Deltas have long played an important role in human history. These fertile areas where rivers flow into large bodies of water have served as fishing, farming, and living sites. Of the great deltas around the world, perhaps none has had a greater role in civilization than the delta of Egypt's Nile River. Greek historian Herodotus (c. 484–c. 425 <span>B.C.E. </span>), considered by many as the "Father of History," studied this great geologic feature. He is credited with coining the term "delta" for this type of landform because its triangular shape reminded him of the Greek letter ∆ (delta).
The shape of the land
A delta is a body of sediment deposited at the mouth of a river or stream where it enters an ocean or lake. Unlike other landforms affected by running water, a delta is not created primarily by water cutting into or eroding the landscape (erosion is the gradual wearing away of Earth surfaces through the action of wind and water). Water does not tear down a delta; instead, it builds up a delta.
A river creates a delta by laying down sediment or rock debris such as gravel, sand, silt, and clay that it has picked up and carried along its course. Alluvium (pronounced ah-LOO-vee-em) is the general term for sediment deposited by running water. A river's depth, its width, and its speed determine how much sediment it can carry. The Mississippi River flows at an average surface speed of about 2 miles (3 kilometers) per hour. Yet it drains between 1.2 and 1.8 million square miles (3.1 and 4.6 million square kilometers), which is more than 40 percent of the total area of the continental United States. Over the course of a year, it moves an average of 159 million tons (144 million metric tons) of sediment.
In general, deltas are similar in shape to another type of landform deposited by flowing water, alluvial (pronounced ah-LOO-vee-al) fans.
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Read more: <span>http://www.scienceclarified.com/landforms/Basins-to-Dunes/Delta.html#ixzz4PTL5B6Bk</span></span>
