River courses

River courses

1. Middle course

   • Meanders
     • As the river erodes laterally, to the right side then the left side, it forms large bends, and then horseshoe-like loops called meanders.
     • The formation of meanders is due to both deposition and erosion and meanders gradually migrate downstream.
     • The force of the water erodes and undercuts the river bank on the outside of the bend where water flow has most energy due to decreased friction.
   • In the middle course the river has more energy and a high volume of water. The gradient here is gentle and lateral (sideways) erosion has widened the river channel. The river channel has also deepened. A larger river channel means there is less friction, so the water flows faster:
   • Oxbow lake
     • upstream a large bend becomes a horseshoe and is eventually cut-off to become an oxbow lake. Downstream the river is eroding its outer bank and depositing on its inner bank to create a new meander.

2. Lower course

   • In the lower course, the river has a high volume and a large discharge. The river channel is now deep and wide and the landscape around it is flat. However, as a river reaches the end of its journey, energy levels are low and deposition takes place.
   • Floodplains
     • The river now has a wide floodplain. A floodplain is the area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich alluvium deposited by floodwaters. This makes floodplains a good place for agriculture. A build up of alluvium on the banks of a river can create levees, which raise the river bank.
   • Delta
     • Deltas are found at the mouth of large rivers - for example, the Mississippi. A delta is formed when the river deposits its material faster than the sea can remove it. There are three main types of delta, named after the shape they create:
     • Types
       • Bird foot
       • Cuspate
       • Arcuate

3. Upper course

   • As the river moves through the upper course it cuts downwards. The gradient here is steep and the river channel is narrow. Vertical erosion in this highland part of the river helps to create steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges.
   • As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs, which look a bit like the interlocking parts of a zip.
   • When a river runs over alternating layers of hard and soft rock, rapids and waterfalls may form.