river changes and landforms
TRANSCRIPT
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River Characteristics,
Changes & Landforms
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CatchmentThe area from which water drains into a particular drainage basin.
Tributary A river which joins a larger river.
ConfluenceThe point at which two rivers join.
Watershed The boundary dividing one drainage basin from another- a ridge of high land.
What is a drainage basin?
SourceThe upland area where the river begins.
MouthWhere the river flows into the sea, or sometimes a lake.
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Watershed
Tributary
Features of a drainage basin on a map.
Confluence
a
b
c
Source
d
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The Long Profile of a River
Changes in the river as it goes downstream from source
to mouth.
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Long ProfileH
eig
ht
abo
ve s
ea l
evel
in
m
eter
s.
0 5
0 1
00
150
200
25
0
35 30 25 20 15 10 5 0
Distance from sea in Kms.
Gradient/slope decreasing
Velocity/flow increasing
Cumecs/discharge increasing
Energy increases
AUpper Course
BMiddle Course C
Lower Course
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Valley & Channel Cross-Sections
A
Upper Course
B
Middle Course
C
Lower Course
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Upper Course Middle Course Lower Course
Long ProfileSteeply sloping towards the lower sections of the river
Shallow slopes towards the mouth of the river
Almost at sea level, very gently sloping towards its
mouth
Cross ProfileSteep sided v-shaped
valley. Thin river channel, deep in places
v-shaped valley remains with a wider valley floor and the
river begins to meander across it. The river channel begins to widen and become
deeper.
Wide, shallow valley, with large flood plains and
meanders. The river channel is wide, deep and smooth
sided.
Erosion & Deposition
Primarily vertical erosion, through attrition, abrasion
and hydraulic action. Large boulders deposited and
eroded in situ.
Continues to cut vertically. But it also begins to cut
laterally as it gets closer to base level. Deposition occurs in the slower moving insides
of meanders.
Primarily cuts laterally as it has almost reached base
level. The erosive energy of the river is almost totally concentrated on cutting
sideways. Much deposition occurs.
Transportation Traction and saltationSaltation, suspension and
solutionMainly suspension and
solution.
FeaturesInterlocking spurs;
waterfalls; V-shaped valley; gorges
Meanders; slip-off slopes; ox-bow lakes
Deltas; flood plains; levees; meanders; ox-bow lakes
Velocity
Relatively slow moving. Despite areas of fast
flowing water, the large amount of material on the river channel bed means that friction will slow the
water down.
The water has increased in speed as the channel widens
and becomes smoother. Some boulders cause friction
to slow it down a little.
The fastest section of the river, as the channel is
widest, with very smooth sides, and the greatest
volume of water.
What are the main features of a river?
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The Upper Course of a river
Learning Objectives: •To know and understand the formation of landforms in a river’s upper course.•To understand the processes that operate in a river’s upper course
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What processes occur in a river?
There are 3 processes taking place in every river. These are:
Erosion
Transportation
Deposition
(The wearing away of the land)
(The movement of eroded material)
(The laying down of eroded material)
There are also two other processes that shape the river valley. These are weathering and mass movement.
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Shaping the river valley.
There are also two other processes that shape the river valley. These are weathering and mass movement.
Weathering = the breakdown of rock material.
Mass movement = the movement downslope of broken down rock material due to gravity.
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Weathering & Mass Movement.
The 3 main types of weathering are show below in the wrong order. Sort the statements out into the right order and copy these onto your sheet. Underneath copy out a definition of mass movement.
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Erosion ProcessesMatch up the key word with the
definition.
• is when the river is loaded with material in suspension and scours away at the river banks. (Sandpaper effect)
• is the shear force of the river impacting on the sides of the river banks.
• is substances carried in solution such as acids. They dissolve rocks away over long periods of time.
• is when bed load collides into each other with the current flow and breaks down into smaller particles.
Abrasion (Corrasion)Abrasion (Corrasion) - - Hydraulic Action Hydraulic Action --
CorrosionCorrosion - - AttritionAttrition --
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Erosion ProcessesMatch up the key word with the
definition.Abrasion (Corrasion)Abrasion (Corrasion) is when the river is loaded
with material in suspension and scours away at the river banks. (Sandpaper effect)
Hydraulic ActionHydraulic Action is the shear force of the river impacting on the sides of the river banks.
CorrosionCorrosion is substances carried in solution such as acids. They dissolve rocks away over long periods of time.
AttritionAttrition is when bed load collides into each other with the current flow and breaks down into smaller particles.
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Key words - Transportation.
• Traction – where large rocks and boulders are rolled along the river bed. Happens most in times of flood, when the current is strongest.
• Saltation – where smaller stones are bounced along the river bed in a leap frogging motion
• Suspension – where very small grains of sand or silt are carried along with the water
• Solution – where some material is dissolved (like sugar in a cup of tea) and is carried downstream. Occurs often in limestone landscapes where the water if very acidic.
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Methods of transportation.
Traction Saltation Suspension Solution
Shows the rate of flow needed
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Upper valley characteristics
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Upper valley characteristicsCan you add an annotation to each arrow to
explain the characteristic?
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Upper valley characteristics
“V”shape valley, vertical erosion dominant
Interlocking spurs
Slumping and landslides - very active hill slopes
Narrow, shallow channel, low velocity and discharge
Large bed load derived from upstream and from valley sides
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Narrow Channel
Lots of tributaries
High land so source of river
Contour lines close together – steep valley sides
Steep river gradient – contours close together
Direction of flow shown by lower land
No flood plain and V-shaped valley
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1 2
3 4
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Interlocking spurs A typical upper course V-Shaped valley with interlocking spurs, steep valley sides and active slope processes.
The diagram below shows the formation of interlocking spurs.
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Can you draw an annotated sketch of this valley to show how it is formed?
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River load in upper course
Boulders are large and semi-rounded, due to attrition within the load and abrasion with the stream bed and banks
Why are they rounded?
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Rapids in the Upper Tees Valley
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Formation of Rapids
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High Force waterfall, R. Tees
WHAT IS A WATERFALL?
A waterfall is formed where water flows over a cliff or very steep drop in the river's bed.
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High Force Waterfall R. Tees
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Formation of a Waterfall.• A waterfall is a steep drop in the course of a river.
• They form when a band of hard resistant rock (cap rock) lies over softer, less resistant rock.
• The softer rock is quickly eroded by hydraulic action and abrasion, causing the harder rock to be undercut.
• The hard rock overhangs until it can no longer carry its own weight.
• The overhang collapses and then breaks up in the water below.
• The great power of the water at the base of the waterfall causes a plunge pool to form.
• The bed of the river below the waterfall contains boulders eroded by splash back from behind the waterfall.
• Over time the process above is frequently repeated and eventually a steep-sided gorge forms as the waterfall retreats up stream.
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Waterfall formationLook at the diagram, How is a waterfall formed?
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Can you put the labels below into the correct place on he diagram?
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High Force waterfall, R. Tees
Waterfalls create a gorge upstream as they recede, This is a steep sided valley with no floodplain.
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Upper Course of a River
Land use:Few settlements, Recreation, Farming, Forestry
Steep valley sides
Evidence of tributaries
Reservoir
High land
Narrow channel and no floodplain
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Waterfalls
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The Middle and Lower Course of a River
•To understand the main processes that operate in the middle and lower course of a river.•To understand how meanders and oxbow lakes are formed.
Learning Objectives
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This is a picture of a river in its middle course. Can you recognise and explain the differences between the upper and middle course of a river?
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Erosion is still an important process.
The river is now flowing over flatter land and so the dominant direction of erosion is lateral (from side to side).
The river has a greater discharge and so has more energy to transport material. Material that is transported by a river is called its load.
Deposition is also an important process and occurs when the velocity of the river decreases or if the discharge falls due to a dry spell of weather.
Processes operating in the middle course of a river
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•Meanders
•Oxbow Lakes
DEPOSITION and EROSION create these landforms
What landforms are found in the middle course?
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A meander= a bend in a river
Deep water A gently sloping area of land on the inside of a meander
Slip off slope Formed on the outside bend of the meander due to erosion.
River cliff Because of the gentle slope, there is a lot of frictional drag and so therefore the river flows at this speed
Fastest flow Maximum depth of the channel. (Note the asymmetrical cross-profile)
Slowest flow There is little frictional drag from the bed and bank at this point and so the river can flow at this speed.
Can you match up the characteristic
s below?
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Meanders
12
3
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Floodplain
Deposits on the inner meander bend where there is low energy
Erosion on the outer bend where there is faster flow. It creates a river cliff
Slip-Off Slope
Direction of meander migrationDirection of meander migration
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Can you match up the labels to the correct place on the diagram?
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Cross section through a meander
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Ox Bow Lake FormationCan you look at the diagram & explain the formation of ox-bow lakes?Can you look at the diagram & explain the formation of ox-bow lakes?
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Ox Bow lake on Mississippi
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More gentle sloping valley sides
Evidence of meanders
Land use
changes –
more urban areas.
Small floodplain begins to
develop on either side of the river,
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The Lower Course of a River
Learning Objectives:To be able to describe and explain the formation of a flood plain, levees, delta and estuary.
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Floodplains, Deltas and Levees.
The pictures below show a floodplain, a delta and levees. Using your prior knowledge of river processes come up with a theory to explain how they are formed. The key words underneath each picture will help.
deposition
Slow flow
alluvium (silt)
flood
flat
deposition
slow
sea/lake
load
channel
blocked
deposit
flood
large load
smaller load
Main Channel
Main Channel Levee
Sea/lake
Floodplain
Floodplain
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Defintions
Flood plains • A flood plain is the wide, flat area of
land on either side of the river in its middle and lower course.
Levees • Levees are natural embankments of silt
along the banks of a river, which are often several metres higher than the flood plain.
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1. Floodplains and leveés are formed by deposition in times of river flood.
2. The river’s load is composed of different sized particles.
3. When a river floods, the river water overflows the banks of the river and immediately slows down due to friction.
4. This drops the larger particles first, building up a raised river bank called a LEVEÉ.
5. The sands, silts and clays are similarly sorted with the sands being deposited next, then the silts and finally the lightest clays. This builds up the floodplain.
Floodplain & Levee formation
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Levee formation
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This is a cross section of a floodplain.
Can you draw a simple sketch of the diagram and the labels below and then annotate it to explain how it is formed?
leveés clays and siltssands
How a floodplain is formed
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Delta FormationDeltas form at the mouths of many of the world’s larger rivers, e.g the Nile (Egypt), the Ganges (Bangladesh), the Mississippi (USA).
A delta is a flat area of sand and silt built into the sea. It is formed by deposition.
1. When a river enters a sea or lake carrying large volumes of fine material, the velocity slows and causes the load to be deposited in layers.
2. Over time, the deposited material blocks channels and forms small islands separated by river channels called distributaries.
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EstuariesThere are no large deltas around the coasts of the UK, instead the tidal mouth of a UK river is typically characterised with an estuary. Estuaries are wide river valleys flooded daily by the tide.
At low tide, large expanses of mud and sandflats are exposed which are mostly composed of material deposited by the river, e.g Thames, Humber, Severn.
Thames Estuary