The Coriolis force in the Northern Hemisphere deflects moving water to the right. In rivers, this creates two opposing effects: the deflected current scours the right bank (erosion), but it also carries suspended sediment toward the right bank (deposition). Which effect dominates depends on what the river is carrying. In low-sediment rivers, erosion wins and the right bank retreats. In the Yellow River -- one of the most sediment-laden rivers on Earth -- deposition wins. Field observations from the Lanzhou section confirm that sand and pebbles accumulate preferentially on the south (right) bank, consistent with Coriolis-driven lateral sediment transport overpowering the erosive force of the deflected current itself.
The structural claim is that a single force can produce opposite outcomes depending on what the medium contains. The Coriolis force does not change; the river's sediment load determines whether the same deflection builds or destroys. This is not a case where two different forces compete. It is one force acting on two properties of the same system -- the water's momentum and the sediment's mass -- and the ratio between those properties selects the result. When a uniform perturbation acts on a heterogeneous system, the system's composition, not the perturbation's direction, determines the net effect. The same policy, the same pressure, the same force can construct in one context what it erodes in another, and the difference is entirely in what the system is already carrying.
(arXiv:2603.16912)