Hint: A river delta is a landform that is generated when sediment that is carried by a river is deposited as the river reaches slower-moving or stagnant water. This happens where a river enters an ocean, lake, reservoir, sea, estuary, or some other river that is unable to carry away the supplied sediment.
Complete answer:
A river mouth, also called estuary, is a place that enters a lake, a large river, or the sea. The estuary is a place with a lot of activity. When the estuary flows, it picks up sediment from the riverbed, erodes the banks and deposits debris on the surface of the water. The estuary is where much of this gravel, sand, silt and clay accumulate. A large amount of alluvium deposits at the mouth of the estuary forms a delta. Once It slows down, the river does not carry all the silt, sand and clay. These deposits form the flat, usually triangular land of the Delta. Many major port cities are built at the estuary. Abundant wildlife and natural transport often create dynamic harbors. The largest deltas in the world are the Ganges Delta in Bangladesh and India. The delta is 350 kilometers in length, and is alongside the Bay of Bengal. As a result of the many rivers empty in the Ganges Delta, giving it the name “Mouth of the Ganges".
Note: All rivers don’t form deltas. For a delta to be formed, the flow of a river must be slow and stable enough for residue to be deposited and built up. Other than Tapi, Narmada also does not form a delta. This is because the Narmada River flows through a rift valley which increases its speed. Also, the west coastal plains are less wide than that necessary for delta formation.
