The erosion of the bed of a stream by running water, principally by attrition of the detritus carried along by the stream, but also by the solvent action of the water.

See abrasion.

erosion by friction

The bits of rock and sand in the river rub along the banks, wearing it down and knocking more particles into the water flow.

the denudation, or degradation, of a fixed or static structure by the action of particles being blown or hurled at its outer surface