whatA river reaches the sea and builds land. Watch its mouth choke on its own sediment: a bar grows exactly where the water slows, the flow splits around it, each branch builds its own bar and splits again — and every so often the whole river gives up on a crowded path and jumps to a new one, abandoning a lobe of coastline it spent minutes building. No one steers it; the switching is the river's own arithmetic. Click the young land to cut a crevasse and tempt the river through it.

whyAvulsion — the river abandoning its course — is how deltas are actually built: the Mississippi has jumped seven times in as many thousand years, and the Wax Lake delta grows new lobes by exactly this rhythm of bifurcation and abandonment. It is a self-defeating process: the better a channel carries sediment, the faster it builds the bar that will kill it. Engineers levee rivers to stop it, which is why New Orleans sinks while its delta starves.

howA reduced-complexity model in the spirit of DeltaRCM: thousands of discrete water parcels walk from the inlet to the sea, each choosing among neighbouring cells by depth and its own momentum; their traffic is the discharge map, drawn as ink. Sand parcels follow the discharge and drop their load wherever the flow weakens — which is always, at first, the river mouth — while mud settles in quiet water between channels. Deposition raises the bed, a raised bed repels water, and the rerouted water carries the sand somewhere new: mouth bars, bifurcations, and avulsions all fall out of that one loop. Erosion is deliberately weak; a river that can always re-cut its channel never leaves it. The counters track new land, active mouths, and each confirmed avulsion. When the delta fills the frame it holds, then the sea takes it back and the river begins again. One integer seeds every parcel's walk.