Erosion and Transportation River Processes Erosion: This is when the river wears away the land. There are four main river erosion processes. Erosion and Transportation

River Erosion 1. Hydraulic action: Water and air is forced into cracks in the river bank and its bed. The sheer force of this movement can wear away the river's bed or cause parts of the river bank to collapse. Lateral erosion Lateral erosion Vertical erosion

River Erosion 2. Abrasion: When particles of rock carried by the river (the load) are thrown against the river bank or hit the river's bed causing erosion. Lateral erosion Lateral erosion Vertical erosion

River Erosion 3. Attrition: When particles of rock carried by the river (the load) smash into each other. This causes them to become ground down into smaller fragments.

River Erosion 4. Corrosion : When rocks in the river are dissolved by the water.

River Processes Transportation: The term used to describe how a river moves the material that forms the river’s load. There are four main transportation processes.

Large stones are rolled along the river bed by the river’s current. River Transportation 1. Traction: Direction of flow Large stones are rolled along the river bed by the river’s current.

River Transportation 2. Saltation: Direction of flow When sand sized particles are bounced along the bed in a leap-frog movement.

When very small particles are carried with the water flow. River Transportation 3. Suspension: Direction of flow When very small particles are carried with the water flow.

When minerals are dissolved in the water. River Transportation 4. Solution: Direction of flow When minerals are dissolved in the water.

How does the velocity of a river affect the river processes? Summer Winter

When the velocity increases Generally speaking, the river can erode more and transport larger pieces of rock because it has got more energy. Some rocks only move when the river floods and the river velocity increases dramatically. When the velocity decreases The river’s energy decreases and it deposits (leaves behind) the larger rocks on the bed of it’s channel. However, the actual process taking place may also depend on the type of particles in the river bank and bed

How does the velocity of a river affect the river processes? 1000 100 10 1 0.1 Erosion Increase in velocity River velocity (cm/s) Clay Silt Sand Gravel Pebbles and Cobbles Type of particle As velocity increases, larger particles can be lifted off the river bed. However, it takes higher velocities to lift very small particles because they stick together.

How does the velocity of a river affect the river processes? 1000 100 10 1 0.1 Erosion Decrease in velocity River velocity (cm/s) Deposition Clay Silt Sand Gravel Pebbles and Cobbles Type of particle When the velocity decreases, particles will be deposited as the river has less energy. The larger particles will be deposited first at higher velocities. Some particles are not deposited even at the slowest velocities because they are so small they are held in suspension.

How does the velocity of a river affect the river processes? 1000 100 10 1 0.1 Erosion River velocity (cm/s) Transportation Deposition Clay Silt Sand Gravel Pebbles and Cobbles Type of particle As the velocity of the river changes, the type of particle it can transport in its load also changes.

The Hjulström curve diagram How does the velocity of a river affect the river processes? 1000 100 10 1 0.1 Erosion River velocity (cm/s) Transportation Deposition Clay Silt Sand Gravel Pebbles and Cobbles Type of particle The Hjulström curve diagram