Agents (red) follow a single rule: move one cell per timestep toward the nearest river cell (blue). When the river erodes an agent's cell, the agent is relocated to the nearest available cell. No agent has any directional preference. Under an asymmetric migration kernel, agents systematically drift along the valley in the direction of the phase lag.
Grid: 500 × 100 •
Frame: 0 / 0 •
Time: 0 yr •
Mean drift: 0 m •
Downstream: 0%
River
Agents (0)
Floodplain
1000
1x
20 m
0
Under the downstream lag (the physically realistic regime for most natural rivers), agents accumulate at the downstream end of the domain. Reversing the lag reverses the drift. The symmetric kernel produces no directional bias. Increasing the migration rate strengthens the drift; increasing agent density suppresses it through crowding.
Upstream lag
Downstream lag
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