The contrast between the flow velocity at which a fine-grained cohesive sediment may be deposited and that at which it will be eroded. F. Hjulström published an important diagram which plots the relationship between grain size and velocity for erosion, transportation, deposition, and settling velocity. One of the many important consequences of these relationships is that although fine-grained cohesive sediments (fine silt and clay) will be deposited only if flow velocities are very low, a very high velocity is required to erode the same sediment, once deposited. This is because of the cohesive nature of the sediment, which makes silt and clay more difficult to erode than pebbly sediment.

Hjulström effect