As a river's meander pattern changes, and the position of the channel shifts, sections of land are suddenly on the other side of the river.
But it must be rather awkward for a farmer if a section of the farm is suddenly across on the other side of the river, especially if the river marked the boundary of the property.
Here's an example on the River Severn.
So sometimes it just isn't convenient to let the river position change. And that's where river engineering comes in.
Structures are built to re-enforce the bank and slow down river processes.
Here willow has been interwoven. It will stop the full force of the water hitting the bank, though looks like it will need regular maintenance.
Here's a more complex structure.
The wooden posts support a metal mesh, which in turn is holding lots of pieces of rock against the bank. So, when the river rises and crashes in there, it hits the hard stones rather than the soft river bank, protecting the bank from the force of the water. And just to be on the safe side, they have left two great big rocks in the way too.
Basically, the more important the land that you want to protect, the more effort and money is invested in the river engineering to control the river's behaviour.