A delta is a landform formed at the mouth of a river where it empties into a standing body of water, such as an ocean or sea. Deposition occurs as the river's velocity decreases and it can no longer carry its sediment load, causing the sediment to settle out and form the delta. Deltas take on various shapes like arcuate, birds foot, or cuspate depending on factors like tidal patterns or river flow. Common examples include the arcuate Nile Delta in Egypt and the birds foot Mississippi Delta in the United States.

1. Depositional Fluvial Landforms

2.  A delta is a Depositional Fluvial Landform in
humid geomorphic region except for Nile delta of
Egypt which is in arid region.
 A delta is a feature of deposition formed when a river
flows into a standing body of water.
 Deposition occurs as the velocity drops on entering the
standing body of water, this reducing the capacity and
competence of the river bed load and suspended
material are ‘dumped’.

3.  Delta forms when
velocity drops as the river
enters a standing body of
water, typically this is at
the coast as the river
flows into the sea.
An example of a delta formed when
a river flows into the sea in south
west Greenland

4.  Flocculation occurs as fresh water mixes with salt
water- e.g where a river flows into the sea -(then called
brackish water), and is the process by which tiny
particles in suspension like clay and silt (which
under normal fresh water conditions would likely
never fall out of suspension) coagulate with the salt in
the water by chemical reaction and become heavy
enough to ‘sink’ and be deposited.

5.  Delta is a site of deposition
 Formation of a delta depends on the estuarine
dynamics
 It also depends on the velocity of river
 In long term processes size & shape of a delta depends
on rock characteristics, rate of erosion, rate of rainfall
in the upper river basin and in the ways river flwos.
Singh, S, 2005

6.  Deltas only form where rate of deposition exceeds
rate of sediment removal. These conditions are
likely where:
 The calibre of the load of the river is very large (therefore
requiring a high amount of energy to keep in transport).
 The costal area into which the river dumps its load has a
small tidal range and weak currents ; meaning there is
limited wave action and therefore little subsequent transport
of sediment taking place after its initial deposition allowing
large deltas to form
 Suitable place in the form of shallow sea or lake shores
 Long courses of river; means long river system
 Relatively calm sea
Singh, S, 2005

7.  Accelerated rate of erosion in the catchment area of
the river
 Large amount of sediment supply
 Geologically inactive sea coast; means almost stable
condition of sea bottom
Singh, S, 2005

8.  Hyperpycual: The density of river water is greater
than the sea water
 Homopycual: The density of river water is same as the
sea water
 Hypopycual: The density of river water is less than
the sea water

9.  Delta is a very complex depositional system including
three morphological process i.e. fluvial, terrestrial and
marine environment.
 Delta’s are usually composed of three types of deposit
 Topset beds: The larger and heavier particles are the first to
be deposited as the river looses energy
 Foreset beds: Medium calibre particles travel a little further
before they are deposited as more steep angled ‘wedges’ of
sediment
 Bottomset Beds: The very finest particles travel the furthest
before very low velocity/flocculation leads to their deposition
Singh, S, 2005

11.  Classification of delta by dominance
 Wave dominated delta –i.e. Nile delta, Egypt
 Tide dominated delta –i.e. Ganges delta, Bangladesh, India
 Estuarine dominated delta –i.e. Mackenzia, Hudson delta
 Classification of delta by shape
 Arcuate –i.e. Ganges delta, Nile delta
 Birds Foot –i.e. Mississippi delta
 Cuspate –i.e. Ebro delta in Spain

12. Delta type:
Arcuate delta
Tide dominated delta
http://eol.jsc.nasa.gov/debrief/STS066/rep2.htm
Ganges Delta, Bangladesh

13. NASA satellite image in false color
Nile Delta, Egypt
Delta type:
Wave dominated delta
Arcuate delta

14. http://earthobservatory.nasa.gov/IOTD/view.php?id=50500
River Deltas, Lake Ayakum, Tibet
Delta type:
Arcuate delta

15. Mississippi Delta
Delta type:
Birds Foot
Jesse Allen, University of Maryland’s Global Land Cover Facility, andLANDSAT 1

16. Okavango Delta, Botswana
Delta type:
Arcuate delta
Tide dominated delta
http://www.flickr.com/people/8942661@N02

17. Colorado River Dry Delta
http://gallery.usgs.gov/photos/10_15_2010_rvm8Pdc55J_10_15_2010_0#.Ur0mcvfTnrd

18.  Web:
 Image [slide 12]: http://eol.jsc.nasa.gov/debrief/STS066/rep2.htm
 Image [slide 13] : NASA satellite image in false color
 Image [slide 13]: http://earthobservatory.nasa.gov/IOTD/view.php?id=50500
 Image [slide 14]: Jesse Allen, University of Maryland’s Global Land Cover Facility,
andLANDSAT 1
 Image [slide 15]: http://www.flickr.com/people/8942661@N02
 Image [slide 16]:
http://gallery.usgs.gov/photos/10_15_2010_rvm8Pdc55J_10_15_2010_0#.Ur0mcvf
Tnrd
 Info:
 www.wikipedia .com
 www.slideshare.com
 Books: Singh, S; Geomorphology, Prayag Pustak
Bhawan, 2005

19. Thank You