I like toying around with World Machine and other procedural terrain generation tools. I'm also trying to learn more about general-purpose GPU programming, so I thought I would see if I could recreate one of my favorite parts of World Machine on the GPU: hydraulic erosion.
World Machine's hydraulic erosion function simulates the effect of precipitation on a heightmap, and has four outputs: an eroded heightmap, a water-flow map, a soil-deposition map, and a wear map (that shows where the erosion occurred). It does a pretty good job, and is relatively fast. The starter map you get on start up can be eroded with default settings in ~10 seconds.
I intend to replicate this basic functionality, but with an increase in speed. This is not meant to be boasting or impressive, just a consequence of using the GPU on a parallelizable problem. However I would like to improve upon it with a new feature: meanders and oxbow lakes. http://en.wikipedia.org/wiki/Meander Meanders are when rivers curve significantly, due to increased water flow and erosive force on the exterior of a bend in the river. Excessive curves may cause the river to erode an extra connection to itself, cutting off part of the river from a water source. This results in horse-shoe shaped lakes next to rivers (which may or may not dry up).
I would like to see if I can get this to happen as an emergent behavior from a properly constructed cellular automata. In order to see this sort of behavior I would need a model that allowed (1) water flowing next to a cell (which is higher than the water) to cause erosion in that cell, (2) water to flow faster on the outside of a bend, (3) faster moving water to be more erosive, (4) slower water to deposit more soil. I'm not entirely sure how to achieve that. Locally computing the gradient of water altitudes to determine flow rate each time step is the simplest method, but it also fails to achieve #2, which is an important property.
Does anyone have any ideas? I feel like I am too close to the problem and am overlooking something simple.
PS: I understand that what I am talking about is, strictly speaking, a finite element method instead of a proper CA. However, I have repeatedly seen this referred to as a CA elsewhere, so I do so here as well.