In the recent floods in CO, several of the rivers changed their course. This article provides an interesting analysis of the use and maintenance of rivers in urban areas. See: Colorado flood recovery process is a lesson in who owns the river
Recovery Diva
Long-Term Recovery from Disasters
Recovery Diva 
I agree it is a big deal. And it is an aspect of floodplain management that I have never seen discussed before.
This is a huge deal. We make all these plans and agreements based on having a predictable landscape, but in the end the rivers always do whatever they feel like, and the rest of us are left scratching our heads about who will pay for it.