River Delta

River delta is defined as the place where river unload their deposits, which is built up from primarily river-borne sediment. It is usually formed when the amount of sediment delivered at the mouth of a river exceeds the amount removed by waves and tidal currents, decreases the current velocity and also the transport capacity of the river.

There are a lot of types of river delta:

Fig 1: An arcuate delta

• Arcuate (fan-shaped) delta - e.g., Nile River.  Has many active, short distributaries taking sediment to their mouths.  The receiving (ambient) waters are rather shallow and have relatively even wave action arriving perpendicular to the shore with minimal longshore current.  As the sediment exits the many distributary mouths, the waves push it back, so the coastline is rather smooth.

Fig 2: a bird-foot delta

• Bird-foot (shaped like a bird foot) delta - e.g., Mississippi River.  Tend to have one or a very few major distributaries near their mouths.  The receiving basin has currents that carry the sediment away as it exits the distributary mouth.  There is a broad, shallow shelf that deepens abruptly, so the trend is to grow long and thin like a bird's toe.

Fig 3: a cuspate delta

• Cuspate (tooth-shaped) delta - e.g., Tiber River of Italy.  Usually has one distributary emptying into a flat coastline with wave action hitting it head-on.  This tends to push the sediment back on both sides of the mouth, with a "tooth" growing out onto the shelf.

Fig 4: an estuarine delta

• Estuarine delta - e.g., Seine River of France.  This type of delta has a river that empties into a long, narrow estuary that eventually becomes filled with sediment (inside the coastline).

Reference:

http://home.swipnet.se/valter/main%20Ri.htm

http://web.bryant.edu/~dlm1/sc366/deltas/deltas.htm

http://www.americaswetlandresources.com/background_facts/detailedstory/RiverDelta.html