Part 2 Quit Landforms and exogenetic processes 2.2 How can a river change the land?

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Landforms and exogenetic processes

2.2 How can a river 2.2 How can a river change the land?change the land?

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What is the discharge of a river?A river can shape the land through exogenetic processes, including ________, ______________ and ___________.

erosion transportationdeposition

How can we know the amount of

energy of a river?

How can we know the amount of

energy of a river?

The energy determines the kinds of work a river can do.

The __________ of a river indicates the amount of energy of a river.discharge

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What is the discharge of a river?

It is the _______ of water in a river passing a given cross-section of its channel within a given amount of time, i.e. its ________.

volume

velocity

The (larger / smaller) the discharge, the more the energy a river has.

Area of stream cross-section (A)= W D (in the unit of m2)

Velocity (V):Measured by an instrument, in the unit of ‘m/sec’

Discharge (Q)= A V (Answer in the unit of m3/sec)

Stream width (W)

Average depth (D)

Velocity (V)

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What are the factors affecting the energy of a river?

1 Amount of channel water

2 Speed of water flow

Energy of a river

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What are the factors affecting the energy of a river?


Energy of a river

A Channel gradient

B Channel friction


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How can a river erode the land?

River water can erode rock materials from the banks and bed through ______________.

fluvial erosionThe rate of erosion is high when:

- the energy of the river is (low / high).

- the resistance of the rocks is (low / high).

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Vertical erosion / Downcuttin

g

Vertical erosion / Downcuttin

g

Lateral erosionLateral erosion

Headward erosion

Headward erosion

Direction of fluvial erosionDirection of fluvial erosion

How can a river erode the land?Three directions of fluvial erosion

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A river removes rocks from its _____.

The valley will be _________.

bed

deepened

Three directions of fluvial erosionVertical erosion / Downcutting

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The valley is ________.

A river removes rock along the _______.banks

widened

Three directions of fluvial erosionLateral erosion

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The valley is increased in _______.

Loose rock debris is brought down by the _________ flow behind the river source.

The river source extends (forward / backward).

length

Three directions of fluvial erosionHeadward erosion

overland

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How can a river erode the land?Four ways of fluvial erosion

In what ways can erosion take place?

In what ways can erosion take place?

Physically and chemically.

Does erosion by water just

remove the rock materials?

Does erosion by water just

remove the rock materials?

No. It can also reduce the size of the rock materials.

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Ways of fluvial erosion

Ways of fluvial erosion

AttritionAttritionCorrosion /

Solution

Corrosion /

SolutionAbrasionAbrasion

Hydraulic

action

Hydraulic

action

How can a river erode the land?Four ways of fluvial erosion

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What factors control the rate of erosion of a river?

How can a river erode the land?

Rate of fluvial erosion

________ power of river

___________ of rock

Erosive

Resistance

Angularity, amount and weight of load

Speed of water flow

Amount of channel water

Water quality (Acidity, temperature)

Rock structure

Mineral composition

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How can a river erode the land?What factors control the rate of erosion of a river?

How do human

activities cause more fluvial

erosion?

How do human

activities cause more fluvial

erosion?

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In what ways does a river carry its load?

Suspension

TractionSolution

Saltation

Suspended load

Bed loadBed load

Dissolved load

The downstream movement of eroded material is called ______________.transportation

Four ways of transportation

Very large particles roll or slide on the river bed

Large particles hop and bounce along the river bed

Small particles are carried in the water without touching the river bed

Dissolved minerals carried by water

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In what ways does a river carry its load?What factors control the amount of load in a river? Why are the colour

of these two rivers different?

Why are the colour of these two rivers

different? Because they carry different

amount of load.

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In what ways does a river carry its load?What factors control the amount of load in a river?1 Energy for transportation

Larger amount of channel water

Higher speed of water flow

A river can carry (more / less) load(More / Less)

energy for transportation A river can carry

(heavier / lighter) load

OR

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In what ways does a river carry its load?What factors control the amount of load in a river?2 Rate of erosion

The erosion rate of the river basin controls the supply of _____.load

(Dense / Sparse) vegetation helps hold the soil and prevents it from fluvial erosion.

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In what ways does a river carry its load?What factors control the amount of load in a river?3 Presence of lakes

The lakes along the river channel help trap the load.

The amount of load in the river then become (smaller / larger).

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____________ occurs when a river loses its energy.

Deposition

The deposited materials are called __________.sediment

What makes a river lose its energy?

Amount of channel water decreases

Speed of water flow decreases

(More / Less) energy for transportation

OR The load deposits

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Please click below for footage

Is there a sequence of deposition?

What makes a river lose its energy?How does a river drop its load?

Yes, there is.What is the sequence?

The largest and heaviest sediment deposits first.

The smallest and lightest sediment deposits last.

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What is a sequence

of deposition

of these four load?

The (lightest / heaviest) load will deposit first and form the bottommost layer.

The finest one forming the top layer.

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The load forms layers at different distances from the mouth of the river.

River

Sea

Pebbles and sand Silt Clay

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The water flowing in a river channel is called ________ flow.

What are the other three

kinds of water flow?

What are the other three

kinds of water flow?_________ flow, ________ flow

and _____ flow.

These three kinds of water

flow will supply water to the

channel flow.

channelOverlandthrough

base


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Overland flow

Throughflow

Base flow

Vegetation cover

Gradient

Drainage density

(more / less) rainfall and snowmelt.

The amount of channel water increases when there is:

(more / less) evaporation.a (larger / smaller) catchment area.

(more / less) vegetation cover.

a (faster / slower) infiltration rate.

a (steeper / gentler) slope gradient.

a (lower / higher) drainage density.

Rainfall

Evaporation

Infiltration

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A Channel gradient

Channel A Channel B

Which channel has a greater

speed of flow?

Which channel has a greater

speed of flow? Channel A.

The steeper the gradient, the (slower / faster) the flow, and the (higher / lower) the energy.

Which channel has a higher

energy?

Which channel has a higher

energy?Channel A.

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B Channel friction

Why does friction affect the speed of water flow?

Why does friction affect the speed of water flow?

It (prevents / helps) water from flowing downstream.

Energy is needed to overcome friction.

Lesser energy causes water flows (faster / slower).

What factors affect channel

friction?

What factors affect channel

friction?

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(less / more) friction

Do you know which channel has a greater

speed of flow?

Do you know which channel has a greater

speed of flow?

Channel A Channel B

Channel (A / B) has a shorter wetted perimeter

The perimeter of the banks and bed which are in contact with the water is called the .wetted perimeter

The wetted perimeter of Channel A:

The wetted perimeter of Channel B:

a Channel shape

The speed of flow becomes (faster / slower) in Channel A.

(more / less) energy

= 21m9m + 6m + 6m

= 24m3m + 3m + 18m

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The _____________ one produces the lowest friction.

Look at the three channels shown. They are of the

same cross-sectional area.

Look at the three channels shown. They are of the

same cross-sectional area.

a Channel shape

semi-circular

a Semi-circular

Which shape of channel

produces the lowest friction?

Which shape of channel

produces the lowest friction?

b Square

c Wide and shallow

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Channel (A / B) has greater friction and lower speed of flow.

Same cross-sectional area

Channel A Channel B

Same cross-sectional area

b Channel roughness

Channel (A / B) is rougher.The wetted perimeter of Channel (A / B) is longer.

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The channel becomes less ________.

The wearing away of the bed and banks by the _____ carried by a river.

Abrasion is the main process in ________ erosion.

uneven

load

Please click above for animation

How can a river erode the land?Four ways of fluvial erosionAbrasion

vertical

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The load becomes (larger / smaller) and (rectangular / rounder) downstream.

knocks againstThe load in the river _______________ each other and break down into small pieces.

How can a river erode the land?Four ways of fluvial erosionAttrition


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The running water is forced into cracks at the banks.

The _____________ breaks up the river bed and banks.

running water

How can a river erode the land?Four ways of fluvial erosionHydraulic action


The cracks are (enlarged / reduced). Rocks are loosened and removed.

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For example: ________ in limestone.

Water dissolves and removes the _______ minerals from rocks.

The rocks are weakened and easily broken up.

soluble

calcium

How can a river erode the land?Four ways of fluvial erosionCorrosion / Solution


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Part 2 Quit Landforms and exogenetic processes 2.2 How can a river change the land?