There are two types of erosion that happen at different stages along a river. Vertical (downwards) erosion often occurs in the upper stages of a river whereas lateral (sidewards) erosion typical occurs in the middle and lower stages of a river.
There are four main processes of erosion. These are:
- Abrasion or corrasion – This is when large pieces of bedload material wear away the river banks and bed;
- Attrition – This is when the bed load itself is eroded when sediment particles knock against the bed or each other and break, becoming more rounded and smaller;
- Hydraulic Action – This is when the force of water erodes softer rock;
- Solution or corrosion – This is when acidic water erodes rock.