Download Rivers Notes S2

THIS NOTES BELONG TO:
SEC 3 GEOGRAPHY
_____________________________
A GEOGRAPHER
RIVERS (SET 2)
Objective:
 To explain the different river processes
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Name and describe the 3 river processes.

They are erosion, transportation and deposition.

Erosion is the removal and movement of rocks downstream by the river.

Transportation occurs when a river has sufficient energy to overcome friction
within the channel, thus allowing materials to be carried or transported
downstream.

Deposition occurs when the river does not have enough energy to either
erode or transport material.
Explain how the river energy determines the type of processes that occurs
along the river.
Fig.1

The river energy is determined by the speed of flow (velocity) of the river and
the volume of the river.

The higher the speed and volume of the river, the higher will be the energy of
the river. (Refer to Fig 1)
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PREPARED BY: MISS SUHAILA MOHAMED NOOR
SEC 3 GEOGRAPHY

The rate of erosion is dependent upon the energy of the river. A river with high
velocity and volume will possess greater energy and hence more erosive
power.

The ability of a river to transport materials downstream is dependent upon the
energy of the river and the size of the materials involved. A river with high
velocity and volume will have sufficient energy to overcome friction within the
channel and transport the materials downstream.

A river will deposit its materials when it loses its energy. As the velocity and
volume of the river is reduced, it will put down or deposit the load it is carrying.
EROSION
Explain the difference between lateral and vertical erosion.

Vertical erosion results in the deepening of the valley while lateral erosion
results in the widening of the valley.

Vertical erosion occurs when rocks and other materials on the river bed are
removed while lateral erosion occurs when rocks and other materials along
the sides of the channel are worn away.
Describe the processes of erosion that occur along river.
Fig. 2 The 4 main types of erosion
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PREPARED BY: MISS SUHAILA MOHAMED NOOR
SEC 3 GEOGRAPHY
TYPE
Hydraulic
Action
EROSIVE
AGENT
Fast -flowing
water
PROCESS
A river with high energy is capable of loosening
the rocks and dislodging them from the river bed
and banks.
The fast flowing water will erode the river channel
by removing the rocks that are protruding and it is
then carried down the river.
Corrasion
(Abrasion)
Rock
Fragments
It occurs when rocks are dragged along the river
bed or against the river banks.
As a result, rocks and soils are scrapped off the
sides and bottom and carried away with the water.
The grinding action causes the river bed and
banks to widen and deepen.
Attrition
Rock
Fragments
The river carries a load of materials which contain
rock fragments and other materials.
These materials constantly collide with one
another as they move.
Overtime larger rocks are slowly broken down and
their rough edges may become smoother.
Solution
Acidic Water
Rainwater reacts with carbon dioxide to form a
weak acid called carbonic acid.
The rainwater will fall into rivers and the weak acid
dissolves the minerals present in the rocks on the
river bed and banks.
An example of this mineral is calcium carbonate in
limestone.
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PREPARED BY: MISS SUHAILA MOHAMED NOOR
SEC 3 GEOGRAPHY
TRANSPORTATION
Describe the processes of transportation that occur along a river.
Source: Waugh, D. (2002)
TYPE
EXAMPLES OF MATERIAL
TRANSPORTED
Traction



Boulders
Pebbles
Gravel
Saltation

Course Sand
Suspension
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

Silt
Clay
Sand
Solution

Calcium carbonate
found in rocks
PROCESS
It involves the transportation of larger
size materials by rolling and sliding
them along the river bed.
This transportation process moves
small materials downstream by lifting
it up and dropping them onto the river
bed in a bouncing motion.
It involves the transportation of fine
particles that are carried along the
river without touching the river bed.
These materials are held in
suspension and form a large portion of
the river load.
Erosion takes places when minerals
found in rocks are dissolved. These
dissolved materials will be transported
by the water downstream.
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PREPARED BY: MISS SUHAILA MOHAMED NOOR
SEC 3 GEOGRAPHY
DEPOSITION
What are the factors that may cause deposition to occur?
Deposition occurs when a river does not have enough energy to either erode or
transport material.
This occurs when the speed or volume of the river is reduced.
As a river loses its energy, large particles such as rocks and boulders are deposited
first, followed by smaller ones such as gravel, sand and silt.
Thus, factors affecting the speed and volume of a river are also factors that
determine whether or not deposition will take place.
Deposition occurs when:

there is a period of low precipitation

a river enters a lake or sea resulting in a decrease in its speed

a river flows along the shallower side of a river channel as there is increased
friction with the river bank causing the river to slow down

the river received a sudden increase in load such as the period after a
landslide

the river channel is obstructed by aquatic plants or protruding bed rocks.
HJULSTROM CURVE
The Hjulstrom curve shows the speed at which particles of different sizes will require
to be eroded, deposited or transported in a river.
The larger the particle, the higher the speed is required for it to be eroded, deposited
and transported.
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PREPARED BY: MISS SUHAILA MOHAMED NOOR
SEC 3 GEOGRAPHY
Erosion
Smaller particles finer than 0.1 mm such as clay require a higher river speed in order
to erode them.
Higher speeds are necessary as clay particles are highly cohesive and would stick to
each other, hence a higher speed is required to loosen the particles.
Transportation and Deposition
After particles are eroded, it will either be transported or deposited, depending on
their sizes and river speed.
Larger particles require higher speeds to be transported.
But if the speed of the river decreases, these large particles will be deposited as they
are heavier.
Smaller particles require low speed (almost none) in order to be transported.
Their small size allows them to be deposited very easily onto the river bed.
The smallest particle will remain in suspension and will not be deposited even when
the river has stopped flowing.
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PREPARED BY: MISS SUHAILA MOHAMED NOOR