Small pebbles and stones are bounced along the river bed.

Find out more about how rivers transport material.

The characteristics of rapids include:

• the turbulent flow of water
• white water
• uneven river bed
• steep gradients.

Find out more about the landforms of erosion in the upper course of a river.

Abrasion or corrasion, attrition, hydraulic action and solution or corrosion.

Find out more about river erosion.

Geology can increase the risk of flooding when:

• The upland bedrock is impermeable, such as slate, which means there is more surface run-off
• Soil in low lying areas is made up of clay. Because it is so compact it is difficult for infiltration to occur.
• Areas of permeable rock, such as limestone, become inundated with water leading to increased surface run-off

Find out more about human and physical causes of flooding.

A steep, V-shaped cross-profile is typical in the upper course. This is because of vertical erosion by the river combined with weathering and mass movement of the valley slopes.

In the middle course, the river is flowing through lower-lying land. The gradient is gentler, so the river begins to meander (bend). As it does this the dominant type of erosion becomes lateral, eroding the valley sides. The makes the valley broader. Also, the rate of weathering increases on the softer rocks of the valley sides.

In the lower course, the river is passing through the low-lying country. Flooding results in deposition building up the flood plain and this, along with migrating meanders builds up and widens the valley further.

Find out more about the cross profile of a river.