My knowledge of the Upper Mississippi is very limited. I had never been to St. Louis until three and a half years ago, and I was surprised at how narrow the river was there.
If you look at maps of the Mississippi at the confluence of the Ohio, you see all that water coming out of the Ohio changes things on the Mississippi. When your flow more than doubles at one point, things happen. If anyone can direct me to a good site or book explaining how the Ohio changes the Mississippi both above and below the confluence, I would appreciate their passing it along.
Now, having said all that, I found this article about how the Upper might be carving a new channel from about Mile 15 to Mile 34, in an area called Dogtooth Bend. The reason this comes to the attention of an Ohio River site is here in this part of the conclusion:
The USACE/MRC mission includes the maintenance of the mainline levees that protect Cairo, Illinois, and the Illinois, Missouri, Kentucky, and Arkansas bottomlands and the maintenance of navigation on the Mississippi River. The USACE cannot strengthen the existing Len SmallFayville levee without increasing the risk of losing their own mainline levees (Cairo levee and floodwall, the Commerce to Birds Point levee and the New Madrid Floodway setback levee). If the Cairo floodwall and levee were to fail, it would put nearly 3,000 residents and 400 structures at risk. If the Commerce to Birds Point levee or the New Madrid Floodway setback levee were to fail, 800,000 ha (2,000,000 ac) in Missouri, Kentucky, and Arkansas bottomlands could be flooded with both crops and soils damaged. The opening of the New Madrid Floodway can be used to reduce the pressure and peak height by as much as 1.2 m (4 ft) on confluence area levees (Olson and Morton 2012). The floodway was used in 1937 and 2011. There is a need for additional floodwater storage in the confluence area of the greater Ohio and Mississippi rivers (Olson and Morton 2016a, 2016b, 2016c). A regional effort on both sides of the Ohio and Mississippi rivers is needed to strategically identify floodplain areas that could provide temporary water storage and policy incentives for landowners of low-lying lands to profitably invest in crops and income alternatives.
Some people might be willing to write off Cairo and say the feds should buy out the town, the same as it has bought out individual properties in the floodplain in the middle part of the Ohio River. As for me, I'm not ready to say Cairo should be destroyed as long as there is hope it can recover from the problems that have plagued it for sixty years or more.
However, what's happening at Dogtooth Bend -- and what has happened elsewhere on the Upper that is driving the changes there -- can affect many other places and needs to be watched closely.
(If that sounds like something you would read in a newspaper editorial, please remember that I used to write editorials for a living).