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
10.
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