hydraulic action

In earth science, the erosive force exerted by water (as distinct from erosion by the rock particles that are carried by water). It can wear away the banks of a river, particularly at the outer curve of a meander (bend in the river), where the current flows most strongly.

Hydraulic action occurs as a river tumbles over a waterfall to crash onto the rocks below. It will lead to the formation of a plunge pool below the waterfall. The hydraulic action of ocean waves and turbulent currents forces air into rock cracks, and therefore brings about erosion by cavitation. In coastal areas hydraulic action is often the most important form of erosion.