What is a delta?
As a river reaches the sea its flow becomes slower, forming an area known as a delta. As the water slows the tiny particles of silt carried by the current settle to the bottom, forming mud banks. These make the river-bed shallower, so the water spreads out to form a wide estuary. In large rivers like the Danube, islands form among these exposed mud banks, and the river water trickles through a maze of small waterways. This region, which is rich in plants and other wildlife, forms the river’s delta.
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Uphill flow!
Water always flows down a river, but occasionally the flow is reversed. This happens only in very large rivers, when very high tides overcome the normal river currents. In narrow parts of the river valley the water begins to pile up, and eventually a wave called a tidal bore passes back up the river, sometimes for a great distance. This happens in the Amazon in South America, where there is a bore as high as 4.5 m. A smaller bore travels up the River Severn in England.
Picture credit: google
