Before 1900, the Mississippi River transported an estimated 400 million metric tons of sediment per year from the interior of the United States to coastal Louisiana and the Gulf of Mexico. During the last two decades, this number was only 145 million metric tons per year.
The Missouri is one of the major tributaries (accounting for about half the volume once it meets up), it's where the a large portion of that 400 Mt comes from
Sort of on topic, here a great 2011 article by Weather Underground's Jeff Masters on one of the major control structures on the Mississippi that prevents it from taking a more direct route to the Gulf of Mexico:
Also in that book: efforts to stop volcano lava flow by massed firehoses in Iceland, and sedimentation and rainfall in the San Gabriel mountains above LA. 100% worthwhile.
Since I grew up in Memphis, that is, on the east bank of the Mississippi River and since Dad liked fishing, early on I got an introduction to how the Mississippi, and likely the Missouri, Rivers can move mud.
Still, that that boat got buried 45 feet deep under a nice, level, dry corn field is surprising.
Here's how it works: The river flows nice and straight. One day the flow is a little less, and some of the silt or sand settles out and forms a sand bar. Then the river starts to flow around the sand bar. One day the flow is higher, and as the river flows around the sand bar, it flows in a curve and eats away at, erodes, the bank of the river on the outside of the curve. Then on the inside of the curve, the flow rate is less and more silt and sand settle out, and the river curves more. Eventually the river curves so much it makes its path nearly a full circle, say, 10 miles in diameter. Then one fine spring, the flow is heavy, the water level rises, and some of the water doesn't go around the circle but just takes the short cut directly from the beginning of the arc to the end of it and, thus, cuts off the circle 10 miles in diameter. So, that circle now becomes a cut off. As go down the Mississippi River, there are old cutoffs on the left and right and left, ..., all the way down.
Soon a cutoff can have no flow at all.
Well, that boat sank in part of the river that became a cutoff. Then with little or no flow, the silt and sand settled out and the water became better for fishing. So, Dad and I did a lot of fishing in such cutoffs -- north and south from Memphis, Tennessee, Mississippi, Arkansas, etc.
One of the cutoffs we fished in had a sunken warship from the Civil War. Sometimes could see the ship -- much closer to the surface than 45 feet deep. So, that ship was getting buried under sand and silt much slower than the case of the ship in the Missouri River cutoff.
So, how could that farm land be so level with the ship 45 feet down? Well, each spring, the river could rise and dump very muddy water into the cutoff. When the spring was over, the silt and sand would settle out and cover the ship with another layer. Then the rest of the year, the water level would fall and flow in the new, main channel and not in the cutoff.
So, okay, if that farm land was fairly low, then just from spring floods, the result could be the level land with the boat buried 45 feet down. Okay.
What is surprising is that, then, the farm land would still about have to be not much higher than the river and would be prone to flooding each spring. Maybe the land does flood each spring. But if the US Corps of Engineers dredges the main channel and/or puts up a levy, then maybe they can keep the river in the main channel and the farm land not flooded.
Before the US Corp of Engineers, dredging and levys, each spring the story in Arkansas was amazing: The Mississippi River would flood about the whole eastern half of Arkansas, over to a geological feature that had the land a little higher. Also, that area is an active earthquake zone, especially at the NW corner of Tennessee. And, IIRC, the geological feature was from earthquake activity, and the eastern half of Arkansas has long been slowly sinking.
Well, then, over the millennia, each spring the river put down another layer of silt and sand in the whole eastern half of Arkansas. So, now, want good silt and sand for top soil? It's 20+ feet deep over the whole eastern half of Arkansas! And it's still moist and not very solid. So, when build a road, nice and straight and flat, come back in 10 years and it looks like a piece of lumber that warped. Tough to build a stable road in that part of Arkansas!
Some of the geology, geography, ecology, etc. of the Missouri, Ohio, and Mississippi Rivers is a surprising subject.
But it isn't just about fishing: Those rivers are needed for commerce, say, barges with coal, wheat, lumber, etc. So, the US Corps of Engineers has to do enough with dredging and levies to let the barges keep moving. So, the Corps has to fight those rivers, really, all the way down to New Orleans.
"Over time, the river shifted a half a mile (800 m to the east). The site of the sinking is in a field in the area of present-day Kansas City, Kansas."
Good answers here, but thinking this way may help. The river was deep. Rivers on flat ground, left to their own devices, migrate laterally a lot. We don't see it much, but if you think of oxbow lakes
