Sunday, January 08, 2006

How Close Did Uptown Come to Getting Hosed?

An anonymous comment on my last post led me to do a little poking around. According to the excellent (and accurate, one can only hope) website of the Army Corps of Engineers, the Corps measured the Mississippi River at Carrollton at 15.5 feet on 29 August 2005. The Corps website allows you to generate your own graph:

It's harder to find exactly what would constitute overtopping. The comment from Anonymous indicates that 20 feet would mean overtopping. Thus, based on what I can figure as an amateur, my house missed getting flooded by a little more than 4.5 feet of surge.

I don't really know exactly how much more storm that would take. The other issue, of course, is that those measurements assume that the levees wouldn't break. After all, the 17th Street Canal did not overtop; it failed. Like everyone else, I look at levees with new eyes now. They're not infallible.

Interestingly, the Corps' website says that the record level for Carrollton was 21.27 Feet on Apr 25, 1922. Does this mean that there was a flood there in 1922? If anyone out there knows, please educate me. Obviously, if anyone out there has real expertise in this area, I welcome an education in this area. I'd love to know what it would take to flood my house on Camp Street in Uptown New Orleans.

You can get the data yourself at this link.


Anonymous said...

According to author John Barry in "Rising Tide" there was no actual overtopping of river levees in the city in the 1922 flood although the river came close to reaching the top of the levee and there was sandbagging in some spots. A crevasse occurred at Poydras and relieved pressure. What would have happened had that not transpired we will obviously never know.

Also, according to the Corps of Engineers the maximum levee height (at Canal St.) is 23 feet.

Seymour D. Fair said...

Ya, I think on the Katrina PBS Frontline a local NO Corps guy said the river raised 11 feet at the Carrollton gauge the morning of Katrina (which matches your graph). The thing to remember is that the river's normal level is low in August . . .

dillyberto said...

It is just amazing to drive to Leake (River Road) and Broadway and look at the platforms in the river at such messed up angles. Bent over not standing. Amazing. You guys say the levees are supposed to be 20 ft or better?

I just kept hearing from those workers on the river that the river was 1 ft or 2 from topping.

Anonymous said...

I'm glad you found the data. After my original query, I attempted to find the data myself. I could not locate it on the Corps web site after being directed their from the NOAA hydrology site (they only track current river/lake issues around the country).

The river was a little higher in February and for longer.

If you want reassurance about the river levees, that's pretty normal for the spring - run plots for several years to see it. The Katrina peak just shows up as an outlier on those long term graphs.

Unless there's a difference based on soil temperature, I'd say you're no worse off during hurricane season. Levees need to stay dry no matter what the season of course. Also, the Mississippi levees are largely armored with concrete on the river side - especially through New Orleans - but also well upriver.

Thanks for finding the data,

Original Anonymous

Anonymous said...

This is what I did find, BTW:

They list 17 foot as flood stage with the 20 foot footnote. Elsewhere in my searching, the action stage is noted.

Tim said...

Two important things to remember about the river levees: they are designed for a more severe flood event than the hurricane levees, and they are 100% owned and operated by the Corps. I think this makes all the difference.

Our brief history shows that since the federal government began taking the river levees seriously (1929), there have been ZERO problems. For hurricanes, we saw flooding in the New Orleans area in 1965, 1969, 2005, and perhaps other years I'm missing.

Mr. Clio said...

Well put. You're actually giving me a little more confidence in the Corps. You should post something along these lines on your blog, or maybe you already have? Thanks for the comment.

Divided responsibility makes for trouble. When everyone's in charge, no one is.

Walking along the river levees does give one more confidence than walking near the canal levees, but I'm no expert (e.g. I'm not one of the levee "experts" like the guys who cut the grass on the tractors).

oyster said...

Perhaps we've had "Zero problems" in terms of overtopping, although I've heard anecdotal reports about seepage on to River Road (or whatever they call it) down by Luling.

And of course the flip side to excellent levees is the causation of wetlands loss down yonder due to lack of replenishing flood sediment.

LatinTeacher said...

Another point to consider, though I don't know the implication, is the speed of the surge or whether the water was just being held up by the wind or if there was any other factor that could have been devastating. A river flowing backwards, for instance, may create havoc on a system designed to deal with water flowing the other way. Also, no one has put "floodwalls" of dubious quality on top of the levee (probably because it is known that they are ineffective.) Was information about water speed and direction given anywhere? Would it matter? Do they even measure stuff like that?

Talking to a friend of mine, I do find it odd that the 17th Street Canal is not just a drainage canal. I mean, it is, but it is also higher than much of the land in its vicinity especially out by the lake. The water has to be pumped UP INTO the canals. I understand that the Industrial Canal has to be that way, but do the Orleans Ave Caanl and 17th St. Canal? What is the advantage to that system and what are the disadvantages? I don't know. Anyone know?