Deposition

Deposition is where a river lays down or drops the sediment or material that it is carrying. Rivers carry lots of different sediment, including rocks, boulders, silt, mud, pebbles and stones.

Rivers need energy to transport material. When energy levels are very high, large rocks and boulders can be transported. When energy levels are low, only small particles can be transported (if any).

Normally, a river has the energy to carry some sediment. The faster a river flows the more energy it has. If the speed of a river drops, the river loses energy and deposits some of the material it has been carrying.

In some places along the Darent, deposition in the centre of the river has allowed small islands to develop. Plants have colonised these islands. The islands act as obstacles encouraging more deposition and so each island grows in size.

The river divides into two smaller channels around the islands. The velocity increases in these narrower channels.

Iron railings stop plant materials and human rubbish from flowing further down the river. The gaps between the railings allow fish to continue their journey up and down the river.