The 3D Soil Erosion & Runoff simulation shows a single slice through a hillslope. This 2D companion runs the identical stream power law — erosion rate E ≈ k · (S · A)^1.5, where S is local slope and A is accumulated upstream flow — but across a full 2D grid viewed from above, so you can watch the drainage network itself take shape instead of a single profile.
Every cell receives rainfall minus infiltration (set by soil type), then routes its water to whichever neighbouring cell sits lowest — the same steepest-descent routing real hydrology software uses to build flow-accumulation maps. Flow compounds downhill, so cells near the bottom edge carry far more water than cells near the top, and because erosion depends on flow raised to a power above 1, that water naturally organises into narrow branching channels rather than eroding the field evenly — a real dendritic drainage pattern, not a decorative one.
Vegetation is seeded as patches across the field (from the vegetation-cover slider) rather than a single global multiplier, and any patch that sits inside a forming gully is stripped away as its cell erodes — watch bare, gullied ground spread outward from the channels exactly as it does after a storm strips a real slope.