Corrasion, otherwise known as abrasion, is the grinding of rock fragments carried by the river against the bed and banks of the river. This action both widens and deepens the channel. The power of the grinding is especially powerful in floods when large fragments of rock are carried along the river bed eroding the bed and the banks. |
Attrition is the knocking of rock fragments in the water against one another. The fragments are broken into smaller pieces and become smoother along the process. |
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For example, when a river stream flows over an area of limestone (calcium carbonate), it erodes the limestone by reacting chemically with it and dissolves it. |
Hydraulic action is the breaking down of rocks and dragging them away from the bed and banks by the force of the running water itself. When water from a fast moving stream enters cracks in a rock, the force breaks up the force into pieces. |