The seemingly simple task of describing and simulating how water is distributed on surfaces or flows in a way that is more suitable for everyday use is of a complexity that should not be underestimated.
For an even approximately meaningful application of tools that perform this description or even the process-like modeling of surface runoff with the help of e.g. digital terrain models and corresponding mathematical models, the entire geographic theory of science has to be applied.
At the same time, dealing with the concepts and tools is a very good and well-founded entry into a scientifically based application of GI techniques in scientific questions.
What is actually the problem? Let’s read up…