Mississippi River flood of 2011 sets all-time flow record, but has crested

The great Mississippi River flood of 2011 crested yesterday and today, and the volume of water being pushed toward the Gulf of Mexico is the largest ever recorded on the Mississippi, said Bob Anderson, a spokesman for the Army Corps of Engineers for the Mississippi Valley Division. "It's never been this high; it's never had this much water," he said. "There's just a tremendous amount of strain on these levees." The Mississippi crested yesterday at Vicksburg, Mississippi, reaching 57.06'. This exceeded the previous all-time record of 56.2', set during the great flood of 1927. The river crested at Natchez, Mississippi early this morning, and is now falling. The flood height at Natchez was also the greatest on record--61.91', nearly three feet higher than the previous record height of 58', set in 1937. The opening of the Morganza Spillway on Saturday helped to reduce the flood heights from Vicksburg to New Orleans by 1 - 3 feet, greatly reducing the pressure on the levees and on the critical Old River Control Structure (which, as I discussed last Friday, is America's Achilles' heel, and must be protected.) According the National Weather Service, the Mississippi River is no longer rising anywhere along its length, and the great flood of 2011 has likely seen its peak. Rainfall over the next five days will not be enough to raise the Mississippi River water levels above the crests recorded yesterday and today. While it is great news that the flood has peaked, and the Old River Control Structure and all of the mainline levees on the Mississippi River have held, the fight is not over yet. Water levels will stay high for many weeks, and these structures will take a sustained pounding that could still cause failures. If another incredible heavy rain event like we experienced in mid-April occurs in June, the levee system and Old River Control Structure will threatened. Let's hope we don't have an early season Gulf of Mexico tropical storm that makes landfall over Louisiana. The latest 2-week forecast from the GFS model is not hinting at anything like this, fortunately. It's a good thing (for the sake of the levees) that Louisiana experienced severe drought over the winter and spring--had the water levels been high throughout winter and spring, like occurred in the run-up to the great 1927 flood, the levees would have been soggy and much more vulnerable to failure once the big flood crest hit.


Figure 1. The flow of the Mississippi River past the Old River Control Structure near Simmesport, Louisiana reached its all-time highest volume on record Thursday, when the flow rate hit 2.3 million cubic feet per second (cfs). The flow of Niagara Falls at normal water levels is 100,000 cfs, so the Mississippi's flow was 23 times that of Niagara Falls. Image credit: Army Corps of Engineers.

Recommended reading
My post on the Old River Control Structure, America's Achilles' heel: the Mississippi River Old River Control Structure, is well worth reading, if you haven't done so. I plan on making a follow-up post next week discussing the economic cost of the failure of this critical flood-control structure.

Our weather historian, Christopher C. Burt, has made a very interesting post on the greatest floods to affect each continent.


Figure 2. Track forecast for Tropical Storm Four.

First typhoon of 2011 coming?
In the Northwest Pacific, Tropical Storm Four has formed, and appears poised to become the first typhoon of 2011 by early next week. The storm is expected to head west-northwest or northwest towards the Philippines. While the GFS model predicts Tropical Storm Four will miss the Philippines and recurve northwards towards Japan late next week, it is too early to be confident of this forecast.

Have a great weekend everyone, and I'll be back Monday with a new post.

Jeff Masters