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2.3 How does a river 2.3 How does a river shape the land along its shape the land along its
different courses?different courses?
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How do the characteristics of a river change along its course?
Can you find these kinds of landform at the same place?Can you find these kinds of landform at the same place?
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Landforms and exogenetic processes
What are the different sections along a river course?
Upper course
Middle course
Lower course
They are different in _________ and _____ _______.
gradientriver
energy
Relatively straight, with bends around obstacles Winding
Big bends occur
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Landforms and exogenetic processes
What are the different sections along a river course?
Gradient of the upper course: ______
Gradient of the middle
course: __________
Gradient of the lower
course: _______
steep
moderategentle
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The energy and work vary along the three courses, different landforms are
formed!
What are the different sections along a river course?
Therefore, different landforms are found at different sections
along a river course.
Upper course
Middle course
Lower course
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What landforms are formed at the upper course?
Is this the impression you
have for the upper course?
Is this the impression you
have for the upper course?
What do you think about the energy of river at the upper
course when compared with the middle and lower
course? (Greater / Less)
What do you think about the energy of river at the upper
course when compared with the middle and lower
course? (Greater / Less)
The catchment areas of the tributaries at the upper course is (large / small). The amount of the channel water is (large / small).
The energy is less because:
Large boulders in the channel (increase / decrease) the channel roughness.
(Much / Less) of the energy are used for overcoming friction.
How much energy is there?
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Landforms and exogenetic processes
What landforms are formed at the upper course?What is the work involved?
The cross-section of a valley at the upper course
________ erosion is the dominant work at the upper course.Vertical
Headward erosion also occurs when water starts to gather.
Because of the small river energy, the rate of erosion is (slow / fast).
(Small / Large) load can be transported.Deposition is (common / rare).
What is the direction of
the erosion at the upper course?
What is the direction of
the erosion at the upper course?
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Landforms and exogenetic processes
What landforms are formed at the upper course?What are the landforms produced?
Landforms at the upper course
Interlocking spurs
Rapids Potholes
Gorges Waterfalls
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Landforms and exogenetic processes
How is the land shaped at the middle course?How much energy is there?
How much energy is there at the middle course when compared with the upper
course? (Greater / Less).
How much energy is there at the middle course when compared with the upper
course? (Greater / Less).
Do you know why?
Do you know why?
More tributaries are joining the river.
The amount of river water (increases / decreases).
The river energy (increases/ decreases).The channel becomes _________. The water flows ______.smootherfaster
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What is the work involved?
How is the land shaped at the middle course?
What is the main work at the
middle course?
What is the main work at the
middle course?
(Erosion / Transportation /
Deposition)
(Erosion / Transportation /
Deposition)Why?Why?
The river flow is faster and with more energy.
Erosion occurs, but there is extra energy for _____________.
transportation
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What are the landforms produced?
How is the land shaped at the middle course?
Landforms at the middle course
Slip-off slopes River cliffs Meanders Bluffs
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Landforms and exogenetic processes
What landforms are formed at the lower course?How much energy is there?
Is the energy large or
small at the lower
course?
Is the energy large or
small at the lower
course?
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Landforms and exogenetic processes
What landforms are formed at the lower course?How much energy is there?
The cross-section of s valley at the lower course
The channel here accommodates (less / more) water than that of the upper course.
The river bed is (smooth / rugged), so the friction here is greatly (reduced / risen).
It has the (smallest / largest) discharge among the three courses.
Therefore, the flows are at a (low / high) speed.
The lower course has the (highest / lowest) energy.
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Landforms and exogenetic processes
What landforms are formed at the lower course?How much energy is there?
Does it mean the river energy is
high all the time at the lower course?
(Yes / No)
Does it mean the river energy is
high all the time at the lower course?
(Yes / No)
The river energy drops when:the channel flow is blocked by sea water at the _______ of the river.
mouththe amount of river water is reduced during the (wet / dry) seasons.
flooding occurs and the flood water has not yet retreated from the valley floor.
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Landforms and exogenetic processes
What landforms are formed at the lower course?What is the work involved?
Erosion- at the (inner / outer) banks of the river.
Transportation- bringing the load towards the mouth of the river.
Deposition- whenever and wherever speed of flow is lowered.
What is the work at the lower course?
(Erosion / Transportation / Deposition)
Ha! Ha! All three work occur at the
lower course!
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Landforms and exogenetic processes
What landforms are formed at the lower course?What are the landforms produced?
Landforms at the lower course
Flood plains Deferred tributaries
Oxbow lakes
Deltas
Levees Braided streams
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Case study: How does the Chang Jiang change along different courses?
Upper course
Middle course
Lower course
Yichang
Hukou
Tuotuo He
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Landforms and exogenetic processes
Case study: How does the Chang Jiang change along different courses?
Do you know any characteristics of the Chang Jiang?
The longest river in China and ______ longest in the world.
Average annual discharge: 30,000 m3/sec.The load is not heavy as compared with the __________.
It flows past the ___________ _______ humid area of China.
About 70- 80% of the river water comes from _______.rainfall
third
Huang He
humidsubtropical
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Case study: How does the Chang Jiang change along different courses?
Middle course
Lower courseUpper course
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Landforms and exogenetic processes
What are the characteristics of the upper course of the Chang Jiang?
The river source: The Tuotuo He
At the Jinsha Jiang
The discharge is small.
The gradient is gentle.
The river flows slowly.
South-flowing.The channel winds through interlocking spurs.
The gradient is steep.The Hutiaoxia at the Jinsha Jiang
Vertical erosion
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What are the characteristics of the upper course of the Chang Jiang?
At the Sichuan Pendi
More rainfallMany large tributaries join the main channel
Discharge increases rapidly
Great erosive power
Forms Sanxia
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What are the characteristics of the middle course of the Chang Jiang?
A big drop in _______ and the _________.altitudegradient
Meanders are formed.
Numerous lakes are found, e.g. Dongting Hu.
286 km
Length of the river between them: 712 km
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What are the characteristics of the lower course of the Chang Jiang?
The land is flat and low, e.g. the Chang Jiang Delta plain.
The tributaries are shorter than those in the middle and upper courses.
Many meanders and braided streams.
Levees and deferred tributaries are found.
Delta and lagoon are formed, e.g. Tai Hu.
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How does a river basin work as a system?What is a system?
It is a group of things that interact within a boundary to perform some functions.
It includes _______, __________ and ________.inputs processes outputs
Open system Closed system
EnergyEnergy
Matter
Input InputProcesses ProcessesOutput Output
Boundary of the system
EnergyEnergy
Matter
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Landforms and exogenetic processes
How does a river basin work as a system?
Inputs Processes Outputs
Solar radiation
Water
Rocks
RadiationConduction
Evaporation
Absorption
Precipitation
Exogenetic
processes
Channel
outflow
Evapo-
transpiration
Transportation
Heat
Water
Vapour
Sediment
Weathering Mass movement Erosion Interception Drip flow/ Stem flow Surface run-off Infiltration
Subsurface run-off Transportation Deposition
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________ erosion deepens the channel and makes the obstacles more marked.
1 Interlocking spurs
What are the landforms produced at the upper course?
They are the spurs interlocking with each other.
Vertical
The river has too little energy to remove obstacles, so the river water flows around them.
Interlocking spurs
Valley is deepened
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Landforms and exogenetic processes
2 Gorges
What are the landforms produced at the upper course?
Downcutting is (slower / faster) than lateral erosion.
This creates a (deep / shallow) and (narrow / wide) V-shaped valley, i.e. gorges.
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3 Rapids
What are the landforms produced at the upper course?
The river water is unable to erode the layer of _________ rock.
resistant
The river bed becomes (even / uneven).
The turbulent currents are called rapids.
Rapids
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4 Waterfalls
What are the landforms produced at the upper course?
Less resistant rock is eroded by river water at a (slower / faster) rate.
The river falls vertically down.The falling water produces strong _________ action, forming a circular hollow filled with water.
hydraulic
Water flowWaterfall forms
Large angular boulders
Plunge pool forms
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5 Potholes
What are the landforms produced at the upper course?
When a river flows over an uneven surface, it causes ___________ in the water.
turbulence
What is this?What is this?
A pothole is formed when the water drills with the load it carries.
How does it form?How does it form?
Pothole
Which type of fluvial erosion is involved within
the potholes?
Which type of fluvial erosion is involved within
the potholes?Abrasion.
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Landforms and exogenetic processes
1 Slip-off slopes and river cliffs
What are the landforms produced at the middle course?
Which part of the river
has the fastest flow?
Which part of the river
has the fastest flow?
Fastest part of the river flow
What are the work
involved at the inner and outer
bank?
What are the work
involved at the inner and outer
bank?
Outer bank: ______________
Inner bank: __________
lateral erosion
deposition
What are the two
landforms produced?
What are the two
landforms produced?
River cliff
Slip-off slope
River cliff
Slip-off slope
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2 Meanders
What are the landforms produced at the middle course?
The outer bank gets worn away through _______.
erosionThe inner bank builds up through __________.
depositionThe river (bends/ straightens).Each bend is called a meander.
Outer bank
Inner bank
Meander appears
Lateral erosion creates river cliffs
More concave
More convex
Slip-off slopes form
Faster stream of water thrown towards outer banks Sediment Low river cliff
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__________ at outer bank are pushed back and join into lines, forming bluffs.
3 Bluffs
What are the landforms produced at the middle course?
Erosion at outer bank creates river cliffs
The meanders migrate downstream.
They remove the interlocking spurs on their way through ________.
River cliffs
erosion
Bluffs
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Landforms and exogenetic processes
1 Flood plains
What are the landforms produced at the lower course?
The load is carried to the valley floors by the flood water.
Repeated flooding and __________ build up a flat area. deposition
The deposits on the flood plain are called ________. They are fertile and good for farming.
alluvium
During floods, water overflows from the
channel to the lands, bringing sediment with it
_________ builds up on the river bed, silting occurs
Sediment
Flood plain
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2 Levees
What are the landforms produced at the lower course?
The flood water overflows from the channel.
The (small / large) load is dropped at the river banks.
The banks are (raised / collapsed).The levees are the ridge-like features at the river banks.
Levee
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3 Deferred tributaries
What are the landforms produced at the lower course?
Tributaries flow _______ to the main channel.parallel
They finally break through the ______ and join the main channel. levees
Defferred tributary
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4 Oxbow lakes
What are the landforms produced at the lower course?
This is an oxbow lake.
It is developed from a meander!
Do you know how?
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4 Oxbow lakes
What are the landforms produced at the lower course?
Oxbow lakes are the product of active ______ erosion and ___________ in the river.lateraldeposition
When two outer banks of two bends meet, a new channel is formed.
_________ silts the original channel.Sediment
An oxbow lake is formed.Water flow
The meanders bend more.The (outer / inner) banks are pushed backward
Sediment
Deposition Little water enters the old channel
Oxbow lake
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5 Braided streams
What are the landforms produced at the lower course?
Water levels (rise / drop) during dry seasons.
(Erosion / Deposition) forms low ridges and blocks the river flow.
In wet seasons, the river is forced to split into several separated channels.
Braided streams
The braided streams rejoin
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Onshore currentOnshore current
Deposits
Onshore current
New deposits during low-flow season
Onshore current
Distributary
Lagoon
Onshore current
Mud-flat or marshes
Delta forms
6 Deltas
What are the landforms produced at the lower course?
A delta is a gently sloping platform of _________ gradually builds up and extends into the ____.
sediment
sea
It is formed at the mouth of the river.The velocity of flow (rises / drops)
It is a fan-shaped mud-flat.