A look at weather extremes and the big-picture climate connections.

Historical Context of the Mississippi River Floods

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Flooding of the Mississippi River in Memphis, Tennessee, on April 30, 2011. Credit: sheknitsone/flickr.

The Army Corps of Engineers is currently using every tool in its arsenal to manage the surge of floodwaters moving down the Lower Mississippi River towards New Orleans and the Gulf of Mexico. The flooding, triggered in large part by relentlessly heavy rains in the Ohio Valley during the past few months, has broken records in numerous locations, and forced the corps to make wrenching decisions of whether to inundate some communities and farmlands in order to spare more heavily populated areas.

This is not the first time the Mississippi has escaped its banks to reclaim parts of its fertile historical floodplain. The benchmark of modern Mississippi floods was set way back in 1927, when the Mississippi was transformed into an inland sea of up to 100 miles in diameter. Thousands died during that "Great Flood" event, which is still considered one of the worst natural disasters in the history of the United States.

To get a historical perspective on the current flooding, I spoke with John M. Barry, who wrote the definitive account on the 1927 flood: “Rising Tide: The Great Mississippi Flood of 1927 and How it Changed America.” In addition to chronicling that event, Barry also plays an active role in managing waterways, as the vice president of the Southeast Louisiana Flood Protection Authority East, which manages three levee districts in metropolitan New Orleans.

Here is an edited transcript of our conversation, which took place on May 10.

AF: I’m looking to see if you can put this current event that’s taking place, where a lot of the records from 1927 are being threatened, and some records from 1937 are being broken as well, into perspective.

JB: First off… most of the water for Mississippi River floods always comes out of the Ohio River. If you don’t have a flood coming out of the Ohio, you are not going to have a flood on the lower Mississippi. So the three greatest floods coming out of the Ohio were probably this one first, ‘37 second and ’27 third.

The difference between ‘27 and these floods is that in ‘27 an enormous amount of water came out of the Arkansas and the White [Rivers], so that was added to a significant but not a record flood coming out of the Ohio…

When you added something approaching well over 800,000 cubic feet per second coming out of the Arkansas and the White [Rivers], then things really started to get serious. That’s why the records above the mouth of the Arkansas are from ‘37, some of them have been broken, some of them still hold, that includes the Memphis records…the reason some of the records may be broken or have been broken is because there were levee breaks [in 1927] that let enormous amounts of water out of the Mississippi River.

The record on the Vicksburg gauge was set on May 4th, which is the same day that there was a break just above Vicksburg on the Louisiana side, which flooded all the way to Monroe, which is 75 miles away.

So if the water had been contained within levees, which was a physical impossibility, the records would have been at least four, and maybe five to six feet higher than they were. When you look at it in that context, this flood would not threaten those records. So there was clearly a hell of a lot more water in the river in 1927. That does not in any way denigrate this flood, this is a great flood, this is a serious situation.

AF: Is that partly just because of where the heavy rains were at that time versus the heavy rains this time around, because most of the heavy rainfall anomalies during the past couple of months have been in the Ohio River Basin and down towards the Tennessee River Valley, rather than farther south.

JB: Well in 1926 it started raining in August and didn’t stop. The average river gauge for every single river in the entire Mississippi River system which had gauges, so that’s certainly the Ohio, the Mississippi itself and the Missouri, and probably the Arkansas, had the highest averaged reading for the last three months of 1926 ever known, so the entire basin was in flood.

The Mississippi flood of 1927. Credit: jwinfred/flickr.

In Vicksburg, the gauge in October had never broken 31 feet, and in October 1926 it broke 40 feet. So you already knew if you had any rain in the spring of 1927 you were going to have a flood. And the rain continued over the entire basin and that’s the result. There was just a tremendous amount of rain over the entire basin. There was more rain over the Ohio Basin, more precipitation this year than in ‘26 and ‘27, but that’s really the only basin that got serious precipitation.

On the Arkansas, most of that area that drains [into the Mississippi River] has a drought, fortunately, or we would be in real trouble. The Arkansas is only carrying 22 percent of the design project flood, the maximum anticipated flow out of the Arkansas... If it were even at 50 percent or 60 percent this would be a much more serious situation.

AF: What comes to mind in terms of adapting to the ebbs and flows of this river which, clearly, historically has had massive floods, and yet we still keep trying to control the river.

JB: Well I don’t think we’re trying to control the Lower Mississippi. I think the big lesson from 1927 is that you can’t control it; you can try to contain it. I think that the argument over floodplain management is a very good argument, and I am by no means on the side of developing and building levees in all cases. But when you get to the lower part of the river, they do have a good comprehensive system with handling the river.

When this flood is over, if the system works perfectly, there will probably be five to 6,000 square miles that were flooded, so they are using part of the river’s floodplain to manage the river, that’s without the Morganza Spillway being opened. If you add Morganza [which was opened after this interview took place] that’s another 2,000 square miles – that’s a pretty significant flood, you’re talking five to six million acres, and that’s with everything working, because they are allowing the river to use some of the floodplain, and that still is going to flood thousands of people.

I think the argument is better made for other areas of the country, where they never really looked at the river in any kind of comprehensive way, it’s not just the Mississipi obviously, the question applies to pretty much any river system. I think the most intelligent management is applied to the Lower Mississippi River system of any river basin in the US that I know of.

AF: Why is it that the management of the Lower Missippi River has been different, is it just because of differences in land ownership and land use, or is there a different reason?

JB: Well, it’s because of the ‘27 flood, it’s very clear. You had the river reclaim almost its entire natural floodplain in 1927. You had 27,000 square miles under water, the river at its widest point was more than 100 miles across...

So some recognition entered people’s consciousness that this force is just too big to contain between some walls on the riverbank…

Although there have been many times when I’ve been quite critical of the corps, on the management of the Lower Mississippi River floods, I think they’ve done a pretty good job in the last 50 or 60 years.

When you look at the entire Mississippi River Basin I would give them an “F,” and the main reason is that they have entirely ignored the impact… of things like sediment retention behind the Upper Missouri River dams on coastal Louisiana and other aspects of management where they have had significant influence on what happens to coastal Louisiana.

For the purposes of flood prevention in Montana, North Dakota, South Dakota, Omaha, Nebraska and so forth, you have dramatically increased the danger for southern Louisiana… the Mississippi River, by the deposit of sediment, created all the land in its floodplain from Cape Giraudoux, MO to the present mouth of the river, that’s in total about 35,000 square miles… Then coastal currents took sediment from the mouth of the river and carried it mostly west and a little bit to the east, and built another 5,000 square miles of land. So you’ve got a total of 40,000 square miles that were created, actually built, by sediment coming out of the Mississippi River.

Everyone agrees less than half of the historic sediment load that used to be in the river is still in the river now… most of the scientists I’m familiar with think it’s down to about 30 percent of what the historic load is. Of the sediment that is missing, half of all of it is sitting behind six dams on the Upper Missouri river, and that has had a dramatic impact I think, although they are by no means the only cause, of the erosion of 2,300 square miles of coastal Louisiana. I think the Corps of Engineers is certainly at least partly responsible for the construction of those dams...

So the whole management of the system has been ignored. There has been no management, there has been no effort to manage the entire [Mississippi River] system.

See this related story for details of how climate change is making heavy rainfall events more likely to occur in North America.

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