You can play with an educational flooding simulation a great developer (not me) at my company built as part of a research project:

https://flood.concord.org/

NOTE: you need to change the model values in the bottom toolbar to see big effects.

It is a cell-based simulation that uses WebGL to calculate cell values based on adjacent cells. The shader that does that is here:

https://github.com/concord-consortium/flooding-model/blob/ma...