Types of River Erosion

Hydraulic Action- 

The Pressure of the water breaks rock particles away from the bed and banks. It is strongest in rapids and Waterfalls 

Abrasion (corrasion)- 

Eroded pieces of rock in the water scrape and rub against the bed and banks, removing material. Most Erosion of river beds and banks happens by Abrasion 

Attrition- Eroded rocks Smash into each other and break into smaller fragments. Their edges get rounded off as the rub together. Attrition doesn't erode the bed and banks- it just makes the particles of rock in the river smaller and more rounded

Caviation-

Air bubbles in turbulent stretches of water implode causing shock waves the break pieces of rock off the banks and bed

Corrosion-

The dissolving of rock by chemical processes. Carbon Dioxide dissolves in water to form a weak acid, which reacts with rocks like limestone and chalk, breaking them down.