A good parent should warn their children about the dangers that surround them in this world and instill fear of things like fast moving water.
Your asking a hypothetical but 1. Do not put your self in that situation by scouting or just not doing it. 2. If you do end up in that situation you do what you need to do. If you need a specific maneuver knowing that there is at least 6 feet of water below you a roll or a wet exit might do the trick.