More Questions About Possible N.O. Flooding

[Hurrilurker]

So we all know that if Ivan directly hits New Orleans, it's going to be flooded and be a disaster. Everyone seems to agree on that. But, has anyone calculated just what conditions would be necessary for it to start flooding (IOW, partially flood)? Assuming, let's just say for the sake of argument, Cat 3 strength, and a median tide, how far away would Ivan's eye have to strike before flooding begins? 25 miles? 100 miles? And my corollary question is, does anyone have tide schedules for along the Gulf Coast for the anticipated lanfall time (looks like early Thursday morning)? I assume it could make a large difference for N.O. if the storm hits at high vs. low tide?

[Sean in New Orleans]

It won't be long before we have low land flooding---it's probably already begun. Lake Pontchartrain has risen almost 3 feet today from Ivan....

[goodlife]

Well...as the storm approaches it's pushing water into the mouth of the river and also into Lake Pontchartrain....
For this storm what they said earlier tonight is that the lake has already risen over 2 ft. since 4 this afternoon...expected to rise over 5 ft before the storm gets here...and then the storm surge..depending on where Ivan decides to make landfall...but it if makes landfall in the Gulfport/Biloxi area then they are talking up to 15 ft....add that to the 5 ft the lake has already risen and you're talking about 20 ft. As the storm moves in...the winds will be from the northeast pushing all of that water into the new orleans area....I do believe the levees are about 8 ft.
Disaster...once the water goes in...there's no way to get the water out.

[Possum Trot]

Try the Tide Server:
http://66.135.8.10/tideserver/

[Rob Beaux]

Sean where that 3 ft data from... I see a small rise at the LUMCON weather station.

http://weather.lumcon.edu/chartdata/def ... hartType=5

Just curious if you have another online source.

[wabbitoid]

Disaster...once the water goes in...there's no way to get the water out.

At the risk of being called an alarmist, goodlife, I believe the water will all find its way out by creating a new channel to the Gulf. Most of those levees are earthen, so once the water washes over them by 5-10 feet they will erode. I have never bought the "fill the bowl" model, as I think water will just exit to the south and west.

The second punch comes when the backed up Mississippi, newly swollen by 20" of rain in the whole valley, runs back down again. This will probably take out anything that wasn't part of the drainage of Ponchartrain.

I'm afraid that just East can be a true nightmare, as the water is thrown up the Mississippi and into Ponchartrain at the same time.

I pray I am wrong, or that we never find out.

[goodlife]

I like the never find out part better....

[FritzPaul]

Wabbitoid since your not familiar w/ south LA geography, I'll fill you in.

The "bowl" is because NO is completely surrounded by levees, so if the levee gets topped, then water fills up the city. Therewouldn't be any way to get the water out sans breaking the levee after the storm.

The MS river doesn't directly connect to lake Pontchartrain, but there is a spillway that does.
This is only used to let water out of the river during the spring when river water is to high from melting snow up north.

[Rob Beaux]

Fritz there is a plan in place to open the spillway to let the lake water drain into the river. THere is also a few locks to let the water in the bowl out, at the intercoastal canal, Bayou Beinvenue, Lake Cahtherine and even at Violet. Just have to think in reverse, if they closed the gates to stop the flow in, they can open them to let the flow out.

There is also a plan in place to blow up part of the levee at Carnarvon to drain the city. This is a area which is used to divert fresh water from the river into the marshes south of the city.

Someone posted the levee diagrams on here a few days ago. I forgot who and the thread title.

[FritzPaul]

Good point!

I think I read his post wrong. It didn't seem to match the topography here.

[wabbitoid]

Fritz:

What I am saying is that if Ponchartrain swells by 20 feet or more, the levees are topped by 5 feet in places. For practical purposes, they don't exist.

Note that the storm surge could be even more than that with a cat 4 just to the east.

As a local, you're assuming the levees protect you -- they may not be able to if this thing comes in just right.

What I'm saying is from the mouth of the Mississippi draw a 100 mile circle counter-clockwise. That's the path of the storm surge. See where it goes.

[LSU2001]

but what about the parts of the city below sea level. This would not drain would it?

[Rob Beaux]

New Orleans have pumps which run 24 hours a day to keep those areas dry. I assuem they woud be fixed and turned on to empty the water. I fI ma not mistaken the New Orleans pumps are some of the best ones in the country for storm water drainage.

[Psychonaut777]

What happens to those pumps in the case of power loss?

[flightpath]

not all pumping stations can generate their own power so if power goes down so do pumps.

[FritzPaul]

Pump don't work underwater.

Their capacity is 1"-2" of rain per hour, and of course the levees being topped would excede their capacity.

[wabbitoid]

Well, the latest update makes it look like it'sll stay enough to the east, so I hope this whole discussion doesn't matter at all.