A delta forms when a river enters a standing body of water and its velocity decreases, causing sediment deposition. As fresh river water mixes with salt water, flocculation occurs, causing fine particles to sink out of suspension. Deltas form where deposition exceeds sediment removal. Deltas are composed of topset, foreset, and bottomset beds and can be arcuate, bird's foot, or cuspate shapes.

1. Depositional Fluvial Landforms

2.  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  bedload and suspended
material are ‘dumped’

3.  Delta’s form 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.  Deltas only form where rate of deposition exceeds rate
of sediment removal – i.e. Where the critical threshold
is no longer met and the system has fallen out of
dynamic equilibrium. 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

6.  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

8.  Delta’s can be categorised into three main shapes
 Arcuate
 Birds Foot
 Cuspate

9. Arcuate
Delta’s
•The most common
shape of delta
•Characteristics:
curving shoreline
(smoothed by long
shore drift), distinct
pattern of drainage
(branching of
distributaries), and
typically more ‘gravely’
deposits .
•Example: the Nile
Delta

10. Birds Foot
Delta
•‘Fingers’ of
deposition build
out into the sea
along the
distributaries
channels giving an
appearance like a
birds claw.
Typically with a
finer sediment
•Example: the
Mississippi delta

11. Cuspate
Delta
•A cuspate delta is
shaped like a tooth
by gentle but regular
opposing currents
in the water body
the river flows into,
or longshore drift
•Example: The river
Ebro delta in Spain

12.  Web:
 Image [slide 3]:
http://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/NarsarsuaqGreenland-
ArcuateDelta.jpg/380px-NarsarsuaqGreenland-ArcuateDelta.jpg
 Image [slide 10] : http://strata.geol.sc.edu/MARINESEDIMENTS/delta/Nile.jpg
 Image [slide 11]:
http://www.es.ucsc.edu/~es10/classnotes/images/MississippiDelta.drawn.jpg
 Image [slide 12]:
http://www.iberianature.com/material/photos/google_earth_spain_2/images/delta_de_ebr
o.jpg
 Info: http://wiki.answers.com/Q/Examples_of_cuspate_deltas
 Books: AQA text book, Oxford dictionary of
Geography