or better in some cases. With new hurricane modeling, we now find we have less than 1% protection. In effect, the goal posts have been moved. So even though a lot of money and effort has been spent on repairs and upgrades, we are still not there. The estimated date for completion is 2011, so hang on to your hats.

Also, I'm not sure, but I have to think that when IPET talks about damage that occurs even without breaches, they must be talking about New Orleans East and the Lower Ninth. They both took significant quantities of water from overtopping. In the case of the Lower Ninth, the overtopping is what took out the wall. Those houses would have been wet even if the wall had somehow survived.

Peace,

Tim