A river erodes its bed and sides. Erosion is the wearing away of rock by moving agent and are carried away by them. When vertical erosion occur, the channel is deepen and thus the river is able to hold more water. When lateral erosion occur, the sides are eroded and the channel is widen. There are four major ways of river erosion.
Rocks that are carried in the river grind and erode the river side and bed. Some of the rock at the sides and bed of the channel are washed away. This type of erosion widens the channel through lateral erosion and deepens the channel by vertical erosion.
Water traveling at a high speed may enter the line of weakness of rock when it hit against these rocks at the side of the channel. The force may cause the rock to break and the broken pieces of rock are swept away
When material in the water collide with one another, they break and become smaller particles. These particles become smoother and rounded.
The river water may also dissolve the minerals in the rock and carry them down the river. Limestone may be dissolved quickly in the river water, especially when there is high concentration, to form soluble calcium hydrogen carbonate