- Ox-bow lake
- Braided stream
Rivers slow down when they enter almost-flat plains of the lower course. Slow moving rivers cannot carry large loads as fast flowing rivers can. So the old rivers deposit their loads. The loads of old rivers consist of light particles such as mud and grains of sand. This material is called alluvium. It is deposited along the riverbed. They are covered in fertile alluvial soils, which are deposited by the river. They can sometimes be flooded. Unable to carry its entire load the river deposits some of it on its bed. This raises the level of water so that it almost reaches the tops of the river banks. In times of heavy rainfall the river water may rise still further overflowing its banks and flooding the nearby plains.
A feature composed of alluvium formed when the deposition of sediment occurs at the mouth of a river, caused by the slowing of water on entering the sea. The name 'delta' is derived from the fact that the feature's shape is similar to that of the Greek letter Æ. There are two main types of delta: an arcuate delta, such as that of the Nile, and a birdfoot delta, likes that of the Mississippi, which is actually a seaward extension of the river's levee system. Deltas are very fertile areas and are important for agriculture; for example, the Nile delta contains 90% of Egypt's farmland.
Deltas also occur under these conditions:
- load deposited in the coast exceeds the amount transported away.
- Active erosion along the course of the rive- River flows through less resistant rock
- Many tributaries to increase load
- No or few lakes to trap load
When the volume of the river cannot carry its load, the river splits into two or more channel. The channels twist and turn and would finally be joined when the deposition no longer obstructs the flow of water.
Ox-bow lakes are formed when two concave banks of the meanders erode and become joined together. The river would then flow straight. Deposition takes places and cuts the river from the meanders loops. As more Deposition takes place, the meander loop becomes independent and is called an ox-bow lake. An ox-bow lake is a horseshoe shaped or crescent shaped lake.