There are three main processes a river does to shape the landscape: erosion, transportation and deposition. Different processes create different river landforms.
Vertical vs. Lateral Erosion Edit
Vertical erosion occurs in the upper course of the river, forming features like v-shaped valleys. In the middle and lower course, lateral (sideways) erosion occurs.
Sediment particles, like rocks are pebbles, are dragged across the river bed and banks - scrapping them off as they go along.
This is when the weak acid in the river dissolves the rock in the water. Most active on rocks containing carbonates, such as limestone and chalk.
The rocks and other particles carried by the river are reduced in size as they collide with the banks and other rocks.
This is the sheer power of the river hitting the banks. The water may enter cracks and crevices on the banks of the river and cause them to break down into the channel.
This happens because the river loses energy. It drops the heavier load first. Deposition is more likely to happen when the velocity of a river decreases. This decrease in velocity is most likely to occur when: 1. There is low discharge of particles in period of low precipitation 2. Less velocity when the river enters a sea or lake 3. The load of sediment and particles suddenly increases ie. from a landslide 4. There is shallow water on the inside of a meander
Larger sediment particles (e.g. boulders) are rolled along the river bed. This requires a lot of energy to occur.
This is where smaller pebbles or sand bounce along the riverbed.
Fine sediment are suspeneded in the water by turbulence. They do not touch the riverbed.
Dissolved particles are carried invisibly in the water.