A good example of what happens when you undertake major river modification without considering sediment transport is the Lower Mississippi River. The purpose of these cutoffs was to lower flood stages, and in their design, much consideration was given to the conveyance of water, but very little to sediment. Much evidence suggests that costs for maintaining the navigation channel in the river were increased by the accelerated erosion and sedimentation that followed the cutoffs. Channel straightening has caused lots of problems all over the world. Studies of Goodwin Creek, a small straightened stream in Northern Mississippi, indicate that the stream carries a very high sediment load, and that 85 percent of this sediment comes from erosion of the channel bed and banks.
Ecosystems tend to be more resilient near the equators and less so nearer the poles.
There are exceptions, but that's something to pay heed to. They are naturally more dynamic and move around a lot more. We tend to try to fix rivers in place, so we can build around the engineered river. Many of the very smallest streams in urban areas are now completely controlled by culverts. If we define restoration as full or partial return to conditions of predisturbance, then all restoration efforts should focus on the watershed.