I did something very similar to what the kids did on your stream Moonlight. The place was a real stinkhole, full of tires and every other sort of debri. The stream bottom was covered in oily mud and rotting vegetation because of all the trash which reduced the stream flow. After I cleaned it out we had a good rain and it was amazing how quickly all the silt and mud flushed out of it, that was about four years ago. Since then the sand has shoaled up in a few midstream sections making it almost impassable for fish.
I was thinking along the same lines as you. That by building some obstructions coming off the bank about halfway out into the channel above the shoals the water would carve out a narrow channel and create a back eddy below the obstruction. This should force the washed out sand up along the bank behind the obstruction rather than in the middle of the channel. I love this stuff.