GCSE Revision - Rivers - The Lower Course

 

The river is now nearing the sea and deposition becomes the dominant process.
The main features of the river channel and river valley are:

  • It is wide and deep with a more efficient shaped channel

  • It is lined with sand and mud so this results in less friction

  • There maybe islands of silt called eyots in the river and the river can split into a number of channels - river braiding

  • The river carries a large load of alluvium

  • There is a wide, flat flood plain either side of the river

  • There are features such as meanders, ox bow lakes and deltas

  • The flood plain is made up of  a thick layer of alluvium

  • A line of river cliffs are found at the edge of the flood plain called bluffs

 

The Flood Plain

The Formation of Ox Bow Lakes

In the lower course the meanders become even larger. Erosion on the outside of bends and deposition on the slip off slopes continue to take place.

The erosion causes the meander neck to narrow until eventually it breaks through. This often takes place when the river has more energy as in times of flood.

The river now follows a straight path. After the meander has been cut through the river seals off the bend by deposition and an ox-bow lake is formed. In time, especially in dry areas the ox-bow lake may dry up to form a meander scar.

 


Levees are basically caused by floods. In times of low flow any deposition takes place on the river bed and this raises the height of the river bed.
In times of flood the water leaves the channel. As it does so it loses energy and the courser and heavier material is deposited near to the river on the banks. Finer material is carried further onto the flood plain. After many floods the river builds a bank on either side of the river and this can lead to catastrophes. As the river has been raised above the flood plain and the banks are often higher still, when the river floods the water can no longer drain back into the river channel and often has to form a new one.
 

Deltas

Some rivers reach the sea in deltas, which form where river mouths become choked with sediment, causing the main river channel to split into hundreds of smaller channels or distributaries.
Deltas only form under certain conditions

  • The river must be transporting a large amount of sediment

  • The sea must have a small tidal range and weak currents

  • The sea must be shallow at the river mouth

Famous deltas consist of the Mississippi delta, The Ganges and Brahmaputra delta (Bangladesh) and of course the Nile delta.


Links - Revision DVD - River Tees
         - Animations - Just click the diagrams above

Common Questions

  • Describe and explain how ox bow lakes are formed

  • Describe how the flood plain was formed

  • Describe and explain how Levees are constructed

  • What are the factors needed for a delta to develop

  • label the main features of a flood plain on a diagram