Simple 2d-formula for Volume / Area-Tests
 

Hey everybody,
I am currently working on a little project for my graduation. It is a program which is supposed to let water flow through a digital elevation model (staggered grid). The goal is to find out which areas might get flooded. Waterspeed, erosion whatsoever isn't needed/interesting for now. I was hoping that there was an easy formula, as only the relief and water of the surrounding cells would have to be considered for computation.
Any thoughts on that?
Thanks in advance,
Daniel