Deltas are landforms formed at river mouths where sediment is deposited as the river enters a sea or lake. They are fan-shaped areas that can span hundreds of kilometers. The Indus River Delta in Pakistan covers 40,000 square kilometers and has a complex network of distributaries. Deltas form as rivers slow down at their mouths, causing sediment to flocculate and settle, building up over time. Different types of deltas include bird's foot, arcuate, and cuspate shapes, depending on factors like tidal influence. Deltas provide fertile land and resources but are also at high risk of flooding and channel migration due to their unstable sediments.

1. Deltas

2. Description
• A delta is a feature of river deposition found at
the end of a river at its mouth where it
reaches the sea or a lake. Deltas are fan-
shaped, low-lying areas of flat land jutting out
to sea. They can be very large and can span
hundreds of km across. They are comprised of
a range of coarse to fine alluvial material and
are characterised by a complicated criss-cross
network of distributaries.

3. Indus River Delta-(example)
Series of complex
distributaries in a criss-cross
pattern.
Coarse and fine alluvial
material
•Location: Pakistan
•Size: 40000 sq. km

4. Formation
• A delta is alluvial landform where the mouth of a
river flows into an ocean. As the river reaches its
mouth it loses energy and competence so
therefore slows down. This reduction in speed
results in the river depositing its load. As the sea
is unable to remove this build up of sediment fast
enough, a delta is formed. When rivers like the
Mississippi reach the sea, the meeting of fresh
and salt water produces an electric charge which
causes clay particles to collect together and to
settle on the seabed. This is a process called
flocculation.

5. • As these particles of sediment flocculate and
therefore increase in size, they are deposited
under the influence of gravity. Over time these
factors result in the build up of sediment both
outwards and in height. Later, a system of multiple,
dividing channels form within the delta and these
are called distributaries. These divide at points of
channel blockage and come together again to form
a maze of active and inactive channels.
• http://www.crescent.edu.sg/crezsphere/applets/G
eography/deposit.html

6. Different types of deltas
• Bird’s foot- where delta formation is river-
dominated and less subject to tidal or wave
action, a delta may take on a bird’s foot shape.
The Mississippi
delta is an
example of a
bird’s foot delta.
The shape of the
delta is like a
claw.

7. • Arcuate delta- has a rounded, convex outer
margin. A good example is the Nile delta
which is dominated a little more by tidal and
wave action.
The land around
the river mouth
arches out into
the sea.
The river splits many
times on the way to
the sea, creating a
fan effect.

8. • Cuspate delta- where the material brought
down by a river is spread out evenly on either
side of its channel. It is like a cup and is
shaped by gentle, regular, but opposing, sea
currents or longshore drift. An example of a
cuspate delta is the Tiber.
Pointed like a
tooth or a cup.

9. Human impacts of deltas
Positive impacts
• Deltas provide fertile land and are associated with
good fishing grounds offshore, and with oil and gas
deposits beneath the surface.
Negative impacts
• Deltas are by their nature very dynamic landforms due
to the fact that they are composed of unstable,
unconsolidated sediments and are subject to channel
migration as well as to subsidence by the sea.
• Deltas flatness makes the land surrounding it high
flood-risk areas.

10. Ganges delta-Human uses
• A large part of the nation of Bangladesh lies in
the Ganges Delta, and many of the country's
people depend on the delta for survival. In fact it
is believed that up to of 300 million people are
supported by the Ganges Delta.
Agriculture and fishing
• Approximately two-thirds of the Bangladesh
people work in agriculture, and grow crops on
the fertile floodplains of the delta. The major
crops that are grown in the Ganges Delta are rice,
tea and a vegetable called jute.

11. • Fish farms have also been set up for the poor by scientists to
improve the local fishing methods. Shrimp and salmon are the
major types of fish farmed here and most of them are
exported and sold.
• However, people have to be careful on the river delta as
severe flooding also occurs. In 1998, the Ganges flooded the
delta, killing about 1,000 people and leaving more than 30
million people homeless. The rice crops were also destroyed
which left may of the surviving people starving.