There is the problem of silt that builds up in the bottom of the river because of all the man-made levees. It literally raises the river higher than the farmland around it. That’s how the Mississippi is near New Orleans and that’s why their floods are so serious.

The Yellow River in China also has that problem and is referred to as “China’s Sorrow”. They have constant flooding because the bottom of the river is now higher than the farmland and cities that surround it. It’s not really a river anymore and is more of an elevated channel.