🌊 Water Simulator: Coastal Erosion - Chalk Cliff Wave Undercutting, River Incision, Sediment Budget and Bruun Rule Shaper Lab

Shape, erode, flow: a 3D chalk-and-clay coast where waves undercut cliffs (Sunamura-type retreat, Green shoaling, breaking at 0.78 depth), rivers cut valleys and drop sediment into deltas (Mei virtual pipes), beaches drift and plants hold slopes. Six tools, six environments, seven scenarios with goals, a full mass ledger, Bruun-rule comparison and nine independent numerical checks.