River Deposition

A river drops its load when the speed or volume of the river decreases. The load, which it carries, is deposited. The heavier material is deposited first and the finer material carried further.
Rivers reduce their speed when they enter flat land, enters a lake or the sea or reach an arid area. The volume can be reduced during a dry season or when the river passes over more porous landscapes  e.g. sand or limestone.

Lower reaches of the River Exe