I had a similar thing happen with my truck, though the floors wern't completely gone, there were some big 'drain holes.' Anyways, I was driving down a country highway on my way home after storm chasing. All of a sudden, I hit a massive flash flood under an overpass. The only way to describe the deceleration would to compare it to one of those supersonic rocket sled tests from the 50s. They used water to decelerate them from Mach 1 to a complete stop in a matter of seconds. Next think I knew, I had water 2/3 the way up my legs. The truck sounded like a 165 mercruiser since the whats left if the exhaust was under water. I was able to drive right out of it though, since it was a pretty gradual incline. Man, I had to pull the rubber floor out since it smelled so bad.