mythbusters took this video and proved that you can't walk on water, the guys even admitted afterwards that there was a glass board underneath in the water, that's why he falls after running so far.. if he was running off of a flat surface onto water, most likely he wouldn't be stepping harder and he wouldn't get much speed. the momentum you gain from running is very little compared to a lot of other things, a spider weighs 1/100 of a pound or less. obviously you need to be very light. you can float, but not walk on water. the surface of water is no different than the water underneath it. when you belly flop, you're most likely doing it from a height thus gaining momentum and all of your body weight is going into it. thats why it hurts.

You obviously have not done very much in school on physics because there are many different variables than what you have posted I will not thumb you down but you seriously don't know enough to even say anything on this matter.