The flow in the shallow areas (2-4ft) could be compared to rapids, and the bottom is really rocky.
Gotcha. Well, I did this in Michigan one salmon season when my two aunts were gonna join my dad and I for a full day (they're not used to wading and would have a hard time with it). Warning - the supplies necessary for this (patio chairs, two extension ladders, paracord, climbing rope) required lots of space, so its not something you could pull off easily without being able to park the truck relatively close:
What I did was bring five pretty sturdy yard / patio chairs in the back of my truck, two big extension ladders, and a climbing rope (9.4 black diamod). I waded out and placed the middle chair first, then the other four (two on each side back toward each bank), trick is to do this in a spot where there's a tree on each side of the bank at your fording/bridge location. Then, I set the ladders across the arm rests of the chairs and lashed em on with the paracord. This part takes the longest as you're gonna have to adjust each chair a bit as you go. Then I but a big rock in the seat of each chair. I ran the climbing rope from a tree on one bank to the other, making it as tight as I could so it's a reliable safety hold. At the middle chair, the ladders (and arm rests of the chair) were actually entirely under water, but only about 8-10 inches. Didn't seem to create any problems, but it did require my aunts to cross barefoot (mud boots or xtratuffs would've worked).
Ended up working pretty well, my old aunts shimmy'd across just fine (albeit barefoot). It was a satisfying project, as well.
That being said, the place I did this had a relatively casual flow. If the water were any faster, I'd want much heavier chairs than what I had.