Erosion & River Carving — 2D Height-Map Simulator

This 2D companion runs the same flat-array hydraulic-erosion model as the 3D version — rain accumulates on a height-map, flows downhill toward lower neighbors, and carves or deposits terrain based on local slope and flow — but renders it as a straight top-down elevation map instead of an orbiting 3D scene, so the carved channel network is readable at a glance.