Traction – The rolling of boulders and pebbles along the river bed by the force of the current

To remember the meaning of the term Traction, use the following mnemonic:

The tractor (traction) could just about roll the big boulder.

The difference between traction and saltation is that, in traction, the material moved by the force of the river's current does not leave the substratum (the riverbed) at all, but is rolled or slid along.

The continuous contact between the rocks and pebbles that are moved and the substratum can cause erosion, through friction, of both the moving material and the riverbed.