I find that when I intentionally flip to do a roll that it is often with more speed and force than in most actual flips. I have accidentally rolled in water that I thought was deeper and it can hurt even in a controlled enviroment.

Shallow water or really shallow water sucks to be upside down in. The key is to get upright as quick as you can any way that you can. If your paddle is in a bad position then use your hands and push off the bottom if you have to.  Remember the roll is all in your hips so you can easily flip back up with one hand.

Having said all of that, sometimes you can wait and see if it gets deeper. You can usually feel this happening. This all goes to experience, and really scouting a rapid.

When you scout a rapid don't just look for the lines but look for potential hazards and see what is downstream as well. If you know it runs into a deep pool maybe you can wait and hope you don't get tagged by a rock.

It is really a bad situation. If you don't bail you could take a hit, if you do bail you will pretty much garuntee a hit but probably not on your head, but then you have a foot entrapment situation.

Just keep your head and do whatever you can to get upright and stay in your boat.

Of course I feel obligated to say: " Don't flip in the first place" and "Full face helmet"

-Bryan