As Hurricane Katrina stalks the historic city of New Orleans, and massive evacuations are ordered, my thoughts turn to an already-stressed structure located several hundred miles upstream of New Orleans at the distributary channel of the Atchafalaya with the Mississippi River. The Old River Control structure was built by the Army Corps of Engineers to prevent the Mississippi drainage from switching to the steeper Atchafalaya channel.
Geologically, the Mississippi River has switched channels many times to build the Mississippi delta. Today, that change would mean stranding the port economy of New Orleans, with farmers and industries along the lower reaches of the Mississippi without the water they need. The expensive levee system erected along the Mississippi would no longer be needed, while a new levee system would have to be built on the Atchafalaya.
In addition, the Atchafalaya River could not accept the Mississippi flow without massive flooding of the basin's bayous, extensive relocations and the upheaval of the social and economic patterns of the area. Since the completion of Old River Control in 1963, therefore, the Corps of Engineers has striven to prevent the river from jumping channels.
But the water will not be denied forever.
Since 1963 the coastal salt marshes, an important buffer for New Orleans against Gulf hurricanes, have diminished as the basin subsided. The Mississippi River continues to raise its bed in a natural process of stream-bed deposition, even as the surrounding ground sinks lower. The result is a city not only mostly below sea level, but also well below river level. Only the levees (whose bases have also been sinking) prevent the Mississippi from over-running its banks and flooding the streets, even in the driest season.
Also since 1963, the Mississippi has experienced several devastating floods. During the high waters of the Flood of 1973, water undercut the Old River Control structure and nearly swept away an entire sidewall. Rather than lose the control structure, the Corps let the water run through into the Atchafalaya basin, restoring the 70% flow to the lower Mississippi River only after the flood waters subsided. The record-breaking flood of 1993, even though its effects were mostly felt along the upper reaches of the river, also required the control to be let run, which further undercut the structure.
Article comments
— go to most recent comments1 - alpha
Fascinating stuff and amazing how little man can really deal with nature. I like New Orleans and hope the gods turn the monster storm at the last minute or, at least, the worst doesn't happen.
Much is just poor, by-passed Southern city but some, mostly serviced by that streetcar named Desire is beautiful and historic and fun and has a spirit not found in other cities.
Better there than here; but better no where where there are masses of people and beautiful buildings.
2 - Eric Berlin
Great piece, DrPat -- it's amazing and horrifying to grapple with the true and very real forces of nature. Thankfully, I can do it from the safety of California (where we all pray The Big One never comes...).
3 - gypsyman
Well done DrPat.
I've always wondered about the artificial barriers created down that way, I saw a wonderful doc. on PBS years ago about the flood, and that's what first got me thinking about it.
North America is full of places where we have redirected the natural flow of water to suit our needs. We seem to forget that Nature doesn't really give a damn about us. Eventually all that we have wrought will one day be reclaimed.
What's truely unfortunate is all the people whose lives will be affected by the hubris of governments and engineers who thought that nature was something they could control.
4 - DrPat
I've written about McPhee's The Control of Nature before, prompted by mudslides in Southern California. "Atchafalaya" was an eye-opener for me, coming from an engineering background, where the "Can Do" attitude is not an approach to a solution, it's a Gospel.
The waters of the Mississippi will run through the Atchafalaya Basin one day. The laws of physics and entropy both demand it. Old River Control is just a last-gasp appeal from this verdict.
5 - Larry
Comment 3 wrote: Snip . . . "What's truely unfortunate is all the people whose lives will be affected by the hubris of governments and engineers who thought that nature was something they could control."
Whoa, Whoa, WHOA! That is bass ackwards! People move where they shouldn't, because it's cheap, or pretty, or otherwise desirable, then expect their representatives to protect them from their own stupidity. I'll not defend, but don't blame the Government for this one.
Let's see, I'll move to a swamp, then complain it's too wet. Then I'll ask the Gov't. to ditch and drain it, then complain when the dried soil starts self-compacting and sinking. Then I'll demand the Gov't. spend millions to protect me from the river, lake, ocean that surround me. Oh, and by the way, did I mention the threat of hurricanes? I'll now demand even bigger levees to protect me from those! What do you mean, I can only have Category 3 protection? Cat 5 is on the way! Dear Gov't, how DARE you leave me to weather this Mother-of-all-Storms by myself?!?
6 - Nancy
Now, this edges onto a sore subject with me: to what point is the government (that is, the rest of us) responsible for 'rescuing' & setting back on their feet people who persist in living in areas with unstable or recurrent dangerous conditions? I can see helping out those subjected to once in 50-year fluke conditions, but what about those idiots who insist on building homes in California canyons that have a documented history of mudslides every 3-4 years, or the halfwits who insist on setting up in an area where hurricanes (or at least severe storms & flooding) come thru at least annually? There surely is a limit to how much willful stupidity should be encouraged & subsidized?
7 - DrPat
Larry - The purpose of assigning such designations as "40-year events" is to determine how much preparation is appropriate, and how much is ridiculous over-expenditure (per Pareto's principle, the "Law of 80-20").
So the Army Corps of Engineers was given the brief to reduce the loss of lives and property due to the periodic floods on the Mississippi. When people first began levee controls for river flows (ancient Egypt, I believe), they were simply extending and heightening the naturally-occuring stopbanks which a river builds during decades of normal flow.
8 - Nancy
As I just posted on another thread, it's dropped to a cat. 2 once it hit land. Some flooding, but nowhere near what was predicted, ditto wind damages, & no one washed out to sea. Watching the weather channel, I get the distinct impression the media are rather disappointed; they seem to have been hoping for a repeat of 1900 Galveston.
9 - John Aiken
DrPat,
Excellent article. It appears to me that in addition to the danger of which you speak, the disaster striking New Orleans is miniscule compared to what might well happen in the next couple of days or weeks!
As you point out, the major threat now facing Gulf Coast area is that the heavy rainfall from Katrina in the incredible large Mississippi River watershed which is right where what is now tropical storm Katrina is dropping a huge amount of water.
However, it seems to me that the potential disaster of equivalent magnitude, and similar shape, to the Great Mississippi Flood of 1927. One can learn a little bit about that disaster in the Wikipedia encyclopedia which one can find by searching on "Great Mississippi Flood of 1927" with google. One correction to that article; 246 is a ridiculously small number for the number of people killed by that disaster. That may be the number of reported deaths; a characteristic of that disaster was that there was almost no recording of the extant of the disaster. It was a case of "the dead don't talk." Based on other information in the Wikipedia article, I would guess that over a million people died. Others more expert than myself (like you) might have better guesses.
If there river does begin to rise, the Bonnie Carrie spillway may well protect New Orleans from leaks below the spillway, but, taking a lesson from the Great Mississippi Flood of 1927, that is not where most of the damage will occur.
Most historians agree that the "Great Mississippi Flood of 1927" was the greatest natural disaster to strike the U.S. in the last 80 years. You will find claims that the great flood of 1993 was the worst disaster to strike the U.S. in "recent history," but, that is simply weasel-wording - the implicit assumption in such claims is that anything whic h happened for than 70 years ago is not "recent history." The Wikipedia artilce does a good job of explaining all that.
So why is the press not talkiing about it? Well, historically, government press releases have downplayed potential dangers to our country. So one can speculate, but, that's all it is. In my opinion, though, the more people who are aware of immeninent danger, danger which makes 9/11 look like child's play, the better. That's why I am writing this letter.
Yours,
John Aiken, PhD, New Orleans native.
10 - Silas Kain
Great reading, DrPat. I've addressed part of this issue in another thread. I'm looking at this entire disaster as an opportunity and not a loss. We need American hubris now more than ever. Let's just utilize it with a mission that really can be accomplished!
11 - John Aiken
Two Footnotes to my Earlier Post (just two above this one)
1) The possibity of repeat of the "Great Mississippi Flood of 1927" was discussed a few days ago in the "The Quaker Economist" number 130,
link.
The issue is well worth reading.
2) On further reflection it seems unlikely that the levees will be broken. This is based on
a) the N.O. flood stage is 17 feet, 20 is the danger level. Hence there is 3 feet of headroom. That's a lot.
b) Katrina's rain only covers about 25% of the Mississippi floodplain.
c) The Ohio river would carry a lot of Katrina's rain to the Mississippi, so one would expect at least some flooking in Ohio if there would be enough water to break the levees. The TV says that there has not been enough rain to make flooding likely in Ohio.
d) Although three to five inches from Katrina over a four day period is a lot of water, it's not that unusual to have three to five inches of rain, and the fourth day will be in Penn., at the very tip top of the Mississippi River water shed.
In summary, although the possibility of the Mississippi River levees breaking just north of N.O. is still a real possibility, it is not as likely as I previously thought.
John Aiken, PhD, New Orleans Native.
12 - Jay Zeee
WAS a New orleans native.
13 - John Aiken
Good point Jay. Was. My family is devastated and we have little hope that things will ever be the same.
14 - HerbLady
Thanks very much, Dr Pat. I had just got out our copy of The Control of Nature to try to fit this week's news into that context.
Larry, how about the Outer Banks (a very large sand bar) which is drifting north along the Atlantic Coast, leaving a lot of pricey homes and condos perched on their pylons (if I have the right word)? And where people even now are pressuring government to spend money to "stabilize" the dunes?
You have to admire Colorado, which doesn't allow developers to build condos on the avalanche runs, no matter how much money they're willing to pay, how breathtaking the view, or how many self-deluding buyers they are sure to be able to palm them off on.
Here in Kentucky, banks will loan money to build McMansions in flood plain, but not for a young farm couple to buy arable ridge land with an old house on it. A developer could buy the same land, level and pave it in the name of economic development, and thereby contribute his mite to the Mississipppi drainage problem.
Well, after clinging to our ridge through yet another July-August drought, all that an old farm couple can say is, "Thanks for the rain, Kat!" If that sounds heartless, here is what we are doing (have done and will continue to do) to assist the devastated flood region: our sustainable woodlot management, pasture maintenance and cultivation of hay (oh, and gravel driveways) have allowed our 100 acres to absorb all but a tiny fraction of that 6 inches of rain. So whatever consequences people are suffering from their own choices, ours aren't adding to them.
15 - Nancy
Well, obviously whoever was updating the news I was listening to was not very savvy & not paying attention. This is horrendous. My vol. dept. has already sent off our ultra-heavy (duty, that is) rescue squad, an EMT/paramedic team, a trailer of supplies, & the inflatable w/the river rescue & diving teams. So...where are the offers of assistance from other countries, or at least the sympathy cards?
16 - DrPat
The Army Corps of Engineers (which is not all deployed to Iraq) is scrambling to repair broken levees and boost the strength of the levee system throughout the lower reaches of the Big Muddy. This effort is not funded out of disaster assistance, but is part of the emergency plan of the Corps, separately funded.
17 - DrPat
The worry about "stream capture" and its subsequent financial havoc, is ON TOP OF the damage being wreaked by the immediate effects of Katrina. Flooding on the Ohio is not a prerequisite for overwhelming Old River Control -- but the extensive damage to the lower Mississippi's levee system is.
18 - DrPat
Old River Control and much of the current levee system did not exist at the time of the devastating flood of 1927. That diaster (which you correctly point out, John, was not completely documented, and, grievous as it was, may have been underestimated) was the strongest argument the government had for controlling the floods along the river.
Subsidence of the basin around New Orleans has been going on forever. When the river can choose its own channel, and braid freely across the basin, soil deposition keeps up with subsidence -- but that means other basins, like the Atchafalya, gradually become inviting lower than the current riverbed (as is the case today). So we have doubled our trouble, because a) we're not letting the river deposit soil to rebuild the current Mississippi basin and b) we need to build higher and higher walls to keep the flow out of the Atchafalaya Basin.
19 - HerbLady
So, Dr Pat, according to your last sentence in Comment 18, wouldn't everything the Corps is doing per Comment 16 be just more "doubling trouble?" In other words, the more they scramble to keep the existing channel from flooding, the more likely capture by the Atchfalaya will become?
Incidentally, while the Ohio Basin (which has gotten most of Katrina's rain) is only one-third of the Mississippi drainage system, it's the most heavily graded and paved.
20 - DrPat
Yes, HerbLady, that's the Catch-22 of controlling the big river. Everything we do to constrain the water to a given channel (keeping it out of fields, cities, off highways, and under bridges) serves to make the river stronger.
At this point, the Corps needs to keep on with the battle to meet the assignment they have to control flooding. They can't simply decide to let the capture happen, or the waters overrun the levees.
Can you spell "liability"?
21 - daysman
What about the Mississippi River Delta; the eye first made landfall there as a category five eyewall; it went right through the center of the Delta; is the Delta still there?
22 - DrPat
Of course it's still there.
Though it may be largely under water right now...
23 - JR
Waiting for satellite pictures; no doubt the coastline of Louisiana looks a bit different now. We're gonna need new maps.
24 - DrPat
Readers of Mark Twain and residents of the affected states all know that the big river changes all the time. You're right, though, that the Louisiana coast may have been altered sufficiently for the effects to be seen from orbit...
25 - New Search Engine
Nature is cruel! Unfortunately the ground beneath us is constantly moving and shifting or errupting.
I encourage everyone to volunteer for or donate to a hurricane relief fund like UNICEF or the Salvation Army (make sure it is reputable)!