# Probability of New Orleans Flooding **URL:** \ **Category:** Factual Questions\ **Created:** [September 15, 2004, 12:31pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539 "2004-09-15T12:31:34Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Kel\_Varnsen\_Latex\_Division](https://avatars.discourse-cdn.com/v4/letter/k/aeb1de/32.png) [@Kel\_Varnsen\_Latex\_Division](https://boards.straightdope.com/u/Kel_Varnsen_Latex_Division)\ **Post date:** [September 15, 2004, 12:31pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/1 "2004-09-15T12:31:34Z")
What is the probability that New Orleans will flood shen Ivan hits land? ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [September 15, 2004, 12:36pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/2 "2004-09-15T12:36:18Z")
Well! I was about to start a new thread, but it was such a similar question that I’ll just piggyback on this one: How does New Orleans drain itself? I’ve been hearing over and over again in the past few days that New Orleans is below sea level. It’s also on the Gulf Coast, which rather begs the question of why it isn’t already under water, and thus part of the Gulf and not the Coast. ---
**Author:** ![World\_Eater](https://avatars.discourse-cdn.com/v4/letter/w/f04885/32.png) [@World\_Eater](https://boards.straightdope.com/u/World_Eater)\ **Post date:** [September 15, 2004, 12:45pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/3 "2004-09-15T12:45:13Z")
> [@Kel Varnsen - Latex Division](#): > > What is the probability that New Orleans will flood shen Ivan hits land? According to this… [http://www.cnn.com/2004/WEATHER/09/15/hurricane.ivan/index.html](http://www.cnn.com/2004/WEATHER/09/15/hurricane.ivan/index.html) > [@](#): > > In New Orleans, Mayor Ray Nagin said there was a **22 percent chance** his city would take a direct hit from Ivan. Since most of the city lies below sea level, surrounded by levees along the Mississippi River, the result would be a catastrophe, he said. > > “If we get a storm like Ivan to hit us directly or to become really close to us, then we could have a situation where we have **12 to 18 feet of water** throughout the city,” Nagin said. I’d love to know how they came up with 22% ---
**Author:** ![Kel\_Varnsen\_Latex\_Division](https://avatars.discourse-cdn.com/v4/letter/k/aeb1de/32.png) [@Kel\_Varnsen\_Latex\_Division](https://boards.straightdope.com/u/Kel_Varnsen_Latex_Division)\ **Post date:** [September 15, 2004, 1:01pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/4 "2004-09-15T13:01:14Z")
Does it require a direct hit? I thought a hit to the west of New Orleans could be just as bad. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 15, 2004, 1:06pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/5 "2004-09-15T13:06:12Z")
> [@](#): > > How does New Orleans drain itself? [From this site](http://www.edsite2.fsnet.co.uk/neworleans.htm): > [@](#): > > Most of New Orleans is below sea level and at the present time it relies on the world’s greatest systems of drainage pumps to keep the water in check. The systems 112 pumps can draw off 25 Billion gallons of water a day. Also 130 Miles of walls (levees) have been built to prevent floods. [More results from google](http://www.google.com/search?num=100&hl=en&lr=&ie=UTF-8&c2coff=1&q=%22new+orleans%22+%22below+sea+level%22+pumps+levees). ---
**Author:** ![El\_Kabong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/el_kabong/32/496_2.png) [@El\_Kabong](https://boards.straightdope.com/u/El_Kabong)\ **Post date:** [September 15, 2004, 1:08pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/6 "2004-09-15T13:08:29Z")
> [@](#): > > I’d love to know how they came up with 22% Probably from [this](http://www.nhc.noaa.gov/text/refresh/MIASPFAT4+shtml/150839.shtml?). ---
**Author:** ![World\_Eater](https://avatars.discourse-cdn.com/v4/letter/w/f04885/32.png) [@World\_Eater](https://boards.straightdope.com/u/World_Eater)\ **Post date:** [September 15, 2004, 1:08pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/7 "2004-09-15T13:08:42Z")
> [@Kel Varnsen - Latex Division](#): > > Does it require a direct hit? I thought a hit to the west of New Orleans could be just as bad. IIRC in the article they said if the eye is slightly east of the city when it hits, that would be the worst case. I think the waves would be worse or something. Maybe because the thing is swirling around clockwise? I’m talking out of my ass here though. ---
**Author:** ![Chairman\_Pow](https://avatars.discourse-cdn.com/v4/letter/c/838e76/32.png) [@Chairman\_Pow](https://boards.straightdope.com/u/Chairman_Pow)\ **Post date:** [September 15, 2004, 1:17pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/8 "2004-09-15T13:17:26Z")
That’s a lot of freakin’ water. Here’s another one: assuming that NO does flood, how will they even try to drain it? Another article mentioned that the Army Corps of Engineers will have to break all the levys, but since they’re still below sea level, that doesn’t sound like it will help much. Will they just have to pump for several weeks? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 15, 2004, 1:20pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/9 "2004-09-15T13:20:05Z")
> [@](#): > > Maybe because the thing is swirling around clockwise? In the northern hemisphere low-pressure areas spin anti-clockwise. ---
**Author:** ![Fiver](https://avatars.discourse-cdn.com/v4/letter/f/e274bd/32.png) [@Fiver](https://boards.straightdope.com/u/Fiver)\ **Post date:** [September 15, 2004, 1:29pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/10 "2004-09-15T13:29:45Z")
> [@Johnny L.A.](#): > > [From this site](http://www.edsite2.fsnet.co.uk/neworleans.htm): > > [More results from google](http://www.google.com/search?num=100&hl=en&lr=&ie=UTF-8&c2coff=1&q=%22new+orleans%22+%22below+sea+level%22+pumps+levees). But the city is 300+ years old, **Johnny L.A.**. It didn’t always have pumps and levees, so there must also be a natural way for it to drain. ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [September 15, 2004, 1:33pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/11 "2004-09-15T13:33:18Z")
Usually it’s better to be slightly south or west of the eye, since the leading edge of the storm has already passed over land. I think that New Orleans is different in that the Gulf waters are closest to the northeast. Ignoring the storm surge, the rain waters alone might overwhelm a system of drainage pumps, but storm tides can be as high as fifteen feet above mean sea level. I don’t know how connected the Mississippi is to the ocean at New Orleans; I assume that there are a lot of swamps at that point. I do know that the bay side of Galveston Island was under several feet of water during Carla, and that land had been raised several feet above sea level to prepare for such an event. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [September 15, 2004, 1:34pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/12 "2004-09-15T13:34:32Z")
> [@World Eater](#): > > IIRC in the article they said if the eye is slightly east of the city when it hits, that would be the worst case. I think the waves would be worse or something. Maybe because the thing is swirling around clockwise? I’m talking out of my ass here though. It a hit just to the west that is the worst case. The storm surge is highest just east of a counterclockwise-rotating storm that hits the Gulf Coast. I forget the exact number, but every time a hurricane approaches the coast, the local news quotes the height of the lowest seawall (maybe 18 feet?), and if the seas get higher than that, it’s bad news. In my lifetime the closest the seas ever got was within a couple of feet. Here’s a map of the [wave forecast](http://www.weather.com/maps/news/atlstorm9/waveforecast_large.html) from [weather.com](http://weather.com) . ---
**Author:** ![micco](https://avatars.discourse-cdn.com/v4/letter/m/5f8ce5/32.png) [@micco](https://boards.straightdope.com/u/micco)\ **Post date:** [September 15, 2004, 1:38pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/13 "2004-09-15T13:38:48Z")
> [@Fiver](#): > > But the city is 300+ years old, **Johnny L.A.**. It didn’t always have pumps and levees, so there must also be a natural way for it to drain. New Orleans is [sinking](http://www.time.com/time/reports/mississippi/orleans.html) at a rate of up to 3 feet per century. It wasn’t nearly as bad a location for a city 300 years ago. ---
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [September 15, 2004, 1:39pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/14 "2004-09-15T13:39:50Z")
So how did they settle the place a few hundred years ago before the advent of pumps and levees? ---
**Author:** ![aruvqan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aruvqan/32/2891_2.png) [@aruvqan](https://boards.straightdope.com/u/aruvqan)\ **Post date:** [September 15, 2004, 1:40pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/15 "2004-09-15T13:40:21Z")
😃 Given that just a heavy rainstorm will have 4-6 inches of water standing on the ground, I would think that _just_ the ancilliary rain from the storm will have at least that much water…adding storm surge on top of that ! Was in New Orleans in 89, was the tail end of the rainy season and we arrived at the end of a 3 day rainstorm. We had planned on camping in our tent but had to get a kamping kabin at the KOA as there was ankle deep water everywhere…boy was the dog we had at the time pissed! she hated being inside buildings and we had to bring her inside with us. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 15, 2004, 1:40pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/16 "2004-09-15T13:40:38Z")
> [@](#): > > But the city is 300+ years old, **Johnny L.A.**. It didn’t always have pumps and levees, so there must also be a natural way for it to drain. From the first link: > [@](#): > > The City was founded in 1718 by Jean Baptiste le Moyne, Sieur de Bienville… > > The original city was laid down by the French engineer Adrien de Pauger, and a series of three foot high levees were built to keep out the flood water, and canals built to drain off the land. So levees and canals were there from the beginning. But you may ask, “If it’s below sea level, why wasn’t it flooded in 1718?” Hell if I know. It was always a swampy area, so maybe it _was_ under water much of the time. I suppose that there was naturally wet and dry periods. Once the levees and canals were built, and later, the pumps added, it was possible to keep it fairly dry most of the time. The levees were built up, and the ones I’ve been on were more than three meters high. Another thing to consider is that the path of the river used to change over time – over hundreds of years. The mouth of the river would “wag” east and west as sediments built up in the delta. When the city was built this natural cycle was interrupted. The river “wants” to move, but human structures have prevented it. Eventually, Nature will prevail. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [September 15, 2004, 1:45pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/17 "2004-09-15T13:45:16Z")
> [@Kel Varnsen - Latex Division](#): > > Does it require a direct hit? I thought a hit to the west of New Orleans could be just as bad. Other stories I’ve come across say the biggest danger is that northerly or northeasterly winds would blow Lake Ponchartrain over its levees and into the city. The lake is huge and shallow, and easily affected by wind. A direct hit by the eye wall would cause the most wind damage, but a slightly-eastern track might cause more flooding. It’s a little disconcerting to be in Jackson Square, right in front of the Cafe du Monde, and look something like 20 feet \*up \* at the ships passing by. ---
**Author:** ![Papermache\_Prince](https://avatars.discourse-cdn.com/v4/letter/p/f05b48/32.png) [@Papermache\_Prince](https://boards.straightdope.com/u/Papermache_Prince)\ **Post date:** [September 15, 2004, 2:02pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/18 "2004-09-15T14:02:46Z")
Does anyone know what the evacuation plans are for those without cars? According to this [AP article](http://abcnews.go.com/wire/US/ap20040915_256.html), > [@](#): > > {There are an} estimated 100,000 people in New Orleans who rely on city transportation to get around, making evacuation impossible for them. Yet, no shelters were open in the city as of Tuesday night and there were no plans to open any. . . .The city was working on setting up a shelter of “last resort,” Mayor Ray Nagin said. No shelters had been set up yet because of concerns about flooding and capacity, Nagin added. . . . .The mayor said that he would “aggressively recommend” that people evacuate, but that it would difficult to order those who rely on public transportation to do so, since they would have no way to leave. In addition, he said 10,000 people were in town for conventions and there was nowhere for many of them to go except high floors in their hotels. ---
**Author:** ![World\_Eater](https://avatars.discourse-cdn.com/v4/letter/w/f04885/32.png) [@World\_Eater](https://boards.straightdope.com/u/World_Eater)\ **Post date:** [September 15, 2004, 2:04pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/19 "2004-09-15T14:04:27Z")
Ah thanks guys, I stand corrected. ---
**Author:** ![bordelond](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bordelond/32/150_2.png) [@bordelond](https://boards.straightdope.com/u/bordelond)\ **Post date:** [September 15, 2004, 4:41pm UTC](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539/20 "2004-09-15T16:41:16Z")
> [@Chairman Pow](#): > > That’s a lot of freakin’ water. Here’s another one: assuming that NO does flood, how will they even try to drain it? Another article mentioned that the Army Corps of Engineers will have to break all the levys, but since they’re still below sea level, that doesn’t sound like it will help much. Will they just have to pump for several weeks? New Orleans native checking in. New Orleans has minor floods often, and major ones maybe once or twice a decade. The pumping stations do run around the clock in the event of a major flood. Evaporation also takes care of a lot of flood water. > [@cornflakes](#): > > Ignoring the storm surge, the rain waters alone might overwhelm a system of drainage pumps, but storm tides can be as high as fifteen feet above mean sea level. I don’t know how connected the Mississippi is to the ocean at New Orleans; I assume that there are a lot of swamps at that point. The Mississippi River is pretty far from the ocean (aka the Gulf of Mexico) at New Orleans. New Orleans really can’t be considered a coastal town the way Galveston can. There’s quite a bit of what “wetlands” (swamps, marshes, and slightly-flooded forest) separating the far southern suburbs of New Orleans from the Gulf. These wetlands make up the “toe” of the “boot” that is Louisana … and why Louisiana juts into the Gulf with no beachfront, where as Mississippi, Alabama, and Florida have coastal beaches on the Gulf. The wetlands also give a significant degree of protection from hurricanes hitting New Orleans from due south. A hurricane coming up the mouth of the Mississippi River towards New Orleans – from due southeast – is a different animal. It is though that a hurricane coming from due southeast could maintain strength from water at the wide part of the river as it made it’s way to the city. Consider also: the Port of New Orleans is a river port, not an ocean port – but it just so happens that ocean-going ships can navigate from the mouth of the river up to New Orleans (maybe 80-100 miles). … **Fiver** , see my comments above. New Orleans really can’t be considered to be on the Gulf Coast. The closest drive to the actual Gulf Coast is about an 45 minutes northeast of the city, to the vicinity of Waveland, Mississippi. Heading due east, southeast, and south from the city, it would take even longer to reach the Gulf (where it’s even passable throught the wetlands. [Next page](https://boards.straightdope.com/t/probability-of-new-orleans-flooding/264539.md?page=2)