Lateral erosion is one of the three different ways that rivers and streams erode their banks and beds. As the term implies, lateral erosion is the erosion that occurs on the sides, or floodplains, of a river or stream, and it is also referred to as bank erosion. The other two forms of erosion are headward erosion and downcutting erosion.
The amount of erosion that occurs is related to the amount and type of sediment particulate load that the stream is carrying. Because water is low on the hardness scale, it can drag and lift the loose material that it flows over or through, but it cannot abrade harder solid materials.
One of the common particulate materials carried by streams is quartz sand, which is more than seven times harder than water. When combined with a powerful current, quartz particles can cause a significant amount of erosion to take place on the banks of a river or stream.