Worst Case Scenario is if storm hits just EAST of NOLA

[logybogy]

http://www.nola.com/hurricane/index.ssf ... one_1.html

"The worst case is a hurricane moving in from due south of the city," said Suhayda, who has developed a computer simulation of the flooding from such a storm. On that track, winds on the outer edges of a huge storm system would be pushing water in Breton Sound and west of the Chandeleur Islands into the St. Bernard marshes and then Lake Pontchartrain for two days before landfall.

"Water is literally pumped into Lake Pontchartrain," Suhayda said. "It will try to flow through any gaps, and that means the Inner Harbor Navigation Canal (which is connected to Breton Sound by the Mississippi River-Gulf Outlet) and the Chef Menteur and the Rigolets passes.

"So now the lake is 5 to 8 feet higher than normal, and we're talking about a lake that's only 15 or 20 feet deep, so you're adding a third to a half as much water to the lake," Suhayda said. As the eye of the hurricane moves north, next to New Orleans but just to the east, the winds over the lake switch around to come from the north.

"As the eye impacts the Mississippi coastline, the winds are now blowing south across the lake, maybe at 50, 80, 100 mph, and all that water starts to move south," he said. "It's moving like a big army advancing toward the lake's hurricane-protection system. And then the winds themselves are generating waves, 5 to 10 feet high, on top of all that water. They'll be breaking and crashing along the sea wall."

Soon waves will start breaking over the levee.

"All of a sudden you'll start seeing flowing water. It'll look like a weir, water just pouring over the top," Suhayda said. The water will flood the lakefront, filling up low-lying areas first, and continue its march south toward the river. There would be no stopping or slowing it; pumping systems would be overwhelmed and submerged in a matter of hours.

"Another scenario is that some part of the levee would fail," Suhayda said. "It's not something that's expected. But erosion occurs, and as levees broke, the break will get wider and wider. The water will flow through the city and stop only when it reaches the next higher thing. The most continuous barrier is the south levee, along the river. That's 25 feet high, so you'll see the water pile up on the river levee."

[TSmith274]

I've always heard that one coming up the mouth of the Mississippi was the worst case. One of the scenarios mentioned in that article is a hurricane making landfall in Mississippi! After reading that, we really need Ivan to stay far enough east. That article worries me. Do any of you New Orleanians on this board know how high the Lake Ponchartrain flood wall is?

[FloridaHawk82]

I am literally sick to my stomach after reading that article, and I live in SE Florida... if you are a believer, prayers can't hurt right now.

I hope CaliDoug reads this... and then ponders his Mobile/DoubleWide comment he just made in another thread.

[calidoug]

What do you have against DoubleWides? They are top of the line.

[TideFreak]

If it makes landfall just to thye west of us, ie Mobile, Pensacola, as you all know we all will get the very worst in all areas from Ivan
Everyone hunker down and take care

[dirtgirl]

these were posted a few days ago but I thought incredibly helpful in understanding "the bowl":

http://www.nola.com/hurricane/images/nolalevees_jpg.jpg

http://www.nola.com/hurricane/images/goingunder_jpg.jpg

look at those and you'll see visually what logybogy is describing here.

[arcticfire]

these were posted a few days ago but I thought incredibly helpful in understanding "the bowl":

http://www.nola.com/hurricane/images/nolalevees_jpg.jpg

http://www.nola.com/hurricane/images/goingunder_jpg.jpg

look at those and you'll see visually what logybogy is describing here.

Seems to me that someone should have thought of installing gates in the river wall. If the above scenario happened the wall along the river would basicly cause more harm then good since the water could not run off into the mississippi. In a way All those levies have created the potential for a man made lake to apear where NO once was.

[vbhoutex]

Unless I have missed something, and I know the NO situation pretty well, how is water from an area that is below sea level going to run off into the river? On top of that, in the situation described the river is going to be above normal levels also, to say the very least.

[wabbitoid]

arcticfire, yes.

The only other possibility I can think of is that since most of the levees are earthen, they will erode as a new channel is cut to the SW to relieve Ponchartrain. That could leave the whole SE Lousisiana under 7' of silt and 3' of water.

[arcticfire]

Unless I have missed something, and I know the NO situation pretty well, how is water from an area that is below sea level going to run off into the river? On top of that, in the situation described the river is going to be above normal levels also, to say the very least.

Well granted I was just looking at the wall system showed in the pics. Are you saying the river actually flows above the city level ? That wouldn't really make sence to me. So if the river is actually flowing on the same level as the streets on either side of it with a 25ft wall seperating the two then a gate would actually allow for runoff.

If you are saying the river walls basicly act like a Dam and the river does actually flow above street level then your right there would be no ability to have runoff once NO was underwater.

So basicly my question is this , does the river flow threw NO at sea level or at NO level?

[kevin]

So basicly my question is this , does the river flow threw NO at sea level or at NO level?<<

If the river was below sea level, how would it go into the ocean?

[arcticfire]

So basicly my question is this , does the river flow threw NO at sea level or at NO level?<<

If the river was below sea level, how would it go into the ocean?

I am obviously tired as that would be the obvious answer. But it still makes me ask the question how could you hold back a river thats flowing higher then you are ? I'm 5'7''. If I was standing on a NO street my head would basicly be under sea level. If the river has to be above sea level to flow into the sea that means the river is above my head also. How on earth would you hold back a river like that ?

[FritzPaul]

The city is below sea level that is why we are surrounded by levees and the city is full of intricate canals and pumping stations.

[gratefulnole]

So basicly my question is this , does the river flow threw NO at sea level or at NO level?<<

If the river was below sea level, how would it go into the ocean?

The river is up to 15 ' above sea level, varying with time of year. The city is a few feet below sea level. To see the river or the lake in New Orleans, you have to walk up hill.

I love visiting that city and hope it makes it through Ivan okay!

[arcticfire]

The city is below sea level that is why we are surrounded by levees and the city is full of intricate canals and pumping stations.

Well obviously then you have figured out a way to hold back the water. If you ask me thow this whole scenario is basicly doomed to happen one day (not tommarow I don't think). It will be horrible no doubt , but at the same time the idea of building a city purposfully surrounded by water higher then the ground is risky at best. I'm no levee expert or anything , I can only say you better pay those levee maintence people well so they do a good job.

[wabbitoid]

arcticfire, you are begining to appreciate just how precarious this situation is.

The walls holding back Ponchartrain are 15-20 feet high. It is entirely possible that water will top them by more than 5 feet, which is to say that those levees do not actually exist for all practical purposes.

Most people's understanding of the hydrology comes from an understanding of the levee system -- but if the Lake is well above that, it becomes a simple matter of where the water can go downhill fast. That would be right over the city, eroding down everything in its path and cutting a new channel.

[arcticfire]

Also thx everyone for your patient replies while I tried to wrap my brain around this concept of living below the water. I live in anchorage alaska myself and the only thing we build even close to that low is a dock to it took a bit of mental rearanging to comprehend that.

[opera ghost]

NO wasn't below sea level when it got started. It's sunk over the years and people are reluctant at best to leave even knowing the risks. (Refering to the building a city below sea level comment)

I'm still wondering how far away the storm has to go before NO is truely safe....

[FritzPaul]

Blame it on the French for founding it here. LOL

[gratefulnole]

Also thx everyone for your patient replies while I tried to wrap my brain around this concept of living below the water. I live in anchorage alaska myself and the only thing we build even close to that low is a dock to it took a bit of mental rearanging to comprehend that.

Look at a map of Louisiana and notice how it juts out around the mouth of the Mississippi. All that land was created from silt coming down the river. Additionally the river naturally wants to move where it dumps into the Gulf from time to time. Levees were put in to keep the river from moving. Though 200 years ago the city was at river level, New Orleans is built on soft ground that is no longer recieving silt from the Mississippi so it is slowly sinking. Levees have been built around it to keep the water out.