| Plains |
| As a river approaches sea level, the slope and flow lessens and the river starts to drop its load of eroded material as sediment. Broad, flat plains can be created as sediment from a large river and its tributaries builds up. Periodic floods deposit sediment some distance from the river itself, forming a floodplain.
Sediment can change the course of a river, with mature rivers in lowland areas, such as the Mississippi, forming looping channels called meanders. Extreme meanders can meet at the neck, allowing the river to flow straight again and leaving behind an "oxbow" lake. The largest river basins - the Amazon in South America and the Congo in Africa - are very flat, leading to multi-braided river channels.
The Mississippi River floodplain shows meanders and oxbow lakes near Memphis, Tennessee. At the coast, the volume of sediment deposited can be very large and some rivers have extended large deltas into the coastal seawaters. The Nile splits into very many streams as it flows over its delta and into the Mediterranean. In contrast, the Mississippi has built up a "crow's foot" delta with one main channel which has shifted around over thousands of years.
The delta of the River Indus glints in the morning sun. |
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