Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 2.3 How does a river shape the land along its different courses?

Part 2

Quit© Oxford University Press 2006

Landforms and exogenetic processes

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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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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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!


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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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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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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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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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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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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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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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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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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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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Middle course

Lower courseUpper course

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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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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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2 Gorges


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


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


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


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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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


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


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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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


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


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


This is an oxbow lake.

It is developed from a meander!

Do you know how?

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4 Oxbow lakes


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


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


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.

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Part 2 Quit © Oxford University Press 2006 Landforms and exogenetic processes 2.3 How does a river shape the land along its different courses?