Hello, I'm new to the forms, but I have been playing Dwarf Fort for a while.
I see many suggestions asking for things like depth in snow, and sand dunes, better water simulation, and more dynamic above ground features. A way to implement this would be to add another depth layer to each tile. So instead of a tile holding 7 units of water / lava, it would have 14 units of anything with a unit value, with 7 of the 14 tiles being removed upon digging.
The advantage this has is that it would be easier to model erosion, due to the fact that you can have the stone where water has been flowing for a while have less depth than the normal 7, eventually digging a channel to the next level, starting with a stone layer filled 14/14, and repeating the process.
This system would also allow sand dunes to form if wind was present. Sandy ground could have 2 or 3 / 7 on top of a more compact layer of sand below, letting some of the excess sand on top be moved by the external forces, like wind, water, or even dwarfs.
Snow could also work in a similar method. Once it had filled up 7 squares worth on the ground level, dwarfs would be able to dig into it, letting them dig about in the event of a blizzard. Snow would also be able to drift. Ice could form layer by layer from the top down, rather than just all at once.