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Class, MS 01

Bahria University Karachi

Submitted to, DR Tabriz

Submitted by, Muhammad Irshad Khan

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Introduction to Deltas

Deltas form where rivers meet the ocean.

They are naturally shaped by the forces of rivers, waves and tides.

Due to their low topography, high productivity, rich biodiversity, and easy transport along

abundant waterways.

Deltas may only comprise 5% of the land area.

Sedimentary Structure

The formation of a delta consists of three main forms: the topset, foreset/frontset, and

bottomset.

(1) The topset beds in turn overlay the foresets, and are horizontal layers of smaller sediment

size that form as the main channel of the river shifts elsewhere and the larger particles of the

bed load no longer are deposited.

As the channels move across the top of the delta, the suspended load settles out in horizontal

beds over the top.

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The topset bed is subdivided into two regions: the upper delta plain and the lower delta plain.

The upper delta plain is unaffected by the tide, while the boundary with the lower delta plain is

defined by the upper limit of tidal influence.

(2) The foreset beds consist of the bed load that the river is moving along which consists of

larger sediments that roll along the main channel.

When it reaches the edge of the form, the bed load rolls over the edge, and builds up in steeply

angled layers over the top of the bottomset beds.

(3) The bottomset beds are created from the suspended sediment that settles out of the water

as the river flows into the body of water and loses energy.

The suspended load is carried out the furthest into the body of water than all other types of

sediment creating a turbidite.

These beds are laid down in horizontal layers and consist of smaller grains.

Formation

River deltas form when a river carrying sediment reaches either (1) a body of standing water,

such as a lake, ocean, or reservoir, (2) another river that cannot remove the sediment quickly

enough to stop delta formation, or (3) an inland region where the water spreads out and

deposits sediments. The tidal currents also cannot be too strong as the sediments would be

washed out into the water body faster than the river can deposit the sediments. And of course

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the river must be carrying enough sediments to be layered into deltas over time. The river's

velocity decreases rapidly causing it to deposit the majority, if not all, of its load. This aluvium

builds up to form the river delta. When the flow enters the standing water, it is no longer

confined to itschannel and expands in width. This flow expansion results in a decrease in the

flow velocity, which diminishes the ability of the flow totransport sediment.As a result, sediment

drops out of the flow anddeposits.

Types of Delta

Deltas are typically classified according to the main control on deposition, which is usually either

a waves, river, or tides.

These controls have a large effect on the shape of the resulting delta.

Wave-dominated deltas

In wave dominated deltas, wave erosion controls the shape of the delta, and much of thesediment emanating from the river mouth is deflected along the coast line.

River delta

A river delta is a landform that is formed at the mouth of a river, where the river flows into an

ocean, sea, lake.

http://en.wikipedia.org/wiki/Stream_channelhttp://en.wikipedia.org/wiki/Sediment_transporthttp://en.wikipedia.org/wiki/Deposition_%28geology%29http://en.wikipedia.org/wiki/Deposition_%28geology%29http://en.wikipedia.org/wiki/Sediment_transporthttp://en.wikipedia.org/wiki/Stream_channel

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Tide-dominated deltas

Erosion is also an important control in tide dominated deltas, such as the Ganges Delta, which

may be mainly submarine, with prominent sand bars and ridges.

Tidal deltas behave differently from river- and wave-dominated deltas, which tend to have a few

main distributaries.

Once a wave- or river- distributary silts up, it is abandoned, and a new channel forms

elsewhere.

In a tidal delta, new distributaries are formed during times when there's a lot of water around

such as floods.

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Gilbert deltas

A Gilbert delta (named after Grove Karl Gilbert) is a specific type of delta that is formed by

coarse sediments, as opposed to gently-sloping muddy deltas such as that of the Mississippi.

For example, a mountain river depositing sediment into a freshwater lake would form this kind

of delta.

While some authors describe both lacustrine and marine locations of Gilbert deltas, others note

that their formation is more characteristic of the freshwater lakes, where it is easier for the river

water to mix with the lake water faster.

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The Ganges Delta in India and Bangladesh is the largest delta in the world and it is also

one of the most fertile regions in the world.

Estuaries

Rivers, particularly those located on coasts with significant tidal range, do not form a delta butenter into the sea in the form of an estuary.

Notable examples include the Saint Lawrence river and the Tangus estuary.

Arcuate Delta

Curved in the shape of a bow. Fan shaped

To the right is a satellite photo of the Nile Delta, notice the fan shape on the right-hand

side of the mount of the river.

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Inland deltas

In rare cases the river delta is located inside a large valley and is called an inverted river delta.

Sometimes a river will divide into multiple branches in an inland area, only to rejoin and

continue to the sea; such an area is known as an inland delta, and often occurs on former lake

beds.

In some cases a river flowing into a flat arid area splits into channels which then evaporate as it

progresses into the desert.

The Inner Niger Delta and the Amazon are notable examples of an inland delta.

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Ecological threats to deltas

Human activities, including diversion of water and the creation of dams for hydroelectric power

or to create reservoirs can radically alter delta ecosystems.

Dams block sedimentation which can cause the delta to erode away.

The use of water upstream can greatly increase salinity levels as less fresh water flows to meet

the salty ocean water.

While nearly all deltas have been impacted to some degree by humans, the Nile Delta and

Colorado River Delta are examples of the ecological devastation caused to deltas by dammingand diversion of water.

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Indus River Delta

The Indus River Delta forms where the Indus River flows into the Arabian Sea in Pakistan.

The delta covers an area of about (16,000 square miles), and is approximately 210 km across

where it meets the sea.

The active part of the delta is 6,000 km in area. The climate is arid, the region only receives

between 25 and 50 cm of rainfall in a normal year.

The Indus River runs through southern Asia and it is one of the longest rivers in the world.

This river flows through the valleys of the Himalayas. It also runs through Pakistan. This river

feeds the forests, plains and countysides. It is a key water resource for the Pakistan economy.

The river plays a major role in the agricultural production and heavy industries in Pakistan.It

flows from the mountain ranges to the sea.The composition deposits in Indus delta mainly

comprise very fine sand , silt and clay.

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Indus River Delta

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REFERENCES

en.wikipedia.org/wiki/River_delta

www.loicz.org/imperia/md/content

en.wikipedia.org/wiki/River_deltawikipedia.org/wiki/River_deltawww.mahalo.com/river-delta

wikipedia.org/wiki/River_deltaen.wikipedia.org/wiki/Estuaryhttps://workspace.novacentral.ca/sites/home

www.questionhub.com/YahooAnswers

en.wikipedia.org/wiki/River_deltaen.wikipedia.org/wiki/Indus_River_Delta

http://www.loicz.org/imperia/md/content/loicz/print/http://www.loicz.org/imperia/md/content/loicz/print/https://workspace.novacentral.ca/sites/home/https://workspace.novacentral.ca/sites/home/http://www.questionhub.com/YahooAnswers/http://www.questionhub.com/YahooAnswers/http://www.questionhub.com/YahooAnswers/https://workspace.novacentral.ca/sites/home/http://www.loicz.org/imperia/md/content/loicz/print/