Hydraulic action is strong enough to loosen sediment along the river bed and banks this will take rocks from the side of the banks and add it to the rivers loads. The water compresses the air in the crack, pushing it right to the back. As the wave retreats, the highly pressurized air is suddenly released with explosive force, capable of chipping away the rockface over time. Thus, the crack is gradually widened so the amount of compressed air increases like a balloon, and hence the explosive force of its release increases. Thus, the problem intensifies (a 'positive feedback' system). It helps the river to get lower (rejuvenation). It is helped in part on cliffs by 'Freeze Thaw'.

Cracks, joints and crevices within the channel can be widened and therefore weakened when the air contained in them becomes compressed with water. Also, this explosive power can weaken the rockface so that it comes to a point where the crack falls away. Hydraulic action occurs as a river tumbles over a waterfall to crash onto the rocks below. It wll 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, mainly from destructive wave

Ocean surface wave

In fluid dynamics, wind waves or, more precisely, wind-generated waves are surface waves that occur on the free surface of oceans, seas, lakes, rivers, and canals or even on small puddles and ponds. They usually result from the wind blowing over a vast enough stretch of fluid surface. Waves in the...

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